SERS Tags Based on Silica Microparticles with Adsorbed Gold Nanostars

The great interest in SERS tags as bioanalysis platforms is due to their combination of strong optical signals, photostability, and narrow spectral lines. Despite significant progress in the synthesis of new types of SERS tags based on gold nanoparticles, obtaining microparticles possessing a Raman scattering intensity sufficient for detecting a single tag using a conventional Raman microscope is not a trivial task. In this work, hybrid colloidal nanocomposites based on silica microparticles and gold nanostars (AuNST) with the SiO₂/AuNSTs/SiO₂ composition have been synthesized and characterized. Two types of AuNSTs, one with a plasmon resonance at 700 nm and the other with two maxima at 650 and 900 nm, have been pre-synthesized and adsorbed on the surface of monodisperse colloidal silica particles 1.5 μm in diameter. Three types of thiolated aromatic molecules have been used as Raman reporters: 4-nitrothiophenol, naphthalenethiol, and 1,4-benzenedithiol. The possibility of measuring the SERS signal from a single microparticle with an intensity variation of no more than 20% has been demonstrated, as well as the possibility of multiplex determination of various microparticles in one Raman image. The stability, including photostability, of the measured SERS signal in time has been comprehensively assessed upon changes in the physicochemical parameters of a microenvironment.