Sensitive Transducer Research Articles

Nanoarchitectonics of Biofunctionalized Hydrogen‐Terminated 2D‐Germanane Heterostructures as Highly Sensitive Biorecognition Transducers: The Case Study of Cocaine Drug

Hydrogen‐terminated 2D‐germanane (2D‐GeH), as one inorganic 2D material akin to graphene, is attracting widespread interest owing to its predicted (opto)electronic properties. Nonetheless, the chemical reactivity of 2D‐GeH requires further exploration to expand its real implementation. Herein, a simple and straightforward bottom‐up biofunctionalization approach is reported aiming at providing the bases toward the robust design of 2D‐GeH‐based biorecognition systems with electrical readout. For this goal, 2D‐GeH has been firstly functionalized with gold nanoparticles (Au‐NPs) via an organometallic approach, followed by the covalent immobilization of a thiolated single‐stranded DNA (ssDNA) aptamer via AuS bond interactions. After an accurate material characterization, the resulting ssDNA/Au@GeH heterostructure is drop‐casted on a fluorine‐doped tin oxide (FTO) electrode for impedimetrically monitoring cocaine as a model drug. Interestingly, the aptamer–cocaine interactions hinder the interfacial electron‐transfer process of the benchmark [Fe(CN)6]3−/4− redox marker with increasing concentration of the cocaine target, leading to a detection limit as low as 4.9 ± 0.1 aM, the lowest one reported in literature by far. Overall, the ssDNA/Au@GeH electrochemical biosensor exhibits outstanding selectivity, specificity, and reproducibility, demonstrating the potential use of 2D‐GeH as an emerging highly sensitive transducer for biosensing applications. The reported method is general and might be simply customized by tailoring the biorecognition component.

Integrating colorimetry with surface sensitive transducers: Advancing molecular diagnostics in biofluids

Colorimetric sensors are preferred for visually detecting target analytes, but achieving ultra-low detection capabilities for food analysis, environmental samples, and molecular diagnostics is challenging. In this study, we interfaced a purpald-based formaldehyde color sensor (as a model probe reaction) with a surface plasmon gold microarray imaging chip. Such hyphenated surface-sensitive signal-amplifying techniques enabled ultra-low detection in biofluids with a linear range of 10−5 – 0.5 ppm compared to the spectrophotometric narrower linear range of 0.01–1 ppm. The detection limit of 86×10−6 ppm from the hyphenated sensing is 140-fold lower than the detection limit from the spectrophotometric method alone (12×10−3 ppm). The absorbance maximum of the purpald-formaldehyde adduct was 553 nm, with no notable tail overlap between the adduct absorbance band beyond 700 nm and the fixed angle source incident wavelength of 800 nm from the surface plasmon instrument. Hence, the possible adduct thiol-surface plasmon gold surface interaction, affinity, and the higher mass and refractive index changes of the adduct are likely causes of the observed signal amplification. We achieved a formaldehyde sample recovery of 92 % from a diluted serum (a minimally invasive assay method), which was comparable to the results in a buffer solution. Further, we extended to demonstrate in diluted urine sample matrices to be noninvasive bioanalysis and determined the interference from urea that could also form a purpald adduct like formaldehyde. In conclusion, coupling a surface-sensitive transducer with less sensitive colorimetric reactions is promising for molecular diagnostics in real samples and can be broadly extended to any other desired molecular targets and sample matrices.

Electromechanical characterization of 3–2 ceramic-air composites

In this study, a type 3–2 ceramic-air composite was designed, and the impact of varying thicknesses on its electromechanical properties was analyzed. Initially, finite element simulation software was employed to model type 3–2 ceramic-air composites of differing thicknesses. This modeling facilitated the determination of resonance and anti-resonance frequencies, calculation of effective electromechanical coupling coefficients, and assessment of frequency discrepancies corresponding to each thickness. Subsequently, type 3–2 ceramic-air composites of various thicknesses were fabricated using the reverse cutting method. The experimental results corroborated the simulation outcomes, demonstrating consistency. In the final analysis, the performance parameters of conventional type 1–3 piezoelectric composites were evaluated alongside those of type 3–2 composites. Findings indicated an improvement of 0.8 in the thickness electromechanical coupling coefficient for type 3–2 composites compared to conventional type 1–3 composites. Consequently, type 3–2 composites show promise for the development of highly sensitive piezoelectric transducers.

