Using various monosaccharides as reductant, we synthesized Ag nanoparticles (NPs) in seconds employing the household microwave method described earlier. The Ag NPs containing colloidal solution showed distinctive colors with varying . The sizes of the NPs formed varied significantly from 10 to 35？nm in good agreement with the localized plasmon resonance ranged from ~300 to ~600？nm. The antimicrobial properties of these NPs were compared in Gram-negative and positive bacteria in liquid culture. Gram-positive bacteria were highly susceptible compared to Gram-negative microbes—the additional lipopolysaccharide layer covering the peptidoglycan cell wall in the latter somewhat lessens the effect. The results indicated that larger NPs produced by glucose inhibited bacterial growth better than the smallest NPs produced by ribose. This may be attributed to the higher aggregation rate for larger NPs on cell wall. SEM analysis showed accumulation of NPs on cell surface and defect in budding, further supporting the cell wall interaction with Ag NPs. These observations suggested that the growth inhibition of Ag NPs is mediated by interfering with the bacterial cell wall peptidoglycan. 1. Introduction The use of nanotechnology in everyday applications continues to increase due to unique chemical, optical, and mechanical properties of nanoparticles (NPs) [1] and it holds promise for multitude of potential applications in the fields of drug delivery [2], catalysis [3], cell and organelle labeling and imaging [4, 5], biological sensing [6], and detection of wide range of biomolecules [7–10]. The important characteristic of NPs that separates them from their bulk counterparts is high surface area to volume ratio. Moreover, it has been shown that materials at the nanoscale level have unique chemical and physical properties compared to their bulk counterpart, and these properties are important for a variety of technological applications. Interaction of NPs with biomolecules and its application in combating microorganisms are a new avenue for research. Increase in bactericide and antibiotic-resistant microbial strains and the toxicity of some of these agents lead to growing interest in new types of safe and cost-effective antimicrobial agents [11]. Recent studies that metal and metal oxide NPs could be used as effective bactericidal materials open the door for development of a new type of antimicrobial materials [12, 13]. Among the noble-metal NPs, silver received attention due to its interesting physiochemical properties and for the well-known toxicity of its ionic form
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