Electrolyte-gated amorphous IGZO transistors with extended gates for prostate-specific antigen detection.

The prostate-specific antigen (PSA) test is considered an important way for preoperative diagnosis and accurate screening of prostate cancer. Current antigen detection methods, including radioimmunoassay, enzyme-linked immunosorbent assay and microfluidic electrochemical detection, feature expensive equipment, long testing time and poor stability. Here, we propose a portable biosensor composed of electrolyte-gated amorphous indium gallium zinc oxide (a-IGZO) transistors with an extended gate, which can achieve real-time, instant PSA detection at a low operating voltage (<2 V) owing to the liquid-free ionic conductive elastomer (ICE) serving as the gate dielectric. The electric double layer (EDL) capacitance in ICE enhances the accumulation of carriers in the IGZO channel, leading to strong gate modulation, which enables the IGZO transistor to have a small subthreshold swing (<0.5 V dec-1) and a high on-state current (∼4 × 10-4 A). The separate, biodegradable, and pluggable sensing pad, serving as an extended gate connected to the IGZO transistor, prevents contamination and depletion arising from direct contact with biomolecular buffers, enabling the IGZO transistor to maintain superior electronic performance for at least six months. The threshold voltage and channel current of the transistor exhibit excellent linear response to PSA molecule concentrations across five orders of magnitude ranging from 1 fg mL-1 to 10 pg mL-1, with a detection limit of 400 ag mL-1 and a detection time of ∼5.1 s. The fabricated biosensors offer a point-of-care system for antigen detection, attesting the feasibility of the electrolyte-gated transistors in clinical screening, healthcare diagnostics and biological management.

Hierarchical Serpentine-Helix Combination for 3D Stretchable Electronics.

3D stretchable electronics attract growing interest due to their new and more complex functionalities compared to 1D or 2D counterparts. Among all 3D configuration designs, a 3D helical structure is commonly used as it can be designed to achieve outstanding stretching ratios as well as highly robust mechanical performance. However, the stretching ratio that mainly focuses on the axis direction hinders its applications. Inspired by hierarchies in a tendon, a novel structural design of hierarchical 3D serpentine-helix combination is proposed. The structural design constructed by a sequence with repeating small units winding in a helical manner around the axis can enable large mechanical forces transferred down to a smaller scale with the dissipation of potentially damaging stresses by microscale buckling, thereby endowing the electronic components made from high-performance but hard-to-stretch materials with large stretchability (≥200%) in x-, y-, or z-axis direction, high structural stability, and extraordinary electromechanical performance. Two applications including a wireless charging patch and an epidermal electronic system are demonstrated. The epidermal electronic system made of several hierarchical 3D serpentine-helix combinations allows for high-fidelity monitoring of electrophysiological signals, galvanic skin response, and finger-movement-induced electrical signals, which can achieve good tactile pattern recognition when combined with an artificial neural network.

Configurable direction sensitivity of skin-mounted microfluidic strain sensor with auxetic metamaterial.

Electromechanical coupling plays a key role in determining the performance of stretchable strain sensor. Current regulation of the electromechanical coupling in stretchable strain sensor is largely restricted by the intrinsic mechanical properties of the device. In this study, a microfluidic strain sensor based on the core-shell package design with the auxetic metamaterial (AM) is presented. By overriding the mechanical properties of the device, the AM in the package effectively tunes the deformation of the microfluidic channel with the applied strain and configures the directional strain sensitivity with a large modulation range. The gauge factor (GF) of the strain sensor in the radial direction of the channel can be gradually shifted from the intrinsically negative value to a positive one by adopting the AMs with different designs. By simply replacing the AM in the package, the microfluidic strain sensor with the core-shell package can be configurated as an omnidirectional or directional stretchable strain sensor. With the directional sensitivity brought by the rational AM design, the application of the AM-integrated strain sensor in the skin-mounted tactile detection is demonstrated with high tolerance to unintended wrist movements.

