MAX IV Staff R&D. Bio-sample preparation methods for X-ray techniques

by Sandra Cuellar Baena (Lund University, Department of Experimental Medical Sciences)

Wednesday 11 Apr 2018, 13:00 → 13:40 Europe/Stockholm

MAX III meeting room (MAX IV Laboratory)

Abstract

The study of biological samples (tissue, cells, plant material) using X-ray based techniques should be preferably conducted closer to their native state, i.e. without labeling or staining that can interfere with the chemical state of the metals/molecules under study, whilst also keeping intact cell membranes and organelles in the specimen. Traditional sample preparation methods for histology include chemical fixation methods, plus the use organic solvents and dehydration steps for polymerization of the supporting resins prior to sectioning. Moreover, the tools for sectioning (blades, tweezers) can give rise to considerable artifacts in the metal maps of interest. Thus, established sample preparation methods and tools used for histology are not readily translated to an X-ray scenario and might not be perfect for measurements using X-ray fluorescence (XRF) and Scanning Transmission X-ray microscopy (STXM) techniques. A different approach is used in sample preparation protocols based on cryofixation methods where the aim is to keep the water inside the cells in its vitreous state by ultra-fast freezing to temperatures below -100 °C, allowing the preservation of outer and inner structures in the sample and where the ion distribution is preserved closest to their native state. In this talk, an overview of the sample preparation methods for biological samples will be provided with an emphasis on the requirements and critical steps to keep in mind when collecting, handling and preparing samples for XRF and STXM experiments at MAX IV or other synchrotron facilities.