Image caption The barrel shape opens and spills its payload when the "locks" come into contact with target cells

Scientists have developed and tested a "DNA robot" that delivers payloads such as drug molecules to specific cells.

The container was made using a method called "DNA origami", in which long DNA chains are folded in a prescribed way.

Then, so-called aptamers - which can recognise specific cell types - were used to lock the barrel-shaped robot.

In lab tests described in Science, the locks opened on contact with cancer cell proteins, releasing antibodies that halted the cells' growth.

The method could find wide use in biological applications, where this kind of "specificity" is highly prized.

Lead author of the research, Shawn Douglas of the Wyss Institute at Harvard University, said the result brings together several recent research strands.

"We've been working on figuring out how to build different shapes using DNA over the past several years, and other researchers have used antibodies as therapeutics, in order to manipulate cell signalling, and yet others have demonstrated that aptamers can be used to target cancer cell types," Dr Douglas told BBC News.

"The novel part is really integrating all those different pieces and putting them together in a single device that works."

In essence, the approach co-opts a number of strategies of our immune systems, with the robots playing the role of white blood cells that hunt down problematic cells and destroy them.

The team tested the robots using several cultures of cancer cells including lymphoma and leukemia, with corresponding payloads of antibodies.

Because DNA is found in nearly all of our cells, Dr Douglas said the robots posed fewer problems of toxicity than many materials would have.

Scientists have already discovered a large number of different aptamers that can "recognise" proteins corresponding to different diseases, so the approach could in principle be adapted to a wide range of applications.

Dr Douglas said that there was still much optimisation to be done on the robots; for now the team will create a great many of them to be tested in an animal model.