Targeted drug delivery is a hot topic of research. Scientists around the world are working on different ways to get drugs into specific cells without negatively impacting the rest of the body.

Now researchers in England and Germany have created gold-studded polymer microcapsules that release compounds into cells by rupturing when exposed to ultraviolet light. The capsules could be useful for researchers studying the effects of drugs on cells, and eventually they could perhaps serve as a clinical tool for administering medication.

"You can keep the capsules in the body for a while, and then you switch [on] the light to release them," says Gleb Sukhorukov, professor of biomaterials at Queen Mary University of London and a researcher on the project.

Sukhorukov says the capsules could be used for administering drugs at the site of surgery a few weeks after an operation, without having to open up the patient again. They could also prove useful for gene therapy, although a method for directing the capsules to the right cells has yet to be developed.

To create the capsules, polymer layers are wound around tiny silica particles. Gold nanoparticles are added to the walls of the capsule during this process, and the silica particles are later dissolved in acid, leaving hollow capsules behind. Sukhorukov says the capsules can be made anywhere from 200 nanometers to 10 microns in size. Once they have been produced, they are heated in a solution containing the compound that is to be delivered to cells. The capsules shrink as they are heated, trapping some of the compound inside. In experiments, the researchers put peptides inside the capsules, but in the future they hope to use drugs.

The capsules were inserted into living cells using electroporation, an existing technique in which a pulse of electricity is applied to the cell to make it temporarily more permeable. Once implanted in the cells, the capsules protect the substance inside from being metabolized. But when exposed to ultraviolet light, the gold nanoparticles in the walls of the capsule heat up, causing the drug to be released.

Getting the peptides into the cells was only the first step, however. Sebastian Springer, a professor of biochemistry and cell biology at Jacobs University Bremen in Germany, who also worked on the project, says the team wanted to prove that the peptides would properly interact with the cell. "We decided that we would see whether this peptide would get picked up by [the] immune system and treated like a normal intracellular peptide that was natural to the cell," Springer says. Indeed, the peptides moved, as hoped, from a compartment in the cell known as the endoplasmic reticulum to the cell's surface.