Design of cobalt-doped graphene quantum dot-decorated vanadium pentoxide nanosheet-based Off-On fluorescent sensor system for tiopronin sensing.

Despite the high medicinal value of tiopronin, there are substantial adverse effects such as yellow skin, yellow eyes, muscle aches, etc. Therefore, there is a huge necessity to identify tiopronin using advanced sensors in provided samples. Recently, the preference for graphene quantum dots (GQDs) and inorganic nanomaterial-based fluorescent sensors for the detection of pharmaceuticals has been extensively documented due to their plentiful advantages. Therefore, in this work, the cobalt-doped GQDs decorated vanadium pentoxide nanosheet-based fluorescence switch 'Off-On' sensor (Co-GQDs@VO-NS) was designed for highly sensitive and selective detection of tiopronin. Briefly, the green synthesis of highly fluorescent Co-GQDs was carried out using a hydrothermal method. Meanwhile, the synthesis of VO-NS was synthesized using the liquid exfoliation method. The synthesis of Co-GQDs@VO-NS was accomplished wherein Co-GQDs adsorbed on the surface of VO-NS that offered the quenching of fluorescence of Co-GQDs. Afterward, the addition of tiopronin into the quenched probe disclosed the proportional recovery of fluorescence of Co-GQDs. Here, the addition of tiopronin provides the decomposition of VO-NS and conversion into the V that aids in releasing the quenched fluorescence of Co-GQDs. The limit of detection and linearity range for tiopronin was found to be 1.43 ng/mL and 10-700 ng/mL, respectively. Moreover, it demonstrated high selectivity, good stability at experimental conditions, and practicality in analyzing tiopronin in spiked sample analysis. Hence, the designed Co-GQDs@VO-NS nanosized sensor enables high sensitivity, selectivity, simplicity, label-free, and eco-friendly tiopronin recognition. In the future, the utility of Co-GQDs@VO-NS can open a new door for sensing tiopronin in provided samples.