Search

Soft, wireless physiological sensors that gently adhere to the skin are capable of continuous clinical-grade health monitoring in hospital and/or home settings, of particular value to critically ill infants and other vulnerable patients, but they present risks for injury upon thermal failure. This paper introduces an active materials approach that automatically minimizes such risks, to complement traditional schemes that rely on integrated sensors and electronic control circuits. The strategy exploits thin, flexible bladders that contain small volumes of liquid with boiling points a few degrees above body temperature. When the heat exceeds the safe range, vaporization rapidly forms highly effective, thermally insulating structures and delaminates the device from the skin, thereby eliminating any danger to the skin. Experimental and computational thermomechanical studies and demonstrations in a skin-interfaced mechano-acoustic sensor illustrate the effectiveness of this simple thermal safety system and suggest its applicability to nearly any class of skin-integrated device technology.

Continuous health monitoring is essential for clinical care, especially for patients in neonatal and pediatric intensive care units. Monitoring currently requires wired biosensors affixed to the skin with strong adhesives that can cause irritation and iatrogenic injuries during removal. Emerging wireless alternatives are attractive, but requirements for skin adhesives remain. Here, we present a materials strategy enabling wirelessly triggered reductions in adhesive strength to eliminate the possibility for injury during removal. The materials involve silicone composites loaded with crystallizable oils with melting temperatures close to, but above, surface body temperature. This solid/liquid phase transition occurs upon heating, reducing the adhesion at the skin interface by more than 75%. Experimental and computational studies reveal insights into effects of oil mixed randomly and patterned deterministically into the composite. Demonstrations in skin-integrated sensors that include wirelessly controlled heating and adhesion reduction illustrate the broad utility of these ideas in clinical-grade health monitoring.

Smart chromatic materials with optical transmittances that can be modified by light scattering upon external stimuli are attracting extensive interest because of their appealing applications in smart windows, privacy protection, electronic displays, etc. However, the development of these scatterers, which are mostly activated by electric fields, is hindered by their intrinsic energy consumption, slow responses, and poor stability. Recently, mechanoresponsive scatterers based on a strain-driven reconfiguration of the surface or internal structure have emerged, featuring fast responses and a simple composition/fabrication. Because there is no energy consumption to maintain the transparency/opacity, this novel scheme for scatterers holds great promise to break the existing bottleneck. This article presents recent advances in the development of mechanoresponsive scatterers and compares different structural design strategies. The scatterers are categorized into 2D, 3D, and other types according to the dimensions of their functioning structures. The fabrication methods, mechanisms, and relationships between the structural parameters and optical modulating performances are discussed for each category. Next, the potential applications of these scatterers are outlined. Finally, the advantages and disadvantages of the mainstream 2D and 3D categories are summarized, followed by a perspective on future research directions.

Gas sensors based on semiconductor metal oxides (SMOs) have gained widespread attention for Internet of Things applications; however, high operating temperatures and low gas selectivity limit their applications. Recently, metal–organic frameworks (MOFs) have demonstrated potential in enhancing gas selectivity through the physical filtration of gas molecules based on their kinetic diameters. However, their application has been predominantly limited to simplistic nanostructured sensors. These sensors exhibit inherently inferior gas sensor performance compared to three‐dimensional nanostructure gas sensors. In this study, a highly periodic, 3D hierarchical ZnO/ZIF‐8 nanostructure is fabricated for photoactivated gas sensing at room temperature. Under UV illumination, the gas sensor exhibited a 17‐fold enhancement in gas response toward 0.1 ppm NO2 compared to pristine ZnO. In addition, the ZIF‐8 coating selectively increased the NO2 gas response compared to ethanol, acetone, and toluene gases, thereby improving the gas selectivity. The gas response improvement by the ZIF‐8 layer coating, which has not been achieved by previous studies, is based on enhanced photoactivation by the solid interaction between ZIF‐8 and ZnO. These results provide a systematic background for controlling the layer thickness of SMO‐MOF nanostructures and the catalytic role of MOF in photoactivated gas sensing. [ABSTRACT FROM AUTHOR]

Environmental pollutants threaten millions of lives and state-of-the-art strategies, mostly based on surface catalytic activities to remediate environmental issues, have emerged. Despite their active capabilities, traditional schemes are only capable of a single function, either sensing hazardous chemicals or their reduction, limiting the identification of clear solutions to environmental problems. This study proposes a material engineering method that adopts both the detection and neutralization of environmental pollutants for remediation. This strategy exploits ultrafast flash lamp-driven thermal engineering to realize ultra-small (<5 nm) polyelemental nanoparticles with a uniform size distribution on a three-dimensional (3D) metal oxide nanostructure. Specifically, an intense pulse light treatment on highly periodic 3D thin-shell TiO2 triggers an intensive photothermal effect, enabling instant reduction of various surface-decorated metal ion precursors into an atomically mixed heterostructure. Experimental and computational studies were conducted to investigate the physicochemical reactions occurring on the heterometal catalysts. As a proof-of-concept, the universal photocatalytic utility of dual-mode photoactivated quaternary phase (PtPdNiCo) NPs incorporated into 3D TiO2 was demonstrated for gaseous chemical sensing and degradation of environmental pollutants in water. [ABSTRACT FROM AUTHOR]

