Transducer Electrodes Research Articles

An electrochemical sensor based on TiO2/activated carbon nanocomposite modified screen printed electrode and its performance for phenolic compounds detection in water samples

ABSTRACTHerein, we reported a titanium oxide (TiO2) modified activated carbon nanocomposite that showed advantageous characteristics in terms of electro-conductivity, catalytic activity and surface area. The designed nanocomposite was employed to modify the screen printed carbon electrode transducer surface in the construction of an electrochemical sensor. The electrode surface modification was characterised by cyclic voltammetry and impedimetric studies. The modified transducer surface was subsequently used for the detection of four phenolic endocrine disruptors, p-nitrophenol, hydroquinone, catechol and 1-naphtol. Under optimal conditions, TiO2 modified activated carbon sensor was evaluated by differential pulse voltammetry showing a good linearity with correlation coefficients higher than 0.99. It showed, in parallel, a high sensitivity where the detection limits were 348 ng/L, 110.1 ng/L, 3.3 ng/L and 7.2 µg/L for the respective studied compounds (S/N = 3). Finally, we validated the method with river water samples, and good recovery values were obtained showing the potential application of the reported biosensor.

Development of a silver functionalised polyaniline electrochemical immunosensor for polychlorinated biphenyls

An electrochemical immunosensor based on a silver nanoparticles (Ag NPs)-doped polyaniline (PANI) modified glassy carbon electrode (GCE) transducer, wherein polyclonal anti-polychlorinated biphenyl (PCB) antibody (Ab) was immobilized by a covalent linkage with glutaraldehyde (GA), was developed.

Abstract 17400: Catecholamine Release Triggered by Epicardial Absolute Refractory Period Stimulation Augments Global Left Ventricular Function

Background: Biventricular epicardial (Epi) pacing can augment left ventricular (LV) function in heart failure. We postulated that these beneficial effects could involve catecholamine release from local autonomic nerve activation. This hypothesis was tested by applying Epi pacing stimuli during the muscle’s absolute refractory period (ARP) thereby activating intrinsic nerves without altering activation sequence. Methods: Anesthetized farm pigs (n=5) were instrumented with a LV high-fidelity pressure transducer, left atrial and LV Epi pacing electrodes, and sonomicrometer segment length (SL) gauges placed proximal and distal to the LV stimulation site. A small catheter was placed into the great cardiac vein adjacent to the LV pacing site for blood sampling. During atrial pacing at constant rate, 3 electrical pulses (0.8ms, 2-3x threshold volts) were applied to the LV Epi electrodes during the ARP. An experimental run consisted of baseline measurements, with 10 minutes of stimulation followed by 5 minutes of recovery repeated 3 times before and with ß- receptor blockade (BB, metoprolol, 5 mg). Coronary venous blood was sampled at baseline and at 5 and 10 minutes of stimulation for norepinephrine analysis (NE by ELISA). Results: ARP stimulation produced a significant increase in coronary venous NE levels (p< 0.01) accompanied by a significant 10-15% increase in LV dP/dt max (p< 0.01). Segment length vs. LV pressure loop area proximal to the stimulus site was significantly decreased (29.8 ± 10.9 mmHg*mm) compared to baseline (92.6 ± 8.2 mmHg*mm) but was unchanged at the distal site. BB abolished the changes in segment function and blocked the increase in LV dP/dt despite continued NE release. Conclusion: These results demonstrate that ARP EPI pacing induces NE release and augments global LV function. This effect may contribute to the beneficial effect of biventricular Epi pacing in some patients with heart failure.

미세입자의 정밀제어를 위한 표면탄성파 장치의 특성연구 및 설계

Surface acoustic wave(SAW) device is used for transporting and patterning micro-scale particles such as cells. In this research, velocity of particles was investigated moved by SAW device with two types of interdigital electrode transducers(IDTs) under various conditions. SAW devices which have single IDTs and double IDTs were designed and fabricated. On the previous studies, resultant velocities of particles were predicted considering output power and power ratio between IDTs-shape. For more accurate prediction, power loss in SAW device and a power difference between two types of IDTs-shape were considered. Maximum error between the test results and predicted values was 5 % so the power loss must be considered in the velocity prediction of the particles.

