Antibacterial effects of graphene- and carbon-nanotube-based nanohybrids on Escherichia coli: Implications for treating multidrug-resistant bacteria

Abstract

Some nanomaterials including Fe⁰, Ag⁰, and ZnO are well known for their antibacterial effects. However, very few studies have examined antibacterial effects of nanohybrids. Given that metal oxides, mainly ZnO and TiO₂, are known to increase mobility, surface area, and photocatalysis when combined with carbon-based nanomaterials, ZnO- and TiO₂-conjugated carbon nanotube and graphene oxide nanohybrids were investigated for their antibacterial effects on Escherichia coli (DH5α, a multidrug-resistant coliform bacterium). Graphene-oxide (GO)-based nanohybrids (ZnO-GO and TiO₂-GO) induced increased dispersion compared to carbon-nanotube (CNT)-based nanohybrids (ZnO-CNT and TiO₂-CNT). Among the four types of nanohybrids, ZnO-conjugated nanohybrids exhibited a higher antibacterial property, resulting in the antibacterial effect (measured with growth inhibition of cells) in the order ZnO-GO > ZnO-CNT > TiO₂-GO > TiO₂-CNT. Among four possible antibacterial mechanisms (generation of reactive oxygen species (ROS), physicochemical characteristics, the steric effect, and release of metal ions), a primary mechanism-ROS generation-was identified; whereas, physicochemical characteristics and the steric effect were part of contributing mechanisms. The increasing dispersion of TiO₂/ZnO on GO may have contributed to the antibacterial effects due to increasing surface areas. Similarly, significant damages to E. coli cell membranes were found by the GO sheet with its sharp edges. Our results suggest that applying GO-based ZnO or TiO₂ could be an effective antibacterial method, especially for the treatment of multidrug-resistant bacteria in the water.

Keywords: Antibacterial activity; Antibacterial-resistant bacteria; Carbon nanotube; E. coli (DH5α); Graphene oxide; Nanohybrids.