A preliminary study on antibacterial mechanisms of silver ions implanted stainless steel

Silver-containing stainless steels have shown broad spectrum antibacterial activities and exhibit potential applications in food industries and medical appliances. However, few results associated with the antibacterial process have been reported to uncover the interaction of silver implanted stainless steel and bacteria. In this paper we made a preliminary study on antibacterial mechanisms of silver implanted AlSI 420 stainless steel. Silver ions exist in metallic state fitted by the Gaussian functions in the implanted layer, with the maximum silver concentration of 3.3 at.% appearing at 45 nm beneath the surface at the extracting voltage of 50 kV. Silver implanted stainless steel possesses excellent antibacterial activities against Escherichia coli at the implantation dose greater than 100 x 1015 ions/cm(2). Antibacterial rate against E. coli improves with the increase of silver implantation dose, from 77.7% at 5 x 1015 ions/cm(2) to 98.4% at 1000 x 1015 ions/cm(2). Dissolved silver ions are crucial for the bactericidal effect. The concentration of released silver ions increases from 35 +/- 16 ppb at silver implantation dose of 5 x 1015 ions/cm(2) to 255 +/- 20 ppb at silver implantation dose of 1000 x 1015 ions/cm(2). Silver implanted stainless steel exhibits long-lasting antibacterial activity (antibacterial rate >90%) after exposure to air or immersion in tap water for over one year. (C) 2012 Elsevier Ltd. All rights reserved.