Custom STEM reaches higher resolutions


Rebecca Pool

Monday, June 12, 2017 - 21:15
Image: Graphene provides welcome boost to low voltage STEM imaging.
Japan-based researchers have used ultrathin graphene with custom sample preparation and loading to enhance low voltage STEM imaging of bio-samples, including viruses.
Studying well-known virus, bacteriophage T4, Professor Tsumoru Shintake from the Quantum Wave Microscopy Unit at Okinawa Institute of Science and Technology Graduate University and colleagues revealed the minuscule fibre-like limbs used to hook bacterial prey.
According to the researchers, imaging at this resolution has not been possible using conventional STEM, and as Shintake highlights: "Our results show that using ultrathin graphene support film markedly improves image signal at low accelerating voltages."
Low energy electrons can potentially be more efficient at imaging biological specimens while single-atom thickness and highly conductive graphene offers excellent specimen support for imaging nanometre-sized viruses.
"Low-energy atoms interact very strongly with matter and are great for imaging biological specimens made of of light materials such as carbon, oxygen and nitrogen - which are basically transparent to high energy electrons," points out Shintake 's colleague, Dr Masao Yamashita.
To optimise imaging resolution further, the researchers first stained the virus samples with low atomic number methylamine vanadate, in order to clearly visualise the fine structure of the T4 at low voltages.
Crucially, to optimise the distribution of the hydrophilic virus onto the hydrophobic graphene film, they also developed a spin sedimentation loading method.
Here the virus was loaded into centrifuge tubes, which on spinning was then evenly deposited across graphene films, lining the bottom of the tubes.
"We have shown that graphene film allows us to achieve great contrast with very low energy electrons, allowing us to enhance tiny details," says Yamashita.
Yamashita and colleagues are now developing a novel method to spray viruses onto graphene film in a sterile vacuum.
Research is published in Microscopy.
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