Oxidant mediated one-step complete conversion of multi-walled carbon nanotubes to graphene quantum dots and their bioactivity against mammalian and bacterial cells

Abstract

It is an essential for any antibacterial agent (for clinical application), that it should have a high and selective toxicity towards the bacterial cells only, and should not affect the human cells at the concentration used. Graphene quantum dots (GQDs) have emerged as a potential candidate for biomedical applications. However, a simple, low cost, safe, easy to execute, one-step synthesis of uniform, and monodispersed GQDs with selective toxicity towards the bacterial cells rather than the mammalian cells, is difficult to achieve. Here, we have reported a one-step, low-cost, aqueous-phase, simple approach for the complete conversion of multiwalled carbon nanotubes into the water-dispersible GQDs with an average size ~3 nm using sodium bismuthate (NaBiO 3 ) as a strong oxidant. The cyclic voltammetry and X-ray photoelectron spectroscopy results indicated that the as-synthesized GQDs suspension possess almost negligible amount of metallic impurities. The cytotoxicity studies of GQDs against mammalian NIH 3T3 (mouse embryo fibroblast cells) and HEK 293T (human embryonic kidney cells) cells showed that the as-synthesized GQDs were non-cytotoxic up to the concentration of ~200 µg mL -1 . The antimicrobial study shows that the synthesized GQDs have high and selective toxicity towards the bacterial cells with minimum inhibitory concentration of as-synthesized GQDs as ~256 µg mL -1 for E. coli and B. subtilis, and ~512 µg mL -1 for P. aeruginosa and S. aureus. The scanning electron microscopy and atomic force microscopy images show the extensive cell damage via the perturbation of bacterial cell walls, which was consistent with the enhancement of reactive oxygen species production by almost two times in the bacterial cells upon incubation with ~256 µg mL -1 of GQDs. Our study suggested that the as-synthesized GQDs can be used as a potential candidate for clinical applications as they possess high toxicity to bacterial cells and low toxicity to mammalian cells.It can be noticed from the figure 2b that for both, the MWCNTs as well as the GQDs, the G-peak splits in two sub-bands, second harmonic G-band and tangential G-band. This splitting is due to the strain induced from curvature and confinement, respectively. The second harmonic G-band peaks for MWCNTs and GQDs were observed at 1605 cm -1 and 1621 cm -1 , respectively. The tangential G-band for MWCNTs and GQDs appeared as a shoulder at 1575 cm -1 and 1582 cm -1 , respectively (Table S1). The gradual shift in the G-band denotes greater lattice and structural disorder in GQDs. 24 Chemical analysis of as-synthesized GQDsThe X-ray photoelectron spectroscopy (XPS) analysis was also performed to determine chemical composition of the as-synthesized GQDs. The XPS survey scan shows the presence of carbon, oxygen, and nitrogen peaks in the GQDs sample ( Figure S5). The absence of bismuth or any other metal ion peak in the 12 h treated GQDs shows that the as-synthesized GQDs were free from the oxidants used to break it down. The presence of nitrogen was found in the XPS spectra bec...

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Carbon and graphene quantum dots: a review on syntheses, characterization, biological and sensing applications for neurotransmitter determination

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Synthesis of graphene quantum dots and their applications in drug delivery

“…In recent years, the applications of GQDs in drug delivery [123][124][125][126][127], sensors [128][129][130][131][132][133][134], bio-imaging [10,63,[135][136][137][138][139][140], magnetic hyperthermia [141][142][143], photothermal therapy [144][145][146][147][148], antibacterial [145,149,150], catalyst [69,[151][152][153][154][155], environmental protection [38,156,157], and energy [158][159][160][161][162][163] has made remarkable accomplishment. In order to better apply GQDs to drug delivery, some researchers had used density functional theory (DFT) calculations [164]…”