Image of the week: imaging biological microstructures

In the experiment performed by Daewoong Nam et al at the Spring-8 Angstrom Compact Free Electron Laser (SACLA) (presented in their paper in JPhysB) they perform “fixed target imaging” of gold nanoparticles and RNAi microsponges.  By collecting diffraction data from these samples, they can reconstruct accurate images of the samples.  The Image of the Week below shows a diffraction pattern for a microsponge exposed to x-ray pulses from SACLA.

Diffraction pattern from a single RNAi microsponge

Diffraction pattern from a single RNAi microsponge, from Daewoong Nam et al 2016 J. Phys. B: At. Mol. Opt. Phys. 49 034008

X-ray free electron lasers can be used to image details on a very small scale without radiation damage.  However, the x-ray pulses they produce are intense, and detroy the specimens they are used to image.  One solution is to use a liquid or aerosol injector to continuously provide sample material (nanoparticles, biological material etc) to the interaction point, which ensures there is always a fresh, undamaged sample in place when the x-ray pulse is is available.  However, this leads to sample material being wasted in between pulses.  An alternative solution is to mount a sample on a membrane, which moves in between pulses to provide fresh sample areas for each pulse, known as “fixed target imaging”.

The biological samples are fixed to a membrane which moves between pulses to image the whole sample.  The researchers find that not only does the sample signal dominate the background noise in the low angle region (the bright bit in the centre), but that the amount of wasted sample is a significant improvement over liquid-jet injection.

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Front Image and article image: Diffraction pattern from a single RNAi microsponge, adapted from Daewoong Nam et al 2016 J. Phys. B: At. Mol. Opt. Phys. 49 034008, Copyright IOP Publishing LTD 2016

Categories: Journal of Physics B: Atomic, Molecular and Optical Physics

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