Carbon Nanodot-Decorated Ag@SiO₂ Nanoparticles for Fluorescence and Surface-Enhanced Raman Scattering Immunoassays

A novel immunoassay protocol was demonstrated by the combination of fluorescent carbon nanodots (CNDs) and Ag@SiO2 surface-enhanced Raman scattering (SERS) tag nanoparticles into ensembles for a bifunctional nanoplatform. The CND-decorated Ag@SiO2 nanoparticles were constructed for sensitive fluorescence and SERS immunoassays. The silica shell thickness and amount of Ag@SiO2 nanoparticles were optimized for availability of strong fluorescence emission. The considerably large Raman scattering cross section of in situ-generated actual Raman reporter, 4,4'-dimercaptoazobenzene, from the apparent reporter p-aminothiophenol modified on the surfaces of Ag nanoparticles upon illumination of laser compensated for the reduction of SERS signals resulting from silica coating to a great degree. The antibody-modified bifunctional nanoparticles were captured by antibody-modified quartz slides in the presence of antigens in the sandwich structures for fluorescence and SERS immunoassays. The bifunctional nanoparticles could be used not only as bimodal probes for biodetection but also as bimodal tracers for bioimaging.