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Analytical Chemistry

Nanobiopsy Technique Samples A Cell Without Killing It

Analytics: Computer-controlled nanopipette nondestructively extracts samples from living cells

by Louisa Dalton
December 12, 2013 | A version of this story appeared in Volume 91, Issue 50

Credit: ACS Nano
A nanopipette with a 100-nm-wide tip (inset) extracts tiny samples from living cells.
Micrograph of a nanopipette tip.
Credit: ACS Nano
A nanopipette with a 100-nm-wide tip (inset) extracts tiny samples from living cells.

When scientists investigate the inner contents of a cell, the methods they use often end up killing it. Now, bioengineers have introduced a kind of cellular biopsy—a system to extract femto­liters of material from a cell without destroying it (ACS Nano 2013, DOI: 10.1021/nn405097u). The technique permits repeat sampling of a living cell, enabling study of its dynamic biochemistry over time.

Current methods that use micropipettes or microdissection to obtain a cell’s contents are generally fatal to the cell. A few groups have found less harmful ways to specifically remove RNA. Yet a method for general extraction from a live cell has remained elusive, says Nader Pourmand, a biomolecular engineer at the University of California, Santa Cruz.

Pourmand and his group customized a scanning ion conductance microscope (SICM) to guide a glass nanopipette into single cells and draw out material. First, the researchers roughly align the nanopipette over a bed of cultured cells. The SICM computer then takes over, guiding the nanopipette toward the cell of interest. The nanopipette stops just before touching the cell, then plunges down 1 μm to pierce the cell membrane.

Once in, the computer applies a negative voltage across the 100-nm-wide pipette tip. The voltage alters the surface tension between an organic solution in the nanopipette and the cell’s aqueous cytoplasm. As a result, the nanopipette sucks about 50 femtoliters of the cell’s contents. After sampling, the cells maintain their shape and membrane integrity, even after 10 punctures.

To show that their method could extract useful material from different regions of a cell, the researchers plucked and sequenced cytoplasmic messenger RNA from human cancer cells and mitochondrial DNA from human fibroblasts.

“You can extract anything. That is the beauty of it,” comments Yuri Korchev, a professor of biophysics at Imperial College London. Such flexibility permits many different types of measurements, such as single-cell diagnostic tests or drug screening, he says. “I see a hundred possibilities.”



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