Research

Core strengths of the Bioelectronic Systems Lab.

System-level implementation of wearables, implantables, and ingestibles for precision health and psychiatry.

Projects

Biophotonic devices

Oximetry, the technique for determining oxygen saturation, optically measures the light absorption of oxygenated and deoxygenated blood and tissue. In 2014, we demonstrated the first all-organic optoelectronic oximeter sensor composed of organic light-emitting diodes (OLEDs) and an organic photodiode (OPD)[1]. After optimizing the sensor design and the printing process, in 2017, we reported a reflection-mode organic oximeter probe and performed blood oxygenation measurements on the wrist [2], [3]. In our most recent work, we demonstrate a flexible reflectance oximeter array (ROA) composed of printed OLEDs and OPDs. Due to the mechanical flexibility, 2D oxygenation mapping capability, and the ability to place the sensor in various locations, the ROA is promising for novel medical sensing applications such as mapping oxygenation in tissues, wounds, or transplanted organs (missing reference). We also reported an organic ambient light oximeter that does not require any controlled light source, which drastically reduces power consumption [4].

Publications:
[1] C. Lochner*, Y. Khan*, A. Arias, Nat. Commun., 2014.
[2] D. Han, Y. Khan, A. Arias, Adv. Mater., 2017.
[3] Y. Khan, A. Arias, IEEE Access 2019.
[5] Y. Khan, A. Arias, PNAS 2018.
[4] D. Han, Y. Khan, A. Arias, Adv. Mater. Technol., 2020.

Bioelectronic devices

Bioelectronic interfaces require electrodes that are mechanically flexible and chemically inert. Flexibility allows pristine electrode contact to skin and tissue, and chemical inertness prevents electrodes from reacting with biological fluids and living tissues. Utilizing the versatility of printing and plastic electronic processes, we fabricated electrode arrays for impedance mapping of conformal surfaces[6]. A more direct application of the array was to non-invasively map pressure-induced tissue damage. Our results demonstrated the feasibility of an automated, non-invasive “smart bandage” for early detection of pressure ulcers [7].

Publications:
[6] Y. Khan, A. Arias, Adv. Funct. Mater., 2016.
[7] S. Swisher, Y. Khan, A. Arias, M. Maharbiz, Nat. Commun., 2015.

Biochemical devices

Biochemical sensors can monitor ions, metabolites, hormones, proteins, and peptides in bodily fluids such as sweat, saliva, and tear. For obtaining an overall snapshot of a person’s physiological state, assessing analytes in bodily fluids is essential [8].

Publications:
[8] A. Zamarayeva, Y. Khan, A. Arias, APL Mater., 2020.

Additive manufacturing

Printing is currently a commercially viable manufacturing technology for fabricating electronics, mainly due to the recent advances in printable metallic, insulating, and semiconducting materials and mature printing techniques. While initial efforts in printed electronics were directed toward display and lighting industries, printed electronics now spans electronic devices, sensors, and even circuits with applications in energy, health, and consumer electronics. In industry and academia, both passive and active electronic devices are manufactured using inkjet printing, screen printing, gravure printing, blade coating, spray coating, and other hybrid printing methods [6], [2], [9].

Publications:
[6] Y. Khan, A. Arias, Adv. Funct. Mater., 2016.
[2] D. Han, Y. Khan, A. Arias, Adv. Mater., 2020.
[9] D. Han, Y. Khan, A. Arias, Adv. Funct. Mater., 2020.

Flexible hybrid electronics

Flexible hybrid electronics (FHE) are a fundamental enabling technology for system-level implementation of novel printed and flexible devices. FHE bring together soft and hard electronics into a single platform, where the soft devices are used for conformal sensor interfaces, and the hard silicon-based devices provide the computational backbone and compatibility with existing electronic systems and standards. The interfacing of soft and hard electronics is a key challenge for flexible hybrid electronics. For a project in collaboration with Binghamton University, i3 Electronics, Lockheed Martin, and American Semiconductor, we demonstrated a single substrate interfacing approach, where soft devices, i.e., sensors, are directly printed on Kapton polyimide substrates that are widely used for fabricating flexible printed circuit boards (FPCBs). Utilizing a process flow compatible with the FPCB assembly process, a wearable sensor patch was fabricated composed of inkjet-printed gold ECG electrodes and a stencil-printed nickel oxide thermistor [10].

Publications:
[10] Y. Khan, A. Arias, Adv. Funct. Mater., 2016.
[11] Y. Khan, A. Arias, Adv. Mater., 2019.

