Journal of Nanomaterials

Journal of Nanomaterials / 2019 / Article
Special Issue

Nanomaterials for Biotechnology: Synthesis, Properties, and Applications

View this Special Issue

Review Article | Open Access

Volume 2019 |Article ID 6248725 | 31 pages |

Recent Advances in the Synthesis, Properties, and Biological Applications of Platinum Nanoclusters

Academic Editor: Teofil Jesionowski
Received03 Apr 2019
Accepted12 Jul 2019
Published08 Sep 2019


Noble metal nanoclusters (M NCs), defined as an aggregation of a few to tens of atoms, are considered a borderline between atoms and metal nanoparticles (M NPs), which tends to exhibit molecule-like behaviours such as discrete electronic state and size-dependent fluorescence. In the past decades, gold and silver nanoclusters (Au NCs and Ag NCs) have been massively explored and utilized in the field of industrial catalysis, optoelectronic devices, biological imaging, environmental detection, clinical diagnoses, and treatment. The analogue of Au and Ag NCs and platinum nanoclusters (Pt NCs), especially their biological applications, is relatively and rarely discussed. This review firstly investigates the synthetic methodology of Pt NCs including template-assisted and template-free approaches and then introduces their unique optical, catalytic, and thermal properties. Particular importance here is the biological applications of Pt NCs such as the bioimaging of various cells as a preferred fluorophore in contrast to traditional fluorescent markers (e.g., organic dye, semiconductor quantum dots, and fluorescent proteins), the usage of Pt NCs-based antitumour drugs as a new class chemotherapeutics for malignant tumour therapy, and the utilization of antibacteria as an alternative of Ag-based antibacterial agent. On the whole, the development of Pt NCs has already gained delectable progress; however, the study of ultrafine Pt NCs is at the beginning stage and there are still plenty of challenges like synthesis of near-infrared (NIR) fluorescent Pt NCs, the explicit signal pathway of cell apoptosis, and attempt in diverse biological applications that need to be urgently tackled in future.

1. Introduction

Noble metal like rhodium (Rh), palladium (Pd), silver (Ag), platinum (Pt), and gold (Au) is one kind of modish and desired material, according to their inherent resistance to oxidation and corrosion even in the moist environment [13]. Its physical and chemical properties appear to be entirely change as the size of metal continuously decreases into nanoscale because of the quantum size effect, surface effect, small size effect, and macroquantum tunnel effect [4]. For example, noble metal nanoparticles (M NPs) which are defined as the particle size ranged from 1 to 100 nm have the high surface-to-volume ratio and electrodynamic interaction, leading to emerge distinct electronic, magnetic, and optical properties in contrast to bulk counterparts or individual atoms [5, 6]. In view of freely moving delocalized electrons in the conduction band, metals in a bulk state are good optical reflectors and electrically conducting (Figure 1). As for M NPs, a specific size-dependent plasma absorption will be presented when the size is smaller than the average free path length of conduction electrons (i.e., <20 nm) based on Mie’s theory [7, 8]. If the M NPs are irradiated by light, strong optical absorption and/or scattering phenomenon will happen forcefully relied on their size, morphology, and dielectric environment, which is recognized as localized surface plasmon resonance (LSPR) [911]. Consequently, M NPs show the intense colours owing to the collective oscillation of conduction electrons upon interaction with light and this particular property has been widely developed in catalysis, optoelectronics, sensing, and surface-enhanced Raman scattering (SERS) [1216]. Further declining the size of metal nanomaterials into around 0.1-2 nm, M NPs turn into metal nanocluster (M NC) region [17]. M NCs as a borderline between M NP and atoms were firstly discovered by Cotton and Haas in 1964 [18]. On this length scale, the electronic band structure of M NCs is broken down into discrete energy levels under the condition of free electrons’ size near Fermi wavelength (i.e., <2 nm), resulting in the acquisition of molecule-like behaviours like the discrete electronic state [1921]. Moreover, M NCs exhibit the intense light absorption and emission by the interaction between NCs and light via electronic transitions between energy levels. This unique electronic properties of M NCs are potently depended on their size, morphology, metal oxidation state, and surrounding ligands [22, 23]. Thus, a plenty of efforts focused on the preparation of desired and versatile M NCs by precise control of their sizes or shapes through meticulously choosing stabilized ligands or templates and the usage of NCs in an optical device [24, 25], chemical detection [2629], catalytic conversion [30], and especially in biological applications [31].

Platinum (Pt), as one of the representative noble metal, has the physicochemical stability and remarkable resistance to corrosion even at high temperature based on its steady electrical structure [2]. Its physical and chemical inertness makes Pt widely employ in the fundamental industrial fields such as electrodes, dentistry equipment, Pt resistance thermometers, and catalytic converters [2, 32]. The fabrication and application of Pt materials on the subnanoscale became a research hotspot in the past few decades, especially in the catalysis and medicine. The most common utilizations of Pt nanomaterials are the catalysis of chemical reaction according to their high surface activity [33]. Based on their scarcity and preciousness, the research priorities of Pt materials are aimed at developing high-performance Pt-based materials through enhancing the catalytic efficiency as well as decreasing the usage amount. Undoubtedly, Pt’s size and morphology play a critical and indispensable role [34]. On the other hand, Pt-based antineoplastic agents (like cisplatin, oxaliplatin, and carboplatin) have been universally used in the clinical chemotherapy against multiple cancers [35]. For example, Pt(II) anticancer drugs could induce the crosslinking of DNA, leading to the inhabitation of DNA synthesis or repair in tumour cells [36].

Up to now, typical Pt NPs demonstrated their applicable and prospective capacities in enormous areas such as gas detection, fuel cells, biosensors, and chemotherapeutics [37]. Besides, the analogues of Pt NCs, namely, Au NCs [38, 39], Ag NCs [40], Pd NCs [41] and Cu NCs [42], have been intensively investigated for their catalytic abilities, biological behaviours, and electrical and optical properties. By comparison of well-studied Pt NPs or congeneric NCs, the investigation of Pt NCs is just at an early stage in the last few decades; herein, this review summarizes the recent advance in the synthetic method of Pt NCs and special physicochemical properties, especially their fascinated biological applications.

2. Synthetic Method of Platinum Nanoclusters

In comparison to metal bulk or M NPs, the preparation of Pt NCs refers to the precise control and rigorous synthetic conditions due to their extreme small size [43]. There are many classification standards of the preparation method (Figure 2) [4447], like physical and chemical method and one-pot and etching method. We generally divided the synthetic protocols of Pt NCs into two aspects: template-assisted method and template-free method.

2.1. Template-Assisted Method

Template-assisted method is based on the presence of various templates during the synthetic process, which plays a role as a protecting agent, a stabilizer, a capping agent, and even as the restrict space provider. The usual templates impart the M NCs’ new unique features or specific structure by means of three main ways [3]: (1) decline of the surface energy to prevent the NCs’ aggregation via electrostatic interaction, chemical bonding, and space steric effect; (2) accurate control and tailor of M NCs’ size, dispersity, and morphology, which will profoundly influence, determine, and enhance their inherent functions; and (3) decoration and modification of the M NCs’ surface to endow some reactive functional groups in order to achieve the further applications. The ideal templates always include electron-rich atoms (e.g., N, P, S, and O) or certain functional groups (e.g., -COOH, -NH2, -OH, and -SH).

Common templates utilized during the synthesis of M NCs are small organic molecules like representative surfactant, thiol compounds, organophosphorus compounds, and amino compounds [4851]. Polymer ligand including nonionic and ionic polymers (such as acrylic polymer, amine polymer, polyethylene glycol, poly(N-vinyl-2-pyrrolidone), polypyrrole, and dendrimer) is another widely used template materials [5254]. A polymer template stabilizes the NCs by chemical bonding and electrostatic effect, as well as steric effect due to large spatial configuration. Compared to small organic molecules, polymer has the easier modification, better controlling ability, and lower toxicity [55, 56], making them a preferred option for synthesis of M NCs. Furthermore, a biomacromolecule template, such as DNA, protein, oligonucleotides, and enzymes, is a kind of prevalent materials used to manufacture the medical and biological metal nanomaterials [57, 58]. Biomacromolecule is always relative to a specific biomolecular recognition function, multifunctional group (-SH, -COOH, -OH, and -NH2), and excellent biocompatibility [59], showing a promising potential in the development of various biofunctional M NCs. In general, a template cannot reduce the metal precursor to form the M NCs without adding any other chemical redundant or with the help of physicochemical means such as the γ-radiolysis method [60], microwave-ultrasonic method [61], sonochemical method [62], photoreduction method [63], and electrochemical method [64].

Chemical etching method also called ligand-induced exchange etching involves two processes: the larger-sized M NPs are formed firstly under the stabilized template with a weak interaction and secondly, ligand-induced etching of larger-sized NPs occurs under the existing excess ligands by a strong interaction between ligands and metal atoms to produce smaller size NCs. Highly blue fluorescent Pt NCs with two peaks at 410/436 nm were synthesized by phase transfer through electrostatic interactions under an etching environment [65]. The presynthesized glutathione- (GSH-) protected Pt NPs were transferred into organic solvent with the support of cetyl trimethyl ammonium bromide (CTAB) to secondly form the fluorescent small Pt NCs. However, this method is always related to a time-consuming and complicated process, which is not suitable for the production of M NCs at a large scale.

Direct reduction in the present of templates and extra chemical reductant is a classical and extensive way to acquire the small size NCs. Atomically precise Pt NCs which consist of 11 atoms (Pt11 NCs) were obtained by a direct chemical reduction using small molecule 4-(tert-butyl)benzyl mercaptan (BBS) as the template and sodium borohydride (NaBH4) as the reducing agent [66]. The structure of NCs was defined as Pt11(BBS)8 by matrix-assisted laser desorption-ionization mass spectrometry (MALDI-MS) and electrospray ionization (ESI) technology. Moreover, special octahedral Pt NCs were successfully synthesized employing glucose as the reducing agent and CTAB as the shape-control templates via one-pot hydrothermal process [67]. The formation mechanism of octahedral NCs is that glucose reduces Pt ions into atoms and then atoms grow to octahedron by the precise control of CTAB, namely, the synergetic effect both of CTAB and glucose. Cho et al. put forward the sol-gel polymerization protocol of poly(2-hydroxyethyl-2-mercaptoethyl aspartamide) (PHMA) capped Pt NCs [47]. PHMA as a polymer template could control the morphology of NCs and organize their structure association, based on binding Pt procurers via amine functional groups and particles via thiol functional groups. For another instance, dendrimer, as a favourable template, has a uniform structure which can supply a predetermined formation environment to accurately control the NCs’ size and morphology [6871]. A linear structural Pt NCs with 4-8 atoms were fabricated inside of polyamidoamine dendrimer by UV irradiation at 254 nm (Figure 3) [72]. The tools of resonance Raman spectra, ultraviolet-visible (UV-Vis) spectroscopy, X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HR-TEM) were employed to clarify that the assemble of Pt nanocrystals is owing to an oriented attachment mechanism.

Physicochemical technique can assist the preparation of ultrafine Pt NCs, instead of using chemical reductants. Microwaves, as the electromagnetic waves, could obtain monodispersed M NCs by the fast and homogeneous heating [61]. Microwaves heat polar molecules rapidly at the high temperature without heating the glass container, leading to the formation of colloidal metal nanomaterials. The synthesized M NCs are always related to the high quality and narrow size distribution. Tu and Liu employed microwave irradiation to prepare the poly(N-vinyl-2-pyrrolidone)-supported Pt NCs with an average size at [73]. This method could continuously produce the uniform Pt NCs even at a large scale, satisfying industrial applications. Photoreduction is a simple, feasible, and nontoxic approach avoiding the usage of additional reducing agents [74]. The reduction mechanism is due to the energy transfer under the condition of light irradiation to generate the reductive hydration electrons or reactive radicals [63], which is frequently utilized to explore the origination of photoluminescence because no other compounds are introduced. The Pt NCs with the size ranged from 1.0 to 2.2 nm were prepared with the aid of UV light under the alkaline environment [75]. The presynthesized NCs have a face-centred cubic spatial structure, and the author inferred that the UV light could achieve the nucleation and growth of NCs, not by the thermal reduction. Finally, electrodeposition is a usual and effective method to control size and shape of metals and decorate the substrate surface by adjusting deposition parameters, involving a plenty of distinct advantages such as low cost, rapid producing rates, and precious controllability [76, 77]. Qian et al. firstly modified the four-generation poly(amidoamine) dendrimer (G4-NH2) onto indium-doped tin oxide (ITO) and then electrodeposited Pt NCs on the surface of G4-NH2 dendrimer to form larger-sized NPs near [78]. The size and morphology could be tailored by polyelectrolytes or the types of PAMAM ligands. These physicochemical techniques mentioned above are environmentally friendly, less time-consuming, and convenient, which are beneficial to investigate the formation process and fluorescence mechanism and meet the demand of green industrial fabrication.