Modeling the trajectory of microparticles subjected to dielectrophoresis in a microfluidic device for field flow fractionation

This article details the development of an experimentally validated model for tracking the movement of microparticles in a continuous flow microfluidic device employing dielectrophoresis for purposes of field-flow fractionation. This device employs interdigitated transducer electrodes on the bottom surface of the microchannel. The electric potential inside the microchannel is defined by Laplace equation while the trajectory of the microparticles is described by governing equations based on Newton’s second law. Forces due to inertia, gravity, buoyancy, dielectrophoresis and virtual mass are accounted for in this model. The governing equations are solved using finite difference method. The model is subsequently used for parametric study; the parameters analyzed include microparticle radius, applied voltage, volumetric flow rate, microchannel height and electrode/gap length. As per the model the levitation height, under steady state conditions, of the microparticles is independent of the microparticle radius, volumetric flow rate and microchannel height, it is dependent on the applied voltage and electrode/gap length. The levitation height, under transient conditions, is dependent on all these parameters.

Fabrication of High Frequency Surface Acoustic Wave (SAW) Devices for Real Time Detection of Highly Toxic Chemical Vapors

Abstract In this paper, a low cost fabrication of sub micron features size SAW device with conventional lithography and their application for toxic chemical vapor detection has been presented. The SAW devices with different interdigital transducer (IDT) electrodes line widths were designed and fabricated. The fabricated SAW devices features had an accuracy of ± 0.1 μm. Frequency response of the SAW devices was measured with vector network analyzer for design parameter confirmation. The fabricated devices have been configured in multisensory oscillator configuration and tested with chemical ware fare agents simulants at very low concentration (ppb).

Highly stretchable dielectric elastomer material based on acrylonitrile butadiene rubber

This study presents a highly stretchable dielectric elastomer material for transducers based on acrylonitrile butadiene rubber (NBR). The material has advantages in that its mechanical and electrical properties can be modified according to the requirements of applications by changing the content of additives such as carbon black (CB), multi-walled carbon nanotubes (MWCNT), and graphite (GP) in the NBR matrix. First, the changes of dielectric permittivity depending on the additives are discussed. Moreover, the electrical resistance is examined in detail by changing the compositions of the additives, and the applicability of the material to the electrodes of transducers is investigated. Finally, the optimal contents of additives for actuators or sensors are discussed.

Electrochemical evaluation of anti-CRP/CRP interaction for the molecular diagnosis of the cardiovascular risk

Background The C-reactive protein (CRP or PTX1) is an acute phase protein, expressed by hepatocytes, that is regarded as a clinical marker for infection and has been increasingly used as a risk indicator in chronic inflammatory diseases [1]. Atherosclerosis is an inflammatory disease that remains a major cause of morbidity and mortality. Its progression is associated with the accumulation of lipoproteins in the endothelium, establishing plaques whose rupture may result in the formation of a thrombus, arising several cardiovascular complications [2]. Studies show there is a correlation between the risk of cardiac events (such as myocardial infarction) and increasing levels of CRP [3]. Currently, there are several methods to detect CRP, including immunoassays and agglutination. However, these methods are not sensitive enough, time-consuming or cost-ineffective [4]. Therefore, new diagnosis methods are being developed. Electrochemical biosensors are small devices that combine the selectivity of biochemical molecular recognition with the sensitivity of electrode transducers, being remarkable for their sspecificity, speed, portability and low cost [5]. In this work, a graphite electrode surface is modified with poly (3-aminotiophenol) and a specific antibody (anti-CRP), aiming the detection of its antigen (CRP), through electrochemical methods.

Piezoelectric thin films for double electrode CMOS MEMS surface acoustic wave (SAW) resonator

CMOS integration for RF-MEMS is desired to yield compact, low-power and portable devices. In this work, we illustrate the usage of double electrode CMOS SAW resonators using both ZnO and AlN as its piezoelectric material. Double electrode transducers were chosen, as they are better at suppressing undesired acoustic reflections compared to single electrodes. The structure and dimension of the device is based on 0.35 μm CMOS process where the IDTs are fabricated using standard CMOS fabrication process. 2D Finite element modeling of the CMOS SAW resonator using COMSOL Multiphysics® is presented. Two-step eigenfrequency and frequency domain analyses were performed. The acoustic velocities generated are 3,925 and 5,953 m/s for ZnO and AlN CMOS SAW resonator respectively. Higher acoustic displacement and surface potential were observed in ZnO compared to AlN. It can be concluded that ZnO thin films have higher electromechanical coupling coefficients and are more efficient than AlN thin films.

