Elemental Imaging in Biology Using Synchrotron X-Ray Fluorescence Microscopy

X-ray Fluorescence Microscopy (XFM), also known as Synchrotron Radiation based X-Ray Fluorescence (SRXRF) or Microprobe Synchrotron X-ray fluorescence (mSXRF), is a powerful and versatile technique for the investigation of elemental content in biological samples. Whole cells can be imaged with resolutions better than 100 nm and their elemental content 3D reconstructed despite a cell thickness of 10 microns or more; with some compromises in the spatial resolution even samples as thick as 100 s of microns can also be imaged in 3D. The resultant elemental map is quantitative – concentrations of the different elements are detected simultaneously pixel by pixel, as the fluorescence radiation emitted is proportional to the atom’s concentration within the sample. Detection limits as low as 0.1–5 ppm can be achieved for metals. With new technical developments such as “fourth generation” synchrotrons, faster detectors and even “X-ray focusing” optics, it is likely that XFM will continue to develop toward ever higher resolution and speed of data acquisition. While XFM can be used for detection of radionuclides in biological material, due to extremely low background for such elements in samples collected in non-contaminated areas, radionuclide quantities are generally low and imaging them is difficult. Moreover, radioactive decay and resultant elemental transitions further decrease numbers of atoms of interest that are available for detection. With the increase in brightness, new generations of synchrotrons and their further updates can be expected to improve sensitivity of radionuclide detection.