An AIE active sulfonyldianiline derived Schiff base for the detection of folic acid, hemoglobin, and glucose†

The excessive intake or deficiency of folic acid (FA), also known as vitamin B₉, can lead to several health problems. Therefore, significant research priority is required to develop facile analytical methods for FA detection. Herein, a V-shaped aggregation-induced emission (AIE) luminogen SDASA was introduced by condensing 4,4′-sulfonyldianiline with two equivalents of salicylaldehyde. The weakly fluorescent SDASA in DMSO showed yellow emission upon increasing the fractions of HEPES buffer (H₂O, 10 mM, pH 7.4) from 80% to 95% because of the combined effects of AIE and ESIPT. The formation of self-aggregates of SDASA was supported by SEM and DLS analyses. AIEgen SDASA (f_HEPES 95%) was employed as probe 1 for FA detection. The fluorescence emission of AIEgen SDASA (λ_em = 550 nm, λ_ex = 390 nm) was blue-shifted and enhanced at 475 nm by FA. The results of DFT, fluorescence lifetime, zeta potential, DLS, and UV-vis absorption studies revealed that the interaction that occurred between FA and SDASA inhibited the intramolecular charge transfer and aggregate morphology of SDASA. With probe 1, the FA concentration can be detected down to 0.83 μM. Further studies with SDASA in DMSO showed strong green emission at 525 nm upon complexation with Zn²⁺ ions. The in situ generated SDASA–Zn²⁺ complex was used as probe 2 for the fluorescent turn-off detection of hemoglobin and glucose with a detection limit of 0.57 nM and 0.32 μM, respectively. Finally, the analytical utility of the developed probes was examined by detecting selective analytes in real blood serum.