Materials science of cells: Electron probe x-ray microanalysis and x-ray mapping in biology
The general aims of Electron Probe X-ray Microanalysis (EPMA) in Biology is similar to that in Materials Science: the determination of composition at sub-micron resolution. Special requirements include stringent precautions for specimen preparation, high sensitivity for detecting low concentrations of elements avoidance, and if not possible, quantitation and control of radiation damage, and spatial resolution of at least tens of nanometers.Special precautions for specimen preparation are dictated by the fact that biological materials exist in an aqueous milieu, and one of the most common objectives of biological EPMA is the localization and quantitation of diffusible elements. Therefore, specimen preparatory techniques must include handling of live tissues in a manner that maintains normal physiological states, and rapid freezing to trap diffusible elements in their physiological compartments. In order to obtain high spatial resolution, ultrathin cryosections have to be obtained, freeze dried and transferred to the microscope under conditions that prevent elemental translocations. Specimen temperatures during cryo-sectioning are usually at about -100°centigrade.