Sensor reveals steak freshness

Michael D. Wheeler

SWANSEA, UK -- Scientists have developed an inexpensive thin-film oxygen sensor with emission bands in the visible region that fluoresces under a simple UV light source. The sensor could have widespread applications in detecting oxygen contamination of vacuum-sealed foods, environmental monitoring and clinical diagnostics.
Most entries in the optical sensor field in the last few years detect fluorescence -- luminescence that is caused by the absorption of radiation at one wavelength followed by reradiation at a different wavelength.

The sensor could find its way into packages of frozen meats or other vacuum-sealed products. Consumers will be able to scan packages quickly with a light-emitting diode or black light bulb to ensure that meat is fresh.

Lately, attention has turned to phosphoresence sensors, differing slightly from fluorescence sensors by exhibiting luminescence that continues even after incident radiation stops. They have several inherent advantages over fluorescence sensors including longer excited-state lifetimes and emission wavelengths more compatible with existing monitoring technology.
One researcher who followed the trend toward phosphoresence sensors is Andrew Mills of the University of Swansea's department of chemistry. Mills set about incorporating minuscule amounts of two gold compounds into a thin plastic film. To his delight, the sensor worked. Viewed under a UV light, the strip indicates the presence of oxygen. It glows a bright pink if the gas is present and remains colorless in its absence. The sensor also is inexpensive.

Researcher finds gold
"When you talk about gold, platinum or palladium it sounds very expensive, but we use them in such small amounts -- 10ths or 100ths of a milligram," Mills said. "The most expensive thing is the piece of glass or plastic [that encapsulates the compounds]."
Furthermore, the sensor withstands temperature changes and resists photobleaching. It also detects dissolved oxygen in nonaqueous solutions such as blood and ethanol.
The sensors' success has led Mills to team up with UK-based Food Packaging Division Ltd. to bring a version of his prototype to the marketplace. The sensor could find its way into packages of frozen meats or other vacuum-sealed products. Consumers will be able to scan packages quickly with a light-emitting diode or black light bulb to ensure that meat is fresh.