Highly stretchable van der Waals thin films for adaptable and breathable electronic membranes.

The conformal integration of electronic systems with irregular, soft objects is essential for many emerging technologies. We report the design of van der Waals thin films consisting of staggered two-dimensional nanosheets with bond-free van der Waals interfaces. The films feature sliding and rotation degrees of freedom among the staggered nanosheets to ensure mechanical stretchability and malleability, as well as a percolating network of nanochannels to endow permeability and breathability. With an excellent mechanical match to soft biological tissues, the freestanding films can naturally adapt to local surface topographies and seamlessly merge with living organisms with highly conformal interfaces, rendering living organisms with electronic functions, including leaf-gate and skin-gate transistors. On-skin transistors allow high-fidelity monitoring and local amplification of skin potentials and electrophysiological signals.

Stretchable Micromotion Sensor with Enhanced Sensitivity Using Serpentine Layout.

The application of the serpentine mesh layout in stretchable electronics provides a feasible method to achieve the desired stretchability by structural design instead of modifying the intrinsic mechanical properties of the applied materials. However, previous works using the serpentine layout mainly focused on the optimization of structural stretchability. In this paper, the serpentine mesh design concept is used to transform the high-performance but hard-to-stretch piezoelectric film into a stretchable form. The serpentine layout design strategies for the piezoelectric film, which aim at not only desired stretchability but also high utilization of the strain in the piezoelectric film during deformation, are discussed with experimental and computational results. A stretchable micromotion sensor with high sensitivity is realized using the piezoelectric film with a serpentine layout. Human voice recognition applications of the sensor, including speech pattern recognition with machine learning, are demonstrated with the sensor integrated with a wireless module. The stretchable micromotion sensor with a serpentine layout illustrates the broader application of serpentine layout design in the functional materials of stretchable electronics, which can further extend the range of available functional materials for novel stretchable electronic devices.

Tailoring the energy band in flexible photodetector based on transferred ITO/Si heterojunction via interface engineering.

Interface engineering is an important method to modulate electronic structures for improving the physical properties of semiconductors as well as designing novel devices. Recently, development of flexible electronic devices based on inorganic thin films on flexible substrates, which provides solutions to meet the emerging technological demands, may also expend the methodology of interface engineering. Herein, a semitransparent photodetector based on an indium-tin oxide (ITO)-on-silicon (Si) heterojunction was fabricated on a flexible substrate and investigated under mechanical bending strains. It is found that the barrier height of the heterojunction can be tailored continuously and reversibly from 0.23 eV to 0 eV, corresponding to the Schottky and Ohmic junctions respectively. Meanwhile, the turn-on voltage and the response time of the as-prepared photodetector can be obviously reduced under bending strain, which can be attributed to the modulation of the Si bandgap and hole mobility. Our experimental studies not only shed new light on the strain modulation mechanism of the heterojunction interface, but also pave a prominent way to integrated high-performance flexible photodetectors.

Highly stretchable and shape-controllable three-dimensional antenna fabricated by "Cut-Transfer-Release" method.

Recent progresses on the Kirigami-inspired method provide a new idea to assemble three-dimensional (3D) functional structures with conventional materials by releasing the prestrained elastomeric substrates. In this paper, highly stretchable serpentine-like antenna is fabricated by a simple and quick "Cut-Transfer-Release" method for assembling stretchable 3D functional structures on an elastomeric substrate with a controlled shape. The mechanical reliability of the serpentine-like 3D stretchable antenna is evaluated by the finite element method and experiments. The antenna shows consistent radio frequency performance with center frequency at 5.6 GHz during stretching up to 200%. The 3D structure is also able to eliminate the hand effect observed commonly in the conventional antenna. This work is expected to spur the applications of novel 3D structures in the stretchable electronics.

Thermal Release Transfer Printing for Stretchable Conformal Bioelectronics.