In addition, the defined templates during the formation of Pt NCs can be extended to a broad range involving multicomponent materials like multimetallic alloy [7983] and doped substrate material [8487]. For instance, bimetallic or multimetallic alloy is designed by a combination concept of different metallic compounds in order to obtain composite performance. Pure Al, Co, and Pt were melted and then dealloyed in alkaline solution at certain temperature to form Al85Co14Pt1 ternary alloy [88]. Even the amount of Pt was quite small, the electrocatalytical activity was improved dramatically and the ampere-metric determination limit of sodium nitrite (NaNO2) was 0.067 μM (). On the other hand, a doped substrate method is allowing Pt NCs doped or dispersed into the substrate materials such as polymer film [8992], inorganic substrate [9396], metal organic framework (MOF) [97], carbon nanotubes (CNTs) [98, 99], and graphene [100102], which could easily adjust and enhance the pure NCs’ chemical and physical performance. Pt NCs with an average diameter of were deposited on SmMn2O5 (SMO) mullite-type oxides by an atomic layer deposition method (ALD), showing the efficient ability to solve the CO poisoning problem for the Pt-based catalyst [103]. This catalytic activity even under low temperature originated from O2 dissociation at the bifunctional interface structure. Lee et al. put forward that monodispersed Pt NCs () were loaded onto three-dimensional graphene-like carbon (3D GLC) which was employed in the electrochemical oxidation reaction [104]. These Pt NCs-doped 3D GLC catalysts possess near superficial area and exhibit excellent glycerol oxidation reaction (GOR) activity and extreme stability via firm adhesion of glycerol on the Pt NCs’ surface. Recently, Pt precursor solution was added into poly(diallyldimethylammonium chloride) and poly(sodium 4-styrenesulfonate) to assemble polyelectrolyte multilayer (PEM) films and then the Pt NCs were in situ yielded with various sizes from 1.2 to 2.3 nm only by tailoring the salt concentration and reduction time, instead of the reduction temperature [105].

2.2. Template-Free Method

Template-free protocol is a method avoiding the introduction of extra substance and has extensive advantages such as effortless postprocessing and pure product [106]. Kawasaki’s group proposed a surfactant-free synthetic approach to obtain Pt NCs consisting of 4 to 6 atoms with blue fluorescence in N,N-dimethylformamide (DMF) solution [107]. These NCs showed extreme stability against strong ionic and variable acid-alkali conditions. Subsequently, Duchesne and Zhang employed X-ray absorption near-edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS) techniques which revealed the details of surfactant-free-synthesized Pt NCs’ local structure and oxidation states [108]. The local structure of Pt is primarily due to the changes in the metal-ligand coordination, not the Pt-Pt bonding. The oxidation of Pt species is a combination of Pt(IV) and Pt(0), indicating that nonmetallic Pt NCs are responsible for their fluorescent properties. Meanwhile, this surfactant-free method synthesized Pt NCs were used to sensitively sense the aqueous Fe3+ ion solution and the limit of detection was 4 ppm (15 μM) under the concentration range of Fe3+ ions from 0.007 to 0.530 mM [109].

3. Properties of Platinum Nanoclusters

The properties of Pt NCs are the consequence of their distinct electronic and structural properties, which have access to NC’s size, morphology, and surface surroundings inseparably. Herein, we summarize the classical features of Pt NCs including optical properties, catalytic properties, and other properties.

3.1. Optical Properties

Optical properties benefit for offering an insight to understand the electronic and geometric structures of M NCs in depth [110]. The applications of M NCs strongly depend on their optical properties, and there are a lot of research reported the NCs’ unique optical phenomenon such as steady-state absorption and fluorescence, temperature-dependent fluorescence, ultrafast fluorescence and transient absorption, fluorescence enhancement, and electrochemiluminescence [21, 111113]. This part, we will introduce about the theoretical and practical progress of size-dependent fluorescence for Pt NCs.

Unlike M NPs which possess apparent surface plasmon resonance (SPR) absorption, Pt NCs lost this particular property, replaced by the size-dependent fluorescence ranging from the visible to near-infrared (NIR) region. Generally, this fluorescence of Pt NCs generated from the electronic transitions between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO). Their finite size is a critical point for molecule-like electronic transitions between HOMO and LUMO energy levels. Energy transitions can be expressed as Equation (1) based on the jellium model [3, 114]: where represents the energy level spacing, is the Fermi energy, and stands for the number of atoms in NCs. The of free electron is only related to the metals’ Wigner-Seitz radius () or the electron density (ρ0) because the free electrons are piled up with constant electron density. Owing to equals to , Equation (1) transfers to Equation (2) using the emission/excitation frequency () and NCs’ radius () expressed as follows:

Equation (2) is suitable for the M NCs when is smaller than 20, which is well depicted by a spherical harmonic potential. Hamiltonian for an electron in a single-particle 3D harmonic oscillator can be described as follows: where represents the single-electron momentum and is the coordinate operators. The small anharmonic distortion term should be taken into consideration under the condition of . Defining the distortion parameter () as a constant value (0.033), the correlated transition energy spacing () is shown as Equation (4) using angular momentum () and shell number () expressed as follows: where represents the angular momentum of excited state and is the angular momentum of ground state. Based on the Equations (2) () and (4) () displayed above, this dependency can be defined as the large size of M NCs is related to the small energy level spacing with longer emission wavelength fluorescence emitted and vice versa (Figure 4(a)).

Besides of the size-dependent fluorescence effect described above, surrounding ligands or templates also play a significant role on the fluorescent properties through ligand-metal charge transfer (LMCT) (Figure 4(b)) [115118]. Not only the enhancement or quenching of fluorescence could be realized by the collaboration between NCs and ligands but also the fluorescent intensity and maximum peak of emission wavelength can be adjusted. Thus, the mechanism of M NCs’ fluorescence is ascribed to the intrinsic electronic transitions between HOMO-LUMO energy levels and the electronic transitions between NCs’ surface and surrounding ligands via LMCT.

Until now, fluorescent Au and Ag NCs have been deeply researched and utilized in various fields [119125]. As for the fluorescent Pt NCs, the number of synthetic methods, usable templates, and optical applications is significantly fewer than Au or Ag counterparts and most reports focused on the blue-, green-, and yellow-emitting fluorescence (Figure 5). The longer emission wavelength, especially near-infrared (NIR) region, is rarely mentioned. NIR fluorescence has a plenty of merits such as easy detection, less autofluorescence interference, and more use safety, making it attractive in both biological sensing and labelling analysis [126]. Furthermore, the fluorescent Pt NCs have the specific advantage than Ag and Au NCs, such as higher photoluminescence quantum yield (QY) and instinct properties like anticancer [127]. Therefore, great efforts payed out to study on the facile and repeatable synthesis of fluorescent Pt NCs with longer emission wavelength in the past decades.

Bovine serum albumin (BSA) supported blue fluorescent Pt NCs (emission wavelength region from 350 to 500 nm) which were fabricated by an easy NaBH4-reduced method. These NCs could achieve the selective examination of hypochlorite among the concentration range from 12 to 240 mM via the visible fluorescence quenching due to the formation of oxidized Pt [128]. A GSH-induced etching process were employed to produce the yellow fluorescent Pt NCs (maximum emission wavelength at 570 nm) with the fluorescent QY at 17% [129]. Most Pt NCs are in the Pt(I) state, and the optimized molar ratio between Pt and GSH is determined at 1 : 10. Afterwards, blue [130] and green [131] fluorescent Pt NCs were precisely synthesized by employing the template of fourth-generation polyamidoamine dendrimer, short for PAMAM (G4-OH), and their absolute QYs reach to 18% and 28% in water, respectively. We previously reported that various aqueous Pt NCs from blue to yellow fluorescence were prepared by a facile method using hyperbranched polyethyleneimine (PEI) as a stabilizing agent and environment-friendly L-ascorbic acid as a reductant [132]. Their optical properties can be tailored by adjusting the molar ratio between Pt ions and protecting ligands. Moreover, these Pt NCs have the ability of quantitative and selective detection for Co2+ ions and the limit of detection is up to 500 nM. Meanwhile, Xu et al. used the same method to prepared blue fluorescent Pt NCs and applied them for sensing nitroimidazoles (MTZ) with the limit concentration of 0.1 μM [133]. As for longer fluorescent emission, García’s group demonstrated that red fluorescent Pt NCs in aqueous solution could be obtained by a chemical reduction method using lipoic acid (LA) as a capping agent [134]. The synthesized NCs with the maximum emission wavelength at 680 nm have a relatively high QY at 47% and present excellent stability towards pH media and high ionic solution. Moreover, hemoglobin-protected Pt NCs appeared to have two fluorescence regions: emission wavelength at 450 nm which is contributed by Pt6 NCs at zero oxidation state and emission wavelength at 760 nm that is due to the formation of aggregated Pt(II)-Hb complexes caused by LMCT effect from N/O to Pt atoms (the structure is assigned to Pt16 NCs) [135]. They also indicated that the NIR fluorescence is too weak to observe clearly because of a lower proportion of Pt(II) on the NC’s surface (only near 13.68%). To our knowledge, it is the longest emission fluorescence reported for Pt NC materials, even for their poor fluorescent intensity.

In spite of the progress discussed above, the synthesis of fluorescent Pt NCs is still in its initial stage. There remains some challenge that needs to be solved, including the acquisition of highly longer emission fluorescent Pt NCs to realize the practice application, clarification of fluorescent mechanism to provide guidance, and large-scale production of Pt NCs to meet industrial demand.

3.2. Catalytic Properties

M NCs have been widely investigated for their catalytic properties from the theory to practical application [32, 136, 137]. Pt-based catalysts are pervasively applied in the development of the cost-effective proton exchange membrane fuel cells (PEMFCs) involving electrochimerical oxygen reduction reaction (ORR), methanol oxidation reaction (MOR), ethanol oxidation reaction (EOR) [138142], and the catalysis of different chemical reactions like hydrogenation reactions [143146]. It is well known that the catalytic reactivity of Pt varies by their sizes, morphology, and dispersion [147].

There are two common views for Pt-based catalysts. One is that Pt NPs (near 2 nm) are thought to be at the limit of their catalytic performance due to too strong Pt-O binding energy on the smaller clusters [148, 149]. That is to say, large Pt NPs with a face-centred-cubic (FCC) structure (near 2 to 3 nm) have the best activity and the ultrasmall Pt NCs are considered to have lower or even no catalytic ability, especially for ORR. However, a recent study rejected this traditional concept and their applicability [150]. It was found that Pt NCs with the size less than 2 nm also emerged a better catalytic performance. Accordingly, the catalytic capacity is no longer dependent on the size effect. Vajda et al. proved that small Pt8-10 NCs loaded on a high-surface area template showed 40-100 times higher catalytic activity for the oxidative dehydrogenation than common Pt-based catalysts and extreme selectivity to produce the propylene [151]. Considering about the hydrogenation of methyl acrylate, the catalytic capacity of Pt-based materials depended on their size ranged from 2.4 to 3.0 nm which could be controlled by the amount of poly(N-vinyl-2-pyrrolidone) (PVP) [152]. Subsequently, Lan’s group modified the counter electrode by PVP-protected Pt NCs for the dye-sensitized solar cell (DSSC) and found that this modified electrode exhibited light soaking durability and high conversion efficiency (near 9.37%) in a highly volatile electrolyte system [153]. Based on the results above, the “uniqueness of size effect” issue for Pt-based catalysts is now reexamined and no longer exist.

The other common view is that certain morphology of Pt NCs like topological magic number structure (e.g., Pt13 and Pt55) with high symmetry could exhibit the higher catalytic ability [148, 154]. Imaoka et al. compared the ORR catalytic capacity between Pt12 NCs with less symmetric structure prepared using a phenylazomethine dendrimer with a tetraphenylmethane core (DPA-TPM) and Pt13 NCs with high symmetry obtained using phenylazomethine dendrimer with a triphenylpyridylmethane core (DPA-PyTPM) (Figure 6) [155]. One interesting finding is that misshapen structure Pt12 has a double catalytic activity compared with that of the topological stable Pt13 with the high symmetry. This distinction is mainly caused by two reasons: (1) less symmetric structure of Pt12 with a smaller number of internal Pt-Pt bonds and (2) structural transition of Pt12 makes the size further decreases against the smallest limit of icosahedral Pt13 NCs. Besides, this group further explored the atomicity-specific catalytic activity of Pt NCs within a significant small atomicity (), revealing Pt17 and Pt19 exhibited higher performance than other series [150]. As a result, the atomic coordination structure is completely different from that of the larger-sized FCC nanomaterial and the catalytic activities for the ORR are significantly altered by the spatial arrangement and atomicity. Hence, the fact discussed above proved the idea that the catalytic activity has weak access to the topological magic number of Pt on the nanoscale.

