MIT creates a budget imaging method with an accuracy of 10 nanometers

A new low-cost imaging technique from MIT engineers will allow scientists to image viruses and,

perhaps even individual biomolecules.It is based on expansion microscopy. This approach involves embedding biological samples into a hydrogel and then expanding them before imaging them with a microscope. For the new imaging technique, the researchers developed a new type of hydrogel. Its feature is that it supports a more uniform configuration. This in turn allows tiny biological structures to be imaged with greater precision.

This degree of precision will help in studying the basic molecular interactions that make life possible, explains Edward Boyden, a professor at MIT. 

Laboratories around the world have begun to useexpansion microscopy since Boyden's lab first introduced it in 2015. With this technique, researchers physically enlarge their samples to approximately four times their linear size before imaging them. This allows them to create high-resolution images without expensive equipment. 

In an article published in 2017, the laboratoryBoydena demonstrated a resolution of about 20 nanometers using a process in which the samples were expanded twice before imaging. This approach, as well as earlier versions of expansion microscopy, are based on an absorbent polymer made from sodium polyacrylate. These gels swell when exposed to water. However, one of their critical limitations is that they are not completely uniform in structure or density. This unevenness leads to slight distortion of the sample shape during its expansion, which limits the achievable accuracy.

To overcome this, MIT has developed a newgel - tetragel, which forms a more predictable structure. By combining tetrahedral polyethylene glycol molecules with tetrahedral sodium polyacrylates, scientists were able to create a lattice structure. It is much more homogeneous than the free radical-synthesized sodium polyacrylate hydrogels that have been used previously.

Scientists have demonstrated the accuracy of the new approachto imaging by using it to expand herpes simplex virus type 1 (HSV-1) particles. They have a characteristic spherical shape. After expanding the viral particles, the researchers compared the shapes to the shapes obtained using electron microscopy. It turned out that the distortion was much lower than in previous versions of expanding microscopy. This made it possible to achieve an accuracy of about 10 nanometers.

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