Dr. Michael I. Recht Profile

Dr. Michael I. Recht

at Palo Alto Research Ctr

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Proceedings Article | 7 March 2019 Paper

High-throughput droplet-based microfluidic optical calorimeter

Michael Recht, Jacob Chamoun, Ashish Pattekar, Joerg Martini

Proceedings Volume 10895, 108950M (2019) https://doi.org/10.1117/12.2511764

KEYWORDS: Temperature metrology, Microfluidics, Calorimetry, Luminescence, Reflectivity, Calcium, Optical testing, Sensors, Microscopes, Liquid crystals

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Calorimetry is a powerful label-free technique for characterizing biochemical interactions. However, conventional calorimeters are limited by large sample requirements and low throughput, relegating their use to a limited number of high-value measurements. To increase the throughput and sensitivity of calorimetry, we have developed a novel microfluidic calorimeter that uses optical methods to measure the temperature change caused by reactions occurring in sub-nanoliter droplets. In this calorimeter, a microfluidic system creates a mixed droplet of reactants, a thermochromic liquid crystal (TLC) reporter converts the temperature change to a spectral shift, and a sensitive optical detector measures the spectral shift. Experimental measurements of the temperature change induced in droplets by the exothermic binding of EDTA to Ca²⁺ show good agreement with a thermal multiphysics model. Our ongoing work to improve the microfluidic mixing of reactants and increase the temperature resolution of the calorimeter has yielded a temperature resolution for this calorimeter of 2.4 mK, which corresponds to an energy resolution of 16 nJ. This resolution is on the same order as commercial isothermal titration calorimeter (ITC) systems and 10-fold better than most nanocalorimeters.

Proceedings Article | 26 February 2010 Paper

Accurate glucose detection in a small etalon

Joerg Martini, Sebastian Kuebler, Michael Recht, Francisco Torres, Jeffrey Roe, Peter Kiesel, Richard Bruce

Proceedings Volume 7572, 757206 (2010) https://doi.org/10.1117/12.842532

KEYWORDS: Glucose, Fabry–Perot interferometers, Sensors, Mirrors, Reflectivity, Vertical cavity surface emitting lasers, Refractive index, Diffusion, Blood, Liquids

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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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