Noninvasive and Wearable Respiration Sensor Based on Organic Semiconductor Film with Strong Electron Affinity

Self-standing perylene diimide covalent organic framework membranes for trace TMA sensing at room temperature

The unprecedented demand for highly selective, real-time monitoring and low-power gas sensors used in food quality control has been driven by the increasing popularity of the Internet of Things (IoT). Herein, the self-standing perylene diimide based covalent organic framework membranes (COFMPDI-THSTZ) were prepared via liquid-liquid interfacial synthesis method. By incorporating the perylene diimide monomer into the COFM through molecular engineering, COFMPDI-THSTZ based sensor demonstrated an outstanding trimethylamine (TMA)-sensing performance at room temperature. Benefited from the TMA-accessible self-standing membrane morphology, π-electron delocalization effect, and extensive surface area with continuous nanochannels, the specific and highly sensitive TMA measurement has been achieved within the range of 0.03-400 ppm, with an exceptional theoretical detection limit as low as 10 ppb. Moreover, the primary internal mechanism of COFMPDI-THSTZ for this efficient TMA detection was investigated through in-situ FT-IR spectra, thereby directly elucidating that the chemisorption interaction of oxygen modulated the depletion layers on sensing material surface, resulting in alterations in sensor resistance upon exposure to the target gas. For practical usage, COFMPDI-THSTZ based sensor exhibited exceptional real-time in-situ sensing capabilities, further confirmed their potential for application in dynamic prediction evaluation of marine fish products and quality monitoring in IoT.

Recent advances in smart wearable sensors for continuous human health monitoring

In recent years, the biochemical and biological research areas have shown great interest in a smart wearable sensor because of its increasing prevalence and high potential to monitor human health in a non-invasive manner by continuous screening of biomarkers dispersed throughout the biological analytes, as well as real-time diagnostic tools and time-sensitive information compared to conventional hospital-centered system. These smart wearable sensors offer an innovative option for evaluating and investigating human health by incorporating a portion of recent advances in technology and engineering that can enhance real-time point-of-care-testing capabilities. Smart wearable sensors have emerged progressively with a mixture of multiplexed biosensing, microfluidic sampling, and data acquisition systems incorporated with flexible substrate and bodily attachments for enhanced wearability, portability, and reliability. There is a good chance that smart wearable sensors will be relevant to the early detection and diagnosis of disease management and control. Therefore, pioneering smart wearable sensors into reality seems extremely promising despite possible challenges in this cutting-edge technology for a better future in the healthcare domain. This review presents critical viewpoints on recent developments in wearable sensors in the upcoming smart digital health monitoring in real-time scenarios. In addition, there have been proactive discussions in recent years on materials selection, design optimization, efficient fabrication tools, and data processing units, as well as their continuous monitoring and tracking strategy with system-level integration such as internet-of-things, cyber-physical systems, and machine learning algorithms.

Highly Sensitive Near-Field Electrochemical Sensor for In Vivo Monitoring of Respiratory Patterns

Real-time tracking of respiratory patterns provides noninvasive and quick access for evaluating pathophysiological conditions yet remains challenging due to limited temporal resolution and poor sensitivity to dig out fingerprints of respiratory waveforms. Here, we report an electrochemical sensor for accurately tracing respiratory patterns of small animal models based on the electrochemical impedance mechanism for wireless coupling of a graphdiyne oxide (GYDO)-modified sensing coil chip and a reader coil chip via near-field magnetic induction. In the electrochemical impedance measurement mode, an alternating current is applied through the reader coil chip to perturb proton transport at the GYDO interface of the sensing coil chip. As demonstrated, a high-frequency perturbing condition significantly reduces the interfacial resistance for proton transport by 5 orders of magnitude under 95% relative humidity (RH) and improves the low-humidity responses with a limit of detection down to 0.2% RH, enabling in vivo accurate profiling of respiratory patterns on epileptic rats. The electrochemical impedance coupling system holds great potential for new wireless bioelectronics.

