Copper (II)-azo complex modified hydrogel: A sensitive colorimetric sensor for visual detection of H₂S gas

Hydrogen sulfide (H₂S) in human breath is important for early diagnosis of halitosis and prevention of oral diseases. The current H₂S sensors suffer from poor specificity or high detection limit, restricting their widespread applications in daily life. In this work, a novel colorimetric sensor for H₂S gas detection was constructed by incorporating copper(II) pyridine diazinonaphthol (Cu-PAN) complex into agarose hydrogel. H₂S can react with Cu-PAN and break the ligand bond between Cu²⁺ and PAN, resulting in an obvious color change. Thanks to the specificity of Cu-PAN complex and excellent loading and diffusion functions provided by three-dimensional structure of hydrogel, the prepared sensor exhibited superior sensing performance in the aspects of sensitivity, selectivity, response time, simplicity, etc. A broad detection range of 1–50 ppm was achieved by this sensor. The feasibility of the Cu-PAN hydrogel sensor for the measurement of H₂S level in human exhaled breath was validated. This work supplies a new way to design a green, simple, rapid, sensitive tool for the detection of other gases.