Revolutionary LED Sensors Detect Food Spoilage and Lethal Gases

A smart device with an infrared light emitting diode (LED) that is tunable to different wavelengths of light could enable a refrigerator to tell when food is spoiled. The device could identify a suite of gases, potentially including lethal ones, improving the safety of firefighters, miners, the military, and plumbers.

Infrared (IR) spectrometers are common laboratory equipment that can identify different materials by analyzing their infrared signatures, which is invisible to the human eye. Just like an AM radio can be tuned to different frequencies of radio wave, IR spectrometers can be tuned to different wavelengths, giving a broad-spectrum analysis of a gas sample. However, these machines are bulky and expensive and not usually practical to take out of the laboratory and into the field.

The new technology bonds a thin layer of black phosphorus crystals to a flexible, plastic-like substrate, allowing it to be bent in ways that cause the black phosphorus to emit light of different wavelengths — essentially creating a tunable infrared LED that allows for the detection of multiple materials. The technology could fit inside smartphones and become part of everyday use.

For example, the bacteria found in meat release various gases as they multiply. The presence of these gases is a good indication that the meat is spoiling and is no longer fit for consumption. The device, placed inside a refrigerator, could send a notification that the meat is spoiling. When pointed at a handbag, for instance, it could reveal whether the bag is made of real leather or a cheaper substitute.

Current materials used for IR photodetectors and light emitting devices can be difficult to manufacture, in large part due to the need for multiple layers of perfectly linked crystals. The new black phosphorus technology requires just one layer, allowing the device to be flexible, giving it unique properties when bent.

The device could make the work of firefighters, miners, and the military safer, allowing them to identify potentially lethal gases from safe distances as the ultra-thin, ultra-light devices can be placed on small drones. Flying such a drone over a building fire could tell firefighters what dangers they face and equipment they’ll need.

The low-cost technology could also make its way into devices for use by plumbers and building managers. The IR photodetectors could be integrated into a camera so that cellphone screens could display gas leaks or emissions and determine what kind of gas it is.