Chemical colorimetric square wave and its derived logic gates based on tunable growth of plasmonic gold nanoparticles

Abstract

Plasmonic changes in the growth process of gold nanoparticles (AuNPs) are not only intriguing for materials science, but also promising for developing new colorimetric biosensors and logic devices. Herein, we report a novel AuNP-based plasmonic phenomenon, namely chemical colorimetric square wave (CCSW) and further develop a series of label-free and simple colorimetric logic gates based on the CCSW. The CCSW refers to the unique phenomenon of silver ion concentration or pH-dependent discontinuous colorimetric signal change (blue-red-blue) observed in the hydrogen peroxide-mediated AuNP generation process. By setting blue and red colors as the OFF and ON colorimetric signals, respectively, the colorimetric signal profile of CCSW can be outputted in the format of OFF–ON–OFF, presenting an analog of an electronic square wave. Thereby, two CCSWs were successfully constructed, namely Ag⁺-CCSW and pH-CCSW. Subsequently, colorimetric AND, INHIBIT and OR logic gates were built via rational integration of two CCSWs. Unlike traditional AuNP-based logic gates with target-triggered AuNP crosslinking, these CCSW-based logic gates relied on the controllable growth of AuNPs, which are facile, fast and cost-efficient, avoiding tedious modification of AuNP probes and complicated operations. Therefore, our proposed CCSW and its derived logic gates present a promising application of plasmonic noble metal nanomaterials.