Real-time Electrical Measurement Research Articles

Electrical monitoring of single-event protonation dynamics at the solid-liquid interface and its regulation by external mechanical forces

Detecting chemical reaction dynamics at solid-liquid interfaces is important for understanding heterogeneous reactions. However, there is a lack of exploration of interface reaction dynamics from the single-molecule perspective, which can reveal the intrinsic reaction mechanism underlying ensemble experiments. Here, single-event protonation reaction dynamics at a solid-liquid interface are studied in-situ using single-molecule junctions. Molecules with amino terminal groups are used to construct single-molecule junctions. An interfacial cationic state present after protonation is discovered. Real-time electrical measurements are used to monitor the reversible reaction between protonated and deprotonated states, thereby revealing the interfacial reaction mechanism through dynamic analysis. The protonation reaction rate constant has a linear positive correlation with proton concentration, whereas the deprotonation reaction rate constant has a linear negative correlation. In addition, external mechanical forces can effectively regulate the protonation reaction process. This work provides a single-molecule perspective for exploring interface science, which will contribute to the development of heterogeneous catalysis and electrochemistry.

Comparing machine learning algorithms for non-invasive detection and classification of failure in piezoresistive bone cement via electrical impedance tomography

At an estimated cost of $8 billion annually in the United States, revision surgeries to total joint replacements represent a substantial financial burden to the health care system and a tremendous mental and physical burden on patients and their caretakers. Fixation failures, such as implant loosening, wear, and mechanical instability of the poly(methyl methacrylate) (PMMA) cement, which bonds the implant to the bone, are the main causes of long-term implant failure. Early and accurate diagnosis of cement failure is critical for developing novel therapeutic strategies and reducing the high risk of a misjudged revision. Unfortunately, prevailing imaging modalities, notably plain radiographs, struggle to detect the precursors of implant failure and are often interpreted incorrectly. Our prior work has shown that the modification of PMMA bone cement with low concentrations of conductive fillers makes it piezoresistive and therefore self-sensing. When combined with a conductivity imaging modality such as electrical impedance tomography (EIT), it is possible to monitor load transfer across the PMMA using cost-effective, physiologically benign, non-contact, and real-time electrical measurements. Despite the ability of EIT for monitoring load transfer across self-sensing PMMA bone cement, it is unable to accurately characterize failure mechanisms. Overcoming this challenge is critical to the success of this technology in practice. Therefore, we herein expand upon our previous results by integrating machine learning techniques with EIT for cement condition characterization with the goal of establishing the feasibility of even off-the-shelf machine learning algorithms to address this important problem. We survey a wide variety of different machine learning algorithms for application to this problem, including neural networks on voltage readings of an EIT phantom for tracking the spatial position of a sample, specifying defect orientation within a sample, and classifying defect types, including cracks and delaminations. In addition, we explore the utilization of principal component analysis (PCA) for pre-treating impedance signals in each of these problems. Within the tested algorithms, our results show clear advantages of neural networks, support vector machines, and K-nearest neighbor algorithms for interpreting EIT signals. We also show that PCA is an effective addition to machine learning. These preliminary results demonstrate that the combination of smart materials, EIT, and machine learning may be a powerful instrumentation tool for diagnosing the origin and evolution of mechanical failure in joint replacements.

DESIGN OF AN INTELLIGENT INFORMATION MEASUREMENT SYSTEM FOR PHOTOVOLTAIC DC MICROGRIDS

The integration of photovoltaic (PV) systems into direct current (DC) microgrids has garnered significant attention as a promising solution for sustainable energy distribution. In this article, the development of intelligent information measurement systems holds the utmost importance to optimize system performance, ensure stability, and facilitate efficient energy management. The aim of the research. This article presents the design of the intelligent information measurement system for PV-DC microgrids to achieve advanced functions such as power prediction, performance monitoring, fault diagnosis, maximum power extraction etc. by performing electrical and non-electrical measurements. These systems enhance data processing capabilities, enabling predictive analytics and adaptive control strategies. The research highlights the synergistic effects of electrical and non-electrical measurements in designing information measurement systems. By leveraging real-time electrical measurements for system control and non-electrical measurements for forecasting energy availability and assessing environmental impact, intelligent decision-making and adaptive control strategies are facilitated, resulting in efficient energy management. Conclusion. An intelligent information measurement system is designed to perform advanced functions to increase the efficiency of these systems. The research also provides a holistic understanding of the importance of measurements in developing intelligent information measurement systems for PV-DC microgrids. The study contributes to advancing microgrid technology and promoting sustainable and decentralised energy solutions. Keywords: Information measurement system, DC-DC converters, DC microgrid, measurements in microgrids.

