A convenient and practical colorimetric chemosensor for sulfide monitoring in pure water: Applications to environmental water, smartphone-based platform, colorimetric food imaging and spoilage

Sulfide is an environmentally harmful and toxic substance. Thus, its sensitive detection is important for water-quality monitoring and food safety. In this work, we synthesized a convenient and practical colorimetric chemosensor DNP (1,3-dimethyl-5-(7-nitrobenzo[c][1,2,5]oxadiazol-4-yl)pyrimidine-2,4,6(1H,3H,5H)-trione) for sensing S^2- in pure water. DNP selectively detected S^2- among varied analytes through color change from red to colorless. The probe DNP showed a low detection limit (2.8 μM) for S^2- in a wide linear range of 0–150 μM, which was significantly below the WHO guideline (14.8 μM). The detecting process of S^2- by DNP was proposed to be a sulfide-triggered reduction of the NBD nitro group, supported by ¹H NMR titration, calculations, and ESI-mass. DNP could certainly quantify S^2- in environmental samples like river water and seawater with recoveries of 98.33 % - 103.49 %. Also, test-strip and smartphone applications were conveniently applied for S^2- sensing. DNP demonstrated the ability for imaging sulfide in mushroom and onion epidermal cells. In particular, DNP-coated strips could be used as a convenient sulfide indicator of foods such as pork, chicken, and garlic. All these results highlighted DNP as a promising and versatile chemosensor for sulfide detection in food and real-field systems.