Tiny robots that swim through our blood vessels attacking invaders have not quite crossed the line that separates science fiction from science—but there might be a way to jump-start their development.
Rather than designing such minuscule machines from scratch, some scientists have been experimenting with the idea of enlisting the thousands of species of bacteria swarming inside our bodies. In recent years researchers have saddled microorganisms with useful nanoparticles and bits of DNA. Although the research is preliminary, some engineers and microbiologists see potential. This past March, at the American Chemical Society’s biannual National Meeting & Exposition in San Diego, biomolecular engineer David H. Gracias of Johns Hopkins University explained how he and his colleagues have decorated nonpathogenic Escherichia coli with tiny beads, rods and crescents made from nickel and tin coated in gold.
Once inside the body, such nanoparticles can be heated from afar with infrared light, thus destroying diseased tissue. Ultimately Gracias dreams of coaxing bacteria to ferry spongy nanoparticles soaked in drugs and outfitting bacteria with mini tools to perform surgery on a single cell.
Similar research by other scientists confirms that engineered bacteria can deliver medical packages directly into diseased or cancerous cells. In earlier work Demir Akin, now at Stanford University, and his colleagues attached the luciferase gene that makes fireflies glow to Listeria monocytogenes, a bacterium responsible for many cases of food poisoning. Three days after Akin injected the germs into living mice, the rodents glowed under a specialized camera, which confirmed not only that the bacteria had entered the mice’s cells but that the cell nuclei had expressed the gene. Akin designed the living micro bots to release their DNA packages inside mammalian cells and replicated these results in human cancer cells in petri dishes.
The advantage of L. monocytogenes is that it has evolved ways to get inside animal cells—but it is not harmless. In contrast, many strains of E. coli are harmless but do not have specific adaptations for entering cells. The key, says Douglas Weibel of the University of Wisconsin–Madison, is working with a harmless microorganism that is a strong swimmer and has no problem butting its way into mammalian cells. In one study, Weibel yoked nanosize polystyrene beads to single-cell green algae and steered the “micro oxen” (algae move toward light)—an early experiment that inspired later work.
Weibel remains fascinated by ongoing research. “Bacteria have evolved amazing motility,” he says. “They can sense changes in their environment and adapt not only on a short timescale but genetically, too. Even if we can’t get them to deliver things in the human body, they could be useful for transporting nanoparticles in the lab. Who knows what advances we’ll have 50 years from now?”
This article was published in print as "Microbial Mule."