Nitrogen-doped carbon dots for sequential ‘ON-OFF-ON’ fluorescence probe for the sensitive detection of Fe3+ and l-alanine/l-histidine

Herein, the innovative and highly effective nitrogen-doped carbon dots (N-CDs) fluorescent probes were conveniently fabricated using spirulina algae and l-arginine as the raw materials by using a one-pot hydrothermal treatment. The as-prepared N-CDs exhibited great stability, exceptional optical performance, superior biocompatibility as well as low cytotoxicity. The fluorescence of N-CDs had the most vigorous green light emission around 530 nm upon excitation at 450 nm with a 32 % quantum yield, which can be employed as a ‘turn-off’ response for Fe3+ detecting. The limit of detection for Fe3+ by the N-CDs is 14.8 nM with a linear response in the range of 0.05–1 µM. Therefore, the static quenching mechanism for the fluorescence of N-CDs for detection was proposed, which was due to the Fe3+could easily be combined with functional groups on the surface of N-CDs and the induced aggregation. The N-CDs nanosensor can serve as a reversible fluorescence quenching nanoprobe for Fe3+. As confirmed by adding amino acids containing l-histidine and l-alanine to the complex of N-CDs-Fe3+ that caused a ‘turn-on’ fluorescence response. Compared to other nanoprobes found in the literature, N-CDs is capable of detecting the l-alanine or l-histidine with a detection limit as low as 52.8 nM and 69 nM with a good linear relationship in the range of 0.5–50 µM, respectively. In addition, the newly developed fluorescence nanosensor was successfully used to determine Fe3+ in tap water and mineral water.