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  • Microscopic solar cells could change cancer therapy

Jan 2011
Dr. Jörg Schwartz,

EL PASO, Texas – When it comes to solar cells, “the larger, the better” may be one of the first thoughts because more surface area helps the cells convert more sunlight into electrical energy. The opposite is true at the University of Texas, however, where a team of researchers is trying to make photovoltaic devices smaller and smaller – with a different goal, of course.

The investigators are looking at improving cancer therapy, where one of today’s most common approaches is injecting chemotherapeutic drugs through an intravenous drip into the bloodstream. The drugs, usually targeting all cells that divide quickly, come in contact with many organs as they travel through the body on the way to their target. But along the way, they also attack noncancerous cells that happen to divide rapidly. Most of the side effects are well-known, including hair loss, reduced production of blood cells and inflammation of the lining of the digestive tract.

If doctors could deliver the drugs only where needed – targeting them specifically to tumor tissue – many unwanted side effects could be avoided. And this is where the solar cells come into play. The idea is that a small current, produced by targeted illumination of a microscopic photovoltaic (PV) device, could be used to detach a drug molecule that would otherwise be tied to the photoactive carrier.

During experiments performed on an in vitro model system, positively or negatively charged “model” drugs were applied to opposite sides of the miniature solar cell as a coating. Upon introduction of a light beam, one side of the device became positively charged, repelling the positive-charged molecules placed there by the researchers; the same thing happened with the negatively charged side and negative model molecules.

This is a microscopic image of a solar device on the scale of a few micrometers. The device can be coated with drugs that will be released upon exposure with IR radiation inside the body. Courtesy of Drs. Gregory Nielson and Jose Luis Cruz-Campa, Sandia National Laboratory.

The good news for applying this to a real organism is that near-IR or laser light can penetrate tissues more than several centimeters deep. But there are still challenges ahead. The first is making an extremely small solar cell.

“For this application, the PV device should ideally be a few micrometers or submicrometers large,” said Dr. Tao Xu, assistant professor and leader of the research. Also on his wish list toward clinical applications are organic solar devices based on biocompatible or even biode-gradable materials.

“We believe we just opened the door of the brand-new applications of the PV or solar cells to medicine,” Xu said, adding that researchers from interdisciplinary fields are realizing more and more the value of this new technology. He predicts that solar cells will be designed specifically for medical applications fairly soon.

After presenting their initial work at the AVS 57th International Symposium & Exhibition 2010 in Albuquerque, N.M., in October, the investigators now will work toward an animal tumor model with prostate cancer and will intravenously inject microsolar devices loaded with anti-tumor drugs.

“We will see if these devices can travel to the tumor sides and if the drugs can be effectively released from the devices and delivered into tumor tissues upon exposure of the infrared laser light,” Xu said. “We will also evaluate the therapeutic effects of this new delivery system.”

solar cell
A device for converting sunlight into electrical energy, consisting of a sandwich of P-type and N-type semiconducting wafers. A photon with sufficient energy striking the cell can dislodge an electron from an atom near the interface of the two crystal types. Electrons released in this way, collected at an electrode, can constitute an electrical current.
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