Research

We use additive manufacturing and hardware-enabled AI to build flexible wearables, implantables, and ingestibles that decode brain and behavior, including brain-gut communication, for precision health and psychiatry.

We combine hardware systems, additive manufacturing, and signal processing to build new devices, circuits, and systems, from the sensor material up to the finished wearable, implantable, or ingestible.

Medical devices and hardware AI, for precision health and precision psychiatry.

From materials and devices, through manufacturing and circuits, to fully integrated wearable, implantable, and ingestible systems.

Focus areas

Soft biophotonic, bioelectronic, and biochemical sensors

Flexible and stretchable sensors are well suited to medical sensing because a conformal skin-sensor interface improves signal-to-noise ratio. We use scalable printing to rapidly prototype and manufacture sensors in diverse sizes and form factors, enabling both population-tailored designs and integrated hardware systems for decoding brain and behavior across three sensing modalities.

Biophotonic sensors optically interface with the body. In 2014, we demonstrated the first all-organic flexible optoelectronic oximeter, built from organic light-emitting diodes (OLEDs) and an organic photodiode (OPD), to measure pulse rate and oxygenation [1]. We then showed the true potential of flexible oximeters with reflection-mode operation, which allows sensor placement on different parts of the body [2], and in 2018 demonstrated the first flexible reflectance oximeter array (ROA), enabling 2D oxygenation mapping for applications like wound and transplanted-organ monitoring [3]. We later reported an organic ambient-light oximeter that needs no controlled light source and drastically reduces power consumption [4].

Bioelectronic interfaces require electrodes that are mechanically flexible and chemically inert. We devised a low-temperature sintering technique to print gold electrode arrays on plastic substrates, first for impedance mapping of conformal surfaces [5], then for a “smart bandage” that non-invasively detects pressure-induced tissue damage before it is visible [6].

Biochemical sensors monitor ions, metabolites, hormones, and peptides in bodily fluids such as sweat, saliva, and tear, giving an overall snapshot of a person’s physiological state [7]. We are developing an integrated sensor platform using ion-selective organic electrochemical transistors (OECTs) for fitness and medical-grade sensing: a wearable platform to combine OECTs with integrated sweat collection and rate measurement. At USC, this device measures lithium levels in sweat to support bipolar disorder management [8].

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, PNAS, 2018.
[4] D. Han, Y. Khan, A. Arias, Adv. Mater. Technol., 2020.
[5] Y. Khan, A. Arias, Adv. Funct. Mater., 2016.
[6] S. Swisher, Y. Khan, A. Arias, M. Maharbiz, Nat. Commun., 2015.
[7] A. Zamarayeva, Y. Khan, A. Arias, APL Mater., 2020.
[8] M. S. Islam, Y. Khan, Device, 2025.

Skin-inspired wearables for decoding mental health

Mental health problems are on the rise worldwide. Globally, 600 million people are affected by depression and anxiety, yet there are no objective, scalable technologies for detecting what type of depression a person is at risk for, what stage they are in, or how best to intervene. In a scoping review, we mapped the physiological stress markers, cortisol, heart rate variability, and skin conductance, that could help distinguish these mental health biotypes [9].

Building on that foundation, we designed and developed a wearable sensor, Mentaid, for understanding mental health biotypes at scale [10]. Mentaid collects the physiological parameters that matter (heart rate variability, skin conductance, and cortisol) alongside contextual information such as light, sound, and activity, using a multi-layer, skin-inspired design that performs biophotonic, bioelectronic, and biochemical sensing at once in one compact, comfortable patch.

Adoption depends on where and how people are willing to wear a sensor. From a 24-subject study blending user preference with biosignal quality, we found that while the wrist is rich for sensing, users tend to prefer more discreet locations like the upper arm, valuing comfort, size, and concealability so as not to be identified as someone in need of mental health support. These human-factors findings now guide how we design every new wearable in the lab.

That line of work led directly to a clinical translation: a wearable OECT-based sensor that continuously measures lithium levels in sweat to help manage bipolar disorder, shown in the video above [8].

