Scientists have developed a method to use a nanosyringe’s tiny needle to penetrate single living cells and extract their content.
In cell cultures, for example, the method would let researchers investigate the interior of the cells. This way, scientists could identify the differences between individual cells at the molecular level, as well as to identify and analyze rare cell types.
The new method enables researchers to sample individual cells of a tissue culture directly in the petri dish.
“This means we can study how a cell affects its neighboring cells,”
says Orane Guillaume-Gentil, a postdoc in the research group of Julia Vorholt, professor in the biology department at ETH Zurich. This type of investigation is not possible using conventional methods because molecular analyses generally require the cells to first be physically separated and then destroyed.
On top of that, the microscopic needle can be controlled so precisely that scientists are able either to harvest the content of the nucleus or collect the intracellular fluid surrounding the nucleus, the cytosol.
In addition, the researchers can determine the amount of intracellular material they extract with incredible accuracy, down to one tenth of a picoliter (one trillionth of a liter). The volume of a cell is 10 to 100 times bigger.
Green colored cytosol is withdrawn from a cell (microscopic view from above). Black is the FluidFM cantilever; the needle is located in the center of the image. (Micrograph: ETH Zurich / Orane Guillaume-Gentil)
Extracting molecules doesn’t kill the cells, so researchers are free to sample the same live cell several times in order to analyze its RNA and proteins—and possibly even metabolites in the future.
“We were surprised to find that the cells we examined survived even after we had extracted most of their cytosol,” says Vorholt.
This underscores the amazing plasticity of biological cells.
Cell Compartment Extraction
The new cell extraction method is based on a microinjection system developed at ETH over the past years, the FluidFM. The device gave biologists a way to inject substances into individual cells.
FluidFM and its nanosyringe were also ideal for gently sucking up cells through underpressure and relocating them elsewhere.
Vorholt and her research group took the system a step further, allowing material to be extracted from the cell compartment as well.
“One particularly important aspect was to find a suitable coating for the needle, to prevent fouling by cell material,” says Guillaume-Gentil.
Another challenge was to adapt the analysis techniques used for the cell molecules—for measuring enzyme activity, for example—to the minute measurement volumes.