Matrix colorimetry for high-resolution visual detection of free cyanide with Au@Au–Ag yolk–shell nanoparticles

Abstract

Although colorimetry has found broad application, its deficiency in the distinguishment of analytes within close concentrations remains a long-standing issue. Herein, Au@Au–Ag yolk–shell nanoparticles (NPs) were synthesized and utilized to develop matrix colorimetry for the detection of cyanide (CN⁻). Exploiting the flexible adjustability of the yolk–shell structures, the etching of CN⁻ towards the NPs with different dimensional core-to-shell ratios exhibits different color change trends, which were combined to get a standard matrix color chart. The limitation of visual distinction of close concentrations of CN⁻ was surmounted by simple color matching of solutions with the standard color chart. Furthermore, a computation program and a smartphone app were developed to facilitate a rapid and objective readout of results. Not only did the developed multiple colorimetry system greatly improve the visual resolution and accuracy of detection between close concentrations by the naked eyes but also the incorporated smartphone app helps to eliminate subjective color recognition differences by different users. The findings in this work are very significant and the methodology can be tailored for prospective applications in colorimetric detection of various analytes.