New method allows for improved ion images of neurons and skin cells

Clear and detailed images of biological cell samples are useful for analysis of lipids, metabolites and their derivatives. Currently, time-of-flight secondary ion mass spectrometry (ToF-SIMS) is used for imaging specimens under a high vacuum environment. However, the vacuum dries out cells, changing their shape and creating challenges for imaging and analysis.

Sun Young Lee et al propose a new method of specimen preparation, which will preserve the shape of cells even as they dry. The team produced improved ion images by using a graphene cover, which allows for cells to dry slowly, and a plasma treatment on the slide substrate, which gets rid of residue that produces unwanted background ion spectra during imaging.

“Previously, few examples of ion imaging of a single cell using ToF-SIMS were performed, because the pretreatment process for cell analysis was complicated and inefficient,” said author Jae Young Kim.

To prepare specimens, the researchers used single-layer graphene that acted as a gasless permeable mesh and slowed evaporation, keeping cells hydrated longer and reducing deformation. Then, they used an air plasma treatment to remove the graphene cover and any organic residues on the glass substrate. Previous methods of cleaning proved ineffective at removing residue, even when cleaned up to 10 times.

The team applied their graphene layer and plasma treatment cleaning method to image neuron cells and human skin cells. Their method produced clear and clean images that allowed for better analysis of structural components, which can be useful for medical diagnostics.

“The next challenge is to develop ion imaging techniques that attach antibodies and metal oxide nanomaterials to the proteins of interest, observing multiple proteins simultaneously by detecting metal oxides,” said Kim.

Source: “Improved ion imaging of slowly dried neurons and skin cells by graphene cover in time-of-flight secondary ion mass spectrometry,” by Sun Young Lee, Heejin Lim, DaeWon Moon, and Jae Young Kim, Biointerphases (2019). The article can be accessed at https://doi.org/10.1116/1.5118259 .