This paper presents a review of the current research activities in the field of gas nanosensors. Nanomaterials are characterized by physical and chemical properties that differ from their macroscopic counterparts and, in particular, by an enhanced chemical reactivity even at room temperature. This effect has stimulated the development of chemical sensors based on several different nanomaterials. Here we focus most attention on carbon nanotubes, silicon and metal oxide nanoparticles and metal nanowires. After introducing a few general definitions a discussion on the fundamental properties of the nanostate used in the sensor field is presented and several nanosensors, based on the aforementioned nanomaterials, are discussed. Finally, some personal conclusions will be drawn.

Girolamo Di Francia

Brigida Alfano

Vera La Ferrara

Conductometric Gas Nanosensors

The quartz crystal microbalance (QCM) is a sensitive device for determining the properties of materials loading it. One of the fundamental means of making these measurements is the so-called impedance (or admittance) spectra method. The resonant properties of the piezoelectric QCM sensor are measured
over a spectral range in the neighborhood of a resonance, both with load and without load. The changes
in the spectrum upon loading can be compared to models that describe the changes based on the mass
density, the shear modulus, and the viscosity of the load. This comparison can be made with confidence
so long as the spectrum corresponds to the model assumption of a single main resonance.
Often, there exists a spurious resonance lying above the main resonance which is not included in the
models. This can change the shape of the spectrum in ways not included in the model analysis. We
describe a method we have used that separates the spur resonance from the main resonance,
permitting the parameters of the main resonance to be isolated from that of the spur. These corrected
parameters of the main resonance can then be used with confidence in model analyses.

Sae Moon Yoon

Nam Joon Cho

Kay Kanazawa

Analyzing Spur-Distorted Impedance Spectra for the QCM

G. Kiriakidis

K. Moschovis

I. Kortidis

R. Skarvelakis

Highly Sensitive InO<sub>x</sub> Ozone Sensing Films on Flexible Substrates

The paper reviews the recent researches implemented in Chinese Academy of Sciences, with achievements on integrated resonant microcantilever sensors. In the resonant cantilevers, the self-sensing elements and resonance exciting elements are both top-down integrated with silicon micromachining techniques. Quite a lot of effort is focused on optimization of the resonance mode and sensing structure for improvement of sensitivity. On the other hand, to enable the micro-cantilevers specifically sensitive to bio/chemical molecules, sensing materials are developed and modified on the cantilever surface with a self-assembled monolayer (SAM) based bottom-up construction and surface functionalization. To improve the selectivity of the sensors and depress environmental noise, multiple and localized surface modifications are developed. The achieved volume production capability and satisfactory detecting resolution to trace-level biological antigen of alpha-fetoprotein (AFP) give the micro-cantilever sensors a great promise for rapid and high-resoluble detection.

Xinxin Li

Haitao Yu

Xiaohua Gan

Xiaoyuan Xia

Pengcheng Xu

Jungang Li

Min Liu

Yongxiang Li

Integrated MEMS/NEMS Resonant Cantilevers for Ultrasensitive Biological Detection

One of the most serious limitations to the practical utilization of solid-state gas sensors is the drift of their signal. Even if drift is rooted in the chemical and physical processes occurring in the sensor, improved signal processing is generally considered as a methodology to increase sensors stability. Several studies evidenced the augmented stability of time variable signals elicited by the modulation of either the gas concentration or the operating temperature. Furthermore, when time-variable signals are used, the extraction of features can be accomplished in shorter time with respect to the time necessary to calculate the usual features defined in steady-state conditions. In this paper, we discuss the stability properties of distinct dynamic features using an array of metal oxide semiconductors gas sensors whose working temperature is modulated with optimized multisinusoidal signals. Experiments were aimed at measuring the dispersion of sensors features in repeated sequences of a limited number of experimental conditions. Results evidenced that the features extracted during the temperature modulation reduce the multidimensional data dispersion among repeated measurements. In particular, the Energy Signal Vector provided an almost constant classification rate along the time with respect to the temperature modulation.

