25 February 2010 Accurate glucose detection in a small etalon
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Abstract
We are developing a continuous glucose monitor for subcutaneous long-term implantation. This detector contains a double chamber Fabry-Perot-etalon that measures the differential refractive index (RI) between a reference and a measurement chamber at 850 nm. The etalon chambers have wavelength dependent transmission maxima which dependent linearly on the RI of their contents. An RI difference of ▵n=1.5·10-6 changes the spectral position of a transmission maximum by 1pm in our measurement. By sweeping the wavelength of a single-mode Vertical-Cavity-Surface-Emitting-Laser (VCSEL) linearly in time and detecting the maximum transmission peaks of the etalon we are able to measure the RI of a liquid. We have demonstrated accuracy of ▵n=±3.5·10-6 over a ▵n-range of 0 to 1.75·10-4 and an accuracy of 2% over a ▵nrange of 1.75·10-4 to 9.8·10-4. The accuracy is primarily limited by the reference measurement. The RI difference between the etalon chambers is made specific to glucose by the competitive, reversible release of Concanavalin A (ConA) from an immobilized dextran matrix. The matrix and ConA bound to it, is positioned outside the optical detection path. ConA is released from the matrix by reacting with glucose and diffuses into the optical path to change the RI in the etalon. Factors such as temperature affect the RI in measurement and detection chamber equally but do not affect the differential measurement. A typical standard deviation in RI is ±1.4·10-6 over the range 32°C to 42°C. The detector enables an accurate glucose specific concentration measurement.
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Joerg Martini, Joerg Martini, Sebastian Kuebler, Sebastian Kuebler, Michael Recht, Michael Recht, Francisco Torres, Francisco Torres, Jeffrey Roe, Jeffrey Roe, Peter Kiesel, Peter Kiesel, Richard Bruce, Richard Bruce, } "Accurate glucose detection in a small etalon", Proc. SPIE 7572, Optical Diagnostics and Sensing X: Toward Point-of-Care Diagnostics, 757206 (25 February 2010); doi: 10.1117/12.842532; https://doi.org/10.1117/12.842532
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