SiPM-based Fiber Photometry and EIS for Cortisol Detection: Common Electronics, Distinct Applications
Date
2024-01-25
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Abstract
This thesis introduces two biomedical measurement systems utilizing the AD5934 impedance converter: a silicon photomultiplier (SiPM)-based low-light fiber photometry system for neural recordings in mice and a wireless electrochemical impedance spectroscopy (EIS) device designed for cortisol detection in human sweat. Despite their apparent differences, both systems share a common foundation—the AD5934 impedance converter chip, generating sinusoidal excitation signals and measuring corresponding system responses. Our fiber photometry system utilizes an SiPM as an alternative photodetector, addressing the power and sensitivity limitations of conventional counterparts. Additional optical excitation at an isosbestic point, often used for mitigating motion artifacts, was also used to correct for SiPM gain variations. Employing two impedance converters enables amplitude modulation with two carriers, which allows for distinguishing the main signal from the isosbestic control signal. Characterization tests confirmed the system's robustness to motion artifacts and temperature variations. In-vivo experiments demonstrated the system's functionality at significantly lower optical excitation powers comparing to commercial fiber photometry systems. In the EIS device, the AD5934 was used for its originally intended purpose of impedance spectroscopy. When used with a cortisol immunosensor, it can determine the concentration of cortisol in a sample by measuring its impedance at a range of frequencies. The device has a compact form-factor, and is wireless and battery-powered. Adaptive gain control was implemented to enhance the device's dynamic range. Characterization tests on resistors, capacitors, and electrochemical samples, and comparative experiments against a commercial potentiostat validated the system's suitability for cortisol concentration measurement. The device showed promise for adaptation into a wearable device for daily semi-continuous cortisol monitoring. The SiPM-based fiber photometry system and the compact EIS device stand as successful implementations of two biomedical measurement systems that benefit from the use of the AD5934 impedance converter chip. These two projects demonstrate the versatility of the AD5934 impedance converter, and meet their individual aims.
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Keywords
Electrochemical Impedance Spectroscopy, Fiber Photometry, Neural recording, Cortisol detection, GCaMP, Fluorescence
Citation
Namazi, M. (2024). SiPM-based fiber photometry and EIS for cortisol detection: common electronics, distinct applications (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.