Gold Coating of Silver Nanoplates for Enhanced Dispersion Stability and Efficient Antimicrobial Activity against Intracellular Bacteria.

Silver nanoparticles have antibacterial activity. However, the nanoparticles are unstable and easily form aggregates, which decreases their antibacterial activity. To improve the dispersion stability of silver nanoparticles in aqueous media and to increase their effectiveness as antibacterial agents, we coated triangular plate-like silver nanoparticles (silver nanoplates, Ag NPLs) with one or two layers of gold atoms (Ag@Au1L NPLs and Ag@Au2L NPLs, respectively). These gold coatings improved the dispersion stability in aqueous media with high salt concentrations. Ag@Au1L NPLs showed stronger antibacterial activity on pathogenic bacteria than Ag NPLs and Ag@Au2L NPLs. Furthermore, the Ag@Au1L NPLs decreased the number of bacteria in RAW 264.7 cells. The Ag@Au1L NPLs displayed no cytotoxicity towards RAW 264.7 cells and could be used as antibacterial agents for intracellular bacterial infections.

Effects of pulsed laser irradiation on gold-coated silver nanoplates and their antibacterial activity.

Gold-coated silver nanoplates, when subjected to pulsed laser irradiation, changed their shape from triangular to spherical, accompanied by a shift of their extinction spectra. The simple single crystal structure of the silver nanoplates changed to multiple small crystal domains. The ratio of silver to gold of the particles also changed from 22 : 1 to 4.5 : 1, enabling more silver to be released. As a result, the antibacterial activity of the gold-coated silver nanoplates was significantly increased after pulsed laser irradiation.

Laser Desorption/Ionization Mass Spectrometry (LDI-MS) of Lipids with Iron Oxide Nanoparticle-Coated Targets.

Iron oxide nanoparticle (NP)-coated target plates were employed for the direct detection and analysis of low molecular weight lipids by laser desorption/ionization (LDI) mass spectrometry (MS). We have demonstrated that the use of the iron oxide NP-coated target provides a simple, direct, and rapid detection method for lipid standards and epidermal surface lipids without any cumbersome sample pretreatment as well as mass spectra that are free of background matrix peaks. Lipid standards (1-stearoyl-sn-glycero-3-phosphocholine, 1,2-dioleoyl-sn-glycerol, 1-palmitoyl-2-oleoyl-3-linoleoyl-rac-glycerol, 1,2-distearoyl-sn-glycero-3-phosphocholine) were detected as either protonated or cationated species. Clean MS/MS spectra for each lipid were also successfully obtained. Pre-MS surface cleaning of the target plates with UV-ozone treatment successfully removed organic contaminants that would interfere with the mass spectra especially in the low molecular weight region. Preliminary application of the presented target plate to the detection of endogenous lipids in latent fingerprints showed promising results and for potential use in the visualization and chemical composition determination of latent fingerprints by nanoparticle assistance.