In summary, the emergence of Pt NCs has already reversed the traditional idea on Pt-based catalysts. The further investigations about the precise control of atomic number, seeking of different steric topological structures, and catalytic application of diverse chemical reactions need to be comprehensively and deeply studied in future.

3.3. Other Properties

Except for the optical and catalytic properties, Pt NCs also have unique physical characteristics, like thermal properties [156]. The phase stability of Ptn NCs (, 147, 309, and 561 atoms) under various temperature conditions was surveyed by the molecular dynamics (MD) simulation combined with an embedded atom scheme (EAM) [157]. Furthermore, Akbarzadeh and Parsafar discussed the melting and thermal physical properties of Ptn NCs in a larger size ( to 8788 atoms) by means of molecular dynamics simulations employing quantum Sutton-Chen (QSC) potential [158]. Both for the larger and relative smaller NCs, the melting temperature goes up as the NCs’ size increased and that of Pt8788 NCs approaches to the Pt bulk limit.

4. Biological Applications of Platinum Nanoclusters

Pt NCs consisting of few to tens of atoms own plenty of outstanding features and possess a great potential in the various applications, e.g., catalysis [159], sensing [133], and cancer therapy [160]. This part, we focus on the Pt NCs’ biological applications which are strongly in accordance with their size-dependent effects and the coordination between NCs and functional surrounding ligands.

4.1. Biological Imaging

In the past decades, fluorescent biological imaging technology which is the process of light emission in living organisms [161] became an indispensable and visualized tool for the drug delivery system [162, 163], gene therapy [164], and cancer diagnoses [165, 166]. The used fluorophore is a key point for successful bioimaging of cells, which concerns about their safety, sensitivity, and wide applicability. Organic dyes [167169], semiconductor quantum dots (QDots) [170, 171], fluorescent proteins [172, 173], lanthanides [174, 175], and carbon dots (CDots) [176, 177] as the common fluorophores have been already explored for practical imaging and extensively presented their merits and drawbacks. For example, organic dyes possess the high fluorescence QY; however, the dramatic cytotoxicity severely handicaps their practical applications [178]. Besides, QDots have unique features such as tunable colours, great photostability, narrow emission spectra, and broad excitation spectra [179]. The disadvantages like large size (>3 nm), on-and-off blinking behaviour, and low biocompatibility are important issues that need to be solved [180, 181]. As an alternative to organic dyes and QDots, M NCs have a crowd of strike features like ultrasmall size, water solubility, high fluorescent efficiency, large Stokes shifts, excellent photostability, and low cytotoxicity [182], making them become the safe and nontoxic clinical fluorescent contrast agents. In comparison to well-studied Au and Ag NCs [31, 183185], relatively little research investigated the bioimaging application of fluorescent Pt NCs. In general, the imaging way of Pt NCs can be divided into two parts: (1) direct labelling without any other materials and (2) combination of certain biomolecule (e.g., proteins and DNA) to targeted imaging. Our previous work reported that fluorescent Pt NCs stabilized by polyamine ligands (average size near 1.4 nm) could accomplish the biostaining of the suspension hematopoietic cell system [186]. The ligand-capped Pt NCs could selectively enter into K562 and BV173 cancer cells compared to the normal peripheral blood mononucleated cells (PBMCs) from healthy donors (Figure 7). This distinction gives an opportunity to achieve the specific labelling of hematopoietic cells during the disease diagnosis. Recently, we extended this fluorescent probe to label the lung cancer [187]. The classical human lung adenocarcinoma cells were chosen to examine their biological imaging ability (Figure 8). Both A549 (normal cells) and A549/DDP (cisplatin-resistant cells) cells exhibit the red fluorescence signal that is emitted from Pt NCs-based drugs, while the cell nuclei are stained by 4,6-diamidino-2-phenylindole (DAPI) exhibiting the blue fluorescence. Most interesting finding is that Pt NCs preferably enter almost cell nuclei in the cisplatin-resistant A549/DDP cell groups, compared to the A549 cell group where the Pt NCs are observed evenly distributed in both cell nuclei and cytoplasm. As a result, Pt NC nanomaterial could realize the visual imaging individually as a fluorophore on the account of the fluorescence effect.

The aim of conjugating the biomolecule is to achieve the deliberate target of the specific tissue. Antibody is a suitable and effective choice. An antibody belonging to proteins has a lot of functional groups (e.g., -NH2 and -COOH) which could feasibly react with those groups on the surrounding ligands of NCs by chemical reaction, and then, the presynthesized Pt NC-antibody complex is delivered to express on the certain targeted position via antigen-antibody reaction. This approach could complete the targeted imaging of lesion location. For example, after bounding to the antichemokine receptor antibody (anti-CXCR4-Ab) through a conjugated protein A, blue fluorescent mercaptoacetic acid- (MAA-) capped Pt NCs were observed on the cell membranes where the receptors are expressed (Figure 9) [130]. In order to check this specific combination of antibody-modified Pt5(MAA)8-protein A-anti-CXCR4-Ab complex and chemokine receptor, Chinese hamster ovary (CHO-K1) cells were selected as a control group due to their negative behaviours against the chemokine receptor. The result indicated that the Pt NC complex cannot stain the CHO-K1 cells, proving the success in the targeted imaging. Simultaneously, the same work was also done for green-emitting Pt NCs [131]. Most importantly, these reported that Pt NCs have the considerably low cytotoxicity and excellent biocompatibility, demonstrating enormous potential in the tracking, imaging, and labelling of cancer cells or other kinds of cells as an alternative fluorescently labelled probe.

Similarly, yellow fluorescent PEI-stabilized Pt NCs (Pt NCs@PEI) could effortlessly conjugate with an antichemokine receptor antibody and then successfully realized the double staining of HeLa cells using DAPI-stained nuclei and Pt NCs@PEI expressed on the cell membrane (Figure 10) [188]. To achieve targeted expression on the cell membrane, a simple glutaraldehyde method was used to conjugate Pt NCs@PEI to the anti-CXCR4-Ab. Confocal fluorescence images show HeLa cell nuclei in blue color (DAPI stained) and cell membranes as yellow color, demonstrating the evidence that the usage of Pt NCs@PEI will not be affected by any other fluorophores, simultaneously. Furthermore, the relationship between NCs and PEI ligands was also checked and the results elucidate that these Pt NCs are stabilized mostly by primary amine. Based on this discovery, the fluorescence of Pt NCs may be originated via two pathways, that is, the electronic transitions between HOMO-LUMO energy levels of Pt NCs and the NCs’ surface surrounding ligands through LMCT.

4.2. Antitumour Drugs

Pt-based antitumour drugs are one of the most effective tools for the treatment of different tumours, and Food and Drug Administration (FDA) authorized the Pt as the effective antitumour drugs for various cancer therapies in 1978 [127, 189192]. Cisplatin in the Pt(II) state as a representative drug emerged a few deficiencies which influences the therapeutic efficiency. For instance, it could have side effect like myelosuppression, nephrotoxicity, and neurotoxicity in the course of medicine treatment [193195]. On the other hand, typical breast, colorectal, and prostate cancers exhibit less sensitive to cisplatin [196, 197]. More serious is that testicular and ovarian cancers intrinsically resist to cisplatin treatment after several cycles of therapy, even though it is efficient at the beginning stage [198]. These drawbacks including the systemic toxicities and poor specificity impede their anticancer efficiency; therefore, developing a new-type Pt-based antitumour drug with little side effect and excellent specificity could afford a powerful supporting technique for diagnosis and treatment of diverse malignant tumours.

In the current years, Pt NPs and NCs have been used to develop the latest Pt-based anticancer nanomedicine and found their preferable ability of inducing the apoptosis of several cancer diseases [160, 199, 200]. Chien et al. reported a low-generation dendrimer-caged Pt NCs (CPN) with 0.93 nm diameter [201]. After attaching to the cleavable polyethylene glycol (PEG) corona and targetable iRGD (CRGDKGPDC), this complex achieved the targeting of human breast cancer cell line MDA-MB-231 and release of toxins against malignant cells by affecting tumour-inside activation for anticancer chemotherapeutics (Figure 11). By means of subcutaneous breast cancer xenograft in mice, the therapeutic effect of CPN was examined via intratumoural injection in vivo and the result indicated that this kind of chemotherapeutics has the same efficacy compared to cisplatin.

Fluorescent GSH-capped Pt NCs were prepared by a green and simple chemical method and employed to biolabel the HepG2 cells [202]. It is worth noting that the synthesized Pt NCs could obviously kill the HeLa cells under the irradiation by infrared (IR) light, while it was not happened under UV light condition. The killing mechanism of cancer cells is contributed to heating effect instead of free radical effect. Xia et al. presented an approach to package the Pt NCs with polypeptide and targeting peptide SP9443 to form the assembled Pt NAs. These Pt NAs could damage DNA through targeting disseminated hepatocellular carcinoma (HCC) tumour-initiating cancer stem-like cells (CSLCs) to achieve inhibiting proliferation of tumours [203]. Gene expression profile analysis proved that ABCG2 and CD24, which expressed highly in the sorted SP+CD24+ cells, could be adjusted by Pt NAs, while the cisplatin could not downregulate. Furthermore, real-time quantitative polymerase chain reaction (RT-qPCR) analysis also demonstrated that Pt NAs induced the downregulation of CCNB1, CDK1, and TOP2A, leading to DNA damage and modulation of the cell cycle (Figure 12). This study verified that the prepared ultrafine Pt NAs have the ability to accelerate the release of toxic Pt ions and overcome the cisplatin-resistant problem for HCC CLSCs.

In a previous study, we used the dual-functional Pt NCs-based anticancer materials to biologically image the blood system suspension cells as the fluorescent markers. Meanwhile, the selective inhibition of hematopoietic K562 and BV173 cancer cells was investigated as well [186]. The relative cell apoptotic rate for K562 and BV173 cancer cells is three times higher than hematopoietic normal cell (PBMCs) via induction of the expression of p53, PUMA, and cleaved caspase-3 proteins (Figure 13). These Pt NCs manifest the evident apoptosis efficacy possibly due to the inherent characteristic of Pt and exhibit a great potential in effective treatment of hematopoietic system disease, especially acute myeloid leukaemia and lymphoma. Currently, the cisplatin-resistant-non-small-cell lung cancer (NSCLC) was chosen as the targeted object because the lung cancer incidence is increasing continually owing to the environment deterioration and smoking. The problem of drug resistance seriously affects the chemotherapy efficiency and survival rate of patients during the treatment with chemotherapy drugs due to multiple mechanism, such as the lack of effective drug concentration in tumour cells, reduction of drug activity, cell apoptosis changes, and DNA repair pathways. The experimental results illustrated that Pt NCs-based anticancer drug could achieve the excellent induced apoptosis in both cisplatin-resistant A549/DDP and non-cisplatin-resistant A549 cells [187]. More interesting is that cisplatin-resistant A549/DDP showed the superior inhibitory and apoptotic effects than non-cisplatin-resistant A549 cells by the way of activating p53 protein and the related signalling pathway, which could be proved through the apparent endocytosis behaviour by the nucleus of cisplatin-resistant A549/DDP cells. As for NSCLC, the synthesized Pt NCs-based anticancer drugs could overcome the toxic side effects and drug resistance to enhance the clinical therapeutic effect.

In contrast to the well-known cisplatin resistance mechanism concerning about antiapoptotic factors that counteract caspase activation (Figure 14(a)), the mechanism for Pt NCs-based nanomedicine is still inconclusive. Some researches assume that ultrafine Pt subnanomaterials possess extreme tiny size approximately 1 nm, leading to near 90% of Pt atoms exposed on the NC’s surface. This kind of high surface-active Pt NCs is affected by intracellular acidic organelles like endosomes and lysosomes and then rapidly decomposed to form oxidation states of Pt (Figure 14(b)) [204]. These corrosive Pt trends to combine with DNA or proteins and then destroy the DNA consequently, resulting in the apoptosis of cancer cells. In addition, ultrafine Pt NCs have an ability to anchor onto the grooves of DNA double helix to further damage the DNA. Thus, the reasonable and receivable mechanism for the Pt NCs-based chemotherapeutics may be summarized as the synergistic effect of both Pt NCs and Pt ions causing the damage of DNA to kill the cancer cells.

