Insights for applying N,S-doped carbon dots as a fluorescent nanoprobe for estimation of some nitro-calcium channel blockers

A facile and simple one-step hydrothermal approach was adopted for fabrication of N and S co-doped carbon quantum dots probe (NSCDs) by using thiosemicarbazide as a dopant and citric acid as a precursor. The prepared NSCDs with a high quantum yield of 0.58 were characterized using UV-visible spectroscopy, IR spectroscopy and high-resolution transmission electron microscopy. The as-obtained NSCDs could be deemed as an effective fluorescent nanosensor for the determination of some anti-hypertensive nitro-calcium channel blockers (Nitro-CCBs) including nicardipine (NIC), nifedipine (NIF) and nimodipine (NIM) whether in pure form or in their pharmaceutical formulations. Measurements of NSCD emission intensity were performed at 416 nm after being excited at 345 nm. Nitro-CCBs could induce quenching in the native fluorescence of NSCDs due to the inner filter effect and static quenching mechanism. The studied compounds were investigated within linear detection range of (10.0-100.0 µM) for NIC, (5.0-60.0 µM) for NIF and (5.0-60.0 µM) for NIM. Correlation coefficients are greater than or equal to 0.9998 and detection limits are ranged between 0.55 and 1.86 µM. The proposed method was extended to estimate the studied compounds in different pharmaceutical samples with high % recoveries ranging from (97.95 to 101.28%) and low % relative standard deviation values (less than 2%). Validation of the developed spectrofluorimetric method was done along with the International Council of Harmonization requirements.