Tunable Sensitivity Research Articles

Tunable High-Sensitivity Four-Frequency Refractive Index Sensor Based on Graphene Metamaterial.

As graphene-related technology advances, the benefits of graphene metamaterials become more apparent. In this study, a surface-isolated exciton-based absorber is built by running relevant simulations on graphene, which can achieve more than 98% perfect absorption at multiple frequencies in the MWIR (MediumWavelength Infra-Red (MWIR) band as compared to the typical absorber. The absorber consists of three layers: the bottom layer is gold, the middle layer is dielectric, and the top layer is patterned with graphene. Tunability was achieved by electrically altering graphene's Fermi energy, hence the position of the absorption peak. The influence of graphene's relaxation time on the sensor is discussed. Due to the symmetry of its structure, different angles of light source incidence have little effect on the absorption rate, leading to polarization insensitivity, especially for TE waves, and this absorber has polarization insensitivity at ultra-wide-angle degrees. The sensor is characterized by its tunability, polarisation insensitivity, and high sensitivity, with a sensitivity of up to 21.60 THz/refractive index unit (RIU). This paper demonstrates the feasibility of the multi-frequency sensor and provides a theoretical basis for the realization of the multi-frequency sensor. This makes it possible to apply it to high-sensitivity sensors.

Coin-sized, fully integrated, and minimally invasive continuous glucose monitoring system based on organic electrochemical transistors.

Continuous glucose monitoring systems (CGMs) are critical toward closed-loop diabetes management. The field's progress urges next-generation CGMs with enhanced antinoise ability, reliability, and wearability. Here, we propose a coin-sized, fully integrated, and wearable CGM, achieved by holistically synergizing state-of-the-art interdisciplinary technologies of biosensors, minimally invasive tools, and hydrogels. The proposed CGM consists of three major parts: (i) an emerging biochemical signal amplifier, the organic electrochemical transistor (OECT), improving the signal-to-noise ratio (SNR) beyond traditional electrochemical sensors; (ii) a microneedle array to facilitate subcutaneous glucose sampling with minimized pain; and (iii) a soft hydrogel to stabilize the skin-device interface. Compared to conventional CGMs, the OECT-CGM offers a high antinoise ability, tunable sensitivity and resolution, and comfort wearability, enabling personalized glucose sensing for future precision diabetes health care. Last, we discuss how OECT technology can help push the limit of detection of current wearable electrochemical biosensors, especially when operating in complicated conditions.

Gate-Tunable Multiband van der Waals Photodetector and Polarization Sensor.

A single photodetector with tunable detection wavelengths and polarization sensitivity can potentially be harnessed for diverse optical applications ranging from imaging and sensing to telecommunications. Such a device will require the combination of multiple material systems with different structures, band gaps, and photoelectrical responses, which is extremely difficult to engineer using traditional epitaxial films. Here, we develop a multifunctional and high-performance photosensor using all van der Waals materials. The device features a gate-tunable spectral response that is switchable between near-infrared/visible and short-/midwave infrared, as well as broad-band operation, at room temperature. The linear polarization sensitivity in the telecommunication O-band can also be directly modulated between horizontal, vertical, and nonpolarizing modes. These effects originate from the balance of photocurrent generation in two of the active layers that can be manipulated by an electric field. The photodetector features high detectivity (>109 cmHz1/2W-1) together with fast operation speed (∼1 MHz) and can be further exploited for dual visible and infrared imaging.

