Background: Hypochlorous acid (HClO) is a crucial disinfectant in the food industry. It can be used to soak perishable foods like vegetables, fruits, eggs, fish, and raw meat before processing and storage, eliminating microorganisms, bacteria, fungi, and pathogens to ensure food safety. HClO also helps preserve vegetables and fruits by reducing ethylene production, delaying rotting, decreasing cell membrane permeability, inhibiting polyphenol oxidase activity, and postponing discoloration. However, excessive HClO residues in food can degrade nutrients and pose health risks. Thus, it's urgent to develop an efficient method for in-situ quantitative determination of HClO in various food samples.

Results: A colorimetric and near-infrared (NIR) fluorescent probe, YQ, has been developed for HClO. In YQ, the 2-(2-methyl-4H-chromen-4-ylidene) malononitrile conjugated 1,2-dihydrocyclopenta[b]chromen-6-ol acts as a NIR fluorophore, and the O-phenyl methanethioate is incorporated as a new recognition group for HClO. When exposed to HClO, the probe shows highly sensitive and selective NIR fluorescence response with detection limit of 74 nM. It also exhibits significant colorimetric changes after sensing reaction, substantially enhancing detection reliability. The probe has been applied for imaging exogenous and endogenous HClO in living cells. The residual HClO concentrations in lettuce leaves after spraying with different concentrations of HClO solutions were also monitored. Test strips made with YQ enable in-situ HClO detection in water samples. Notably, to accomplish in-situ quantitative detection, a portable optical signal detection system was devised. Probe YQ, together with this self-fabricated system, has been implemented for in-situ quantitative detection of HClO in tomatoes and strawberries.

Significance: Existing methods for quantifying HClO typically require costly equipment, advanced technical skills, and complex sample preparation, making them unsuitable for in-situ quantification. Here, the developed colorimetric and NIR fluorescent probe for HClO avoids background interference from the food matrix and enhances detection reliability. More importantly, when coupled with the self-made portable optical signal detection system, this probe can be served as a powerful tool for in-situ quantitative measurement of HClO in diverse foods.

Keywords: Custom-designed system; Fluorescent probe; Food; HClO; In-situ detection.

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