A film composed of PEDOT:PSS/PVA as a sensitive medium for pH sensor in optical fiber

In this work, a pH sensitive transducer element attached to a multimode optical fiber section is proposed. The sensitive element is a PEDOT:PSS/PVA composite film that exhibited sensitivity at low pH values in the range of 1–7 pH. The addition of PVA was important for the adhesion process to the optical fiber surface. The morphology of the PEDOT:PSS polymers allowed characterization at pH stimuli that were based on the optical power transmission generated from the interaction of the light propagating in the optical fiber core and the optical fiber section coated with the sensitive film. A sensitivity of −0.05 dB/pH and a linear fit R2 of 0.93 was obtained, the response time was 3 s, while the sensor recovery time was 50 s maintaining stability higher than 10 min.

Research and fabrication of bimetallic plate transducer based on finite element analysis

By enhancing the type 1–3 piezoelectric composite material, a highly sensitive hydroacoustic transducer sensitive element structure is suggested for uses in sonar systems, such as small target identification and fine imaging. A lower metal plate, a piezoelectric ceramic column array, and an upper metal plate make up the piezoelectric material structure. The resonance frequency of the bimetal plate type piezoelectric ceramic array material was theoretically analyzed, the sensitive element geometry of the bimetal plate piezoelectric material was studied using finite element simulation, the material choice for the metal plate affected the material’s performance, and the parameters of each size of the sensitive element were determined. These findings served as a guide for the production of a highly sensitive hydroacoustic transducer, as well as the structure of the piezoelectric material transducer in the water performance test. Results indicate that the structure transducer has a maximum transmit voltage response of 178 dB and a −3 dB bandwidth of approximately 25 kHz; the transducer may be efficiently tuned for a maximum receive sensitivity of −172 dB.

A Compensator Microelectromechanical Acceleration Transducer with a Piezoelectric Sensing Element and Optical Reading

Introduction.Modern mobile control objects require the use of highly sensitive transducers of motion parameters, e.g., acceleration, with a wide measurement range. Increased sensitivity to measured parameters can be achieved by using precision optics, e.g., based on the tunneling effect. However, operating ranges of induced movements are less than a micrometer, which creates difficulties in positioning the sensing element. In order to improve manufacturability, to extend the measurement range and to reduce errors of acceleration transducers with optical tunneling, compensation circuits with a piezoelectric actuator as an active sensor can be used.Aim.To extend the measurement range of microelectromechanical acceleration transducers through the use of an integrated approach, including the introduction of a compensation circuit for sensor movements based on the inverse piezoelectric effect and detection of these movements by optical means.Materials and methods.An approach to compensating sensor movements is proposed. This approach consists in using a bimorph piezoelectric plate as an inertial element. The use of optical reading of sensor sub-micrometer displacements is considered.Results.A block scheme and a functional scheme of a compensator micro-opto-electromechanical acceleration transducer with a bimorph piezoelectric sensing element are developed. Deformations in the sensing element under the influence of accelerations (up to 100 m/s2) and compensation voltages, whose amplitude does not exceed several volts, are investigated to ensure the possibility of using the optical tunneling effect in the proposed transducer.Conclusion.A mathematical model of the transducer was developed and studied. A 2.5-fold increase in the measurement range was achieved. It was shown that the introduction of compensation feedback does not decrease the permissible frequency range of measured accelerations.

Ultrasensitive detection of vital biomolecules based on a multi-purpose BioMEMS for Point of care testing: digoxin measurement as a case study

