Graphene keeps cells viable in new nanoimaging technique
Scientists from Daegu Gyeongbuk Institute of Science and Technology (DGIST) are using graphene to keep living, wet cells viable in an ultrahigh-vacuum environment, enabling high-resolution visualisation of the undistorted molecular structure and distribution of lipids in cell membranes. Described in the journal Nature Methods, their technique could enhance our bioimaging abilities considerably, improving our understanding of the mechanisms underlying complex diseases.
With every passing day, technology becomes better able to look into biological processes and molecular and cellular structures, thereby gaining greater understanding of the mechanisms underlying diseases such as cancer and Alzheimer’s. Nanoimaging is one such cutting-edge technology, and is widely used to structurally characterise subcellular components and cellular molecules such as cholesterol and fatty acids — but it is not without its limitations.
“Most advanced nanoimaging techniques use accelerated electron or ion beams in ultrahigh-vacuum environments,” explained DGIST Professor Dae Won Moon, lead scientist of the new study. “To introduce cells into such an environment, one must chemically fix and physically freeze or dry them. But such processes deteriorate the cells’ original molecular composition and distribution.”
Prof Moon and his team wanted to find a way to avoid this deterioration. As explained by team member Dr Heejin Lim, “We wanted to apply advanced nanoimaging techniques in ultrahigh-vacuum environments to living cells in solution without any chemical and physical treatment, not even fluorescence staining, to obtain intrinsic biomolecular information that is impossible to obtain using conventional bioimaging techniques.”
Their technique involves placing wet cells on a collagen-coated wet substrate with microholes, which in turn is on top of a cell culture medium reservoir. The cells are then covered with a single layer of graphene. It is the graphene that is expected to protect the cells from desiccation and cell membranes from degradation.
Through optical microscopy, the scientists confirmed that, when prepared this way, the cells remain viable and alive up to 10 min after placing in an ultrahigh-vacuum environment. The scientists also performed nanoimaging — specifically, secondary ion mass spectrometry imaging — in this environment for up to 30 min. The images they captured within the first 10 min paint a highly detailed (submicrometre) picture of the true intrinsic distribution of lipids in their native states in the cell membranes; for this duration, the membranes underwent no significant distortion.
As part of this method, a cascade of ion beam collisions at a point on the graphene film can create a big enough hole for some of the lipid particles to escape. But while this degradation to the cell membrane does occur, it is not within the 10-minute window and there is no solution leakage. Furthermore, the graphene molecules react with water molecules to self-repair. The method is therefore a useful way to learn about cell membrane molecules in their native state in high resolution.
“I imagine that our innovative technique can be widely used by many biomedical imaging laboratories for more reliable bioanalyses of cells and eventually for overcoming complex diseases,” Prof Moon said.
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