4.3. Antibacteria

The usage of noble metal (Ag and Au) as antimicrobial agents was largely investigated, especially for Ag-based nanomaterials [205]. The mechanisms of antibacteria are related to the DNA damage, membrane damage, and production of some active radicals (e.g., reactive oxygen species (ROS)). Because of the ultrafine size of NCs, Ag NCs with higher surface-to-volume ratios and abundant surface atoms express higher antimicrobial efficiency. However, the antibacterial feature of Pt NCs is rarely studied. Subramaniyan et al. put forward the green synthesis protocol employing phytoprotein obtained from spinach leaves as a ligand to gain spherical Pt NCs with the average size of 5 nm and self-assembled species at the size range from 100 to 250 nm [206]. These protein-stabilized Pt NCs have the excellent Salmonella typhi-inhibiting ability, and the minimum inhibitory concentration (MIC) was determined at 12.5 μM (Figure 15). The inhibition effect was proved as the damage of established biofilms, confirmed by scanning electron microscopy (SEM) and fluorescence microscopy. Moreover, intracellular ROS generated by Pt NCs was also the ancillary killer to Salmonella typhi via oxidative injury against the antioxidant defence.

5. Conclusions and Outlook

Conclusively, Pt NCs containing few to dozens of atoms exhibit unique physicochemical properties due to their molecule-like behaviours such as discrete electronic state and size-dependent fluorescence. The synthesis of Pt NCs can be divided into two ways: template-assisted approach that is related to designed properties, controllable size, and specific morphology and template-free protocol which has access to the feasible posttreatment process and pure product. Subsequently, the optical, catalytic, and thermal properties of Pt NCs were introduced and these features have a strong relationship with the distinct electronic and structural characteristics, as well as the various surrounding ligands. Breaking the traditional concepts, ultrafine Pt NCs exhibit the favourable catalytic abilities even in the form of less symmetric topological structure. Most importantly, the diverse biological applications of Pt NCs were summarized in detail. Fluorescent Pt NCs have already bioimaged different kinds of tumours like HeLa cells, hematopoietic K569 and BV173 cells, NSCLC A549 cells, and HepG2 cells, as a preferred fluorophore in contrast to traditional fluorescent labels. Moreover, Pt NCs were employed as new class chemotherapeutics in the diagnoses and treatment of hematopoietic, lung, and hepatocellular malignant tumours, exhibiting excellent therapy effect, especially overcoming the problem of cisplatin resistance. Finally, Pt NCs were identified to possess a good antibacterial capacity which could be used as an alternative of the Ag antibacterial material.

Despite these exciting and promising progress of Pt NCs mentioned above, the study of ultrafine Pt NCs is at the beginning stage and there still remains a great challenge as follows: (1) synthesis of NIR fluorescent Pt NCs with outstanding optical features, (2) evident clarification of the apoptosis pathway and mechanism of Pt NCs for hematopoietic tumour and cisplatin-resistant NSCLC, (3) valid combination of Pt NCs with other materials to endow multifunctionality, and (4) comprehensive utilization of Pt NCs in diverse biological applications, not only for the different tissue systems (like osteocarcinoma and pancreatic carcinoma) but also the application types that need to be extended such as gene therapy, DNA sensing, and protein detection.

Conflicts of Interest

The authors declare that there is no conflict of interest regarding the publication of this paper.


This research was funded by the National Natural Science Foundation of China (21807121), Key Scientific Research Projects of High Education of Henan Province (18A430005), and Project for Fundamental Research Funds of Zhongyuan University of Technology (K2018YY020). Dr. X.H. gratefully acknowledges the Collaborative Innovation Centre of Textile and Garment Industry, Henan Province, for their assistance and the support from the 2019 Youth Talents Promotion Project of Henan Province, the 2018 Backbone Teachers of Zhongyuan University of Technology, and the Program for Interdisciplinary Direction Team in Zhongyuan University of Technology, China.


