Abstract: In this study, using agar hydrogel as the matrix and gold-silver iodide dimer nanoparticles (Au-AgI NPs) as the recognition probe, a highly sensitive and visualized colorimetric hydrogel patch was successfully prepared for the rapid detection of cyanide ion (CN-) in liquor. Agar hydrogels, with their excellent softness and permeability, had a three-dimensional porous structure that could quickly adsorb Baijiu samples, causing CN- to react specifically with Au-AgI NPs to produce color changes. The color development mechanism was due to that fact that CN- underwent a metathesis reaction with AgI in Au-AgI NPs to generate Ag(CN)2-, resulting in etching of AgI and a change in the localized surface plasmon resonance (LSPR) of Au-AgI NPs and thereby causing the color of the hydrogel patch to change from blue-green to red. The concentration of CN- (c) within the range of 1-100 μmol/L had a good linear relationship with the red/(green + blue) ratio [R/(G + B)] of Au-AgI NPs hydrogel, which was fitted as follows: R/(G + B) = 0.006 53c + 0.163 75, with a correlation coefficient (R2) of 0.990. The detection limit (LOD) was as low as 0.633 μmol/L, and the response time was less than 20 s. This method was successfully applied to the detection of CN- in commercially available light-aroma and strong-aroma Baijiu, with spiked recovery rates ranging from 96.04% to 104.57%. The hydrogel patch enabled naked-eye identification of 40 μmol/L CN- in the Baijiu samples, and when combined with a smart phone, it allowed for rapid and accurate on-site quantitative analysis of CN-. This study provides an efficient and convenient new approach for the rapid screening of cyanide in Baijiu.

Key words: cyanide; gold-silver iodide dimer nanoparticles; hydrogel; colorimetry; rapid detection