Bright light and big ideas


Rebecca Pool

Friday, March 10, 2017 - 13:30
Image: Sirius XT team; shaking up microscopy
Just last year, Ireland-based SiriusXT bagged a hefty €3 million in European Union funds to commercialize a powerful X-ray imaging technology that could shake-up the established worlds of fluorescence and electron microscopy.
The bench-top soft X-ray tomography microscope - dubbed SXT100 - can image sub-cellular detail in whole, hydrated cells up to 15 µm thick, approaching 30 nm 3D spatial resolution.
Samples need little preparation, no stains or contrast agents. And as SiriusXT chief executive, Tony McEnroe, tells Microscopy and Analysis: "The grant is a godsend and we will now take the technology from prototype to product."
"Synchrotrons have already established the value of soft-X-ray tomography," he adds. "But we will deliver synchrotron performance in a compact microscope that will turn this imaging modality into an affordable and efficient laboratory tool."
Soft X-ray microscopy enables whole-cell imaging in near-native environments at intermediate length-scales, neatly plugging the gap between light and electron microscopy.
Crucially, water is transparent to soft X-rays, while carbon and nitrogen found in cells are absorbing, producing a high natural contrast that can be exploited when imaging.
Shining example of what soft X-ray tomography can reveal from cell biologist and microscopist, Professor Carolyn Larabell from University of California San Francisco: Cryo-SXT and cryo-fluorescence microscopy show the first 3D view of the Xi-transcriptionally silenced female chromosome. [Larabell/UCSF]
"Soft X-rays provide this high resolution and natural high contrast that you just don't get with electrons or light," points out McEnroe. "As a result, a whole cell can be imaged in its natural state without staining, slicing it, as necessary for electron microscopy, or adding fluorescent markers for super-resolution microscopy."
But despite the clear advantages, soft X-ray imaging has suffered from a key problem; its light source. To date, the only X-ray sources bright enough to illuminate a soft X-ray microscope have been produced by synchrotrons. And as any synchrotron user knows, beam-time is limited and has to be applied for, months in advance.
SiriusXT is set to change this. Spinning out from University College Dublin in 2015, the company was founded by plasma physicists, Dr Kenneth Fahy, Dr Fergal O'Reilly and Dr Paul Sheriden, who have spent the last decade developing dazzling soft X-ray light sources for benchtop imaging.
Prototype of SXT100: soon to be equipped with a cryo-stage for wet cell imaging, a product should reach market by the first half of 2018.
The SXT 100 microscope relies on laser-produced plasma emission alongside smart optics to produce a lab-scale, stable and robust light source for soft X-ray tomography. Here, a high power pulsed laser is focused onto a solid density target to produce a plasma that is hot enough to efficiently emit soft X-rays for cell imaging.
Laser-induced plasma emission isn't new, but as McEnroe highlights, past instruments based on such a set-up have floundered as during emission, the plasma also produces metal debris that destroys the X-ray collection and laser-focusing optics.
So, to overcome this problem, the SiriusXT founders have devised and patented a novel 'self-healing' optical system to protect these optical components. Here, a liquid coating is applied to the surface of components to act as an optical surface; the coating is described as perfectly smooth and provides diffraction limited performance.
"This self-healing liquid coating is continuously replenished so the optics can last indefinitely, even in these extreme conditions; this is unique," highlights McEnroe.
"We have also optimized the target to create the maximum density of photons at the X-ray wavelength we want," he adds. "Other researchers have developed [microscopes] in the laboratory using different approaches but I believe that none of them has produced a source of X-rays that is sufficiently simple and stable with enough photons for a commercial microscope product."
So with the prototype in place, commercialization continues apace. The SiriusXT team is currently awaiting delivery of a cryo-stage for wet cell imaging and will soon release its first 3D tomographs of cryo-frozen biological samples.
What's more, McEnroe and colleagues have been working with key soft X-ray imaging users, including researchers at the Francis Crick Institute, UK, to hone the technology. According to the chief executive, target customers will include research laboratories currently using electron microscopy or high resolution fluorescence microscopy for bioimaging.
"We don't see our soft X-ray microscopes as displacing or even competing with these imaging modalities, but very much complementing them," says McEnroe. "Many researchers are now using correlative imaging and could, for example, superimpose a cryo-EM image over a soft X-ray image to get more information."
"Soft X-ray imaging could also be a very nice way to pre-screen the whole cell to identify an area of interest at 30 nm resolution, prior to higher resolution electron microscopy," he adds. "We reckon there are probably more than fifty core imaging laboratories in the UK alone that could benefit from using soft X-ray imaging in these ways."
Soft X-ray tomography uncovers nuclear organization and chromatin topology in olfactory epithelial cells. [Larabell/UCSF]
Drug discovery is set to be a key industry for SiriusXT. As McEnroe points out, pharmaceutical businesses have tended to shy away from using soft X-ray analysis at government-funded synchrotron facilities due to the difficulty of organizing an effective research program with only a few days of access to beamline time per year.
"The pharmaceutical industry has told us that they would love to use soft X-ray imaging but are not willing to share results," he asserts. "So we see both disease research and drug discovery as untapped markets. for our instrument."
But when it comes to performance, can the microscope really compete with soft X-ray microscopy at a mighty synchrotron? McEnroe thinks so, saying: "The image quality is identical as we're using identical X-ray wavelengths."
However, while a synchrotron can create a 3D tomograph - typically comprising 180 2D images - within ten minutes, SiriusXT's microscope will complete the same task in around an hour.
"Initially our instrument is five to six times slower but once you factor in sample preparation to fly cell samples to, say, the synchrotron in Barcelona, as well as the time taken to get there, then this is a price end users will be willing to pay," he says. "To acquire a 3D image in an hour, in the lab, is acceptable. And because we can use a relatively broad band of soft x-rays for SXT, we should even be able to bridge this gap in our second generation instruments."
Yeast cell at the main stages of cell division. [Larabell/UCSF]
Right now, Sirius XT employs 12 staff but McEnroe expects numbers to swell to 15 by mid-2017 as new product developers are recruited. Pilot studies should be complete by the end of 2017 and if all goes to plan, a commercial product will be ready in the first half of 2018.
As McEnroe  highlights, the microscope will be 'high-value instrumentation', but will certainly be a fraction of the cost of a state-of-the-art multi-million dollar cryo-electron microscope. The company also keeps costs down by, for example, using industry-sourced lasers. 
"We're consumerising a technique that's been available for ten to fifteen years," says McEnroe. "I expect the market to grow over many years, and if we get to a quarter of the size of the electron microscope market, we'd be very very happy."
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