Green Synthesized Cu@Carbon Quantum Dots for Histidine and Arsenate Sensing

In this work, we report green synthesis of Cu-doped carbon quantum dots (CQDs), abbreviated as Cu@CQDs, using CQDs derived from
Citrus limetta
waste pulp, as a reducing and capping agent. Synthesis parameters are optimized in terms of synthesis temperature and thus optimized Cu@CQDs are characterized for their structural and optical properties. They exhibit a surface plasmon peak at ~575 nm and are of size ~6 nm. The as prepared Cu@CQDs are studied for colorimetric and absorbance based sensing of histidine and arsenate (As (V)), respectively. The imidazole side chain of histidine act as a coordinating ligand, and the results into aggregation of Cu@CQDs, leading to their color change from colorless to blue. With this approach, Cu@CQDs is found to detect histidine with high selectivity and in a wide concentration range of 10 to 100 mM. The detection limit is further found to be 17.82 mM, Moreover, the rich surface functionalities of Cu@CQDs are also utilized for absorbance based detection of As (V) detection. The Cu@CQDs were found to detect As (V) in 10–1000 ppb concentration range with a detection limit of ~18 ppb (standard deviation ~0.03).