Phase imaging

The idea behind the centre came from physicist Professor Keith Nugent, best known for his work in phase imaging, a way of measuring light refraction from materials in a quantitative manner.

Phase imaging has been used quite extensively in materials science and for physical structures and is now being applied to biological structures.

"If you look at a cell without staining, you basically can't see anything," Nugent says. "But the cell is affecting the light, the phase of the light. It's just like a lens - they are transparent but they affect the light by bending it. Phase imaging is rendering that aspect of the light visible."

Techniques Nugent has helped develop such as X-ray phase contrast has been used to create the beautiful images we can now see of tiny insects fossilised in amber. The ideas are now being applied to structures within living cells.

"With protein crystallography, you shine X-rays at the crystals and you get the diffraction pattern from an array of proteins; from that you can determine the molecular structure," he says.

"Coherent X-ray diffraction applies those same ideas except you don't need crystals. You shine a coherent beam of X-rays onto a single object and measure the scattering of the X-rays. You don't need a focusing lens for this so you are not limited by the resolution of the lens. By inverting the diffraction pattern you can generate very high resolution images."

The CXS Biological Science group has long worked with both light microscopy and electron microscopy but sees X-rays as a new way forward. Leann Tilley is studying Plasmodium falciparum in red blood cells and the way the parasite manages to avoid being detected. The parasite produces proteins that make the host cell membrane stick to receptors on capillary walls.

"The parasite lives inside a vacuole in the cell and it needs to get the adhesion proteins out to the red cell membrane" she says.

"The parasite subverts the red blood cell's physiology and converts it from a one-function a sack of haemoglobin to a more fully functional erythrocytic cell. It puts membrane structures into the red cell's cytoplasm, which it uses to export the adherence proteins and insert them into the red cell membrane. It is these structures which we would like to image at very high resolution."

Tilley's team currently uses light microscopy imaging using green fluorescent protein, which is useful for labeling specific proteins and watching what is happening, but light microscopy is limited by its low resolution, she says.

"Electron microscopy also works really well because you get really good resolution, but because electrons can't get through matter very readily you have to work with really thin slices. X-rays are in between. The wavelength of X-rays is in between the wavelength of electrons and the wavelength of light, so you get increased resolution, but X-rays also have very good penetrating powers so you can see the inside of the cell, rather than just the surface."