Reliability and Biosensor Development

E-mail Barbara Goode

Plenty of engineering work is inspired by nature. But some of it—biosensor development, for instance—goes beyond inspiration and actually incorporates biological components. Interestingly, some of the folks doing that development indicate that biosensors are more reliable than man-made sensors.

From Macro to Micro
In his blog entry titled It Doesn't Have to Be that Complicated, Tom Kevan reported last week on a couple of macro-scale biosensor applications, including a system that uses fish to continuously monitor the public water supplies of New York City and San Francisco for contamination and potential terrorism incidents.

"Nature has provided us with an extremely powerful, reliable, and accurate early warning capability unmatched in any known man-made sensor," says Jeff Goodrich, CEO of Intelligent Automation Corp. (IAC), the company that set up the water-supply monitoring systems. Goodrich goes on to say that his system has yielded zero false positives and has received unanimous positive feedback.

Recent news on biosensors has focused mainly on micro-scale developments, though, and only time will tell whether these provide similar reliability.

One of them derives from macro-scale creatures: A substance found in crab shells is the key component in a nanoscale sensor system that researchers at the University of Maryland's A. James Clark School of Engineering are developing. The sensor can detect minute quantities of explosives, bioagents, chemicals, and other dangerous materials in air and water, potentially leading to security and safety innovations for airports, hospitals, and other public locations.

The substance, called chitosan (pronounced "kite-o-san"), is found in the shells of the Chesapeake Bay's famous blue crab, and researchers are using it to coat multiple miniature vibrating cantilevers within the MEMS device. Different cantilevers can detect different substances and concentrations. When a targeted substance enters the device from the air or water, the chitosan interacts with it and changes the vibration on the corresponding cantilever. An optical sensing system detects the change and signals the presence of the substance.

"This is an exciting and complex microsystem that bridges biotechnology and nanotechnology to address critical needs of homeland security applications," says Reza Ghodssi, one of the project's leaders. Ghodssi and his collaborators recently submitted a proposal to the National Institutes of Health to develop a sensor system to detect avian flu.

Porous Silicon to Improve Sensitivity
NanoSensors Inc., a nanotechnology company that develops instruments and sensors to detect explosives, chemicals, and biological agents, says that porous silicon serves to heighten sensitivity, and has begun to evaluate a generic biosensor design that will accommodate a sensor on a chip. The company is working up process details on how the sensor will detect specific agents. Prototypes will be completed by year-end and independent third-party testing will take place in Q1 2007.

According to NanoSensors CEO Dr. Ted Wong, "The company believes in the value of using porous silicon as a sensor substrate to vastly improve the sensitivity for the detection of targeted agents, and now with the [Michigan State University] license, the company will be able to build its first sensors using this platform." Wong is referring to NanoSensors' recent technology license agreement with Michigan State University, which gives it exclusive worldwide patent-pending rights to use for commercial purposes nanoporous silicon-based electrochemical DNA biosensors for detecting certain selected bacteria.

Bead-Based Flow Cytometry
Luminex Corp. has received a $300,000 research grant from the Defense Advanced Research Projects Agency (DARPA) that focuses on developing the company's emerging chip-scale technology (called xMAP) for bio-defense applications. The chip-scale concept is a new approach that leverages xMAP—a bead-based flow cytometry solution for multiplexing biological assays—to detect bio-pathogens on the scale of a microchip.

"A successful and practical solution for biosensors to combat terrorism will require a compact and relatively inexpensive detector capable of doing species identification with high sensitivity and specificity; that is precisely the goal of the chip-scale xMAP technology project," says Luminex vice president of research and development Dr. John Carrano.

Inherent Benefit?
Echoing the sentiments of Jeff Goodrich, the Swedish company Biosensor, which claims to detect both explosives and narcotics simultaneously on the molecular level, says its technology distinguishes itself by its "very high probability of detection in combination with low false alarm rates at use in the field."

Of course the micro-scale biosensors mentioned above include plenty of man-made components in addition to biological materials. But it will be interesting to see whether they produce a trend of increased reliability.

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