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The sensor not only can monitor the growth of a single bacterium throughout its life cycle and over multiple generations, but it can also determine when an individual bacterium stops growing, in response to treatment with an antibacterial drug, for instance.

“You can basically tell, within minutes, whether or not the antibiotic is working,” says University of Michigan graduate student Paivo Kinnunen, one of the lead authors on a paper published in the journal Biosensors and Bioelectronics.

Because it also detects the response of individual cancer cells, the sensor could someday be used as well in cancer drug development and treatment.

The device, called an asynchronous magnetic bead rotation (AMBR) sensor, uses a spherical, magnetic bead that asynchronously spins in a magnetic field. Just as a pencil attached to a child’s toy top creates drag that affects the way the top spins, anything attached to the bead slows its rate of rotation.

In the current work, the researchers attached individual, rod-shaped Escherichia coli bacteria to individual beads and watched what happened, using the newly developed AMBR sensor.

“When one bacterium gets attached, it’s hanging out there like a little hotdog, and it changes the drag tremendously, slowing down the rate of rotation by a factor of four,” says Raoul Kopelman, a professor of biomedical engineering, biophysics and chemical biology. “If the bacterium grows even a tiny bit, the drag increases even more, and we can monitor that nano-growth by observing changes in the rate of rotation.”

“The method can detect growth of as little as 80 nanometers, making it far more sensitive than even a powerful optical microscope, which has a resolution limit of about 250 nanometers,” says Kinnunen.

In the near future, “we expect it will be possible to make the determination even quicker,” says graduate student Irene Sinn, the paper’s other lead author. “This is something we are actively working on.”

The device also can be used for monitoring the growth and drug susceptibility of other types of cells, says Kinnunen. “The sensor is very sensitive to small changes in growth, so this method can be applied to any applications in the microscale or nanoscale where there are small changes in size. That includes the growth of yeast and cancer cells as well as bacteria.”

More news from the University of Michigan: http://ns.umich.edu/