Sulfur and nitrogen co-doped carbon quantum dots as fluorescent probes for the determination of some pharmaceutically-important nitro compounds

Abstract

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.

White sustainable luminescent determination of nifuroxazide using nitrogen–sulphur co-doped carbon quantum dots nanosensor in bulk and various pharmaceutical matrices

“…The inner filter effect, previously thought to be an analytical error, has recently begun to establish itself in the field of analysis as a substantial quenching mechanism involving an energy conversion unrelated to radiation. 28,44 The presence of a complementary inner filter effect was suggested by the overlap between the excitation spectra of NSC-dots and the UV-visible absorption spectrum of NFX Fig. 3B.…”

“…The quenching mechanism can generally be divided into a variety of categories, including dynamic quenching, static quenching, and the inner filter effect (IFE). 43,44…”

“…In order to clarify the potential quenching mechanism, the following Stern–Volmer equation was followed: 28,44,45 F 0 / F = 1 + K sv [NFX] = 1 + K q τ 0 [NFX]where F 0 and F stands for the fluorescence intensities in the absence and presence of drug, respectively, K q represents the bimolecular quenching rate constant, K sv refers to the Stern–Volmer quenching constant. The average lifetime (10 −8 s) is symbolled by τ 0 , and [NFX] is the drug molar concentration.…”

“…As these values exceeded the maximum diffusion rate constant (2.0 × 10 10 L mol −1 s −1 ) by a significant amount, 43 as a result, it was concluded that, static quenching mechanism was found to be responsible for the NSC-dots fluorescence intensity quenching in presence of the studied drug. 43,44…”

Green Synthesis of Sulfur- and Nitrogen-Doped Carbon Quantum Dots for Determination of L-DOPA Using Fluorescence Spectroscopy and a Smartphone-Based Fluorimeter

“…S,N-CQDs are among the most distinguished doped CQDs because nitrogen has an atomic radius comparable to carbon. Also, sulfur and carbon have similar electronegativity . It is believed that S,N-CQDs can interact with L-DOPA, leading to fluorescence quenching of the S,N-CQDs .…”