Scientists from Rice University (Houston), the MD Anderson Cancer Center (Houston), and Baylor College of Medicine (Houston) are developing new methods to inject drugs and genetic payloads directly into cancer cells. By delivering chemotherapy drugs using light-harvesting nanoparticles to convert laser energy into "plasmonic nanobubbles," 30 times more cancer cells could be killed than by using traditional drug treatment. These nanobubbles could also enable clinicians to use less than one-tenth of the standard clinical dose of chemotherapy drugs.

Delivering drugs and therapies selectively is a major obstacle in drug-delivery applications. While efforts to sort cancer cells from healthy cells has been successful, it is both time-consuming and expensive. Researchers have also used nanoparticles to target cancer cells, but because nanoparticles can be absorbed by healthy cells, attaching drugs to the nanoparticles can also kill healthy cells. "We are delivering cancer drugs or other genetic cargo at the single-cell level," notes Rice's Dmitri Lapotko, a biologist and physicist. "By avoiding healthy cells and delivering the drugs directly inside cancer cells, we can simultaneously increase drug efficacy while lowering the dosage."

The Rice scientists' nanobubbles are not nanoparticles. Short-lived events, they are tiny pockets of air and water vapor that are created when laser light strikes a cluster of nanoparticles and converts them instantly into heat. As the bubbles expand and burst just below the surface of cancer cells, they briefly open small holes in the surface of the cells and allow cancer drugs to enter.

The nanobubbles are generated when a pulse of laser light strikes a plasmon, a wave of electrons that sloshes back and forth across the surface of a metal nanoparticle. By matching the wavelength of the laser to that of the plasmon and dialing in just the right amount of laser energy, the team can ensure that nanobubbles form only around clusters of nanoparticles in cancer cells.

To form the nanobubbles, the researchers must first insert gold nanoclusters into cancer cells. They accomplish this by tagging individual gold nanoparticles with an antibody that binds to the surface of the cancer cell. Cells ingest the gold nanoparticles and sequester them together in tiny pockets just below their surfaces. While a few gold nanoparticles are taken up by healthy cells, the cancer cells take up far more. The technology selectivity capability results from the fact that the minimum threshold of laser energy needed to form a nanobubble in a cancer cell is too low to form a nanobubble in a healthy cell.