High-sensitivity Measurements Research Articles

Fiber-Optic Sensors and Their Practical Research in the Internet of Things

With the rapid development of the Internet of Things (IoT) technology, fiber-optic sensors, as a kind of high-precision and high-sensitivity measurement tool, are increasingly widely used in the field of IoT. This paper outlines the advantages of fiber-optic sensors over traditional sensors, such as high precision, strong resistance to electromagnetic interference, and long transmission distance. On this basis, the paper discusses the application scenarios of fiber-optic sensors in the Internet of Things, including environmental monitoring, intelligent industry, medical and health care, intelligent transportation, and other fields. It is hoped that this study can provide theoretical support and practical guidance for the further development of fiber-optic sensors in the field of the Internet of Things, as well as promote the innovation and application of IoT.

The Method and Experiment of Detecting the Strength of Structural Components Utilizing the Distributed Strain of Sensing Optical Fibers Demodulated by OFDR.

Defects occurring during the welding process of metal structural components directly affect their overall strength, which is crucial to the load-bearing capacity and durability of the components. This signifies the importance of accurate measurement and assessment of weld strength. However, traditional non-destructive testing methods such as ultrasonic and non-contact camera inspection have certain technical limitations. In response to these issues, this paper analyzes the detection principle of weld strength, revealing that weld defects reduce the effective area of the structural bearing section and cause stress concentration around them. Through repeated experimental data analysis of samples, strain distribution data along the one-dimensional direction caused by defects such as slag inclusion and porosity were obtained. Experimental results show that this method can identify defect types in welds, including slag inclusion, porosity, and unevenness, and accurately measure the location and size of defects with a precision of 0.64 mm, achieving qualitative analysis of weld defects. Additionally, by deploying distributed optical fiber sensors (DOFS) at different vertical distances along the weld direction, the propagation law of stress induced by different types of weld defects on samples was thoroughly analyzed. This further validates the advantages of this method in weld strength detection, including high spatial resolution, high sensitivity, and non-destructive measurement.

PMF based Sagnac interferometric sensor for simultaneous measurement of strain, temperature, and torsion

We propose a Sagnac interferometric sensor for simultaneous strain, temperature, and torsion measurement based on a polarization-maintaining fiber (PMF). The Sagnac sensor consists of a single-mode fiber (SMF), PMF and SMF spliced sequentially to form an SMF-PMF-SMF structure. The designed Sagnac interferometric sensor exhibits different wavelength shifts for strain, temperature and torsion measurements. Therefore, we observed three selected dips in the interferogram and measured strain, temperature and torsion simultaneously by their wavelength shifts. The maximum sensitivity of the sensor to strain, temperature, and torsion were experimentally measured to be 28.9 pm/µε. (10-12 m), −1.7504 nm/°C, and −1.0964 nm/(rad/m), and the measurement ranges were 0∼720 με, 25 °C–39 °C, and −7.679 rad/m∼4.887 rad/m (−110°–70°), respectively. In the subsequent experiments, we also verified the feasibility of the sensor for simultaneous measurements, and the errors of the results obtained were less than 10%. And we have successfully increased the temperature measurement range to 25°C∼85°C by cascading FBG in the original structure. The designed sensor has the advantages of easy fabrication, high sensitivity, and bi-directional torsional measurement, which have a wide range of applications in the fields of structural health detection, industrial control, and aircraft attitude recognition.

Mid-infrared methane standoff sensor using a frequency channel attention based convolutional neural network filter

Highly sensitive standoff methane detection is vital for atmospheric science, environmental protection, and production safety. We develop a mid-infrared methane standoff sensor using a cooperative target based on tunable diode laser absorption spectroscopy (TDLAS). To enhance sensor sensitivity, we propose a one-dimensional frequency channel attention-based convolutional neural network (1D-FCACNN) filter, which can effectively denoise the methane absorbance signals and its second harmonic signals. The filter model is adequately trained on a simulated spectrum dataset, which we constructed based on data augmentation. In comparison with reported filtering algorithms, the proposed filter shows the best performance in both measuring modes and evaluation metrics. Real-time measurements show that the measuring accuracy and limit of detection (LOD) of the proposed sensor reach a minimum of 30.40 ppb and 5.04 ppb over a 10-meter optical range, a significant improvement compared to previous reports of methane standoff sensors. The proposed methane standoff sensor proves the feasibility of enhancing the performance of TDLAS gas sensors with the attention mechanism, bringing a new option for high-sensitivity measurements of methane and other atmospheric trace gases.

