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We developed a simple and effective method for the SERS-based detection of protein-small molecule complexes and label-free proteins using avidin-induced silver aggregation. Upon excitation with light of the appropriate wavelength (633 and 532 nm), the aggregated silver nanoparticles generate a strong electric field that couples with the resonance of the molecules (atto610 and cytochrome c), increasing the characteristic signals of these molecules and resulting in sensitive detection. The detection limit of biotin with the proposed method is as low as 48 ng/mL. The most important aspect of this method is the induction of silver aggregation by a protein (avidin), which makes the silver more biocompatible. This technique is very useful for the detection of protein-small molecule complexes.

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In this study, we present a method of achieving highly sensitive immunoassays based on surface‐enhanced Raman scattering (SERS). The biofunctional‐nanoprobe‐linked immunosorbent assay is a closely related technique with a good linear range and the ability to simultaneously detect antigens with high sensitivity. Herein, we report a novel method based on a sandwich structure composed of a silver monolayer and biocompatible Au‐mercaptobenzoic acid (MBA)@SiO2 that was assembled through an immune recognition reaction. To induce a strong plasmonic contribution of the nanoprobes, two or more MBA‐adsorbed gold nanoparticles were saturated and loaded into silica. Silica‐protected gold nanoaggregates exhibit stable SERS activity and biocompatibility for proteins. The capabilities of the proposed sandwich structure for analytical applications were demonstrated through the use of the SERS technique to detect antigens at very low concentrations. These techniques may prove to be superior to current protocols for biomarker research and clinical diagnosis, which require high sensitivity and quantitation over an extended range.