Microscopy method with femtogram accuracy delves into cell growth

Looking to discover whether cells grow at a constant rate or exponentially, a research team from the University of Illinois developed an imaging method called spatial light interference microscopy (SLIM) that can measure cell mass using two beams of light.

Looking to discover whether cells grow at a constant rate or exponentially, a research team from the University of Illinois (Champaign, IL) developed an imaging method called spatial light interference microscopy (SLIM) that can measure cell mass using two beams of light.

An extremely sensitive method, SLIM can quantitatively measure mass with femtogram accuracy; by comparison, a micron-sized droplet of water weighs 1,000 fg. It can measure the growth of a single cell and even mass transport within the cell for bacteria, mammalian cells, adherent cells, nonadherent cells, single cells and populations, says Mustafa Mir, a graduate student and a first author of the paper.

SLIM, which combines phase-contrast microscopy and holography, does not require staining or any other special preparation. The noninvasive method uses white light and can be combined with more traditional microscopy techniques, such as fluorescence, to monitor cells as they grow.

“We were able to combine more traditional methods with our method because this is just an add-on module to a commercial microscope,” says Mir. “Biologists can use all their old tricks and just add our module on top.”

Because of SLIM’s sensitivity, the researchers could monitor cells’ growth through different phases of the cell cycle. They found that mammalian cells show clear exponential growth only during the G2 phase of the cell cycle, after the DNA replicates and before the cell divides. This information has great implications not only for basic biology, but also for diagnostics, drug development and tissue engineering.

The researchers hope to apply their new knowledge of cell growth to different disease models. For example, they plan to use SLIM to see how growth varies between normal cells and cancer cells, and the effects of treatments on the growth rate.

Electrical and computer engineering professor Gabriel Popescu, a member of the Beckman Institute for Advanced Science and Technology at the U of I and who led the research team, is establishing SLIM as a shared resource on campus, hoping to harness its flexibility for basic and clinical research in a number of areas.

The National Science Foundation and the Grainger Foundation supported this work, which has been published in the in the Proceedings of the National Academy of Sciences.

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