Dual parameter sensor for RI and temperature detection by cascading Ag/WO3 film PCF and Ag/MoS2/PDMS film PCF.

Multi-parameter surface plasmon resonance (SPR) sensors generally have low detection sensitivity due to detection wavelength limitations. We developed a two-parameter SPR sensor for refractive index (RI) and temperature detection by cascading Ag/WO3 film photonic crystal fiber (PCF) and Ag/MoS2 film PCF together. By using WO3 film with a low effective refractive index to prevent oxidation of silver-based PCF and maintain a wider RI sensing channel detection band; at the same time, MoS2 film with a high effective refractive index is used to modulate the detection range of temperature sensing channel. The detection performance and stability of the two-parameter SPR sensor were verified by software simulation and experiments. The data results indicate that the sensor can perform stable and independent tests during RI and temperature detection. The maximum sensitivity of the sensor within the RI detection range of 1.333 to 1.395 is as high as 6443 nm/RIU; the maximum temperature sensitivity within the temperature detection range of 40 °C∼90 °C is 8.72 nm/°C. This sensor can achieve high-sensitivity RI measurement in a high-temperature environment. This will have broad application prospects in the field of biochemistry.

Development and verification of crossing priming amplification on rapid detection of virulent and viable L. monocytogenes: In-depth analysis on the target and further application on food screening

Virulent Listeria monocytogenes is responsible for listeriosis, a highly fatal foodborne illness that impairs human health. One of the major causes of its pathogenicity is the carriage of virulence factor, listeriolysin O, encoded by hylA gene. Herein, the specificity and conservativity of hylA gene sequences were analyzed, with most conservative region selected. Then, a crossing priming amplification (CPA) assay targeting hylA conservative region was established under an isothermal condition (63 °C) to identify virulent L. monocytogenes within 60 min. Forty-four reference strains including two standard L. monocytogenes strains and forty-two strains of other species were selected to assess sensitivity and specificity. The CPA assay showed strong specificity and sensitivity (genomic DNA at 5.66 pg/μL). The practicality of the CPA assay was further confirmed in four artificially contaminated rice-flour products with limit of detection at 104 CFU/mL. In addition, a PMA-CPA assay was developed to direct detect L. monocytogenes viable cells with rice-flour products as a model system. In conclusion, the developed CPA method has advantages of high sensitivity, specificity and quick measurement in the detection of virulent L. monocytogenes, showing considerably feasible promise for future food safety.

Fiber optic strain sensor based on enhanced harmonic Vernier effect

In sensors utilizing the traditional harmonic Vernier effect, it is imperative to isolate the reference interferometer to mitigate the impact of external environmental fluctuations on the reference spectrum, thereby averting measurement inaccuracies. However, achieving such isolation between interferometers in compact fiber optic sensors poses significant challenges. We propose a fiber optic strain sensor based on the enhanced harmonic Vernier effect. In the enhanced harmonic Vernier effect, two interferometers are simultaneously involved in sensing. Hence, the isolation of interferometers is no longer a concern. Furthermore, the two interferometers exhibit responses with opposite signs, leading to a greater displacement of the envelope. Consequently, the sensitivity of the sensor is further enhanced without altering the harmonic order. Firstly, we conducted numerical simulations to analyze the enhanced harmonic Vernier effect. Secondly, we fabricated a Fabry–Perot interferometer (FPI) and a Mach–Zehnder interferometer (MZI) with strain sensitivity of opposite signs, generating a first-order harmonic. The experimental results indicate that the sensor’s sensitivity is 15.1 pm/μϵ, which is 1.41 and 2.80 times higher than the traditional harmonic Vernier effect using FPI and MZI as sensing interferometers, respectively. The proposed sensor and enhancement method hold promising potential for applications in high-sensitivity measurement fields.

