Ultrasensitive Organic Humidity Sensor with High Specificity for Healthcare Applications

Flexible Humidity Sensor Based on a Graphene Oxide-Carbon Nanotube-Modified Co3O4 Nanoparticle-Embedded Laser-Induced Graphene Electrode

To meet evolving humidity monitoring needs, the development of flexible, high-performance humidity sensors is crucial. This study introduces an innovative flexible humidity sensor using a single-step laser scribing technique to fabricate a flexible in situ Co3O4 nanoparticle-embedded laser-induced graphene (Co3O4-LIG) composite electrode. Compared to conventional LIG electrodes, the Co3O4-LIG electrode exhibits improved conductivity and hydrophilicity, enhancing charge transfer and water molecule affinity. The unique two-dimensional structure and exceptional water permeability of graphene oxide (GO) combine with the rapid water response and high specific surface area of carboxylated multiwalled carbon nanotubes (MWCNTs), thereby assuming a crucial function in the modification and optimization of the performance of humidity sensors. Through the application of a homogenously blended aqueous solution comprising GO and MWCNTs in precise proportions onto the Co3O4-LIG composite electrode, an excellent humidity-responsive layer is established, culminating in the realization of a cutting-edge GO-MWCNTs@Co3O4-LIG flexible humidity sensor. Noteworthy attributes of this sensor include a heightened sensitivity [959.1% (ΔR/R0)], rapid response and recovery times (within 5 and 26 s, respectively), and a noteworthy linearity (R2 = 0.994) across a relative humidity range of 14 to 95%. The findings presented herein offer valuable insights and a practical blueprint for the design and production of flexible humidity sensors.

Two Decades' advancements and Research trends in needle-type Sensor technology: A scientometric analysis

Needle-type sensor, characterized by its slender, elongated shape, is a promising sensing method due to its rapid response, high sensitivity, and portability. Recently, the needle-type sensor technology has garnered increasing attention, leading to its accelerated development and extensive use in medical and healthcare, environmental monitoring, and geosciences. However, there remains a need for a comprehensive review of existing research. Here, we utilize scientometric analysis, which is booming recently, to conduct a comprehensive investigation of the needle-type sensor field. This analysis covers various aspects, including annual trends, journals, institutions, countries, disciplines, authors, references, and keywords of 136,667 publications from the Web of Science Core Collection (WoSCC) database spanning from January 1, 2004, to January 1, 2024. Additionally, we identify current hotspots, frontiers, and predict future trends. Eventually, three research hotspots are refined: multidisciplinary materials science, sensor miniaturization and integration, and biomedical engineering, indicating that further investigations may focus on creating biocompatible materials to enhance sensing properties, optimizing sensor structure through miniaturization and integration methods, and improving clinical applications in biomedical engineering. This work may facilitate the development of needle-type sensors.

Room Temperature Humidity Tolerant Xylene Sensor Using a Sn-SnO2 Nanocomposite

Xylene is one of the representative indoor pollutants, even in ppb levels, that affect human health directly. Due to the non-polar and less reactive nature of xylene, its room temperature detection is challenging. This work demonstrates a metallic tin-doped Sn-SnO₂ nanocomposite under controlled pH conditions via a simple solvothermal route. The Sn nanoparticles are uniformly distributed inside the SnO₂ nanospheres of ∼70 nm with a high specific surface area of 118.8 m²/g. The surface of the Sn-SnO₂ nanocomposite exhibits strong affinity toward benzene, toluene, ethylbenzene, and xylene (BTEX) compared to other polar volatile organic compounds (VOCs) such as ethanol, acetone, isopropyl alcohol, formaldehyde, and chloroform tested in this study. The sensor's response is highest for xylene among BTEX molecules. Under ambient room temperature conditions, the sensor exhibits a linear response to xylene in the 1-100 ppm range with a sensitivity of ∼255% at 60 ppm within ∼1.5 s and recovers in ∼40 s. The sensor is hardly affected by humidity variations (40-70%), leading to enhanced reliability and repeatability under dynamic environmental conditions. The meso and microporous nanosphere morphology act as a nanocontainer for non-polar VOCs to diffuse inside the nanostructures, providing easy accessibility. The metallic Sn increases the affinity for less reactive xylene at room temperature. Thus, the nanocatalytic Sn-SnO₂ nanocomposite is an active gas/VOC sensing material and provides an effective solution for sensing major indoor pollutants under humid conditions.