Alexander Vergara

Eugenio Martinelli

Eduard Llobet

Arnaldo D&#39;Amico

Corrado Di Natale

Optimized Feature Extraction for Temperature-Modulated Gas Sensors

The unique structure 
                  of carbon nanotubes endows them with fantastic 
                  physical and chemical characteristics. Carbon 
                  nanotubes have been widely studied due to their 
                  potential applications in many fields including 
                  conductive and high-strength composites, energy 
                  storage and energy conversion devices, sensors, 
                  field emission displays and radiation sources, 
                  hydrogen storage media, and nanometer-sized 
                  semiconductor devices, probes, and quantum 
                  wires. Some of these applications have been 
                  realized in products, while others show great 
                  potentials. The development of carbon 
                  nanotubes-based sensors has attracted intensive 
                  interest in the last several years because of 
                  their excellent sensing properties such as high 
                  selectivity and prompt response. Carbon nanotube-based gas sensors are summarized 
                  in this paper. Sensors based on single-walled, 
                  multiwalled, and well-aligned carbon nanotubes 
                  arrays are introduced. Modification of carbon 
                  nanotubes with functional groups, metals, 
                  oxides, polymers, or doping carbon 
                  nanotubes with other elements to enhance the 
                  response and selectivity of the sensors is also 
                  discussed.

Wei-De Zhang

Wen-Hui Zhang

Carbon Nanotubes as Active Components for Gas Sensors

The quartz crystal microbalance sensor has a resonant frequency <svg style="vertical-align:-2.34499pt;width:10.675px;" id="M1" height="13.4875" version="1.1" viewBox="0 0 10.675 13.4875" width="10.675"  xmlns="http://www.w3.org/2000/svg">
	<g transform="matrix(1.25,0,0,-1.25,0,13.4875)">
		<g transform="translate(72,-61.21)">
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				<tspan style="font-size: 12.50px; " x="0" y="0">𝑓</tspan>
			</text>

		</g>
	</g>
</svg> and a quality factor <svg style="vertical-align:-1.90608pt;width:12.325px;" id="M2" height="12.925" version="1.1" viewBox="0 0 12.325 12.925" width="12.325"  xmlns="http://www.w3.org/2000/svg">
	<g transform="matrix(1.25,0,0,-1.25,0,12.925)">
		<g transform="translate(72,-61.66)">
			<text transform="matrix(1,0,0,-1,-71.95,63.61)">
				<tspan style="font-size: 12.50px; " x="0" y="0">𝑄</tspan>
			</text>

		</g>
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</svg> which can be used to probe the properties of nanometer thick film loads. A recent review by Arnau (2008) has discussed many of the considerations necessary to accurately probe for these properties. To avoid needless duplication but to still provide an adequate background for the new user, we briefly outline the basic measurement methodologies and analytical techniques that were covered in the review. Details will be provided on some specific perspectives of the authors. For example, the special precautions necessary when dealing with soft films (polymeric and biological) under liquid are overviewed. To illustrate applications of the QCM technique, simple bilayer and vesicle behaviors are discussed, along with the structural transformation resulting from protein adsorption onto an intact vesicle adlayer. The amphipathic <svg style="vertical-align:-0.1254pt;width:8.9375px;" id="M3" height="7.1750002" version="1.1" viewBox="0 0 8.9375 7.1750002" width="8.9375"  xmlns="http://www.w3.org/2000/svg">
	<g transform="matrix(1.25,0,0,-1.25,0,7.175)">
		<g transform="translate(72,-66.26)">
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				<tspan style="font-size: 12.50px; " x="0" y="0">𝛼</tspan>
			</text>

		</g>
	</g>
</svg>-helical (AH) peptide interaction is given as a particular example. Lastly, we summarize a top-down approach to functionalize a surface with a cell membrane and to study its interaction with proteins.

K. Kanazawa

Nam-Joon Cho

Quartz Crystal Microbalance as a Sensor to Characterize Macromolecular Assembly Dynamics

An adsorption equilibrium and a kinetic study of <i>Bacillus atrophaeus</i> on Single-Wall Carbon Nanotubes (SWCNTs) were here performed to provide the basis for developing biosensor devices for detecting threatening micro-organisms in water supply systems. <i>B. atrophaeus</i> spores and carbon nanotubes were subjected to a batch adsorption process to document their equilibria and kinetics. Here, commercial nanotubes were either studied as received or were acid-purified before adsorption experiments. The <i>Bacillus</i> spores appear to show higher affinity towards the purified nanotubes than to the as-received nanomaterial. The effective diffusivity of the spores onto the purified nanotubes was found to be approximately 30 percent higher than onto the as-received nanotubes. It seems that the removal of amorphous carbon from the as-received nanotubes through a purification process yielded an intimate nantoubes-spore interaction as revealed by transmission electron microscopy. Freundlich model successfully correlated the adsorption equilibrium data for the nanotubes-spore interaction. Transmission electron micrographs showed extensive contact between the <i>Bacillus</i> and the purified nanotubes, but the association appeared less intimate between the spores and the as-received nanotubes.

