LEDs Shed Light on Whether Food is going Bad

If you’ve ever carefully sniffed the food behind your fridge, wondering if it’s still safe to eat, help may come along the way. If you are at risk of food poisoning with bites, simple devices can tell you soon. The same technology can help people decide whether it is safe to enter a confined space with suspicious smelling gas. Each gas has a different spectrum fingerprint; it identifies the wavelength when it is absorbed when a wide portion of the electromagnetic spectrum is illuminated through it.

What we know about the structure of stars comes from analyzing almost the same spectrum, and laboratories around the world use the infrared spectrum to detect more terrestrial matter. The researchers thought that such devices could be taken anywhere and anyone could use them without returning the samples to the lab. Published in Nature, a team has shown the ability to detect gases such as methane and water vapor that can be attached to smartphones with small enough materials.

Study author Professor Kenneth Crozier of the University of Melbourne said in a statement, “Our new technology encapsulates a thin layer of black phosphorus crystals in a flexible, plastic-like layer, allowing it to bend in such a way that the black phosphorus emits light of different wavelengths, creating a harmonious infrared LED that allows the detection of multiple materials.” Black phosphorus can be induced to release infrared radiation with wavelengths from 2.3-5.5 micrometers (55-130THz) on which it is pressed. It is wide enough that the most relevant gas absorption line can be identified.

Phosphorus replaces the need to use a variety of materials that collectively cover a large part of the spectrum, but the combination of which makes for a heavy and expensive device. Crozier sees lots of applications; “When pointing to a handbag, it can indicate whether the bag is made of genuine leather or a cheaper alternative.” 

Perhaps the most important application of Crozier’s work is the most seemingly mundane. “The device placed inside a fridge can send a notification that the meat is going off,” he said. It is estimated that one-third of the world’s food is wasted, spoiled, or eaten by insects between crops and dinner plates. This is the most obvious way to cut the growing population without turning it into agriculture.