Recent development of noble metal-based bimetallic nanoparticles for colorimetric sensing

Colorimetric sensors with instant visual readout are significant and highly required for convenient detection of various analytes, especially in the post-COVID-19 era. Noble metal-based bimetallic nanoparticles (NMBNPs), considered as promising nanoprobes for colorimetric sensing, are significantly superior to monometallic nanoparticles due to their improved optical property, catalytic activity, stability and selectivity. In this review, we focus on the recent progress in the colorimetric sensors based on NMBNPs with alloy, core-shell, core-satellite and Janus nanostructures. Firstly, we comprehensively introduce the synthesis approaches of NMBNPs which can be classified into three classes, including the top-down physical methods, bottom-up chemical methods and other emerging methods. Depending on these NMBNPs, the main sensing strategies exploiting their unique localized surface plasmon resonance (LSPR) property and nanozyme activity for various applications in colorimetric detection are critically summarized and discussed in detail. Finally, challenges and opportunities for the future development of NMBNPs-based colorimetric sensors are proposed and summarized. We hope that this review will help readers to better understand the current research status of NMBNPs for colorimetric sensing.