Biological Applications of A Unique Cryomicroscope

Robertson, J.

Abstract

The Duke University Cryomicroscope is the only electron microscope in the world with an iron-core superconducting objective lens and high-brightness and high-coherence field emission electron source. Its stability and operational control allow accurate measurements to be made. It allows rapid insertion of multiple specimens, and frozen specimens may be inserted while kept at 77.K. It is therefore particularly well-suited for practical biological studies, taking advantage of the low (4.2K) stage temperature and ultra-high vacuum that is inherent in its construction. No other low-temperature stage or cryomicroscope has this combination of advantages. At low temperature, the resolution of crystalline diffraction patterns of organic materials is improved, and the sensitivity of biological specimens to radiation damage is reduced by at least a factor of 5. We propose to use this unique cyromicroscope to solve the high-resolution structures of crystalline membranes and similar specimens of current research interest, while also seeking improvements of specimen preparation materials and methods to maximize the capabilities of low temperature microscopy. A variety of organic crystals will be studied to determine what compounds may be most capable of improvement. A range of temperatures will be studied to determine an optimum for resolution and radiation protection. A series of substrates will be used to find the highest conductivity consistent with proper specimen adhesion. Various embedding materials will be examined to find the best in terms of both radiation protection and structure preservation. Of particular promise is the observation of frozen hydrated specimens. We will concentrate our studies on urinary bladder epithelial cell membranes and the crystalline junctions of lens cell membranes.