Nutrients play critical roles in maintaining core physiological functions and in preventing diseases. Technologies for delivering these nutrients and for monitoring their concentrations can help to ensure proper nutritional balance. Eccrine sweat is a potentially attractive class of biofluid for monitoring purposes due to the ability to capture sweat easily and noninvasively from nearly any region of the body using skin‐integrated microfluidic technologies. Here, a miniaturized system of this type is presented that allows simple, rapid colorimetric assessments of the concentrations of multiple essential nutrients in sweat, simultaneously and without any supporting electronics – vitamin C, calcium, zinc, and iron. A transdermal patch integrated directly with the microfluidics supports passive, sustained delivery of these species to the body throughout a period of wear. Comparisons of measurement results to those from traditional lab analysis methods demonstrate the accuracy and reliability of this platform. On‐body tests with human subjects reveal correlations between the time dynamics of concentrations of these nutrients in sweat and those of the corresponding concentrations in blood. Studies conducted before and after consuming certain foods and beverages highlight practical capabilities in monitoring nutritional balance, with strong potential to serve as a basis for guiding personalized dietary choices. [ABSTRACT FROM AUTHOR]

For the last several years, indoor air quality monitoring has been a significant issue due to the increasing time portion of indoor human activities. Especially, the early detection of volatile organic compounds potentially harmful to the human body by the prolonged exposure is the primary concern for public human health, and such technology is imperatively desired. In this study, highly porous and periodic 3D TiO2 nanostructures are designed and studied for this concern. Specifically, extremely high gas molecule accessibility throughout the whole nanostructures and precisely controlled internecks of 3D TiO2 nanostructures can achieve an unprecedented gas response of 299 to 50 ppm CH3COCH3 with an extremely fast response time of less than 1s. The systematic approach to utilize the whole inner and outer surfaces of the gas sensing materials and periodically formed internecks to localize the current paths in this study can provide highly promising perspectives to advance the development of chemoresistive gas sensors using metal oxide nanostructures for the Internet of Everything application. [ABSTRACT FROM AUTHOR]

One of the well‐known strategies for achieving high‐performance light‐activated gas sensors is to design a nanostructure for effective surface responses with its geometric advances. However, no study has gone beyond the benefits of the large surface area and provided fundamental strategies to offer a rational structure for increasing their optical and chemical performances. Here, a new class of UV‐activated sensing nanoarchitecture made of highly periodic 3D TiO2, which facilitates 55 times enhanced light absorption by confining the incident light in the nanostructure, is prepared as an active gas channel. The key parameters, such as the total 3D TiO2 film and thin‐shell thicknesses, are precisely optimized by finite element analysis. Collectively, this fundamental design leads to ultrahigh chemoresistive response to NO2 with a theoretical detection limit of ≈200 ppt. The demonstration of high responses with visible light illumination proposes a future perspective for light‐activated gas sensors based on semiconducting oxides. [ABSTRACT FROM AUTHOR]

Recent advances in passive flying systems inspired by wind-dispersed seeds contribute to increasing interest in their use for remote sensing applications across large spatial domains in the Lagrangian frame of reference. These concepts create possibilities for developing and studying structures with performance characteristics and operating mechanisms that lie beyond those found in nature. Here, we demonstrate a hybrid flier system, fabricated through a process of controlled buckling, to yield unusual geometries optimized for flight. Specifically, these constructs simultaneously exploit distinct fluid phenomena, including separated vortex rings from features that resemble those of dandelion seeds and the leading-edge vortices derived from behaviors of maple seeds. Advanced experimental measurements and computational simulations of the aerodynamics and induced flow physics of these hybrid fliers establish a concise, scalable analytical framework for understanding their flight mechanisms. Demonstrations with functional payloads in various forms, including bioresorbable, colorimetric, gas-sensing, and light-emitting platforms, illustrate examples with diverse capabilities in sensing and tracking., (© The Author(s) 2024. Published by Oxford University Press on behalf of National Academy of Sciences.)

NO 2 is a major air pollutant that should be monitored due to its harmful effects on the environment and human health. Semiconducting metal oxide-based gas sensors have been widely explored owing to their superior sensitivity towards NO 2 , but their high operating temperature (>200 °C) and low selectivity still limit their practical use in sensor devices. In this study, we decorated graphene quantum dots (GQDs) with discrete band gaps onto tin oxide nanodomes (GQD@SnO 2 nanodomes), enabling room temperature (RT) sensing towards 5 ppm NO 2 gas with a noticeable response (( R a / R g ) - 1 = 4.8), which cannot be matched using pristine SnO 2 nanodomes. In addition, the GQD@SnO 2 nanodome based gas sensor shows an extremely low detection limit of 1.1 ppb and high selectivity compared to other pollutant gases (H 2 S, CO, C 7 H 8 , NH 3 , and CH 3 COCH 3 ). The oxygen functional groups in GQDs specifically enhance NO 2 accessibility by increasing the adsorption energy. Strong electron transfer from SnO 2 to GQDs widens the electron depletion layer at SnO 2 , thereby improving the gas response over a broad temperature range (RT-150 °C). This result provides a basic perspective for utilizing zero-dimensional GQDs in high-performance gas sensors operating over a wide range of temperatures., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)