Soft neural electrode arrays that are mechanically matched between neural tissues and electrodes offer valuable opportunities for the development of disease diagnose and brain computer interface systems. Here, a thermal release transfer printing method for fabrication of stretchable bioelectronics, such as soft neural electrode arrays, is presented. Due to the large, switchable and irreversible change in adhesion strength of thermal release tape, a low-cost, easy-to-operate, and temperature-controlled transfer printing process can be achieved. The mechanism of this method is analyzed by experiments and fracture-mechanics models. Using the thermal release transfer printing method, a stretchable neural electrode array is fabricated by a sacrificial-layer-free process. The ability of the as-fabricated electrode array to conform different curvilinear surfaces is confirmed by experimental and theoretical studies. High-quality electrocorticography signals of anesthetized rat are collected with the as-fabricated electrode array, which proves good conformal interface between the electrodes and dura mater. The application of the as-fabricated electrode array on detecting the steady-state visual evoked potentials research is also demonstrated by in vivo experiments and the results are compared with those detected by stainless-steel screw electrodes.

Ultrafast response flexible breath sensor based on vanadium dioxide.

Real-time monitoring of breath can provide clinically relevant information about apnea syndrome and other important aspects of human physiology. Here, we introduce a flexible skin-like breath sensor developed by transfer-printing vanadium dioxide (VO2) thin films on PDMS substrates. This flexible breath sensor can conformably laminate on the skin under the nose with different curvatures and operate at different environment temperatures through day and night. Attributed to the high temperature coefficient of resistance of VO2, the enhanced breath sensing performance was demonstrated and the response time and recovery time can be as fast as 0.5 s. The excellent sensing performance and fast response time indicate that the VO2-based breath sensor is feasible in monitoring breath for prevention of apnea syndrome.

A Ferroelectric Ceramic/Polymer Composite-Based Capacitive Electrode Array for In Vivo Recordings.

A new implantable capacitive electrode array for electrocorticography signal recording is developed with ferroelectric ceramic/polymer composite. This ultrathin and electrically safe capacitive electrode array is capable of attaching to the biological tissue conformably. The barium titanate/polyimide (BaTiO3 /PI) nanocomposite with high dielectric constant is successfully synthesized and employed as the ultrathin dielectric layer of the capacitive BaTiO3 /PI electrode array. The performance of the capacitive BaTiO3 /PI electrode array is evaluated by electrical characterization and 3D finite-element modeling. In vivo, neural experiments on the visual cortex of rats show the reliability of the capacitive BaTiO3 /PI electrode array. This work shows the potentials of capacitive BaTiO3 /PI electrode array in the field of brain/computer interfaces.

Flexible infrared detectors based on p-n junctions of multi-walled carbon nanotubes.

Different types of multi-walled carbon nanotubes (CNTs), synthesized by chemical vapor deposition, are used to fabricate infrared (IR) detectors on flexible substrates based on CNT p-n junctions. It is found that this kind of detector is sensitive to infrared signals with a power density as low as 90 µW mm(-2) even at room temperature. Besides, unlike other devices, the detector with this unique structure can be bent for 100 cycles without any damage and its functionality does not degenerate once it recovers to the initial state. The results give a good reference for developing efficient, low-cost, and flexible IR detectors.

Self-Powered, Wireless, Remote Meteorologic Monitoring Based on Triboelectric Nanogenerator Operated by Scavenging Wind Energy.

Meteorologic monitoring plays a key role on weather forecast and disaster warning and deeply relies on various sensor networks. It is an optimal choice that grabbing the environmental energy around sensors for driving sensor network. Here, we demonstrate a self-powered, wireless, remote meteorologic monitoring system based on an innovative TENG. The TENG has been proved capable of scavenging wind energy and can be employed for self-powered, wireless meteorologic sounding. This work not only promotes the development of renewable energy harvesting, but also exploits and enriches promising applications based on TENGs for self-powered, wireless, remote sensing.