A Novel Biosensing Approach: Improving SnS2 FET Sensitivity with a Tailored Supporter Molecule and Custom Substrate.

The exclusive features of two-dimensional (2D) semiconductors, such as high surface-to-volume ratios, tunable electronic properties, and biocompatibility, provide promising opportunities for developing highly sensitive biosensors. However, developing practical biosensors that can promptly detect low concentrations of target analytes remains a challenging task. Here, a field-effect-transistor comprising n-type transition metal dichalcogenide tin disulfide (SnS2 ) is developed over the hexagonal boron nitride (h-BN) for the detection of streptavidin protein (Strep.) as a target analyte. A self-designed receptor based on the pyrene-lysine conjugated with biotin (PLCB) is utilized to maintain the sensitivity of the SnS2 /h-BN FET because of the π-π stacking. The detection capabilities of SnS2 /h-BN FET are investigated using both Raman spectroscopy and electrical characterizations. The real-time electrical measurements exhibit that the SnS2 /h-BN FET is capable of detecting streptavidin at a remarkably low concentration of 0.5 pm, within 13.2s. Additionally, the selectivity of the device is investigated by measuring its response against a Cow-like serum egg white protein (BSA), having a comparative molecular weight to that of the streptavidin. These results indicate a high sensitivity and rapid response of SnS2 /h-BN biosensor against the selective proteins, which can have significant implications in several fields including point-of-care diagnostics, drug discovery, and environmental monitoring.

Stabilization of PbS colloidal-quantum-dot gas sensors using atomic-ligand engineering

Colloidal quantum dots (CQDs) are promising materials candidates for next-generation semiconductor gas sensors, due to their high surface activity and solution-processability. Despite the improved sensitivity demonstrated by PbS CQDs, their long-term stability remains a challenge for practical applications. In this paper, we propose a stabilization strategy for PbS CQD gas sensors by using atomic-ligand engineering. The oleic acid ligands surrounding PbS CQDs are replaced by halide ligands (Cl–, Br– and I–, respectively) via a phase-transfer ligand exchange method. The sensitivity and long-term stability of the PbS CQD gas sensor towards nitrogen dioxide (NO2) at room temperature are impressively improved. The excellent humidity stability of the iodine ligand exchanged PbS CQD gas sensor is also demonstrated. The mechanism is investigated by real-time electrical measurement, combined with operando diffuse reflection Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis. The results indicate that the large atomic radius and high binding energy of iodide ligands enhance surface passivation and provide favorable conditions for NO2 adsorption and charge transfer. This study highlights the importance of surface ligand engineering in the development of practical CQD gas sensors.

Highly Efficient, Non-Covalent Functionalization of CVD-Graphene via Novel Pyrene-Based Supporter Construct

Ultra-thin two-dimensional (2D) materials have attained huge interest for biosensing applications because of their strong electrostatic coupling with target molecules such as spike proteins and DNA. One such 2D material is graphene, which is extremely thin and flexible and has a strong non-covalent interaction with the supporting constructs needed to detect biomolecules. This work aimed to develop a way to efficiently functionalize the surface of 2D material using a pyrene-based supporter construct to detect the target protein. For this purpose, high-quality, pristine graphene was grown via the chemical vapor deposition (CVD) method and transferred over the Si/SiO2 substrate for its functionalization using our engineered pyrene–lysine-based supporter construct (PLB). The construct was synthesized using the solid-phase peptide synthesis (SPPS) method and utilized to functionalize the graphene-channel-based field-effect transistor (FET) device via non-covalent π−π stacking interaction. The optimum concentration of the functionalized PLB was evaluated via atomic force microscopy (AFM), Raman spectroscopy, and real-time electrical measurements. The characterization techniques successfully provide an overview of the effect of the concentration of PLB used for functionalization. Moreover, the performance was tested and compared in terms of the percentage response of the device generated after the detection of various concentrations of the streptavidin protein. This research could be useful in determining how to functionalize any 2D material by designing a supporter construct without material degradation and owing to over-stacking or bypassing surface screening effects.

