@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{saha_fang_yokus_mukherjee_bozkurt_daniele_dickey_velev_2021, title={A Wearable Patch for Prolonged Sweat Lactate Harvesting and Sensing}, ISSN={["1558-4615"]}, DOI={10.1109/EMBC46164.2021.9630881}, abstractNote={Operating at low sweat rates, such as those experienced by humans at rest, is still an unmet need for state-of-the-art wearable sweat harvesting and testing devices for lactate. Here, we report the on-skin performance of a non-invasive wearable sweat sampling patch that can harvest sweat at rest, during exercise, and post-exercise. The patch simultaneously uses osmosis and evaporation for long-term (several hours) sampling of sweat. Osmotic sweat withdrawal is achieved by skin-interfacing a hydrogel containing a concentrated solute. The gel interfaces with a paper strip that transports the fluid via wicking and evaporation. Proof of concept results show that the patch was able to sample sweat during resting and post-exercise conditions, where the lactate concentration was successfully quantified. The patch detected the increase in sweat lactate levels during medium level exercise. Blood lactate remained invariant with exercise as expected. We also developed a continuous sensing version of the patch by including enzymatic electrochemical sensors. Such a battery-free, passive, wearable sweat sampling patch can potentially provide useful information about the human metabolic activity.}, journal={2021 43RD ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE & BIOLOGY SOCIETY (EMBC)}, author={Saha, Tamoghna and Fang, Jennifer and Yokus, Murat A. and Mukherjee, Sneha and Bozkurt, Alper and Daniele, Michael A. and Dickey, Michael D. and Velev, Orlin D.}, year={2021}, pages={6863–6866} }
 @article{yokus_daniele_2021, title={Integrated non-invasive biochemical and biophysical sensing systems for health and performance monitoring: A systems perspective}, volume={184}, ISSN={["1873-4235"]}, DOI={10.1016/j.bios.2021.113249}, abstractNote={Advances in materials, bio-recognition elements, transducers, and microfabrication techniques, as well as progress in electronics, signal processing, and wireless communication have generated a new class of skin-interfaced wearable health monitoring systems for applications in personalized medicine and digital health. In comparison to conventional medical devices, these wearable systems are at the cusp of initiating a new era of longitudinal and noninvasive sensing for the prevention, detection, diagnosis, and treatment of diseases at the molecular level. Herein, we provide a review of recent developments in wearable biochemical and biophysical systems. We survey the sweat sampling and collection methods for biochemical systems, followed by an assessment of biochemical and biophysical sensors deployed in current wearable systems with an emphasis on their hardware specifications. Specifically, we address how sweat collection and sample handling platforms may be a rate limiting technology to realizing the clinical translation of wearable health monitoring systems; moreover, we highlight the importance of achieving both longitudinal sensing and assessment of intrapersonal variation in sweat-blood correlations to have the greatest clinical impact. Lastly, we assess a snapshot of integrated wireless wearable systems with multimodal sensing capabilities, and we conclude with our perspective on the state-of-the-art and the required developments to achieve the next-generation of integrated wearable health and performance monitoring systems.}, journal={BIOSENSORS & BIOELECTRONICS}, author={Yokus, Murat A. and Daniele, Michael A.}, year={2021}, month={Jul} }
