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In the present study, we have investigated the influence of Lanthanum doping concentration on the structural, microstructural, dielectric, and humidity sensing performance of rare earth Lanthanum cobalt chromite nanoparticles. These nanomaterials were synthesized by the solution combustion method using glucose and urea as fuels. Structural investigations revealed that the synthesized materials are single-phase, highly crystalline, and porous, with spherical agglomerated nanoparticles of crystallite size ranging from 13 nm to 17 nm. Particle size distribution and pore area distribution were plotted using imageJ software. Energy dispersive spectroscopy confirmed the accurate elemental composition of all samples, consistent with the calculated stoichiometry. Optical absorption studies showed a blue shift in the peak as the doping concentration increased, indicating a quantum confinement effect. Dielectric constant and electrical resistivity measurements ensured that the materials are electrically conducting, which is necessary for humidity sensing applications. Humidity sensing measurements demonstrated that the capacitive humidity sensitivity coefficient (SC) and resistive humidity sensitivity coefficient (SR) were highest for the La (0.05) sample. The XPS survey spectra and high-resolution core-level spectra provide a thorough understanding of the elemental composition, oxidation states, and electronic environments in La-doped cobalt chromite nanoparticles. This detailed analysis is critical for tailoring the material's properties for specific applications in catalysis, electronics, and magnetic devices. [ABSTRACT FROM AUTHOR]

Humidity sensors using triboelectric nanogenerators (TENGs) technology can provide continuous operation without the need for additional batteries. These sensors provide sustainable and self-powered humidity monitoring solutions, that can be utilized in various agriculture platforms and food processing industries. In this work, a sol-gel method is utilized to process the bismuth ferrite (abbreviated as BFO) materials and a simple mould pressing method to obtain freestanding Ethylene-vinyl acetate (abbreviated EVA)-BFO composites. These composites were characterized to shed light upon structural and microstructural properties. The single electrode mode operating TENG was fabricated having 2 cm × 2 cm active area at various wt.% of BFO onto EVA-based composites to compare the electrical response. The 5 wt.% BFO-EVA-based composites/FEP-based TENG generates a voltage and current of 45 V and 800 nA. Further, the TENG device was tested for long-term stability for 400 s, and charging of various capacitors having capacitance values such as 0.1 μF, 1 μF, 4.7 μF, and 10 μF along with 3 times charging/discharging cycles of 0.1 μF capacitor have been demonstrated. The humidity sensing mechanism elucidated which follows the conduction process based on the Grotthuss proton hopping mechanism. The TENG demonstrates a sensitivity of 0.53 V/RH% over the relative humidity range from 25 % to 85 %. The powering of the wristwatch confirms that fabricated TENG can be a reliable power source for future low-power electronics. [ABSTRACT FROM AUTHOR]

A humidity sensor array can be used in applications requiring non-contact sensing and contactless interface localization, which became a significant area of research after COVID-19 and reduced the risk of bacterial transmission associated with conventional touch displays. In this study, a thin film humidity sensor has been designed using calcium (Ca) doped zinc ferrite (ZnFe2O4) nanomaterial, which has been prepared by the sol-gel auto-ignition process. The synthesized nanomaterial was characterized using Powder X-Ray Diffraction (PXRD), Fourier Transform Infrared (FTIR) spectroscopy, Field Emission Scanning Electron Microscopy (FESEM), and Energy Dispersive X-Ray (EDX) techniques. The doping of Ca reduces the crystallite size and increases the lattice constant. Attempts have been made to determine the different humidity sensing parameters. The developed humidity sensor has a response time of 12 seconds and a recovery time of 66 seconds. The developed humidity sensor has good repeatability and a negligible aging effect. [ABSTRACT FROM AUTHOR]

Two‐dimensional conductive metal‐organic frameworks (MOFs) featuring structural diversity and high porosity represent promising platforms for chemiresistive humidity sensing. The precise control of the structure of lanthanide‐based MOFs and an exploration of its impact on charge transport and sensing applications have consistently been focal points for researchers. In this study, we present the synthesis and characterization of Lu‐HHTP (HHTP=2,3,6,7,10,11‐hexahydroxytriphenylene) as highly crystalline and conductive porous materials. The polymeric framework of Lu‐HHTP encompasses 1D hexagonal channels and exhibits interlayer π–π stacking, resulting in a material with a high surface area and uniform rod‐like microstructure. Benefiting from its elevated electrical conductivity, the Lu‐HHTP‐based humidity sensor exhibited commendable sensing properties within the relative humidity range of 33 % to 95 % at room temperature (25 °C), achieving a response value as high as 19 at 95 % relative humidity. Furthermore, the sensor displayed superior repeatability, characterized by rapid response and recovery speeds in the presence of moisture. These findings indicate that Lu‐HHTP holds substantial promise as a material for humidity sensors. [ABSTRACT FROM AUTHOR]

In the current study, the effect of rGO ratio on the N-dopped TiO2 has been synthesized through sol–gel method. The prepared N-doped TiO2/rGO composites were examined for humidity sensing applications. The relationship between optical properties and the humidity sensing properties was studied. The structure, morphology, and bonding interaction have been examined using XRD, FT-IR, PL and HRTEM respectively. The average particle size as estimated from XRD and HRTEM was found to be about 9 nm. The optical properties have been studied using UV/ Vis. Spectroscopy. Further, optical parameters including refractive index and optical band gap energy have been estimated. The humidity sensing behavior of the resultant composites were evaluated in a wide range of humidity (7%–97% RH) at different testing frequencies. The optical band gap was found to be decreased as the amount of rGO increase. Among all prepared samples, both the optical parameters and humidity sensing experiments confirmed that the 0.5% rGO@N-dopped TiO2 sample is the best candidate for the humidity sensing applications. The best optimum testing frequency was demonstrated to be 50 Hz. The sensor demonstrates a fast response and recovery times of 13 s and 33 s with low hysteresis and large sensitivity. The humidity sensing mechanism was studied using complex impedance spectroscopy at different RH levels under testing frequency range from 50 Hz to 5 MHz and testing voltage of 1 VAC. The produced structure demonstrated a promising material for humidity measuring devices. [ABSTRACT FROM AUTHOR]