Publications:
[9] M. Chesnut, Y. Khan, L. Williams, Chronic Stress, 2021.
[10] Y. Khan, J. Kim, M. Chesnut, Z. Bao. In preparation.
Y. Khan, M. Mauriello, et al., CHI, 2024.
[8] M. S. Islam, Y. Khan, Device, 2025.

Bioelectronics for the brain and gut

Building on our prior work in bioelectronics, biophotonics, and skin-inspired sensing, we started the Khan Lab at USC in 2022 to develop AI-enabled wearables, implantables, and ingestibles aimed at understanding the brain-gut axis and its role in precision health and psychiatry. The gut, often called the “second brain,” communicates directly with the brain and plays a crucial role in regulating both physical and mental health. Patients with gastrointestinal disorders frequently experience anxiety and stress, while psychological factors can, in turn, worsen GI issues.

We are building the underlying bioelectronics for the gut from the ground up: an application-specific integrated circuit (ASIC) for ingestible miniaturization [11], an ingestible capsule that maps gas concentrations in the gut using AI-enabled sensing, shown in the video above [12], and most recently a single-chip ingestible platform for continuously sensing gut neurotransmitters like serotonin and dopamine [13], alongside self-severing ingestible circuits that reduce obstruction risk by breaking into smaller, passable pieces on command [14].

Publications:
[11] A. Abdigazy, Y. Khan, Nat. Electron., 2024.
[12] A. Abdigazy, Y. Khan, Cell Rep. Phys. Sci., 2024.
[13] A. Abdigazy, Y. Khan, bioRxiv, 2026.
[14] S. Healy, A. Abdigazy, Y. Khan, A. Abramson, bioRxiv, 2026.

Hardware AI and in-sensor processing with soft circuits

The human brain is far more efficient at pattern recognition than conventional Von Neumann computer architectures. Machine learning algorithms that mimic the brain’s biological processes are promising for wearable sensor systems because they allow faster, more agile parallel processing of sensor data close to where it is collected. We integrate both rigid silicon integrated circuits and organic electronics to implement machine learning directly in wearable and implantable sensors (missing reference).

Publications:
[15] A. Moin, Y. Khan, A. Arias, J. Rabaey, Nat. Electron., 2020.
[16] M. Sadeghi, Y. Khan, J. Rabaey, A. Arias, Matter & Light, 2026. Cover article.

MRI-compatible wearables and soft receive coils

Magnetic resonance imaging is a crucial diagnostic tool, and dynamic musculoskeletal and cardiac MRI enable real-time visualization of joint, tissue, and heart movement for improved diagnosis. MRI signal acquisition relies on receive-only coil arrays, where surface coils improve signal-to-noise ratio and enable the accelerated imaging that dynamic applications require. Flexible MRI coils have historically been difficult to fabricate; we instead use direct-3D-write printing of highly conductive silver ink for precise, reproducible, and cost-effective flexible receiver coils, demonstrated for dynamic imaging of the wrist and heart at 0.55T [17].

Wearable sensors inside the MRI environment also enable real-time monitoring of vital signs, including heart rate, respiration rate, blood pressure, temperature, and biochemical markers, during a scan. Our results show a custom Bluetooth Low Energy PPG sensor operates effectively at 0.55T without affecting sensor signal integrity or MRI image quality [18].

Publications:
[17] F. Muñoz, Y. Khan, Nat. Commun., 2026.
[18] F. Muñoz, K. Nayak, Y. Khan, IEEE Sens. Lett., 2025.

Additive manufacturing and flexible hybrid electronics

Printing is now a commercially viable manufacturing technology for electronics, spanning sensors, circuits, and devices for energy, health, and consumer applications. We use inkjet printing, screen printing, and other hybrid printing methods to rapidly prototype and scale the soft devices described throughout our work [5], [2], [19].

Flexible hybrid electronics (FHE) bring soft and hard electronics together on a single platform: soft devices provide conformal sensor interfaces, while hard silicon-based devices supply the computational backbone. In collaboration with Binghamton University, i3 Electronics, Lockheed Martin, and American Semiconductor, we demonstrated a single-substrate interfacing approach where sensors are printed directly on the polyimide substrates used for flexible printed circuit boards, fabricating a wearable sensor patch with inkjet-printed gold ECG electrodes and a stencil-printed nickel oxide thermistor [20].