Carrier Transport Switching of Ferroelectric BTBT Derivative

Alkylamide-substituted [1]benzothieno[3,2-b][1]benzothiophene (BTBT) derivative of BTBT-NHCOC14H29 (1), which has ferroelectric N-H···O= hydrogen-bonding network of alkylamide group and two-dimensional (2D) electric structure of BTBT π-cores, was prepared to design the external electric field-responsive organic semiconductors. The short-chain derivative of BTBT-NHCOC3H7 (1') revealed the coexistence of a 2D electronic band structure based on the herringbone BTBT arrangement and the one-dimensional (1D) hydrogen-bonding chain. 1 formed a smectic E (SmE) liquid crystal phase above 412 K and showed ferroelectric hysteresis in the electric field-polarization (P-E) curves at 403-433 K. The remanent polarization (Pr) and coercive electric field (Ec) of 1 at 408 K, 0.1 Hz were 24.0 μC cm-2 and 5.54 V μm-1, respectively. By thermal annealing of thin-film 1 at 443 K, the molecular assembly structure of 1 changed from a monolayer to a bilayer structure with high crystallinity, resulting in conducting layers of BTBT parallel to the substrate surface. The organic field-effect transistor (OFET) device with thermally annealed thin-film 1 showed p-type semiconducting behavior with the hole mobility of 1.0 × 10-3 cm2 V-1 s-1. Furthermore, device 1 showed switching behavior of semiconducting properties by electric field poling and thermal annealing cycle. The electric field response of ferroelectrics modulated the molecular orientation and conduction properties of organic semiconductors, resulting in external electric field control of carrier transport properties.

Handheld Crop Pest Sensor Using Binary Catalyst-Loaded Nano-SnO2 Particles for Oxidative Signal Amplification

In agriculture, pest management is a major challenge. Crop releases volatiles in response to the pest; hence, sensing these volatile signals at a very early stage will ease pest management. Here, binary catalyst-loaded SnO2 nanoparticles of <5 nm were synthesized for the repeated capture and oxidation of the signature volatile and its products to amplify the chemoresistive signal to detect concentrations as low as ≈120 ppb. The sensitivity may be due to the presence of the elements in the Sn-Fe-Pt bond evidenced by extended X-ray absorption fine-structure spectroscopy (EXAFS) that captures and oxidize the volatile without escaping. This strong catalyst may oxidize nontarget volatiles and can cause false signals; hence, a molecular sieve filter has been coupled to ensure high selectivity for the detection ofTuta absolutainfestation in tomato. Finally, with the support of a mobile power bank, the optimized sensor has been assembled into a lightweight handheld device.

The influence of advanced materials on the analytical performance of semiconductor-based gas sensors

Chemiresistive gas sensors are metal oxide-based sensors that have received significant attention in different fields. Ambient gas sensors are especially important in the fabrication of wearable probes for the real-time detection of biomarkers in human body samples. Usually, room temperature sensors are affordable due to their low power consumption, resulting in simple instrumentation and maintenance. To fabricate versatile gas sensors, i.e. sensitive, selective, ambient temperature operating gas sensors, and improve the sensing performance of the traditionally used sensor, new materials play an important role. In other words, new advanced materials are essential for designing and fabricating new gas sensors. Hence, in this review, the application and impact of new advanced materials in the fabrication of reliable gas sensors are discussed in detail. Special emphasis is given to the effect of new materials in the fabrication of room-temperature operating systems. Finally, future research outlook and possible challenges that may be encountered by reliable gas sensors are also explained.

