@article{saha_songkakul_knisely_yokus_daniele_dickey_bozkurt_velev_2022, title={Wireless Wearable Electrochemical Sensing Platform with Zero- Power Osmotic Sweat Extraction for Continuous Lactate Monitoring}, volume={7}, ISSN={["2379-3694"]}, url={https://doi.org/10.1021/acssensors.2c00830}, DOI={10.1021/acssensors.2c00830}, abstractNote={Wearable and wireless monitoring of biomarkers such as lactate in sweat can provide a deeper understanding of a subject's metabolic stressors, cardiovascular health, and physiological response to exercise. However, the state-of-the-art wearable and wireless electrochemical systems rely on active sweat released either via high-exertion exercise, electrical stimulation (such as iontophoresis requiring electrical power), or chemical stimulation (such as by delivering pilocarpine or carbachol inside skin), to extract sweat under low-perspiring conditions such as at rest. Here, we present a continuous sweat lactate monitoring platform combining a hydrogel for osmotic sweat extraction, with a paper microfluidic channel for facilitating sweat transport and management, a screen-printed electrochemical lactate sensor, and a custom-built wireless wearable potentiostat system. Osmosis enables zero-electrical power sweat extraction at rest, while continuous evaporation at the end of a paper channel allows long-term sensing from fresh sweat. The positioning of the lactate sensors provides near-instantaneous sensing at low sweat volume, and the custom-designed potentiostat supports continuous monitoring with ultra-low power consumption. For a proof of concept, the prototype system was evaluated for continuous measurement of sweat lactate across a range of physiological activities with changing lactate concentrations and sweat rates: for 2 h at the resting state, 1 h during medium-intensity exercise, and 30 min during high-intensity exercise. Overall, this wearable system holds the potential of providing comprehensive and long-term continuous analysis of sweat lactate trends in the human body during rest and under exercising conditions.}, journal={ACS SENSORS}, publisher={American Chemical Society (ACS)}, author={Saha, Tamoghna and Songkakul, Tanner and Knisely, Charles T. and Yokus, Murat A. and Daniele, Michael A. and Dickey, Michael D. and Bozkurt, Alper and Velev, Orlin D.}, year={2022}, month={Jul} }
 @article{songkakul_peterson_daniele_bozkurt_2021, title={Preliminary Evaluation of a Solar-Powered Wristband for Continuous Multi-Modal Electrochemical Monitoring}, ISSN={["1558-4615"]}, DOI={10.1109/EMBC46164.2021.9630105}, abstractNote={Continuous, non-invasive wearable measurement of metabolic biomarkers could provide vital insight into patient condition for personalized health and wellness monitoring. We present our efforts towards developing a wearable solar-powered electrochemical platform for multimodal sweat based metabolic monitoring. This wrist-worn wearable system consists of a flexible photovoltaic cell connected to a circuit board containing ultra low power circuitry for sensor data collection, energy harvesting, and wireless data transmission, all integrated into an elastic fabric wristband. The system continuously samples amperometric, potentiometric, temperature, and motion data and wirelessly transmits these to a data aggregator. The full wearable system is 7.5 cm long and 5 cm in diameter, weighs 22 grams, and can run directly from harvested light energy. Relatively low levels of light such as residential lighting (∼200 lux) are sufficient for continuous operation of the system. Excess harvested energy is stored in a small 37 mWh lithium polymer battery. The battery can be charged in ∼14 minutes under full sunlight and can power the system for ∼8 days when fully charged. The system has an average power consumption of 176 µW. The solar-harvesting performance of the system was characterized in a variety of lighting conditions, and the amperometric and potentiometric electrochemical capabilities of the system were validated in vitro.Clinical relevance—The presented solar-powered wearable system enables continuous wireless multi-modal electrochemical monitoring for uninterrupted sensing of metabolic biomarkers in sweat while harvesting energy from indoor lighting or sunlight.}, journal={2021 43RD ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE & BIOLOGY SOCIETY (EMBC)}, author={Songkakul, Tanner and Peterson, Kaila and Daniele, Michael and Bozkurt, Alper}, year={2021}, pages={7316–7319} }
