Bioresource-derived multifunctional carbon quantum dots as a fluorescence and electrochemical sensing platform for picric acid and noncytotoxic food storage application

This work deals with the synthesis of facile, water-soluble, and blue-emitting carbon quantum dots (CQDs) from Plumbago indica leaves by a hydrothermal method with a quantum yield of 16 %. The biomass Plumbago indica leaves exhibit several advances such as easy availability, cost-effectiveness, non-toxic, green source, and not requiring any sophisticated techniques to develop the sensor. The optical, morphological, structural, and compositional properties of the CQDs were confirmed by various characterization methods. As a fluorescent probe, CQDs exhibited good linear response to picric acid (PA) with a limit of detection (LOD) of 18 nM. The sensing mechanism involves a combination of static quenching and fluorescence resonance energy transfer (FRET). In the electrochemical sensing method, the differential pulse voltammetric (DPV) technique was performed using a CQD-modified gold electrode with a LOD of 0.35 nM for PA. Using fresh carrots as a model sample, the antioxidant activity of PVA, CQD, and a PVA-CQD mixture was qualitatively determined. The in vitro cytotoxicity analysis of CQDs by MTT assay using the L6 cell line confirmed its non-toxic behaviour. This work is noteworthy because it offers a new attempt to identify toxic PA from biomass-derived precursor material and finds future applications in the food industry.