Nano-sized copper particles: Chemical synthesis, characterization, and their size and surface charge dependent antibacterial potential

Copper nanoparticles (Cu NPs) were studied extensively for their antibacterial potential compared to other metal NPs in the recent past. However, comparative analysis of different reducing and stabilizing agents in the synthesis of Cu NPs and their possible effect in antibacterial activity is not clearly stated. Herein, authors report the synthesis of Cu NPs using three reducing and stabilizing agents such as sodium borohydride (SBH), tri-sodium citrate (TSC), and oxalic acid (OA), individually. The as-synthesized Cu NPs were studied for their optical, physicochemical, and morphological properties followed by their role (shape and surface charge of NPs) in defining its antibacterial potential. Cu NPs@SBH showed moderate to good antibacterial activity against Escherichia coli (15.23 +/- 0.65 mm), Lactococcus lactis (20.65 +/- 0.96 mm), Micrococcus luteus (21.48 +/- 1.12 mm), Bacillus sp. (14.33 +/- 0.52 mm), and Pseudomonas putida (19.58 +/- 0.43 mm). Cu NPs@SBH had average particle size of 46.8 nm and surface charge of -42.1 mV. The results indicate that both size and surface charge played a vital role in the antibacterial activity of Cu NPs.