 @article{hiraka_tsugawa_asano_yokus_ikebukuro_daniele_sode_2021, title={Rational design of direct electron transfer type L-lactate dehydrogenase for the development of multiplexed biosensor}, volume={176}, ISSN={["1873-4235"]}, DOI={10.1016/j.bios.2020.112933}, abstractNote={The development of wearable multiplexed biosensors has been focused on systems to measure sweat l-lactate and other metabolites, where the employment of the direct electron transfer (DET) principle is expected. In this paper, a fusion enzyme between an engineered l-lactate oxidase derived from Aerococcus viridans, AvLOx A96L/N212K mutant, which is minimized its oxidase activity and b-type cytochrome protein was constructed to realize multiplexed DET-type lactate and glucose sensors. The sensor with a fusion enzyme showed DET to a gold electrode, with a limited operational range less than 0.5 mM. A mutation was introduced into the fusion enzyme to increase Km value and eliminate its substrate inhibition to construct “b2LOxS”. Together with the employment of an outer membrane, the detection range of the sensor with b2LOxS was expanded up to 10 mM. A simultaneous lactate and glucose monitoring system was constructed using a flexible thin-film multiplexed electrodes with b2LOxS and a DET-type glucose dehydrogenase, and evaluated their performance in the artificial sweat. The sensors achieved simultaneous detection of lactate and glucose without cross-talking error, with the detected linear ranges of 0.5–20 mM for lactate and 0.1–5 mM for glucose, sensitivities of 4.1 nA/mM∙mm2 for lactate and 56 nA/mM∙mm2 for glucose, and limit of detections of 0.41 mM for lactate and 0.057 mM for glucose. The impact of the presence of electrochemical interferants (ascorbic acid, acetaminophen and uric acid), was revealed to be negligible. This is the first report of the DET-type enzyme based lactate and glucose dual sensing systems.}, journal={BIOSENSORS & BIOELECTRONICS}, author={Hiraka, Kentaro and Tsugawa, Wakako and Asano, Ryutaro and Yokus, Murat A. and Ikebukuro, Kazunori and Daniele, Michael A. and Sode, Koji}, year={2021}, month={Mar} }
 @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} }
 @misc{rivera_yokus_erb_pozdin_daniele_2019, title={Measuring and regulating oxygen levels in microphysiological systems: design, material, and sensor considerations}, volume={144}, ISSN={["1364-5528"]}, DOI={10.1039/c8an02201a}, abstractNote={Quantifying and regulating oxygen in a microphysiological models can be achievedviaan array of technologies, and is an essential component of recapitulating tissue-specific microenvironments.}, number={10}, journal={ANALYST}, author={Rivera, Kristina R. and Yokus, Murat A. and Erb, Patrick D. and Pozdin, Vladimir A. and Daniele, Michael}, year={2019}, month={May}, pages={3190–3215} }
 @article{yokus_jur_2016, title={Fabric-Based Wearable Dry Electrodes for Body Surface Biopotential Recording}, volume={63}, ISSN={["1558-2531"]}, DOI={10.1109/tbme.2015.2462312}, abstractNote={A flexible and conformable dry electrode design on nonwoven fabrics is examined as a sensing platform for biopotential measurements. Due to limitations of commercial wet electrodes (e.g., shelf life, skin irritation), dry electrodes are investigated as the potential candidates for long-term monitoring of ECG signals. Multilayered dry electrodes are fabricated by screen printing of Ag/AgCl conductive inks on flexible nonwoven fabrics. This study focuses on the investigation of skin-electrode interface, form factor design, electrode body placement of printed dry electrodes for a wearable sensing platform. ECG signals obtained with dry and wet electrodes are comparatively studied as a function of body posture and movement. Experimental results show that skin-electrode impedance is influenced by printed electrode area, skin-electrode interface material, and applied pressure. The printed electrode yields comparable ECG signals to wet electrodes, and the QRS peak amplitude of ECG signal is dependent on printed electrode area and electrode on body spacing. Overall, fabric-based printed dry electrodes present an inexpensive health monitoring platform solution for mobile wearable electronics applications by fulfilling user comfort and wearability.}, number={2}, journal={IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING}, author={Yokus, Murat A. and Jur, Jesse S.}, year={2016}, month={Feb}, pages={423–430} }
