Aggregation enhanced emissive orange carbon dots for information encryption and detection of Fe3+ and tetracycline.

In this study, N-doped fluorescent carbon dots with aggregation enhanced emission (N-CDs) were synthesized by a simple and rapid microwave-assisted method using o-phenylenediamine (OPD) and urea as raw materials and water as solvent. The fluorescence quantum yield of N-CDs was 20.64 %. N-CDs can be applied as invisible inks for message encryption. Furthermore, the fluorescence intensity of N-CDs can be quenched by Fe³⁺ and enhanced by tetracycline (TC). Therefore, two fluorescent probes were simultaneously designed in this study. Namely, "turn-off" fluorescence probe for Fe³⁺ and "turn-on" fluorescence probe for TC. The linear detection range of Fe³⁺ is from 1 to 70 μM, and detection limit is 0.1011 μM; the linear detection range of TC is from 0.1 to 10 μM, and the detection limit can be as low as 0.0555 μM. In this paper, the mutual interference between Fe³⁺ and TC was investigated for the first time. The detection of Fe³⁺ and TC was made more accurate by optimizing pH conditions and adding masking agent.