Hardware AI

The human brain is extremely efficient at pattern recognition and classification tasks compared to conventional Von Neumann computer architectures. Machine learning algorithms that mimic the biological process of the brain utilizing Hebbian learning is promising for wearable sensor systems as they allow faster and more agile parallel processing of the sensor data. Wearable and implantable sensors, and the area of flexible electronics can greatly benefit from near- and in-sensor data classification. We use both rigid silicon integrated circuits (ICs) and organic electronics for implementing machine learning algorithms in wearable and implantable sensors [12].

Publications:
[12] A. Moin, Y. Khan, A. Arias, J. Rabaey, Nat. Electron., 2020.

Wearables

A skin-like flexible and wearable sensor patch, seamlessly measuring body’s vital signs - realizing this device is a major goal of my doctoral and Postdoctoral work.

Wearable and flexible sensors are promising for medical sensing because they provide an improved signal-to-noise ratio (SNR) by establishing a conformal skin-sensor interface [13]. Moreover, in my work, printing techniques are used to fabricate the sensors, which ensures large-area scaling of the devices. Additionally with the rapid prototyping capability of printing, the sensors can be designed in different sizes and shapes, accommodating the needs of a diverse population.

Publications:
[13] Y. Khan, A. Arias, Adv. Mater., 2016.

References:

  1. All-organic optoelectronic sensor for pulse oximetry Claire M Lochner*, Yasser Khan*, Adrien Pierre*, and Ana C Arias Nature communications, 2014 5, *Equal contribution. Media coverage: UC Berkeley Grad News, NSF Science 360 News, UC Berkeley News Center, Phys.Org, ScienceDaily, MSN News, Yahoo News, and many more.

    Pulse oximetry is a ubiquitous non-invasive medical sensing method for measuring pulse rate and arterial blood oxygenation. Conventional pulse oximeters use expensive optoelectronic components that restrict sensing locations to finger tips or ear lobes due to their rigid form and area-scaling complexity. In this work, we report a pulse oximeter sensor based on organic materials, which are compatible with flexible substrates. Green (532 nm) and red (626 nm) organic light-emitting diodes (OLEDs) are used with an organic photodiode (OPD) sensitive at the aforementioned wavelengths. The sensor’s active layers are deposited from solution-processed materials via spin-coating and printing techniques. The all-organic optoelectronic oximeter sensor is interfaced with conventional electronics at 1 kHz and the acquired pulse rate and oxygenation are calibrated and compared with a commercially available oximeter. The organic sensor accurately measures pulse rate and oxygenation with errors of 1% and 2%, respectively.

    @article{lochner2014all, title = {All-organic optoelectronic sensor for pulse oximetry}, author = {Lochner*, Claire M and Khan*, Yasser and Pierre*, Adrien and Arias, Ana C}, journal = {Nature communications}, volume = {5}, pages = {5745}, year = {2014}, publisher = {Nature Publishing Group}, url = {http://dx.doi.org/10.1038/ncomms6745}, doi = {10.1038/ncomms6745}, thumbnail = {lochner2014all.png}, pdf = {lochner2014all.pdf}, note = {*Equal contribution. Media coverage: }, media_1 = {UC Berkeley Grad News, }, media_1_link = {http://grad.berkeley.edu/news/headlines/engineering-team-invents-medical-sensor/}, media_2 = {NSF Science 360 News, }, media_2_link = {http://news.science360.gov/obj/story/d8f7fa4c-4e41-4bcb-8ccd-1939dc4af3da/organic-electronics-lead-cheap-wearable-medical-sensors}, media_3 = {UC Berkeley News Center, }, media_3_link = {http://newscenter.berkeley.edu/2014/12/10/organic-electronics-cheap-wearable-medical-sensors/}, media_4 = {Phys.Org, }, media_4_link = {http://phys.org/news/2014-12-electronics-cheap-wearable-medical-sensors.html}, media_5 = {ScienceDaily, }, media_5_link = {https://www.sciencedaily.com/releases/2014/12/141210131356.htm}, media_6 = {MSN News, }, media_6_link = {https://www.msn.com/en-us/news/technology/is-the-next-fitbit-a-tattoo/ar-BBHIYih}, media_7 = {Yahoo News, }, media_7_link = {https://in.news.yahoo.com/device-cheap-wearable-fitness-sensors-081008659.html}, media_8 = {and many more.}, media_8_link = {https://www.altmetric.com/details/2972740} }

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  1. Flexible blade-coated multicolor polymer light-emitting diodes for optoelectronic sensors Donggeon Han, Yasser Khan, Jonathan Ting, Simon M King, Nir Yaacobi-Gross, Martin J Humphries, Christopher J Newsome, and Ana C Arias Advanced Materials, 2017 29, 22.

