Ultrafast sensitive colorimetric detection of cyanide based on dissolving AgI on Au-AgI heterodimeric nanoparticles via UV–vis spectroscopy and single nanoparticle imaging

Abstract

The high toxicity of cyanide and its great variety of uses in industrial processes make it necessary to develop sensitive and selective sensors for its determination in food and environmental samples. However, the developed methods usually require long time and expensive instrument, hindering on-site detection. In this work, novel colorimetric assays for cyanide detection were achieved by using UV–vis spectroscopy and single nanoparticle (NP) imaging technology based on a mechanism wherein cyanide dissolves AgI on Au-AgI heterodimeric NPs by forming Ag(CN)2-. The reaction occurred in less than 1 s, leading to the change from Au-AgI NPs to Au NPs and thus blueshift of localized surface plasmon resonance. The solution color turned to purple, and then pink from blue, while single NPs under darkfield microscopy transformed from red to yellow and green. In UV–vis spectroscopy, the shift of peak wavelength (Δλ) is linear to cyanide concentration with an equation of Δλ=0.8784 Ccyanide-2.4910 over the range of 0–75 µM. Under darkfield microscopy, the linear regression equations were G/R=0.0677 Ccyanide+0.3717 (R2=0.992) with cyanide over the range of 0.2–4.0 μM and G/R=0.2945 Ccyanide+0.4835(R2=0.994) in the range of 4.0–15.0 μM, where G/R is the intensity ratio in green and red channel. The methods were applied for analysis of waters and foods, achieving recovery rates of 97.4–106.3% for UV–vis spectroscopy and 98.6–108.1% for single NP imaging. The techniques offer expeditious, highly discriminating, and on-site capable solutions for cyanide detection, with high practicality.