 @article{songkakul_wu_ahmmed_reynolds_zhu_bozkurt_2021, title={Wearable Bioimpedance Hydration Monitoring System using Conformable AgNW Electrodes}, ISSN={["1930-0395"]}, url={http://dx.doi.org/10.1109/sensors47087.2021.9639469}, DOI={10.1109/SENSORS47087.2021.9639469}, abstractNote={Monitoring hydration level could be vital for maintaining physiological and cognitive performance during physical exertion and thermal stress. We present a custom miniaturized wearable bioimpedance spectroscopy (BIS) system consisting of a Bluetooth-enabled system-on-a-chip and an analog front-end circuit integrated with conformable, flexible, and stretchable silver-nanowire electrodes. This system is capable of performing four-electrode BIS at a range of frequencies between 5 kHz and 195 kHz, transmitting the data wirelessly to a data aggregator, and configuring the front-end circuit parameters over-the-air when needed. A 150 mAh lithium polymer battery can power the system for 18 hours. In this study, proof-of-concept in-vitro validation of the system generated promising results.}, journal={2021 IEEE SENSORS}, publisher={IEEE}, author={Songkakul, Tanner and Wu, Shuang and Ahmmed, Parvez and Reynolds, William D., Jr. and Zhu, Yong and Bozkurt, Alper}, year={2021} }
 @article{yokus_songkakul_pozdin_bozkurt_daniele_2020, title={Wearable multiplexed biosensor system toward continuous monitoring of metabolites}, volume={153}, ISSN={["1873-4235"]}, DOI={10.1016/j.bios.2020.112038}, abstractNote={Comprehensive metabolic panels are the most reliable and common methods for monitoring general physiology in clinical healthcare. Translation of this clinical practice to personal health and wellness tracking requires reliable, non-invasive, miniaturized, ambulatory, and inexpensive systems for continuous measurement of biochemical analytes. We report the design and characterization of a wearable system with a flexible sensor array for non-invasive and continuous monitoring of human biochemistry. The system includes signal conditioning, processing, and transmission parts for continuous measurement of glucose, lactate, pH, and temperature. The system can operate three discrete electrochemical cells. The system draws 15 mA under continuous operation when powered by a 3.7 V 150 mAh battery. The analog front-end of the electrochemical cells has four potentiostats and three multiplexers for multiplexed and parallel readout from twelve working electrodes. Utilization of redundant working electrodes improves the measurement accuracy of sensors by averaging chronoamperometric responses across the array. The operation of the system is demonstrated in vitro by simultaneous measurement of glucose and lactate, pH, and skin temperature. In benchtop measurements, the sensors are shown to have sensitivities of 26.31 μA mM−1·cm−2 for glucose, 1.49 μA mM−1·cm−2 for lactate, 54 mV·pH−1 for pH, and 0.002 °C-1 for temperature. With the custom wearable system, these values were 0.84 ± 0.03 mV μM−1·cm−2 or glucose, 31.87 ± 9.03 mV mM−1·cm−2 for lactate, 57.18 ± 1.43 mV·pH−1 for pH, and 63.4 μV·°C−1 for temperature. This miniaturized wearable system enables future evaluation of temporal changes of the sweat biomarkers.}, journal={BIOSENSORS & BIOELECTRONICS}, author={Yokus, Murat A. and Songkakul, Tanner and Pozdin, Vladimir A. and Bozkurt, Alper and Daniele, Michael A.}, year={2020}, month={Apr} }
 @article{starliper_mohammadzadeh_songkakul_hernandez_bozkurt_lobaton_2019, title={Activity-Aware Wearable System for Power-Efficient Prediction of Physiological Responses}, volume={19}, ISSN={["1424-8220"]}, url={https://doi.org/10.3390/s19030441}, DOI={10.3390/s19030441}, abstractNote={Wearable health monitoring has emerged as a promising solution to the growing need for remote health assessment and growing demand for personalized preventative care and wellness management. Vital signs can be monitored and alerts can be made when anomalies are detected, potentially improving patient outcomes. One major challenge for the use of wearable health devices is their energy efficiency and battery-lifetime, which motivates the recent efforts towards the development of self-powered wearable devices. This article proposes a method for context aware dynamic sensor selection for power optimized physiological prediction using multi-modal wearable data streams. We first cluster the data by physical activity using the accelerometer data, and then fit a group lasso model to each activity cluster. We find the optimal reduced set of groups of sensor features, in turn reducing power usage by duty cycling these and optimizing prediction accuracy. We show that using activity state-based contextual information increases accuracy while decreasing power usage. We also show that the reduced feature set can be used in other regression models increasing accuracy and decreasing energy burden. We demonstrate the potential reduction in power usage using a custom-designed multi-modal wearable system prototype.}, number={3}, journal={SENSORS}, author={Starliper, Nathan and Mohammadzadeh, Farrokh and Songkakul, Tanner and Hernandez, Michelle and Bozkurt, Alper and Lobaton, Edgar}, year={2019}, month={Feb} }