P. Cortes

S. Deng

G. B. Smith

The Adsorption Properties of <i>Bacillus atrophaeus</i> Spores on Single-Wall Carbon Nanotubes

Screen-printing technology is a low-cost process, widely used in electronics production, especially in the fabrication of disposable electrodes for (bio)sensor applications. The pastes used for deposition of the successive layers are based on a polymeric binder with metallic dispersions or graphite, and can also contain functional materials such as cofactors, stabilizers and mediators. More recently metal nanoparticles, nanowires and carbon nanotubes have also been included either in these pastes or as a later stage on the working electrode. This review will summarize the use of nanomaterials to improve the electrochemical sensing capability of screen-printed sensors. It will cover mainly disposable sensors and biosensors for biomedical interest and toxicity monitoring, compiling recent examples where several types of metallic and carbon-based nanostructures are responsible for enhancing the performance of these devices.

Elena Jubete

Oscar A. Loaiza

Estibalitz Ochoteco

Jose A. Pomposo

Hans Grande

Javier Rodr&#237;guez

Nanotechnology: A Tool for Improved Performance on Electrochemical Screen-Printed (Bio)Sensors

A simple technique has been developed to prepare core colloids that are modified using zirconium oxychloride, based on heating a solution of core colloid composites, consisting of poly (ethylenimine) (PEI) and zirconium oxychloride. The interaction of zirconium oxychloride with the polystyrene (PS) core colloids has been investigated using Fourier transform-infrared spectroscopy (FT-IR), energy dispersive X-ray spectroscopy (EDX), and scanning electron microscopy (SEM) data. FT-IR studies confirm the occurrence of amine groups present in PEI which are oxidized to carboxyl groups after the reaction. The EDX data and the SEM images confirm the presence of zirconium particles immobilized on the polystyrene surfaces. Demeton, a highly toxic nerve agent, was used due to its ability to easily bind through its organophosphate group illustrating a practical application of the PS-PEI-Zr particles. Attenuated Total Reflection (ATR) Spectroscopy  was used to assess the interactions between the toxic nerve agent demeton-S and the PS-PEI-Zr particles. The results show that the presented technique for coating polystyrene core colloids with zirconium was successfully accomplished, and the newly formed particles easily bond with demeton agents through the P=O functional group.

Diana Chira

Seong S. Seo

Designing Zirconium Coated Polystyrene Colloids and Application

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<p><em>Journal of Sensors</em> publishes research focused on all aspects of sensors, from their theory and design, to the applications of complete sensing devices.</p>


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<p>Chief Editor, Professor Harith Ahmad, is currently the director of the Photonics Research Center, University of Malaya, Malaysia. His current research is in the exploration of various 2D and 3D nanomaterials for optoelectronics applications.</p>


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Journal of Sensors publishes research focused on all aspects of sensors, from their theory and design, to the applications of complete sensing devices.

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Journal of Sensors

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Journal of Sensors

Nanomaterials for Chemical Sensing Technologies

Nanomaterials for Chemical Sensing Technologies

Articles

Conductometric Gas Nanosensors

Analyzing Spur-Distorted Impedance Spectra for the QCM

Highly Sensitive InO_x Ozone Sensing Films on Flexible Substrates

Integrated MEMS/NEMS Resonant Cantilevers for Ultrasensitive Biological Detection

Optimized Feature Extraction for Temperature-Modulated Gas Sensors

Carbon Nanotubes as Active Components for Gas Sensors

Quartz Crystal Microbalance as a Sensor to Characterize Macromolecular Assembly Dynamics

The Adsorption Properties of Bacillus atrophaeus Spores on Single-Wall Carbon Nanotubes

Nanotechnology: A Tool for Improved Performance on Electrochemical Screen-Printed (Bio)Sensors

Designing Zirconium Coated Polystyrene Colloids and Application

Journal of Sensors

Nanomaterials for Chemical Sensing Technologies

Nanomaterials for Chemical Sensing Technologies

Articles

Conductometric Gas Nanosensors

Analyzing Spur-Distorted Impedance Spectra for the QCM

Highly Sensitive InOx Ozone Sensing Films on Flexible Substrates

Integrated MEMS/NEMS Resonant Cantilevers for Ultrasensitive Biological Detection

Optimized Feature Extraction for Temperature-Modulated Gas Sensors

Carbon Nanotubes as Active Components for Gas Sensors

Quartz Crystal Microbalance as a Sensor to Characterize Macromolecular Assembly Dynamics

The Adsorption Properties of Bacillus atrophaeus Spores on Single-Wall Carbon Nanotubes

Nanotechnology: A Tool for Improved Performance on Electrochemical Screen-Printed (Bio)Sensors

Designing Zirconium Coated Polystyrene Colloids and Application

Highly Sensitive InO_x Ozone Sensing Films on Flexible Substrates