A multidisciplinary team at Purdue University is developing a method for detecting harmful bacteria using a silicon wafer coated with proteins. The researchers hope that the work will lead to a rapid, cheap, disposable means of testing everything from food to medical samples. "Our goal is to use electronic detection, which is amenable to the production of portable, handheld devices to be eventually used in the field," explained Rashid Bashir, an assistant professor of electrical and computer engineering at the university. Scientists have long used proteins that selectively bind to the cell walls of specific bacteria. These proteins have been combined with fluorescent dyes to create the fluorescent labels that are crucial to microbiology. The Purdue group has coupled this technology with circuit design for conventional microprocessors. Using photolithography techniques from the semiconductor industry, the researchers create electrodes and their corresponding circuits on a silicon wafer. Proteins are then adsorbed on the electrodes, Bashir said. By monitoring the interfacial capacitance of the electrodes, the group hopes to detect any bacteria that have been bound by the proteins. Team member Michael Ladisch, a professor of agricultural, biological and biomedical engineering, said the group plans to make the device small so only a few drops of a sample will be needed. A sample under test will be presented to the chip on a swab or through a pipette. In proof-of-concept experiments, the researchers attached the protein avidin to the chip and watched fluorescently labeled biotin molecules bind to it. Bashir said they are developing cost estimates for the mass production of the chips and are preparing a device that will test food for Listeria monocytogenes. Such a test should produce results in minutes, rather than the days typically taken to culture bacteria for conventional laboratory analysis.