Part of managing diabetes involves piercing a finger several times daily to monitor blood sugar levels. Attempts have been made for decades to find a suitable spectroscopic method to replace this invasive procedure for monitoring glucose with a painless one. A number of spectroscopic techniques, including near infrared (NIR), have shown promise, but now instrumental developments in Raman spectroscopy may offer a solution.

Two former graduate students at MIT’s George R. Harrison Spectroscopy Laboratory, Chae-Ryon Kong and Ishan Barman, detail in AIP Advances (doi: 10.1063/1.3646524) how to potentially reduce the overall size of this sensor. Their Raman spectrograph works by shining a low-powered laser though the thin fold of skin between the thumb and forefinger. Due to the inefficiency of Raman scattering, it is important to capture as many scattered photons as possible, then filter out everything but the Raman photons. Optical filters can do this, but they are only effective when the photons hit them within a narrow range of angles. Previous researchers have used a compound parabolic concentrator (CPC) for this purpose, yet it takes a very large CPC to achieve the high degree of collimation needed. Kong and Barman turned to a more compact mirror, a compound hyperbolic concentrator (CHC), which uses a lens to focus light into the necessary tight beam. “The new design is from five to 20 times smaller than if we used a CPC to achieve the same performance,” Kong said. This development is the first step toward making portable Raman spectroscopy possible. According to Ramachandra Dasari, the lab’s associate director, such portable Raman spectrographs could also be used to identify other blood chemical markers of disease, and to determine if biopsies contain cancerous tissue. The corresponding tests would take about one minute. The current prototype is the size of a shopping cart. “Our next step is to miniaturise this and make it portable,” he said. Dasari expects to build a portable prototype over the next couple of years.

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