Femtosecond laser etching C-type fiber optic vernier sensor for seawater temperature and salinity measurements

In this work, we demonstrate a dual C-type fiber optic vernier sensor based on femtosecond laser etching for measuring seawater temperature and salinity. The C-type fibers are etched using femtosecond laser microfabrication technology on hollow-core fibers (HCF), including temperature and salinity cavities. The seawater can fully flow into the salinity cavity as a sensing medium, and the polydimethylsiloxane (PDMS) is filled into the temperature cavity as a sensitizing medium. Combined with the vernier effect, dual parameter high sensitivity simultaneous measurement is achieved. Through simulation and experimental testing, the sensor can achieve high sensitivity measurement of seawater salinity and temperature, with sensitivities of −2.69 nm/‰ and −4.54 nm/℃, respectively. In the stability tests of salinity and temperature, the maximum interference wavelength shifts are 0.52 nm and 0.64 nm, respectively. In the repeated measurement experiment, the maximum deviation of sensitivity for salinity cavity and temperature cavity measurements are 0.03 nm/‰ and 0.18 nm/℃, respectively, indicating that the structure has good measurement stability and repeatability. This sensor has the advantages of strong stability, good repeatability, and low cost, which can be used as a new type of sensor to achieve high-sensitivity detection of seawater parameters.

Proposal for a New Differential High-Sensitivity Refractometer for the Simultaneous Measurement of Two Refractive Indices and Their Differences.

The refractive index of a liquid serves as a fundamental parameter reflecting its composition, thereby enabling the determination of component concentrations in various fields such as chemical research, the food industry, and environmental monitoring. Traditional methods for refractive index (RI) measurement rely on light deflection angles at interfaces between the liquid and a material with a known refractive index. In this paper, the authors present a new differential refractometer for the highly sensitive measurement of RI differences between two liquid samples. Using a configuration with two cells equipped with flat parallel plates as measuring elements, the instrument facilitates accurate analysis. Namely, the sensor signals from both the solution and the solvent cuvette are generated simultaneously with one laser pulse, reducing the possible fluctuations in the laser radiation intensity. Our evaluation shows the high sensitivity of RI measurements <7×10-6), so this differential refractometer can be proposed not only as a high-sensitivity sensing tool that can be used for mobile detection of nanoparticles in solution samples but also to determine the level of environmental nano-pollution using water (including rain, snow) samples from various natural as well as industrial sources, thus helping to solve some important environmental problems.

A Differential and High-Sensitivity Thickness Measurement Sensor for Dielectric Solid Materials Using a Branch Line Coupler

A Differential and High-Sensitivity Thickness Measurement Sensor for Dielectric Solid Materials Using a Branch Line Coupler

Bulk lysis procedures alter target cell population counts.

To achieve high-sensitivity cell measurements (<1 in 105 cells) by flow cytometry (FCM), the minimum number of acquired cells must be considered and conventional immunophenotyping protocols fall short of these numbers. The bulk lysis (BL) assay is a standardized erythrocyte lysing approach that allows the analysis of the millions of cells required for high-sensitivity measurable residual disease (MRD) detection. However, this approach has been associated with significant cell loss, along with potential over or underestimates of rare cells when using this method. The aim of this study was to evaluate bulk lysis protocols and compare them with minimal sample perturbation (MSP) protocols, which are reported to better preserve the native cellular state and avoid significant cell loss due to washing steps. To achieve this purpose, we first generated an MRD model by spiking fresh peripheral blood with K562 cells, stably expressing EGFP, at known percentages of EGFP positive cells to leukocytes. Samples were then prepared with BL and MSP protocols and analyzed using FCM. For all percentages of K562 cells established and evaluated, a significant decrease of this population was detected in BL samples compared with MSP samples, even at low K562 cell percentages. Significant decreases for non-necrotic cells were also observed in BL samples relative to MSP samples. In conclusion, the evaluation of the potential effects of BL protocols in obtaining the final count is of great interest, especially for over- or under-estimation of target cells, as in the case of measurable residual disease. Since conventional flow cytometry or minimal sample perturbation assays fall short in obtaining the minimum numbers required to reach high sensitivity measurements, significant efforts may be needed to improve bulk lysis solution reagents.

