SERS-based sensing platforms: Multilayer thin films, anisotropic nanoparticles, and core-shell structures

A technique capable of both qualitative and quantitative detection is Raman spectroscopy. Large enhancements in Raman scattering intensity can be realized when the analyte is in close proximity (<20 A) to an appropriately roughened, noble metal surface. When analytes are examined in such a position the technique is known as surface enhanced Raman scattering (SERS), and enhancements as high as 1014 have been reported.; This thesis examines the improvement of SERS substrate performance. The second and third chapters describe the preparation and application of a multilayer metal film as a substrate for SERS. A novel substrate architecture was created by evaporating a discontinuous film of Ag over an Ag-clad colloidal Au submonolayer. This solid support substrate has an enhancement of 2 x 10 6 and better than 15% reproducibility in signal. Analytes in more complex sample matrices can be examined when a thin film of polydimethyl siloxane (PDMS) is spin coated over the substrate. The PDMS film acts as a solid phase microextraction (SPME) medium, thereby concentrating hydrophobic analyte molecules near the SERS-active surface.; Analytes positioned between two metal surfaces have enlarged Raman scatting because the signal is modulated by both metal surfaces. Chapter 4 addresses the deterministic preparation of these geometries, known as SERS sandwiches, that will be suitable for detailed study. Au-Ag-Au, rod-shaped nanoparticles can be prepared by membrane templated electrodeposition. Once these nanoparticles are immobilized on a surface the Ag strip can be etched leaving a closely space two particle surface feature. Details of preparing suitable films for the study of SERS sandwiches are reported.; The final chapter describes the development of a SERS-active, core-shell particle to be used as a tagging system in bioassays. Glass-coated, analyte-tagged nanoparticles (GANs) are core-shell structures where a nanometer scale Au or Ag core is functionalized with a Raman active molecule and encapsulated in a glass shell. GANs particles are identified by the Raman spectrum of the attached Raman-tag. Scattering from that Raman-tag is amplified through SERS. Furthermore, biorecognition chemistry (i.e. nucleic acids, antibodies, antigens) can be attached to the glass shell without interfering with the Raman response.