The present investigation portrayed the synthesis of bare LaZn2O4 material and La2-xAlxZnO4 material (x = 0.1–0.4 mol) by sol–gel auto combustion technique. All these materials were characterized by various prime nano characterization technique to investigate the structural and surface properties. X-ray diffraction pattern for LaZn2O4 material confirms the hexagonal wurtzite lattice for this material. The surface characterization and topographical parameters were confirmed from scanning electron microscopy, while the elemental composition of various concentrations Al3+ modified LaZn2O4 was confirmed from energy dispersive spectroscopy. High resolution transmission electron microscopy technique was utilized to substantiate the lattice parameter and polycrystalinity of the fabricated material. UV-DRS technique was used to validate the tuned band gap of the fabricated materials. The Brunauer–Emmett–Teller was employed to calculate total surface area of the prepared materials. The La2-xAlxZnO4 is having highest surface area 85.59 m2/g and pore radius 80.85 Å. Sensor materials with varied composition of Al3+ (x = 0.1–0.4 mol) were fabricated by photolithographic technique having 40 s, mesh number 355. The various toxic gases such as CO, NO2, LPG, and Acetone were investigated for varied gas concentrations. Among all sensors La2-xAlxZnO4 (LZO, x = 0.2) sensor shows highest response for acetone vapors with 88.80% at lowest 60°C. The humidity sensing for the sensors shows that the sensor LZO is operational at moderate humid conditions. The rapid response recovery, reusability, thermal stability, good porosity, high surface area, operational at lower temperature is the characteristics of LZO-2 sensor. [ABSTRACT FROM AUTHOR]

Dispersion‐based graphene materials are promising candidates for various sensing applications. They offer the advantage of relatively simple and fast deposition via spin‐coating, Langmuir–Blodgett deposition, or inkjet printing. Film uniformity and reproducibility remain challenging in all of these deposition methods. Here, a scalable structuring method is demonstrated, characterized, and successfully applied for graphene dispersions. The method is based on a standard lift‐off process, is simple to implement, and increases the film uniformity of graphene devices. It is also compatible with standard semiconductor manufacturing methods. Two different graphene dispersions are investigated via Raman spectroscopy and Atomic Force Microscopy and observe no degradation of the material properties by the structuring process. Furthermore, high uniformity of the structured patterns and homogeneous graphene flake distribution is achieved. Electrical characterizations show reproducible sheet resistance values correlating with material quantity and uniformity. Finally, repeatable humidity sensing is demonstrated with van der Pauw devices, with sensing limits of less than 1% relative humidity. [ABSTRACT FROM AUTHOR]

We propose a multimode fiber laser sensor utilizing PI-SMF (polyimide-coated single mode fiber) for low-error relative humidity (RH) measurement, which is temperature compensated based on FBG. The PI-SMF in the laser cavity is used as a sensing element, and its length varies with humidity and temperature by volume-variation induced strain, which leads to frequency shift of the longitudinal mode beat frequency signal (BFS). When the 2000 MHz BFS is selected as the sensing signal, a RH sensitivity of −2.68 kHz/%RH and a temperature sensitivity of −14.05 kHz/°C are achieved. The peak shift of the FBG-based laser emission spectrum is only sensitive to temperature rather than RH with a temperature sensitivity of 9.95 pm/°C, which is used as the temperature compensation for RH measurements. By monitoring the response of the BFS and the laser wavelength, the cross-sensitivity effect of RH and temperature is overcome, and low-error RH measurement in the temperature range of 20 to 65 °C is realized with errors within ±0.67 %RH (25 to 85 %RH). The scheme does not require the design and production of complex structures and hygroscopic material coating processes, owning the advantages of simple structure, easy operation and high accuracy, and is expected to be practically applied in food safety and environmental monitoring. [ABSTRACT FROM AUTHOR]

Proton conductors are ceramic materials with a crystalline or amorphous structure, which allow the passage of an electrical current through them exclusively by the movement of protons: H+. Recent developments in proton-conducting ceramics present considerable promise for obtaining economic and sustainable energy conversion and storage devices, electrolysis cells, gas purification, and sensing applications. So, proton-conducting ceramics that combine sensitivity, stability, and the ability to operate at low temperatures are particularly attractive. In this article, the authors start by presenting a brief historical resume of proton conductors and by exploring their properties, such as structure and microstructure, and their correlation with conductivity. A perspective regarding applications of these materials on low-temperature energy-related devices, electrochemical and moisture sensors, is presented. Finally, the authors' efforts on the usage of a proton-conducting ceramic, polyantimonic acid (PAA), to develop humidity sensors, are looked into. [ABSTRACT FROM AUTHOR]

Abstract Gas sensors based on micro‐electromechanical systems (MEMS) offer advantages such as a broad spectrum of potentially sensitive materials and analytes, easy miniaturization and integration, high sensitivity, and low costs. This paper introduces a novel MEMS sensor platform utilizing a suspended gate field effect transistor (SGFET) transducer. In this approach, the flexible gate membrane of the SGFET is coated with a sensitive material exhibiting responsive swelling behavior. For the proof of concept, kraft lignin hydrogel is chosen as a biorenewable material for humidity sensing. A precision dispensing technique is used to deposit kraft lignin hydrogel on the SGFETs. The sensor measurements yield reversible shifts in the sensor's output current of up to 9% in response to 5000 ppm water vapor. The results successfully demonstrate the feasibility of this new sensing platform.

Packaging solutions have recently evolved to become smart and intelligent thanks to technologies such as RFID tracking and communication systems, but the integration of sensing functionality in these systems is still under active development. In this paper, chipless RFID humidity sensors suitable for smart packaging are proposed together with a novel strategy to tune their performances and their operating range. The sensors are flexible, fast, low-cost and easy to fabricate and can be read wirelessly. The sensitivity and the humidity range where they can be used are adjustable by changing one of the sensor's structural parameters. Moreover, these sensors are proposed as double parameter sensors, using both the frequency shift and the intensity variation of the resonance peak for the measure of the relative humidity. The results show that the sensitivity can vary remarkably among the sensors proposed, together with the operative range. The sensor suitability in two specific smart packaging applications is discussed. In the first case, a threshold sensor in the low-humidity range for package integrity verification is analyzed, and in the second case, a more complex measurement of humidity in non-hermetic packages is investigated. The discussion shows that the sensor configuration can easily be adapted to the different application needs. [ABSTRACT FROM AUTHOR]

Drawing inspiration from the architecture of bacterial tentacles, a novel humidity-sensitive material has been engineered by grafting sulfonates onto the exterior of a fullerene cage. This innovative material with high hydrophilicity and fast response demonstrates superior humidity sensing capabilities, making it apt for non-contact humidity monitoring. [Display omitted] In this work, a straightforward method for synthesizing fullerene derivatives with tentacle structures has been explored for monitoring environmental humidity, which involves introducing sulfonate onto the fullerenes. The structure and number of polar groups in three fullerene derivatives determined by a series of structural tests greatly affect their hydrophilicity and morphology, resulting in changes in humidity sensitive properties. In particular, the hysteresis and response time of the sensors display a great correlation with hydrophilicity. C 60 -Ho, the best performing derivative of this work, has exhibited high response values (∼3500 times), good linearity (R2 = 97.3 %), and rapid response/recovery times (0.3/4.4 s), making it suitable for various applications such as non-contact detection of respiration, finger distance, and soil humidity. [ABSTRACT FROM AUTHOR]