Fully integrated wearable humidity sensor for respiration monitoring

Respiration monitoring is a promising alternative to medical diagnosis of several diseases. However, current techniques of respiration monitoring often require expensive and cumbersome devices which greatly limit their medical applications. Here, we present a fully integrated wearable device consisting of a flexible LCP-copper interdigital electrode, a sensing layer and a wireless electrochemical analysis system. The developed humidity sensor exhibits a high sensitivity, a good repeatability and a rapid response/recover time. The long-term stability is over 30 days at different relative humidity. By integrating the flexible humidity sensor with miniaturized electrochemical analysis system (0.8 cm × 1.8 cm), response current concerning respiration can be wirelessly transmitted to App-assisted smartphone in real time. Furthermore, the fabricated humidity sensor can realize skin moisture monitoring in a touch-less way. The large-scale production of miniaturized flexible sensor (4 mm × 6 mm) has significantly contributed to commercial deployment.

Neuro-inspired electronic skin for robots

Touch is a complex sensing modality owing to large number of receptors (mechano, thermal, pain) nonuniformly embedded in the soft skin all over the body. These receptors can gather and encode the large tactile data, allowing us to feel and perceive the real world. This efficient somatosensation far outperforms the touch-sensing capability of most of the state-of-the-art robots today and suggests the need for neural-like hardware for electronic skin (e-skin). This could be attained through either innovative schemes for developing distributed electronics or repurposing the neuromorphic circuits developed for other sensory modalities such as vision and audio. This Review highlights the hardware implementations of various computational building blocks for e-skin and the ways they can be integrated to potentially realize human skin-like or peripheral nervous system-like functionalities. The neural-like sensing and data processing are discussed along with various algorithms and hardware architectures. The integration of ultrathin neuromorphic chips for local computation and the printed electronics on soft substrate used for the development of e-skin over large areas are expected to advance robotic interaction as well as open new avenues for research in medical instrumentation, wearables, electronics, and neuroprosthetics.

Innovative Approach to Photo-Chemiresistive Sensing Technology: Surface-Fluorinated SnO2 for VOC Detection

Transparent electronics continues to revolutionize the way we perceive futuristic devices to be. In this work, we propose a technologically advanced volatile organic compound (VOC) sensor in the form of a thin-film transparent display fabricated using fluorinated SnO₂ films. A solution-processed method for surface fluorination of SnO₂ films using Selectfluor as a fluorinating agent has been developed. The doped fluorine was optimized to be <1%, resulting in a significant increase in conductivity and reduction in persistent photoconductivity accompanied by a faster decay of the photogenerated charge carriers. A combination of these modified properties, together with the intrinsic sensing ability of SnO₂, was exploited in designing a transparent display sensor for ppm-level detection of VOCs at an operating temperature of merely 150 °C. Even a transparent metal mesh heater is integrated with the sensor for ease of operation, portability, and less power usage. A sensor reset method is developed while shortening the UV exposure time, enabling complete sensor recovery at low operating temperatures. The sensor is tested toward a variety of polar and nonpolar VOCs (amines, alcohols, carbonyls, alkanes, halo-alkanes, and esters), and it exhibits an easily differentiable response with sensitivity in line with the electron-donating tendency of the functional group present. This work opens up the door for multiplexed sensor arrays with the ability to detect and analyze multiple VOCs with specificity.