Roter, B. | Search bioRxiv

bioRxiv2026

X-ray fluorescence microscopy exposure estimates using a single excitation energy

Scanning fluorescence x-ray microscopy is widely used for quantitative mapping of elemental concentrations, including in studies of essential, but low-concentration metals in cells, tissues, and organs. Practical studies often use a single incident photon energy to excite fluorescence from many elements. We present calculations of the number of incident photons per pixel required to detect a specified areal concentration of an element in the case of non-resonant excitation, along with the calculated radiation dose consequently imparted in a simple model tissue. We also show how certain approximations can lead to less accurate estimates. These results can be used to guide experimental planning for studies of the role of low-concentration elements in biological tissues.

biophysics↗

bioRxiv2025

Multifunctional bending magnet beamline with a capillary optic for X-ray fluorescence studies of metals in tissue sections

Scanning fluorescence X-ray microscopy lets one non-destructively and quantitatively map the distribution of most biologically-important metals in cells and tissues. For studies on large-scale tissues and organs, a spatial resolution of several micrometers is often sufficient; in this case, bending magnets at synchrotron light sources provide abundant X-ray flux. We describe here the use of bending magnet beamline 8-BM-B at the Advanced Photon Source (APS) with two distinct microscopy stations: a pre-existing one with Kirkpatrick-Baez (KB) mirror optics for slightly higher throughput and the ability to accommodate samples tens of centimeters across, and a new prototype station with an axially-symmetric, single-bounce, capillary optic with slightly less flux, but slightly higher fluence (which affects achievable resolution at low metal concentration) and higher spatial resolution. The KB station provides{delta} res = 10.5 {micro}m spatial resolution at a per-pixel exposure time of tdwell = 100 ms and a fluence per time of 5.8x 107 photons /({micro}m2 {middle dot}s), while the prototype capillary station provides{delta} res = 6.3 {micro}m at tdwell = 50 ms and a fluence per time of 6.1x 107 photons ({micro}m2 {middle dot}s). We used image power spectral density to estimate the achieved spatial resolution{delta} res from individually acquired images, with{delta} res depending-on the optic, the fluorescence signal strength of the sample being imaged, and the method used to process raw fluorescence spectral data.

biophysics↗