Herein, nickel oxide (NiO) nanoparticles have been synthesized through a simple co-precipitation route. The obtained samples were calcinated at two different temperatures (500 °C and 900 °C) using a muffle furnace. The structural, morphological, and optical properties of nanoparticles were examined by X-ray diffraction, Scanning electron microscopy, Energy dispersive X-ray, Fourier infrared spectroscopy and UV–Vis absorption spectroscopy. The resistive type humidity sensing behavior was studied through a locally fabricated experimental setup. The XRD pattern of the samples revealed that the as-prepared sample appeared in the β-Ni(OH)2 hexagonal phase, and the samples calcinated at 500 °C and 900 °C, are crystallized in the cubic structure of NiO phase. The formation of highly agglomerated and irregular shaped particles was noticed form SEM images. FTIR analysis confirmed the formation of β-Ni(OH)2 and pure NiO phases, which is supported by EDX analysis. UV–Vis absorption studies showed a red shift of absorption edge and a varying band gap of NiO nanoparticles with calcination temperature due to the crystal growth and increase in crystallinity of samples. The sample calcinated at 900 °C has shown a humidity sensitivity of 0.3 K-cm/% RH, a limit of detection of 7% RH and good linearity with a correlation co-efficient of 0.995. [ABSTRACT FROM AUTHOR]

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Respiration is one of the most important physiological processes of the human body. Continuous monitoring of respiration with wearable sensors can provide abundant information related to the health status of the respiratory system. However, the vast majority of the developed respiration sensors are constructed on nontextile substrates, resulting in dissatisfactory convenience, comfortness, and aesthetics. Additionally, special micro‐/nanomaterials are inevitably involved to construct the respiration sensors, which pose potential hazards to the human body due to the exfoliation and inhalation of these micro‐/nanomaterials. Here, humidity‐ and temperature‐sensitive electronic textiles (e‐Textiles) are presented, which are fabricated based on easily accessible and biofriendly materials (e.g., sodium chloride, glycerin, aluminum fiber, carbon fiber, and polyvinyl alcohol). Moreover, the proposed e‐Textiles use a potentiometric sensing mechanism, featuring self‐powered signal outputs and ultralow power consumption. The humidity and temperature‐sensing functionalities can also be in situ integrated into commercial masks for constructing full‐textile and all‐in‐one e‐Masks for comprehensive respiration monitoring. As demonstrations, both single‐point respiration monitoring (e.g., intensity, frequency, etc.) and 2D respiratory analysis (i.e., airflow distribution) can be realized with the e‐Masks. This work provides a facile and scalable approach to manufacture self‐powered and fully fabric respiration sensors for comprehensive respiratory analysis. [ABSTRACT FROM AUTHOR]

Respiration is an important physiological parameter used to assess human health and metabolic activity. Herein, we propose a laser-induced graphene (LIG)-based humidity sensor for respiratory monitoring. This sensor is fabricated through a combination of laser irradiation and intense pulsed light (IPL) sintering techniques. Initially, an ink containing copper nanoparticles (CuNPs) and graphene nanoplatelets (GnPs) is coated onto a polyimide (PI) substrate. The LIG is formed on the PI film using laser irradiation. To establish a reliable electrical connection between the LIG and the copper electrode, the ink undergoes rapid IPL sintering, resulting in an IPL-sintered copper electrode. This technique not only optimizes the fabrication process but also obviates the need for traditional approaches, such as copper wire bonding, electrode patterning, or the application of conductive paint on the LIG sensor. The humidity-sensing capabilities of the sensor are assessed under various relative humidity (RH) conditions. The sensor's response escalates from roughly 15 to 92% as RH levels increase from 13 to 67%. The sensor showed minimal response to various potential interfering gases like ammonia, ethanol, carbon monoxide, sulfur dioxide, and nitrogen dioxide (with responses of 0.4, 1.87, 0.102, 0.12, and 0.29%, respectively), confirming its high selectivity for RH (91.2%). Additionally, the sensor demonstrates exemplary reproducibility, as evidenced by its consistent responses (approximately 47.65, 49.13, 48.65, 49.09, and 49.39) over five cycles at 40% RH. The LIG sensor is used to monitor a wide range of respiratory patterns, including normal, slow, fast, and apnea events. The sensor effectiveness is proven through the consistent detection of human breathing patterns over 30 min, demonstrating its stability and reliability for extended use in continuous respiratory monitoring. These findings highlight the significant potential of LIG sensors as advanced precision devices in clinical respiratory monitoring with potential integration into modern medical practices. [ABSTRACT FROM AUTHOR]

This review aims to present a critical overview of indium tin oxide (ITO) thin film preparation methods, structure–property relationship, and its humidity sensing. A range of passive and active humidity sensors with thin films (based on metal oxides) detects humidity. ITO thin film has advantageous properties, such as low resistivity and high stability, making it highly suitable for humidity sensing applications. ITO thin film has shown the efficient level of humidity sensing, and a compatible size of humidity sensor can monitor the interface conditions humidity. So far, the application of ITO thin film for humidity measurement has yet to be explored at commercial scale, specifically in the detection of lower environmental humidity range (below 5% relative humidity (RH)). The research reveals a gap in improving the ITO thin film properties with an optimal range of preparation conditions. The research opportunities in the preparation, properties, characteristics, and efficient humidity sensitivity of ITO thin film are reviewed in this work. [ABSTRACT FROM AUTHOR]

The imperative to meet the energy needs of contemporary electronic devices has spurred extensive exploration into self‐powered systems. Given the anticipated ubiquity of sensor networks in future cities, a novel battery‐free sensing paradigm, rooted in triboelectric nanogenerators (TENG), has gained prominence. Utilizing mechanical energy otherwise wasted daily for electricity generation presents a promising alternative to conventional sensors. Embedding the sensing electrode within the TENG structure enables the creation of gas sensors suitable for portable and wireless applications. This study focuses on fabricating a 3D microporous sponge of polydimethylsiloxane (PDMS) using sugar cubes and graphene oxide (GO) nanosheets. Leveraging the hydrophilic properties of the GO enhances moisture absorption, elevating the humidity sensor's responsivity. In addition, the porous structure not only improves sensitivity to high humidity but also mitigates surface saturation issues prevalent in nonporous sensors. The porous self‐powered sensor, composed of PDMS with 0.5 wt% of GO, exhibits a response of up to 2500%, quantified as ((ΔV/V) × 100%), to relative humidity changes from 20% to 99%. Furthermore, the response and recovery times stand at 1.2 and 2.3 s, respectively. These findings underscore the feasibility of integrating TENG electrodes, utilizing a porous PDMS–GO nanocomposite, to create various types of integrated gas sensors. [ABSTRACT FROM AUTHOR]