 @article{yokus_foote_jur_2016, title={Printed Stretchable Interconnects for Smart Garments: Design, Fabrication, and Characterization}, volume={16}, ISSN={["1558-1748"]}, DOI={10.1109/jsen.2016.2605071}, abstractNote={This paper explores stretchability and fatigue life of inexpensive printed stretchable interconnects for smart garments. Multilayer stretchable interconnects are created on a knit fabric by screen printing of Ag/AgCl conductive inks on thermoplastic polyurethane film (TPU). Heat lamination of this layer onto a knit fabric and its protective encapsulation with a second TPU layer yields a multilayer stretchable interconnect structure. Design and optimization of the printed meandering interconnects are performed experimentally. The effect of processing steps, area of substrate, and encapsulation layers on the electro-mechanical properties of the stretchable interconnects are investigated. Washing endurance of the printed lines is also explored. The meandering stretchable printed line demonstrates stretchability of over 100% strain and fatigue life of 1000 cycles at 20% strain. Washing endurance of 100 cycles is reported. This paper presents an inexpensive method of realization of electronics integration on textiles by maintaining textile comfort and wearability.}, number={22}, journal={IEEE SENSORS JOURNAL}, author={Yokus, Murat A. and Foote, Rachel and Jur, Jesse S.}, year={2016}, month={Nov}, pages={7967–7976} }
 @article{yokus_daniele_2016, title={Skin Hydration Sensor for Customizable Electronic Textiles}, volume={1}, ISSN={["2059-8521"]}, DOI={10.1557/adv.2016.540}, abstractNote={This paper introduces the design and simulated operation of a capacitive hydration sensor for integration into textile-based electronics. The multilayer patch is composed of a textile layer and an attached series of serpentine-interdigitated electrodes. The model used for simulations incorporated this design onto a representative model of skin. The serpentine-interdigitated electrodes are electrodes for capacitive measurement of skin hydration. In this study, the capacitance change relative to skin hydration was simulated using finite element analysis. The simulation results suggest the fabric layer had little effect on the capacitance of the sensor. Furthermore, the frequency domain simulations indicated that the capacitance of the sensor decreased with increasing frequency, and the decrease in capacitance was more significant for the dry skin compared to the wet skin. Therefore, the variation in the capacitance value of the serpentine-interdigitated electrodes can be employed for continuous skin hydration detection.}, number={38}, journal={MRS ADVANCES}, author={Yokus, Murat A. and Daniele, Michael A.}, year={2016}, pages={2671–2676} }
 @inproceedings{dieffenderfer_goodell_bent_beppler_jayakumar_yokus_jur_bozkurt_peden_2015, title={Wearable wireless sensors for chronic respiratory disease monitoring}, DOI={10.1109/bsn.2015.7299411}, abstractNote={We present a wearable sensor system consisting of a wristband and chest patch to enable the correlation of individual environmental exposure to health response for understanding impacts of ozone on chronic asthma conditions. The wrist worn device measures ambient ozone concentration, heart rate via plethysmography (PPG), three-axis acceleration, ambient temperature, and ambient relative humidity. The chest patch measures heart rate via electrocardiography (ECG) and PPG, respiratory rate via PPG, wheezing via a microphone, and three-axis acceleration. The data from each sensor is continually streamed to a peripheral data aggregation device, and is subsequently transferred to a dedicated server for cloud storage. The current generation of the system uses only commercially-off-the-shelf (COTS) components where the entire electronic structure of the wristband has dimensions of 3.1×4.1×1.2 cm3 while the chest patch electronics has a dimensions of 3.3×4.4×1.2 cm3. The power consumptions of the wristband and chest patch are 78 mW and 33 mW respectively where using a 400 mAh lithium polymer battery would operate the wristband for around 15 hours and the chest patch for around 36 hours.}, booktitle={2015 IEEE 12th International Conference on Wearable and Implantable Body Sensor Networks (BSN)}, author={Dieffenderfer, J. P. and Goodell, H. and Bent, B. and Beppler, E. and Jayakumar, R. and Yokus, M. and Jur, J. S. and Bozkurt, A. and Peden, D.}, year={2015} }