A false-colour surface rendering of relative electron density for a shaped electron bunch. It was measured with a microchannel plate, phosphor screen and CCD (charge-coupled device) camera.
Credit: Andrew McCulloch and David Sheludko, Nature Physics
False-colour images of detected electron patterns. The researchers were able to produce cold electron bunches. Each bunch can be arbitrarily shaped, and because the electrons are very cold, the bunches retain their shape as they travel to the electron detector.
Credit: Andrew McCulloch and David Sheludko
It has never been possible to produce such arbitrary bunches in three dimensions, nor to see such patterns with conventional hot electron sources.
Credit: Andrew McCulloch and David Sheludko
BRIGHTON: A new source of very cold electrons could help improve the resolution and speed of nanoscale imaging.
According to researchers from the University of Melbourne, this could not only improve the imaging of small atoms and molecules, but also allow the real-time imaging of dynamic processes within the cell for more effective drug design.
"Enhanced nanoimaging using this cold source will enable us to design better drugs for more targeted treatments. Having a better visibility of the structure of a cell membrane protein and how it functions will assist in more targeted drug design," said lead author Robert Scholten of the paper published in a recent issue of Nature Physics.
A trillionth of a second
X-ray diffraction is a method used to look at very small things, like molecules and atoms. To visualise a molecule, the signal needs amplifying (i.e. we need a lot of the molecule) and it has to be arranged in a very precise manner called a crystal. Many molecules of interest like proteins do not readily form crystals.
This is where electron diffraction comes in. Instead of firing X-rays, a single electron - 10,000 times stronger - is fired. The problem here is that the electron beam is very weak and the molecule of interest has to be analysed over long periods of time. When organised in a beam together, electrons repeal each other (following Coloumb's Law) making it impossible to create a stronger and brighter beam.
Scholten and his team have now developed a technique of shaping electrons into a pattern where they don't repel each other. In this arbitrarily created shape, the electrons have small transverse coherence and allow for a much faster, higher resolution imaging technique only taking a trillionth of a second.
Very cold electrons
But finding the right pattern is only the first step. Normally electron bunches don't remain in particular shapes as they are too hot and make the beam to expand outside its original pattern.
By cooling atoms to just above absolute zero and extracting electrons from them, the team was able to create and maintain a beam of very cold electrons in a uniform ellipsoidal bunch.
Scholten described his method, "Our electrons are just 10 degrees above absolute zero, so the electron bunches retain the shape they start with. We make the electron bunches from a cloud of cold atoms, suspended in space, and poke them with laser beams from all sides to shape them into whatever pattern we need."
Better imaging for better drug design
When trying to understand what a particular protein looks like or how it works in the body, getting a clear and fast image of it is very important. With this new technology, it will be possible to visualise dynamic processes like protein folding which will in turn allow for a better understanding of interactions that are crucial to designing effective drugs.
Whist nanoimaging using electron microscopy can show a detailed image, it can take several hours of exposure to get a quality result. Even then, the image is not always very clear.
"The images that they show are remarkably clear, and obtained with a relatively small number of experimental cycles," commented Steve Buckman from the Centre of Anti-Matter Studies in Canberra. "The technique shows great promise for fast, real time imaging of structural properties and dynamical processes in biosystems, for example."
