Surface-Enhanced Raman Scattering Sensing of Various Analytes Based on the Polymer-Metal Composite Sensor Particles

Surface-enhanced Raman scattering (SERS) spectroscopy is one of the most powerful analytical techniques to detect trace amounts of various analytes, in which significant field enhancement can be realized upon adsorption of molecules (analytes) on the surface of metal nanostructure. A key component for better results and analysis through this method is the SERS substrate that needs to be equipped with plenty of hotspots as well as metallic-rich and relatively roughened surfaces. Despite a large number of SERS substrates being routinely utilized, there is still room and hence search is continuing for the dynamic substrates that reveal the extraordinary sensing outcomes. Particle-based SERS substrates based on polymer-metal composite particles in which polymer as support can provide the platform to meet such requirements by systematically depositing metal nanostructures at the surface of polymer particles. The characteristics of the polymers such as biocompatibility, swellability, porosity, transparency, metal loading ability, and high surface area are particularly useful in the formation of the efficient particle-based substrate. Microfluidics is a promising technique for the fabrication of polymer-supported sensor particles of nanoscale and microscale with uniformity because of their advantages over the batch platform. For nanoscale sensor particles, the metal nanoparticles can be incorporated and anchored at the surface of polymer nanoparticles electrostatically in the swellable shell layer, and a ligand-free metal layer can be deposited by a metal-catalyzed metal enforcement process. Here, the development of the polymer-metal composite particles at nanometer and micrometer length scales, and their applications as sensor particles for SERS sensing are presented. Microfluidic techniques were utilized for the generation of uniform sensor particles of micrometer length scale with the precise distribution of metal nanoparticles in the interior and at the surface. Furthermore, metal-catalyzed metal enforcement approaches initiated for achieving a ligand-free metal surface for direct analyte interactions because of the availability of a large number of hotspots in roughened metallic surface, and experimental demonstration of sequential SERS analysis of multiple analytes through microfluidics has been established that is demonstrated in this work.