Bacterial response to nanodiamonds and graphene oxide sheets

Carbon nanomaterials such as nanodiamond (ND) and graphene oxide (GO) attract increasing attention for biomedical applications due their unique and adjustable properties. Here we report on antibacterial activity of NDs and GO as evaluated by bacterial colony counting. ND and GO were used in oxidized (O-ND, GO) or reduced (H-ND, rGO) forms. ND or GO are mixed in Mueller–Hinton (MH) broth with Escherichia coli at the concentration of 1 mg ml ⁻¹. The resulting suspensions were cultivated for 5 and 24 h at 37 °C in a shaker. After each period, a sample of the suspension was spread on the MH agar and cultivated for 24 h at 37° C. The effect of nanomaterials on colony forming ability (CFA) of E. coli was evaluated and compared with the negative control sample. The most noticeable effect was that after 5 h H-ND decreased the CFA of E. coli in the MH broth by 60% and GO by 50%. After 24 h, H-ND decreased CFA by 50%. Other nanomaterials had no statistically significant antibacterial effect. Factors influencing ND and GO antibacterial activity against the E. coli and possibly against other bacteria are discussed.