We present a new approach to enhance the sensitivity of resistive sensors and enable threshold switching that can be used for actuation, providing a simple binary readout method. The concept is based on electrically coupling a resistive sensor with a resonant MEMS structure. Results are demonstrated for two case studies involving a resistive temperature sensor and a chemiresistive humidity sensor based on the nanocomposite material Ti3C2Tx. By tracking the resonance frequency shifts of the coupled microstructure operated near buckling, the results show significant sensitivity enhancement (more than 5-6 times) for both the temperature and humidity sensors compared to directly monitoring the resistance changes of the resistive sensors. Furthermore, results are shown for the conversion of the resonator into a tunable electrical switch based on the nonlinear pull-in phenomenon. Such a switch can simplify sensor-actuator systems and can be used as a simple binary readout method for resistive sensors.

Despite the remarkable advancements to develop low-cost low-energy individual chemiresistive sensors, the complete sensor-actuator systems remain complex due to the implementation of energy-hungry components, such as transmitters, microcontrollers, and analog-to-digital and digital-to-analog converters. In an effort to alleviate this problem, we introduce a simple sensor-actuator platform by electrically coupling a chemiresistive material with a clamped-clamped microbeam and utilizing the nonlinear instabilities of buckling and pull-in. As a case study, we demonstrate the concept using the chemiresistive material Ti3C2Tx MXene for humidity sensing and actuation. The device can trigger actions when exceeding a pre-determined relative humidity (RH) threshold. It can also function as a sensor with a quasi-digital resonance frequency output in the sensing mode. Analytical results based on the Galerkin approach are obtained and compared to the experimental data. The results indicate that as RH levels increase, the coupled system of the chemiresistive material with the resonator has more sensitivity compared to the individual chemiresistive sensor. Simulation results are shown to demonstrate the capability of tuning and adjusting the switching thresholds to meet various application needs.

Highway work zones are critical areas where accidents frequently occur, often because of the proximity of workers to heavy machinery and ongoing traffic. With technological advancements in sensor technologies and the Internet of Things, promising solutions are emerging to address these safety concerns. This paper provides a systematic review of existing studies on the application of sensor technologies in enhancing highway work zone safety, particularly in preventing intrusion and proximity hazards. Following the PRISMA (preferred reporting items for systematic reviews and meta-analyses) protocol, the review examines a broad spectrum of publications on various sensor technologies, including GPS (global positioning system), radar, laser, infrared, radio-frequency identification, Bluetooth, ultrasonic, and infrared sensors, detailing their application in reducing intrusion and proximity incidents. The review also assesses these technologies in relation to their accuracy, range, power consumption, cost, and user-friendliness, with a specific emphasis on their suitability for highway work zones. The findings highlighted the potential of sensor technologies to significantly enhance work zone safety. As there are a wide range of sensor technologies to choose from, the review also revealed that the selection of sensors for a particular application needs careful consideration of pertinent factors. Finally, although sensor technologies offer promising solutions for enhancing highway work zone safety, their effective implementation requires comprehensive consideration of various factors beyond their technological capabilities, including developing integrated, cost-effective, user-friendly, and secure systems, and creating regulatory frameworks to support the rapid development of these technologies.

This work numerically studies the dynamics of a droplet, uncharged and freely suspended in an immiscible fluid, driven to move by the fringe electric field generated by parallel plate capacitors. Both the droplet and the suspending fluid are considered as leaky dielectrics. The deformation and migration of the droplet through the fringe electric field into or away from the parallel plate capacitors is our focus. A three-dimensional spectral boundary element method for interfacial dynamics in electrical fields is modified and adopted for the current study. The influences of the material properties of the pair of immiscible fluids including the viscosity ratio, surface tension, conductivity, and permittivity on the direction and velocity of the droplet migration will be investigated. The effects of operational and design parameters on droplet motion, including the electrical field strength and the parallel plates’ gap width will be explored as well. In this preliminary study the numerical method will then be applied to investigate the entrapment processes of fine CO2 bubbles in two-dimensional MXene-membranes, a novel membrane technology newly developed for CO2 sensing, capture and reduction. This technology is being developed for an over-arching goal of understanding changes in ocean carbon cycle and controlling CO2 level globally. The efficiency of such a device will be discussed from the view point of fluid dynamics.