Multifunctional Photodetector with Tunable Response Bandwidth and Polarization Sensitivity

AbstractMultifunctional organic photodetectors (MFOPDs) have garnered significant attention due to their remarkable potential for integrating diverse device functionalities. In contrast to previous MFOPDs that have primarily emphasized the integration of various response bands, a pioneering multifunctional photodetector is introduced based on the P3HT:PC61BM system capable of selectively responding to both wavelength and polarization. Under positive bias, the device operates in a wide‐band, polarization‐insensitive mode, achieving an external quantum efficiency (EQE) of up to 7.01 × 104%. The EQE dichroic ratio (DR) of the device remains <1.01 (at 650 nm). Conversely, under negative bias, the device transitions into a narrow‐band, polarization‐sensitive mode, achieving an EQE of up to 4.82 × 104% with a narrow full width at half maximum (FWHM) of only 25 nm at 650 nm. The EQE DR exceeds 10 in this mode, marking it as one of the highest values within the field of polarization‐sensitive organic photodetectors. This versatile operation is made possible through the strategic use of double‐sided barriers, an oriented light harvesting layer, and a charge injection narrowing (CIN) approach. This work represents a significant advancement toward the realization of multifunctional photodetectors capable of selecting response bands and polarization sensitivity.

Multi-Layer Polyurethane-Fiber-Prepared Entangled Strain Sensor with Tunable Sensitivity and Working Range for Human Motion Detection.

The entanglement of fibers can form physical and topological structures, with the resulting bending and stretching strains causing localized changes in pressure. In this study, a multi-layer polyurethane-fiber-prepared (MPF) sensor was developed by coating the CNT/PU sensing layer on the outside of an elastic electrode through a wet-film method. The entangled topology of two MPFs was utilized to convert the stretching strain into localized pressure at the contact area, enabling the perception of stretching strain. The influence of coating mechanical properties and surface structure on strain sensing performance was investigated. A force regulator was introduced to regulate the mechanical properties of the entangled topology of MPF. By modifying the thickness and length proportion of the force regulator, the sensitivity factor and sensitivity range of the sensor could be controlled, achieving a high sensitivity factor of up to 127.74 and a sensitivity range of up to 58%. Eight sensors were integrated into a sensor array and integrated into a dance costume, successfully monitoring the multi-axis motion of the dancer's lumbar spine. This provides a new approach for wearable biomechanical sensors.

Electrodeposited Silver Dendrites on Laser‐Induced Graphene for Electrochemical Detection of Nitrate with Tunable Sensor Properties

AbstractLaser‐induced graphene (LIG) is a promising technology enabling cost‐effective, scalable, and high surface area 3D‐porous graphene electrodes for electrochemical applications. Nitrate in water bodies is a harmful contaminant to humans and the ecosystems. Its detection by electrochemical sensors is challenging due to the interference from nitrite. Herein, for the first time, a LIG‐based electrochemical sensor modified with electrodeposited silver dendrites (EdAg/LIG) without using surfactants is proposed for the detection of nitrate with tunable selectivity and sensitivity. The modified electrode surface is extensively characterized by spectroscopic and electrochemical methods and the underlying mechanism for the formation of dendrites is substantiated. The developed EdAg dendrites/LIG electrode shows excellent sensing properties for the detection of nitrate at pH 2. The interference with nitrite in acidic media is eliminated by implementing a novel strategy to shift the working pH of the electrode to 7. The achieved sensor properties at both pH values surpass other LIG‐based sensors with limit of detection of 0.46 at pH 2 and 5.53 µm at pH 7. The developed sensor also shows good recovery characteristics in mineral, tap, and groundwater across a wide range of concentrations and also demonstrates good stability under temperature fluctuations and deformations.

Stretchable Multifunctional Polydimethylsiloxane Composites with Cage‐Like Conductive Architecture for Integrated Thermosensitive and Electromagnetic Interference Shielding Performance

