Synthesis and evaluation of the antimicrobial activity of purified and unpurified multi-walled carbon nanotubes

Multi-walled carbon nanotubes (MWCNTs) were purified and unpurified in this study to obtain hybrid materials with improved activity. The production stage comprised a chemical purification of the produced sample. Raman spectroscopy analyzed the structural composition of purified and unpurified samples. The disc diffusion assay, minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and time-kill assessment analyzed antimicrobial activity. MWCNT performed well against the tested bacteria (Klebsiella pneumoniae, Pseudomonas aeruginosa, Enterobacter aerogenes, Staphylococcus aureus, and Streptococcus sp. Staphylococcus epidermidis). The disc diffusion assay revealed inhibition zone differences caused by purified and unpurified MWCNTs. MIC and MBC values of purified and unpurified MWCNTs were similar. The purified and unpurified nanotubes of Staphylococcus epidermidis (ATCC 35985) exhibited inhibition zone diameters of approximately 8 mm and 9 mm, respectively. The microdilution method revealed a MIC of 1.23 mg/ml for the purified nanotube and 0.156 mg/ml for the unpurified nanotube against the same microorganism. The killing curve analysis demonstrated that unpurified carbon nanotubes were more effective against all tested microorganisms. MWCNTs represent a promising method for microbiology, but studies on the toxicity of these materials remain scarce.