Research Projects

Surface enhanced Raman scattering (SERS) spectroscopy has emerged, in the recent past, as an ultra-sensitive and versatile tool for detection of biomolecules, , monitor chemical reactions, providing insight into molecular structure and bonds etc. Raman optical activity (ROA) is hinged upon the idea that the Raman scattering signal from chiral analyte molecules show distinct difference with left circularly polarized (LCP) and right circularly polarized (RCP) light excitation. Surface enhanced Raman optical activity (SEROA) uses plasmonic nanoparticles to enhance the inherently low signal-to-noise-ratio (SNR) of ROA and has been able to detect chiral signatures at single molecule detection limit. SEROA is an extremely important tool which has implications not only in fundamental scientific research but also in a myriad of applications in areas such as molecular biology and pharmacy. Because of low reproducibility and higher acquisition times associated wide-area SEROA based molecular detection and imaging many practical applications like detection and quantification of pollutants, anti-counterfeiting of currency notes etc have not been realized. The central theme of the proposal is to devise a wide-area and sensitive SEROA detection platform for effective data acquisition and analysis. The plan includes a combined approach of designing reproducible SERS substrates using bottom-up lithography procedures and a comprehensive Raman imaging tool based on the application of in-line holography to spontaneous Raman scattering. The SEROA substrate planned is a regular array of bowtie antennas fabricated using template assisted nanosphere lithography (NSL) ensuring reproducibility of SERS signatures. The antennas will be coated with a thiol-based Raman label (4-Mercaptopyridine) and the analyte molecule (L/D Ala) induces chirality to the intrinsically achiral Raman label ensuring accurate measurements with amplified signals. We will apply shearing interferometry to chiral sensing through capturing not only differential intensity but also differential optical phase from chiral molecules. The SEROA substrate will be illuminated with LCP/RCP light and the Raman shifted signals from the molecules will be collected. The SEROA imaging will be performed in two steps: (i) through Michelson interferometer, which provides access to the spectral content of Raman signals and (ii) shearing interferometer, which provides intensity and phase maps for a particular spectral content. The project is designed to push the boundaries of SEROA analysis by massively reducing the acquisition times from hours to seconds yet providing an excellent spatial resolution, reproducibility, and accuracy. We will also unravel unique relation between the phase of Raman scattered light and the chirality of the molecule. We believe that we will open up real-time applications of SEROA in counterfeit currency detection and chiral sensing on a microfluidic chip etc.