It’s Magnetism 1 – Gravity 0. Using magnets, a team at Stanford University has devised a way to make living cells hover. The technique, which measures the density of individual cells, may be useful for testing new drugs or monitoring diseases.

We’ve levitated living things using magnets before, including frogs, mice and strawberries, but we didn’t have the delicate touch required to control magnetic fields precisely enough to levitate smaller objects. “Everything has its own magnetic blueprint,” says team member Utkan Demirci. “We started thinking about scaling it all the way down to a single cell.”

Their device suspends cells soaked in a magnetic solution between two neodymium magnets. Each cell floats up a to height specific to its density, regardless of its actual cell volume. This density is a fundamental property that can help tell cells apart. “You can do it in real time, within minutes,” says team member Lars Steinmetz.

In a series of demonstrations, the team put the technology through its paces. Under the magnets, a mix of different types of cancer cells separated into layers – breast cancer here, lung cancer there, and so on. They could pry apart white blood cells from red.

And they could even see single cells die, getting slightly denser in the process. They watched breast cancer cells succumb to an acid bath, and E. coli and yeast die one by one from antibiotics and antifungals, respectively. Understanding the varied responses of cells could be a great boon to testing out new drugs and diagnosing diseases, they say.

The technique, like others to measure cell density, comes with strengths and weaknesses. “This whole levitation thing exploits unusual magnetic properties of very weird elements,” says William Grover of the University of California Riverside.

Grover’s own technique can weigh cells in a fluid known not to affect their density – something the Stanford team can’t yet be sure of, Grover says. It’s important to show that the magnetic fluid the cells are bathed in doesn’t itself change their density.

But one plus for the new technique is that it can process higher numbers of cells at a time, useful for picking out rare cells needed in a diagnosis.

Grover’s reservations are echoed by George Whitesides of Harvard University, who pioneered much of the magnetic levitation technology at play – and has also developed a non-magnetic way to test cell density. The fluid will have to be closely calibrated, Whitesides says.

But the fact that the Stanford team can separate out cells shows that the device is working, and confirms that density is a useful thing to look at.

“The nice thing about mag lev is it’s pretty simple to do,” says Whitesides. “Now what has to be done is the hard work that comes with any new analytical method.”

Journal reference: PNAS, DOI: 10.1073/pnas.1509250112

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