High-sensitivity strain sensor based on an asymmetric tapered air microbubble Fabry-Pérot interferometer with an ultrathin wall

A Fabry-Pérot interferometer (FPI) with an asymmetric tapered structure and air microbubble with an ultrathin wall is designed for high-sensitivity strain measurement. The sensor contains an air microbubble formed by two single-mode fibers (SMF) prepared by fusion splicer arc discharge, and a taper is applied to one side of the air microbubble with a wall thickness of 3.6 µm. In this unique asymmetric structure, the microbubble is more easily deformed under stress, and the strain sensitivity of the sensor is up to 15.89 pm/µɛ as evidenced by experiments.The temperature sensitivity and cross-sensitivity of the sensor are 1.09 pm/°C and 0.069 µɛ/°C in the temperature range of 25-200°C, respectively, thus reducing the measurement error arising from temperature variations. The sensor has notable virtues such as high strain sensitivity, low-temperature sensitivity, low-temperature cross-sensitivity, simple and safe process preparation, and low cost. Experiments confirm that the sensor has good stability and repeatability, and it has high commercial potential, especially strain measurements in complex environments.

Ammonia-trapping multilayer polymer urease film amplifier coated surface plasmon resonance sensor for ultra-sensitive urea detection

In this paper, we have developed a new urea signal amplification technology based on a multilayer urease polymer film self-assembly structure for the first time, enabling the realization of ultra-accurate urea optical detection. We demonstrate the effectiveness of this technique based on surface plasmon resonance (SPR) platform. When the urea signal amplifier is combined with SPR sensors, multilayer urease polymer film contacts with urea molecules, the urea molecules are oxidated into NH3 and CO2, causing the pH increase, which weakens the electrostatic interaction between different polymer layers and induces the RI reduction of the multilayer urease film, thereby causing the shift of the SPR spectrum. Experiment results confirm that urea sensitivity has been improved 12-fold, and the limit of detection (LOD) has been optimized to less than 10−3 mmol/L. Furthermore, the anti-interference has been improved 22.8-fold and is kept even the interference signal strength increases by 100 times. Moreover, multilayered urease polymer leads to the increase of urease on the sensor surface, thus expanding the detection range of urea by 3.5 times. This provides a new way to solve the contradiction between high sensitivity and large measurement range of optical fiber biosensor. Importantly, the concept of using enzyme-loaded polymer films for signal amplification can be adapted for the detection of various other biomolecules by replacing the enzyme with a specific recognition element for the target molecule. This opens doors for developing highly sensitive and specific biosensors for diverse applications in healthcare, environmental monitoring, and food safety.

Optical Fiber Surface Plasmon Resonance Sensor for Glyceryl Tributyrate Detection Based on the PAA/CS Composite Hydrogel Embedding Protease Method.

Glycerol tributyrate as a low-density lipoprotein plays a crucial role in drug development and food safety. In this work, a novel high-stability fiber optic sensor for glyceryl tributyrate based on the poly(acrylic acid) (PAA) and chitosan (CS) composite hydrogel embedding method is first proposed. Compared with traditional functionalization, the lipase in a polymer network structure used in this article can not only avoid chemical reactions that cause damage to the enzyme structure but also avoid the instability of ionic bonds and physical adsorption. Therefore, the PAA/CS hydrogel method proposed in this article can effectively retain enzyme structure. First, the impact of different layers (one to five layers) of PAA/CS on pH sensing performance was explored, and it was determined that layers 1-3 could be used for subsequent sensing experiments. Within the linear detection range of 0.5-10 mM, the detection sensitivities of the one to three layers of the biosensor are divided into 0.65, 0.95, and 1.51 nm/mM, respectively, with the three layers having the best effect. When the number of coating layers is three, the detection limit of the sensor is 0.47 mM, meeting the millimole level detection standard for anticancer requirement. Furthermore, the stability and selectivity of the sensor (in the presence of hemoglobin, urea, cholesterol, acetylcholine, and glucose) were analyzed. The three-layer sensor is used for sample detection. At concentrations of 1-10 mM, the absolute value of the recovery percentage (%) is 82-99%, which can accurately detect samples. The sensor proposed in this paper has the advantages of low sample consumption, high sensitivity, simple structure, and label-free measurement. The enzyme-embedding method provides a new route for rapid and reliable glyceryl tributyrate detection, which has potential applications in food safety as well as the development of anticancer drugs.