Rapid and label-free detection of very low concentrations of biomarkers in disease diagnosis or therapeutic drug monitoring is essential to prevent disease progression in Point of Care Testing. For this purpose, we propose a multi-purpose optical Bio-Micro-Electro-Mechanical-System (BioMEMS) sensing platform which can precisely measure very small changes of biomolecules concentrations in plasma-like buffer samples. This is realized by the development of an interferometric detection method on highly sensitive MEMS transducers (cantilevers). This approach facilitates the precise analysis of the obtained results to determine the analyte type and its concentrations. Furthermore, the proposed multi-purpose platform can be used for a wide range of biological assessments in various concentration levels by the use of an appropriate bioreceptor and the control of its coating density on the cantilever surface. In this study, the present system is prepared for the identification of digoxin medication in its therapeutic window for therapeutic drug monitoring as a case study. The experimental results represent the repeatability and stability of the proposed device as well as its capability to detect the analytes in less than eight minutes for all samples. In addition, according to the experiments carried out for very low concentrations of digoxin in plasma-like buffer, the detection limit of LOD = 300 fM and the maximum sensitivity of S = 5.5 × 1012 AU/M are achieved for the implemented biosensor. The present ultrasensitive multi-purpose BioMEMS sensor can be a fully-integrated, cost-effective device to precisely analyze various biomarker concentrations for various biomedical applications.

Highly sensitive self-focused ultrasound transducer with a bionic back-reflector for multiscale-resolution photoacoustic microscopy.

In this study, we designed a self-focused ultrasonic transducer made of polyvinylidene fluoride (PVDF). This transducer involves a back-reflector, which is modeled after tapetum lucidum in the eyes of some nocturnal animals. The bionic structure reflects the ultrasound, which passes through the PVDF membrane, back to PVDF and provides a second chance for the PVDF to convert the ultrasound to electric signals. This design increases the amount of ultrasound absorbed by the PVDF, thereby improving the detection sensitivity. Both ultrasonic and photoacoustic (PA) experiments were conduct to characterize the performance of the transducer. The results show that the fabricated transducer has a center frequency of 13.07 MHz, and a bandwidth of 96% at -6 dB. With an acoustic numerical aperture (NA) of 0.64, the transducer provides a lateral resolution of 140µm. Importantly, the bionic design improves the detection sensitivity of the transducer about 30%. Finally, we apply the fabricated transducer to optical-resolution (OR) and acoustic-resolution photoacoustic microscopy (AR-PAM) to achieve multiscale-resolution PA imaging. Imaging of the bamboo leaf and the leaf skeleton demonstrates that the proposed transducer can provide high spatial resolution, better imaging intensity and contrast. Therefore, the proposed transducer design will be useful to enhance the performance of multiscale-resolution PAM.

Multi-role conductive hydrogels for flexible transducers regulated by MOFs for monitoring human activities and electronic skin functions.

Metal organic frameworks (MOFs) have garnered significant attention in the development of stretchable and wearable conductive hydrogels for flexible transducers. However, MOFs used in hydrogel networks have been hampered by low mechanical performance and poor dispersibility in aqueous solutions, which affect the performance of hydrogels, including low toughness, limited self-recovery, short working ranges, low conductivity, and prolonged response-recovery times. To address these shortcomings, a novel approach was adopted in which micelle co-polymerization was used for the ex situ synthesis of Zn-MOF-based hydrogels with exceptional stretchability, robust toughness, anti-fatigue properties, and commendable conductivity. This breakthrough involved the ex situ integration of Zn-MOFs into hydrophobically cross-linked polymer chains. Here the micelles of EHDDAB had two functions, first they uniformly dispersed the Zn-MOFs and secondly they dynamically cross-linked the polymer chains, profoundly influencing the mechanical characteristics of the hydrogels. The non-covalent synergistic interactions introduced by Zn-MOFs endowed the hydrogels with the capacity for high stretchability, high stress, rapid self-recovery, anti-fatigue properties, and conductivity, all achieved without external stimuli. Furthermore, hydrogels based on Zn-MOFs can serve as durable and highly sensitive flexible transducers, adept at detecting diverse mechanical deformations with swift response-recovery times and high gauge factor values. Consequently, these hydrogels can be tailored to function as wearable strain sensors capable of sensing significant human joint movements, such as wrist bending, and motions involving the wrist, fingers, and elbows. Similarly, they excel at monitoring subtle human motions, such as speech pronunciation, distinguishing between different words, as well as detecting swallowing and larynx vibrations during various activities. Beyond these applications, the hydrogels exhibit proficiency in distinguishing and reproducing various written words with reliability. The Zn-MOF-based hydrogels hold promising potential for development in electronic skin, medical monitoring, soft robotics, and flexible touch panels.