Outstanding Humidity Chemiresistors Based on Imine-Linked Covalent Organic Framework Films for Human Respiration Monitoring

Human metabolite moisture detection is important in health monitoring and non-invasive diagnosis. However, ultra-sensitive quantitative extraction of respiration information in real-time remains a great challenge. Herein, chemiresistors based on imine-linked covalent organic framework (COF) films with dual-active sites are fabricated to address this issue, which demonstrates an amplified humidity-sensing signal performance. By regulation of monomers and functional groups, these COF films can be pre-engineered to achieve high response, wide detection range, fast response, and recovery time. Under the condition of relative humidity ranging from 13 to 98%, the COFTAPB-DHTA film-based humidity sensor exhibits outstanding humidity sensing performance with an expanded response value of 390 times. Furthermore, the response values of the COF film-based sensor are highly linear to the relative humidity in the range below 60%, reflecting a quantitative sensing mechanism at the molecular level. Based on the dual-site adsorption of the (-C=N-) and (C-N) stretching vibrations, the reversible tautomerism induced by hydrogen bonding with water molecules is demonstrated to be the main intrinsic mechanism for this effective humidity detection. In addition, the synthesized COF films can be further exploited to effectively detect human nasal and oral breathing as well as fabric permeability, which will inspire novel designs for effective humidity-detection devices.

High-performance and wearable hazardous gases sensor based on n-n heterojunction film of NGO and tetrakis(1-pyrenyl)porphyrin

The popularity of "Internet of Things" and portable electronic devices creates unprecedented demands for wearable gas sensors with excellent performance. In this study, the flexible n-n heterojunction film is firstly produced from metalloporphyrin complex 5,10,15,20-tetrakis(1-pyrenyl) porphyrin cobalt (II) (CoTPyrP) and nitrogen-doped graphene oxide (NGO) film, using solution-processing quasi-Langmuir-Shäfer (QLS) method and employed as the electrochemical identification layer for the wearable sensor. Thanks to the attractive electron-transfer properties from porphyrin to NGO, and the local regulation of electron transport by N and C atoms with different electronegativity on NGO, the resulting sensor shows good responses to NO₂, SO₂, NH₃, H₂S gases with the low detection limit (LOD) of 6, 74, 113 and 178 ppb, respectively. The uniform and compact structure of the heterojunction films provide excellent mechanical flexibility and suppress the penetration of gases into the film to obtain fast recovery speed. In addition, a sensor array consisting of NGO/CoTPyrP heterojunction and CoTPyrP film sensor is established, achieving selective identification of four hazardous gases. The present work provides potential application for hazardous gases identification in actual systems, and proposes an effective method to develop new flexible n-n heterojunctions for wearable gas sensors.

Recent developments in sensors for wearable device applications

Wearable devices are a new means of human-computer interaction with different functions, underlying principles, and forms. They have been widely used in the medical and health fields, in applications including physiological signal monitoring; sports; and environmental detection, while subtly affecting people's lives and work. Wearable sensors as functional components of wearable devices have become a research focus. In this review, we systematically summarize recent progress in the development of wearable sensors and related devices. Wearable sensors in medical health applications, according to the principle of measurement, are divided into physical and chemical quantity detection. These sensors can monitor and measure specific parameters, thereby enabling continuously improvements in the quality and feasibility of medical treatment. Through the detection of human movement, such as breathing, heartbeat, or bending, wearable sensors can evaluate body movement and monitor an individual's physical performance and health status. Wearable devices detecting aspects of the environment while maintaining high adaptability to the human body can be used to evaluate environmental quality and obtain more accurate environmental information. The ultimate goal of this review is to provide new insights and directions for the future development and broader application of wearable devices in various fields.Graphical abstract.

Fiber-Based Sensors and Energy Systems for Wearable Electronics

Wearable electronics have been receiving increasing attention for the past few decades. Particularly, fiber-based electronics are considered to be ideal for many applications for their flexibility, lightweight, breathability, and comfortability. Furthermore, fibers and fiber-based textiles can be 3D-molded with ease and potentially integrated with everyday clothes or accessories. These properties are especially desired in the fields of bio-related sensors and energy-storage systems. Wearable sensors utilize a tight interface with human skin and clothes for continuous environmental scanning and non-invasive health monitoring. At the same time, their flexible and lightweight properties allow more convenient and user-friendly experiences to the wearers. Similarly, for the wearable devices to be more accessible, it is crucial to incorporate energy harvesting and storage systems into the device themselves, removing the need to attach an external power source. This review summarizes the recent applications of fibers and fiber-based textiles in mechanical, photonic, and biomedical sensors. Pressure and strain sensors and their implementation as electronic skins will be explored, along with other various fiber sensors capable of imaging objects or monitoring safety and health markers. In addition, we attempt to elucidate recent studies in energy-storing fibers and their implication in self-powered and fully wireless wearable devices.