Publications:
[20] Y. Khan, A. Arias, Adv. Funct. Mater., 2016.
[21] Y. Khan, A. Arias, Adv. Mater., 2019.
[19] D. Han, Y. Khan, A. Arias, Adv. Funct. Mater., 2018.

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} }

    PDF

  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} }

    PDF

  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} }

    PDF

  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

    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}, 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} }

    PDF

  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.}, cover = {khan2016inkjet.png} }

    PDF

  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} }

    PDF

  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} }

    PDF

  1. Wearable organic-electrochemical-transistor-based lithium sensor for precision mental health Mohammad Shafiqul Islam, Brince Paul Kunnel, Munia Ferdoushi, Md Farhad Hassan, Sangwon Cha, Wenxin Cai, Adam Frank, and Yasser Khan Device, 2025 Media coverage: USC News, Newsweek, Psychiatrist.com, and many more.

    Mental health disorders, including bipolar disorder, pose significant challenges worldwide, necessitating precise monitoring of lithium, a gold-standard medication for this condition. We introduce a fully printed, wearable organic electrochemical transistor (OECT)-based sensor for non-invasive and continuous monitoring of lithium levels in sweat. This sensor integrates inkjet and 3D printing to fabricate multilayer OECTs with an ion-selective membrane alongside iontophoretic sweat induction and microfluidic guidance for real-time sensing. Our sensor demonstrates a sensitivity of ΔIds/I0 = 0.5/decade, a 0.1 mM detection limit in artificial sweat, and selectivity for lithium over common interfering ions. A complete wearable system with wireless readout enables real-time data transmission to a smartphone interface. Validation in both healthy individuals and bipolar patients confirms the device’s ability to detect therapeutically significant lithium levels. This article provides a promising path for precision mental health management, presenting a first-of-its-kind wearable real-time monitoring solution for lithium—a vital medication in treating bipolar disorder.

    @article{islam2025lithium, title = {Wearable organic-electrochemical-transistor-based lithium sensor for precision mental health}, author = {Islam, Mohammad Shafiqul and Kunnel, Brince Paul and Ferdoushi, Munia and Hassan, Md Farhad and Cha, Sangwon and Cai, Wenxin and Frank, Adam and Khan, Yasser}, journal = {Device}, year = {2025}, publisher = {Cell Press}, doi = {10.1016/j.device.2025.100862}, thumbnail = {islam2025lithium.png}, url = {http://dx.doi.org/10.1016/j.device.2025.100862}, pdf = {islam2025lithium.pdf}, note = {Media coverage: }, media_1 = {USC News, }, media_1_link = {https://viterbischool.usc.edu/news/2025/07/new-wearable-sensor-made-at-usc-could-help-bipolar-patients-track-medication-levels-through-sweat/}, media_2 = {Newsweek, }, media_2_link = {https://www.newsweek.com/bipolar-disorder-wearable-sensor-medication-tracker-2104162}, media_3 = {Psychiatrist.com, }, media_3_link = {https://www.psychiatrist.com/news/smart-patch-offers-breakthrough-in-bipolar-disorder-monitoring/}, media_4 = {and many more.}, media_4_link = {https://www.altmetric.com/details/179474695} }

    PDF

  1. Stress Markers for Mental States and Biotypes of Depression and Anxiety: A Scoping Review and Preliminary Illustrative Analysis Megan Chesnut, Sahar Harati, Pablo Paredes, Yasser Khan, Amir Foudeh, Jayoung Kim, Zhenan Bao, and Leanne M. Williams Chronic Stress, 2021 5,