Design, analysis and testing of monometallic plate stepped broadband high sensitivity transducer

In order to improve the performance of the sonar system, a stepped broadband high-sensitivity hydroacoustic transducer is developed. Through theoretical analysis and finite element simulation, the feasibility of expanding the operating bandwidth and improving the sensitivity of the monometallic plate stepped piezoelectric material sensitive element is analyzed, and the dimensional parameters of this sensitive element are optimized. Compared with the traditional composite material, the sensitive element has excellent piezoelectric performance, with broadband and high sensitivity properties. The monometallic plate stepped piezoelectric material transducer and the same size stepped composite transducer were prepared, and their hydroacoustic performance was tested. The test results show that the monometallic plate stepped piezoelectric material transducer has far superior sensitivity performance than the same size stepped composite transducer and also has broadband performance. The peak transmits voltage response of the monometallic plate stepped transducer is 166 dB, and the −3 dB bandwidth reaches 60 kHz; the peak receives sensitivity is −183 dB, and the −3 dB bandwidth reaches 55 kHz, which can effectively improve the performance of the sonar system.

Multimodal force and temperature tactile sensor based on a short-channel organic transistor with high sensitivity

In this manuscript, we report on a novel architecture for the fabrication of highly sensitive multimodal tactile transducers, for the simultaneous detection of temperature and force. Such devices are based on a flexible Organic Charge Modulated Field Effect Transistor (OCMFET) coupled with a pyro/piezoelectric element, namely a commercial film of poly-vinylene difluoride (PVDF). The reduction of the channel length, obtained by employing a low-resolution vertical channel architecture, allowed to maximize the ratio between the sensing area and the transistor’s channel area, a technological approach that allows to considerably enhance both temperature and force sensitivity, while at the same time minimize the sensor’s dimensions. Thanks to the employment of a straightforward, up-scalable, and highly reproducible fabrication process, this solution represents an interesting alternative for all those applications requiring high-density, high-sensitivity sensors such as robotics and biomedical applications.

Small-Molecule Analysis Based on DNA Strand Displacement Using a Bacteriorhodopsin Photoelectric Transducer: Taking ATP as an Example.

A uniformly oriented purple membrane (PM) monolayer containing photoactive bacteriorhodopsin has recently been applied as a sensitive photoelectric transducer to assay color proteins and microbes quantitatively. This study extends its application to detecting small molecules, using adenosine triphosphate (ATP) as an example. A reverse detection method is used, which employs AuNPs labeling and specific DNA strand displacement. A PM monolayer-coated electrode is first covalently conjugated with an ATP-specific nucleic acid aptamer and then hybridized with another gold nanoparticle-labeled nucleic acid strand with a sequence that is partially complementary to the ATP aptamer, in order to significantly minimize the photocurrent that is generated by the PM. The resulting ATP-sensing chip restores its photocurrent production in the presence of ATP, and the photocurrent recovers more effectively as the ATP concentration increases. Direct and single-step ATP detection is achieved in 15 min, with detection limits of 5 nM and a dynamic range of 5 nM-0.1 mM. The sensing chip exhibits high selectivity against other ATP analogs and is satisfactorily stable in storage. The ATP-sensing chip is used to assay bacterial populations and achieves a detection limit for Bacillus subtilis and Escherichia coli of 102 and 103 CFU/mL, respectively. The demonstration shows that a variety of small molecules can be simultaneously quantified using PM-based biosensors.

Comparative sensitivity and accuracy of 24vs.18 MHz ultrasound probes for the diagnosis of flexor tendon repair integrity.

To determine whether a 24 MHz transducer significantly improves sensitivity, specificity and accuracy in evaluating flexor tendon repair integrity compared with an 18 MHz transducer. One hundred and twelve cadaveric digits were randomised to an intact repair or simulated 'failed' repair, and to a two- or eight-strand repair of a flexor digitorum profundus laceration. A blinded sonologist evaluated specimens in static mode using 18 and 24 MHz transducers. Gaps were remeasured after scanning, and final gap width recorded. McNemar's exact test calculated differences between sensitivity, specificity and accuracy, and chi-squared test to compare sensitivity, specificity and accuracy between number of strands (2 vs. 8) and repair gap (≥4 mm). The 24 MHz transducer had higher sensitivity (81 vs. 59%), lower specificity (67 vs. 70%) and higher overall accuracy (74 vs. 64%), than the 18 MHz transducer. The difference for sensitivity was significant (P = 0.011), but not differences for specificity and overall accuracy (P > 0.05). Pearson's correlation (r = 0.61) demonstrated a moderate-to-strong positive correlation between measured and true gap sizes. Increased number of suture strands (2 vs. 8) did not impair sensitivity, specificity nor accuracy. Ultrasound may tend to overestimate gap width, and a slight risk that some intact repairs, or those with small, clinically insignificant gaps may undergo surgical exploration that may not be indicated. A 24 MHz transducer is a more sensitive and accurate transducer for assessing flexor tendon repair integrity and measuring small gaps.