Abstract Dispersion‐based graphene materials are promising candidates for various sensing applications. They offer the advantage of relatively simple and fast deposition via spin‐coating, Langmuir–Blodgett deposition, or inkjet printing. Film uniformity and reproducibility remain challenging in all of these deposition methods. Here, a scalable structuring method is demonstrated, characterized, and successfully applied for graphene dispersions. The method is based on a standard lift‐off process, is simple to implement, and increases the film uniformity of graphene devices. It is also compatible with standard semiconductor manufacturing methods. Two different graphene dispersions are investigated via Raman spectroscopy and Atomic Force Microscopy and observe no degradation of the material properties by the structuring process. Furthermore, high uniformity of the structured patterns and homogeneous graphene flake distribution is achieved. Electrical characterizations show reproducible sheet resistance values correlating with material quantity and uniformity. Finally, repeatable humidity sensing is demonstrated with van der Pauw devices, with sensing limits of less than 1% relative humidity.

This scientific investigation emphasizes the essential integration of nature's influence in crafting multifunctional surfaces with bio-inspired designs for enhanced functionality and environmental advantages. The study introduces an innovative approach, merging color decoration, humidity sensing, and antiviral properties into a unified surface using chitosan, an organo-biological polymer, to create cost-effective multilayered films through sol-gel deposition and UV photoinduced deposition of metal nanoparticles. The resulting chitosan films showcase diverse structural colors and demonstrate significant antiviral efficiency, with a 50% and 85% virus inhibition rate within a rapid 20 min reaction, validated through fluorescence cell expression and real-time qPCR (polymerase chain reaction) assays. Silver-deposited chitosan films further enhance antiviral activity, achieving remarkable 91% and 95% inhibition in independent assays. These films exhibit humidity-responsive color modifications across a 25–90% relative humidity range, enabling real-time monitoring validated through simulation studies. The proposed three-in-one functional surface can have versatile applications in surface decoration, medicine, air conditioning, and the food industry. It can serve as a real-time humidity sensor for indoor and outdoor surfaces, find use in biomedical devices for continuous humidity monitoring, and offer antiviral protection for frequently handled devices and tools. The customizable colors enhance visual appeal, making it a comprehensive solution for diverse applications. [ABSTRACT FROM AUTHOR]

Malleable thermosets as dynamic covalent cross‐linked polymers, simultaneously possessing the advantages of thermosets and thermoplastics, have attracted considerable attention. Although several reprocessing concepts have been demonstrated, the fabrication of fast‐curing bio‐based strong and tough malleable thermosets for advanced applications in electronics remains a great challenge. Herein, a novel construction strategy of combining hindered urea bonds (HUB) and radical polymerization is developed to prepare fast‐photocurable and mechanically robust cellulose‐based malleable bio‐thermosets (CMTs). In this strategy, the functional cellulose macromonomer simultaneously has acrylate groups and HUB is first synthesized and employed as a macro‐crosslinker to react with plant oil‐based monomer to construct the malleable bio‐thermosets with "soft (plant oil‐based polymer)" and "hard (rigid cellulose)" phase architecture through the fast photocuring. The CMTs exhibit excellent flexibility and high toughness (2.89 MJ m−3), and the introduction of dynamic HUB endows the CMTs with excellent malleability and reprocessability by heating compression molding or solvent regeneration, the recovery efficiency reached 94.7%. More impressively, the CMTs can be used as substrates to fabricate CMTs/silver composite for anti‐icing or de‐icing devices, and CMTs‐based capacitive sensors for monitoring environmental humidity or human health. This work paves a new strategy to develop new‐generation fast‐photocurable mechanically robust, malleable bio‐thermosets for multifunctional electronic devices. [ABSTRACT FROM AUTHOR]

Herein in this work, the synthesis as well as study of Magnesium-oxide loaded mesoporous silica KIT-6 (a 3D material, first synthesised by Ryoo's research group in 2003 material, in Korean Institute of Technology) for sensing at room temperature was done by employing KIT-6 as a hard template. The unique arrangement mesoporous KIT-6 having Ia3d symmetry along with a three-dimensional cubic arrangement of pore provides more tunnels for transportation of charge carriers. Water molecules are more effectively adsorbable due to KIT-6's extremely porous structure, and the mesoporous framework's broad, uniform pore channels make it simple for charged ions to flow freely. Despite these qualities, undoped KIT-6 does not exhibit a superior relative humidity (RH) sensitivity in humid environments hence metallic nanoparticles (MgO/KIT-6) have been used to improve the sensing capabilities of RH sensors. In the current work, we offer a straightforward, easy-to-follow hydrothermal synthesis method for producing effective humidity sensing materials made of MgO-loaded KIT-6. Different MgO concentrations (1, 5 and 10 wt%) were added to KIT-6 in order to employ it as a humidity sensor material to effectively monitor and regulate humidity levels. Here at MgO/KIT-6 presents swift humidity response and recovery time along with it change in ≥3 orders of magnitude in resistance were observed over as compared to pure KIT-6 in the 11%–98% RH range at room temperature. The structural insights were examined using X-ray diffraction (XRD), Fourier transform infrared, High-resolution transmission electron microscopy , Field emission scanning electron microscopy with energy dispersive x-ray (EDX) microanalysis and textural properties of the synthesised mesoporous KIT-6 silica and MgO/KIT-6 (X) nanocomposites were examined in depth with the N2 adsorption-desorption isotherm from which it was analysed that as the amount of MgO is incremented, the surface area gets decreased. Among all the tested samples of different weight%, optimal results obtained for 5 weight% MgO-loaded KIT-6 [abbreviated as MgO/KIT-6(5)] exhibits impressive humidity sensing responsiveness, little hysteresis, short response as well as recovery time (31 s/35 s), consistent linearity, extremely high accuracy over a varied working temperature range, repeatability and great stability in the 11–98% RH range. The investigation of humidity sensing properties of MgO/KIT-6 hybrid nanocomposite justifies that this material is good candidates to be used as a innovative high performance humidity sensor. [ABSTRACT FROM AUTHOR]