    A method to print two materials of different functionality during the same printing step is presented. In printed electronics, devices are built layer by layer and conventionally only one type of material is deposited in one pass. Here, the challenges involving printing of two emissive materials to form polymer light-emitting diodes (PLEDs) that emit light of different wavelengths without any significant changes in the device characteristics are described. The surface-energy-patterning technique is utilized to print materials in regions of interest. This technique proves beneficial in reducing the amount of ink used during blade coating and improving the reproducibility of printed films. A variety of colors (green, red, and near-infrared) are demonstrated and characterized. This is the first known attempt to print multiple materials by blade coating. These devices are further used in conjunction with a commercially available photodiode to perform blood oxygenation measurements on the wrist, where common accessories are worn. Prior to actual application, the threshold conditions for each color are discussed, in order to acquire a stable and reproducible photoplethysmogram (PPG) signal. Finally, based on the conditions, retrieved PPG and oxygenation measurements are successfully performed on the wrist with green and red PLEDs.

    @article{han2017flexible, title = {Flexible blade-coated multicolor polymer light-emitting diodes for optoelectronic sensors}, author = {Han, Donggeon and Khan, Yasser and Ting, Jonathan and King, Simon M and Yaacobi-Gross, Nir and Humphries, Martin J and Newsome, Christopher J and Arias, Ana C}, journal = {Advanced Materials}, volume = {29}, number = {22}, pages = {1606206}, year = {2017}, publisher = {Wiley Online Library}, url = {http://dx.doi.org/10.1002/adma.201606206}, doi = {10.1002/adma.201606206}, thumbnail = {han2017flexible.png}, pdf = {han2017flexible.pdf} }

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  1. Organic Multi-Channel Optoelectronic Sensors for Wearable Health Monitoring Yasser Khan, Donggeon Han, Jonathan Ting, Maruf Ahmed, Ramune Nagisetty, and Ana C. Arias. IEEE Access, 2019 , .

    Recent progress in printed optoelectronics and their integration in wearable sensors have created new avenues for research in reflectance photoplethysmography (PPG) and oximetry. The reflection-mode sensor, which consists of light emitters and detectors, is a vital component of reflectance oximeters. Here, we report a systematic study of the reflectance oximeter sensor design in terms of component geometry, light emitter and detector spacing, and the use of an optical barrier between the emitter and the detector to maximize sensor performance. Printed red and near-infrared (NIR) organic light-emitting diodes (OLEDs) and organic photodiodes (OPDs) are used to design three sensor geometries: (1) Rectangular geometry, where square OLEDs are placed at each side of the OPD; (2) Bracket geometry, where the OLEDs are shaped as brackets and placed around the square OPD; (3) Circular geometry, where the OLEDs are shaped as block arcs and placed around the circular OPD. Utilizing the bracket geometry, we observe 39.7% and 18.2% improvement in PPG signal magnitude in the red and NIR channels compared to the rectangular geometry, respectively. Using the circular geometry, we observe 48.6% and 9.2% improvements in the red and NIR channels compared to the rectangular geometry. Furthermore, a wearable two-channel PPG sensor is utilized to add redundancy to the measurement. Finally, inverse-variance weighting and template matching algorithms are implemented to improve the detection of heart rate from the multi-channel PPG signals.

    @article{khan2019organic, author = {Khan, Yasser and Han, Donggeon and Ting, Jonathan and Ahmed, Maruf and Nagisetty, Ramune and Arias., Ana C.}, title = {Organic Multi-Channel Optoelectronic Sensors for Wearable Health Monitoring}, journal = {IEEE Access}, volume = {}, number = {}, pages = {}, year = {2019}, publisher = {IEEE}, url = {http://dx.doi.org/10.1109/ACCESS.2019.2939798}, doi = {10.1109/ACCESS.2019.2939798}, thumbnail = {khan2019organic.png}, pdf = {khan2019organic.pdf} }

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  1. A flexible organic reflectance oximeter array Yasser Khan, Donggeon Han, Adrien Pierre, Jonathan Ting, Xingchun Wang, Claire M Lochner, Gianluca Bovo, Nir Yaacobi-Gross, Chris Newsome, Richard Wilson, and Ana C Arias Proceedings of the National Academy of Sciences, 2018 115, 47. Media coverage: Physics World, UC Berkeley News Center, KCBS Radio, Innovators Magazine, The Engineer (UK), Medgadget, ScienceDaily, and many more.

