Antibacterial effects of copper- and silver-coated carbon nanotubes synthesized by plasma-enhanced chemical vapor deposition on Staphylococcus aureus and Escherichia coli: a comparative study

The use of copper (Cu) and silver (Ag) nanoparticles in coatings can eliminate surface microbial contamination. This study compared antibacterial activity of Cu- (Cu/CNTs) and Ag-coated carbon nanotubes (Ag/CNTs) synthesized by plasma-enhanced chemical vapor deposition (PECVD) against Escherichia coli and Staphylococcus aureus. Initially, the PECVD technique was applied to deposit the CNTs on high-resistivity silicon wafers previously decorated by nickel catalyst using an Electron Beam Gun. Then, the nanotubes were coated by Cu and Ag thin films in a vacuum evaporator using the Direct Current (DC) Magnetron Sputtering method. Finally, the antibacterial effects were determined by Standard Plate Count (SPC, with film thicknesses of 0, 10, 30 and 60 nm) and Disk Diffusion Test (based on zone of inhibition (ZOI) with nanoparticle concentrations of 5, 10 and 15 µg/mL). According to the SPC findings, the highest antibacterial activity of Cu/CNTs was found for the film thickness of 60 nm against E. coli (66%), and the lowest activity was related to the film thickness of 19 nm against S. aureus (28.8%). The antibacterial activity of Ag/CNTs was about 70% against E. coli with the highest thickness and about 34.12% against S. aureus. The lowest ZOI was measured for the bare CNTs at a concentration of 5 µg/mL (12 mm), and the highest ZOI was related to Ag/CNTs with a concentration of 15 µg/mL against S. aureus (18 mm). To conclude, the carbon nanotube composites coated with copper or silver nanoparticles can be used to control bacterial growth in aqueous solutions.