The current study introduces a spectrofluorimetric methodology for the assessment of palbociclib without the need for any pre-derivatization steps for the first time. This approach relied on the palbociclib quenching effect on the native fluorescence of newly synthesized nitrogen-doped carbon quantum dots (N-CQDs). An innovative, facile, and rapid microwave-assisted pyrolysis procedure was applied for the synthesis of N-CQDs using available and economic starting materials (the carbon source is orange juice and the nitrogen source is urea) in less than 10 minutes. Full characterization of the prepared QDs was carried out using various techniques. The prepared N-CQDs exhibited good fluorescence emission at 417 nm after excitation at 325 nm with stable fluorescence intensity and good quantum yield (29.3%). They showed spherical shapes and narrow size distribution with a particle size of around 2–5 nm. Different experimental variables influencing fluorescence quenching were examined and optimized. A good linear correlation was exhibited alongside the range of 1.0 to 20.0 μg mL⁻¹ with a correlation coefficient of 0.9997 and a detection limit of 0.021 μg mL⁻¹. The proposed methodology showed good selectivity allowing its efficient application in tablets with high percentage recoveries and low percentage RSD values. The mechanism of quenching was proved to be static by applying the Stern–Volmer equation at four different temperatures. The method was validated in accordance with ICHQ2 (R1) recommendations. Intriguingly, N-CQDs demonstrated good biocompatibility and low cytotoxicity, which permitted cellular imaging and palbociclib detection in living cancer cells. Therefore, the proposed method may have potential applications in cancer therapy and related mechanism research.

In this study, highly fluorescent sulfur and nitrogen co-doped carbon quantum dots (SN-CQDs) were synthesized by a simple one-pot hydrothermal method using thiosemicarbazide and citric acid as starting materials. Various spectroscopic and microscopic techniques were applied to characterize the prepared SN-CQDs. The synthesized SN-CQDs’ maximum fluorescence emission was obtained at 430 nm after excitation at 360 nm. Rifampicin (RFP), tinidazole (TNZ), ornidazole (ONZ), and metronidazole (MNZ) all quantitatively and selectively quenched the SN-CQDs’ native fluorescence, which was the base-for their-spectrofluorimetric estimation without the need for any tedious pre-treatment steps or high-cost instrumentation. SN-CQDs demonstrated a “turn-off” fluorescence response to RFP, TNZ, ONZ, and MNZ over the ranges of 1.0–30.0, 10.0–200.0, 6.0–200.0, and 5.0–100.0 μM with detection limits of 0.31, 1.76, 0.57, and 0.75 μM and quantitation limits of 0.93, 5.32, 1.74, and 2.28 μM respectively. The suggested method was successfully used to determine the investigated drugs in their commercial dosage forms. The method was further extended to their determination in spiked human plasma samples, with satisfactory mean % recoveries (99.44–100.29) and low % RSD values (< 4.52). The mechanism of fluorescence quenching was studied and discussed. The suggested method was validated in accordance with ICH recommendations.

A validated, sensitive, and simple spectrofluorimetric method was developed for the analysis of two important CNS-acting drugs, olanzapine and diazepam, in their commercial tablets without the need for any pretreatment steps. The developed method relied on the quantitative quenching effect of each of olanzapine and diazepam on the native fluorescence of nitrogen and sulfur-doped carbon quantum dots (NS@CQDs). NS@CQDs were prepared from thiosemicarbazide and citric acid by a facile one-pot hydrothermal technique. The synthesized NS@CQDs were characterized by different spectroscopic and microscopic techniques. NS@CQDs produced a maximum emission peak at 430 nm using 360 nm as an excitation wavelength. Calibration curves showed a good linear regression over the range of 5.0–200.0 and 1.0–100.0 μM with detection limits of 0.68 and 0.29 μM for olanzapine and diazepam, respectively. The adopted method was used for the determination of the investigated drugs in their tablets with high % recoveries (98.84–101.70%) and low % RSD values (< 2%). As diazepam is one of the most commonly abused benzodiazepines, the developed method was successfully applied for its determination in spiked human plasma with high % recoveries and low % RSD values, providing further insights for monitoring its potential abuse. The quenching mechanism was also studied and confirmed to be through dynamic and static quenching for olanzapine and diazepam, respectively. Due to the high selectivity and sensitivity, content uniformity testing of low-dose tablets was successfully performed by applying the United States Pharmacopoeia guidelines. The method's validation was performed in compliance with ICHQ2 (R1) recommendations.