  1. W. P. Griffith, The Chemistry of the Rarer Platinum Metals (Os, Ru, Ir, and Rh), Interscience Publishers, 1967.
  2. F. R. Hartley, The Chemistry of Platinum and Palladium: With Particular Reference to Complexes of the Elements, Applied Science Publishers Ltd., 1973.
  3. X. Huang, Polymer Ligand Stabilized Fluorescent Platinum Nanoclusters: Synthesis, Characterization, and Their Applications, Osaka University, 2016.
  4. R. W. Siegel, “Nanostructured materials -mind over matter,” Nanostructured Materials, vol. 4, no. 1, pp. 121–138, 1994. View at: Publisher Site | Google Scholar
  5. P. C. Ray, “Size and shape dependent second order nonlinear optical properties of nanomaterials and their application in biological and chemical sensing,” Chemical Reviews, vol. 110, no. 9, pp. 5332–5365, 2010. View at: Publisher Site | Google Scholar
  6. X. Jiang, B. Du, Y. Huang, and J. Zheng, “Ultrasmall noble metal nanoparticles: breakthroughs and biomedical implications,” Nano Today, vol. 21, pp. 106–125, 2018. View at: Publisher Site | Google Scholar
  7. G. Mie, “Beiträge zur optik trüber medien, speziell kolloidaler metallösungen (Contributions to the optics of diffuse media, especially colloid metal solutions),” Annals of Physics, vol. 330, no. 3, pp. 377–445, 1908. View at: Publisher Site | Google Scholar
  8. P. K. Jain, X. Huang, I. H. El-Sayed, and M. A. El-Sayed, “Noble metals on the nanoscale: optical and photothermal properties and some applications in imaging, sensing, biology, and medicine,” Accounts of Chemical Research, vol. 41, no. 12, pp. 1578–1586, 2008. View at: Publisher Site | Google Scholar
  9. M. Faraday, “XLVII. Experimental relations of gold (and other metals) to light. – The Bakerian lecture,” The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science, vol. 14, no. 95, pp. 401–417, 1857. View at: Publisher Site | Google Scholar
  10. H. Kang, J. T. Buchman, R. S. Rodriguez et al., “Stabilization of silver and gold nanoparticles: preservation and improvement of plasmonic functionalities,” Chemical Reviews, vol. 119, no. 1, pp. 664–699, 2019. View at: Publisher Site | Google Scholar
  11. A. Amirjani and D. F. Haghshenas, “Ag nanostructures as the surface plasmon resonance (SPR)?based sensors: a mechanistic study with an emphasis on heavy metallic ions detection,” Sensors and Actuators B: Chemical, vol. 273, pp. 1768–1779, 2018. View at: Publisher Site | Google Scholar
  12. M. M. Alvarez, J. T. Khoury, T. G. Schaaff, M. N. Shafigullin, I. Vezmar, and R. L. Whetten, “Optical absorption spectra of nanocrystal gold molecules,” The Journal of Physical Chemistry B, vol. 101, no. 19, pp. 3706–3712, 1997. View at: Publisher Site | Google Scholar
  13. S. K. Ghosh and T. Pal, “Interparticle coupling effect on the surface plasmon resonance of gold nanoparticles: from theory to applications,” Chemical Reviews, vol. 107, no. 11, pp. 4797–4862, 2007. View at: Publisher Site | Google Scholar
  14. E. Konował, A. Modrzejewska-Sikorska, M. Motylenko et al., “Functionalization of organically modified silica with gold nanoparticles in the presence of lignosulfonate,” International Journal of Biological Macromolecules, vol. 85, pp. 74–81, 2016. View at: Publisher Site | Google Scholar
  15. A. Modrzejewska-Sikorska, E. Konował, A. Cichy, M. Nowicki, T. Jesionowski, and G. Milczarek, “The effect of silver salts and lignosulfonates in the synthesis of lignosulfonate-stabilized silver nanoparticles,” Journal of Molecular Liquids, vol. 240, pp. 80–86, 2017. View at: Publisher Site | Google Scholar
  16. Q. Tong, W. Wang, Y. Fan, and L. Dong, “Recent progressive preparations and applications of silver-based SERS substrates,” TrAC Trends in Analytical Chemistry, vol. 106, pp. 246–258, 2018. View at: Publisher Site | Google Scholar
  17. G. Schmid, “Large clusters and colloids. Metals in the embryonic state,” Chemical Reviews, vol. 92, no. 8, pp. 1709–1727, 1992. View at: Publisher Site | Google Scholar
  18. F. A. Cotton and T. E. Haas, “A molecular orbital treatment of the bonding in certain metal atom clusters,” Inorganic Chemistry, vol. 3, no. 1, pp. 10–17, 1964. View at: Publisher Site | Google Scholar
  19. L. Yu, L. Zhang, G. Ren et al., “Multicolorful fluorescent-nanoprobe composed of Au nanocluster and carbon dots for colorimetric and fluorescent sensing Hg2+ and Cr6+,” Sensors and Actuators B: Chemical, vol. 262, pp. 678–686, 2018. View at: Publisher Site | Google Scholar
  20. M. I. Halawa, J. Lai, and G. Xu, “Gold nanoclusters: synthetic strategies and recent advances in fluorescent sensing,” Materials Today Nano, vol. 3, pp. 9–27, 2018. View at: Publisher Site | Google Scholar
  21. H. Yu, B. Rao, W. Jiang, S. Yang, and M. Zhu, “The photoluminescent metal nanoclusters with atomic precision,” Coordination Chemistry Reviews, vol. 378, pp. 595–617, 2019. View at: Publisher Site | Google Scholar
  22. R. Jin, “Atomically precise metal nanoclusters: stable sizes and optical properties,” Nanoscale, vol. 7, no. 5, pp. 1549–1565, 2015. View at: Publisher Site | Google Scholar
  23. R. Jin, C. Zeng, M. Zhou, and Y. Chen, “Atomically precise colloidal metal nanoclusters and nanoparticles: fundamentals and opportunities,” Chemical Reviews, vol. 116, no. 18, pp. 10346–10413, 2016. View at: Publisher Site | Google Scholar
  24. T.-H. Lee, J. I. Gonzalez, J. Zheng, and R. M. Dickson, “Single-molecule optoelectronics,” Accounts of Chemical Research, vol. 38, no. 7, pp. 534–541, 2005. View at: Publisher Site | Google Scholar
  25. S. Morawiec, M. J. Mendes, F. Priolo, and I. Crupi, “Plasmonic nanostructures for light trapping in thin-film solar cells,” Materials Science in Semiconductor Processing, vol. 92, pp. 10–18, 2019. View at: Publisher Site | Google Scholar
  26. F. Lu, H. Yang, Z. Yuan, T. Nakanishi, C. Lu, and Y. He, “Highly fluorescent polyethyleneimine protected Au8 nanoclusters: one-pot synthesis and application in hemoglobin detection,” Sensors and Actuators B: Chemical, vol. 291, pp. 170–176, 2019. View at: Publisher Site | Google Scholar
  27. N. Xiao, J. X. Dong, S. G. Liu et al., “Multifunctional fluorescent sensors for independent detection of multiple metal ions based on Ag nanoclusters,” Sensors and Actuators B: Chemical, vol. 264, pp. 184–192, 2018. View at: Publisher Site | Google Scholar
  28. S. Ghosh, J. R. Bhamore, N. I. Malek, Z. V. P. Murthy, and S. K. Kailasa, “Trypsin mediated one-pot reaction for the synthesis of red fluorescent gold nanoclusters: sensing of multiple analytes (carbidopa, dopamine, Cu2+, Co2+ and Hg2+ ions),” Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, vol. 215, pp. 209–217, 2019. View at: Publisher Site | Google Scholar
  29. X. Y. Wang, G. B. Zhu, W. D. Cao et al., “A novel ratiometric fluorescent probe for the detection of uric acid in human blood based on H2O2-mediated fluorescence quenching of gold/silver nanoclusters,” Talanta, vol. 191, pp. 46–53, 2019. View at: Publisher Site | Google Scholar
  30. J. D. Aiken III and R. G. Finke, “A review of modern transition-metal nanoclusters: their synthesis, characterization, and applications in catalysis,” Journal of Molecular Catalysis A: Chemical, vol. 145, no. 1–2, pp. 1–44, 1999. View at: Publisher Site | Google Scholar
  31. Y. Zhang, C. Zhang, C. Xu et al., “Ultrasmall Au nanoclusters for biomedical and biosensing applications: a mini-review,” Talanta, vol. 200, pp. 432–442, 2019. View at: Publisher Site | Google Scholar
  32. L. N. Lewis, “Chemical catalysis by colloids and clusters,” Chemical Reviews, vol. 93, no. 8, pp. 2693–2730, 1993. View at: Publisher Site | Google Scholar
  33. J. Wu and H. Yang, “Platinum-based oxygen reduction electrocatalysts,” Accounts of Chemical Research, vol. 46, no. 8, pp. 1848–1857, 2013. View at: Publisher Site | Google Scholar
  34. Z. Peng and H. Yang, “Designer platinum nanoparticles: control of shape, composition in alloy, nanostructure and electrocatalytic property,” Nano Today, vol. 4, no. 2, pp. 143–164, 2009. View at: Publisher Site | Google Scholar
  35. H. Xiao, L. Yan, E. M. Dempsey et al., “Recent progress in polymer-based platinum drug delivery systems,” Progress in Polymer Science, vol. 87, pp. 70–106, 2018. View at: Publisher Site | Google Scholar
  36. A. V. Klein and T. W. Hambley, “Platinum drug distribution in cancer cells and tumors,” Chemical Reviews, vol. 109, no. 10, pp. 4911–4920, 2009. View at: Publisher Site | Google Scholar
  37. A. Chen and P. Holt-Hindle, “Platinum-based nanostructured materials: synthesis, properties, and applications,” Chemical Reviews, vol. 110, no. 6, pp. 3767–3804, 2010. View at: Publisher Site | Google Scholar
  38. R. Jin, “Quantum sized, thiolate-protected gold nanoclusters,” Nanoscale, vol. 2, no. 3, pp. 343–362, 2010. View at: Publisher Site | Google Scholar
  39. Y. Wang, H. Guo, Y. Zhang et al., “Achieving highly water-soluble and luminescent gold nanoclusters modified by β–cyclodextrin as multifunctional nanoprobe for biological applications,” Dyes and Pigments, vol. 157, pp. 359–368, 2018. View at: Publisher Site | Google Scholar
  40. I. Diez and R. H. A. Ras, “Fluorescent silver nanoclusters,” Nanoscale, vol. 3, no. 5, pp. 1963–1970, 2011. View at: Publisher Site | Google Scholar
  41. C.-H. Lu and F.-C. Chang, “Polyhedral oligomeric silsesquioxane-encapsulating amorphous palladium nanoclusters as catalysts for heck reactions,” ACS Catalysis, vol. 1, no. 5, pp. 481–488, 2011. View at: Publisher Site | Google Scholar
  42. X. Liu and D. Astruc, “Atomically precise copper nanoclusters and their applications,” Coordination Chemistry Reviews, vol. 359, pp. 112–126, 2018. View at: Publisher Site | Google Scholar
  43. Q. Yao, T. Chen, X. Yuan, and J. Xie, “Toward total synthesis of thiolate-protected metal nanoclusters,” Accounts of Chemical Research, vol. 51, no. 6, pp. 1338–1348, 2018. View at: Publisher Site | Google Scholar
  44. B. Helmut and S. Nagabhushana Kyatanahalli, “Chapter 2 - metal nanoclusters: synthesis and strategies for their size control,” in Metal nanoclusters in catalysis and materials science: the issue of size control, pp. 21–48, Elsevier, 2008. View at: Publisher Site | Google Scholar
  45. O. Kylián, J. Prokeš, O. Polonskyi et al., “Deposition and characterization of Pt nanocluster films by means of gas aggregation cluster source,” Thin Solid Films, vol. 571, pp. 13–17, 2014. View at: Publisher Site | Google Scholar
  46. K. Sokołowska, S. Malola, M. Lahtinen et al., “Towards controlled synthesis of water-soluble gold nanoclusters: synthesis and analysis,” Journal of Physical Chemistry C, vol. 123, no. 4, pp. 2602–2612, 2019. View at: Publisher Site | Google Scholar
  47. S. W. Cho, H. J. Kim, Y. N. Cho, J. H. Jeong, and H. Kong, “Top-down synthesis of polyaspartamide morphogens to derive platinum nanoclusters,” Materials Letters, vol. 168, pp. 184–187, 2016. View at: Publisher Site | Google Scholar
  48. R. R. Nasaruddin, T. Chen, N. Yan, and J. Xie, “Roles of thiolate ligands in the synthesis, properties and catalytic application of gold nanoclusters,” Coordination Chemistry Reviews, vol. 368, pp. 60–79, 2018. View at: Publisher Site | Google Scholar
  49. W. W. Weare, S. M. Reed, M. G. Warner, and J. E. Hutchison, “Improved synthesis of small (dCORE ≈ 1.5 nm) phosphine-stabilized gold nanoparticles,” Journal of the American Chemical Society, vol. 122, no. 51, pp. 12890-12891, 2000. View at: Publisher Site | Google Scholar
  50. Ö. Metin, S. Duman, M. Dinç, and S. Özkar, “Oleylamine-stabilized palladium(0) nanoclusters as highly active heterogeneous catalyst for the dehydrogenation of ammonia borane,” The Journal of Physical Chemistry C, vol. 115, no. 21, pp. 10736–10743, 2011. View at: Publisher Site | Google Scholar
  51. J. Xu, X. Wu, G. Fu et al., “Fabrication of phosphonate functionalized platinum nanoclusters and their application in hydrogen peroxide sensing in the presence of oxygen,” Electrochimica Acta, vol. 80, pp. 233–239, 2012. View at: Publisher Site | Google Scholar
  52. J. Ma, S. Reng, D. Pan, R. Li, and K. Xie, “PVP-Pt nanoclusters supported zeolite catalysts for converting methane to higher hydrocarbon at low temperature,” Reactive and Functional Polymers, vol. 62, no. 1, pp. 31–39, 2005. View at: Publisher Site | Google Scholar
  53. I. Díez, M. Pusa, S. Kulmala et al., “Color tunability and electrochemiluminescence of silver nanoclusters,” Angewandte Chemie International Edition, vol. 48, no. 12, pp. 2122–2125, 2009. View at: Publisher Site | Google Scholar
  54. R. M. Crooks, B. I. Lemon, L. Sun, L. K. Yeung, and M. Zhao, “Dendrimer-encapsulated metals and semiconductors: synthesis, characterization, and applications,” in Dendrimers III, F. Vögtle, Ed., vol. 212 of Topics in Current Chemistry, pp. 81–135, Springer, Berlin, Heidelberg, 2001. View at: Publisher Site | Google Scholar
  55. X. Huang, H. Zhang, L. Liang, and B. Tan, “Preparation of nanoparticles with multi-functional water-soluble polymer ligands,” Progress in Chemistry, vol. 22, no. 5, pp. 953–961, 2010. View at: Google Scholar
