Light induced bacterial deactivation using graphene quantum dot

Abstract

Graphene quantum dots (GQD) are one of the most promising antimicrobial agents since they possess high germicidal activity against a broad range of microbes. In our project, we aim to investigate GQD with methylene blue (MB) as an effective, inexpensive and available compound which will hold even higher antimicrobial activity and lower toxicity toward human blood. GQDs were grown by focusing nanosecond laser pulses into benzene and were later combined with MB. The Gram-negative bacteria, Escherichia coli, and Gram-positive bacteria, Micrococcus luteus, were deactivated by GQD/MB. Detailed characterization was performed with transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier-transform infrared (FTIR), UV-Visible (UV-Vis), and photoluminescence (PL) spectra. Furthermore, MBGQD singlet oxygen generation was investigated by measuring the rate of photobleaching. Combining MB with GQDs caused enhanced singlet oxygen generation. Our results show that the MB-GQD combination is more effective than QGD and MB alone in destroying bacteria. MTT assay was used to determine if GQDs in dark conditions caused human cellular side-effects and affected cancer and non-cancer cellular viability. We found that even high concentrations of GQDs do not alter viability under dark conditions. These results suggest that the MB-GQD combination is a promising form of photodynamic therapy. Further, the cytotoxicity of GQDs, MB and MB-GQD mixture toward MCF-7 breast cancer cells were evaluated.