    Depression and anxiety disrupt daily function and their effects can be long-lasting and devastating, yet there are no established physiological indicators that can be used to predict onset, diagnose, or target treatments. In this review, we conceptualize depression and anxiety as maladaptive responses to repetitive stress. We provide an overview of the role of chronic stress in depression and anxiety and a review of current knowledge on objective stress indicators of depression and anxiety. We focused on cortisol, heart rate variability and skin conductance that have been well studied in depression and anxiety and implicated in clinical emotional states. A targeted PubMed search was undertaken prioritizing meta-analyses that have linked depression and anxiety to cortisol, heart rate variability and skin conductance. Consistent findings include reduced heart rate variability across depression and anxiety, reduced tonic and phasic skin conductance in depression, and elevated cortisol at different times of day and across the day in depression. We then provide a brief overview of neural circuit disruptions that characterize particular types of depression and anxiety. We also include an illustrative analysis using predictive models to determine how stress markers contribute to specific subgroups of symptoms and how neural circuits add meaningfully to this prediction. For this, we implemented a tree-based multi-class classification model with physiological markers of heart rate variability as predictors and four symptom subtypes, including normative mood, as target variables. We achieved 40% accuracy on the validation set. We then added the neural circuit measures into our predictor set to identify the combination of neural circuit dysfunctions and physiological markers that accurately predict each symptom subtype. Achieving 54% accuracy suggested a strong relationship between those neural-physiological predictors and the mental states that characterize each subtype. Further work to elucidate the complex relationships between physiological markers, neural circuit dysfunction and resulting symptoms would advance our understanding of the pathophysiological pathways underlying depression and anxiety.

    @article{chesnut2021stress, author = {Chesnut, Megan and Harati, Sahar and Paredes, Pablo and Khan, Yasser and Foudeh, Amir and Kim, Jayoung and Bao, Zhenan and Williams, Leanne M.}, title = {Stress Markers for Mental States and Biotypes of Depression and Anxiety: A Scoping Review and Preliminary Illustrative Analysis}, journal = {Chronic Stress}, volume = {5}, year = {2021}, doi = {10.1177/24705470211000338}, thumbnail = {chesnut2021stress.png}, url = {http://dx.doi.org/10.1177/24705470211000338}, pdf = {chesnut2021stress.pdf} }

    PDF
  1. Mentaid: a skin-inspired wearable for decoding mental health Yasser Khan*, Jayoung Kim*, Megan Chesnut*, Nicholas Vitale, Sahar Harati, Matthew L. Mauriello, Parsa Nowruzi, Jinxing Li, Min-gu Kim, Jan Liphardt, Keith D. Sudheimer, Pablo E.Paredes, Leanne Williams, Boris Murmann, and Zhenan Bao , 202X In preparation

    @article{khan2021mentaid, author = {Khan*, Yasser and Kim*, Jayoung and Chesnut*, Megan and Vitale, Nicholas and Harati, Sahar and Mauriello, Matthew L. and Nowruzi, Parsa and Li, Jinxing and Kim, Min-gu and Liphardt, Jan and Sudheimer, Keith D. and E.Paredes, Pablo and Williams, Leanne and Murmann, Boris and Bao, Zhenan}, note = {In preparation}, title = {Mentaid: a skin-inspired wearable for decoding mental health}, year = {202X} }

  1. On Stress: Combining Human Factors and Biosignals to Inform the Placement and Design of a Skin-like Stress Sensor Yasser Khan, Matthew Louis Mauriello, Parsa Nowruzi, Akshara Motani, Grace Hon, Nicholas Vitale, Jinxing Li, Jayoung Kim, Amir Foudeh, Dalton Duvio, and others In Proceedings of the CHI Conference on Human Factors in Computing Systems, 2024

    @inproceedings{khan2024stress, title = {On Stress: Combining Human Factors and Biosignals to Inform the Placement and Design of a Skin-like Stress Sensor}, author = {Khan, Yasser and Mauriello, Matthew Louis and Nowruzi, Parsa and Motani, Akshara and Hon, Grace and Vitale, Nicholas and Li, Jinxing and Kim, Jayoung and Foudeh, Amir and Duvio, Dalton and others}, booktitle = {Proceedings of the CHI Conference on Human Factors in Computing Systems}, pages = {1--13}, url = {http://dx.doi.org/10.1145/3613904.3643473}, doi = {10.1145/3613904.3643473}, thumbnail = {khan2021design.png}, pdf = {khan2024stress.pdf}, year = {2024} }