Capabilities of eddy current ndt of soldered current-carrying joints in submersible electrical equipment

The paper shows the possibility to test the quality of soldering of small current-carrying non-ferromagnetic joints in submersible electrical equipment for oil and gas systems by the amplitude eddy current method using a highly sensitive primary transducer with a U-shaped core. The sensitivity of soldering quality testing under different conditions of generating an exciting signal is compared. It has been found that the sensitivity of NDT in the case of current amplitude stabilized in the excitation coil (current generator) is significantly higher than that in case of voltage amplitude stabilized in it (voltage generator). Possible errors in determining the level of soldering of the joints due to the variation of their cross section within the limits of tolerance according to the technology of their manufacture have been detected. Circuit solutions and software have been developed to test the level of soldering of such joins. Approbation of soldering quality testing was carried out on products manufactured under production conditions.

Development of a floating element photoelastic force balance

We present a floating element force balance design that uses an optical measurement of the force using photoelastic stress analysis. The force sensing element consists of pins embedded in photoelastic polyurethane pads, which generate an internal stress when the floating element is loaded that is observed via a transmission polariscope. A series of known loads and their corresponding fringe patterns allow a calibration matrix to be derived using a polynomial model solved by least squares regression. Finite element analysis (FEA) simulation is carried out to validate the proposed method. The balance then measured a lift curve of the NACA0015 wing at low speed. A comparison of the photoelastic balance and a commercial, 6-axis strain-gauge load cell showed typical differences of less than 6%. This optical approach enables accurate measurements with inexpensive and simple components inside the sensor. This work demonstrates that a photoelastic balance is a simple, inexpensive, and sensitive force transducer.

Low-Cost Online Partial Discharge Monitoring System for Power Transformers

The article presents in detail the construction of a low-cost, portable online PD monitoring system based on the acoustic emission (AE) technique. A highly sensitive piezoelectric transducer was used as the PD detector, whose frequency response characteristics were optimized to the frequency of AE waves generated by discharges in oil-paper insulation. The popular and inexpensive Teensy 3.2 development board featuring a 32-bit MK20DX256 microcontroller with the ARM Cortex-M4 core was used to count the AE pulses. The advantage of the system is its small dimensions and weight, easy and quick installation on the transformer tank, storage of measurement data on a memory card, battery power supply, and immediate readiness for operation without the need to configure. This system may contribute to promoting the idea of short-term (several days or weeks) PD monitoring, especially in developing countries where, with the dynamically growing demand for electricity, the need for inexpensive transformer diagnostics systems is also increasing. Another area of application is medium-power transformers (up to 100 MVA), where temporary PD monitoring using complex measurement systems requiring additional infrastructure (e.g., control cabinet, cable ducts for power supply, and data transmission) and qualified staff is economically unjustified.

A selectivity-enhanced fluorescence imprinted sensor based on yellow-emission peptide nanodots for sensitive and visual smart detection of λ-cyhalothrin