Detecting diseases via noninvasive methods is in high demand in contemporary medicine and health management. Among different noninvasive disease detection methods, exhale human breath analysis is an up-and-coming field of research work with great potential for diagnosing diseases. Volatile organic compounds in exhaled breath are essential as the breath is directly linked to one's metabolic activity and contains information about health conditions (e.g. infections or metabolic-related diseases). It is simple, noninvasive, offering easy sample access, and a point-of-care process for monitoring disease and evaluating environmental exposure in human beings. It is primarily famous in the medical field and in examining the health status of individuals. A newly developed two-dimensional ( 2D ) MXene nanosheets provides advantages for sensing detection because of their hydrophilicity, biocompatibility, large surface area, and functionalization due to the presence of surface functional groups. This chapter aims to review the development and challenges of breath sensors for lung cancer diagnostics based on different structures and functional properties of 2D MXene and study the direct effect of higher temperature and concentration of the etchants on MXenes.

Pancreatic cancer is increasingly prevalent and characterized by a high mortality rate. Due to the limitations of current diagnostic methods, early-stage detection remains elusive, contributing to persistently low survival rates among affected individuals. Nanomaterials have garnered significant attention in cancer research for their potential diagnostic applications. Among these, MXenes – a novel family of two-dimensional nanomaterials composed of transition metal carbides, nitrides, and carbonitrides – are of particular interest due to their unique properties. These include high electrical conductivity, hydrophilicity, thermal stability, large interlayer spacing, tunable structure, and high surface area. These characteristics make MXenes highly effective for detecting trace amounts of various analytes. In addition, their tunable structure enables precise manipulation of their properties, allowing for optimized sensing responses. Montmorillonite nanoclay (MMT), a member of the smectite group of natural clay minerals, is known for its ability to promote bone development and influence cell behavior. When combined with MXenes, MMT forms promising nanocomposites for early pancreatic cancer detection through sensing applications. The Ti3C2 MXene-MMT nanocomposites exhibit potential as scaffold sensors capable of distinguishing cancerous from non-cancerous samples by observing the distinctive patterns in resistance changes. In addition, MXenes possess excellent selectivity, allowing for the reliable identification of targeted analytes from a complex mixture of chemical and biological analytes. Due to the advanced sensing capabilities of MXene-MMT composite scaffold sensors, they hold great promise for early cancer diagnosis and tissue regeneration, providing a novel therapeutic approach to improving patient outcomes.

This study provides new insights into the development of high-performance MXene-reinforced coatings to strengthen polymeric nanocomposites by enhancing microstructure, anti -aging properties, corrosion resistance, and robustness. MXene nanoparticles, labeled 25C and 80C, were synthesized using two different methods and incorporated at concentrations ranging from 0.1 to 2.0 wt% into epoxy composites. The results demonstrated that 80C MXene, characterized by its finer morphology and superior dispersion, significantly improved the composite's performance compared to 25C. Electrochemical Impedance Spectroscopy (EIS) tests, along with longterm exposure assessments, suggested that incorporating both types of MXene nanoparticles enhances the corrosion protection performance of epoxy coatings over time. Micro -CT analysis revealed that both types of MXene substantially reduced defects and voids in the polymeric matrix, resulting in enhanced protective performance. This void reduction confirms that the incorporation of both 25C and 80C MXene improves microstructural integrity by filling voids and creating a more continuous, uniform structure, particularly in samples with 0.1 % to 1.0 % MXene flakes. The findings also highlighted MXene's potential in modifying the anti -aging properties of epoxy by inhibiting free radical generation and enhancing the composite's resistance against corrosion. Both 25C and 80C MXene-epoxy groups exhibited a clear trend of diminishing free radical intensity with increasing MXene concentration up to 1.0 %, with free radical intensity reduced by over 40 % compared to neat epoxy. The relationship between MXene concentration and reinforcement was also investigated, revealing superior corrosion protection properties at concentrations of 0.5 - 1.0 wt%. This research offers a profound understanding of MXene's potential in polymer -based composites, laying a foundation for future investigations aimed at utilizing MXene to achieve superior material properties for a wide range of applications, particularly in the realm of metallic surface protection.

This study explored the enhancement potential of MXene, a novel two-dimensional material, in epoxy-based nanocomposites; which comprehensively examined the influence of MXene on epoxy's viscosity, void formation, aging resistance, mechanical properties, and anti-wear properties. MXene nanofillers, labeled as 25C and 80C, fabricated via different acid-etching methods, were incorporated into epoxy resin at varying weight percentages (0.1-2.0 wt%). Observations revealed that for both varieties of MXene, inclusion of 1.0 wt% MXene led to the mitigation of void content, whereas the incorporation of 2.0 wt% MXene yielded maximal enhancements in both tensile strength and abrasion resistance. Additionally, the integration of 1.0 and 2.0 wt% MXene displayed superior aging resistance, with around 80 % reduction in free radical formation compared to the unmodified epoxy, while maintaining its excellent mechanical properties after QUV exposure. Therefore, both MXene types significantly enhanced the performance of epoxy composites, with the 80C-MXene displaying marginally superior enhancement due to its smaller particle size and higher purity, as identified by SEM and TEM images.

