Smaller patterns make big analytical difference

Engineers at Purdue University have developed a technique that might be used to glue cells or DNA to the surfaces of computer ‘biochips,’ a technology devised to allow diagnostic devices to be implanted in the body or used to quickly analyse food and laboratory samples.

The microfabrication technique, normally used for etching electronic circuits, is used to fashion micropatterns out of a material made primarily from polyethylene glycol.

‘The patterns’ smallest features were 5 micrometers, or about one-twentieth as wide as a human hair, which makes them as small as some cells,’ said Rashid Bashir, an assistant professor of electrical and computer engineering at Purdue University.

Purdue engineers had previously announced that they had made the first protein biochips, in which a protein mated to a silicon computer chip might be used to detect chemicals, microbes and disease. However, researchers say they hope to attach many other types of biological entities, such as cells and DNA, capable of quickly detecting a wider range of substances, either in the body or in laboratory samples.

Unlike many synthetic materials, polyethylene glycol is not attacked by the body’s immune system, making it suitable for implantation.

The polymer is said to be ideal for microfabrication because of its optical properties: these allow it to be formed into patterns by using ultraviolet light employing photolithography.

The plastic is applied to the surface of silicon chips as a film and covered with a photomask, which is opaque in some places and transparent in others. The UV light is shined on the mask, dissolving the polymer wherever it is exposed to the radiation. When the mask is removed, a plastic pattern remains.

The technique might be used to form precise polymer patterns containing certain regions that attract water and others that repel water. Depending on the design of such patterns, specific cells or molecules would stick to the polymer.

Then, the glued biological materials on a biochip’s surface would precisely fit specific cells, molecules and strands of DNA in a sample being analysed. When a targeted substance passed by the chip, it would become attached to the surface and the chip would signal that the substance had been detected.

Such a technology might be used in the laboratory for quick chemical and genetic screening of blood and other biological materials; to instantly analyse food products for contamination; and in intrusive medical devices that continuously monitor glucose in a diabetic person’s blood and then automatically administer insulin.