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Ultrasound Controls Nanomotors Inside Living Cells

Optical microscope image of a HeLa cell containing several gold-ruthenium nanomotors. Arrows indicate the trajectories of the nanomotors, and the solid white line shows propulsion. Near the center of the image, a spindle of several nanomotors is spinning.  Inset: Electron micrograph of a gold-ruthenium nanomotor. The scattering of sound waves from the two ends results in propulsion. (Courtesy Mallouk lab, Penn State University
Optical microscope image of a HeLa cell containing several gold-ruthenium nanomotors. (Courtesy Mallouk lab, Penn State University)

A research team at Penn State University composed of chemists and engineers has successfully introduced tiny synthetic motors inside live human cells, then used ultrasound to propel them while steering them magnetically.

The team explains their accomplishments in "Acoustic propulsion of nanorod motors inside living cells" by Wang et al. in Angewandte Chemie International Edition, published in February.

The team used HeLa cells, an immortal line of human cervical cancer cells frequently used in research, for their experiments. The nanomotors were gold and ruthenium rods about 300 nm in diameter and about 3 ?m long. These nanomotors attach themselves to the external surface of the cells, then incubation for 24 hours or longer causes the cells to ingest them.

The ultrasonic pulses control whether the nanomotors move forward or whether they spin around, and the researchers can control their direction using magnetism. "As these nanomotors move around and bump into structures inside the cells, the live cells show internal mechanical responses that no one has seen before," says Tom Mallouk, PhD, professor of materials chemistry and physics at Penn State, and the paper's last author.

At low ultrasonic power, Mallouk explains, the nanomotors have little effect on the cells. But when the power is increased, the nanomotors' velocity increases, and they start moving around and bumping into the organelles, the structures within the cell that perform specific functions. At lower ultrasound powers, the HeLa cells remain viable. But driven by higher ultrasonic power, the nanomotors can act like egg beaters to effectively homogenize the cell's contents, or they can act as battering rams to puncture the cell membrane.

Mallouk continues, "This research is a vivid demonstration that it may be possible to use synthetic nanomotors to study cell biology in new ways."

The article's abstract states, "Ultrasonic propulsion of nanomotors may thus provide a new tool for probing the response of living cells to internal mechanical excitation, for controllably manipulating intracellular organelles, and for biomedical applications."

And Mallouk prognosticates, "We might be able to use nanomotors to treat cancer and other diseases by mechanically manipulating cells from the inside. Nanomotors could perform intracellular surgery and deliver drugs noninvasively to living tissues."

Stephen Levy is a contributor to Qmed and MPMN.

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