A challenge for optical fiber biosensor is to achieve ultrahigh sensitivity with narrow full width at half maximum (FWHM) of the spectrum. To address this challenge, an ultrahigh-sensitivity microfiber interferometer fiber ring laser (FRL) biosensor is proposed and investigated for Listeria monocytogenes (L. monocytogenes) detection. The fiber biosensor is composed of a singlemode- tapered no core-singlemode (STNS) fiber configuration, which is functionalized with the anti-L. monocytogenes antibodies. An Erbium Doped Fiber Amplifier is applied to the sensor to excite laser and thus reduce the FWHM of the spectrum, which significantly improved the limit of detection (LoD). The proposed STNS FRL biosensor has excellent reproducibility, specificity and sensitivity for L. monocytogenes. The developed STNS FRL biosensor can directly detect L. monocytogenes cells with LoD as low as 1.0 cell/mL, indicating the capability for detecting single cell of L. monocytogenes. Real lettuce and milk samples have been tested and test result in lettuce and milk samples has deviations within +/- 30 % from that of Phosphate-buffered saline (PBS) for L. monocytogenes concentrations vary from 101 to 103 cells/mL(g). The developed STNS FRL biosensor has ultrahigh sensitivity, good stability, reproducibility, and specificity, which has potential applications in diseases/medical diagnostics.

The need for precision agriculture in today and future farming cannot be overstressed. Recent agriculture is characterized by numerous challenges such as environmental stressors and resource constraints resulting in low crop yield and unsustainable agriculture practices. Understanding plant growth mechanism and growth rate under the external influence is a bedrock towards precision agriculture practices ensuring optimum yield and sustainable utilization of resources. The current study addresses this need by developing and applying an affordable and stable sensor for monitoring plant growth. The sensor was fabricated by in-situ chemical polymerization of aniline on an elastic band substrate by dip coating. The sensor was characterized using optical imaging and Fourier-transformed infrared spectroscopy (FTIR), calibrated for strain sensing, and its stability was analyzed under cycling loading and temperature variations. When applied to sunflower and soybean stems, the sensor detected a rhythmic growth pattern with higher growth during the dark cycle in sunflower plants but a continuous growth for both the light and dark cycle for soybean. The similarities between growth rate and growth pattern observed on these plants with available information on plant growth indicate the fitness of the sensor for such precision measurement for plant health and suggest a step towards the development of precision sensing capability for agriculture.

Thecorrosion protection of MXene-based composite coatingsis challengingdue to the relatively low dispersion of MXene in organic coatings.In this work, waterborne polyurethane (WPU) composites containinghybrid nanoadditives of Ti3C2T (x) MXene and functionalized carbon nanotubes (CNTs) were fabricated.The thermal stability, surface hydrophobicity, surface roughness,and mechanical properties of the nanocomposites containing MXene orMXene/CNT hybrid additives were studied. Electrochemical methods,including electrochemical impedance spectroscopy (EIS) and potentiodynamicpolarization scans, were utilized to evaluate the anticorrosion propertiesof the nanocomposite coatings when applied to copper substrates. Thepolyurethane sample with 0.95 wt % Ti3C2T (x) MXene and 0.05 wt % CNTs showed the lowestcorrosion rate of 2.1 x 10(-3) & mu;m year(-1). Additionally, the EIS results revealed that thecorrosion resistance of WPU/MXene coatings significantly increasedby adding 0.05 wt % CNTs. The mechanism of the improved anticorrosionperformance of the WPU/MXene/CNT composite coating is illustrated.Moreover, the importance of optimizing the concentration of the CNTsis discussed to obtain better corrosion protection. The polyurethanenanocomposite coatings reported in this work present great potentialas corrosion protection coatings for metals and other surfaces.

Studies of optical properties of doped nanocrystals of tungsten trioxide can elucidate new information about the material. A novel molecule-enhanced photoluminescence (PL) of potassium-doped tungsten trioxide (K x WO) was explored in the presence of different gases to understand charge transfer between molecules and K x WO on the properties of the material. We performed Raman spectroscopy and PL experiments in the presence of gaseous acetone or ethanol mixed with other gases (N2 and O2). PL at 630 nm from K x WO was observed and further enhanced when the sample was continuously irradiated with a 532 nm CW laser in acetone. A mechanism of strong emission of the PL induced by the charge transfer between the acetone and the K x WO is proposed.

