Ultrasensitive turn-off fluorescent sensor for estimation of the new influenza antiviral prodrug baloxavir marboxil in its pharmaceutical formulation.

Carbon quantum dots (CQDs) are a recently developed class of fluorescent nanoparticles made from carbon. Co-doping with heteroatoms such as nitrogen and sulfur improved the properties and generated a high quantum yield. In the proposed study, we utilized a simple, cost-effective, single-stage hydrothermal approach to produce extreme photoluminescence co-doped, nitrogen and sulfur, CQDs (N,S-CODs). Thiosemicarbazide was used as a nitrogen and sulfur source, while citric acid was used as a carbon source to produce fluorescent probes. The prepared N,S-CQDs were subjected to extensive characterization. The generated N,S-CQDs yielded strong fluorescence emission at 430.0 nm after excitation at 360.0 nm, with a relatively high quantum yield of 41.3% utilizing quinine sulfate as a reference fluorescent compound. These N,S-CQDs were applied as fluorescent nanosensors for the ultrasensitive spectrofluorimetric determination of baloxavir marboxil (BXM) directly without pre-derivatization for the first time. BXM effectively quenches the native fluorescence of N,S-CQDs. Considering the optimal conditions, the fluorescence intensity reduction of N,S-CQDs exhibited a 'turn-off' response to BXM at concentrations of 10.0-100.0 ng ml, with detection limits of 1.88 ng ml and quantitation limits of 5.69 ng ml, respectively. The proposed method determined BXM successfully in its tablet dosage form and further expanded to confirm the content uniformity of the tablet units in agreement with USP guidelines.