Bead-on-string Ag/AgCl heterostructures enable nonpolarizable stretchable dry electrodes for long-term, high-fidelity electrophysiological interfaces

Abstract

Wearable electrophysiological interfaces demand bioelectrodes that combine low-impedance, stable ion-electron transduction with high mechanical deformability, yet these requirements remain fundamentally incompatible in existing systems. Here, we present a nonpolarizable stretchable dry electrode based on a bead-on-string Ag/AgCl heterostructure, in which AgCl nanoparticles (NPs) are selectively assembled along percolated silver nanowire networks embedded within an elastomer matrix. This architecture spatially decouples Faradaic reaction sites from conductive pathways, constructing abundant, mechanically robust Ag/AgCl heterointerfaces for efficient ion-electron transduction while preserving continuous electron transport under large deformation. By systematically tuning the size of AgCl NPs (50-800 nm), the spatial distribution and interfacial length scale of Faradaic domains are optimized to maximize electrochemical performance. The resulting electrode achieves ultralow interfacial impedance (49 kΩ, 10 Hz), stable electrode potentials, and tolerance to severe mechanical deformation (ε > 370%), with minimal degradation over 500 stretch cycles. It enables low-noise, high-fidelity signal acquisition in the low-frequency regime, effectively suppressing motion artifacts and maintaining stable operation over 120 days of storage in air. When integrated with a spatiotemporal neural network for electrooculography decoding, the system achieves 98% accuracy in hands-free game control, demonstrating a robust paradigm for next-generation wearable bioelectronics.

Keywords

Stretchable dry electrodes / Ag/AgCl heterostructure / Faradaic interfaces / electrophysiological interfacing / human-machine interfaces

References

[1] Wang S,Song X.Non-invasive brain-computer interfaces: converging frontiers in neural signal decoding and flexible bioelectronics integration.Nanomicro Lett2026;18:193 PMCID:PMC12791105

[2] An X,Chen J.Flexible electronics in robotics systems: from devices to applications.SmartBot2026;2:e70017

[3] Dong W.Research progress of wearable electrochemical biosensors based on metal–organic frameworks (MOFs) for sweat detection.Adv Compos Hybrid Mater2025;8:1357

[4] Dong W,Zhai J.Structure and application of metal-organic frameworks in wearable electrochemical sweat sensors.TrAC Trends Anal Chem2026;197:118738

[5] Zhu P,Pang J,Zhang S.Latest developments and trends in electronic skin devices.Soft Sci2024;4:17

[6] Zou J,Song B.Bionic spider web flexible strain sensor based on CF-L and machine learning.ACS Appl Mater Interfaces2024;16:23761-70

[7] Liang A.A non-contact porous composite fiber paper-based humidity sensor for wearable breathing and skin humidity monitoring.J Mater Chem A2024;12:29081-91

[8] Liang A,Li X.A novel dual-mode paper fiber sensor based on laser-induced graphene and porous salt-ion for monitoring humidity and pressure of human.Chem Eng J2024;502:158184

[9] Buxi D,van Helleputte N.Correlation between electrode-tissue impedance and motion artifact in biopotential recordings.IEEE Sensors J2012;12:3373-83

[10] Kim K,Shin JH.Materials and structures of skin-interfaced electrodes for reducing motion artifacts in neural recording.Small Methods2026;10:e01708

[11] Song D.Stable and reliable bio-interfacing electrodes based on conductive hydrogels.Nat Electron2024;7:432-3

[12] Farago E,Suk M.A review of techniques for surface electromyography signal quality analysis.IEEE Rev Biomed Eng2023;16:472-86

[13] Grimnes S.Chapter 7 - Electrodes. In Bioimpedance and bioelectricity basics. Elsevier; 2015. pp. 179-254.