A near and far-field monitoring technique for damage detection in concrete structures

Real-time near and far-field monitoring of concrete structural components gives enough information on the time and condition at which damage occurs, thereby facilitating damage detection while in the same time evaluate the cause of the damage. This paper experimentally investigates an integrated monitoring technique for near and far-field damage detection in concrete structures based on simultaneous use of electromechanical admittance technique in combination with guided wave propagation. The proposed sensing system does not measure the electromechanical admittance itself but detect time variations in output voltages of the response signal obtained across the electrodes of piezoelectric transducers bonded on surfaces of concrete structures. The damage identification is based on the spectral estimation MUSIC algorithm. Experimental results show the efficiency and performance of the proposed measuring technique.

Influence of maternal body mass index on accuracy and reliability of external fetal monitoring techniques

To evaluate the performance of external electronic fetal heart rate and uterine contraction monitoring according to maternal body mass index. Secondary analysis of prospective equivalence study. Three US urban teaching hospitals. Seventy-four parturients with a normal term pregnancy. The parent study assessed performance of two methods of external fetal heart rate monitoring (abdominal fetal electrocardiogram and Doppler ultrasound) and of uterine contraction monitoring (electrohystero-graphy and tocodynamometry) compared with internal monitoring with fetal scalp electrode and intrauterine pressure transducer. Reliability of external techniques was assessed by the success rate and positive percent agreement with internal methods. Bland-Altman analysis determined accuracy. We analyzed data from that study according to maternal body mass index. We assessed the relationship between body mass index and monitor performance with linear regression, using body mass index as the independent variable and measures of reliability and accuracy as dependent variables. There was no significant association between maternal body mass index and any measure of reliability or accuracy for abdominal fetal electrocardiogram. By contrast, the overall positive percent agreement for Doppler ultrasound declined (p=0.042), and the root mean square error from the Bland-Altman analysis increased in the first stage (p=0.029) with increasing body mass index. Uterine contraction recordings from electrohysterography and tocodynamometry showed no significant deterioration related to maternal body mass index. Accuracy and reliability of fetal heart rate monitoring using abdominal fetal electrocardiogram was unaffected by maternal obesity, whereas performance of ultrasound degraded directly with maternal size. Both electrohysterography and tocodynamometry were unperturbed by obesity.

A novel approach for differentiation of liquid samples with surface acoustic wave transducers and embedded microcavities

We discuss a novel method for sensing and differentiation of analytes trapped in a microcavity with an emphasis on liquids. The proposed sensing mechanism relies on capturing the analyte of interest in a microcavity etched on the delay line in contrast to the conventional mass loading method. The structure mainly consists of input and output interdigitated transducer (IDT) electrodes in an otherwise standard delay line configuration operated in Rayleigh mode along with a microcavity etched between the IDTs to trap minute amounts of liquids. Firstly, the responses of the system with the microcavity are explored using finite element method (FEM) analysis. Then, experimental results from delay lines on two different substrates, namely, Y-Z lithium niobate and ST-X quartz are analyzed. The system can distinguish between liquids with glycerin concentrations ranging from 60% to 90% in water and less than 5pL in volume in the high frequency range of 197MHz and 213MHz based on frequency and phase shift readings. Lithium niobate samples with 1.2μm deep microcavities provide an overall frequency sensitivity of −7.7kHz/(% glycerin). Quartz samples with 8.5μm deep microcavities have a sensitivity of −0.13°/(% glycerin). The minimum density–viscosity product experimentally differentiated using embedded microcavities is 1.9kg/m2√s. It is concluded that this method can be used to trap and interrogate minute amounts of liquids with different properties. Experimental results demonstrate that our approach can possibly be extended to certain solids, and to more complex structures like single biological cells.

Design and Fabrication of Nanoscale IDTs Using Electron Beam Technology for High‐Frequency SAW Devices

High‐frequency Rayleigh‐mode surface acoustic wave (SAW) devices were fabricated for 4G mobile telecommunications. The RF magnetron sputtering method was adopted to grow piezoelectric aluminum nitride (AlN) thin films on the Si3N4/Si substrates. The influence of sputtering parameters on the crystalline characteristics of AlN thin films was investigated. The interdigital transducer electrodes (IDTs) of aluminum (Al) were then fabricated onto the AlN surfaces by using the electron beam (e‐beam) direct write lithography method to form the Al/AlN/Si3N4/Si structured SAW devices. The Al electrodes were adopted owing to its low resistivity, low cost, and low density of the material. For 4G applications in mobile telecommunications, the line widths of 937 nm, 750 nm, 562 nm, and 375 nm of IDTs were designed. Preferred orientation and crystalline properties of AlN thin films were determined by X‐ray diffraction using a Siemens XRD‐8 with CuKα radiation. Additionally, the cross‐sectional images of AlN thin films were obtained by scanning electron microscope. Finally, the frequency responses of high‐frequency SAW devices were measured using the E5071C network analyzer. The center frequencies of the high‐frequency Rayleigh‐mode SAW devices of 1.36 GHz, 1.81 GHz, 2.37 GHz, and 3.74 GHz are obtained. This study demonstrates that the proposed processing method significantly contributes to high‐frequency SAW devices for wireless communications.