The development of precise and efficient detection technologies to recognize λ-cyhalothrin (LC) in agricultural products has attracted attention worldwide due to its widespread use and notable toxic effects on humans. Herein, a novel fluorescence biomimetic nanosensor was elaborately designed based on Zn(II)-doped cyclo-ditryptophan (c-WW)-type peptide nanodots and incorporating molecularly imprinted polymer (c-WW/Zn-PNs@MIP) for LC assays. C-WW/Zn-PNs obtained by self-assembly with aromatic cyclic dipeptides as basic building blocks and coordination with Zn(II) have low-toxicity, photostability, and bright yellow fluorescence emission, as a sensitive signal transducer. High-affinity imprinting sites further endow c-WW/Zn-PNs@MIP with superior selectivity and reusability. Based on prominent merits, c-WW/Zn-PNs@MIP demonstrated a good linear range (1–360 μg/L) with a low limit of detection (LOD) (0.93 μg/L), fast kinetics in target capture (10 min), and strong practicability in the capture of LC from real samples (spiked recovery of 81.0–107.7%). Additionally, to attain onsite profiling of LC, a visual platform was developed by integrating c-WW/Zn-PNs@MIP with a smartphone-assisted optical device. This smart evaluation system can capture concentration-dependent fluorescent images and accurately digitize them, enabling quantitative analysis of LC. This study developed a fluorescent c-WW/Zn-PNs@MIP-based smart evaluation system as a novel platform for LC monitoring applications, which not only has enormous economic value but also great environmental health significance.

A Novel Enzyme Biosensor Based on Ag/Reduced Graphene Oxide/Chitosan Membrane with Potentiometer for Pesticide Detection

Long-term accumulation of pesticides in the environment to human and animal health. Acetylcholinesterase (AChE) biosensors with highly sensitive potentiometer transducers based on the membranes of Ag, reduced graphene oxide (rGO), and chitosan (CS) has been successfully developed. The membrane was made with a composition of 0.5 mM AgNO3, 2.5 mg/mL rGO, and 2% (w/v) CS coated on the surface of the Au electrode. The composition of the membrane with three ratios, namely 1:1:2, 2:1:3, and 3:1:4. Then, membrane Ag/rGO/CS and the enzyme AChE were immobilized on the membrane surface. The prepared biosensor has excellent conductivity, catalytic activity, and biocompatibility attributed to the synergistic effect of Ag/rGO/CS and glutaraldehyde (GTA) as crosslinkers and providing a hydrophilic surface for AChE adhesion. The linear range in biosensors is 1 × 10-8 to 1 µg L-1 with a regression coefficient of 0.9803 for 1:1:2 membrane, 0.9836 for 2:1:3 membrane, and 0.9850 for 3:1:4 membrane. The LOD is about 1 × 10-7 µg L-1 for all membranes. In addition, the biosensor showed good sensitivity, acceptable reproducibility, and stability, having an RSD of less than 5%. This biosensor makes it possible to provide a new and promising tool for analyzing pesticides, especially organophosphates.

Research on monometallic plate piezoelectric ceramic column array broadband high sensitivity transducer

A kind of broadband and highly sensitive underwater acoustic transducer with increased bandwidth and sensitivity is proposed. The effective electromechanical coupling coefficient of the piezoelectric material and the sensitivity of the transducer are improved by using air instead of polymer in the piezoelectric composite and by covering the upper surface of the piezoelectric column array with metal plates. Besides, the operating bandwidth of the transducer is increased through bandwidth superposition. Theoretical analysis is conducted to determine the resonance conditions of the monometallic plate piezoelectric ceramic array material as a sensitive element. With the dimensional parameters of the sensitive component determined by means of finite element simulation, the transducer is designed and produced. According to the test results, the bandwidth of the transducer reaches 60 kHz, the maximum transmit voltage response is 152.1 dB and the receiving sensitivity is −182.5 dB, which is effective in improving both the receiving sensitivity and bandwidth of the transducer.

Development of methods and devices for air-coupled ultrasonic through transmission testing of large-sized objects made of polymer composite materials

It is shown that in order to increase the sensitivity of air-coupled ultrasonic through transmission testing of products made of polymer composite materials, it is necessary to develop highly sensitive low-frequency wideband air-coupled piezoelectric transducers. The methods of providing both high sensitivity and a wideband of air-coupled ultrasonic piezoelectric transducer are considered. Air-coupled ultrasonic highly sensitive broadband piezoelectric transducer based on the use of mosaic contact piezoelectric transducer technology, the choice of optimal matching layers and the use of various options for excitation of piezoelectric transmitter have been proposed and developed. It is shown that by use of mosaic air-coupled low-frequency broadband piezoelectric transducers, it is possible to ensure high sensitivity of testing and ensure the accuracy of measurement of acoustic characteristics (ultrasound velocity, density, etc.) with air-coupled ultrasonic low-frequency through transmission testing of large-sized objects made of polymer composite materials.