Synthesis and application of surface enhanced Raman scattering (SERS) tags of Ag@SiO2 core/shell nanoparticles in protein detection

A simple method has been developed to prepare silica-encapsulated Ag (Ag@SiO2) Raman tags, embedded with the reporter molecules 4-mercaptobenzoic acid (MBA), using environmental-friendly solvents (mixed solvents of ethanol and water) without vitreophilic pretreatment. The Ag@SiO2 Raman tags exhibited excellent stability resistance to high-concentration salts and long-term storage. Sensitivity of the Ag@SiO2 SERS tags could be enhanced by increasing MBA coverage and reducing the silica shell thickness, and the Ag@SiO2 SERS tags had versatility for bioassays. Myoglobin (Mb)conjugated Ag@SiO2 Raman tags specifically bound to iminodiacetic acid (IDA)-functionalized wafers through the coordination interactions of IDA-Cu2+-histidine residues available on the Mb surfaces for SERS detection. Mb could be directly detected by means of the formation of the Mb-sandwiched structures via Cu2+ coordination between the IDA-functionalized wafers and IDA-modified Ag@SiO2Au composite nanoparticles, where Au nanoparticles were adsorbed onto aminated Ag@SiO2 Raman tags followed by modifying with IDA. It is clear that the prepared Ag@SiO2 Raman tags can be applied for assays of other proteins or biomolecules if corresponding specific ligands are used and have potential application in immunoassays.