BAKGROUND: Biological methods for metal nanoparticle synthesis using plant extracts have been suggested as possible ecofriendly alternatives to chemical and physical methods. In the present study, copper nanoparticles were biologically synthesized using Magnolia kobus leaf extract as reducing agent and their antibacterial activity was evaluated against Escherichia coli. RESULTS: On treatment of aqueous solution of CuSO4 center dot 5H(2)O with Magnolia kobus leaf extract, stable copper nanoparticles were formed. UV-vis spectroscopy was used to monitor the quantitative formation of copper nanoparticles. The synthesized nanoparticles were characterized with inductively coupled plasma spectrometry (ICP), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HR-TEM). Electron microscopy analysis of copper nanoparticles indicated that they ranged in average size from 37 to 110 nm. Antibacterial tests were carried out by counting viable E. coli cells after 24 h growth in shake flasks containing latex foams coated with copper nanoparticles. As a result, foams coated with biologically synthesized copper nanoparticles showed higher antibacterial activity compared with foams untreated and foams treated with chemically synthesized copper nanoparticles using sodium borohydride and Tween 20. The antibacterial activities were inversely proportional to the average nanoparticle sizes. CONCLUSION: The present results show that stable copper nanoparticles can be ecofriendly synthesized using Magnolia kobus leaf extract, offering an inexpensive alternative to antibacterial silver nanoparticles. (C) 2013 Society of Chemical Industry