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.