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.