Miniature spectrometer with potential food applications

In the future, it could be possible to assess the decomposition of foods for consumption and recognise fake drugs via a miniature spectrometer integrated on a smartphone in a quick, cost-effective and straightforward way.

The process is being made possible by a chip spectrometer, weighing just one gram, from the Fraunhofer Institute for Electronic Nano Systems ENAS. The researchers aim is to mass-produce this component for around a euro (AU$1.58) using conventional technologies.

Current infrared spectrometers weigh several kilograms and cost thousands of dollars to produce. And although transportable devices weighing slightly less do exist, they are unsuitable for the mass market — in terms of cost and size and also in terms of operation and analysing the results.

“Our infrared spectrometer weighs only about a gram and we plan for it to cost less than a euro to produce,” said Dr Alexander Weiß, Head of Department Multi Device Integration at Fraunhofer ENAS. “This will allow it to be integrated into smartphones, for instance.”

Applications

The potential applications of the miniature spectrometer are by no means limited to recognising fake drugs. Other applications include:

• assessing the maturity or microbial decomposition of foods for human and animal consumption;
• measuring the air quality of interiors and vehicles for effective climate control;
• detecting pollutants in air, water or foodstuffs.

How does it work?

Just like conventional infrared spectrometers, the miniature spectrometer works by emitting light beams in the infrared range. The light of different wavelengths is then fragmented using a tunable filter and conducted to a detector by means of integrated waveguides.

Measurement set-up with wafer prober, optical fibre probes and wafer with test structures. Image credit: © Fraunhofer ENAS.

Grating couplers with nanostructures bundle the light reflected by, for example, a pill being tested into integrated waveguides.

If the air quality is to be tested, the light enters a special absorption cell integrated in one plane instead.

By plotting how much light reaches the detector at which wavelength, a characteristic spectrum for each sample is achieved, similar to a fingerprint.

For example, a fake pill with different ingredients will be detected as it has a different spectrum to that of the original drug.

“Conventional spectrometers usually consist of discrete, more or less well-integrated components. We, on the other hand, integrated the beam guidance, the splitting of the individual wavelengths and the detection function in one plane — we are therefore also calling this an inplane spectrometer,” Weiß explained.

If the spectrometer is to be capable of being integrated into smartphones, for example, the researchers had to think about more than just size. Operation must be easy and intuitive and the system must then provide the user with clear evaluations.

The researchers developed a concept: smart learning algorithms.

“If many people use the technology, the system will learn quickly,” Weiß said.

The user will simply need to pull out their phone, start the spectrometer via a special app and hold it over one of the products, for example, a pill. The user will also see an instruction that guides them through the measurement process.

The spectrometer generates the spectrum automatically and the software compares it to reference spectra entered into a database by specialists beforehand. The more people who come to use the system, the greater the possibility for making comparisons. The user sees only the result, “original drug”, for example.

Keeping the cost down

From the outset, the researchers kept the cost of producing the spectrometer in mind.

“We designed the spectrometer in a way that would allow it to be mass-produced inexpensively using conventional microsystems engineering technologies. Manufacturers can use the processes that are standard on the large fabrication lines, fabs for short,” Weiß explained.

The researchers have already produced the first spectrometer chips and provided proof of concept.

A number of different characterisations are now on the agenda and the equipment required for this has been financed by the Research Fab Microelectronics Germany.

If these investigations go as hoped, the spectrometer could be on its way to the mass market in around two years’ time.

Image credit: ©stock.adobe.com/au/pikselstock