    PDF

  1. End-to-end design of ingestible electronics Angsagan Abdigazy, Mohammed Arfan, Gianluca Lazzi, Constantine Sideris, Alex Abramson, and Yasser Khan Nature Electronics, 2024

    Ingestible electronics can potentially be used to track and treat gastrointestinal diseases in real time. In the past decade, substantial improvements have been made to ingestible electronic pills at the sensor, circuit and system levels, which has improved the clinical applicability of the technology by increasing device sensitivity, lifetime and location awareness. Here we explore the development of ingestible electronics and provide a step-by-step guide for the design of ingestible capsules at the system level. We consider the anatomical and physiological characteristics of gastrointestinal organs, which set requirements and constraints on ingestible electronics in terms of size, shape, topology and the materials used for packaging. We then examine the key design components: sensors and actuators, integrated circuits, communication, power, packaging, localization and locomotion. We also consider the challenges that must be addressed to realize the full application potential of ingestible electronics.

    @article{abdigazy2024end, title = {End-to-end design of ingestible electronics}, author = {Abdigazy, Angsagan and Arfan, Mohammed and Lazzi, Gianluca and Sideris, Constantine and Abramson, Alex and Khan, Yasser}, journal = {Nature Electronics}, pages = {1--17}, year = {2024}, publisher = {Nature Publishing Group UK London}, doi = {10.1038/s41928-024-01122-2}, thumbnail = {abdigazy2024end.jpg}, url = {http://dx.doi.org/10.1038/s41928-024-01122-2}, pdf = {abdigazy2024end.pdf} }

    PDF

  1. 3D gas mapping in the gut with AI-enabled ingestible and wearable electronics Angsagan Abdigazy, Mohammed Arfan, June Shao, Mohammad Shafiqul Islam, Md Farhad Hassan, and Yasser Khan Cell Reports Physical Science, 2024 Media coverage: USC News, Interesting Engineering, Neuroscience News, and many more.

    Gas measurements in the gastrointestinal (GI) tract aid in the diagnosis and continuous monitoring of disorders such as irritable bowel syndrome, inflammatory bowel disease, and food intolerances. Traditional methods for measuring and locating these gases are often invasive, typically requiring hospital-based procedures. Ingestible electronics provide a more convenient solution, yet locating these devices remains challenging. Here, we present a wearable platform that implements a magnetic-field-based 3D localization of ingestibles with millimeter-scale resolution: <2.2 mm with lookup-table-based and <4.2 mm with neural-network-based algorithms, respectively. Our ingestible pill, equipped with optoelectronic gas sensors, can detect oxygen (O2) in 0%–20% and ammonia (NH3) in the 0–100 ppm concentration range. The NH3 measurements can serve as a proxy for identifying Helicobacter pylori, a bacterium linked to peptic ulcers, gastritis, and gastric cancers. Overall, this work aims to empower patients to conveniently assess their GI gas profiles from the comfort of home and manage digestive health.

    @article{abdigazy20243d, title = {3D gas mapping in the gut with AI-enabled ingestible and wearable electronics}, author = {Abdigazy, Angsagan and Arfan, Mohammed and Shao, June and Islam, Mohammad Shafiqul and Hassan, Md Farhad and Khan, Yasser}, journal = {Cell Reports Physical Science}, year = {2024}, publisher = {Cell Press}, doi = {10.1016/j.xcrp.2024.101990}, thumbnail = {abdigazy20243d.png}, url = {http://dx.doi.org/10.1016/j.xcrp.2024.101990}, pdf = {abdigazy20243d.pdf}, note = {Media coverage: }, media_1 = {USC News, }, media_1_link = {https://viterbischool.usc.edu/news/2024/06/from-wearables-to-swallowables-usc-engineering-researchers-create-gps-like-smart-pills-with-ai/}, media_2 = {Interesting Engineering, }, media_2_link = {https://interestingengineering.com/innovation/wearable-coil-smart-ingestible-pill-gut-tracking}, media_3 = {Neuroscience News, }, media_3_link = {https://neurosciencenews.com/ai-gi-pill-neuroscience-26323/}, media_4 = {and many more.}, media_4_link = {https://www.altmetric.com/details/164481315} }