    Transmission-mode pulse oximetry, the optical method for determining oxygen saturation in blood, is limited to only tissues that can be transilluminated, such as the earlobes and the fingers. The existing sensor configuration provides only single-point measurements, lacking 2D oxygenation mapping capability. Here, we demonstrate a flexible and printed sensor array composed of organic light-emitting diodes and organic photodiodes, which senses reflected light from tissue to determine the oxygen saturation. We use the reflectance oximeter array beyond the conventional sensing locations. The sensor is implemented to measure oxygen saturation on the forehead with 1.1% mean error and to create 2D oxygenation maps of adult forearms under pressure-cuff–induced ischemia. In addition, we present mathematical models to determine oxygenation in the presence and absence of a pulsatile arterial blood signal. The mechanical flexibility, 2D oxygenation mapping capability, and the ability to place the sensor in various locations make the reflectance oximeter array promising for medical sensing applications such as monitoring of real-time chronic medical conditions as well as postsurgery recovery management of tissues, organs, and wounds.

    @article{khan2018flexible, title = {A flexible organic reflectance oximeter array}, author = {Khan, Yasser and Han, Donggeon and Pierre, Adrien and Ting, Jonathan and Wang, Xingchun and Lochner, Claire M and Bovo, Gianluca and Yaacobi-Gross, Nir and Newsome, Chris and Wilson, Richard and Arias, Ana C}, journal = {Proceedings of the National Academy of Sciences}, volume = {115}, number = {47}, pages = {E11015--E11024}, year = {2018}, publisher = {National Academy of Sciences}, url = {http://dx.doi.org/10.1073/pnas.1813053115}, doi = {10.1073/pnas.1813053115}, thumbnail = {khan2018flexible.png}, pdf = {khan2018flexible.pdf}, note = {Media coverage: }, media_1 = {Physics World, }, media_1_link = {https://physicsworld.com/a/flexible-sensor-maps-blood-oxygen-levels/}, media_2 = {UC Berkeley News Center, }, media_2_link = {https://news.berkeley.edu/2018/11/07/skin-like-sensor-maps-blood-oxygen-levels-anywhere-in-the-body/}, media_3 = {KCBS Radio, }, media_3_link = {https://omny.fm/shows/kcbsam-on-demand/uc-berkeley-research-shows-new-sensor-detects-oxyg}, media_4 = {Innovators Magazine, }, media_4_link = {https://www.innovatorsmag.com/wearable-monitors-blood-oxygen-levels/}, media_5 = {The Engineer (UK), }, media_5_link = {https://www.theengineer.co.uk/flexible-oximeter-blood-oxygen/}, media_6 = {Medgadget, }, media_6_link = {https://www.medgadget.com/2018/11/flexible-led-sensor-monitors-blood-oxygenation-levels-through-skin.html}, media_7 = {ScienceDaily, }, media_7_link = {https://www.sciencedaily.com/releases/2018/11/181107172917.htm}, media_8 = {and many more.}, media_8_link = {https://www.altmetric.com/details/50956419} }

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  1. Pulse Oximetry Using Organic Optoelectronics under Ambient Light Donggeon Han, Yasser Khan, Jonathan Ting, Juan Zhu, Craig Combe, Andrew Wadsworth, Iain McCulloch, and Ana C. Arias Advanced Materials Technologies, 2020 n/a, n/a.

    Light absorption in oxygenated and deoxygenated blood varies appreciably over the visible and near-infrared spectrum. Pulse oximeters use two distinct wavelengths of light to measure oxygen saturation SpO2 of blood. Currently, light-emitting diodes (LEDs) are used in oximeters, which need additional components to drive them and negatively impact the overall size of the sensor. In this work, an ambient light oximeter (ALO) is demonstrated, which can measure photoplethysmography signals and SpO2 using various kinds of ambient light, avoiding the use of LEDs. Spectral filters are combined with organic photodiodes to create the ALO with sensitivity peaks at green (525 nm), red (610 nm), and near-infrared (740 nm) wavelengths. Finally, the wearable ALO is used to measure photoplethysmography signals and SpO2 on the index finger in different indoor and outdoor lighting conditions and the measurements are validated with commercial pulse oximeters under normal and ischemic conditions.

    @article{han2020pulse, author = {Han, Donggeon and Khan, Yasser and Ting, Jonathan and Zhu, Juan and Combe, Craig and Wadsworth, Andrew and McCulloch, Iain and Arias, Ana C.}, title = {Pulse Oximetry Using Organic Optoelectronics under Ambient Light}, journal = {Advanced Materials Technologies}, volume = {n/a}, number = {n/a}, year = {2020}, pages = {1901122}, keywords = {flexible electronics, organic photodiodes, oximeters, photoplethysmography, wearable sensors}, doi = {10.1002/admt.201901122}, url = {http://dx.doi.org/10.1002/admt.201901122}, thumbnail = {han2020pulse.png}, pdf = {han2020pulse.pdf}, eprint = {https://onlinelibrary.wiley.com/doi/pdf/10.1002/admt.201901122} }

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  1. Inkjet-printed flexible gold electrode arrays for bioelectronic interfaces Yasser Khan*, Felippe J Pavinatto*, Monica C Lin, Amy Liao, Sarah L Swisher, Kaylee Mann, Vivek Subramanian, Michel M Maharbiz, and Ana C Arias Advanced Functional Materials, 2016 26, 7. Cover article.

