Gold nanorod etching-based multicolorimetric sensors: strategies and applications

Gold nanorod (AuNR) colorimetric sensors have emerged as powerful tools in various chemosensing and biosensing applications due to their localized surface plasmon resonance (LSPR) extinction in the visible range. More significantly, AuNRs as an effective chromogenic substrate in these colorimetric sensors have two plasmonic bands: a transverse mode band and longitudinal mode band. Utilizing this excellent optical property, researchers have found that AuNRs are extremely sensitive to their aspect ratio (length/width), which leads to sensitive signal changes in the longitudinal absorption bands toward different target analytes, often accompanied by a visible and distinctive multicolor change. Herein, this review focused on the newly developed AuNR multicolorimetric sensing mode, where the etching of AuNRs induces multicolorimetric changes, namely, AuNR etching-based multicolorimetric sensors. This type of sensor has attracted increasing interest due to its exciting advantages of being instrument-free and excellent visual sensitivity with a naked-eye-detectable readout, as well as its technologically simple and potential application in different analysis fields. Particularly, the limited color display of classical colorimetric sensors can be avoided and the accuracy of visual inspection improved through the rainbow-like multicolor change readout of AuNR etching-based multicolorimetric sensors. This review highlights the recent progress on the strategies and application of AuNR etching-based multicolorimetric sensors. We also provide some personal insights into the current challenges associated with AuNR etching-based multicolorimetric sensors and propose future research directions.