Label-free SPR fiber microfluidic sensor with PDA-MA cross-linked lipase for specific detection of tributyrin

As a precursor to butyric acid and also a short-chain triglyceride, tributyrin plays an important role in repairing small intestinal villi, promoting the absorption and utilization of nutrients, and monitoring human health. The traditional carboxylation functionalization method of optical fiber sensors takes a long time and is complicated to operate. Therefore, we need a sensor with a functional period, high sensitivity, and the ability to quickly detect samples to achieve specific detection of tributyrin. In this paper, based on the chemical cross-linking method of polydopamine-maleic acid (PDA-MA), a novel fiber-optic microfluidic surface plasmon resonance (SPR) sensor was proposed to realize the detection of tributyrin. Compared with the traditional functionalization method, the fixation method of PDA-MA chemical cross-linking method not only shortens the functionalization time, but also increases the sensitivity of the sensor. Experimental results show that the sensitivity of the microfluidic sensor coated with PDA reaches 3392.7 nm/RIU, which is 1.75 times that of the uncoated sensor. The sensor has a sensitivity of 8.22 nm/mM in the range of 0.5–5 mM and a response time of only 8 min at the concentration of 1 mM. In addition, the sample detection error of the sensor is within 12 % in the range of 0.5–5 mM. The proposed sensor offers the advantages of low sample consumption (100 μL), high sensitivity, good selectivity, good repeatability, anti-interference ability, and label-free measurement. The sensor holds promising applications in food safety and health monitoring due to its superior performance.

The Implementation of AFM-Based Nanoscale Diagnostic Methods in the Investigation of the Degradation Process of Bacteriostatic Acrylic Film with Silver Nanoparticles

In this paper, a custom-tailored investigation protocol aimed at the tests of the resistance of bacteriostatic acrylic-based film containing silver nanoparticles is presented. As hospital appliance applications were considered, it was necessary to provide a unique approach, enabling specific media exposure and utilizing high-sensitivity measurement methods to observe fine indications of material wear. Due to the presence of nanoparticles in the tested film, nanometer-resolution surface imaging is necessary. Therefore, the main source of information about its degradation process is atomic force microscopy (AFM) measurements. This particular tool is an appreciated source of information, providing quantitative data about both morphological and mechanical changes in the properties of the surface. Using such an approach, supported by standard diagnostic methods, such as colorimetry and wettability angle determination, it was possible to enable insights into the way the bacteriostatic film deteriorates and evaluate its usefulness in medical appliance applications. Further tests of various films developed by companies can be performed using the described protocol to determine the lifetime of certain products. This paper reveals the company’s practical utilization of both standardized and novel test techniques in the evaluation of new products.

Experimental study on ultra-high sensitivity gold-based SPR sensor for refractive index and temperature measurement

We have experimentally demonstrated an ultra-high sensitivity gold-based fiber refractive index (RI) sensor whose main structure is composed of multimode fiber (MMF) and photonic crystal fiber (PCF). The gold film is deposited on V-shaped PCF by magnetron sputtering, and sensing experiments are performed based on the principle of surface plasmon resonance (SPR). Numerical simulation results indicate that the cladding mode of the V-shaped PCF is more capable of stimulating the SPR effect than the core mode. The experimental results show that the RI measurement range of the sensor is 1.333–1.421, with a maximum sensitivity of 10015 nm/RIU. In addition to RI sensing, sensing probes can be coated with polydimethylsiloxane (PDMS) on a gold film for temperature sensing. For temperature detection, the range is from 10 to 100 °C and the maximum sensitivity is 3.5 nm/℃. Besides high sensitivity in RI measurement, the proposed sensor also has good sensing performance in temperature sensing. With the advantages of high sensitivity, good stability, and easy preparation, this sensor has become an important reference in the field of high-performance sensing.

