Sensing local nano-environment with coherent Raman microspectroscopy

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ABSTRACT This exploratory research proposal which aims to investigate a novel approach for interrogating local nano- environments within a living cell by improving the detection sensitivity of coherent Raman microspectroscopy as applied to live-cell imaging. The proposed new approach overcomes the existing shortcomings of coherent Raman spectroscopy. It provides an exquisite tool of microscopic chemically specific imaging with greatly improved sensitivity of detection and exceptional sensitivity to the local nano-environment. The central hypothesis is that vibrational coherence excited by two broadband pulses is sensitive to the local environment and can be precisely measured by interrogating this coherence using a third pulse at a variable time delay. By choosing a molecular vibration with a relatively narrow spectral line that corresponds to a long relaxation time, and measuring time-delayed response, background signal can be substantially reduced at long delay times of the probe pulse. This adjustment makes low-concentration measurements possible. The overall research goal of the proposed program is to validate this hypothesis by demonstrating sensitivity of coherent Raman microspectroscopy to a local nano-environment and by improving the detection sensitivity of Raman spectroscopy. The specific aims of the proposed activities are focused on constructing a prototype of a microscope and exploring its capabilities using both in vitro and in vivo systems. The proposed research program is expected to deliver a novel and label-free optical imaging modality with enhanced sensitivity and specificity that is suitable for live-cell imaging.