Water soluble monodisperse copper nanoparticles of about 10 nm diameter were prepared by microwave irradiation using starch as green capping agent. The resulting Cu-starch conjugate were characterized by FTIR and energy dispersive X-ray analysis (EDX). The study confirmed the presence of copper embedded in polysaccharide matrix. The aqueous solution of starch capped copper nanoparticles (SCuNPs) exhibited excellent bactericidal action against both gram negative and gram positive bacteria. The in vitro cytotoxicity evaluation of the nanoparticles was carried out using mouse embryonic fibroblast (3T3L1) cells by MIT cell viability assay, extracellular lactate dehydrogenase (LDH) release and dark field microscopy imaging. The capped nanoparticles exhibited cytotoxicity at much higher concentration compared to cupric ions. Minimum bactericidal concentration (MBC) of SCuNPs was well below the in vitro cytotoxic concentration. Statistical analysis demonstrated p < 0.05 for significant results and p > 0.05 for non-significant ones as compared to untreated cells. The non-cytotoxic green Cu-starch conjugate offers a rational approach towards antimicrobial application and for integration to biomedical devices. (C) 2011 Elsevier B.V. All rights reserved.