    Bioelectronic interfaces require electrodes that are mechanically flexible and chemically inert. Flexibility allows pristine electrode contact to skin and tissue, and chemical inertness prevents electrodes from reacting with biological fluids and living tissues. Therefore, flexible gold electrodes are ideal for bioimpedance and biopotential measurements such as bioimpedance tomography, electrocardiography (ECG), electroencephalography (EEG), and electromyography (EMG). However, a manufacturing process to fabricate gold electrode arrays on plastic substrates is still elusive. In this work, a fabrication and low-temperature sintering (≈200 °C) technique is demonstrated to fabricate gold electrodes. At low-temperature sintering conditions, lines of different widths demonstrate different sintering speeds. Therefore, the sintering condition is targeted toward the widest feature in the design layout. Manufactured electrodes show minimum feature size of 62 μm and conductivity values of 5 × 10 6 S m−1. Utilizing the versatility of printing and plastic electronic processes, electrode arrays consisting of 31 electrodes with electrode-to-electrode spacing ranging from 2 to 7 mm are fabricated and used for impedance mapping of conformal surfaces at 15 kHz. Overall, the fabrication process of an inkjet-printed gold electrode array that is electrically reproducible, mechanically robust, and promising for bioimpedance and biopotential measurements is demonstrated.

    @article{khan2016inkjet, title = {Inkjet-printed flexible gold electrode arrays for bioelectronic interfaces}, author = {Khan*, Yasser and Pavinatto*, Felippe J and Lin, Monica C and Liao, Amy and Swisher, Sarah L and Mann, Kaylee and Subramanian, Vivek and Maharbiz, Michel M and Arias, Ana C}, journal = {Advanced Functional Materials}, volume = {26}, number = {7}, pages = {1004--1013}, year = {2016}, publisher = {Wiley Online Library}, url = {http://dx.doi.org/10.1002/adfm.201503316}, doi = {10.1002/adfm.201503316}, thumbnail = {khan2016inkjet.png}, pdf = {khan2016inkjet.pdf}, note = {Cover article.} }

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  1. Impedance sensing device enables early detection of pressure ulcers in vivo Sarah L Swisher, Monica C Lin, Amy Liao, Elisabeth J Leeflang, Yasser Khan, Felippe J Pavinatto, Kaylee Mann, Agne Naujokas, David Young, Shuvo Roy, Michael R Harrison, Ana C Arias, Vivek Subramanian, and Michel M Maharbiz Nature communications, 2015 6, Media coverage: BBC News, UC Berkeley News Center, Futurity, NSF News, ACM Communications, and many more.

    When pressure is applied to a localized area of the body for an extended time, the resulting loss of blood flow and subsequent reperfusion to the tissue causes cell death and a pressure ulcer develops. Preventing pressure ulcers is challenging because the combination of pressure and time that results in tissue damage varies widely between patients, and the underlying damage is often severe by the time a surface wound becomes visible. Currently, no method exists to detect early tissue damage and enable intervention. Here we demonstrate a flexible, electronic device that non-invasively maps pressure-induced tissue damage, even when such damage cannot be visually observed. Using impedance spectroscopy across flexible electrode arrays in vivo on a rat model, we find that impedance is robustly correlated with tissue health across multiple animals and wound types. Our results demonstrate the feasibility of an automated, non-invasive ‘smart bandage’ for early detection of pressure ulcers.

