BACKGROUND: A chemical engineer at Drexel University has developed a handheld, simple to use sensor that can quickly spot contamination by deadly strains of the E coli or by listeria, helping food producers find out whether their products are have dangerous amounts of E coli or Listeria before they are shipped out to consumers. It can also detect other food pathogens, as well as anthrax in liquid and air, cryptosporin in drinking water, and endotoxins in pharmaceuticals. It could also be used to detect early cancer signatures in urine and blood. Detecting E. coli can take 24 hours or more with conventional tests. The Drexel device can detect the presence of E. coli within 10 minutes.
HOW IT WORKS: The device works by detecting how the presence of just a few E. coli cells changes the vibration of a miniature glass beam. The sensor is a sliver of glass fixed at one end, and on the other end a layer of a ceramic that changes shape when it is electrified. The glass sliver is then coated with antibodies to E. coli. An alternating voltage is then applied to the ceramic layer, causing it to expanding and contract. The glass sliver vibrates in response, and that vibration is strongest in the sliver's natural resonance frequency. As E. coli binds to the antibodies, the frequency of the up-and-down motion changes. That way, the engineers can spot high concentrations of E. coli.
UNDER PRESSURE: Pressure sensors date back to the advent of the steam engine. They are still used to daily monitor the pressure of fluids in pipes, engines, hydraulics, or in nature to determine the depth of an ice pack, for example, of the density of a rock layer. They exploit a phenomenon known as piezoresistance: pressure causes a piezoelectric material, like quartz or ceramic, to conduct electricity; the intensity of the current corresponds to how much pressure is being applied. This charge is detected and recorded by a computer and displayed for analysis by scientists.
WHAT ARE MEMS: Microelectro-mechanical systems (MEMs) integrate electronic and moving parts onto a microscopic silicon chip, making them ideal for new sensor technology. The term MEMS was coined in the 1980s. A MEMS device is usually only a few micrometers wide; for comparison, a human hair is 50 micrometers wide. Among other everyday applications, MEMS-based sensors are used in cars to detect the sudden motion of a collision and trigger release of the airbag. They are also found in ink-jet printers, blood pressure monitors, and projection display systems.
The American Society for Microbiology contributed to the information contained in the TV portion of this report.