AbstractHigh‐performance sensors with outstanding sensitivity, wide working range, and multifunctional properties are highly desirable in modern integrated smart wearable electronics. Herein, polydimethylsiloxane (PDMS)‐based stretchable pyroresistive sensors composed of tightly‐assembled silver nanowires (Ag NWs)‐encapsulated PDMS microspheres (PM) and expandable microspheres (EM) are fabricated. The synergistic cage‐like conductive network and EM endow the temperature sensor with tunable sensitivity (Max TCR: 27.4% °C−1), broad sensing range (25–85 °C), low perception limit (0.1 °C), and excellent anti‐interference ability. Interestingly, at elevated temperature field (> 90 °C), a remarkable conduction‐insulation transition is observed, which is employed to facilitate an early fire alarm system. In addition, the selectively distributed Ag NWs constructs segregated conductive pathways at an ultralow content (Pc = 0.014 vol%), leading to efficient electromagnetic interference shielding (40.0 dB). The underlying mechanism responsible for the observed superior thermosensation and EMI shielding performance is elucidated, and possible applications are demonstrated. Consequently, this work offers a novel strategy for the design of flexible, multifunctional pyroresistive sensors toward artificial intelligence and emerging wearable electronics.

Tongue-inspired gelatin/poly(acrylate-co-acrylamide)-Fe3+ organic hydrogel with tunable mechanical, electrical, and sensory properties

Conductive hydrogels have emerged as one of the most promising candidates for the next generation of wearable soft electronics. However, they face limitations during practical implementation owing to their unbalanced overall properties. In this study, we present a dynamic cross-linked gelatin/poly(acrylic acid-co-acrylamide) (GxPyFez) hydrogel with tunable mechanical strength, self-healing, freezing resistance, electrical conductivity, and high sensitivity, which was prepared by incorporating Fe3+ ions. The hydrogel was prepared based on the tongue, in which gelatin/poly(acrylic acid-co-acrylamide) and Fe3+ ions mimic the connective tissue and receptor cells of the human tongue. The synergistic effect of reversible crosslinking, along with the modulation of rigid and flexible components enabled tunable flexible structures that exhibit excellent mechanical properties such as elongation at break (569 %) and toughness (8.82 MJ m−3). Notably, the G2P3Fe0.1 hydrogel exhibited remarkable self-healing ability, even at room temperature, while maintaining a good freezing resistance. Furthermore, the G2P3Fe0.1 demonstrated fast response characteristics along with a high sensitivity (GF = 2.75). Consequently, it could be assembled into sensors capable of effectively detecting various movements of the human body; it serves as an electronic skin that responds to diverse external stimuli and monitors underwater motion signals. This study provides new insights into the design of conductive hydrogels with tunable overall properties that can be modified to suit specific application scenarios.

Distributed sensing along fibers for smart clothing.

Textile sensors transform our everyday clothing into a means to track movement and biosignals in a completely unobtrusive way. One major hindrance to the adoption of "smart" clothing is the difficulty encountered with connections and space when scaling up the number of sensors. There is a lack of research addressing a key limitation in wearable electronics: Connections between rigid and textile elements are often unreliable, and they require interfacing sensors in a way incompatible with textile mass production methods. We introduce a prototype garment, compact readout circuit, and algorithm to measure localized strain along multiple regions of a fiber. We use a helical auxetic yarn sensor with tunable sensitivity along its length to selectively respond to strain signals. We demonstrate distributed sensing in clothing, monitoring arm joint angles from a single continuous fiber. Compared to optical motion capture, we achieve around five degrees error in reconstructing shoulder, elbow, and wrist joint angles.

Probing light quark Yukawa couplings through angularity distributions in Higgs boson decay

We propose to utilize angularity distributions in Higgs boson decay to probe light quark Yukawa couplings at e+e− colliders. Angularities τa are a class of 2-jet event shapes with variable and tunable sensitivity to the distribution of radiation in hadronic jets in the final state. Using soft-collinear effective theory (SCET), we present a prediction of angularity distributions from Higgs decaying to quark and gluon states at e+e− colliders to NNLL + \U0001d4aa(αs) accuracy. Due to the different color structures in quark and gluon jets, the angularity distributions from H → \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$q\\overline{q }$$\\end{document} and H → gg show different behaviors and can be used to constrain the light quark Yukawa couplings. We show that the upper limit of light quark Yukawa couplings could be probed to the level of ~ 15% of the bottom quark Yukawa coupling in the Standard Model in a conservative analysis window far away from nonperturbative effects and other uncertainties; the limit can be pushed to ≲ 7 – 9% with better control of the nonperturbative effects especially on gluon angularity distributions and/or with multiple angularities.