Conductive adhesive based shingled solar cells: Electrical degradation under cyclic loading

Shingled solar cells based on electrically conductive adhesive (ECA) interconnection have emerged as a commercially viable option for photovoltaic (PV) modules with attractive attributes including no soldering process (lead-free), tight packing with no gap between cells, and resulting efficiency gains. Reliability of such modules is, however, less certain due to the lack of long-term outdoor performance data. Here we report numerical simulation of thermo-mechanical stress in shingled solar cells using finite element modelling, and identify stress concentration in silicon in the interconnect region not anticipated from simpler analytical models. We also present design and fabrication of samples using ECA interconnection with geometry and characteristics that closely match production modules for realistic fatigue testing under cyclic loading. The setup is combined with real-time electrical measurements that permit monitoring of fatigue-induced changes in the electrical resistance of ECA joint. Detailed measurements are presented using samples with different types ECA and varying patterns of the glue-line aimed at evaluating reduced material usage for cost-reduction. This study demonstrates that the sample structure and experimental setup presented here can be effectively used to evaluate electrical and mechanical degradation of shingled PV modules to guide their design process.

Complete deciphering of the dynamic stereostructures of a single aggregation-induced emission molecule

<h2>Summary</h2> The realization of functional molecular devices is inseparable from deep understanding of the intrinsic structure-property relationship of molecules. However, due to limited detection sensitivity and temporal resolution of current methods, there are rare reports on fully probing <i>in situ</i> dynamic changes of the molecular stereostructures at the single-molecule level in real time. Here, we present a complete deciphering of the dynamic stereostructures of a single aggregation-induced emission molecule using molecular junctions, which are capable of executing rapid real-time electrical measurements to achieve the unprecedented electrical mapping, thus feeding back the dynamic changes of the molecular stereostructures. Experimental and theoretical investigation consistently verify the intramolecular motions under electric field and the isomerization dynamics with strong temperature and electric field dependence, offering new insights into the development of ultra-sensitive devices. We anticipate that further integration of optical measurements with this approach will enable sophisticated synchronous monitoring of broad single-molecule photochemistry and photophysics.

Interplay of Voltage Control of Magnetic Anisotropy, Spin-Transfer Torque, and Heat in the Spin-Orbit-Torque Switching of Three-Terminal Magnetic Tunnel Junctions

We use three-terminal magnetic tunnel junctions (MTJs) designed for field-free switching by spin-orbit torques (SOTs) to systematically study the impact of dual voltage pulses on the switching performances. We show that the concurrent action of an SOT pulse and an MTJ bias pulse allows for reducing the critical switching energy below the level typical of spin transfer torque while preserving the ability to switch the MTJ on the sub-ns time scale. By performing dc and real-time electrical measurements, we discriminate and quantify three effects arising from the MTJ bias: the voltage-controlled change of the perpendicular magnetic anisotropy, current-induced heating, and the spin transfer torque. The experimental results are supported by micromagnetic modeling. We observe that, depending on the pulse duration and the MTJ diameter, different effects take a lead in assisting the SOTs in the magnetization reversal process. Finally, we present a compact model that allows for evaluating the impact of each effect due to the MTJ bias on the critical switching parameters. Our results provide input to optimize the switching of three-terminal devices as a function of time, size, and material parameters.

Nanoelectronic Biomolecular Sensors Based on Graphene Field-Effect Transistors for Protein Biomarker Detection

Field-effect transistor devices based on functionalized graphene (G-FETs) are a promising technology for biomolecular sensing applications due to the several advantages they present, including the label-free detection of biomolecules with direct electrical read-out, real-time detection and multiplexing capability. The development of highly selective and sensitive sensors for protein biomarkers is especially desirable to open novel technological avenues for the early detection and monitoring of biomarkers associated with cancer diseases. In this presentation, I’ll describe our recent progress on the design and development of a label-free immunosensor based on antibody-modified graphene field-effect transistors for protein biomarker detection. Specifically, monoclonal antibodies were selected to target a protein biomarker specific to MLL translocated acute myeloid leukemia and we tested approaches for their immobilization on graphene. We found that the antibodies can spontaneously adhere to the graphene surface but this adhesion is partially reversible under solution flow. In order to stabilize the immobilization of antibodies, we developed a protocol based on electrochemically-driven chemistry to form stable covalent anchor groups at the graphene surface which can then capture antibodies. We optimized the rate of formation of anchor groups at the surface in order to maximize the density of anchor groups while maintaining high electrical currents in the graphene. We were then able to record a specific electrical signature showing irreversible immobilization of antibodies on the graphene surface, thus allowing further optimization of target detection. Employing a combination of microfluidics and real-time electrical measurements, we then investigated the response of the sensors to non-specific interactions with graphene as well as their response to specific antibody-antigen interactions in phosphate buffer solution. Finally, the sensors response to different concentrations of target protein was characterized to assess their performance parameters.