    PDF

  1. Single-chip End-to-End Ingestible Electronics for Gut Neurotransmitter Sensing Angsagan Abdigazy, Mohammad Shafiqul Islam, Sandra Lara Galindo, Md Farhad Hassan, Xiang Zhang, Wooseong Choi, Mark McHugh, Sudipta Saha, Hossein Hashemi, Dong Song, and others bioRxiv, 2026 Preprint

    Neurotransmitters in the gut play a vital role in human health and neuroscience, and their real-time monitoring is essential for understanding underlying physiological mechanisms. However, bioelectronic systems capable of measuring neurotransmitters in vivo at the anatomical site of interest remain underdeveloped and largely depend on bulky, off-the-shelf electronic components, thereby constraining the development of systems that are both practical and minimally invasive. Here, we report a miniature ingestible pill that is capable of real-time in vivo sensing of two key neurotransmitters: serotonin (5-HT) and dopamine (DA). The system incorporates a fully printed three-electrode-based electrochemical sensor for neurotransmitter sensing and a custom application-specific integrated circuit (ASIC) that integrates all major functional blocks on a single chip, enabling a platform for fully wireless monitoring of gut neurotransmitters. The pill, measuring 5.8 mm in diameter and 19 mm in length, supports multiple electrochemical sensing techniques, including amperometry and voltammetry, with only 42 uA of average current consumption. We demonstrate the ingestible platform through in vivo studies in rat animal models, enabling real-time monitoring of gut neurotransmitters.

    @article{abdigazy2026single, title = {Single-chip End-to-End Ingestible Electronics for Gut Neurotransmitter Sensing}, author = {Abdigazy, Angsagan and Islam, Mohammad Shafiqul and Galindo, Sandra Lara and Hassan, Md Farhad and Zhang, Xiang and Choi, Wooseong and McHugh, Mark and Saha, Sudipta and Hashemi, Hossein and Song, Dong and others}, journal = {bioRxiv}, note = {Preprint}, year = {2026}, publisher = {Cold Spring Harbor Laboratory}, doi = {10.64898/2026.03.28.715054}, thumbnail = {abdigazy2026single.jpg}, url = {https://doi.org/10.64898/2026.03.28.715054}, pdf = {abdigazy2026single.pdf} }

    PDF

  1. Self-severing circuits facilitate passage of ingestible electronic sensor-guided therapeutics Sean Healy, Angsagan Abdigazy, McKenna Clinch, Jason Y. Chin, Mohammad Shafiqul Islam, Zachary Lee, Julia Z. Ding, Joy Jackson, Ramy Ghanim, Xavier Manigault, and others bioRxiv, 2026 Preprint

    Ingestible electronics enable the tracking and treatment of gastrointestinal and systemic diseases. However, bulky batteries and circuit boards require large capsules that can result in bowel obstruction, a medical emergency. Here, we engineered a 9 x 26 mm electronic pill capable of triggered severing into tiny pieces with sizes clinically proven to reduce obstruction risk. Our capsule enables multicomponent circuit boards to connect with separately encapsulated powering elements via conductive, interlocking connections. Heat induced softening of polyethylene glycol/polycaprolactone channels activates a spring to separate encapsulated components into inert 9 x 15 mm segments, facilitating intestinal passage. Separation triggers included closed-loop sensors and time-delay circuits. In vivo swine studies demonstrate the ability of our capsules to sense luminal oxygen changes via an optoelectronic sensor, locally trigger upadacitinib delivery, and facilitate safe excretion.

