Highly Sensitive "On-off" Fluorescent Probe TPA-DNBS Based on Triphenylamine Derivative for Selective Detection of Cysteine.

Cysteine (Cys) plays a critical role in both physiological and food domains, with abnormal levels being closely linked to various diseases. Therefore, the development of highly selective and sensitive detection methods is essential. In this study, a "On-off" fluorescent probe, TPA-DNBS, based on a triphenylamine (TPA) derivative, was designed. Compared to traditional probes, TPA-OH offers greater rigidity, stronger conjugation, and a larger Stokes shift, demonstrating superior signal-to-noise ratio and detection stability in complex biological and environmental samples. The probe exhibits specific response to Cys via a photo-induced electron transfer (PET) mechanism: in the presence of Cys, the DNBS quencher group is cleaved, leading to a significant increase in fluorescence. The probe shows excellent detection performance, with a linear range from 1 × 10⁻³ M to 1 × 10⁻⁹ M and a detection limit as low as 1.05 nM, along with good selectivity, interference resistance, stability, and reproducibility. In practical sample analysis, the recovery rates of spiked Cys in milk and mineral water were 99.7%-106.6% and 102.1%-103.3%, respectively, with relative standard deviations below 2.5%. These results indicate the broad applicability of the probe in complex samples.