This document presents a study on the humidity sensing properties of zinc oxide (ZnO) nanotubes. The nanotubes were created using the hydrothermal method and exhibited a hexagonal shape and wurtzite crystal structure. The conductivity of the nanotubes was influenced by temperature and humidity, with protonic conduction dominating at higher humidity levels. The findings suggest that ZnO nanotubes have potential for use in highly sensitive humidity sensors, and emphasize the importance of material selection in humidity sensing applications. [Extracted from the article]

We propose a humidity sensor using an excessively tilted fiber grating (Ex-TFG) coated with agarose fabricated using femtosecond laser processing. The processed grating showcases remarkable differentiation between TE and TM modes, achieving an exceptionally narrow bandwidth of approximately 1.5 nm and an impressive modulation depth of up to 15 dB for both modes. We exposed the agarose-coated TFG sensor to various relative humidity levels and monitored the resonance wavelength to test its humidity sensing capability. Our findings demonstrated that the sensor exhibited a rapid response time (2–4 s) and showed a high response sensitivity (18.5 pm/%RH) between the humidity changes and the resonant wavelength shifts. The high sensitivity, linearity, repeatability, low hysteresis, and excellent long-term stability of the TFG humidity sensor, as demonstrated in our experimental results, make it an attractive option for environmental monitoring or biomedical diagnosis. [ABSTRACT FROM AUTHOR]

Respiration is one of the most important physiological processes of the human body. Continuous monitoring of respiration with wearable sensors can provide abundant information related to the health status of the respiratory system. However, the vast majority of the developed respiration sensors are constructed on nontextile substrates, resulting in dissatisfactory convenience, comfortness, and aesthetics. Additionally, special micro‐/nanomaterials are inevitably involved to construct the respiration sensors, which pose potential hazards to the human body due to the exfoliation and inhalation of these micro‐/nanomaterials. Here, humidity‐ and temperature‐sensitive electronic textiles (e‐Textiles) are presented, which are fabricated based on easily accessible and biofriendly materials (e.g., sodium chloride, glycerin, aluminum fiber, carbon fiber, and polyvinyl alcohol). Moreover, the proposed e‐Textiles use a potentiometric sensing mechanism, featuring self‐powered signal outputs and ultralow power consumption. The humidity and temperature‐sensing functionalities can also be in situ integrated into commercial masks for constructing full‐textile and all‐in‐one e‐Masks for comprehensive respiration monitoring. As demonstrations, both single‐point respiration monitoring (e.g., intensity, frequency, etc.) and 2D respiratory analysis (i.e., airflow distribution) can be realized with the e‐Masks. This work provides a facile and scalable approach to manufacture self‐powered and fully fabric respiration sensors for comprehensive respiratory analysis.

Abstract This review aims to present a critical overview of indium tin oxide (ITO) thin film preparation methods, structure–property relationship, and its humidity sensing. A range of passive and active humidity sensors with thin films (based on metal oxides) detects humidity. ITO thin film has advantageous properties, such as low resistivity and high stability, making it highly suitable for humidity sensing applications. ITO thin film has shown the efficient level of humidity sensing, and a compatible size of humidity sensor can monitor the interface conditions humidity. So far, the application of ITO thin film for humidity measurement has yet to be explored at commercial scale, specifically in the detection of lower environmental humidity range (below 5% relative humidity (RH)). The research reveals a gap in improving the ITO thin film properties with an optimal range of preparation conditions. The research opportunities in the preparation, properties, characteristics, and efficient humidity sensitivity of ITO thin film are reviewed in this work.

Precise measurement of humidity is of high significance in diverse fields like instrumentation, automated systems, agriculture and climatology. Herein as a first ever attempt, we report ceria-graphene oxide (CeO2-GO) composites as resistive type humidity sensor, that shows attractive response to moisture. High surface area ceria is synthesised via ammonia mediated precipitation from salt precursor, and CeO2-GO composites are achieved via hydrothermal route. The composites are well characterized using various analytical tools. Experiments using different mass ratios of GO in the composite show that there is an optimum amount of GO to realise maximum efficiency in the test parameters. It is further noted that the performance of the sensor is controlled by the active adsorption sites, which is proportional to surface area of the composite. An optimized CeO2-GO matrix yielded a response and recovery time of 19 s and 10 s respectively. The narrow hysteresis in moisture adsorption-desorption study and excellent stability for about 60 days are also observed for the system, warranting the successful utility of the system for practical applications.

Proton conductors are ceramic materials with a crystalline or amorphous structure, which allow the passage of an electrical current through them exclusively by the movement of protons: H+. Recent developments in proton-conducting ceramics present considerable promise for obtaining economic and sustainable energy conversion and storage devices, electrolysis cells, gas purification, and sensing applications. So, proton-conducting ceramics that combine sensitivity, stability, and the ability to operate at low temperatures are particularly attractive. In this article, the authors start by presenting a brief historical resume of proton conductors and by exploring their properties, such as structure and microstructure, and their correlation with conductivity. A perspective regarding applications of these materials on low-temperature energy-related devices, electrochemical and moisture sensors, is presented. Finally, the authors’ efforts on the usage of a proton-conducting ceramic, polyantimonic acid (PAA), to develop humidity sensors, are looked into.

The tetragonal rutile Sb doped Sn O2 (0, 0.5, 1 at.%) is successfully synthesized by hydrothermal method. The XRD analysis shows that the average crystallite size of SnO2 decreases from 29.59 to 20.53 nm with the increase of the doping concentration. SEM images depict the spherical grain morphology of the SnO2 sample. With the increase of the doping ratio, the optical bandgap value of the SnO2 samples increases from 3.6 to 3.86 eV and then decreases to 3.47 eV, showing a trend of first increasing and then decreasing. XPS results indicate that oxygen vacancy defects and substitutional defects(SbSn)are formed into the SnO2 lattice, which changes the electronic effect of Sn element to tune the oxygen vacancy concentration. The humidity‐sensitive testing data shows that 1 at.% Sb‐doped SnO2 humidity sensor presented excellent sensitivity and linearity at a working frequency of 100 Hz as compared to the pure SnO2 sample. [ABSTRACT FROM AUTHOR]

