Biochips Mate Silicon with Proteins
Peter Singer, Editor-in-Chief -- Semiconductor International, 3/1/2001
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Michael Ladisch, professor of agricultural and biological engineering and biomedical engineering at Purdue, said that if the first real-world tests of the biochips are successful, the protein-encrusted silicon chips could appear in dozens of applications in a few years. Physicians could use devices containing biochips to quickly diagnose common diseases or test the efficacy of chemotherapy. Soldiers might rely on sensors on the battlefield to sound the alarm in the event of a biological or chemical attack. Farmers could place sensors in their fields to alert them to crop diseases. Medical scientists could use the biochips to investigate whether certain plants popular as folk remedies actually contain biochemicals that have beneficial biological activity.
In the most recent work, Purdue engineers have developed a technique that might be used to glue cells or DNA to the surface biochips. The microfabrication technique is used to pattern a polymer, polyethylene glycol, with features measuring about 5 µm. With this process, the engineers hope to attach many types of biological entities, such as cells and DNA, to a computer chip. "This polymer layer could be the intermediate layer between the biological entities and the chip," said Rashid Bashir, assistant professor of electrical and computer engineering. "The protein would go on top of the polymer."
Unlike many synthetic materials, polyethylene glycol is not attacked by the body's immune system, making it suitable for implantation. The polymer also is ideal for microfabrication. "These polymer films can be patterned on surfaces in cellular dimensions or smaller," said Nicholas A. Peppas, Purdue's Showalter Distinguished Professor of Chemical and Biomedical Engineering, who worked with Bashir to co-direct the research of former chemical engineering graduate student Jennifer Ward.
The technique might be used, for example, 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 analyzed, enabling a lock-and-key sort of attachment. 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 speedy chemical and genetic screening of blood and other biological materials; to instantly analyze food products for contamination; and in future implantable medical devices that continuously monitor glucose in a diabetic person's blood and then automatically administer insulin.
So far, the smallest features within the patterns, while achieving cellular scale, are still more than 30 times larger than the features in today's microelectronic circuits, Bashir said, adding that future attempts will be made to reduce the size of pattern features. "I think this is actually a first step. We will be working on trying to make it smaller. But it's important to note that, for some biological applications, the 5 µm size we have achieved is actually small enough," he said, because cells range in size from 1-10 µm across.
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