4D microscopy offers material insights

US researchers have found a way to measure the stiffness of DNA and other biological nanostructures, which could improve understanding of how they work.

The team from the California Institute of Technology (Caltech) led by Nobel Prize-winner Ahmed Zewail have developed a kind of microscope that records the stiffness as well as the visual structure of bio-structures by measuring how they vibrate when hit with a laser.

This form of ‘4D microscopy’ has already been used to study protein tissue known as amyloids that are believed to play a role in neurodegenerative diseases, but the scientists say it could also be used to study nanostructures in other materials.

‘We are providing the methodology to find out—directly—the stiffness of a biological network that has nanoscale properties,’ said Zewail, a professor of physics and chemistry at Caltech, who led the research.

‘It was surprising that we could do this with a complex network,’ he said in a statement. ‘And yet by cutting and probing, we could go into a selective area of the network and find out about its behaviour and properties.’

The new technique makes use of electron microscopy, where a stream of electrons are fired at and scattered off of a structure to produce an image of structures much smaller than can be seen with a visible light microscope.

The scientists stretched DNA over a hole in a thin carbon film and electrons were used to cut several DNA filaments away from the film to leave a three-dimensional, free-standing structure.

As electron pulses were used to visualise the DNA, the researchers also used laser heat to vibrate the structure and then measured the frequency and amplitude of the resulting oscillations, from which they calculated the structure’s stiffness.

Zewail won the 1999 Nobel Prize for chemistry for his work on femtochemistry, the study of chemical reactions within very short timescales.

The research was funded by the National Science Foundation and the Air Force Office of Scientific Research, and published in the Proceedings of the National Academy of Sciences (PNAS).