How much does life weigh?

Novel Libra can weigh the weight of a single living cell

The new scale can measure the mass of this single cell - and even record millisecond changes. © Martin Oeggerli, micronaut.ch / ETH Zurich / Uni Basel
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Fast and accurate: researchers have developed a scale that can weigh living cells in real time. For the first time ever, even tiny weight changes can be recorded - with a resolution of milliseconds and trillionth of a gram. Even the first weighing tests revealed surprising results: The mass of living mammalian cells fluctuates constantly every second. This subtle oscillation reflects processes in cell metabolism, as the researchers report in the journal "Nature".

Whether earthworm, sunflower or human - we all consist of cells. Their shape, size and weight are determined crucially by the metabolic processes within these smallest units of life. The weight of living cells, and especially their change, can therefore provide valuable information about what is going on inside them. But measuring these changes in real time has not been possible. There was simply no suitable method of measurement.

Hung upside down

This has changed now. Daniel Müller from ETH Zurich and his colleagues have developed a novel cell scale that can do just that. For weighing, the cells are placed under controlled conditions in a cell culture chamber. The wafer arm, a wafer-thin, transparent silicon wafer coated with collagen or fibronectin, shuts down to the bottom of the chamber. If he touches a cell, he picks it up.

"For the measurements, the cell hangs almost head-first on the underside of a tiny cantilever, " explains Gotthold Fläschner of ETH Zurich. A blue, pulsed laser now makes the base of the cantilever vibrate. A second, infrared laser beam measures the vibrations at the front end, where the cell hangs, once with and once without a cell.

Vibration difference reveals mass

"From the difference of the two oscillations, the mass of the cells can be calculated, " explains David Martínez-Martin. A computer screen displays the weight and its change as a graph. Researchers can read this in real time over the entire measurement period, be it milliseconds or days. display

For example, it can be seen how the weight changes during cell cycle and cell division, what influence different substances have on the mass of cells or what happens when a virus attacks them. Because the measuring apparatus and cell culture are mounted directly on the stage of a fluorescence microscope, in addition to the weight measurement, everything that happens at the same time inside the cells can be filmed and observed.

Subtle fluctuations

Even the first measurements with this cell scale revealed surprisingly: "We have found that the weight of living cells fluctuates continuously by one to four percent, " reports Mart nez-Mart n. Driven by energy balance and water transport, cells show such rapid and subtle mass fluctuations throughout their cell cycle. Dead cells, on the other hand, do not show these fluctuations in the second range, as the biophysicists discovered.

The researchers are enthusiastic: "We see things that nobody has ever seen before us, " says Fl schner. However, the cell scale is not only of interest for basic cell biological research, but also for the medical and pharmaceutical industries. It could be used to study the pathological growth of cells or to test the influence of drugs on cell metabolism. Even material scientists are already interested in the balance. "It's all about the so-called functionalization of nanoparticles, which means changing the surfaces of very small particles, " explains Mart nez-Mart n.

The scientists have patented their new weighing method. The Swiss company Nanosurf AG already works as a licensee on a production-ready device. The chance that scientists of various disciplines will soon be able to use the cell scales is therefore good. (Nature, 2017; doi: 10.1038 / nature24288)

(Swiss Federal Institute of Technology Z rich (ETH Zurich), 27.10.2017 - NPO)