Highly sensitive and selective dual-signal ratiometric fluorescent sensor based on N, S co-doped carbon dots and...

Nowadays, heavy metal pollutants have emerged as a significant global environment affecting human health. Herein, in this work, a highly sensitive and selective dual-signal ratiometric fluorescent sensor for heavy metal Pb²⁺ ions detection in aquatic environments was developed by employing the combined highly fluorescent nitrogen and sulfur co-doped carbon dots (N,S-CDs) with rhodamine B (RhB) as a new dual-signal fluorescent probe. The nanostructure, optical properties and a self-calibration mechanism based on the intensity ratio of dual emission peaks were discussed, and, the co-doping of nitrogen and sulfur increased the electron transfer rate and enhanced the coordination interaction between the N,S-CDs and Pb²⁺ ions were revealed in the dual-signal ratiometric fluorescent sensor. Moreover, the new sensor exhibited a robust linear response to Pb²⁺ ions within the 0-180 μM range, achieving a limit of detection (LOD) of 0.45 μM (93 μg/L) in the actual measurement environment, which is observed to be commensurate with the Grade I standard limit for lead as prescribed in China's "Integrated Wastewater Discharge Standard" (100 μg/L). Furthermore, specificity experiments demonstrated the sensor's superior recognition of Pb²⁺ ions over other common metal ions (e.g., Cu²⁺, Fe³⁺, Al³⁺). In practical industrial wastewater analysis, spike recoveries of 94.20-97.53 % were achieved, with relative standard deviations (RSDs) below 1.32 %, thus validating the method's reliability. This work has been recognized to provide significant potential for environmental monitoring applications.