MXenes with numerous superior properties have great potential for portable and conformal humidity sensing, which can meet the ever-increasing requirements for noncontact medical diagnosis, noninvasive epidermal detection, and environmental monitoring. Due to the ambiguous mechanism, the absence of an efficient approach for improving the sensitivity and selectivity remains a big obstacle for realization of MXene-based humidity sensing. In this work, the evolution of humidity sensing mechanisms of few-layered Nb2CTx nanosheets before and after self-oxidation in aqueous solutions are clarified depending on a systematic comparison. The evolution of structure and chemical bonds in few-layered Nb2CTx nanosheets after different incubation durations has been investigated to understand the in situ self-oxidation process and establish the relationship between the oxidation degree and humidity sensing performance. Meanwhile, the humidity sensing mechanism of sensors for different few-layered Nb2CTx nanosheets has been also clarified, and the humidity sensitivity has been optimized to −2.3 × 104 with a relative humidity of 53%. Compared with the sensor prepared from as-prepared few-layered Nb2CTx nanosheets, the humidity sensing selectivity from oxidized few-layered Nb2CTx nanosheets has been improved, contributed to by the transformation of the sensing mechanism from electronic conduction to ionic conduction. Finally, the oxidized few-layered Nb2CTx nanosheets have been prepared on a PI substrate to demonstrate its application in a flexible humidity sensor, providing a facile solution for ultrasensitive wearable gas sensing. [ABSTRACT FROM AUTHOR]

In this study, the effect of strontium (Sr) concentration on the ultrafast humidity sensing performance of Sr doped zinc oxide (SrxZn1–xO) nanostructured thin films was reported. The sol gel method was used in the synthesis of undoped zinc oxide (ZnO) and SrxZn1–xO (x = 0.01, 0.02, 0.03, 0.04, and 0.10) nanoparticles. According to the x-ray diffraction analysis, all films had a hexagonal wurtzite structure. By doping Sr into the ZnO lattice, the preferential orientation changed from the (002) plane to the (101) plane. Scanning electron microscopy micrographs showed that all films had a structure containing nanosized grains and capillary-nanopores, and the nanosized grains were homogeneously and uniformly distributed on the surface of films. The presence of zinc, oxygen and Sr elements in nanostructured thin films was proved by energy dispersive x-ray spectra. The relative humidity sensing performances of undoped ZnO and SrxZn1–xO films were tested with electrical resistance measurements in the range of 40–90% RH at room temperature. SrxZn1–xO films had high sensitivity, excellent stability, reliable and reproducible character, and fast response and recovery times. Sr0.10Zn0.90O was accepted as the best sample in terms of having the highest humidity sensitivity (657.59x) and the fastest response (0.8 s) and recovery (9.8 s) times. This study clearly revealed that SrxZn1–xO nanostructured thin films have great potential for high performance humidity sensor applications due to their ultrafast humidity sensing performance. Highlights: Sol–gel method to synthesize Sr-doped ZnO nanoparticles. For RH-sensing performances, electrical resistance changes depending on %RH. Structural, morphological and elemental analyses with XRD, SEM and EDS. High-humidity sensitivity of 657.59x with Sr doping into ZnO. Ultra-fast response (0.8 s) and recovery (9.8 s) times with Sr doping into ZnO. [ABSTRACT FROM AUTHOR]

Reduced graphene oxide (rGO) has attracted attention as an active electrode material for flexible electrochemical devices due to its high electric conductivity and large surface area. Compared to other reduction processes, laser reduction is a precise, low-cost, and chemical-free process that is directly applied to graphene oxide (GO) membranes. This study aims to develop rGO through laser irradiation for application as electrodes in thin flexible electrochemical sensors. Laser irradiation parameters will be optimized to achieve reduction of a low oxygen to carbon (O/C) ratio and surface impedance. The influence of humidity on the impedance of rGO electrodes will be studied. The observed instability of the rGO electrode is related to incomplete reduction and oxygenated defects involved in reduction. Partially removed oxygenated functional groups not only influence the impedance of the electrode but make it sensitive to the humidity of the working environment. The result provides references for GO's laser reduction optimization, demonstrates the potential of applying rGO as an electrode in sensing applications, but also reveals the limitation of applying the laser reduced rGO electrode in a non-constant humidity environment. [ABSTRACT FROM AUTHOR]

We propose a multimode fiber laser sensor utilizing PI-SMF (polyimide-coated single mode fiber) for low-error relative humidity (RH) measurement, which is temperature compensated based on FBG. The PI-SMF in the laser cavity is used as a sensing element, and its length varies with humidity and temperature by volume-variation induced strain, which leads to frequency shift of the longitudinal mode beat frequency signal (BFS). When the 2000 MHz BFS is selected as the sensing signal, a RH sensitivity of −2.68 kHz/%RH and a temperature sensitivity of −14.05 kHz/°C are achieved. The peak shift of the FBG-based laser emission spectrum is only sensitive to temperature rather than RH with a temperature sensitivity of 9.95 pm/°C, which is used as the temperature compensation for RH measurements. By monitoring the response of the BFS and the laser wavelength, the cross-sensitivity effect of RH and temperature is overcome, and low-error RH measurement in the temperature range of 20 to 65 °C is realized with errors within ±0.67 %RH (25 to 85 %RH). The scheme does not require the design and production of complex structures and hygroscopic material coating processes, owning the advantages of simple structure, easy operation and high accuracy, and is expected to be practically applied in food safety and environmental monitoring.

Packaging solutions have recently evolved to become smart and intelligent thanks to technologies such as RFID tracking and communication systems, but the integration of sensing functionality in these systems is still under active development. In this paper, chipless RFID humidity sensors suitable for smart packaging are proposed together with a novel strategy to tune their performances and their operating range. The sensors are flexible, fast, low-cost and easy to fabricate and can be read wirelessly. The sensitivity and the humidity range where they can be used are adjustable by changing one of the sensor’s structural parameters. Moreover, these sensors are proposed as double parameter sensors, using both the frequency shift and the intensity variation of the resonance peak for the measure of the relative humidity. The results show that the sensitivity can vary remarkably among the sensors proposed, together with the operative range. The sensor suitability in two specific smart packaging applications is discussed. In the first case, a threshold sensor in the low-humidity range for package integrity verification is analyzed, and in the second case, a more complex measurement of humidity in non-hermetic packages is investigated. The discussion shows that the sensor configuration can easily be adapted to the different application needs.

The synthesis of MoS2 with chemical vapor deposition (CVD) using sodium molybdate (Na2MoO4) as the Mo precursor produces a big number of large flakes (∼100-300 μm) compared to other CVD methods that use different precursors. In this work, humidity sensors based on MoS2 are developed, whereby MoS2 is grown using this Mo precursor in an aqueous solution form. The final devices exhibit a response-switching during operation under high (>50%) relative humidity conditions, due to the presence of Na2MoO4 residues on their surface. By decreasing the concentration of the aqueous Mo precursor during the CVD process we partially diminish the switching effect, as the Na2MoO4 residue is reduced To completely overcome this issue, we present a post-fabrication surface treatment using hydrochloric acid that removes the Na2MoO4 residue from the devices' surface. Rinsing the devices with an HCl solution results in the elimination of the response-switching effect and the sensors demonstrate a constant positive response from the initial operation steps.

