New H2S colorimetric probe based on aggregation of poly(allylamine) grafted by perylene diimide radicals: mechanism and application in analysis of sulfur-containing protein spoilage.

The detection of trace hydrogen sulfide (H2S) enables early warning of food spoilage, serving as a key technology for food safety and quality control. Here, with the research purpose of developing a simple, rapid and sensitive method for real-time monitoring of the freshness of sulfur-containing protein foods, a poly(allylamine)-stabilized perylene diimide radical anion (QFPDI-PAA, a stable π-radical) is reported which can be used colorimetric detection of H2S and monitoring spoilage process of sulfur-containing protein. The colorimetric mechanism is that H2S induced the intramolecular and intermolecular aggregation in QFPDI-PAA promotes the aggregation of perylene diimide radical fragments. Its detection limit for H2S in the naked-eye is 3 μM, and the spectral detection limit is as low as 0.184 μM. In real food detection, this radical achieved real-time monitoring of the production of H2S during the deterioration process of Short-Necked Clams, eggs, chicken and shrimp products. The visual detected times at 25 °C are as follows: raw yolk 60 h, raw mixed egg liquid 72 h, cooked yolk 60 h, cooked egg-white 36 h, cooked mixed egg pieces 24 h, raw clams 25 h, cooked Short-Necked Clams 35 h, raw chicken 12 h, raw shrimp 9 h. The visual inspection times at 0 °C are as follows: raw chicken 72 h, raw shrimp 24 h. This study establishes, for the first time, an effective strategy for the food spoilage monitoring by stable π-radicals.