Near- to mid-IR spectral purity transfer with a tunable frequency comb: Methanol frequency metrology over a 1.4 GHz span

We report the upgrade and operation of a frequency-comb-assisted high-resolution mid-infrared molecular spectrometer, allowing us to combine high spectral purity, International System of Units (SI)-traceability, wide tunability, and high sensitivity. An optical frequency comb is used to transfer the spectral purity of a SI-traceable 1.54 μm metrology-grade frequency reference to a 10.3 μm quantum cascade laser (QCL). The near-infrared reference is operated at the French time/frequency metrology institute, calibrated there to primary frequency standards, and transferred to Laboratoire de Physique des Lasers via the REFIMEVE fiber network. The QCL exhibits a linewidth of δν ∼ 0.1 Hz and a sub-10−15 relative frequency stability from 0.1 to 10 s, and its frequency is traceable to the SI with a total relative uncertainty better than 4 × 10−14 after 1 s averaging time. We have developed the instrumentation allowing comb modes to be continuously tuned over 9 GHz, resulting in a QCL of record spectral purity uninterruptedly tunable at the precision of the reference over an unprecedented span of Δν = 1.4 GHz. We have used our apparatus to conduct sub-Doppler spectroscopy of methanol in a multi-pass cell, demonstrating state-of-the-art frequency uncertainties down to the few kilohertz level (∼10−10 in relative value). We have observed weak intensity resonances unreported so far, resolved subtle doublets never seen before, and brought to light discrepancies with HITRAN. This demonstrates the potential of our apparatus for probing subtle internal molecular processes, building accurate spectroscopic models of polyatomic molecules of atmospheric or astrophysical interest, and carrying out precise spectroscopic tests of fundamental physics.

Tunable plasmonic superchiral light for ultrasensitive detection of chiral molecules.

The accurate detection, classification, and separation of chiral molecules are pivotal for advancing pharmaceutical and biomolecular innovations. Engineered chiral light presents a promising avenue to enhance the interaction between light and matter, offering a noninvasive, high-resolution, and cost-effective method for distinguishing enantiomers. Here, we present a nanostructured platform for surface-enhanced infrared absorption-induced vibrational circular dichroism (VCD) based on an achiral plasmonic system. This platform enables precise measurement, differentiation, and quantification of enantiomeric mixtures, including concentration and enantiomeric excess determination. Our experimental results exhibit a 13 orders of magnitude higher detection sensitivity for chiral enantiomers compared to conventional VCD spectroscopic techniques, accounting for respective path lengths and concentrations. The tunable spectral characteristics of this achiral plasmonic system facilitate the detection of a diverse range of chiral compounds. The platform's simplicity, tunability, and exceptional sensitivity holds remarkable potential for enantiomer classification in drug design, pharmaceuticals, and biological applications.

Facile fabrication of covalently grafted functionalized graphene-PVDF composites as strain sensor with tunable sensitivity: Application to the structural health and human motion monitoring

The rapid development of smart strain sensors has contributed enormously in the field of building construction, physiological health monitoring, soft robotics and wearable devices with the accelerating proliferation of smart electronics. However, the low stretchability and sensitivity of conventional metals or inorganic semiconductor-based piezoresistive sensors have severely restricted their applications in this field. Herein, facile and efficient fabrication of 1-(3-aminopropyl) imidazole functionalized rGO-PVDF composites was introduced for the applications ranging from drastic to subtle deformation monitoring. This article focused into the potential uses of strain sensors and elaborated their diverse applications in various disciplines. Structural constitution and multilayered structure of piezoresistive sensors exhibited substantial electrical conductivity, linearity and electron tunneling capability. Meanwhile, the flexible strain sensor showed a significant change in resistance by ∼40% in the 9% strain range, with a gauge factor (GF) value of 4.562 that is twice as high as that of traditional strain gauges. The sensor's response and recovery time of less than 100 ms enhanced its applicability in biomedical arena where continuous monitoring of human health is required. This work offered a new insight towards the development of highly efficient flexible strain sensor for the applications in continuous structural health monitoring and human-machine interface.

