Cells that are dying, turning cancerous, or responding to drugs undergo physical changes. They might become stiffer or squishier. Or they might get heavier or lighter. The instruments for detecting these changes in individual cells are usually complex and expensive, which is why microbiologists still assess the state of a disease by waiting for cells to grow in a lab, and why doctors examine whether a drug is working by waiting to see whether the patient worsens or improves.
Gozde Durmus has invented a simple, fast method for detecting cells’ telling physical characteristic: making them levitate in a magnetic field and measuring how high they rise. White blood cells, red blood cells, cancer cells, and different bacteria each rise to a different height, because they have a characteristic density that determines the balance between the pull of gravity on the cell and the push of the magnetism. And Durmus has found that when a bacterial cell has responded to an antibiotic, it tends not to rise as high in the magnetic field as it did before. This change can be detected in about an hour, instead of the day traditionally required to determine how a microbe responds to a drug.
At her bench at the Stanford Genome Technology Center, Durmus makes cell-levitating devices by sliding a few laser-cut pieces of plastic over two small bar magnets. This keeps them from flipping and sticking together, so a magnetic field can be created in the space between them. She puts a thin capillary tube into that space. Then she adds two mirrors that will beam an image of the tube up to a conventional microscope. Samples of the cells to be levitated go into the tube along with a solution of gadolinium, an element that’s used as an MRI contrast agent. “It helps the cells fly in the magnetic field,” says Durmus. Their height can then be measured under the microscope.
Durmus knows from experience how important rapid, personalized drug monitoring could be. When she was a child in Izmir, Turkey, she had a bacterial infection that lasted three years, and she vividly remembers going to the hospital for painful and ineffective penicillin shots until she got the right treatment.
Her work also has a more whimsical inspiration. In 1997, physicists in the Netherlands used an ultrastrong magnet to levitate a living frog. Subsequent efforts to levitate things in weak magnetic fields—even objects much smaller than frogs—required toxic magnetic solvents. Durmus figured out how to do levitation without toxic materials, using only cheap magnets and some pieces of plastic.
