Oxidative stress and antibacterial properties of a graphene oxide-cystamine nanohybrid

Abstract

Oxidative stress can damage proteins, DNA, and lipids, and is involved in the progression of many diseases. Damage to infected cells caused by oxidative stress is related to increased levels of reactive oxygen species, including hydrogen peroxide. During oxidative stress, hydrogen peroxide levels are often increased and catalase level decreased inside cells. This can lead to the death of skin and other cells. Hydrophobic low molecular weight compounds are useful in treating hemorrhagic conditions of the skin. To this end, cystamine has been successfully conjugated with graphene oxide (GO) as a drug carrier. The current study used the microdilution method to determine the minimum inhibitory concentrations of cystamine-conjugated GO against four types of pathogenic bacteria. Minimum inhibitory concentrations values were 1 μg/mL against Escherichia coli and Salmonella typhimurium, 6 μg/mL against Enterococcus faecalis, and 4 μg/mL against Bacillus subtilis. Toxicity of the conjugate against squamous cell carcinoma 7 cells was minimal at low concentrations, but increased in a dose-dependent manner. These results demonstrated that our protocol produced a cystamine-conjugated GO with low cytotoxicity, but strong reactive oxygen species effects and high antibacterial activity. This nanohybrid may be useful in the treatment of dermatological disorders. Moreover, this class of nanohybrid may have other biomedical applications due to their low cytotoxicity and high antibacterial activity.

Keywords: antibacterial; cystamine conjugate; graphene; oxidative stress; oxide; reactive oxygen species.

Figure 1

Images of graphene oxide (GO) (A) and cystamine-conjugated GO (B) by atomic force microscope (AFM). Note: Magnified AFM images of GO showed its height 0.8 nm whereas cystamine-conjugated GO shows its height 1.2 nm.

Figure 2

A typical scanning electron microscope (SEM) image of (A) dried graphene oxide (GO) and (B) dried cystamine-conjugated GO. Note: SEM image showed conjugation of cystamine with GO which is confirmed by the reduction of the size of cystamine-conjugated GO.

Figure 3

Cytotoxicity and ROS studies of cystamine conjugated GO Notes: (A) Cell viability of cystamine-conjugated graphene oxide (GO). (B) Reactive oxygen species (ROS) studies of GO (black color), and cystamine-conjugated GO (red color). Abbreviations: MTT, (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide); au, arbitrary unit; DCF, dichlorofluorescein.

Figure 4

UV–Vis spectrum of cystamine, GO, and cystamine-conjugated GO. Notes: (A) UV–Vis spectrum of cystamine (red color), GO (black color), and cystamine-conjugated GO (blue color). The peak of GO at 232 nm remains stable in cystamine-conjugated GO. (B) Fourier transform infrared (FT-IR) spectroscopy of cystamine (red color), GO (black color), and cystamine-conjugated GO (blue color). FT-IR confirmed the conjugation of cystamine with GO. Abbreviations: UV–Vis, ultraviolet-visible; GO, graphene oxide; au, arbitrary unit.

Figure 5

High resolution C1_S XPS spectra of (A) GO and (B) cystamine-conjugated GO. Abbreviations: GO, graphene oxide; XPS, X-ray photoelectron spectroscopy; au, arbitrary unit.

Figure 6

Scanning electron microscope (SEM) images of antibacterial activities. Notes: SEM images of antibacterial activities of cystamine-conjugated graphene oxide (GO) against (A) Escherichia coli (B) Bacillus subtilis (C) Enterococcus faecalis (D) Salmonella typhimurium. Cystamine-conjugated GO is more toxic to Gram-negative bacteria (E. coli and S. typhimurium) as compared to Gram-positive bacteria (B. subtilis and E. faecalis).