Sulfur and nitrogen doped carbon quantum dots for detection of glutathione and reduction of cellular nitric oxide in microglial cells

Purpose This article details the application of pristine nitrogen and sulfur doped carbon quantum dots (CQDs) as a novel fluorescence biosensor for the detection of glutathione. The second object of this study is to evaluate reduction of cellular nitric oxide in microglial cells. Methods Microwave assisted hydrothermal method was used for the fabrication of CQDs. Unlike conventional methods which utilize metallic or transition metal coating over CQDs for the fabrication of fluorescence switch on/off probes, our simple yet efficient CQDs itself performed as a biosensor that is both selective and sensitive towards glutathione (GSH). Particle size analyzer, scanning electron microscope, atomic force microscopy, high-performance X-ray photoelectron spectroscopy, fourier-transform infrared spectroscopy were used for physicochemical characterization of developed CQDs. Photoluminescence properties of CQDs were analyzed using photoluminescence spectroscope for glutathione detection. Furthermore, microglial cells were used to evaluate reduction of cellular nitric oxide. Results The developed biosensor was able to detect GSH within a short time of 2 min. Hemolysis assay confirmed negligible red blood cell lysis even at a higher concentration of 0.2 mg/mL. Furthermore, the developed CQDs demonstrated enhanced cellular uptake, which resulted in generating fluorescence from the BV-2 microglial cells. Interestingly, the developed CQDs were able to mitigate the secretion of toxic pro-inflammatory cytokine, nitric oxide (NO) from the lipopolysaccharide (LPS) insulted BV-2 microglial cells. A 50% reduction in the secretion of NO was observed after treating with CQDs in the LPS treated BV-2 cells. Conclusion These novel fluorescent CQDs with low manufacturing costs, high selectivity and sensitivity towards GSH and shorter detection time manifest them as a promising nanomaterial for diverse biomedical applications.