spaceSpace and Physics

LEDs Shed Light On Whether Food Is Going Bad


Stephen Luntz

Stephen has a science degree with a major in physics, an arts degree with majors in English Literature and History and Philosophy of Science and a Graduate Diploma in Science Communication.

Freelance Writer

let there be light

LEDs that tell you when the food in your fridge is getting close to going off allow us to feed a growing population without having to turn ever-more wilderness to agriculture. Image Credit: GC Images/

If you've ever cautiously sniffed food left at the back of your fridge wondering if it's still safe to eat, help could be on the way. Simple devices could soon tell you if you risk food poisoning by taking a bite. The same technology could help people decide whether it is safe to enter an enclosed space with suspicious smelling gas.

Every gas has a different spectral fingerprint, marking the wavelengths it absorbs when a broad part of the electromagnetic spectrum is shone through it. Almost everything we know about the composition of stars comes from analyzing similar spectra, and laboratories worldwide use infrared spectrometers to identify more Earthly materials.


Researchers pondered how useful it would be if such devices could be taken anywhere and used by anyone without having to return samples to the lab. Published in Nature, a team has demonstrated the capacity to identify gases such as methane and water vapor with materials small enough that they could be added to smart phones.

“Our 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 tuneable infrared LED that allows for the detection of multiple materials,” study author Professor Kenneth Crozier of the University of Melbourne said in statement.

Black phosphorus can be induced to release infrared radiation with wavelengths from 2.3-5.5 micrometers (55-130THz) depending on the strain it is placed under. That's broad enough that most relevant gases' absorption lines can be detected. The phosphorus replaces the need to use a variety of materials that collectively cover a large part of the spectrum, but whose combination makes for a bulky and expensive instrument.

Crozier sees abundant applications; “When pointed at a handbag, it could reveal whether the bag is made of real leather or a cheaper substitute,” he noted. Most dramatically, people like firefighters, miners, and even plumbers who sometimes encounter gases of unknown composition could find carrying a handy device like this a matter of life and death.


Perhaps the most important application of Crozier's work is the most apparently mundane. “The device placed inside a fridge could send a notification that meat is going off,” he said.

It is estimated that a third of the world's food is wasted, going bad or being consumed by pests between harvest and dinner plate. Cutting that is the most obvious way to feed a growing population without turning more land over to agriculture.

A surprising proportion of this waste food goes bad after reaching the consumer. The bacteria responsible release gases that this new sensor could detect, providing a reminder to eat the food before it is too late. The same sensors could give the all-clear to food that might otherwise be thrown out.



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