Sugar Cube-Sized Spectrometer Inspects Foodstuffs

An inexpensive spectrometer no bigger than a sugar cube could soon help shoppers decide whether the quality of fruits, meats and cheese is suitable for purchase.

The novel device, developed at Fraunhofer Institute for Photonic Microsystems IPMS, can be installed into smartphones and used in grocery stores to determine the ripeness of a piece of fruit or the tenderness of a slab of meat. The application is based on a near-infrared spectrometer that measures the amount of water, sugar, starch, fat and protein present in products by “looking” several centimeters below the outer surface of the foodstuffs. For instance, it can detect whether the core of an apple is already rotting.

How does the device actually work, you ask? All you need to do is hold your smartphone near the product in question, activate the app, choose the food type from the menu, and voila, your device will tell you if that piece of fruit you’re eyeing has a high enough fructose content to deem it juicy enough to buy.

All of this is possible by shining a broad-bandwidth light onto the item being tested. The item will reflect various wavelengths of light in the near-infrared range with different intensities, resulting in a spectrum that tells scientists what amounts of which substances are present in foodstuffs.

Complete with integrated diffraction grating, grating drive, position detector and optical gaps, the spectrometer is much more compact than those currently on the market. (Image: ©Fraunhofer IPMS)

The Fraunhofer spectrometer is 30 percent smaller than a sugar cube, substantially more compact than its commercially available counterparts, which are about 350 times larger. The new devices also are inexpensive to make and are suitable for mass production.

“We expect spectrometers to develop in the same way that digital cameras did,” said Dr. Heinrich Grüger, who manages the business unit of Fraunhofer IPMS, where the system is being developed. “A camera that cost €500 ten years ago is far less capable than the ones you get virtually for free today in your cell phone.”

Conventional spectrometers are manufactured by assembling individual components: the mirrors, optical gaps, grating and detector each have to be put into place individually and properly aligned.

The Fraunhofer researchers instead manufacture the individual optical gaps and gratings directly onto silicon wafers, which are large enough to hold the components of several hundred spectrometers, enabling hundreds of near-infrared systems to be created at one time. The scientists stack the wafers containing the integrated components on top of the ones bearing the optical components, and then align and bind them, isolating them to form individual spectrometers. The resulting devices are more robust than their handmade counterparts.

The scientists are working on a corresponding infrastructure for the device say it could be ready for market launch within the next three to five years.

“We are developing intelligent algorithms that analyze the recorded spectrums immediately, compare them with the requirements and then advise the consumer whether or not to buy the item,” Grüger said. “This advice is based solely on quality features such as ripeness and water content. The system cannot carry out a microbiological or toxicological analysis.”

Aside from inspecting foodstuffs, the researchers are confident that the spectrometer could be used, for example, to detect forgeries or to verify whether a product is made of high-quality original materials or just a cheap knockoff. It also could reveal whether parts of a vehicle’s body has been repainted as well as test the contents of cosmetic creams and drugs.

A prototype of the spectrometer will be on display May 22-24 at Sensor + Test 2012 in Nuremberg.

For more information, visit: www.fraunhofer.de