Good news: cheap microscopes can also get super-resolution images
The team of nanologists Ali Shaib and Silvio Rizzoli at the University Medical Centre in Göttingen, Germany, has developed a method for ordinary light microscopy - the ONE Microscope technique - which records images of individual proteins and never-before-seen cell structures in a level of detail that exceeds even that of a multi-million dollar "super-resolution" microscope. multi-million dollar "super-resolution" microscopes. The findings were published on the preprint website bioRxiv.
"There should be some form of democracy in microscopy technology." Rizzoli points out that the high resolution of the new technology is applicable to the many, not the few affluent labs.
The capabilities of conventional optical microscopes are limited by the laws of optics, which means that observations of objects smaller than 200 nm are fuzzy, Rizzoli said, adding that researchers have developed beyond-physics super-resolution methods that can reduce this limit to around 10 nm. This method, which won the 2014 Nobel Prize in chemistry, uses optical tricks to pinpoint fluorescent molecules attached to proteins.
In 2015, researchers proposed another way to circumvent the optical limit. A team of researchers led by Edward Boyden, a neural engineer at the Massachusetts Institute of Technology in the US, showed that inflatable tissues (using an absorbent compound found in nappies) could keep cellular objects away from each other. The technique, known as inflation microscopy, has led to a quantum leap in microscope resolution, allowing structures of around 20nm to be resolved.
Shaib and Rizzoli's technique fuses the two methods to achieve sub-1nm resolution. This clarity is enough to reveal the shape of individual proteins, which previously were typically imaged in more detail using more expensive structural biology methods, such as cryo-electron microscopy.
The simplicity of expansion microscopy is part of its appeal, and Boyden estimates that more than 1,000 labs have adopted the technique. Samples are treated with chemicals that immobilise the proteins on a polymer, which swells to 1,000 times its original size when water is added, allowing the molecules to be separated.ONE microscopy technique also uses heat or enzymes to break down the proteins, so that individual fragments are stretched in different directions during the swelling process.
The researchers have used their method to record pictures of a neuromolecule, the GABAA receptor, which closely resembles high-resolution cryo-electron microscopy and X-ray crystallography maps of proteins. They have also captured the outline of a large chunk of a protein called ototoxin, whose structure has not yet been determined, that helps to transmit audio signals in the brain. The shape is similar to structural predictions made by the AlphaFold deep learning network.
While the method can't match the resolution of cryo-electron microscopy, which in some cases can reveal near-atomic-level detail smaller than 0.2 nm, cryo-electron microscopy techniques are both puny and expensive, Rizzoli said, adding that ONE microscopy, by contrast, can provide a quick and easy way to understand the structure of almost any molecule.
Part of the motivation for developing the technology was to expand the accessibility of cutting-edge optical microscopes, Rizzoli said. the ONE microscope method is simple enough to be applicable to fluorescence microscopes, which became obsolete in the 1990s.
Salma Tammam, a pharmaceutical technologist at German University in Cairo, plans to send a PhD student to study the technique this summer. Her lab studies how nanoparticles move through cells, and they want to see details of the particles and their carriers. But like many researchers in low- and middle-income countries, they don't have access to expensive super-resolution microscopes.
Expanding the use of super-resolution microscopy is also important for scientists at well-funded institutions, says Noa Lipstein, a synapse biologist at the Leibniz Centre for Molecular Pharmacology in Germany. She recently founded an independent research group and chose to apply ONE microscopy to their studies of synaptic details.
