Mini spectrometer could be integrated into smartphones

Researchers at the Fraunhofer Institute for Electronic Nano Systems ENAS are developing a chip spectrometer, weighing just one gram, that could be used for applications from drug testing to water sampling — all from a conventional smartphone.

At present, infrared spectrometers weigh several kilograms and cost thousands of dollars to produce. 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.

“Our spectrometer lends itself to all kinds of uses — such as 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, or detecting pollutants in air, water or foodstuffs.”

Just like conventional infrared spectrometers, the spectrometer works by emitting light beams in the infrared range. The light of different wavelengths is then fragmented using a tuneable filter and conducted to a detector by means of integrated waveguides. Grating couplers with nanostructures bundle the light reflected by a pill to be tested, for example, 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 have a different spectrum to that of the original drug.

“Conventional spectrometers usually consist of discrete more or less well-integrated components,” Dr Weiß said. “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.”

In order to make their spectrometer capable of integration into smartphones, the researchers had to think about more than size. Operation must be easy and intuitive, and the system must provide the user with clear evaluations. For this, the researchers developed the concept of smart learning algorithms.

“If many people use the technology, the system will learn quickly,” Dr Weiß said. The user will simply need to pull out their phone, start the spectrometer via a special app and hold it over a product such as a pill. They 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.

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,” Dr Weiß said. “Manufacturers can use the processes that are standard on the large fabrication lines, fabs for short.”

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

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