    @article{swisher2015impedance, title = {Impedance sensing device enables early detection of pressure ulcers in vivo}, author = {Swisher, Sarah L and Lin, Monica C and Liao, Amy and Leeflang, Elisabeth J and Khan, Yasser and Pavinatto, Felippe J and Mann, Kaylee and Naujokas, Agne and Young, David and Roy, Shuvo and Harrison, Michael R and Arias, Ana C and Subramanian, Vivek and Maharbiz, Michel M}, journal = {Nature communications}, volume = {6}, pages = {6575}, year = {2015}, publisher = {Nature Publishing Group}, url = {http://dx.doi.org/10.1038/ncomms7575}, doi = {10.1038/ncomms7575}, thumbnail = {swisher2015impedance.png}, pdf = {swisher2015impedance.pdf}, note = {Media coverage: }, media_1 = {BBC News, }, media_1_link = {http://www.bbc.com/news/health-31903367}, media_2 = {UC Berkeley News Center, }, media_2_link = {http://newscenter.berkeley.edu/2015/03/17/smart-bandages-detect-bedsores/}, media_3 = {Futurity, }, media_3_link = {http://www.futurity.org/smart-bandage-bedsores-876942/}, media_4 = {NSF News, }, media_4_link = {https://www.nsf.gov/news/news_summ.jsp?cntn_id=134610}, media_5 = {ACM Communications, }, media_5_link = {https://cacm.acm.org/news/184717-smart-bandage-detects-bedsores-before-they-are-visible-to-doctors/fulltext}, media_6 = {and many more.}, media_6_link = {https://www.altmetric.com/details/3798805} }

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  1. Optimization of printed sensors to monitor sodium, ammonium, and lactate in sweat Alla M. Zamarayeva, Natasha A. D. Yamamoto, Anju Toor, Margaret E. Payne, Caleb Woods, Veronika I. Pister, Yasser Khan, James W. Evans, and Ana Claudia Arias APL Materials, 2020 8, 10.

    We describe the optimization of a flexible printed electrochemical sensing platform to monitor sodium ion (Na+), ammonium ion (NH4+), and lactate in human sweat. We used previously reported material systems and adapted them to scalable fabrication techniques. In the case of potentiometric Na+ and NH4+ sensors, ion-selective electrodes (ISEs) required minimum optimization beyond previously reported protocols, while a reference electrode had to be modified in order to achieve a stable response. We incorporated a carbon nanotube (CNT) layer between the membrane and the silver/silver chloride (Ag/AgCl) layer to act as a surface for adsorption and retention of Cl−. The resulting reference electrode showed minimal potential variation up to 0.08 mV in the solutions with Cl concentration varying from 0.1 mM to 100 mM. Increasing the ionophore content in the NH4+ ISE sensing membrane eliminated an offset in the potential readout, while incorporating CNTs into the sensing membranes had a marginal effect on the sensitivity of both Na+ and NH4+ sensors. Na+ and NH4+ sensors showed a stable near-Nernstian response with sensitivities of 60.0 ± 4.0 mV and 56.2 ± 2.3 mV, respectively, long-term stability for at least 60 min of continuous operation, and selectivity to Na+ and NH4+. For the lactate sensor, we compared the performance of the tetrathiafulvalene mediated lactate oxidase based working electrode with and without diffusion-limiting polyvinyl chloride membrane. The working electrodes with and without the membrane showed sensitivities of 3.28 ± 8 A/mM and 0.43 ± 0.11 μA/mM with a linear range up to 20 mM and 30 mM lactate, respectively.

    @article{zamarayeva2020optimization, author = {Zamarayeva, Alla M. and Yamamoto, Natasha A. D. and Toor, Anju and Payne, Margaret E. and Woods, Caleb and Pister, Veronika I. and Khan, Yasser and Evans, James W. and Arias, Ana Claudia}, title = {Optimization of printed sensors to monitor sodium, ammonium, and lactate in sweat}, volume = {8}, number = {10}, journal = {APL Materials}, pages = {100905}, year = {2020}, doi = {10.1063/5.0014836}, thumbnail = {zamarayeva2020optimization.png}, url = {http://dx.doi.org/10.1063/5.0014836}, pdf = {zamarayeva2020optimization.pdf}, publisher = {AIP Publishing} }

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  1. Emission Area Patterning of Organic Light-Emitting Diodes (OLEDs) via Printed Dielectrics Donggeon Han, Yasser Khan, Karthik Gopalan, Adrien Pierre, and Ana C Arias Advanced Functional Materials, 2018 28, 37.

    Solution-processibility is one of the distinguished traits of organic light-emitting diodes (OLEDs) compared to existing solid-state LED technologies. It allows new opportunities which can simplify the fabrication and potentially reduce the cost of manufacturing process. Emission area patterning is one of the crucial fabrication steps and it usually involves subtractive methods, such as photolithography or etching. Here, printing techniques are used to pattern the emission area of blade-coated OLED layers. The print qualities of a number of printing schemes are characterized and compared. Spray coating and screen printing are used to deposit dielectrics with desired patterns on the OLED layers. At luminance of 1000 cd m−2 the OLEDs patterned using spray-coated and screen-printed dielectric show current density of 8.2 and 10.1 mA cm−2, external quantum efficiency (EQE) of 2.1% and 2.1%, and luminous efficacy of 5.5 and 6.3 lm W−1, respectively. The OLED characteris-tics and features of each printing scheme in depositing the dielectric layer are discussed. The printing methods are further applied to demonstrate displays with complex shapes and a seven-segment display.