    @article{healy2026self, title = {Self-severing circuits facilitate passage of ingestible electronic sensor-guided therapeutics}, author = {Healy, Sean and Abdigazy, Angsagan and Clinch, McKenna and Chin, Jason Y. and Islam, Mohammad Shafiqul and Lee, Zachary and Ding, Julia Z. and Jackson, Joy and Ghanim, Ramy and Manigault, Xavier and others}, journal = {bioRxiv}, note = {Preprint}, year = {2026}, publisher = {Cold Spring Harbor Laboratory}, doi = {10.64898/2026.03.27.714561}, thumbnail = {healy2026self.jpg}, url = {https://doi.org/10.64898/2026.03.27.714561}, pdf = {healy2026self.pdf} }

    PDF
  1. All-optical sensing of dermal activity enables an AI-powered wearable ring for continuous stress monitoring Md Farhad Hassan, Shounak Das, Dolendra Vikas Addepalli, Leikhang Xiong, Mohammad Shafiqul Islam, A.K.M. Rakib, Samiha Tasnim, Xiao Yu, Emily Rowson, Mohammad Arfan, Adam Frank, and Yasser Khan Nature Communications, 202X In Review

    @article{hassan2026all, author = {Hassan, Md Farhad and Das, Shounak and Addepalli, Dolendra Vikas and Xiong, Leikhang and Islam, Mohammad Shafiqul and Rakib, A.K.M. and Tasnim, Samiha and Yu, Xiao and Rowson, Emily and Arfan, Mohammad and Frank, Adam and Khan, Yasser}, journal = {Nature Communications}, note = {In Review}, title = {All-optical sensing of dermal activity enables an AI-powered wearable ring for continuous stress monitoring}, year = {202X} }

  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 4, 1.

    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 = {4}, number = {1}, pages = {54-63}, 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} }

    PDF

  1. Machine learning classifier based on printed organic electronics Mahsa Sadeghi, Rozhan Rabbani, Ali Moin, Burak Eminoglu, Seiya Ono, Anju Toor, Yasser Khan, Jan Rabaey, and Ana C. Arias Matter & Light, 2026 Cover Article

    Confronting the challenge of dense data processing in AI hardware, this research introduces an in-sensor computing approach that reduces bandwidth by transmitting only salient features. Using flexible printed electronics, it enables sensory platforms beyond the limits of conventional rigid electronics. The study presents two in-sensor classifier models: one based on organic thin-film transistors (OTFTs) that classify sensor input data and one based on organic phototransistors (OPTs) that integrate sensing and classification within a single device. On the MNIST dataset, the OTFT-based circuit achieved 91.3% average accuracy for binary classification of digits 0 and 7, while the OPT-based system achieved 94.1%. Extending the framework to 10-class classification without hardware modification yielded average accuracies of 87.1% (OTFT) and 91.5% (OPT). Evaluation on Fashion-MNIST demonstrated generalizability, achieving 86.5% (OTFT) and 81.1% (OPT), highlighting the feasibility of AI sensory hardware based on printed organic electronics.

    @article{sadeghi2026machine, title = {Machine learning classifier based on printed organic electronics}, author = {Sadeghi, Mahsa and Rabbani, Rozhan and Moin, Ali and Eminoglu, Burak and Ono, Seiya and Toor, Anju and Khan, Yasser and Rabaey, Jan and Arias, Ana C.}, journal = {Matter \& Light}, year = {2026}, publisher = {Elsevier}, doi = {10.1016/j.matlit.2026.100064}, thumbnail = {sadeghi2026machine.jpg}, url = {https://doi.org/10.1016/j.matlit.2026.100064}, pdf = {sadeghi2026machine.pdf}, note = {Cover Article} }

    PDF

  1. Improved dynamic MRI of the wrist and heart at 0.55 T enabled by rapid 3D printed flexible coils Félix Muñoz, Ye Tian, Ted Lê, Jaehwan Jang, Helmut Stark, Mohammad Shafiqul Islam, Min-gu Kim, Krishna S Nayak, and Yasser Khan Nature Communications, 2026 Media coverage: USC News, USC Viterbi News, 3D Printing Industry, and many more.

