Super-high resolution optical nanoscopy based on microlenses

Southern Illinois University Carbondale, Carbondale IL

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Abstract

DESCRIPTION (provided by applicant): Optical microscopy is an invaluable characterization tool in biological, chemical, and materials sciences from both fundamental studies and applied viewpoints. There is a physical limitation imposed on the spatial resolution of an optical microscope (through Abbe's law) below which the optical features cannot be resolved. We demonstrate here the use of salt-based plano-convex microlenses (MLs) composed of high-refractive index (n, 1.47<n<1.73) materials greatly enhances the spatial resolution of images acquired using a conventional inverted microscope. The proposed imaging technique can resolve features below 100 nm and provides magnification between x2 and x6 using a low intensity broad band white light illumination source. High-resolution images can be acquired in atmospheric conditions where biological samples are active. The proposed method is inexpensive, easy to use, and does not require extensive sample preparation. The fabrication of MLs is extremely simple and an array of highly reproducible MLs can be self-assembled in a wet-lab. Our proposed ML-based nanoscope can be used in many different modes including bright- and dark-fields, phase-contrast, and fluorescence - for imaging of biological specimens under atmospheric conditions. Specific aims for the proposed work: Aim 1: We plan to experimentally and theoretically investigate the physical parameters of MLs that affect the imaging quality including magnification, spatial resolution and contrast. In general, the size, shape, refractive index of MLs, and ML-specimen distance affect the physical parameters (focal length, focal spot size, spatial resolution, magnification and depth of focus) of the microlens. These studies are crucial for enhancing our understanding of interaction of light with MLs, and for optimizing the performance of MLs for imaging applications in life-, biomedical- and materials-sciences. Through this specific aim, we intend to experimentally and theoretically investigate the effect of ML dimension, ML curvature (size), refractive index, and ML-specimen distance on magnification and spatial resolution. The experimental results will be corroborated with calculations based on geometric optics and electromagnetic theory using ray tracing and Finite Difference Time Domain (FDTD) methods. Aim 2: Imaging using optimized microlens-based nanoscopy. We plan to utilize the optimized MLs to acquire super-high resolution using a conventional optical microscope. The knowledge gained in aim 1 on optimization of MLs for super- high resolution will be utilized for imaging nanoscale biological particles and nanolithographic fabricated nanopatterns. Our nanoscope will consist of three major components: a conventional optical microscope, a (or an array) microlens(es) and a piezoelectric scanning stage. For the proof-of-concept experiments, we will perform both fluorescence and bright- field imaging and scanning of protein and DNA nanoarrays, bacteriophage and viruses particles in the 70-150 nm dimension range. Ultimately, the proposed imaging tool would be useful for scientists, engineers, and clinicians for chemical and biochemical imaging, probing cellular dynamics and processes on or near cell surfaces, and biosensing applications.