Thin films of polyimide (PI) and graphene oxide (GO) were exposed to the accelerated Cu-ions with an energy of 1500 keV at different ion fluences (3.75 × 1012; 3.75 × 1014; 1 × 1016) cm−2. The reason for Cu-ion irradiation lies in the modification of thin PI and GO layers and their subsequent use in electronics, photo-catalysis and humidity sensing. It was expected that three ways would primarily carry out modification: i) interaction of the accelerated ions with atoms and electrons of the irradiated films, ii) implantation of Cu ions inside the matrices and their attachment to the structures in the form of CuO, and iii) formation of C and Cu aggregates and Cu nanoparticles in the subsurface layer to form an electrically conductive network. The effects of the interactions of energetic Cu-ions on the PI and GO matrices, including the prediction of the depth of Cu ion penetration, were simulated by SRIM software. Elemental changes, including the depth profiles of implanted Cu-ions, were investigated by Rutherford backscattering spectrometry (RBS) and Elastic recoil detection analysis (ERDA). Changes in the chemical bonding on the PI and GO surfaces were studied by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The effect of energetic Cu-ions on the surface morphology was analyzed by Atomic force microscopy (AFM). For the possible application of PI and GO composites in electronics and sensory, the sheet resistivity were measured by the two- point method and the effect of air humidity on electrical properties was studied. Furthermore, the degradation of Rhodamine B solution in the presence of prepared composites under UV-light irradiation was measured for possible use in photo-catalysis. It was found that the interaction of Cu- ions with the matrix leads to the release of oxygen and hydrogen, resulting in an increase in carbon concentration. The increase in carbon concentration leads to an increase in the electrical conductivity of both materials. The irradiation with Cu ion fluence of 1 × 1016 cm−2 probably formed in PI a subsurface conducting network that reduced the sheet resistivity by almost eleven orders of magnitude. The ion irradiation by Cu ion with fluences below 1 × 1016 cm−2 enhances the photo- catalytic properties of both used materials and the best result was achieved in the case of PI irradiated by the ion fluence of 3.75 × 1014 cm−2. [ABSTRACT FROM AUTHOR]

Humidity sensors are of huge importance in diverse domains. Several types of materials present a moisture-sensing capacity; however, frequently, their electrical response does not display time stability. Due to its high thermal stability, high ionic conductivity, and different conduction mechanism contributing to its overall conductivity, polyantimonic acid (PAA) is seen as a promising material for humidity-sensing devices. In the present work, crystalline PAA was obtained via a simple and safe hydrolysis technique using SbCl3 as a precursor. Bulky sensor samples were produced using different amounts of polyvinyl alcohol (10–20 wt.% PVA) as a binder. The obtained PAA solid sensors were tested at room temperature (RT) in order to evaluate their moisture detection/measuring ability in the relative humidity range 0–100%; the evaluation was carried out with electrical impedance spectroscopy. The sample's structure and morphology were studied using diverse experimental techniques (porosimetry, scanning electron microscopy, X-ray diffraction analysis, and thermogravimetry analysis, etc.). The sensors' electrical response was in line with the found structural and morphological features. The slope of the resistance variation with an RH percentage concentration between 1 kΩ and 1.5 kΩ was noted for all sensors (showing no changes with time) in the interval between 30 and 100% RH. A good repeatability and reproducibility of the evaluated sensors' electrical response was observed: the ones that displayed a higher sensitivity were the ones with a high PVA binder content, higher than previously published results for PAA, as well as a very good time stability along the time and low hysteresis. [ABSTRACT FROM AUTHOR]

Immediate research is needed to determine why monolayer carbon atom (rGO) composites function so poorly as humidity sensors. Here, an attempt is made on (x)rGo+(1-x)CoCr 2 O 4 (x = 0,0.1,0.2 and 0.3) composite for humidity sensor. The method is straightforward, cheap, and basic, making it ideal for mass-producing (x)rGo+(1-x)CoCr 2 O 4 composite. In this research, we investigate whether or not the (x)rGo+(1-x)CoCr 2 O 4 composite can be used to improve the responsiveness of humidity sensors at ambient temperature. The use of X-ray diffraction allows for the investigation of crystallinity, phase, and structure (XRD). Crystallite size were estimated and found 9–11 nm. Morphology of the samples were seen ultrathin, wrinkled, paper-like, spherical type image. Samples were subjected to study the humidity sensing behavior. Within the range of 11%–97% RH, CCR-most rGO's impressive sensing response was 92%. The compound's stability was evaluated over the course of three months, and its response time was found to be between 32 and 36 s. To illustrate the mechanism of humidity sensing, we will use the stages of an adsorption process. For x = 0.3 concentration we observed high sensing response. [ABSTRACT FROM AUTHOR]

This work reports the measurement of impedance variations under various humidity conditions at frequency ranges between 100 Hz and 5 MHz. An electrochemical polymerization process has been used in the synthesis including varying the mass ratios of graphene oxide (GO) in polyaniline. An electrochemical deposition method has been used to produce a sample film on an indium tin oxide glass slide. The percentage relative humidity (RH%) of the samples has been estimated to be 20–90%. Impedance and humidity had an inverse relationship, i.e. the impedance value decreased with an increase in humidity. In contrast with platinum capacitive humidity sensors (HS), the GO‐based HS had a sensitivity of 75–99%, which was ~10‐fold more than that of traditional sensors. With three different parameter weight % of GO, the frequency range have been 100 Hz to 5 MHz and RH% has been found to 20–90%. The HS showed a fast response and recovery time. Therefore, GO appears to be a useful material for building HS with high sensitivity for a comprehensive approach. [ABSTRACT FROM AUTHOR]

Recently, abundant active materials are developed to achieve the wearable detection of human body humidity. However, the limited response signal and sensitivity restrict further application due to their moderate affinity to water. Herein, we propose a flexible COF‐5 film synthesized by a brief vapor‐assisted method at room temperature. Intermediates are calculated by DFT simulation to investigate the interaction between COF‐5 and water. The adsorption and desorption of water molecule result in a reversible deformation of COF layers while creating new conductive path by π–π stacking. The as‐prepared COF‐5 films are applied to the flexible humidity sensors, exhibiting a resistance change in 4 orders of magnitude with remarkable linear relation between log function of resistance and relative humidity (RH) in 11 %–98 % RH range. Applications including respiratory monitoring and non‐contact switch are tested, providing a promising prospect for the detection of human body humidity. [ABSTRACT FROM AUTHOR]

