Green microwave-prepared N and S Co-doped carbon dots as a new fluorescent nano-probe for tilmicosin detection.

A straightforward, rapid, and selective fluorescent probe for determination of tilmicosin has been developed based on novel nitrogen and sulfur co-doped CDs (NS-CD). The NS-CDs were synthesized, for the first time, through green, simple one step microwave pyrolysis in only 90 s using glucose as carbon source and l-cysteine as nitrogen and sulfur source. This proposed synthesis method was energy-efficient and resulted in NS-CDs with high production yield (54.27 wt%) and narrow particle size distribution. Greenness of NS-CDs synthesis method was assessed using EcoScale and was proven to be excellent green synthesis. The produced NS-CDs were applied as a nano-probe for determination of tilmicosin in its marketed formulation and milk based on dynamic quenching mechanism. The developed probe showed a good performance for tilmicosin detection in marketed oral solution and pasteurized milk and linearity range of 9-180 µM and 9-120 µM, respectively.

Innovative spectrofluorimetric determination of vildagliptin based on a "switch off/on" NS-doped carbon dot nanosensor.

A simple, fast, and green one-step microwave pyrolysis approach was proposed for the synthesis of highly fluorescent nitrogen/sulfur-doped carbon dots (NS-CDs). The proposed NS-CDs were prepared in only one minute from citric acid and thiosemicarbazide. In the presence of Cu2+, the fluorescence of NS-CDs was significantly quenched ("turn off") through the formation of a non-fluorescent NS-CDs/Cu2+ complex. This designed sensor could be applied for label-free determination of vildagliptin based on the competition between vildagliptin and the functional groups on NS-CDs for Cu2+ complexation, and hence NS-CD fluorescence recovery ("turn on"). Under the optimized conditions, the developed probe (NS-CDs/Cu2+) demonstrated a good sensing performance for vildagliptin with linearity in the range of 45-240 µM and a detection limit of 13.411 µM. Owing to its sensitivity, this sensor was successfully applied for vildagliptin determination in human urine samples.

Rapid microwave synthesis of N,S-doped carbon quantum dots as a novel turn off-on sensor for label-free determination of copper and etidronate disodium.

An environmentally-friendly, selective and rapid turn off-on fluorescent probe for both copper (Cu2+) and etidronate disodium (ETD) detection was derived from nitrogen/sulfur co-doping of carbon dot (N,S-CD). The N,S-CDs were produced, for first time, through microwave-assisted pyrolysis in only 60 s using readily accessible and cheap precursors (citric acid and thiosemicarbazide). The proposed synthesis method resulted in N,S-CDs with narrow particle size distribution, high product yield (64.38 wt%) and high doping efficiency (N, 28.56% and S, 8.47%). The turn off-on sensor was developed after demonstrating the ability of Cu2+ to quench fluorescence of the produced CDs and probable fluorescence restoration through complexation of Cu2+ by the bisphosphonate group of ETD. The developed sensor showed a good performance for Cu2+ and ETD detection with a linear range of 5-125 µM and 30-210 µM, respectively. This developed platform could be applied for routine analysis of Cu2+ and ETD with good recoveries.

N-Doped Carbon Dots as a Fluorescent Nanosensor for Determination of Colchicine Based on Inner Filter Effect.

In this study, a novel and simple fluorescent carbon quantum dots (CQDs) based nano-sensor for colchicine determination has been prepared. The nitrogen doped CQDs probe was prepared using uric acid as a carbon/nitrogen source via a one-step pyrolysis. The sensor is based on inner filter effect (IFE) where colchicine acts as a powerful absorber that affects the excitation of the fluorescer (CQDs). This overlap results in a quantitative attenuation of the fluorescence of CQDs with increasing colchicine concentration in the range of 2-25 µM. The developed sensor has the advantages of simplicity, less time-consuming, convenience and satisfactory selectivity for colchicine determination in pharmaceutical dosage forms.

Simultaneous determination of amlodipine and metoprolol in their combined dosage form using a synchronous fluorescence spectrofluorimetric method.

Highly sensitive, rapid, accurate and precise synchronous fluorescence spectrofluorimetric method has been developed for simultaneous analysis of a mixture of amlodipine (AMD) and metoprolol (MET). The method relies on measuring the relative synchronous fluorescence intensity of both drugs at Δλ of 90 nm in acetate buffer solution at pH 5. The experimental parameters influencing the developed method were investigated and optimized. The method was linear over the ranges 0.2-2 µg/ml and 0.5-10 µg/ml for AMD and MET, respectively. The limits of detection were 50 ng/ml for AMD and 130 ng/ml for MET while the limits of quantitation were 150 ng/ml for AMD and 390 ng/ml for MET. The developed method was applied successfully for the determination of the two drugs in their co-formulated tablet. The mean percent recoveries were found to be 100.51 and 99.57 for AMD and MET, respectively.