This proposal was received in response to Nanoscale Science and Engineering initiative, NSF 04-043, category NER.
The nonlinear technique of surface-enhanced hyper-Raman spectroscopy (SEHRS) will be explored for its possible applications to bioanalytical sensing and imaging. The linear analog, surface-enhanced Raman spectroscopy (SERS) is a well-known technique widely applied for obtaining vibrational spectra of analytes at low concentrations, in some cases down to the single-molecule level. SERS is proving valuable for biological sensing applications including intracellular detection, but its limitations include the usual sensitivity of Raman-based methods to interference from fluorescence and sample photodegradation. SEHRS, in which red or nearinfrared laser excitation produces Raman scattering in the near-uv to visible, has a number of potential advantages including less sensitivity to fluorescence, less sample photodamage, greater selectivity for the analyte of interest, better spatial resolution in imaging applications, and the ability to use a simpler detection system because of the large difference between the excitation and detection frequencies. The main disadvantage is the usual weakness of the effect. The goal of this research is to determine the extent to which this can be mitigated by combining the small focal volume of a Raman microscope with metallic nanoparticle surface enhancement of the incident and/or scattered electromagnetic fields from intrinsically hyper-Raman-active chromophores.
