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Smallest-yet spectrophotometer works at room temperature

Device for detecting visible and infrared light could soon fit into smartphones

by Laurel Oldach
November 3, 2022


A photograph shows a gloved hand holding a microchip on the tip of the index finger.
Credit: Oregon State University
A new spectrophotometer fits onto a microchip.

Researchers have miniaturized a spectrophotometer onto a single chip that can analyze any wavelength of visible light and part of the infrared spectrum (Science 2021, DOI: 10.1126/science.add8544). The device, the smallest that works at ambient temperatures, could see widespread uptake in portable instruments, according to its inventors.

Spectrophotometry is a longstanding staple of sample analysis. The technique entails measuring how much light of a particular wavelength passes through a sample or is emitted from it to determine its composition. Benchtop spectrophotometers have had to be large enough to house the optics to diffract light to numerous photodetectors. Smaller spectrophotometers, which separate light wavelengths computationally, are temperature sensitive and must be operated under cryogenic conditions.

The new device relies on the photovoltaic properties of a material made of two single-atomic-layer semiconductors: molybdenum disulfide and tungsten diselenide. A team led by Aalto University engineer Zhipei Sun applied a range of voltages to the device and shined either monochromatic or broad spectrum light on it from a laser. When light hit the material, it generated a current that depended on the incoming wavelengths and the voltage.

The researchers then trained an algorithm to recognize the currents caused by incoming light under different voltages and showed that a detector less than 200 µm2 can analyze broadband light with resolution and accuracy comparable to a benchtop machine.

The technology performs “well beyond the current state of the art” and might someday expand researchers’ insight into very far infrared wavelengths, Alberto Morpurgo, a physicist at the University of Geneva who was not involved in the study, says in an email.

The authors propose that their spectrophotometer chip could fit into smartphones, enabling field analyses such as detecting counterfeit drugs. The chip could also fit in drones, which could be used in large-scale processes such as monitoring crop growth. Study lead author Hoon Hahn Yoon, a postdoc at Aalto, says that the chip is fabricated with techniques widely used at semiconductor foundries, so “if a company wanted to implement our spectrometer… we expect that it might only take a few years.”



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