A novel AIE “on-off-on” fluorescence sensor for highly selective and sensitive sequential detection of Fe3+ and HSO3− in foods

• The first report on the AIE properties of 4, 4′-stilbene dicarboxylic acid(H 2 SDC). • Constructing the "on-off-on" method firstly to detect Fe 3+ and HSO 3 − in samples. • The method has the potential to detect Fe 3+ and residual SO 2 in samples on-site. It was discovered for the first time that 4,4′-stilbene dicarboxylic acid (H 2 SDC) had an aggregation-induced emission (AIE) property. H 2 SDC has a very weak fluorescence emission in DMF, but it can emit bright cyan light in DMF/H 2 O (v:v = 1:9, pH 4.0) solution in the aggregated state. The fluorescence of H 2 SDC in the aggregated state can be quenched by Fe 3+ through a dynamic quenching mechanism and has a good selectivity. Also, HSO 3 − can restore the fluorescence of the H 2 SDC-Fe 3+ system by redox. Therefore, Fe 3+ and HSO 3 − can be detected by constructing an “on-off-on” method. The detection limits of Fe 3+ and HSO 3 − are about 18.5 and 38.4 nM, respectively. And the method has a reasonable recovery rate and a relatively small standard deviation in the actual detection of functional foods. The “on-off-on” phenomenon of H 2 SDC fluorescence can also be seen under the portable UV lamp (365 nm), indicating that H 2 SDC has the potential to detect Fe 3+ and HSO 3 − colorimetrically on site.