Sensitive and selective nitrite assay based on fluorescent gold nanoclusters and Fe²⁺/Fe³⁺ redox reaction

In recent years, gold nanoclusters (AuNCs) have received considerable attention as optical transducers in chemo/biosensors. Herein, a facile and efficient assay for NO₂^- has been successfully developed based on the fluorescence quenching of AuNCs co-modified by bovine serum albumin and 3-mercaptopropionic acid (BSA/MPA-AuNCs). In the presence of NO₂^- under acidic conditions, Fe²⁺ can be readily oxidized and transformed to Fe³⁺, which can significantly suppress the fluorescence of BSA/MPA-AuNCs via non-radiative electron-transfer mechanism. The linear range and detection limit for this system were found to be 5-30 μM (r = 0.9975) and 0.7 μM, respectively. Other common anions and cations showed only very minor interference with the NO₂^- detection. Furthermore, the effectiveness of the proposed sensing strategy was validated by the demonstration of good performance in the determination of the amount of NO₂^- in ham samples, rendering it a powerful tool for the assessment of food security and water quality.