Enzyme-assisted metal nanoparticles etching based plasmonic ELISA: Progress and insights

The unique size and shape tunable localized surface plasmon resonance (LSPR) properties of the noble metal nanoparticle have been extensively exploited to realize a variety of enzyme-based optical biosensors. Although approaches like metal film deposition, nanoparticle aggregation, and synthesis & growth of metal nanoparticles are quite useful, metal nanoparticle etching-based biosensors offer greater sensitivity, selectivity, and stability against various environmental factors which makes this strategy easy to use for field applications. This review discusses the current state-of-art of plasmonic nanoparticle etching-based enzyme-linked immunosorbent assay (ELISA) realized for visual detection of various analytes. The naked eye detection, i.e. without any optical readout device, is the additional advantage of this sensing approach that reduces the analysis cost significantly making it feasible under resource-constrained settings. This review paper provides deeper insights into biocatalytic etching mechanisms of various plasmonic nanoparticles resulting in vivid color change as a function of analyte concentration. Although nanoparticle etching-based ELISA has huge potential, steps need to be taken to realize a point-of-care (POC) nanodiagnostic before its translation to a commercial technique or product that can be achieved in near future by integrating it with microfluidics technology and other technological avenues.