While the human eye is impressive, it’s far from being the most advanced natural light sensor out there. “The eyes of the Mantis shrimp have 16 different types of cells, which are sensitive to ultra­violet light, visible, and near-infrared light,” says Kaylee Hakkel, member of the TU Eindhoven Photonics and Semi­conductor Nanophysics group. “And measuring the spectrum in the infrared is most interesting for appli­cations in industry and agriculture, but there’s one major issue – current near-infrared spectro­meters are just too big and expensive.” Hakkel and her colla­borators have solved this issue by developing a near-infrared sensor that fits onto a small chip.

Just like the eye of the Mantis shrimp, it’s got 16 different sensors – but they are all sensitive in the near-infrared. “Miniaturi­zation of the sensors while keeping costs low was a major challenge. So, we designed a new wafer-scale fabri­cation process to achieve this. It’s low-cost because we can produce multiple sensors at the same time, and it’s ready, right now, for use in practical appli­cations in the real world,” Hakkel adds. “The sensor chip is small and could even be embedded in future smartphones.”

Andrea Fiore, research lead from the Department of Applied Physics and the Eind­hoven Hendrik Casimir Institute, is delighted with their research team’s work. “We’ve been investi­gating this techno­logy for a number of years. And now we’ve success­fully integrated the spectral sensors on a chip, while also dealing with another key issue – efficient use of the data” Normally, when a sensor measures light, the generated signal is used to reconstruct the optical spectrum for the material. Sensing algorithms are then used to analyze the data. In this new approach, the researchers show that the step of spectral recon­struction isn’t needed. In other words, the signals generated by the sensors can be sent straight to the analysis algorithms. “This signi­ficantly simpli­fies the design require­ments for the device,” notes Fiore.

With the sensor in hand, the researchers then tested the sensor in a number of experiments, as explained by Maurangelo Petruz­zella, who is also working at the startup company Manti­Spectra. “We used the sensor to measure the nutritional properties of many materials including milk. Our sensor provided comparable accuracy in the prediction of fat content in milk as conven­tional spectro­meters. And then we used the sensor to classify different types of plastic.” The nutri­tional properties of milk determine its economic value, and the sensor has been proven to accurately measure these properties. In addition, these measure­ments could be used to monitor the cow’s overall health. Classification of plastic types using the sensor can help to optimize waste sorting processes.

“Besides these appli­cations, we anticipate that the sensor could be used for personalized health care, precision agriculture (monitoring the ripeness of fruit and vegetable for instance), process control, and lab-on-chip testing. We now have a full develop­ment kit available based on this techno­logy, the SpectraPod, that companies and research institutes are using to build their applications. And the great thing is that this sensor could even be commonplace in the smartphones of the future meaning that people could use it at home to check the quality of their food or check aspects of their health,” adds Petruz­zella.

And things are just starting to get exciting for Hakkel. Soon, she’ll be joining Petruz­zella at the startup company Manti­Spectra where they will strive to advance the sensor for more practical appli­cations. “I’m really excited to start working on the next phase of the sensor develop­ment with Manti­Spectra. This sensor could contribute to a cleaner environment and address food waste, appli­cations that are important for everyone.” (Source: TU Eindhoven)

Reference: K. D. Hakkel et al.: Integrated near-infrared spectral sensing, Nat. Commun. 13, 103 (2022); DOI: 10.1038/s41467-021-27662-1

Link: Hendrik Casimir Institute, Eindhoven University of Technology, Eindhoven, The Netherlands • Photonics and Semiconductor Nanophysics Group, Eindhoven University of Technology, Eindhoven, The Netherlands • MantiSpectra, Eindhoven, The Netherlands