Engineered DNA bonsai system for ultrasensitive wide-field determination and intracellular dynamic imaging of protein with tunable dynamic range and sensitivity

Herein, an engineered DNA bonsai system was assembled using DNA nanocube (DNC) as pot and a group of DNA recognition hairpins (RHpn, n = 1–5) as plants for ultrasensitive wide-field detection and dynamic intracellular imaging of matrix metalloproteinase-2 (MMP-2) with tunable dynamic range and sensitivity. Impressively, by changing the stem length of the RHpn (n = 1–5), the thermodynamic parameter free energy (△G) of RHpn was regulated to control the binding reaction between RHpn and output target (OT) (like changing the plants species of bonsai, Bonsai 4-RHpn, n = 1–5). When the △G of RHpn was low, the target detection in high concentration range could be achieved. Conversely, the target detection within the low concentration range also could be realized with the high △G of RHpn. Therefore, the developed biosensing platform based on the engineered DNA bonsai system could achieve the ultrasensitive wide-field determination of MMP-2 with 150000-fold tuned detection sensitivity. Meanwhile, by virtue of the spatial restriction effect of DNC to vary the loaded number and the local concentration of RHp1 (like changing the plants density of bonsai, Bonsai n-RHp1, n = 1–4), the kinetic property of the binding process between RHp1 and OT could be manipulated, in which a low substrate concentration leaded to a low reaction efficiency and a high local concentration resulted in a quick reaction rate with high collision probability. Moreover, the designed DNA bonsai system with the highest local concentration (Bonsai 4-RHp1) could achieve rapid detection of the target MMP-2, which easily conquered the main predicaments of dynamic detection methods: limited dynamic range and low detection efficiency. Most importantly, the programmable DNA bonsai system had been successfully applied in ultrasensitive and high-efficient dynamic visualization of protein MMP-2 in living cells, which could not only make it possible to quickly and precisely monitor disease related proteins with tiny changes at different concentration ranges, but also possess tremendous potential to provide high-precision disease information at different stages in disease diagnosis and prognosis monitoring.

An interfacial host-guest inclusion complex regulated supramolecular nanocomposite hydrogel showing tunable mechanical strength, self-healing, strain sensitivity and NIR responsiveness.

The development of supramolecular nanocomposite hydrogels with good mechanical properties and multifunctional characteristics remains challenging. The reinforced role of interfacial weak interactions is important for the mechanical properties of nanocomposite hydrogels. Here, a dynamic host-guest inclusion complex from the host molecule CB[7] and guest units was employed to prepare Fe3O4 hybrid supramolecular nanocomposite hydrogels. The results show that the as-obtained hydrogel with a porous structure was prepared. The CB[7]-modified Fe3O4 (Fe3O4@CB[7]) nanoparticles severed as a cross-linker for fabricating the hydrogel's network. By changing the Fe3O4@CB[7] content, their tensile stress ranged from 0.102 to 0.403 MPa and their compression stress ranged (70% compression strain) from 0.059 to 0.775 MPa. By changing the guest units, their tensile stress ranged from 0.3 MPa to 0.403 MPa. The self-healing efficiency of the hydrogels was 99% after 48 h at room temperature. The as-obtained hydrogels with strain sensitivity can be applied for detecting the movement of an elbow and finger. The supramolecular hydrogel exhibits NIR responsiveness, self-healing, injectability, tunable mechanical strength and conductive ability, and can be used in flexible electronics.

