Fluorescent-based biodegradable microneedle sensor array for tether-free continuous glucose monitoring with smartphone application.

Continuous glucose monitoring (CGM) allows patients with diabetes to manage critical disease effectively and autonomously and prevent exacerbation. A painless, wireless, compact, and minimally invasive device that can provide CGM is essential for monitoring the health conditions of freely moving patients with diabetes. Here, we propose a glucose-responsive fluorescence-based highly sensitive biodegradable microneedle CGM system. These ultrathin and ultralight microneedle sensor arrays continuously and precisely monitored glucose concentration in the interstitial fluid with minimally invasive, pain-free, wound-free, and skin inflammation-free outcomes at various locations and thicknesses of the skin. Bioresorbability in the body without a need for device removal after use was a key characteristic of the microneedle glucose sensor. We demonstrated the potential long-term use of the bioresorbable device by applying the tether-free CGM system, thus confirming the successful detection of glucose levels based on changes in fluorescence intensity. In addition, this microneedle glucose sensor with a user-friendly designed home diagnosis system using mobile applications and portable accessories offers an advance in CGM and its applicability to other bioresorbable, wearable, and implantable monitoring device technology.

Strain-Insensitive Stretchable Fiber Conductors Based on Highly Conductive Buckled Shells for Wearable Electronics.

Based on their high applicability to wearable electronics, fiber-based stretchable electronics have been developed via different strategies. However, the electrical conductivity of a fiber electrode is severely degraded, following deformation upon stretching. Despite the introduction of conductive buckled structures to resolve this issue, there still exist limitations regarding the simultaneous realizations of high conductivity and stretchability. Here, we exploit the dense distribution of the Ag nanoparticle (AgNP) network in polyurethane (PU) to fabricate a strain-insensitive stretchable fiber conductor comprising highly conductive buckled shells via a facile chemical process. These buckled AgNPs/PU fibers exhibit stable and reliable electrical responses across a wide range (tensile strain = ∼200%), in addition to their high electrical conductivity (26,128 S/m) and quality factor (Q = 2.29). Particularly, the negligible electrical hysteresis and excellent durability (>10,000 stretching-releasing cycles) of the fibers demonstrate their high applicability to wearable electronics. Furthermore, we develop buckled fiber-based pH sensors exhibiting stable, repeatable, and highly distinguishable responses (changing pH is from 4 to 8, response time is 5-6 s) even under 100% tensile strain. The buckled AgNPs/PU fibers represent a facile strategy for maintaining the stable electrical performances of fiber electrodes across the strain range of human motion for wearable applications.

Tailored Self-Assembled Monolayer using Chemical Coupling for Indium-Gallium-Zinc Oxide Thin-Film Transistors: Multifunctional Copper Diffusion Barrier.

Controlling the contact properties of a copper (Cu) electrode is an important process for improving the performance of an amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistor (TFT) for high-speed applications, owing to the low resistance-capacitance product constant of Cu. One of the many challenges in Cu application to a-IGZO is inhibiting high diffusivity, which causes degradation in the performance of a-IGZO TFT by forming electron trap states. A self-assembled monolayer (SAM) can perfectly act as a Cu diffusion barrier (DB) and passivation layer that prevents moisture and oxygen, which can deteriorate the TFT on-off performance. However, traditional SAM materials have high contact resistance and low mechanical-adhesion properties. In this study, we demonstrate that tailoring the SAM using the chemical coupling method can enhance the electrical and mechanical properties of a-IGZO TFTs. The doping effects from the dipole moment of the tailored SAMs enhance the electrical properties of a-IGZO TFTs, resulting in a field-effect mobility of 13.87 cm2/V·s, an on-off ratio above 107, and a low contact resistance of 612 Ω. Because of the high electrical performance of tailored SAMs, they function as a Cu DB and a passivation layer. Moreover, a selectively tailored functional group can improve the adhesion properties between Cu and a-IGZO. These multifunctionally tailored SAMs can be a promising candidate for a very thin Cu DB in future electronic technology.

Ultrasensitive and Stretchable Conductive Fibers Using Percolated Pd Nanoparticle Networks for Multisensing Wearable Electronics: Crack-Based Strain and H2 Sensors.

The need for wearable electronic devices continues to grow, and the research is under way for stretchable fiber-type sensors that are sensitive to the surrounding atmosphere and will provide proficient measurement capabilities. Currently, one-dimensional fiber sensors have several limitations for their extensive use because of the complex structures of the sensing mechanisms. Thus, it is essential to miniaturize these materials with durability while integrating multiple sensing capabilities. Herein, we present an ultrasensitive and stretchable conductive fiber sensor using PdNP networks embedded in elastomeric polymers for crack-based strain and H2 sensing. The fiber multimodal sensors show a gauge factor of ∼2040 under 70% strain and reliable mechanical deformation tolerance (10,000 stretching cycles) in the strain-sensor mode. For H2 sensing, the fiber multimodal sensors exhibit a wide sensing range of high sensitivity: -0.43% response at 5 ppm (0.0005%) H2 gas and -27.3% response at 10% H2 gas. For the first time, we demonstrate highly stretchable H2 sensors that can detect H2 gas under 110% strain with mechanical durability. As demonstrated, their stable performance allows them to be used in wearable applications that integrate fiber multimodal sensors into industrial safety clothing along with a microinorganic light-emitting diode for visual indication, which exhibits proper activation upon H2 gas exposure.

Recent Advances in 1D Stretchable Electrodes and Devices for Textile and Wearable Electronics: Materials, Fabrications, and Applications.

Research on wearable electronic devices that can be directly integrated into daily textiles or clothes has been explosively grown holding great potential for various practical wearable applications. These wearable electronic devices strongly demand 1D electronic devices that are light-weight, weavable, highly flexible, stretchable, and adaptable to comport to frequent deformations during usage in daily life. To this end, the development of 1D electrodes with high stretchability and electrical performance is fundamentally essential. Herein, the recent process of 1D stretchable electrodes for wearable and textile electronics is described, focusing on representative conductive materials, fabrication techniques for 1D stretchable electrodes with high performance, and designs and applications of various 1D stretchable electronic devices. To conclude, discussions are presented regarding limitations and perspectives of current materials and devices in terms of performance and scientific understanding that should be considered for further advances.

Development of an Electrogenerated Chemiluminescence Biosensor using Carboxylic acid-functionalized MWCNT and Au Nanoparticles.

A COOH-F-MWCNT-Nafion-Ru(bpy)(3) (2+)-Au-ADH electrogenerated chemiluminescence (ECL) electrode using COOH-functionalized MWCNT (COOH-F-MWCNT) and Au nanoparticles synthesized by the radiation method was fabricated for ethanol sensing. A higher sensing efficiency for ethanol for the ECL biosensor prepared by PAAc-g-MWCNT was measured compared to that of the ECL biosensor prepared by PMAc-g-MWCNT, and purified MWCNT. Experimental parameters affecting ethanol detection were also examined in terms of pH and the content of PAAc-g-MWCNT in Nafion. Little interference of other compounds was observed for the assay of ethanol. Results suggest this ECL biosensor could be applied for ethanol detection in real samples.