High temperature stability of electrically conductive Pt–Rh/ZrO2 and Pt–Rh/HfO2 nanocomposite thin film electrodes

Nanocomposite films made up of either Pt–Rh/ZrO2 or Pt–Rh/HfO2 materials were co-deposited using multiple e-beam evaporation sources onto langasite (La3Ga5SiO14) substrates, both as blanket films and as patterned interdigital transducer electrodes for surface acoustic wave sensor devices. The films and devices were tested after different thermal treatments in a tube furnace up to 1,200 °C. X-ray diffraction and electron microscopy results indicate that Pt–Rh/HfO2 films are stabilized by the formation of monoclinic HfO2 precipitates after high temperature exposure, which act as pinning sites to retard grain growth and prevent agglomeration of the conductive cubic Pt–Rh phase. The Pt–Rh/ZrO2 films were found to be slightly less stable, and contain both tetragonal and monoclinic ZrO2 precipitates that also helps prevent Pt–Rh agglomeration. Film conductivities were measured versus temperature for Pt–Rh/HfO2 films on a variety of substrates, and it was concluded that La and/or Ga diffusion from the langasite substrate into the nanocomposite films is detrimental to film stability. An Al2O3 diffusion barrier grown on langasite using atomic layer deposition was found to be more effective than a SiAlON barrier layer in minimizing interdiffusion between the nanocomposite film and the langasite crystal at temperatures above 1,000 °C.

Gold nanoparticle modified capacitive sensor platform for multiple marker detection

The detection and quantification of cancer biomarkers in human blood is crucial to diagnose patients in the early stage of a disease. The recent advances in biosensor technology can improve detection by reducing the application time and cost without an invasive approach. In this study, a highly sensitive, novel nanoparticle-modified capacitive sensor was developed for the detection of cancer markers. The current work mainly focused on developing a surface modification protocol for achieving higher sensitivity using Au-NPs. An interdigitated electrode (IDE) transducer was modified using gold nanoparticles (Au-NPs) for signal enhancement, the platform was initially optimized with a small size IL-6 protein and the methodology was then applied for multiple marker detection with the aim of precise disease diagnostics. Carcinoembryonic antigen (CEA) and epidermal growth factor receptor (hEGFR) could be successfully detected in the concentration range of 20-1000 pg mL(-1) while cancer antigen 15-3 (CA15-3) was detected in the range of 10-200 U mL(-1). These results show an increase of sensitivity by five-fold with respect to those not modified, demonstrating a highly sensitive and specific capacitive immunoassay that has a great potential for the use of early diagnosis of cancer disease.

English

Introduction In the past few decades, ethanol has assumed the role of the most widespread psychotropic agent in Western society because of its availability to the youth and adults and also because it is generally considered legal in many societies. It is known that the alcohol can have significant relapses on the central nervous system; hence, there is a need for monitoring the toxicokinetics and the effects of ethanol on the brain with the most appropriate techniques. Among the techniques that aim to measure ethanol concentration in the brain, microdialysis has been the most widely used, but because of its invasiveness, associated with low temporal resolution, and the necessity of using connecting tubes to carry out the experiments, it is not particularly suitable for clinical trials. Recently, electrochemical biosensors, also minimally invasive, have been developed, which offer the possibility of monitoring the real-time variations of ethanol concentrations in the brain of animal models due to the very small dimensions of the transducer electrode. Recently, non-invasive methods have been used for the direct monitoring of alcohol in the brain, which use spectroscopic techniques such as magnetic resonance spectroscopy and magnetic resonance imaging or positron emission tomography, which are principally used to monitor ethanol metabolites. The aim of this review is to discuss all the techniques used to monitor brain ethanol and highlight their strengths and weaknesses. Conclusion Microdialysis and biosensors are primarily used in preclinical studies; both are very reliable techniques, but for invasiveness, they can only be used in animal models. Alternatively, spectroscopic techniques are suitable for both preclinical and clinical studies, and are not exclusive for animal models.

