Printable Transparent Microelectrodes toward Mechanically and Visually Imperceptible Electronics

Abstract

Flexible and transparent electrodes are highly useful in wearable optoelectronic systems for healthcare and biosensing applications for conducting multimodal assessments with electrophysiological and optical measures. In such systems, the electrodes should exhibit a low sheet resistance, high visible transmittance, and small feature size, for reliable electrical sensing, optical observation of attached objects, and integration of devices for mapping local biology events, respectively. Herein, fine-printed, flexible, and transparent microelectrodes that allow biosensing and device integration are reported. The microelectrodes containing cross-aligned silver nanowire (AgNW) networks are patterned via a selective wetting deposition technique on a 1 μm-thick polymer substrate. A low sheet resistance of 25 Ω sq À1 and a visible transmittance of 96%-99% are achieved with a small pattern width of 25 μm. The biosensing application is demonstrated by detecting the leaf electric potential; the leaf cells under the microelectrodes are observed because of visible transparency. Furthermore, device integration is demonstrated by electronic circuits with ultrathin and transparent organic transistors. The transistors exhibit white-light illumination stability and mechanical stability to bending stress. These demonstrations provide a basis for developing ultraimperceptible wearable sensor systems with ultrathinness and high visible transmittance.

Heterogeneous Functional Dielectric Patterns for Charge‐Carrier Modulation in Ultraflexible Organic Integrated Circuits

“…[41,42] This transparency is potentially useful in the application of imperceptible electronics. [43] In this study, the PNDPE solution is spin-coated to form ultrathin gate dielectrics, in which the thickness is 13.6 ± 0.5 nm (the number of sample: N = 9) on an aluminum gate electrode, which is anodized to form an AlO x layer (thickness: 6 nm). The thickness of each layer was determined through the capacitance measurement (more details are mentioned in Section 4).…”

“…In addition, its solution is visibly transparent because its absorption occurs in the UV range [41,42]. This transparency is potentially useful in the application of imperceptible electronics [43]. In this study, the PNDPE solution is spin-coated to form ultrathin gate dielectrics, in which the thickness is 13.6 ± 0.5 nm (the number of sample: N = 9) on an aluminum gate electrode, which is anodized to form an AlO x layer (thickness: 6 nm).…”

Emerging Biomedical Applications of Organic Light‐Emitting Diodes

“…[24][25][26][27] Alternatives comprise the use of dielectric/metal/dielectric films, [28][29][30] where common dielectrics are high-refractive index materials such as MoO 3 , WO 3 , and ZnS. Other flexible transparent electrode materials include conductive polymers, [31,32] graphene, [33][34][35] carbon nanotubes, [36,37] metal nanowires, [38][39][40][41] and metal meshes [42,43] as reviewed in refs. [22,[44][45][46][47].…”

Conductive Polymer‐Based Bioelectronic Platforms toward Sustainable and Biointegrated Devices: A Journey from Skin to Brain across Human Body Interfaces

“…[251] Also in this field nanomaterials and nanopatterning techniques have been exploited so that interconnected networks of cross-aligned Ag NW, besides featuring a sheet resistance of 5 Ω sq −1 , have achieved high light transmission (96%), a remarkable property for integrating bioelectric potentials devices and wearable platforms. [252] Indeed, stretchable and transparent conductive tracks demonstrating high biocompatibility (for 5 months implantation) have been fabricated using Ag/Au core-shell nanowires that served as connections for an ECoG device. [253] However, moving from planar configurations, the rise of ultra-conformable bioelectronic platforms complying with the curvilinear profile of human tissues has recently highlighted the lack of adequate wiring technologies since out-of-plane and self-standing interconnections are evidently required to operate 3D-designed devices.…”

“…[ 251 ] Also in this field nanomaterials and nanopatterning techniques have been exploited so that interconnected networks of cross‐aligned Ag NW, besides featuring a sheet resistance of 5 Ω sq −1 , have achieved high light transmission (96%), a remarkable property for integrating bioelectric potentials devices and wearable platforms. [ 252 ] Indeed, stretchable and transparent conductive tracks demonstrating high biocompatibility (for 5 months implantation) have been fabricated using Ag/Au core–shell nanowires that served as connections for an ECoG device. [ 253 ]…”