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@V2O5-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 V2O5-NS was synthesized using the liquid exfoliation method. The synthesis of Co-GQDs@V2O5-NS was accomplished wherein Co-GQDs adsorbed on the surface of V2O5-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 V2O5-NS and conversion into the V4+ 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@V2O5-NS nanosized sensor enables high sensitivity, selectivity, simplicity, label-free, and eco-friendly tiopronin recognition. In the future, the utility of Co-GQDs@V2O5-NS can open a new door for sensing tiopronin in provided samples.

Improvement of Cs detection performance and formation of CsCl and Cs nanoparticles by tuning graphene oxide quantum dot-based nanocomposite

A new nanocomposite was developed using functionalized graphene oxide quantum dots (GOQDs) with cesium green molecules for the first time. Although the cesium green molecule works effectively only in the solid-state, without water, and in basic conditions, the functionalized GOQDs with cesium green made the nanocomposite work well as a cesium (Cs) detector in mixed solution (distilled water/THF). The nanocomposite can be employed as a Cs detector in both acidic and basic conditions. The present study revealed that the nanocomposite of GOQDs with cesium green showed an enhanced photoluminescence in basic conditions, while the intensity of the photoluminescence in acidic conditions is the superposition of the photoluminescence of the corresponding components. The photoluminescence of the nanocomposite was quenched (turned OFF) after Cs treatment in basic conditions. On the other hand, in the acidic conditions it was found that the photoluminescence intensity of this nanocomposite was enhanced (turned ON) by the Cs addition in two different Cs concentrations, 0.06 mmol L^-1 and 0.12 mmol L^-1. In addition, the movement of the nanocomposite (after Cs addition) under the electron beams through TEM measurement was observed. The formation of CsCl and Cs nanoparticles was identified. Specifically, the Cs cluster occurrence is discussed by taking into account the mobility effect of the adatoms on the composite layer under electron beam irradiation.