Magnetoelectric thin film composites with interdigital electrodes

Magnetoelectric (ME) thin film composites on silicon cantilevers are fabricated using Pb(Zr0.52Ti0.45)O3 (PZT) films with interdigital transducer electrodes on the top side and FeCoSiB amorphous magnetostrictive thin films on the backside. These composites without any direct interface between the piezoelectric and magnetostrictive phase are superior to conventional plate capacitor-type thin film ME composites. A limit of detection of 2.6 pT/Hz1/2 at the mechanical resonance is determined which corresponds to an improvement of a factor of approximately 2.8 compared to the best plate type sensor using AlN as the piezoelectric phase and even a factor of approximately 4 for a PZT plate capacitor.

Measuring body layer vibration of vocal folds by high-frame-rate ultrasound synchronized with a modified electroglottograph

The body-cover concept suggests that the vibration of body layer is an indispensable component of vocal fold vibration. To quantify this vibration, a synchronized system composed of a high-frame-rate ultrasound and a modified electroglottograph (EGG) was employed in this paper to simultaneously image the body layer vibration and record the vocal fold vibration phase information during natural phonations. After data acquisition, the displacements of in vivo body layer vibrations were measured from the ultrasonic radio frequency data, and the temporal reconstruction method was used to enhance the measurement accuracy. Results showed that the modified EGG, the waveform and characteristic points of which were identical to the conventional EGG, resolved the position conflict between the ultrasound transducer and EGG electrodes. The location and range of the vibrating body layer in the estimated displacement image were more clear and discernible than in the ultrasonic B-mode image. Quantitative analysis for vibration features of the body layer demonstrated that the body layer moved as a unit in the superior-inferior direction during the phonation of normal chest registers.

Functioning of antimony film electrode in acid media under cyclic and anodic stripping voltammetry conditions

New insights into the functioning, i.e. electrochemical behaviour and analytical performance, of in situ prepared antimony film electrodes (SbFEs) under square-wave anodic stripping (SW-ASV) and cyclic (CV) voltammetry conditions are presented by studying several key operational parameters using Pb(II), Cd(II) and Zn(II) as model analyte ions. Five different carbon- and metal-based substrate transducer electrodes revealed a clear advantage of the former ones while the concentration of the precursor Sb(III) ion exhibited a distinct influence on the ASV functioning of the SbFE. Among six acids examined as potential supporting electrolytes the HNO3 was demonstrated to yield nearly identical results in conducting ASV experiments with SbFE as so far almost exclusively used HCl. This is extremely important as HNO3 is commonly employed acidifying agent in trace metal analysis, especially in elemental mass spectrometry measurements. By carrying out a systematic CV and ASV investigation using a medium exchange protocol, we confirmed the formation of poorly soluble oxidized Sb species at the substrate electrode surface at the end of each stripping step, i.e. at the potentials beyond the anodic dissolution of the antimony film. Hence, the significance of the cleaning and initializing the surface of a substrate electrode after accomplishing a stripping step was thoroughly studied in order to find conditions for a complete removal of the adhered Sb-oxides and thus to assure a memory-free functioning of the in situ prepared SbFE. Finally, the practical analytical application of the proposed ASV method was successfully tested and evaluated by measuring the three metal analytes in ground (tap) and surface (river) water samples acidified with HNO3. Our results approved the appropriateness of the SbFE and the proposed method for measuring low μgL−1 levels of some toxic metals, particularly taking into account the possibility of on-field testing and the use of low cost instrumentation.

Design and implementation of high data capacity RFID tag using eight-phase encoding

Enhancing the data capacity of surface acoustic wave (SAW) radio frequency identification (RFID) tags using the combination of time position and phase encoding with fewer number of reflectors is investigated in this work. Simulation and fabrication of SAW RFID tags are performed using COMSOL Multiphysics and standard photolithography process. Lithium Tantalite (LiTaO3) is used as a substrate and Aluminium metal electrodes are used to realise the interdigital transducer (IDT) electrodes. The data capacity enhancement is tested using a SAW RFID tag consisting of a single-phase unidirectional transducer (SPUDT) transducer and four code reflectors. By designing the width of SPUDT electrodes and floating electrodes and proper positioning of reflectors, eight phases (i.e. 0°, −45°, −90°, −135°, −180°, −225°, −270° and −315°) are detected which correspond to 3 bits of data per reflector. These eight phases would result to have one more data bit per reflector. Therefore, eight phase states along with four time positions lead to 32 different states (i.e. 5 bits of data per reflector). To facilitate the realisation of our idea, the fabrication process has been performed at 250 MHz; however, it can easily be implemented at higher frequencies (i.e. GHz range).