Synthesis of novel silica-encapsulated core-satellite nanotags for enhanced SERS detection

Developing a SERS nanotag with high signal intensity, excellent signal stability, and biocompatibility is of significant importance in the fields of food safety, drug testing, and virus detection. In this work, silica-encapsulated, indocyanine green (ICG)-modified Au octahedral core-small Au spherical nanoparticles (NPs) satellite nanostructures (Au/Au@ICG@SiO₂) are uniformly synthesized as surface-enhanced Raman scattering (SERS) tags, which provide abundant “hot spots” and also increase the stability of Raman reporter molecule ICG to greatly facilitate subsequent functionalization and detection. Both experimental and numerical results demonstrate that this Au/Au@ICG nanostructure achieve a detection limit of 10⁻⁷ M for ICG in aqueous solution ascribed to the increased number of hot spots compared with Au octahedral NPs. As-prepared Au/Au@ICG@SiO₂ SERS nanotags are further integrated with a lateral flow immunoassay (LFIA) for the detection of the SARS-CoV-2 nucleocapsid protein. Compared to the traditional bio-recognition method on LFIA strips with the detection limit of 8 pg/mL, the detection capability for the SARS-CoV-2 nucleocapsid protein is improved approximately 16 times (500 fg/mL) based on this novel SERS tag and custom-built adaptive Raman mapping spectrometer. This Au/Au@ICG@SiO₂ SERS tag is expected to play a significant role in early detection, prevention, and control of similar infectious viruses in the future.