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 biocom-patibility 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 mu M. 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 mu M, respectively. In addition, the newly developed fluorescence nanosensor was successfully used to determine Fe3+ in tap water and mineral water.

Automated summary

In this study, nitrogen-doped carbon dots (N-CDs) fluorescent probes were conveniently synthesized using spirulina algae and L-arginine through a one-pot hydrothermal treatment. The N-CDs exhibited excellent stability, exceptional optical performance, superior biocompatibility, and low cytotoxicity. They can be used as a "turn-off" response for Fe3+ detection, with a detection limit of 14.8 nM and a linear response in the range of 0.05-1 μM. The fluorescence quenching mechanism of N-CDs was proposed to be due to the easy combination of Fe3+ with functional groups on the surface of N-CDs and induced aggregation. The N-CDs nanosensor also showed the ability to detect L-alanine and L-histidine, with detection limits as low as 52.8 nM and 69 nM, respectively, in a good linear relationship in the range of 0.5-50 μM.