Multifunctional films have potential applications in smart wearable devices and portable electronic products. Yet, it is always a challenge to ensure these materials simultaneously to have flexible, strong, and functional properties during the material preparation process. Herein, bacterial cellulose/polydopamine modified by MXene (BC/PM) multi-layer films is prepared by vacuum-assisted self-assembly. The micromorphology, phase composition, and application performance of this composite film were systematically characterized. The mechanical properties test indicates that the BC/PM multi-layer film exhibits an excellent reinforcement effect. The tensile strength and elongation of the three-layer BC/PM film reach 181.6 MPa and 8.9%, respectively. For multifunctional applications, the BC/PM multi-layer film shows remarkable electric heating and excellent photothermal properties, for example, it can be heated up to 85 °C at a constant voltage of 6 V for 20 s, and its temperature can increase from room temperature to 90 ℃ after 250 W infrared lamp is irradiated for 30 s. Furthermore, the sample has potential high sensitivity and high response speed to humidity changes. This research will provide a data basis and theoretical reference for the practical application of bacterial cellulose-based multifunctional films. [ABSTRACT FROM AUTHOR]

The influence of surface charge on tribo-layer is a crucial parameter in improving the performance of triboelectric nanogenerators (TENG). Nevertheless, most researchers focus on the structure and design of TENG rather than increasing the surface charge density, which is the main parameter for energy harnessing in nanogenerators. Herein, we tweaked the surface charge density of polydimethylsiloxane (PDMS) via incorporating different types of carbon allotropes to shift the charge density (positive to negative and vice versa) for high output TENG. The PDMS/GO TENG device generated a voltage of 234 V; higher compared to that of bare PDMS and other nanocomposite films, which is attributed to the high surface charge of PDMS/GO confirmed via Kelvin probe force microscopic (KPFM) analysis. As a proof concept, we have demonstrated the use of PDMS/GO-based TENG device for self-powered humidity sensor. [Display omitted] [ABSTRACT FROM AUTHOR]

Humidity sensors are in high demand for many applications, such as environmental monitoring and air and food quality control. Despite many inorganic and organic materials exhibit moisture sensing properties, the electrical response of many existing sensors is not stable along the time. Polyantimonic acid (PAA) is characterized by elevated proton conductivity and by high thermal stability: consequently, it is seen as promising proton conductor for usage in humidity sensing devices. In this work, for the first time, PAA-based bulk solid membranes were produced and tested as potential materials for relative humidity (RH) detection and their moisture sensitivity was evaluated. Two different amounts of binder were used for moulding the solid sensors: the ones with 10% of binder were designated as 90PAA, while the ones with 20% were named 80PAA. The structures of the solid samples were investigated by X-ray diffraction (XRD) technique, adsorption–desorption curves via Brunauer–Emmett–Teller (BET), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) techniques. The electrical behaviour was examined at ambient temperature by electrical impedance spectroscopy in the entire relative humidity (RH) interval (0–100%) and in the frequency range of 40 Hz up to 60 MHz. Electrical response of the materials was correlated with the structural features of the membranes. Both 90PAA and 80PAA sensors showed total resistance 3 × 105 and 3.5 × 105 Ω at 10% RH, respectively. A linear decrease of the resistance on RH was observed in the range 30–90% RH for both sensors. The electrical response of the evaluated PAA-based sensors displays good repeatability and reproducibility: the ones with lower binder content showed higher moisture sensitivity as well as very good time stability over 1 year. [ABSTRACT FROM AUTHOR]

This scientific investigation emphasizes the essential integration of nature’s influence in crafting multifunctional surfaces with bio-inspired designs for enhanced functionality and environmental advantages. The study introduces an innovative approach, merging color decoration, humidity sensing, and antiviral properties into a unified surface using chitosan, an organo-biological polymer, to create cost-effective multilayered films through sol-gel deposition and UV photoinduced deposition of metal nanoparticles. The resulting chitosan films showcase diverse structural colors and demonstrate significant antiviral efficiency, with a 50% and 85% virus inhibition rate within a rapid 20 min reaction, validated through fluorescence cell expression and real-time qPCR (polymerase chain reaction) assays. Silver-deposited chitosan films further enhance antiviral activity, achieving remarkable 91% and 95% inhibition in independent assays. These films exhibit humidity-responsive color modifications across a 25–90% relative humidity range, enabling real-time monitoring validated through simulation studies. The proposed three-in-one functional surface can have versatile applications in surface decoration, medicine, air conditioning, and the food industry. It can serve as a real-time humidity sensor for indoor and outdoor surfaces, find use in biomedical devices for continuous humidity monitoring, and offer antiviral protection for frequently handled devices and tools. The customizable colors enhance visual appeal, making it a comprehensive solution for diverse applications.

We propose a humidity sensor using an excessively tilted fiber grating (Ex-TFG) coated with agarose fabricated using femtosecond laser processing. The processed grating showcases remarkable differentiation between TE and TM modes, achieving an exceptionally narrow bandwidth of approximately 1.5 nm and an impressive modulation depth of up to 15 dB for both modes. We exposed the agarose-coated TFG sensor to various relative humidity levels and monitored the resonance wavelength to test its humidity sensing capability. Our findings demonstrated that the sensor exhibited a rapid response time (2–4 s) and showed a high response sensitivity (18.5 pm/%RH) between the humidity changes and the resonant wavelength shifts. The high sensitivity, linearity, repeatability, low hysteresis, and excellent long-term stability of the TFG humidity sensor, as demonstrated in our experimental results, make it an attractive option for environmental monitoring or biomedical diagnosis.

Molybdenum disulfide (MoS2) was introduced into the polyacrylamide/chitosan (PAM/CS) hydrogel system by free radical polymerization, and the PAM/CS/MoS2 composite polymer hydrogel with interpenetrating network structure was prepared. The composition and morphology of the hydrogels were analyzed by Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, and laser scanning confocal microscopy. The mechanical properties and hydrophilic properties were tested by a universal testing machine and a contact angle measuring instrument. Finally, the application of the composite hydrogel film in the field of humidity sensing was explored by a quartz crystal microbalance (QCM). The PAM/CS/MoS2-0.4 (mass of MoS2 in this system is 0.4 mg) composite hydrogel has a maximum compressive stress of 584.6 kPa and a maximum compressive strain of 83.8%. The introduction of MoS2 improves the hydrophilicity of the composite hydrogel. As the relative humidity of the environment increases from 11% to 95%, the frequency response of the QCM humidity sensor modified by the composite hydrogel film reaches a maximum of 2 642 Hz, and its sensitivity of 1% change of relative humidity is 31.45 Hz, which is expected to be applied in the field of humidity sensing. [ABSTRACT FROM AUTHOR]