Quintuple-Decker Heteroleptic Phthalocyanine Heterometallic Samarium-Cadmium Complexes. Synthesis, Crystal Structure, Electrochemical Behavior, and Spectroscopic Investigation

A one-pot synthesis methodology was employed for obtaining diverse quintuple-decker phthalocyanine heterometallic lanthanide-cadmium complexes. By using the reaction of a double-decker homoleptic/heteroleptic phthalocyanine samarium compound with metal-free phthalocyanine and cadmium acetate in 1,2,4-trichlorobenzene at 200 °C, two novel quintuple-decker heteroleptic phthalocyanine heterometallic samarium-cadmium compounds, {(Pc)Sm(Pc)Cd(Pc*)Cd(Pc)Sm(Pc)} (1) and {(Pc)Sm(Pc*)Cd(Pc*)Cd(Pc*)Sm(Pc)} (2), together with one homoleptic phthalocyanine species, {(Pc*)Sm(Pc*)Cd(Pc*)Cd(Pc*)Sm(Pc*)} (3), were successfully fabricated, where H₂Pc and H₂Pc* represent unsubstituted phthalocyanine and 2,3,9,10,16,17,23,24-octakis(n-pentyloxy)phthalocyanine, respectively. Their quintuple-decker structures have been disclosed by various spectroscopic techniques and single-crystal X-ray diffraction. In addition, valence tautomerization of these three quintuple-decker complexes has been achieved by the addition of phenoxathiin hexachloroantimonate, giving three oxidized forms including one-, two-, and three-electron oxidation products. From 1 to 3 with the same oxidation state, the increased number of n-pentyloxy substituents of phthalocyanine ligands induces the blue shift of electronic absorption in the IR region due to the increased gap associated with the introduction of electron-donating substituents. In particular, the electronic absorption spectra of one- and two-electron oxidation products for 1 exhibit a rare band in the middle-IR region around 3000 nm, being one of the farthest electronic transitions captured by UV-vis spectroscopy. The three-electron oxidation product of 1 displays two bands at 2231 and 2740 nm, respectively. These data are well confirmed by IR spectroscopic data and theoretical calculation results.

3D synergistical rGO/Eu(TPyP)(Pc) hybrid aerogel for high-performance NO2 gas sensor with enhanced immunity to humidity

The prevalence of Internet of Things and portable electronics create an unprecedented demand for the high performance gas sensors. To pursuit such sensor, sandwich-type (phthalocyaninato)(porphyrinato) europium double-decker complex Eu(TPyP)(Pc) [TPyP = meso-tetra(4-pyridyl)porphyrin; Pc = phthalocyanine] was in situ self-assembled on the surface of reduced graphene oxide (rGO) driven by the π-π interaction, forming a 3D synergistical rGO/Eu(TPyP)(Pc) hybrid aerogel. The resulting aerogel not only effectively integrates the gas sensing of Eu(TPyP)(Pc) and good conductivity of rGO, but also exhibited a prominent synergy effect. Ascribed to the attractive properties, the fabricated NO₂ gas sensor exhibits superior sensitivity and selectivity in the range of 0.5 to 100 ppm with an extremely low theoretical limit level of detection (80 ppb) at ambient temperature. The response and recovery time of rGO/Eu(TPyP)(Pc) hybrid aerogel based sensor to20 ppm NO₂ were 172 and 828 s, respectively. Remarkably, the hydrophobic porous structure of rGO/Eu(TPyP)(Pc) hybrid aerogel endows the prepared sensor with excellent immunity to high relative humidity, which conquered the key technical issue of real application. The present sensor, simultaneously featured with high performance, low-power consumption, and good tolerance to environmental variations, is anticipated to offer the "on-site" and "on-line" measurement tool in real samples.