Glycerophospholipid polyunsaturation modulates resveratrol action on biomimetic membranes

The phytoalexin resveratrol has received increasing attention for its potential to prevent oxidative damages in human organism. To shed further light on molecular mechanisms of its interaction with lipid membranes we study resveratrol influence on the organisation and mechanical properties of biomimetic lipid systems composed of synthetic phosphatidylcholines with mixed aliphatic chains and different degree of unsaturation at sn-2 position (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, POPC, and 1-palmitoyl-2-docosahexaenoyl-sn-glycero-3-phosphocholine, PDPC). High-sensitivity isothermal titration calorimetric measurements reveal stronger spontaneous resveratrol association to polyunsaturated phosphatidylcholine bilayers compared to the monounsaturated ones resulting from hydrophobic interactions, conformational changes of the interacting species and desolvation of molecular surfaces. The latter is supported by the results from Laurdan spectroscopy of large unilamellar vesicles providing data on hydration at the glycerol backbones of glycerophospholipides. Higher degree of lipid order is reported for POPC membranes compared to PDPC. While resveratrol mostly enhances the hydration of PDPC membranes, increasing POPC dehydration is reported upon treatment with the polyphenol. Dehydration of the polyunsaturated lipid bilayers is measured only at the highest phytoalexin content studied (resveratrol/lipid 0.5 mol/mol) and is less pronounced than the effect reported for POPC membranes. The polyphenol effect on membrane mechanics is probed by thermal shape fluctuation analysis of quasispherical giant unilamellar vesicles. Markedly different trend of the bending elasticity with increasing resveratrol concentration is reported for the two types of phospholipid bilayers studied. POPC membranes become more rigid in the presence of resveratrol, whereas PDPC-containing bilayers exhibit softening at lower concentrations of the polyphenol followed by a slight growth without bilayer stiffening even at the highest resveratrol content explored. The new data on the structural organization and membrane properties of resveratrol-treated phosphatidylcholine membranes may underpin the development of future liposomal applications of the polyphenol in medicinal chemistry.

Robust high-order petal-mode laser with tunable topological charge pumped by an axicon-based annular beam

In this work, we demonstrate a watt-level laser producing high-order, petal-shaped output modes with tunable topological charge, by using an axicon-based divergent annular pump beam. The topological charge of the output beam could be varied in the range of 34–72 by adjusting the position of the Nd:YVO4 crystal relative to the focal plane of the pump beam. The highest order petal-mode beam generated from the system had a topological charge of 72 and a power of 1.3 W. The highest output power up to 2.1 W with a topological charge of 34 was achieved at an absorbed pump power of 5.8 W. The generated output modes were observed to be robust under power scaling and on propagation, with the same spatial profiles being maintained in the near- and far-fields. We anticipate that this system design may find use as a laser source in applications such as 3D optical trapping, fabrication of optical vortex arrays, optical communications, and high-sensitivity spatial measurement.

Study of the frequency characteristics of a tremor analysis system based on a capacitive proximity sensor

The technique of tremor control using a capacitive sensor to ensure high sensitivity and stability of measurement results requires the correct selection of operating parameters of the system. Study of the influence of operating parameters, selection of the optimal antenna design and frequency-setting elements in a system for analyzing tremor of the upper limbs based on a capacitive proximity sensor. The tremor sensor being developed is based on a rectangular pulse generator, the generation frequency of which depends on the capacitance. The dependence of the generation frequency on the distance between the antenna and the limb was studied for various values of capacitance and resistance of the resistor in the generator circuit. It is proposed to use a circuit without a capacitor in the frequency-setting RC circuit, which allows for the largest frequency increment and clearly detects tremor with both large and small amplitude. An experimental study of various antenna designs was carried out. It has been shown that when using a helical antenna, the maximum sensitivity of the sensor is observed with the smallest diameter, however, the use of a small diameter reduces the area of interaction between the electric field and the tissues of the human limb. The electromagnetic method is a promising method for digitizing tremor, allowing for rapid non-contact diagnostics. The experimental results obtained make it possible to justify the choice of optimal parameters for the tremor analysis system.