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 (Cu) 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 Cu to quench fluorescence of the produced CDs and probable fluorescence restoration through complexation of Cu by the bisphosphonate group of ETD. The developed sensor showed a good performance for Cu 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 Cu and ETD with good recoveries.