MIT scientists develop quantum dot spectrometers for use in smart phones

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Scientists from the Massachusetts Institute of Technology (MIT) have developed quantum dot spectrometers that can be integrated inside a smart phone camera. The device, which was described in this month’s issue of Nature, could allow smart phone users to diagnose diseases, detect environmental pollutants, or determine the quality of the food they're about to buy.

Miniaturisation and better manufacturing methods have allowed for small, robust, and cost-effective spectrometers to carry out analysis without having to take samples to a laboratory. These miniature, portable instruments are widely used in a variety of applications, particularly for inspection, where the spectrometer is integrated into a processing line to inspect the quality of products. As miniaturisation and cost reductions continue, spectrometers are soon set to move into the consumer market.

The new MIT instrument is small enough to function within a smartphone, enabling portable light analysis for the consumer. The research also represents a new application for quantum dots, which up until now have been used primarily for labelling cells and biological molecules, as well as in computer and television screens.

‘Using quantum dots for spectrometers is such a straightforward application compared to everything else that we’ve tried to do, and I think that’s very appealing,’ said Moungi Bawendi, the Lester Wolfe Professor of Chemistry at MIT and the paper’s senior author.

The new quantum dot spectrometer, which is about the size of a US quarter coin, deploys hundreds of quantum dot materials that each filter a specific wavelength range. The quantum dot filters are printed into a thin film and placed on top of a photodetector, such as the charge-coupled devices (CCDs) found in smart phone cameras.

An algorithm created by the MIT team analyses the percentage of photons absorbed by each filter, and then recombines the information from each one to calculate the intensity and wavelength of the original rays of light.

The more quantum dot materials there are, the more wavelengths can be covered and the higher resolution can be obtained. In this case, the researchers used about 200 types of quantum dots spread over a range of about 300 nanometres. With more dots, such spectrometers could be designed to cover an even wider range of light frequencies.

If incorporated into small handheld devices, this type of spectrometer could be used to diagnose skin conditions or analyse urine samples, noted Jie Bao, a former MIT postdoc and the lead author of a paper. They could also be used to track vital signs, such as pulse and oxygen level, or to measure a person's exposure to different frequencies of ultraviolet light, which vary greatly in their ability to damage skin.

The manuafacturing process is also simple — the quantum dot filters — are generated by printing liquid droplets. This approach is advantageous in terms of flexibility, simplicity, and cost reduction, as other spectrometer approaches have complicated systems in order to create the optical structures needed.

‘The central component of such spectrometers — the quantum dot filter array — is fabricated with solution-based processing and printing, thus enabling significant potential cost reduction,’ added Bao.

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