  56. N. Erathodiyil and J. Y. Ying, “Functionalization of inorganic nanoparticles for bioimaging applications,” Accounts of Chemical Research, vol. 44, no. 10, pp. 925–935, 2011. View at: Publisher Site | Google Scholar
  57. A. Lopez and J. Liu, “DNA-templated fluorescent gold nanoclusters reduced by good’s buffer: from blue-emitting seeds to red and near infrared emitters,” Canadian Journal of Chemistry, vol. 93, no. 6, pp. 615–620, 2015. View at: Publisher Site | Google Scholar
  58. W. Y. Mu, R. Yang, A. Robertson, and Q. Y. Chen, “A near-infrared BSA coated DNA-AgNCs for cellular imaging,” Colloids and Surfaces B: Biointerfaces, vol. 162, pp. 427–431, 2018. View at: Publisher Site | Google Scholar
  59. A. Aires, I. Llarena, M. Moller, J. Castro-Smirnov, J. Cabanillas-Gonzalez, and A. L. Cortajarena, “A simple approach to design proteins for the sustainable synthesis of metal nanoclusters,” Angewandte Chemie International Edition, vol. 58, no. 19, pp. 6214–6219, 2019. View at: Publisher Site | Google Scholar
  60. S. M. Ghoreishian, S. M. Kang, G. Seeta Rama Raju et al., “γ-Radiolysis as a highly efficient green approach to the synthesis of metal nanoclusters: a review of mechanisms and applications,” Chemical Engineering Journal, vol. 360, pp. 1390–1406, 2019. View at: Publisher Site | Google Scholar
  61. B. A. Roberts and C. R. Strauss, “Toward rapid, “green”, predictable microwave-assisted synthesis,” Accounts of Chemical Research, vol. 38, no. 8, pp. 653–661, 2005. View at: Publisher Site | Google Scholar
  62. H. Xu, B. W. Zeiger, and K. S. Suslick, “Sonochemical synthesis of nanomaterials,” Chemical Society Reviews, vol. 42, no. 7, pp. 2555–2567, 2013. View at: Publisher Site | Google Scholar
  63. K. Watanabe, D. Menzel, N. Nilius, and H.-J. Freund, “Photochemistry on metal nanoparticles,” Chemical Reviews, vol. 106, no. 10, pp. 4301–4320, 2006. View at: Publisher Site | Google Scholar
  64. R. A. Hackendorn and A. V. Virkar, “Synthesis of platinum nanoclusters and electrochemical investigation of their stability,” Journal of Power Sources, vol. 240, pp. 618–629, 2013. View at: Publisher Site | Google Scholar
  65. X. Yuan, Z. Luo, Q. Zhang et al., “Synthesis of highly fluorescent metal (Ag, Au, Pt, and Cu) nanoclusters by electrostatically induced reversible phase transfer,” ACS Nano, vol. 5, no. 11, pp. 8800–8808, 2011. View at: Publisher Site | Google Scholar
  66. I. Chakraborty, R. G. Bhuin, S. Bhat, and T. Pradeep, “Blue emitting undecaplatinum clusters,” Nanoscale, vol. 6, no. 15, pp. 8561–8564, 2014. View at: Publisher Site | Google Scholar
  67. L. Wang, S. Ouyang, B. Liu, R. Yang, T. Wang, and S. Wang, “One-pot synthesis of octahedral platinum nanoclusters with enhanced electrocatalytic activities,” Materials Research Bulletin, vol. 61, pp. 357–362, 2015. View at: Publisher Site | Google Scholar
  68. R. W. J. Scott, O. M. Wilson, and R. M. Crooks, “Synthesis, characterization, and applications of dendrimer-encapsulated nanoparticles,” The Journal of Physical Chemistry B, vol. 109, no. 2, pp. 692–704, 2005. View at: Publisher Site | Google Scholar
  69. Y. Borodko, C. M. Thompson, W. Huang, H. B. Yildiz, H. Frei, and G. A. Somorjai, “Spectroscopic study of platinum and rhodium dendrimer (PAMAM G4OH) compounds: structure and stability,” The Journal of Physical Chemistry C, vol. 115, no. 11, pp. 4757–4767, 2011. View at: Publisher Site | Google Scholar
  70. P. Maity, S. Yamazoe, and T. Tsukuda, “Dendrimer-encapsulated copper cluster as a chemoselective and regenerable hydrogenation catalyst,” ACS Catalysis, vol. 3, no. 2, pp. 182–185, 2013. View at: Publisher Site | Google Scholar
  71. H. Lim, Y. Ju, and J. Kim, “Tailoring catalytic activity of Pt nanoparticles encapsulated inside dendrimers by tuning nanoparticle sizes with subnanometer accuracy for sensitive chemiluminescence-based analyses,” Analytical Chemistry, vol. 88, no. 9, pp. 4751–4758, 2016. View at: Publisher Site | Google Scholar
  72. Y. Borodko, P. Ercius, V. Pushkarev, C. Thompson, and G. Somorjai, “From single Pt atoms to Pt nanocrystals: photoreduction of Pt2+ inside of a PAMAM dendrimer,” The Journal of Physical Chemistry Letters, vol. 3, no. 2, pp. 236–241, 2012. View at: Publisher Site | Google Scholar
  73. W. Tu and H. Liu, “Continuous synthesis of colloidal metal nanoclusters by microwave irradiation,” Chemistry of Materials, vol. 12, no. 2, pp. 564–567, 2000. View at: Publisher Site | Google Scholar
  74. H. Zhang, X. Huang, L. Li et al., “Photoreductive synthesis of water-soluble fluorescent metal nanoclusters,” Chemical Communications, vol. 48, no. 4, pp. 567–569, 2012. View at: Publisher Site | Google Scholar
  75. J. Quinson, L. Kacenauskaite, T. L. Christiansen, T. Vosch, M. Arenz, and K. M. Ø. Jensen, “Spatially localized synthesis and structural characterization of platinum nanocrystals obtained using UV light,” ACS Omega, vol. 3, no. 8, pp. 10351–10356, 2018. View at: Publisher Site | Google Scholar
  76. P. Wang, F. Li, X. Huang, Y. Li, and L. Wang, “In situ electrodeposition of Pt nanoclusters on glassy carbon surface modified by monolayer choline film and their electrochemical applications,” Electrochemistry Communications, vol. 10, no. 2, pp. 195–199, 2008. View at: Publisher Site | Google Scholar
  77. F. Liu, Y. Deng, X. Han, W. Hu, and C. Zhong, “Electrodeposition of metals and alloys from ionic liquids,” Journal of Alloys and Compounds, vol. 654, pp. 163–170, 2016. View at: Publisher Site | Google Scholar
  78. L. Qian, Y. Liu, Y. Song, Z. Li, and X. Yang, “Electrodeposition of Pt nanoclusters on the surface modified by monolayer poly(amidoamine) dendrimer film,” Electrochemistry Communications, vol. 7, no. 12, pp. 1209–1212, 2005. View at: Publisher Site | Google Scholar
  79. J. Camacho-Bunquin, M. S. Ferrandon, H. Sohn et al., “Atomically precise strategy to a PtZn alloy nanocluster catalyst for the deep dehydrogenation of n-butane to 1,3-butadiene,” ACS Catalysis, vol. 8, no. 11, pp. 10058–10063, 2018. View at: Publisher Site | Google Scholar
  80. H. Shi, P. S. Thapa, B. Subramaniam, and R. V. Chaudhari, “Oxidation of glucose using mono- and bimetallic catalysts under base-free conditions,” Organic Process Research & Development, vol. 22, no. 12, pp. 1653–1662, 2018. View at: Publisher Site | Google Scholar
  81. J. Zhang, W. L. Yu, S. H. Zhou, Y. Li, Y.-F. Zhang, and W.-K. Chen, “Nanoclusters Au19Pd and Au19Pt catalyzing CO oxidation: a density functional study,” Chinese Journal of Structural Chemistry, vol. 37, no. 12, pp. 1849–1859, 2018. View at: Publisher Site | Google Scholar
  82. K. Li, Y. Li, Y. Wang, J. Ge, C. Liu, and W. Xing, “Enhanced electrocatalytic performance for the hydrogen evolution reaction through surface enrichment of platinum nanoclusters alloying with ruthenium in situ embedded in carbon,” Energy & Environmental Science, vol. 11, no. 5, pp. 1232–1239, 2018. View at: Publisher Site | Google Scholar
  83. X. L. Chen, L. Zhang, J. J. Feng et al., “Facile solvothermal fabrication of polypyrrole sheets supported dendritic platinum-cobalt nanoclusters for highly efficient oxygen reduction and ethylene glycol oxidation,” Journal of Colloid and Interface Science, vol. 530, pp. 394–402, 2018. View at: Publisher Site | Google Scholar
  84. V. Sharma, S. Kumar, and V. Krishnan, “Homogeneously embedded Pt nanoclusters on amorphous titania matrix as highly efficient visible light active photocatalyst material,” Materials Chemistry and Physics, vol. 179, pp. 129–136, 2016. View at: Publisher Site | Google Scholar
  85. A. S. Maldonado, C. I. N. Morgade, S. B. Ramos, and G. F. Cabeza, “Comparative study of CO adsorption on planar and tetrahedral Pt nanoclusters supported on TiO2(110) stoichiometric and reduced surfaces,” Molecular Catalysis, vol. 433, pp. 403–413, 2017. View at: Publisher Site | Google Scholar
  86. M. Torabi, R. Karimi Shervedani, and A. Amini, “High performance porous graphene nanoribbons electrodes synthesized via hydrogen plasma and modified by Pt-Ru nanoclusters for charge storage and methanol oxidation,” Electrochimica Acta, vol. 290, pp. 616–625, 2018. View at: Publisher Site | Google Scholar
  87. L. Sun, B. Wang, and Y. Wang, “A Schottky-junction-based platinum nanoclusters@silicon carbide nanosheet as long-term stable hydrogen sensors,” Applied Surface Science, vol. 473, pp. 641–648, 2019. View at: Publisher Site | Google Scholar
  88. L. Lu, “Highly sensitive detection of nitrite at a novel electrochemical sensor based on mutually stabilized Pt nanoclusters doped CoO nanohybrid,” Sensors and Actuators B: Chemical, vol. 281, pp. 182–190, 2019. View at: Publisher Site | Google Scholar
  89. X. Zuo, H. Liu, D. Guo, and X. Yang, “Enantioselective hydrogenation of pyruvates over polymer-stabilized and supported platinum nanoclusters,” Tetrahedron, vol. 55, no. 25, pp. 7787–7804, 1999. View at: Publisher Site | Google Scholar
  90. K. A. Carrado, G. Sandi, R. Kizilel, S. Seifert, and N. Castagnola, “Platinum nanoclusters immobilized on polymer–clay nanocomposite films,” Applied Clay Science, vol. 30, no. 2, pp. 94–102, 2005. View at: Publisher Site | Google Scholar
  91. Z. Marco, C. Paolo, and C. Benedetto, “Chapter 10 - metal nanoclusters supported on cross-linked functional polymers: a class of emerging metal catalysts,” in Metal Nanoclusters in Catalysis and Materials Science: the issue of size control, pp. 201–232, Elsevier, 2008. View at: Publisher Site | Google Scholar
  92. L. Jia, D. A. Bulushev, O. Y. Podyacheva et al., “Pt nanoclusters stabilized by N-doped carbon nanofibers for hydrogen production from formic acid,” Journal of Catalysis, vol. 307, pp. 94–102, 2013. View at: Publisher Site | Google Scholar
  93. M. F. Luo, W. H. Wen, C. S. Lin, C. I. Chiang, S. D. Sartale, and M. S. Zei, “Structures of Co and Pt nanoclusters on a thin film of Al2O3/NiAl(100) from reflection high-energy electron diffraction and scanning-tunnelling microscopy,” Surface Science, vol. 601, no. 10, pp. 2139–2146, 2007. View at: Publisher Site | Google Scholar
  94. M. F. Luo, W. R. Lin, W. H. Wen, and B. W. Chang, “Methanol electro-oxidation and induced sintering on Pt nanoclusters supported on thin-film Al2O3/NiAl(100),” Surface Science, vol. 602, no. 21, pp. 3258–3265, 2008. View at: Publisher Site | Google Scholar
  95. C. S. Chao, T. W. Liao, C. X. Wang, Y. D. Li, T. C. Hung, and M. F. Luo, “Obstruction by CO of the decomposition of methanol on Pt nanoclusters on a thin film of Al2O3/NiAl(100),” Applied Surface Science, vol. 293, pp. 352–358, 2014. View at: Publisher Site | Google Scholar
  96. A. S. Bazhenov and K. Honkala, “Globally optimized equilibrium shapes of zirconia-supported Rh and Pt nanoclusters: insights into site assembly and reactivity,” The Journal of Physical Chemistry C, vol. 123, no. 12, pp. 7209–7216, 2019. View at: Publisher Site | Google Scholar
  97. M. Mon, M. A. Rivero-Crespo, J. Ferrando-Soria et al., “Synthesis of densely packaged, ultrasmall Pt02 clusters within a thioether-functionalized MOF: catalytic activity in industrial reactions at low temperature,” Angewandte Chemie International Edition, vol. 57, no. 21, pp. 6186–6191, 2018. View at: Publisher Site | Google Scholar
  98. C. Feng and P. He, “Atomistic investigation on the diffusion mechanism of Pt nanoclusters on well-aligned multi-walled carbon nanotubes,” Computational Materials Science, vol. 103, pp. 157–164, 2015. View at: Publisher Site | Google Scholar
  99. H. Huang, Z. He, X. Lin, W. Ruan, Y. Liu, and Z. Yang, “Ultradispersed platinum nanoclusters on polydopamine-functionalized carbon nanotubes as an excellent catalyst for methanol oxidation reaction,” Applied Catalysis A: General, vol. 490, pp. 65–70, 2015. View at: Publisher Site | Google Scholar
  100. I. Fampiou and A. Ramasubramaniam, “Influence of support effects on CO oxidation kinetics on CO-saturated graphene-supported Pt13 nanoclusters,” The Journal of Physical Chemistry C, vol. 119, no. 16, pp. 8703–8710, 2015. View at: Publisher Site | Google Scholar
  101. P. Y. Cai, Y. W. Huang, Y. C. Huang et al., “Atomic structures of Pt nanoclusters supported on graphene grown on Pt(111),” The Journal of Physical Chemistry C, vol. 122, no. 28, pp. 16132–16141, 2018. View at: Publisher Site | Google Scholar
  102. F. Düll, F. Späth, U. Bauer et al., “Reactivity of CO on sulfur-passivated graphene-supported platinum nanocluster arrays,” The Journal of Physical Chemistry C, vol. 122, no. 28, pp. 16008–16015, 2018. View at: Publisher Site | Google Scholar
  103. X. Liu, Y. Tang, M. Shen et al., “Bifunctional CO oxidation over Mn-mullite anchored Pt sub-nanoclusters via atomic layer deposition,” Chemical Science, vol. 9, no. 9, pp. 2469–2473, 2018. View at: Publisher Site | Google Scholar