Thermochromic and conductive hydrogels with tunable temperature sensitivity for dual sensing of temperature and human motion

Skin-like body sensors have important applications in soft-bodied intelligent robots, electronic skins, and medical health monitoring.

Structure and photoluminescence of Mn2+/4+-activated doubly ordered spinel Mg4(Ga/Al)SbO8: site-selective Al3+-to-Ga3+ substitution enabling Mn4+ accumulation, excellent anti-thermal quenching of Mn2+ green emission, and optical thermometry

The site-selective Al3+-to-Ga3+ substitution in doubly ordered spinel Mg4(Ga/Al)SbO8:Mn2+/4+ can manipulate the Mn distributions, thereby resulting in a tunable emission color and controllable optical thermometry sensitivity.

All-fiber cascade system for high-sensitive temperature monitoring: An exploration of the tunability of Ti3C2-MKRs

A tunable all-fiber optical cascade temperature system is demonstrated with two microfiber knot resonators (MKRs) as sensing device (MKR_s) and reference device (MKR_r), respectively. The temperature monitoring device is prepared by depositing Ti3C2 onto MKR_s by optical deposition. Sufficient experimental evidence for temperature sensing sensitivity of the dual sensor device cascade system (MKR_r + Ti3C2-MKR_s) is 4.33 nm/°C, which is a 10.13-fold increase in sensitivity compared with the temperature sensing sensitivity of 0.427 nm/°C of the Ti3C2-MKR_s. After depositing Ti3C2 materials (∼400 μm) on the bare MKR_r, we further improve the sensitivity of the cascade system (Ti3C2-MKR × 2) to 9.20 nm/°C, which represents a significant 21.5 times improvement in sensitivity compared to Ti3C2-MKR_s. The sensitivity of cascade fiber optic sensors is controlled by varying the modified length of Ti3C2 materials optically deposited on the MKR_r surface. Overall, this study not only enhances device utilization but also provides a new research direction for the preparation of all-fiber sensors with tunable sensitivity.

Actively manipulating the temperature characteristics of photonic spin Hall effect in quasi-PT symmetric structure

The photonic spin Hall effect (PSHE) manifests itself as the spin-dependent transverse shift, and has many applications including precise metrology and optical sensing. However, some common ways to control PSHE have the limitation of less flexible and convenient manipulation. We report here an approach to actively manipulate the temperature characteristics of the PSHE in the quasi-PT symmetric structure by means of tunable graphene conductivity under optical pumping. The underlying mechanism is the flexible control of exceptional point by influencing graphene conductivity. We find that the PSHE shift is significantly enhanced near the exceptional point, and the enhanced PSHE shift can be manipulated by temperature. Moreover, the variation of temperature causes the inversion of the sign of the PSHE shift, and the temperature properties of the shift change as the optical pumping power varies. Based on the tunable PSHE shift, we design a temperature sensor with tunable sensitivity by combining weak measurement amplification techniques.

Fast and Flexible Multiagent Decision-Making

A multiagent system should be capable of fast and flexible decision-making to successfully manage the uncertainty, variability, and dynamic change encountered when operating in the real world. Decision-making is fast if it breaks indecision as quickly as indecision becomes costly. This requires fast divergence away from indecision in addition to fast convergence to a decision. Decision-making is flexible if it adapts to signals important to successful operation, even if they are weak or rare. This requires tunable sensitivity to input for modulating regimes in which the system is ultrasensitive and in which it is robust. Nonlinearity and feedback in the decision-making process are necessary to meeting these requirements. This article reviews theoretical principles, analytical results, related literature, and applications of decentralized nonlinear opinion dynamics that enable fast and flexible decision-making among multiple options for multiagent systems interconnected by communication and belief system networks. The theory and tools provide a principled and systematic means for designing and analyzing decision-making in systems ranging from robot teams to social networks.