A MXene-Based Wearable Biosensor System for High-Performance In Vitro Perspiration Analysis

Heterogeneous, 3D Architecturing of 2D Titanium Carbide (MXene) for Microdroplet Manipulation and Voice Recognition

Mismatched deformation in a bilayer composite with rigid coating on a soft substrate results in complex and uniform topographic patterns, yet it remains challenging to heterogeneously pattern the upper coatings with various localized structures. Herein, a heterogeneous, 3D microstructure composed of Ti₃C₂T_x titanium carbide (MXene) and single-walled carbon nanotubes (SWNTs) was fabricated using a one-step deformation of a thermally responsive substrate with designed open holes. The mechanically deformed SWNT-MXene (s-MXene) structure was next transferred onto an elastomeric substrate, and the resulting s-MXene/elastomer bilayer device exhibited three localized surface patterns, including isotropic crumples, periodic wrinkles, and large papillae-like microstructures. By adjusting the number and pattern, the s-MXene papillae arrays exhibited superhydrophobicity (>170°), strong and tunable adhesive force (52.3-110.6 μN), and ultra-large liquid capacity (up to 35 μL) for programmable microdroplet manipulation. The electrically conductive nature of s-MXene further enabled proper thermal management on microdroplets via Joule heating for miniaturized antibacterial tests. The s-MXene papillae were further fabricated in a piezoresistive pressure sensor with high sensitivity (11.47 kPa^-1). The output current changes of s-MXene sensors were highly sensitive to voice vibrations and responded identically with prerecorded profiles, promising their application in accurate voice acquisition and recognition.

Muscle-Inspired Self-Healing Hydrogels for Strain and Temperature Sensor

Recently, self-healing hydrogel bioelectronic devices have raised enormous interest for their tissue-like mechanical compliance, desirable biocompatibility, and tunable adhesiveness on bioartificial organs. However, the practical applications of these hydrogel-based sensors are generally limited by their poor fulfillment of stretchability and sensitivity, brittleness under subzero temperature, and single sensory function. Inspired by the fiber-reinforced microstructures and mechano-transduction systems of human muscles, a self-healing (90.8%), long-lasting thermal tolerant and dual-sensory hydrogel-based sensor is proposed, with high gauge factor (18.28) within broad strain range (268.9%), low limit of detection (5% strain), satisfactory thermosensation (-0.016 °C^-1), and highly discernible temperature resolution (2.7 °C). Especially by introducing a glycerol/water binary solvent system, desirable subzero-temperature self-healing performance, high water-retaining, and durable adhesion feature can be achieved, resulting from the ice crystallization inhibition and highly dynamic bonding. On account of the advantageous mechanoreception and thermosensitive capacities, a flexible touch keyboard for signature identification and a "fever indicator" for human forehead's temperature detection can be realized by this hydrogel bioelectronic device.

Recent advances in solid-contact ion-selective electrodes: functional materials, transduction mechanisms, and development trends

This article presents a comprehensive overview of recent progress in the design and applications of solid-contact ion-selective electrodes (SC-ISEs).

Elementary processes governing V2AlC chemical etching in HF

MXenes are synthesized by chemically exfoliating well-defined V2AlC, single-crystal pillars. Exfoliation is studied as a function of orientation and time using HF. This reveals that no etching can take place by HF penetration through the basal planes.

Recent advances of tissue-interfaced chemical biosensors

This review discusses recent advances of tissue interfaced chemical biosensors, highlights current challenges and gives an outlook on future possibilities.

Self-Sustainable Wearable Textile Nano-Energy Nano-System (NENS) for Next-Generation Healthcare Applications

Wearable electronics presage a future in which healthcare monitoring and rehabilitation are enabled beyond the limitation of hospitals, and self-powered sensors and energy generators are key prerequisites for a self-sustainable wearable system. A triboelectric nanogenerator (TENG) based on textiles can be an optimal option for scavenging low-frequency and irregular waste energy from body motions as a power source for self-sustainable systems. However, the low output of most textile-based TENGs (T-TENGs) has hindered its way toward practical applications. In this work, a facile and universal strategy to enhance the triboelectric output is proposed by integration of a narrow-gap TENG textile with a high-voltage diode and a textile-based switch. The closed-loop current of the diode-enhanced textile-based TENG (D-T-TENG) can be increased by 25 times. The soft, flexible, and thin characteristics of the D-T-TENG enable a moderate output even as it is randomly scrunched. Furthermore, the enhanced current can directly stimulate rat muscle and nerve. In addition, the capability of the D-T-TENG as a practical power source for wearable sensors is demonstrated by powering Bluetooth sensors embedded to clothes for humidity and temperature sensing. Looking forward, the D-T-TENG renders an effective approach toward a self-sustainable wearable textile nano-energy nano-system for next-generation healthcare applications.

Recent Advances in Skin Chemical Sensors

This review summarizes the latest developments in the field of skin chemical sensors, in particular wearable ones. Five major applications are covered in the present work: (i) sweat analysis, (ii) skin hydration, (iii) skin wounds, (iv) perspiration of volatile organic compounds, and (v) general skin conditions. For each application, the detection of the most relevant analytes is described in terms of transduction principles and sensor performances. Special attention is paid to the biological fluid collection and storage and devices are also analyzed in terms of reusability and lifetime. This review highlights the existing gaps between current performances and those needed to promote effective commercialization of sensors; future developments are also proposed.

A versatile, cost-effective, and flexible wearable biosensor for in situ and ex situ sweat analysis, and personalized nutrition assessment

Point-of-care (POC) diagnostics have shown excellent potential in rapid biological analysis and health/disease monitoring. Here, we introduce a versatile, cost-effective, flexible, and wearable POC biomarker patch for effective sweat collection and health monitoring. We design and fabricate channels/patterns on filter paper using wax printing technology, which can direct sweat to collection and biomarker detection zones on the proposed platform. The detection zones are designed to measure the amount of collected sweat, in addition to measuring the sweat pH, and glucose (a potential diabetic biomarker), and lactate concentrations. It is significantly challenging to measure glucose in human sweat by colorimetric methods due to the extremely low glucose levels found in this medium. However, we overcame this issue by effectively engineering our wearable biosensor for optimal intake, storage, and evaporation of sweat. Our design concentrates the colorant (indicator) into a small detection zone and significantly increases the sensitivity for the sweat glucose sensing reactions. The device can thus detect glucose in physiological glucose concentration range of 50-300 μM. This cost-effective and wearable biosensor can provide instant in situ quantitative results for targets of interest, such as glucose, pH, and lactate, when coupled with the imaging and computing functionalities of smartphones. Meanwhile, it is also feasible to extract the air-dried sweat from the storage zone for further ex situ measurements of a broader portfolio of biomarkers, leading to applications of our wearable biosensor in personalized nutrition and medicine.