Gel-sol and colorimetric dual-modal sensor for highly selective and sensitive detection of iodide ions based on gelatin fabricated AuNPs

Excessive intake or lack of iodide ions (I-) will have serious impact on human growth and health. Therefore, the highly selective and sensitive detection of I- is particularly urgent. Herein, a dual-modal sensor based on colorimetric and gel-sol signal responses has been developed for the visual detection of I-. Visual sensing based on I- triggered dual-signal simultaneous response can reduce the interference of false positive signals and improve detection accuracy. This dual-modal sensor (Gel-AuNPs) is constructed by the in situ reduction of chloroauric acid using gelatin (Gel) with unique topological structure and reduction properties to prepare gold nanoparticles (AuNPs). The presence of I- can induce a noticeable color change from red to yellow (attributed to the occurrence of redox reaction), and the selective visual detection of I- was realized in a wide concentration range with a linear fitting coefficient of 0.9983 and a limit of detection (LOD) of 30.1 μM. Simultaneously, based on the change in viscosity in the gel-sol phase transformation process (attributed to the salting-in effect of I-), the quantitative relationship of I- detection (R2 = 0.9937) was then established. Furthermore, the Gel-AuNPs hydrogel exhibited high sensitivity for detecting I- in actual water samples such as seawater and tap water. More importantly, the in situ synthesized Gel-AuNPs showed good solid-state stability and strong salt tolerance, implying the potential scope of their practical application in different harsh conditions. As such, this visual sensing system with dual signal responses will have prospective applications in detection and analysis in due course.