A novel “ON–OFF–ON” fluorescent sensor based on N,Br-doped carbon dots for the rapid detection of tannic acid and erythromycin

In this study, the hexane extract of Asters tataricus was used as the carbon source, and ethylenediamine and 4-bromophenylene diamine were selected as dopants to prepare nitrogen and bromine co-doped carbon dots (N,Br-CDs) by the hydrothermal synthesis method. The obtained fluorescent probe has a uniform particle size distribution, good water solubility and high stability, with a fluorescence quantum yield of 48.43%. Under 420 nm excitation conditions, N,Br-CDs exhibited the strongest fluorescence emission at 513 nm, indicating that the sensing system was in the “ON” state. Subsequently, TA was introduced as a quencher to induce static quenching of the N,Br-CDs system, significantly weakening the fluorescence intensity and switching the sensing system from “ON” to “OFF”. Finally, after EM was introduced into the N,Br-CDs/TA system, EM preferentially formed a complex with TA and weakened its quenching effect on the quantum dots, thereby achieving fluorescence recovery and returning the sensing system from the “OFF” state to the “ON” state. Based on the above mechanism, an “ON-OFF-ON” fluorescence sensing system with N,Br-CDs as the luminescent substrate was constructed for the sensitive detection of TA and EM. The results showed that the system exhibited good linear response to TA, with the linear ranges being 1.50–22.94 μM and 34.88–348.42 μM, respectively, and the limits of detection being 0.2168 μM and 2.1797 μM, respectively (LOD, S/N = 3). The linear range for EM was 1.93–377.08 μM, with a detection limit of 0.6693 μM. Furthermore, the sensor system was capable of quantitatively determining TA and EM in human serum, Huangshui River water, and milk matrices, demonstrating its potential for broad application in environmental monitoring and bioanalysis.