Deciphering the mechanism of undoped and heteroatom doped-carbon dots for detection of lead ions at nanomolar level

Herein, two types of facile, simple, and eco-friendly nanosensors were developed for the sensing of Pb2+ ions follow the aggregation-induced emission enhancement (AIEE) and dynamic quenching mechanism. Two types of carbon dots i.e., undoped carbon dots (u-Cdots) and nitrogen, sulfur co-doped carbon dots (N, S-Cdots) were developed by a rapid single-step approach under high-temperature treatment without any solvent. Both the prepared carbon dots showed high water solubility and excellent stability. The particle size of u-Cdots and N, S-Cdots were determined to be 7.5 nm and N, S-Cdots 1.8 nm, respectively which was examined through transmission electron microscope (TEM). The incorporation of heteroatom doping into the N, S-Cdots was examined through X-ray photoelectron spectroscopy (XPS). The u-Cdots shows excitation-dependent PL behaviour whereas, N, S-Cdots shows excitation-independent PL behaviour. Further, both the carbon dots act as sensitive and selective sensing platforms for Pb2+ ions in nanomolar range. Different photophysical investigations (fluorescence quantum yield, average lifetime, and radiative and non-radiative deactivation channels) were thoroughly studied to support the different PL mechanisms. Both the prepared sensing platforms exhibited a good limit of detection (LOD) i.e., 30 nM and 7 nM for u-Cdots and N, S-Cdots, respectively. The developed sensing platforms were also used in real sample analysis for the detection of Pb2+ ions.