IR NEAR FIELD MICROSCOPY FOR SUB-CELLULAR APPLICATIONS

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DESCRIPTION (provided by applicant): There is a critical need for analysis and monitoring of cellular and sub-cellular biological functions, especially for understanding pharmacological and disease processes. Optical microscopy has been previously used for biological sample characterization but has a diffraction limited resolution of lambda/2. However, scanning near-field optical microscopy can be used to achieve nanoscale resolution on the order of lambda/30 and better. The technique combines the properties of atomic force microscopy in the non-contact mode with optical microscopy, by utilizing a fiber optic probe tip that scans over a sample surface and simultaneously acquires shear force and optical signals to produce topographical and optical images, respectively. Optical fiber microtips fabricated from silica fibers have been used for this technique in the visible wavelength region with at least 100 nm resolution. However, these fibers cannot be used in the infrared because they do not transmit at wavelengths longer than 2 micro meters. We propose to develop the technique using infrared-transmitting optical fiber microtips capable of accessing the "fingerprint" region from 2-10 micro meters, where molecular species can be readily identified by their characteristic vibrational absorption bands. The goals of this program are: Develop the new technique of Scanning Near Field Infrared Microscopy using state-of-the-art low optical loss IR transmitting optical fibers which NRL has developed for a variety of applications. NRL will fabricate IR-transmitting microtips capable of probing the 2-10 um infrared wavelength region that has previously been unavailable. NRL will collaborate with Vanderbilt scientists in the implementation of the microtips with a Near Field Microscope. Demonstrate nanoscale optical resolution of at least 100 nm in the infrared with the SNIM system using the IR fiber microtips. Utilize the scanning near-field infrared microscopy (SNIM) in the 2-10 um wavelength region to investigate spectroscopic imaging of biological structures such as living cells at <100 nm resolution in an aqueous environment. The optical and topographical resolution as well as spectroscopic imaging capability of the probes will be evaluated in a biological cellular environment, to analyze cellular functions such as membrane transport and molecular recognition processes in biological samples. This new capability will be critical for the understanding of a wide variety of pharmacological and disease processes.