[14] Polachan K,Weigand S.Human body-electrode interfaces for wide-frequency sensing and communication: a review.Nanomaterials2021;11:2152 PMCID:PMC8401560

[15] Biesheuvel PM,Dykstra JE. The difference between Faradaic and non-Faradaic electrode processes. arXiv 2018, arXiv:1809.02930. Available online: https://doi.org/10.48550/arXiv.1809.02930. (accessed 2026-07-03)

[16] Kang TW,Kwon Y,Yeo WH.Recent progress in the development of flexible wearable electrodes for electrocardiogram monitoring during exercise.Adv NanoBiomed Res2024;4:2300169

[17] Yang L,Zhang Z.Insight into the contact impedance between the electrode and the skin surface for electrophysical recordings.ACS Omega2022;7:13906-12 PMCID:PMC9088920

[18] Malghan PG.A review on ECG filtering techniques for rhythm analysis.Res Biomed Eng2020;36:171-86

[19] Joutsen A,Kaappa E.ECG signal quality in intermittent long-term dry electrode recordings with controlled motion artifacts.Sci Rep2024;14:8882 PMCID:PMC11024137

[20] Li J,Zhong J.Laser‐induced graphene‐assisted patterning and transfer of silver nanowires for ultra‐conformal breathable epidermal electrodes in long‐term electrophysiological monitoring.Adv Funct Mater2025;35:2504481

[21] Miyamoto A,Cooray NF.Inflammation-free, gas-permeable, lightweight, stretchable on-skin electronics with nanomeshes.Nat Nanotechnol2017;12:907-13

[22] Cao C,Wang X.Liquid metal‐enhanced highly adhesive electrodes for multifunctional epidermal bioelectronics.Adv Funct Mater2024;34:2403671

[23] Peng Y,Zhang Y.Permeable, wet-adhesive, and EMI-resistant liquid metal electronic skin for high-fidelity electrophysiological monitoring in sweaty and electromagnetic environments.Adv Mater2025;37:e08041

[24] Ma J,Sa Z.High-precision electrohydrodynamic printing of EGaIn-AgNPs biphasic conductive ink for conformal and lightweight bioelectrodes.Soft Sci2025;5:50

[25] Liang X,Dou J.Stable and biocompatible carbon nanotube ink mediated by silk protein for printed electronics.Adv Mater2020;32:e2000165

[26] Sun B,Goswami S.Gas-permeable, multifunctional on-skin electronics based on laser-induced porous graphene and sugar-templated elastomer sponges.Adv Mater2018;30:e1804327

[27] Du X,Wang Y.An ultra-conductive and patternable 40 nm-thick polymer film for reliable emotion recognition.Adv Mater2024;36:e2403411

[28] Shin JH,June K,Kim TI.Polymeric conductive adhesive-based ultrathin epidermal electrodes for long-term monitoring of electrophysiological signals.Adv Mater2024;36:e2313157

[29] Tan P,Xiao F.Solution-processable, soft, self-adhesive, and conductive polymer composites for soft electronics.Nat Commun2022;13:358 PMCID:PMC8766561

[30] Hu R,Geng Y.High-fidelity bioelectrodes with bidirectional ion-electron transduction capability by integrating multiple charge-transfer processes.Adv Mater2024;36:e2403111

[31] Wang T,Shao LH.Stretchable Ag/AgCl nanowire dry electrodes for high-quality multimodal bioelectronic sensing.Sensors2024;24:6670 PMCID:PMC11511051

[32] Sun J,Luo G.A novel flexible Ag/AgCl quasi-reference electrode based on silver nanowires toward ultracomfortable electrophysiology and sensitive electrochemical glucose detection.J Mater Res Technol2020;9:13425-33

[33] Cho KR,Kim B,Lee S.Investigation of the AgCl formation mechanism on the Ag wire surface for the fabrication of a marine low-frequency-electric-field-detection Ag/AgCl sensor electrode.ACS Omega2022;7:25110-21 PMCID:PMC9330149

[34] Lim H,Kwon Y,Choa Y.Ultrathin, long-term stable, solid-state reference electrode enabled by enhanced interfacial adhesion and conformal coating of AgCl.Sens Actuators B Chem2020;309:127761

[35] Pargar F,Koleva DA.Microstructure, surface chemistry and electrochemical response of Ag|AgCl sensors in alkaline media.J Mater Sci2018;53:7527-50