A polymer-based micro-bottle resonator coated with graphene oxide (GO) film is presented to improve the relative humidity (RH) sensing performance. Polymeric material Loctite 3525 was coated onto a quartz fiber and cured by using UV light irradiation and thermal reflow technology. A layer of GO film was prepared on the micro-bottle resonator by the dip impregnation method, which realized a high Q-factor (>10(4)) transmission of energy by appropriately designing a wave-guide resonator coupling. By optimizing the concentration of GO dip impregnation solution, high sensitivity and figure of merit (FoM) of 0.161 nm/%RH and 2.01/%RH were achieved in the RH range of 22-81%. In addition, after high-temperature annealing at 300.C, the temperature sensitivity decreased by an order of magnitude from 0.793 nm/degrees C to 0.068 nm/degrees C, which significantly reduces the cross-sensitivity between humidity and temperature. The proposed resonator has the advantages of being compact in size, low in cost, high sensitivity, and low in temperature crosstalk.

A high sensitivity human chorionic gonado-tropin (hCG) detection was conducted by a tapered side-polished (TSP) optical fiber sensor. Experimentally, the TSP fiber sensor was made by side polishing a short section of single mode fiber to a D shape structure and tapering the D shape section to a small diameter ( $ < 10~\mu \text{m}$ in the experiments). By functionalizing the primary antibody of hCG onto the TSP fiber surface, the sensor was used for detecting hCG concentration. Experimental results show that when the hCG concentration is 0.1 mIU/mL, the sensor has an average wavelength shift of 0.82 nm. The limit of detection (LoD) of the hCG is estimated 0.058 mIU/mL, assuming three times of maximum wavelength variation ( ${3}\times {0}.{15}=0.45$ nm) in Phosphate buffer saline (PBS) to the measurement limit. The specificity has also been tested by immersing the sensor into a mixed biomaterial solution (hCG - 1 mIU/mL, pig-IgG - 1 $\mu \text{g}$ /mL, Staphylococcus aureus $-{6}\times {10}^{{5}}$ CFU/mL and Escherichia coli - ${2.5}\times {10}^{{5}}$ CFU/mL). The result showed that the TSP optical fiber sensor has excellent specificity. The biosensor has potential application in clinical/medical diagnostics, human health, environmental quality and food safety monitoring.

Recent advances in nanotechnology have led researchers to investigate various approaches to the development of nanofluids with enhanced thermal conductivities that can replace conventional industrial coolants. Of particular interest have been MXene based nanofluids. The current investigation focuses on MXene/water and MXene/ethylene-glycol/water nanofluids with particle concentrations ranging from 0.1 to 0.5 wt% of MXene. The results of this investigation found as much as a 30.6% improvement in the effective thermal conductivity of the 0.5 wt% MXene/water nanofluid compared to the pure water base fluid. In addition, an improvement of 27.3% in the effective thermal conductivity was observed in MXene/ethylene-glycol/water nanofluid. MXene was found to provide superior enhancement in the effective thermal conductivity when compared with other particles, such as metal, metal oxide, and graphene, both in DI water and in ethylene glycol. In addition, MXene did not significantly increase the viscosity as is typically the case for other nanosuspensions containing carbon nano materials, e.g. nanotubes, graphene. The physical properties indicated that MXene based nanofluids present a number of very attractive thermophysical properties for application as industrial coolants.

The rates of diabetes throughout the world are rising rapidly, impacting nearly every country. New research is focused on better ways to monitor and treat this disease. Breath acetone levels have been defined as a biomarker for diabetes. The development of a method to monitor and diagnose diabetes utilizing breath acetone levels would provide a fast, easy, and non-invasive treatment option. An ideal material for point-of-care diabetes management would need to have a high response to acetone, high acetone selectivity, low interference from humidity, and be able to operate at room temperature. Chemiresistive gas sensors are a promising method for sensing breath acetone due to their simple fabrication and easy operation. Certain semiconductor materials in chemiresistive sensors can react to acetone in the air and produce changes in resistance that can be correlated with acetone levels. While these materials have been developed and show strong responses to acetone with good selectivity, most of them must operate at high temperatures (compared to RT), causing high power consumption, unstable device operation, and complex device design. In this paper, we systematically studied a series of 2-dimensional MXene-based nanocomposites as the sensing materials in chemiresistive sensors to detect 2.86 ppm of acetone at room temperature. Most of them showed great sensitivity and selectivity for acetone. In particular, the 1D/2D CrWO/Ti3C2 nanocomposite showed the best sensing response to acetone: nine times higher sensitivity than 1D KWO nanowires. To determine the sensing selectivity, a CrWO/Ti3C2 nanocomposite-based sensor was exposed to various common vapors in human breath. The result revealed that it has excellent selectivity for acetone, and far lower responses to other vapors. All these preliminary results indicate that this material is a promising candidate for the creation of a point-of-care diabetes management device.