    @article{han2018emission, title = {Emission Area Patterning of Organic Light-Emitting Diodes (OLEDs) via Printed Dielectrics}, author = {Han, Donggeon and Khan, Yasser and Gopalan, Karthik and Pierre, Adrien and Arias, Ana C}, journal = {Advanced Functional Materials}, volume = {28}, number = {37}, pages = {1802986}, year = {2018}, url = {http://dx.doi.org/10.1002/adfm.201802986}, doi = {10.1002/adfm.201802986}, thumbnail = {han2018emission.png}, pdf = {han2018emission.pdf} }

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  1. Flexible hybrid electronics: Direct interfacing of soft and hard electronics for wearable health monitoring Yasser Khan, Mohit Garg, Qiong Gui, Mark Schadt, Abhinav Gaikwad, Donggeon Han, Natasha AD Yamamoto, Paul Hart, Robert Welte, William Wilson, Steve Czarnecki, Mark Poliks, Zhanpeng Jin, Kanad Ghose, Frank Egitto, James Turner, and Ana C Arias Advanced Functional Materials, 2016 26, 47.

    The interfacing of soft and hard electronics is a key challenge for flexible hybrid electronics. Currently, a multisubstrate approach is employed, where soft and hard devices are fabricated or assembled on separate substrates, and bonded or interfaced using connectors; this hinders the flexibility of the device and is prone to interconnect issues. Here, a single substrate interfacing approach is reported, where soft devices, i.e., sensors, are directly printed on Kapton polyimide substrates that are widely used for fabricating flexible printed circuit boards (FPCBs). Utilizing a process flow compatible with the FPCB assembly process, a wearable sensor patch is fabricated composed of inkjet-printed gold electrocardiography (ECG) electrodes and a stencil-printed nickel oxide thermistor. The ECG electrodes provide 1 mVp–p ECG signal at 4.7 cm electrode spacing and the thermistor is highly sensitive at normal body temperatures, and demonstrates temperature coefficient, α ≈ –5.84% K–1 and material constant, β ≈ 4330 K. This sensor platform can be extended to a more sophisticated multisensor platform where sensors fabricated using solution processable functional inks can be interfaced to hard electronics for health and performance monitoring, as well as internet of things applications.

    @article{khan2016flexible, title = {Flexible hybrid electronics: Direct interfacing of soft and hard electronics for wearable health monitoring}, author = {Khan, Yasser and Garg, Mohit and Gui, Qiong and Schadt, Mark and Gaikwad, Abhinav and Han, Donggeon and Yamamoto, Natasha AD and Hart, Paul and Welte, Robert and Wilson, William and Czarnecki, Steve and Poliks, Mark and Jin, Zhanpeng and Ghose, Kanad and Egitto, Frank and Turner, James and Arias, Ana C}, journal = {Advanced Functional Materials}, volume = {26}, number = {47}, pages = {8764--8775}, year = {2016}, publisher = {Wiley Online Library}, url = {http://dx.doi.org/10.1002/adfm.201603763}, doi = {10.1002/adfm.201603763}, thumbnail = {khan2016flexible.png}, pdf = {khan2016flexible.pdf} }

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  1. A New Frontier of Printed Electronics: Flexible Hybrid Electronics Yasser Khan, Arno Thielens, Sifat Muin, Jonathan Ting, Carol Baumbauer, and Ana C. Arias Advanced Materials, 2019 n/a, n/a.

    The performance and integration density of silicon integrated circuits (ICs) have progressed at an unprecedented pace in the past 60 years. While silicon ICs thrive at low-power high-performance computing, creating flexible and large-area electronics using silicon remains a challenge. On the other hand, flexible and printed electronics use intrinsically flexible materials and printing techniques to manufacture compliant and large-area electronics. Nonetheless, flexible electronics are not as efficient as silicon ICs for computation and signal communication. Flexible hybrid electronics (FHE) leverages the strengths of these two dissimilar technologies. It uses flexible and printed electronics where flexibility and scalability are required, i.e., for sensing and actuating, and silicon ICs for computation and communication purposes. Combining flexible electronics and silicon ICs yields a very powerful and versatile technology with a vast range of applications. Here, the fundamental building blocks of an FHE system, printed sensors and circuits, thinned silicon ICs, printed antennas, printed energy harvesting and storage modules, and printed displays, are discussed. Emerging application areas of FHE in wearable health, structural health, industrial, environmental, and agricultural sensing are reviewed. Overall, the recent progress, fabrication, application, and challenges, and an outlook, related to FHE are presented.

