Nonlinear optical microtomography of biological structures

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Nonlinear optical (NLO) microscopy is a noninvasive imaging modality that is rapidly gaining in popularity due to its ability to visualize label free noncentrosymmetrically organized molecular aggregates and interfaces in biological structures. In addition to employing signal intensity as a contrast mechanism, biological samples can be investigated using spectroscopic and polarization measurements of nonlinear signals in the microscope revealing molecular organization of the visualized structures. Combination of the polarization and spectroscopic imaging methods with ab initio calculations of nonlinear optical properties of biomolecules renders a powerful structural investigation tool that provides possibility to reconstruct molecular organization of the highlighted structures. Therefore, we propose to develop nonlinear optical microtomography method to study molecular structure of biological crystals and ordered aggregates. The NLO microtomography will be based on nonlinear microscopy measurements of second harmonic generation (SHG) and vibrational sum frequency generation (V-SFG). The obtained information about molecular organization will be used to study collagen and myosin fibrils, amyloid aggregates, as well as starch granules and cellulose fibrils. The fundamental understanding about the nonlinear optical properties of proteins and polysaccharides will help to advance several application areas: The collagen structural properties and content are linked to the development of cancer, therefore NLO imaging of collagen will provide with method for noninvasive cancer diagnostics in vivo. Dynamic imaging of myosin structure in muscles during contraction will enable to study contractility mechanisms of the nanomotors and will aid in studying cardiac arrhythmias and various types of myopathies. The study of amyloid structures will help to understand the toxicity of aggregates involved in progression of the neurodegenerative disorders. Investigations of synthesis and degradation of starch granules and cellulose fibers will provide basis for using nonlinear microscopy in food, pulp and paper industry for quality control of pharmaceuticals, paper, biodegradable plastics, and biofuel.