Design of high performance fluorescent probe-based test strips for hydrogensulfite determination by chemical grafting

A rapid on-site determination of hydrogensulfite in food is of great importance for our health. Herein, a novel benzoindole-based fluorescent probe tethered with hydroxyl groups was synthesized. The probe displayed a good selectivity, fast response time (<68 s), and low determination limit (0.72 μM) in solution. In order to prepare high performance test strips, various immobilization methods of probes onto paper substrates were investigated, including physical absorption of probe onto filter paper (test strip-1) and chemical immobilization of probe onto BP-PAA-attached paper (test strip-2) or probe-attached BP-PAA onto paper (test strip-3). Results showed that the determination limit of test strip-2 was 9 μM, which was lower than that of test strip-1 (55 μM) and test strip-3 (104 μM). This phenomenon could be due to the deposition of most probes on the paper surfaces in the test strip-2 instead of the whole 3D paper structure (test strip-1) or the upper half of paper (test strip-3), which facilitated their reaction with hydrogensulfite. In particular, the test strip-2 could rapidly determine the amount of bisulfide in white-rot fungus, shiitake mushroom, and dried shrimp with good recoveries (91.8-104.1%), indicating the great application prospect of our proposed fluorescent test strip.