Colorimetric detection of mercury(II) based on gold nanoparticles, fluorescent gold nanoclusters and other gold-based nanomaterials

• Colorimetric detection of mercury(II) (Hg2+) based on gold nanoparticles (AuNPs).
• Detection of Hg2+ based on fluorescent gold nanoclusters (AuNCs).
• Synthesis and functionalization of AuNPs and their optical properties.
• Development of test strips and applications to real samples.
• Gold nanorods, gold nanoflowers and gold nannostars used for colorimetric detection.

This review focuses on colorimetric and visual assays for determination of mercury(II) (Hg2+) ions based on gold nanoparticles (AuNPs), fluorescent gold nanoclusters (AuNCs), gold nanorods (AuNRs), gold nanoflowers (AuNFs) and gold nanostars (AuNSs). The analytical colorimetric approaches based on AuNPs can be categorized according to the aggregation or disaggregation mechanisms of functionalized or unmodified AuNPs. The colorimetric concept involves change of the color of a solution of AuNPs from deep red to purple or blue. Disaggregation assays involve reversing the color from blue to red. Detection using AuNCs is based on Hg2+-induced fluorescence quenching of functionalized AuNCs and label-free AuNCs. The benefits of these systems are simplicity, rapidity, cost-effective production, ease of usage, easy visualization of the color change, and detection using spectrophotometry, fluorometry and the naked eye. We summarize applications to real samples, limits of detection, and the development of test strips.