Seminars at the Franklin: Dr Kenneth Fahy

30th May 2024, 10:30 – 11:30 am


Correlative cryo soft x-ray tomography and fluorescent microscopy of biological samples in the laboratory


Soft x-ray tomography (SXT) uses low energy x-rays to image frozen-hydrated biological specimens such as entire mammalian cells or thick tissue slabs with a few tens of nanometers of spatial resolution. The technique takes advantage of the biological water window whereby water is relatively transparent to x-rays from 284 to 543 eV (2.34 to 4.4 nm) but carbon-based organelles are absorbing. This native contrast imaging allows high resolution imaging of bulk specimens with minimal sample preparation.

While SXT has traditionally been confined to synchrotrons, the recent development of a laboratory scale SXT microscope opens the possibility of integrating this novel technique into light and electron imaging workflows. The SXT microscope features an integrated light microscope for overview imaging and fluorescence targeting, this allows for swift acquisition of 2D and 3D x-ray images covering extensive areas on the specimen and enables efficient and rapid identification of cells of interest.

The utility of the microscope is currently being demonstrated through 2 EU-funded consortia. Recent case studies have included correlative imaging of whole, virus infected cells treated with anti-viral drugs; imaging the 3D distribution of therapeutic-laden nanoparticles in whole cells; and the development of correlative workflows for tissue imaging across scales. An alternative sample carrier in the form of a thin-walled glass capillary was also developed, further enhancing the novelty of the lab-based microscope.

Integrated cryo fluorescence was used to screen an entire EM grid for cell selection and correlation with SXT. Low magnification/large field of view 2D x-ray mosaics were then acquired over large areas of the grid before acquiring tilt series from ±60° on selected targets. Data cellular organelles and nanoparticles provide proof of concept for the lab-based microscope and associated workflows.

Workflows of correlative light, electron and soft x-ray mircoscopy combines the strengths of each modality. The recent availability of a compact soft x-ray microscope will accelerate the development of novel workflows and biological imaging applications that can benefit from this technique. We will present our microscope workflows and application data.


Dr Kenneth Fahy holds a PhD in experimental physics and during his time as a researcher at University College Dublin, he began exploring plasma-based light sources for imaging and metrology applications. He subsequently co-founded SiriusXT with the aim of developing and commercialising a soft x-ray microscope for biological imaging in the ‘water window’.