Turn-off fluorescence of S,N-doped carbon dots for determination of two nitro-containing drugs in dosage forms and human plasma

This study describes the development of an environmentally-friend optical nanosensor for the rapid spectrofluorimetric assessment of two nitro-compounds, namely nitrofurantoin and dantrolene in their dosage forms and plasma samples. A one-step synthetic technique successfully created very bright water-soluble carbon quantum dots doped with sulfur and nitrogen (S,N-CQDs). Carbon was derived from citric acid, while nitrogen and sulfur were obtained from thiosemicarbazide. The dimensions of the synthesized dots were measured using a high-resolution transmission electron microscope. FT-IR spectroscopy was used to determine which functional groups were located on their surfaces. The nanosensor's fluorescence emission peaked intensely at 415 nm after excitation at 345 nm with a quantum yield of about 0.52. The inherent fluorescence of the nanosensors gradually decreased upon addition of the studied analytes in increasing concentrations. The fluorescence reduction of nanosensor with the concentrations of the investigated drugs demonstrated linear correlation within the ranges of 0.5-8.0 μg/mL and 1.0-10.0 μg/mL with limits of detection of 0.14 μg/mL (0.59 μM) and 0.23 μg/mL (0.73 μM) for nitrofurantoin and dantrolene, respectively. The recommended method was used to determine the concentrations of the investigated drugs in their commercial capsules, with recoveries ranging from 97.90 % to 101.57 % and low percent RSD values less than 2 %. Moreover, the method was adapted for the in-vitro analysis of the two analytes in spiked human plasma samples with % recoveries from 95.20 % to 102.20 %. The mechanism of interaction between each analyte and the dots was also investigated. The selectivity of the approach for measuring analytes concentration in the presence of excipients, co-formulated medications, or co-administered pharmaceuticals was further evaluated through an interference study. The suggested method's validity was evaluated in accordance with ICH criteria.