Review Article

Alternative Antimicrobial Approach: Nano-Antimicrobial Materials

Table 1

Representative synthesis/preparation method for selected antimicrobial nanomaterials.

MaterialNanomaterial/particles descriptionRepresentative synthesis/preparation methodReference

Titanium oxide (TiO2)Nanosilver-decorated titanium dioxide (TiO2) nanofibers with antimicrobial activity were synthesized which displayed a self-cleaning property and toxic decomposition potentialTitanium nanofibers were prepared by electrospinning. Briefly, pluronic and PVP were each dissolved in ethanol. A TiO2 solution was prepared by adding titanium isopropoxide (TiP) in a mixture of ethanol and HCl. The solution was mixed with the PVP-pluronic solution followed by stirring at room temperature and the resulting precursor gel was heated at 50°C for 24 hrs. The gel was then electrospun and the formed fibers were calcined at 500°C for 4 hrs under air to form crystalline titanium dioxide nanofibers [168]

Silver (Ag) compoundsIn situ production of silver nanoparticles on cotton fabric is described and their antimicrobial potential is evaluatedCotton fabric was introduced into a loading bath containing silver nitrate. To this solution CTAB and glucose were added and the mixture was shaken at 50°C. Subsequently, sodium hydroxide and water were added and the mixture was further shaken at 50°C. The coated samples were thoroughly rinsed with water and dried. The silver coated samples were washed with nonionic detergent (Triton X-100) and then the fabrics were dried [169]

Copper oxide (CuO)Copper oxide nanoparticles prepared by electrochemical reduction displayed excellent antibacterial activity against Escherichia coli and Staphylococcus strainsCopper oxide nanoparticles were prepared by electrochemical reduction, using an electrolysis cell in which a copper metal sheet served as a sacrificial anode and a platinum (inert) sheet acted as a cathode. For this process tetrabutylammonium bromide in an organic medium acted as a structure-directing agent which was used with acetonitrile (ACN) at a 4 : 1 ratio. The reduction process was allowed to takes place under an inert atmosphere of nitrogen for 2 hrs. Desired particle size was achieved by controlling parameters such as density, solvent polarity, distance between electrodes, and concentration of stabilizers [170]

Iron oxide (Fe3O4) & zinc oxide (ZnO)Zinc oxide was combined with iron oxide to produce magnetic composite nanoparticles with improved colloidal aqueous stability and adequate antibacterial activityTo prepare the Fe oxide nanoparticles, FeCl2·4H2O solution was added to a porcine gelatine aqueous solution, followed by addition of a NaNO3 solution and allowed to react for 10 min. Then the pH was raised to 9.5 by adding a NaOH aqueous solution (1 N).
The Zn/Fe oxide composite nanoparticles were prepared similarly except for substituting the Fe2+ ions for a mixture of Fe2+ and Zn2+ of different weight ratios. The mixtures containing weight ratios [Zn]/[Fe] of 1 : 9, 3 : 7, 1 : 1, 8 : 2, and 9 : 1 were prepared by mixing different volumes of FeCl2·4H2O solution with the appropriate volumes of ZnCl2 solution. The procedure that followed was as described for the iron oxide nanoparticles
[171]

Magnesium oxide (MgO)Magnesium oxide (MgO) nanowires (diameter, 6 nm; length, 10 m) were synthesized. These nanowires showed bacteriostatic activity against Escherichia coli and Bacillus speciesA microwave hydrothermal technique was used to prepare MgO nanowires. In brief, an aqueous solution of a fixed concentration of urea was added dropwise to an aqueous magnesium acetate solution. The solution was then loaded into a microwave furnace. The product obtained was collected, dried, and calcined to obtain a white-colored final material [172]

Nitric oxide (NO) nanoparticlesNitric oxide- (NO-) releasing nanoparticle technology was used for the treatment of methicillin-resistant Staphylococcus aureus First a hydrogel/glass composite was synthesized by adding tetramethyl orthosilicate, polyethylene glycol, chitosan, glucose, and sodium nitrite in sodium phosphate buffer. In this glass composite, nitrite was reduced to NO due to redox reactions initiated with thermally generated electrons from glucose. After the redox reaction, the ingredients were combined and dried using a lyophilizer, resulting in a fine powder consisting of nanoparticles containing NO. The water channels inside the particles of the hydrogel/glass composite opened in an aqueous environment, facilitating the release of the trapped NO over extended periods of time [105]

Polyethylenimine and quaternary ammonium compoundsAntibacterial activity of quaternary ammonium polyethylenimine (PEI) nanoparticles embedded at 1% w/w in hybrid dental composite resins was determinedAn ethanol solution of PEI was cross-linked with 8.7 mmol dibromopentane (PEI monomer/dibromopentane). The generated HBr was neutralized by treatment with sodium hydroxide and the resulting residue was purified from NaBr by gravitational filtration and dried under reduced pressure. The cross-linked PEI was further alkylated with bromooctane, as described above, to produce octane alkylated PEI. Octane alkylated PEI dispersed in anhydrous THF was reacted with methyl iodide in the presence of 2% cross-linked 4-vinylpyridine. The product was filtered to remove 4-vinylpyridinium salt and the filtrate was evaporated to dryness under reduced pressure [173]

Chitosan & polyguanidinesGuanidinylated chitosan derivatives of different molecular weights were synthesized. Guanidinylated chitosan exhibited a fourfold lower inhibitory concentration compared with chitosanA chitosan solution was prepared in HCl and then adjusted to pH 8-9 by 5% w/v aqueous sodium carbonate. The precipitate was washed with water and the desired amount of aminoiminomethanesulfonic acid was added. The reaction was kept at 50°C for 15 min and then the mixture was cooled to room temperature. Once cooled it was poured into saturated aqueous sodium sulfate, and the precipitate was filtered off, washed thoroughly with water and ethanol, and then dried under vacuum to give guanidinylated chitosan [174]