[36] Kim S,Kwon J,Kim W.Facile synthesis of silver chloride nanocubes and their derivatives.Bull Korean Chem Soc2010;31:2918-22

[37] Zheng Y,Huang Z.Directional water collection on wetted spider silk.Nature2010;463:640-3

[38] Work RW.Dimensions, birefringences, and force-elongation behavior of major and minor ampullate silk fibers from orb-web-spinning spiders - the effects of wetting on these properties.Text Res J1977;47:650-62

[39] Zhang P,Hu J.Silver nanowires: synthesis technologies, growth mechanism and multifunctional applications.Mater Sci Eng B2017;223:1-23

[40] Corzo D,C A.High-performing organic electronics using terpene green solvents from renewable feedstocks.Nat Energy2023;8:62-73

[41] Lu Y,Yoon S.High-performance stretchable conductive composite fibers from surface-modified silver nanowires and thermoplastic polyurethane by wet spinning.ACS Appl Mater Interfaces2018;10:2093-104

[42] Stauch C,Luxenhofer R,Segets D.Quantifying surface properties of silica particles by combining Hansen parameters and Reichardt’s dye indicator data.Part Part Syst Charact2018;35:1800328

[43] Hansen CM.The universality of the solubility parameter.Ind Eng Chem Res Dev1969;8:2-11

[44] Ravve A.Principles of polymer chemistry, 3rd ed.; Springer New York, 2012.

[45] Bergin SD,Streich PV.Towards solutions of single‐walled carbon nanotubes in common solvents.Adv Mater2008;20:1876-81

[46] Süß S,Peukert W,Segets D.Determination of Hansen parameters for particles: a standardized routine based on analytical centrifugation.Adv Powder Technol2018;29:1550-61

[47] Gårdebjer S,Engström J,Persson M.Using Hansen solubility parameters to predict the dispersion of nano-particles in polymeric films.Polym Chem2016;7:1756-64

[48] Berggren M.How conducting polymer electrodes operate.Science2019;364:233-4

[49] Han L,Zhu C,Dong S.Facile solvothermal synthesis of cube-like Ag@AgCl: a highly efficient visible light photocatalyst.Nanoscale2011;3:2931-5

[50] Lin X,Guo B.Synthesis of AgCl/Ag/AgCl core-shell microstructures with enhanced photocatalytic activity under sunlight irradiation.J Environ Chem Eng2016;4:4021-8

[51] Yuk H,Zhao X.Hydrogel bioelectronics.Chem Soc Rev2019;48:1642-67

[52] Webster JG. Medical instrumentation: application and design, 4th ed.; John Wiley & Sons, 2009. https://books.google.com/books?id=muRmDwAAQBAJ&lpg=PR5&ots=xXIqtPVfFT&dq=Medical%20instrumentation%3A%20application%20and%20design%2C%202009&lr&hl=zh-CN&pg=PR9#v=onepage&q=Medical%20instrumentation:%20application%20and%20design,%202009&f=false. (accessed 2026-07-03)

[53] Romero MC.Impedance analysis for the study of biofilm formation on electrodes: an overview.J Mex Chem Soc2023;67:547-65

[54] Kumar G,Singh JP.Efficacy of various dry electrode-based ECG sensors: a review.J Biomed Mater Res A2025;113:e37845

[55] Ameri SK,Kuang IA.Imperceptible electrooculography graphene sensor system for human–robot interface.npj 2D Mater Appl2018;2:64

[56] Wang J,Liu H.Flexible electrodes for brain-computer interface system.Adv Mater2023;35:e2211012

[57] Li J,Li G,Jia R.Flexible brain electronic sensors advance wearable brain-computer interface.NPJ Biomed Innov2025;2:24 PMCID:PMC13055064

[58] Vourvopoulos A,Bermudez i Badia S.Brain–computer interfacing with interactive systems - case study 2. In: Eslambolchilar, P.; Komninos, A.; Dunlop, M.; editors. Intelligent computing for interactive system design. Association for Computing Machinery; 2021. pp. 237-72.

[59] Li Y,Teng J.Advancing EEG-based brain-computer interface technology via PEDOT:PSS electrodes.Matter2024;7:2859-95