Highly effective recognition of Fe3+ and lysine based on hydrosoluble N-doped carbon dots

In this study, dual-color nitrogen-doped carbon dots (NCDs) were synthesized using a simple solvothermal method. These fluorescent NCDs displayed excitation-independent emission in red (598 nm in ethanol) and orange (553 nm in water) due to their effect of two different solvents. Both types of NCDs exhibited high stability under UV irradiation for 80 min. The water-soluble NCDs showed excellent sensitivity to Fe3+ ions by the quenching of their photoluminescent (PL) intensity. Quantitative analysis revealed a gradual decline in PL intensity, with a low detection limit of approximately 0.97 µM. Interestingly, the quenched fluorescence of NCDs caused by Fe3+ could be restored by the addition of lysine to the (NCDs + Fe3+) solution, with an estimated detection limit of about 0.37 µM. This phenomenon could be explained in the terms of non-radiative electron/hole recombination, leading to aggregation through efficient photo-induced electron transfer (PET). Utilizing their high selectivity and sensitivity, these NCDs served as “On-Off-On” switches and were successfully employed for the detection of Fe3+ in real water samples, contributing to environmental safety and control efforts.