  104. D. Lee, Y. Kim, Y. Kwon et al., “Boosting the electrocatalytic glycerol oxidation performance with highly-dispersed Pt nanoclusters loaded on 3D graphene-like microporous carbon,” Applied Catalysis B: Environmental, vol. 245, pp. 555–568, 2019. View at: Publisher Site | Google Scholar
  105. Z. Wang, G. Zhang, Z. Zhong, Y. Lin, and Z. Su, “In-situ synthesis of platinum nanoclusters in polyelectrolyte multilayer films,” Thin Solid Films, vol. 660, pp. 59–64, 2018. View at: Publisher Site | Google Scholar
  106. M. Hyotanishi, Y. Isomura, H. Yamamoto, H. Kawasaki, and Y. Obora, “Surfactant-free synthesis of palladium nanoclusters for their use in catalytic cross-coupling reactions,” Chemical Communications, vol. 47, no. 20, pp. 5750–5752, 2011. View at: Publisher Site | Google Scholar
  107. H. Kawasaki, H. Yamamoto, H. Fujimori, R. Arakawa, M. Inada, and Y. Iwasaki, “Surfactant-free solution synthesis of fluorescent platinum subnanoclusters,” Chemical Communications, vol. 46, no. 21, pp. 3759–3761, 2010. View at: Publisher Site | Google Scholar
  108. P. N. Duchesne and P. Zhang, “Local structure of fluorescent platinum nanoclusters,” Nanoscale, vol. 4, no. 14, pp. 4199–4205, 2012. View at: Publisher Site | Google Scholar
  109. A. George, H. Gopalakrishnan, and S. Mandal, “Surfactant free platinum nanocluster as fluorescent probe for the selective detection of Fe (III) ions in aqueous medium,” Sensors and Actuators B: Chemical, vol. 243, pp. 332–337, 2017. View at: Publisher Site | Google Scholar
  110. P. Yu, X. Wen, Y.-R. Toh, X. Ma, and J. Tang, “Fluorescent metallic nanoclusters: electron dynamics, structure, and applications,” Particle & Particle Systems Characterization, vol. 32, no. 2, pp. 142–163, 2015. View at: Publisher Site | Google Scholar
  111. H. Jiang and X.-M. Wang, “Progress of metal nanoclusters-based electrochemiluminescent analysis,” Chinese Journal of Analytical Chemistry, vol. 45, no. 12, pp. 1776–1785, 2017. View at: Publisher Site | Google Scholar
  112. D. Li, Z. Chen, and X. Mei, “Fluorescence enhancement for noble metal nanoclusters,” Advances in Colloid and Interface Science, vol. 250, pp. 25–39, 2017. View at: Publisher Site | Google Scholar
  113. S. H. Kim, K. C. Kim, Y. S. Kim, and H. J. Kim, “Abnormal optical changes with the formation of Pt nanoclusters,” Current Applied Physics, vol. 6, no. 6, pp. 1036–1039, 2006. View at: Publisher Site | Google Scholar
  114. J. Zheng, P. R. Nicovich, and R. M. Dickson, “Highly fluorescent noble-metal quantum dots,” Annual Review of Physical Chemistry, vol. 58, no. 1, pp. 409–431, 2007. View at: Publisher Site | Google Scholar
  115. A. Heuer-Jungemann, N. Feliu, I. Bakaimi et al., “The role of ligands in the chemical synthesis and applications of inorganic nanoparticles,” Chemical Reviews, vol. 119, no. 8, pp. 4819–4880, 2019. View at: Publisher Site | Google Scholar
  116. Z. Wu and R. Jin, “On the ligand’s role in the fluorescence of gold nanoclusters,” Nano Letters, vol. 10, no. 7, pp. 2568–2573, 2010. View at: Publisher Site | Google Scholar
  117. J. M. Forward, D. Bohmann, J. P. Fackler, and R. J. Staples, “Luminescence studies of gold(I) thiolate complexes,” Inorganic Chemistry, vol. 34, no. 25, pp. 6330–6336, 1995. View at: Publisher Site | Google Scholar
  118. M. S. Devadas, J. Kim, E. Sinn, D. Lee, T. Goodson III, and G. Ramakrishna, “Unique ultrafast visible luminescence in monolayer-protected Au25 clusters,” Journal of Physical Chemistry C, vol. 114, no. 51, pp. 22417–22423, 2010. View at: Publisher Site | Google Scholar
  119. X. Huang, B. Li, L. Li et al., “Facile preparation of highly blue fluorescent metal nanoclusters in organic media,” The Journal of Physical Chemistry C, vol. 116, no. 1, pp. 448–455, 2012. View at: Publisher Site | Google Scholar
  120. X. Yuan, M. I. Setyawati, A. S. Tan, C. N. Ong, D. T. Leong, and J. Xie, “Highly luminescent silver nanoclusters with tunable emissions: cyclic reduction-decomposition synthesis and antimicrobial properties,” NPG Asia Materials, vol. 5, no. 2, article e39, 2013. View at: Publisher Site | Google Scholar
  121. E. Gwinn, D. Schultz, S. Copp, and S. Swasey, “DNA-protected silver clusters for nanophotonics,” Nanomaterials, vol. 5, no. 1, pp. 180–207, 2015. View at: Publisher Site | Google Scholar
  122. Y. S. Ang, W. W. E. Woon, and L. Y. L. Yung, “The role of spacer sequence in modulating turn-on fluorescence of DNA-templated silver nanoclusters,” Nucleic Acids Research, vol. 46, no. 14, pp. 6974–6982, 2018. View at: Publisher Site | Google Scholar
  123. M. Liu, F. Tang, Z. Yang, J. Xu, and X. Yang, “Recent progress on gold-nanocluster-based fluorescent probe for environmental analysis and biological sensing,” Journal of Analytical Methods in Chemistry, vol. 2019, Article ID 1095148, 10 pages, 2019. View at: Publisher Site | Google Scholar
  124. S. Shadpour, J. P. Vanegas, A. Nemati, and T. Hegmann, “Amplification of chirality by adenosine monophosphate-capped luminescent gold nanoclusters in nematic lyotropic chromonic liquid crystal tactoids,” ACS Omega, vol. 4, no. 1, pp. 1662–1668, 2019. View at: Publisher Site | Google Scholar
  125. L. Yang, X. Lou, F. Yu, and H. Liu, “Cross-linking structure-induced strong blue emissive gold nanoclusters for intracellular sensing,” Analyst, vol. 144, no. 8, pp. 2765–2772, 2019. View at: Publisher Site | Google Scholar
  126. J. V. Frangioni, “In vivo near-infrared fluorescence imaging,” Current Opinion in Chemical Biology, vol. 7, no. 5, pp. 626–634, 2003. View at: Publisher Site | Google Scholar
  127. B. Rosenberg, L. Vancamp, J. E. Trosko, and V. H. Mansour, “Platinum compounds: a new class of potent antitumour agents,” Nature, vol. 222, no. 5191, pp. 385-386, 1969. View at: Publisher Site | Google Scholar
  128. X. Xia, Y. Zhang, and J. Wang, “Novel fabrication of highly fluorescent Pt nanoclusters and their applications in hypochlorite assay,” RSC Advances, vol. 4, no. 48, pp. 25365–25368, 2014. View at: Publisher Site | Google Scholar
  129. X. Le Guével, V. Trouillet, C. Spies, G. Jung, and M. Schneider, “Synthesis of yellow-emitting platinum nanoclusters by ligand etching,” The Journal of Physical Chemistry C, vol. 116, no. 10, pp. 6047–6051, 2012. View at: Publisher Site | Google Scholar
  130. S.-I. Tanaka, J. Miyazaki, D. K. Tiwari, T. Jin, and Y. Inouye, “Fluorescent platinum nanoclusters: synthesis, purification, characterization, and application to bioimaging,” Angewandte Chemie International Edition, vol. 50, no. 2, pp. 431–435, 2011. View at: Publisher Site | Google Scholar
  131. S.-I. Tanaka, K. Aoki, A. Muratsugu, H. Ishitobi, T. Jin, and Y. Inouye, “Synthesis of green-emitting Pt8 nanoclusters for biomedical imaging by pre-equilibrated Pt/PAMAM (G4-OH) and mild reduction,” Optical Materials Express, vol. 3, no. 2, pp. 157–165, 2013. View at: Publisher Site | Google Scholar
  132. X. Huang, K. Aoki, H. Ishitobi, and Y. Inouye, “Preparation of Pt nanoclusters with different emission wavelengths and their application in Co2+ detection,” ChemPhysChem, vol. 15, no. 4, pp. 642–646, 2014. View at: Publisher Site | Google Scholar
  133. N. Xu, H.-W. Li, and Y. Wu, “Hydrothermal synthesis of polyethylenimine-protected high luminescent Pt-nanoclusters and their application to the detection of nitroimidazoles,” Analytica Chimica Acta, vol. 958, pp. 51–58, 2017. View at: Publisher Site | Google Scholar
  134. J. García Fernández, L. Trapiella-Alfonso, J. M. Costa-Fernández, R. Pereiro, and A. Sanz-Medel, “Aqueous synthesis of near-infrared highly fluorescent platinum nanoclusters,” Nanotechnology, vol. 26, no. 21, article 215601, 2015. View at: Publisher Site | Google Scholar
  135. F. Molaabasi, M. Sarparast, M. Shamsipur et al., “Shape-controlled synthesis of luminescent hemoglobin capped hollow porous platinum nanoclusters and their application to catalytic oxygen reduction and cancer imaging,” Scientific Reports, vol. 8, no. 1, article 14507, 2018. View at: Publisher Site | Google Scholar
  136. F. Klasovsky and P. Claus, “Chapter 8 - metal nanoclusters in catalysis: effects of nanoparticle size, shape, and structure,” in Metal Nanoclusters in Catalysis and Materials Science: the issue of size control, pp. 167–181, Elsevier, 2008. View at: Publisher Site | Google Scholar
  137. J. Ustarroz, I. M. Ornelas, G. Zhang et al., “Mobility and poisoning of mass-selected platinum nanoclusters during the oxygen reduction reaction,” ACS Catalysis, vol. 8, no. 8, pp. 6775–6790, 2018. View at: Publisher Site | Google Scholar
  138. J. Huang and M. Eikerling, “Modeling the oxygen reduction reaction at platinum-based catalysts: a brief review of recent developments,” Current Opinion in Electrochemistry, vol. 13, pp. 157–165, 2019. View at: Publisher Site | Google Scholar
  139. F. T. Wagner, B. Lakshmanan, and M. F. Mathias, “Electrochemistry and the future of the automobile,” The Journal of Physical Chemistry Letters, vol. 1, no. 14, pp. 2204–2219, 2010. View at: Publisher Site | Google Scholar
  140. X. Zhou, Y. Gan, J. du et al., “A review of hollow Pt-based nanocatalysts applied in proton exchange membrane fuel cells,” Journal of Power Sources, vol. 232, pp. 310–322, 2013. View at: Publisher Site | Google Scholar
  141. F. Zhang, F. Jiao, X. Pan et al., “Tailoring the oxidation activity of Pt nanoclusters via encapsulation,” ACS Catalysis, vol. 5, no. 2, pp. 1381–1385, 2015. View at: Publisher Site | Google Scholar
  142. G. Ercolano, S. Cavaliere, J. Rozière, and D. J. Jones, “Recent developments in electrocatalyst design thrifting noble metals in fuel cells,” Current Opinion in Electrochemistry, vol. 9, pp. 271–277, 2018. View at: Publisher Site | Google Scholar
  143. J. Zhang, X. Yan, and H. Liu, “The effects of tin on the hydrogenation of α-diketones over platinum nanoclusters,” Journal of Molecular Catalysis A: Chemical, vol. 176, no. 1-2, pp. 281–286, 2001. View at: Publisher Site | Google Scholar
  144. A. S. Crampton, “Hydrogenation reactions on small platinum clusters,” in Encyclopedia of Interfacial Chemistry, pp. 465–476, Elsevier, 2018. View at: Publisher Site | Google Scholar
  145. C. Adlhart and E. Uggerud, “Reactions of platinum clusters Ptn±, n=1–21, with CH4: to react or not to react,” Chemical Communications, no. 24, pp. 2581-2582, 2006. View at: Publisher Site | Google Scholar
  146. K. Kon, S. M. A. Hakim Siddiki, and K.-I. Shimizu, “Size- and support-dependent Pt nanocluster catalysis for oxidant-free dehydrogenation of alcohols,” Journal of Catalysis, vol. 304, pp. 63–71, 2013. View at: Publisher Site | Google Scholar
  147. R. M. Rioux, H. Song, P. Yang, and G. A. Somorjai, “Chapter 7 - platinum nanoclusters’ size and surface structure sensitivity of catalytic reactions,” in Metal nanoclusters in catalysis and materials science: the issue of size control, pp. 149–166, Elsevier, 2008. View at: Publisher Site | Google Scholar
  148. M. Shao, A. Peles, and K. Shoemaker, “Electrocatalysis on platinum nanoparticles: particle size effect on oxygen reduction reaction activity,” Nano Letters, vol. 11, no. 9, pp. 3714–3719, 2011. View at: Publisher Site | Google Scholar
  149. H. Yano, J. Inukai, H. Uchida et al., “Particle-size effect of nanoscale platinum catalysts in oxygen reduction reaction: an electrochemical and 195Pt EC-NMR study,” Physical Chemistry Chemical Physics, vol. 8, no. 42, pp. 4932–4939, 2006. View at: Publisher Site | Google Scholar
  150. T. Imaoka, H. Kitazawa, W.-J. Chun, and K. Yamamoto, “Finding the most catalytically active platinum clusters with low atomicity,” Angewandte Chemie International Edition, vol. 54, no. 34, pp. 9810–9815, 2015. View at: Publisher Site | Google Scholar
  151. S. Vajda, M. J. Pellin, J. P. Greeley et al., “Subnanometre platinum clusters as highly active and selective catalysts for the oxidative dehydrogenation of propane,” Nature Materials, vol. 8, no. 3, pp. 213–216, 2009. View at: Publisher Site | Google Scholar
  152. Y. Shiraishi, M. Nakayama, E. Takagi, T. Tominaga, and N. Toshima, “Effect of quantity of polymer on catalysis and superstructure size of polymer-protected Pt nanoclusters,” Inorganica Chimica Acta, vol. 300-302, pp. 964–969, 2000. View at: Publisher Site | Google Scholar
  153. J.-L. Lan, C.-C. Wan, T.-C. Wei, W.-C. Hsu, and Y.-H. Chang, “Durability test of PVP-capped Pt nanoclusters counter electrode for highly efficiency dye-sensitized solar cell,” Progress in Photovoltaics: Research and Applications, vol. 20, no. 1, pp. 44–50, 2012. View at: Publisher Site | Google Scholar
  154. H. Li, L. Li, and Y. Li, “The electronic structure and geometric structure of nanoclusters as catalytic active sites,” Nanotechnology Reviews, vol. 2, no. 5, pp. 515–528, 2013. View at: Publisher Site | Google Scholar
  155. T. Imaoka, H. Kitazawa, W. J. Chun, S. Omura, K. Albrecht, and K. Yamamoto, “Magic number Pt13 and misshapen Pt12 clusters: which one is the better catalyst?” Journal of the American Chemical Society, vol. 135, no. 35, pp. 13089–13095, 2013. View at: Publisher Site | Google Scholar
