Catalyzed Deposition of Signal Reporter for Highly\nSensitive Surface-Enhanced Raman Spectroscopy Immunoassay Based on\nTyramine Signal Amplification Strategy

Abstract

A novel\nsurface-enhanced Raman spectroscopy (SERS) sensor was proposed\nfor an ultrasensitive detection immunoassay based on tyramine signal\namplification (TSA) strategy. In this study, an immune sandwich was\nprepared with a capture antibody and a horseradish peroxidase (HRP)-conjugated\nantibody upon the addition of a target antigen. In the presence of\nH₂O₂, HRP can convert tyramine to a short-lived\nradical intermediate that forms covalent compounds with aromatic amino\nacids on the surfaces of proteins. By labeling the tyramine with SERS\ntags in the form of gold nanoparticles (AuNPs) functionalized with\na Raman-active probe (4-mercaptobenzoic acid, 4-MBA), AuNPs@4-MBA\nwas deposited and aggregated near the proteins, so the SERS signal\nof 4-MBA could be detected and amplified. On the basis of the TSA\nstrategy, the developed SERS-based immunoassay can discriminate concentrations\nas low as 0.01 ng/mL of the target antigen and exhibited approximately\n10 times stronger SERS signal intensity than traditional SERS-based\nimmunoassays. These results demonstrated the application potential\nof this TSA-based SERS biosensor for the detection of important proteins\nin biomedical research.