    @article{khan2019new, author = {Khan, Yasser and Thielens, Arno and Muin, Sifat and Ting, Jonathan and Baumbauer, Carol and Arias, Ana C.}, title = {A New Frontier of Printed Electronics: Flexible Hybrid Electronics}, journal = {Advanced Materials}, volume = {n/a}, number = {n/a}, year = {2019}, pages = {1905279}, keywords = {environmental sensors, flexible electronics, printed electronics, structural health monitoring, wearable health monitoring}, doi = {10.1002/adma.201905279}, url = {http://dx.doi.org/10.1002/adma.201905279}, thumbnail = {khan2019new.png}, pdf = {khan2019new.pdf} }

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  1. A wearable biosensing system with in-sensor adaptive machine learning for hand gesture recognition Ali Moin, Andy Zhou, Abbas Rahimi, Alisha Menon, Simone Benatti, George Alexandrov, Senam Tamakloe, Jonathan Ting, Natasha Yamamoto, Yasser Khan, Fred Burghardt, Luca Benini, Ana C. Arias, and Jan M. Rabaey Nature Electronics, 2020 n/a, n/a.

    Wearable devices that monitor muscle activity based on surface electromyography could be of use in the development of hand gesture recognition applications. Such devices typically use machine-learning models, either locally or externally, for gesture classification. However, most devices with local processing cannot offer training and updating of the machine-learning model during use, resulting in suboptimal performance under practical conditions. Here we report a wearable surface electromyography biosensing system that is based on a screen-printed, conformal electrode array and has in-sensor adaptive learning capabilities. Our system implements a neuro-inspired hyperdimensional computing algorithm locally for real-time gesture classification, as well as model training and updating under variable conditions such as different arm positions and sensor replacement. The system can classify 13 hand gestures with 97.12% accuracy for two participants when training with a single trial per gesture. A high accuracy (92.87%) is preserved on expanding to 21 gestures, and accuracy is recovered by 9.5% by implementing model updates in response to varying conditions, without additional computation on an external device.

    @article{moin2020wearable, author = {Moin, Ali and Zhou, Andy and Rahimi, Abbas and Menon, Alisha and Benatti, Simone and Alexandrov, George and Tamakloe, Senam and Ting, Jonathan and Yamamoto, Natasha and Khan, Yasser and Burghardt, Fred and Benini, Luca and Arias, Ana C. and Rabaey, Jan M.}, title = {A wearable biosensing system with in-sensor adaptive machine learning for hand gesture recognition}, journal = {Nature Electronics}, volume = {n/a}, number = {n/a}, pages = {}, year = {2020}, doi = {10.1038/s41928-020-00510-8}, thumbnail = {moin2020wearable.png}, url = {http://dx.doi.org/10.1038/s41928-020-00510-8}, pdf = {moin2020wearable.pdf} }

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  1. Monitoring of vital signs with flexible and wearable medical devices Yasser Khan, Aminy E Ostfeld, Claire M Lochner, Adrien Pierre, and Ana C Arias Advanced Materials, 2016 28, 22.

    Advances in wireless technologies, low-power electronics, the internet of things, and in the domain of connected health are driving innovations in wearable medical devices at a tremendous pace. Wearable sensor systems composed of flexible and stretchable materials have the potential to better interface to the human skin, whereas silicon-based electronics are extremely efficient in sensor data processing and transmission. Therefore, flexible and stretchable sensors combined with low-power silicon-based electronics are a viable and efficient approach for medical monitoring. Flexible medical devices designed for monitoring human vital signs, such as body temperature, heart rate, respiration rate, blood pressure, pulse oxygenation, and blood glucose have applications in both fitness monitoring and medical diagnostics. As a review of the latest development in flexible and wearable human vitals sensors, the essential components required for vitals sensors are outlined and discussed here, including the reported sensor systems, sensing mechanisms, sensor fabrication, power, and data processing requirements.

    @article{khan2016monitoring, title = {Monitoring of vital signs with flexible and wearable medical devices}, author = {Khan, Yasser and Ostfeld, Aminy E and Lochner, Claire M and Pierre, Adrien and Arias, Ana C}, journal = {Advanced Materials}, volume = {28}, number = {22}, pages = {4373--4395}, year = {2016}, publisher = {Wiley Online Library}, url = {http://dx.doi.org/10.1002/adma.201504366}, doi = {10.1002/adma.201504366}, thumbnail = {khan2016monitoring.png}, pdf = {khan2016monitoring.pdf} }

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Last modified: 2020-11-26