http://www.newscientist.com/article/dn24508-skeletal-chains-could-help-algae-deliver-drugs.html#.UnUUNHCL9Xs

Skeletal chains could help algae deliver drugs

Skeletons of single-celled algae have been modified while they are still alive to incorporate molecular chains that can harness chemical cargo. The algal bodies are then dissolved away so that their remains can be used to deliver drugs or clean up contaminated water.

The microscopic algae known as diatoms are supported by skeletons made of silica that are about 10 micrometres across. Each species grows intricate innards that yield a range of shapes, from barrels to stars and doughnuts. Tiny folds and crevices give diatom skeletons a much larger surface area than simple spheres or other nanoscale capsules, making them an ideal choice for drug delivery.

Previous work created artificial casts of the skeletons, usually made from biodegradable polymers, by coating the skeleton and then washing away the biological components. But modifying these casts to reliably carry drugs and other molecules has been a challenge, because the method requires harsh organic solvents applied in completely dry conditions that can be costly and time consuming to use. Now Abhay Pandit of the National University of Ireland, Galway, and his colleagues have found a way to make living diatoms incorporate thiols – sulphur-bearing molecular chains – directly into their skeletons as they grow, meaning their casts can carry drugs without having to be treated first.

"This is the first piece of a big puzzle to functionalise diatoms without disturbing the design of their intricate architecture in a substantial way," says Pandit.

Purifying algae

The team grew the diatom species Thalassiosira weissflogii in a nutrient-rich solution at room temperature and exposed it to a light-dark cycle that mimicked a natural day. They added thiol compounds to the growth solution multiple times over eight days, which allowed the algae to take up the molecules as they grew. Thiol-rich diatoms were then treated to make polymer casts. The chains remained attached to the casts even after the rest of the diatom's structure was dissolved away.

Molecular cargo such as drugs could be attached to the chains hanging from the cast's inner wall or outer surface. This would help deliver substances to parts of the body in medical treatments, says Pandit. Thiol chains can also bind with heavy metals so, in future, diatoms with more porous structures could be used for nanoscale water purification, he says.

Nils Kröger at the Dresden University of Technology in Germany is not convinced that modifying live diatoms will prove to be more efficient than growing thiols on casts of their skeletons. But he thinks figuring out the best approach will lead to myriad applications for chain-wielding diatoms.

"Having thiols exposed on the surface of diatoms opens the doors for introducing a host of biomolecules including enzymes, receptors and drugs," he says.

Journal reference: Nature Communications, DOI: 10.1038/ncomms3683