Microrockets Take Off

Although microscale motors can't yet take a "Fantastic Voyage" through the human body like the one portrayed in the 1966 science-fiction film, a new study suggests that in vitro assays for detecting disease with microrockets might not be far away (Angew. Chem. Int. Ed., DOI: 10.1002/anie.201100115).

Nanoengineers Joseph Wang and Liangfang Zhang of the University of California, San Diego, and coworkers show that tube-shaped microrockets functionalized with antibodies can cruise through human blood serum. As they zoom along, the rockets capture cancer cells that express corresponding antigenic surface proteins. "This exciting piece of work demonstrates two important milestones for micromotors," says Thomas E. Mallouk, a nanoscale materials chemist at Pennsylvania State University, "namely, their ability to function in biological fluids and the selective attachment and transport of cancer cells."

Just a few tumor cells in blood are enough to spread cancer to other parts of the body. A micromotor-based method to detect the rogue cells with minimal sample processing would be a powerful diagnostic tool, the researchers say.

The rockets, fabricated via lithography, whiz through solution in the presence of hydrogen peroxide, a fuel that breaks down on the tubes' inner platinum surfaces to form oxygen. Accumulated gas bubbles then propel the tiny engines through the fluid.

The microrockets' outer gold surfaces give the researchers a platform on which to attach the cancer-specific antibodies via thiol chemistry, and layers of iron sandwiched between the gold and platinum allow the scientists to guide the miniature motors through solution with a magnetic field. By linking single-stranded DNA, rather than antibodies, to the rockets with similar surface chemistry, Wang's group also recently demonstrated the isolation of complementary strands of DNA from a biological sample (Nano Lett., DOI: 10.1021/nl2005687).

The new technology "offers numerous potential applications in biomedical diagnostics, environmental monitoring, and forensic analysis," Wang says, adding that the microrockets would be able to collect and concentrate cells and DNA in a lab-on-a-chip device for further analysis.