    Dynamic MRI at low field is limited by reduced signal-to-noise ratio (SNR) and additional losses imposed by accelerated acquisitions required for high temporal resolution. Flexible, anatomically conformal coils can recover SNR by maintaining proximity during motion, but lower conductor conductivity introduces resistive losses, requiring careful material optimization. We demonstrate high-quality dynamic imaging at 0.55 T using coils fabricated via two rapid, low-cost digital methods: direct-ink-write silver printing and screen printing of copper-doped EGaIn. Four-element wrist arrays were fabricated in 8 minutes per element at approximately $30 in consumable materials. In three subjects, both arrays achieved up to 4x higher contrast and 5x greater sharpness than a commercial coil during dynamic wrist imaging. To demonstrate generalizability, a seven-element silver-ink cardiac array produced cine images comparable to a commercial coil. These results establish digitally fabricated flexible coils as a scalable and accessible solution for dynamic musculoskeletal and cardiac MRI at low field.

    @article{munoz2026improved, title = {Improved dynamic MRI of the wrist and heart at 0.55 T enabled by rapid 3D printed flexible coils}, author = {Mu{\~n}oz, F{\'e}lix and Tian, Ye and L{\^e}, Ted and Jang, Jaehwan and Stark, Helmut and Islam, Mohammad Shafiqul and Kim, Min-gu and Nayak, Krishna S and Khan, Yasser}, journal = {Nature Communications}, year = {2026}, publisher = {Nature Publishing Group UK London}, doi = {10.1038/s41467-026-71817-x}, thumbnail = {munoz2026improved.png}, url = {https://doi.org/10.1038/s41467-026-71817-x}, pdf = {munoz2026improved.pdf}, note = {Media coverage: }, media_1 = {USC News, }, media_1_link = {https://today.usc.edu/for-the-tiniest-patients-new-usc-tech-brings-clearer-mri-images/}, media_2 = {USC Viterbi News, }, media_2_link = {https://viterbischool.usc.edu/news/2026/05/usc-researchers-develop-3d-printable-mri-coils-for-low-cost-improved-dynamic-imaging/}, media_3 = {3D Printing Industry, }, media_3_link = {https://3dprintingindustry.com/news/usc-researchers-print-mri-coils-for-a-fraction-of-the-cost-251840/}, media_4 = {and many more.}, media_4_link = {https://www.miragenews.com/usc-tech-enhances-mri-clarity-for-tiny-patients-1725460/} }

    PDF

  1. Wearable Sensing in Low-Field (0.55T) MRI Environment Felix Muñoz, Krishna S. Nayak, and Yasser Khan IEEE Sensors Letters, 2025

    Wearable sensors in the magnetic resonance imaging (MRI) environment enable the use of wearable devices to monitor vital signs such as heart rate, respiration rate, blood pressure, temperature, and biochemical markers during an MRI scan. Here, we demonstrate the efficacy of Bluetooth Low Energy (BLE)-enabled optical photoplethysmogram (PPG) sensors at a low-field MRI strength of 0.55 Tesla. We evaluate the noise in a wearable device caused by eddy currents from the rapidly switching MRI gradients, as well as the MRI noise and artifacts introduced by the BLE wearable into the MR receiver. Our results show that a custom-made BLE PPG sensor can operate effectively during 0.55T MRI scanning, providing precise (within 20ms) wireless monitoring of PPG with no observable effect on either the sensor signal or image quality. These results are encouraging for future wearable sensing in the MRI environment.

    @article{munoz2025wearable, title = {Wearable Sensing in Low-Field (0.55T) MRI Environment}, author = {Muñoz, Felix and Nayak, Krishna S. and Khan, Yasser}, journal = {IEEE Sensors Letters}, year = {2025}, publisher = {IEEE}, doi = {10.1109/LSENS.2025.3528305}, thumbnail = {munoz2025wearable.png}, url = {http://dx.doi.org/10.1109/LSENS.2025.3528305}, pdf = {munoz2025wearable.pdf} }

    PDF

  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} }

    PDF

  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} }

    PDF

  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, 2020 32, 15.

    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 = {32}, number = {15}, year = {2020}, 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} }

    PDF

Last modified: 2026-08-21