  156. V. S. Baidyshev, Y. Y. Gafner, S. L. Gafner, and L. V. Redel, “Thermal stability of Pt nanoclusters interacting to carbon sublattice,” Physics of the Solid State, vol. 59, no. 12, pp. 2512–2518, 2017. View at: Publisher Site | Google Scholar
  157. S. H. Lee, S. S. Han, J. K. Kang, J. H. Ryu, and H. M. Lee, “Phase stability of Pt nanoclusters and the effect of a (0001) graphite surface through molecular dynamics simulation,” Surface Science, vol. 602, no. 7, pp. 1433–1439, 2008. View at: Publisher Site | Google Scholar
  158. H. Akbarzadeh and G. A. Parsafar, “A molecular-dynamics study of thermal and physical properties of platinum nanoclusters,” Fluid Phase Equilibria, vol. 280, no. 1-2, pp. 16–21, 2009. View at: Publisher Site | Google Scholar
  159. M. Farrag, “Preparation, characterization and photocatalytic activity of size selected platinum nanoclusters,” Journal of Photochemistry and Photobiology A: Chemistry, vol. 318, pp. 42–50, 2016. View at: Publisher Site | Google Scholar
  160. D. Pedone, M. Moglianetti, E. De Luca, G. Bardi, and P. P. Pompa, “Platinum nanoparticles in nanobiomedicine,” Chemical Society Reviews, vol. 46, no. 16, pp. 4951–4975, 2017. View at: Publisher Site | Google Scholar
  161. J. Niu, X. Wang, J. Lv, Y. Li, and B. Tang, “Luminescent nanoprobes for in-vivo bioimaging,” TrAC Trends in Analytical Chemistry, vol. 58, pp. 112–119, 2014. View at: Publisher Site | Google Scholar
  162. F. Su, Q. Jia, Z. Li et al., “Aptamer-templated silver nanoclusters embedded in zirconium metal-organic framework for targeted antitumor drug delivery,” Microporous and Mesoporous Materials, vol. 275, pp. 152–162, 2019. View at: Publisher Site | Google Scholar
  163. S. Jin and K. Ye, “Nanoparticle-mediated drug delivery and gene therapy,” Biotechnology Progress, vol. 23, no. 1, pp. 32–41, 2007. View at: Publisher Site | Google Scholar
  164. A. K. Salem, P. C. Searson, and K. W. Leong, “Multifunctional nanorods for gene delivery,” Nature Materials, vol. 2, no. 10, pp. 668–671, 2003. View at: Publisher Site | Google Scholar
  165. J. Xu and L. Shang, “Emerging applications of near-infrared fluorescent metal nanoclusters for biological imaging,” Chinese Chemical Letters, vol. 29, no. 10, pp. 1436–1444, 2018. View at: Publisher Site | Google Scholar
  166. Z. Popović, W. Liu, V. P. Chauhan et al., “A nanoparticle size series for in vivo fluorescence imaging,” Angewandte Chemie International Edition, vol. 49, no. 46, pp. 8649–8652, 2010. View at: Publisher Site | Google Scholar
  167. V. Parthasarathy, S. Fery-Forgues, E. Campioli, G. Recher, F. Terenziani, and M. Blanchard-Desce, “Dipolar versus octupolar triphenylamine-based fluorescent organic nanoparticles as brilliant one- and two-photon emitters for (bio)imaging,” Small, vol. 7, no. 22, pp. 3219–3229, 2011. View at: Publisher Site | Google Scholar
  168. A. Shao, X. Wu, and W. Zhu, “Chapter 5. Bioimaging nanomaterials based on near infrared organic dyes,” in Near-Infrared Nanomaterials: Preparation, Bioimaging and Therapy Applications, pp. 125–157, Royal Society of Chemistry, 2016. View at: Publisher Site | Google Scholar
  169. M. J. Schnermann, “Organic dyes for deep bioimaging,” Nature, vol. 551, no. 7679, pp. 176-177, 2017. View at: Publisher Site | Google Scholar
  170. M. Bruchez Jr., M. Moronne, P. Gin, S. Weiss, and A. P. Alivisatos, “Semiconductor nanocrystals as fluorescent biological labels,” Science, vol. 281, no. 5385, pp. 2013–2016, 1998. View at: Publisher Site | Google Scholar
  171. R. Freeman and I. Willner, “Optical molecular sensing with semiconductor quantum dots (QDs),” Chemical Society Reviews, vol. 41, no. 10, pp. 4067–4085, 2012. View at: Publisher Site | Google Scholar
  172. X. Shu, A. Royant, M. Z. Lin et al., “Mammalian expression of infrared fluorescent proteins engineered from a bacterial phytochrome,” Science, vol. 324, no. 5928, pp. 804–807, 2009. View at: Publisher Site | Google Scholar
  173. F. V. Subach and V. V. Verkhusha, “Chromophore transformations in red fluorescent proteins,” Chemical Reviews, vol. 112, no. 7, pp. 4308–4327, 2012. View at: Publisher Site | Google Scholar
  174. J.-C. G. Bünzli, “Lanthanide luminescence for biomedical analyses and imaging,” Chemical Reviews, vol. 110, no. 5, pp. 2729–2755, 2010. View at: Publisher Site | Google Scholar
  175. S. V. Eliseeva and J.-C. G. Bunzli, “Lanthanide luminescence for functional materials and bio-sciences,” Chemical Society Reviews, vol. 39, no. 1, pp. 189–227, 2010. View at: Publisher Site | Google Scholar
  176. X. Zhang, S. Wang, C. Zhu et al., “Carbon-dots derived from nanodiamond: photoluminescence tunable nanoparticles for cell imaging,” Journal of Colloid and Interface Science, vol. 397, pp. 39–44, 2013. View at: Publisher Site | Google Scholar
  177. P. Das, M. Bose, S. Ganguly et al., “Green approach to photoluminescent carbon dots for imaging of gram-negative bacteria Escherichia coli,” Nanotechnology, vol. 28, no. 19, article 195501, 2017. View at: Publisher Site | Google Scholar
  178. U. Resch-Genger, M. Grabolle, S. Cavaliere-Jaricot, R. Nitschke, and T. Nann, “Quantum dots versus organic dyes as fluorescent labels,” Nature Methods, vol. 5, no. 9, pp. 763–775, 2008. View at: Publisher Site | Google Scholar
  179. W. W. Yu, E. Chang, R. Drezek, and V. L. Colvin, “Water-soluble quantum dots for biomedical applications,” Biochemical and Biophysical Research Communications, vol. 348, no. 3, pp. 781–786, 2006. View at: Publisher Site | Google Scholar
  180. S. F. Lee and M. A. Osborne, “Brightening, blinking, bluing and bleaching in the life of a quantum dot: friend or foe?” ChemPhysChem, vol. 10, no. 13, pp. 2174–2191, 2009. View at: Publisher Site | Google Scholar
  181. M. M. Barroso, “Quantum dots in cell biology,” Journal of Histochemistry & Cytochemistry, vol. 59, no. 3, pp. 237–251, 2011. View at: Publisher Site | Google Scholar
  182. X. Le Guével, “Recent advances on the synthesis of metal quantum nanoclusters and their application for bioimaging,” IEEE Journal of Selected Topics in Quantum Electronics, vol. 20, no. 3, pp. 45–56, 2014. View at: Publisher Site | Google Scholar
  183. L. Ma, V. Andoh, H. Liu, J. Song, G. Wu, and L. Li, “Biological effects of gold nanoclusters are evaluated by using silkworm as a model animal,” Journal of Materials Science, vol. 54, no. 6, pp. 4997–5007, 2019. View at: Publisher Site | Google Scholar
  184. G. Zuber, E. Weiss, and M. Chiper, “Biocompatible gold nanoclusters: synthetic strategies and biomedical prospects,” Nanotechnology, vol. 30, no. 35, article 352001, 2019. View at: Publisher Site | Google Scholar
  185. K. Zheng, X. Yuan, N. Goswami, Q. Zhang, and J. Xie, “Recent advances in the synthesis, characterization, and biomedical applications of ultrasmall thiolated silver nanoclusters,” RSC Advances, vol. 4, no. 105, pp. 60581–60596, 2014. View at: Publisher Site | Google Scholar
  186. X. Chen, J. Zhou, X. Yue et al., “Selective bio-labeling and induced apoptosis of hematopoietic cancer cells using dual-functional polyethylenimine-caged platinum nanoclusters,” Biochemical and Biophysical Research Communications, vol. 503, no. 3, pp. 1465–1470, 2018. View at: Publisher Site | Google Scholar
  187. Y. Xin, X. Huang, Z. Li et al., “Versatile Pt NCs-based chemotherapeutic agents significantly induce the apoptosis of cisplatin-resistant non-small cell lung cancer,” Biochemical and Biophysical Research Communications, vol. 512, no. 2, pp. 218–223, 2019. View at: Publisher Site | Google Scholar
  188. X. Huang, H. Ishitobi, and Y. Inouye, “Formation of fluorescent platinum nanoclusters using hyper-branched polyethylenimine and their conjugation to antibodies for bio-imaging,” RSC Advances, vol. 6, no. 12, pp. 9709–9716, 2016. View at: Publisher Site | Google Scholar
  189. T. Boulikas and M. Vougiouka, “Cisplatin and platinum drugs at the molecular level (review),” Oncology Reports, vol. 10, no. 6, pp. 1663–1682, 2003. View at: Publisher Site | Google Scholar
  190. K. Barabas, R. Milner, D. Lurie, and C. Adin, “Cisplatin: a review of toxicities and therapeutic applications,” Veterinary and Comparative Oncology, vol. 6, no. 1, pp. 1–18, 2008. View at: Publisher Site | Google Scholar
  191. K. N. Sugahara, T. Teesalu, P. P. Karmali et al., “Tissue-penetrating delivery of compounds and nanoparticles into tumors,” Cancer Cell, vol. 16, no. 6, pp. 510–520, 2009. View at: Publisher Site | Google Scholar
  192. X. Wang, X. Wang, and Z. Guo, “Functionalization of platinum complexes for biomedical applications,” Accounts of Chemical Research, vol. 48, no. 9, pp. 2622–2631, 2015. View at: Publisher Site | Google Scholar
  193. M. A. Fuertes, C. Alonso, and J. M. Pérez, “Biochemical modulation of cisplatin mechanisms of action: enhancement of antitumor activity and circumvention of drug resistance,” Chemical Reviews, vol. 103, no. 3, pp. 645–662, 2003. View at: Publisher Site | Google Scholar
  194. N. C. Schmitt and E. W. Rubel, “Osteopontin does not mitigate cisplatin ototoxicity or nephrotoxicity in adult mice,” Otolaryngology-Head and Neck Surgery, vol. 149, no. 4, pp. 614–620, 2013. View at: Publisher Site | Google Scholar
  195. G. Mandriota, R. Di Corato, M. Benedetti, F. De Castro, F. P. Fanizzi, and R. Rinaldi, “Design and application of cisplatin-loaded magnetic nanoparticle clusters for smart chemotherapy,” ACS Applied Materials & Interfaces, vol. 11, no. 2, pp. 1864–1875, 2019. View at: Publisher Site | Google Scholar
  196. H. M. Kieler-Ferguson, J. M. J. Fréchet, and F. C. Szoka Jr., “Clinical developments of chemotherapeutic nanomedicines: polymers and liposomes for delivery of camptothecins and platinum(II) drugs,” WIREs Nanomedicine and Nanobiotechnology, vol. 5, no. 2, pp. 130–138, 2013. View at: Publisher Site | Google Scholar
  197. H. S. Oberoi, N. V. Nukolova, A. V. Kabanov, and T. K. Bronich, “Nanocarriers for delivery of platinum anticancer drugs,” Advanced Drug Delivery Reviews, vol. 65, no. 13-14, pp. 1667–1685, 2013. View at: Publisher Site | Google Scholar
  198. L. Gatti, G. Cassinelli, N. Zaffaroni, C. Lanzi, and P. Perego, “New mechanisms for old drugs: insights into DNA-unrelated effects of platinum compounds and drug resistance determinants,” Drug Resistance Updates, vol. 20, pp. 1–11, 2015. View at: Publisher Site | Google Scholar
  199. I. J. Majoros, B. B. Ward, K. H. Lee et al., “Chapter 8 - progress in cancer nanotechnology,” in Progress in Molecular Biology and Translational Science, vol. 95, pp. 193–236, Academic Press, 2010. View at: Publisher Site | Google Scholar
  200. S. Dilruba and G. V. Kalayda, “Platinum-based drugs: past, present and future,” Cancer Chemotherapy and Pharmacology, vol. 77, no. 6, pp. 1103–1124, 2016. View at: Publisher Site | Google Scholar
  201. C.-T. Chien, J. Y. Yan, W. C. Chiu, T. H. Wu, C. Y. Liu, and S. Y. Lin, “Caged Pt nanoclusters exhibiting corrodibility to exert tumor-inside activation for anticancer chemotherapeutics,” Advanced Materials, vol. 25, no. 36, pp. 5067–5073, 2013. View at: Publisher Site | Google Scholar
  202. D. Chen, S. Gao, W. Ge, Q. Li, H. Jiang, and X. Wang, “One-step rapid synthesis of fluorescent platinum nanoclusters for cellular imaging and photothermal treatment,” RSC Advances, vol. 4, no. 76, pp. 40141–40145, 2014. View at: Publisher Site | Google Scholar
  203. H. Xia, F. Li, X. Hu et al., “pH-sensitive Pt nanocluster assembly overcomes cisplatin resistance and heterogeneous stemness of hepatocellular carcinoma,” ACS Central Science, vol. 2, no. 11, pp. 802–811, 2016. View at: Publisher Site | Google Scholar
  204. X. Hu, F. Li, N. Noor, and D. Ling, “Platinum drugs: from Pt(II) compounds, Pt(IV) prodrugs, to Pt nanocrystals/nanoclusters,” Science Bulletin, vol. 62, no. 8, pp. 589–596, 2017. View at: Publisher Site | Google Scholar
  205. X. Yuan, M. I. Setyawati, D. T. Leong, and J. Xie, “Ultrasmall Ag+-rich nanoclusters as highly efficient nanoreservoirs for bacterial killing,” Nano Research, vol. 7, no. 3, pp. 301–307, 2014. View at: Publisher Site | Google Scholar
  206. S. B. Subramaniyan, A. Ramani, V. Ganapathy, and V. Anbazhagan, “Preparation of self-assembled platinum nanoclusters to combat Salmonella typhi infection and inhibit biofilm formation,” Colloids and Surfaces B: Biointerfaces, vol. 171, pp. 75–84, 2018. View at: Publisher Site | Google Scholar

Copyright © 2019 Xin Huang et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

More related articles

1406 Views | 854 Downloads | 1 Citation
 PDF  Download Citation  Citation
 Download other formatsMore
 Order printed copiesOrder

Related articles

We are committed to sharing findings related to COVID-19 as quickly and safely as possible. Any author submitting a COVID-19 paper should notify us at to ensure their research is fast-tracked and made available on a preprint server as soon as possible. We will be providing unlimited waivers of publication charges for accepted articles related to COVID-19. Sign up here as a reviewer to help fast-track new submissions.