Functionalization of Polymer-Wrapped Silver Nanoclusters and Potential Applications as Antimicrobial Mask Materials

The poly(methacrylic acid) (PMAA) polymer stabilized silver nanoclusters Ag (n = 2-9), synthesized in aqueous solution by the selected light wavelength irradiation photolysis approach, have been functionalized with thiol and amine ligands and successfully transferred from aqueous to organic media. Low- or high-resolution positive mass spectra showed constant species composites with the molecular formula AgL [n = 2 to ∼9, L = butylmercaptan (C₄H₉S), thiolphenol (C₆H₅S), or dodecanethiol (C₁₂H₂₅S)] and proved that the molecules consist of deprotonated sulfur ligands in each species with one positive charge. Fourier transform infrared and X-ray photoelectron spectroscopy are consistent, indicating deprotonated sulfur, while silver has a zero valence value. The composition of the functionalized silver clusters is in agreement with that observed from polymer-wrapped "naked" silver clusters, which strongly indicates their real existence. For the silver cluster amine systems (heptylamine, dodecylamine, and oleylamine), only "naked" silver cluster species were detected from mass spectroscopy, similar to the polymer-wrapped case, indicating they are not stable enough in the gas phase. The development of a new antibacterial mask material is very important. The dodecylamine-capping silver nanoclusters were selected by coating the coffee filter surface to conduct antibacterial tests with Staphylococcus aureus and Escherichia coli, demonstrating very efficient antimicrobial properties even with organic capping ligands. Experiments also show that they work on mask material. One nanowire assembly with polystyrene and dodecylamine-capping silver nanoclusters was prepared, showing uniform nanofibers generated via the electrospray technique.