Single-Molecule Electrical Detection: A Promising Route toward the Fundamental Limits of Chemistry and Life Science.

The ultimate limit of analytical chemistry is single-molecule detection, which allows one to visualize the dynamic processes of chemical/biological interactions with single-molecule or single-event sensitivity and hence enables the study of stochastic fluctuations under equilibrium conditions and the observation of time trajectories and reaction pathways of individual species in nonequilibrated systems. In addition, such studies may also allow the direct observation of novel microscopic quantum effects and fundamental discoveries of underlying molecular mechanisms in organic reactions and biological processes that are not accessible in ensemble experiments, thus providing unique opportunities to solve the key problems of physical, chemical, and life sciences. Consequently, the field of single-molecule detection has received considerable attention and has witnessed tremendous advances in different directions in combination with other disciplines. This Account describes our ongoing work on the development of groundbreaking methods (termed "single-molecule electrical approaches") of translating the detailed processes of chemical reactions or biological functions into detectable electrical signals at the single-event level on the platform of single-molecule electronic devices, with a particular focus on graphene-molecule-graphene single-molecule junctions (GMG-SMJs) and silicon-nanowire-based single-molecule electrical nanocircuits. These nanocircuit-based architectures are complementary to conventional optical or mechanical techniques but exhibit obvious advantages such as the absence of problems associated with bleaching and fluorescent labeling. Dash-line lithography (DLL) is an efficient lithographic method of cutting graphene and forming carboxylic-acid-functionalized nanogapped graphene point contact arrays developed to address the formidable challenges of molecular device fabrication difficulty and poor stability. Molecules of interest terminated by amines on both ends can be covalently sandwiched between graphene point contacts to create high-throughput robust GMG-SMJs containing only one molecule as the conductive element. In conjunction with the ease of device fabrication and device stability, this feature distinguishes GMG-SMJs as a new testbed platform for single-molecule analysis characterized by high temporal resolution and superior signal-to-noise ratios. By exploiting the DLL method, we have fabricated molecular devices that are sensitive to external stimuli and are capable of transducing chemical/biochemical events into electrical signals at the single-molecule level, with notable examples including host-guest interaction, hydrogen bond dynamics, DNA intercalation, photoinduced conformational transition, carbocation formation, nucleophilic addition, and stereoelectronic effect. In addition to GMG-SMJs and considering compatibility with the silicon-based industry, we have also developed a reliable method of point-functionalizing silicon-nanowire-based nanotransistors to afford single-molecule electrical nanocircuits. This approach proved to be a robust platform for single-molecule electrical analysis capable of probing fast dynamic processes such as single-protein detection, DNA hybridization/polymorphism, and motor rotation dynamics. The above systematic investigations emphasize the importance and unique advantages of universal single-molecule electrical approaches for realizing direct, label-free, real-time electrical measurements of reaction dynamics with single-event sensitivity. These approaches promise a fascinating mainstream platform to explore the dynamics of stochastic processes in chemical/biological systems as well as gain information in fields ranging from reaction chemistry for elucidating the intrinsic mechanisms to genomics or proteomics for accurate molecular and even point-of-care clinical diagnoses.

Nanocarbon-Based Field-Effect Transistor Biosensors (bioFETs) for Real-Time Detection of DNA Sequences

Field-effect transistor devices based on functionalized nanocarbon materials (2-D graphene thin layers and 1-D carbon nanotubes) are a promising technology for biomolecular sensing applications. In particular, this type of devices allows for label-free detection of DNA hybridization with the advantage of an easy and direct electrical readout in comparison with most routine techniques. In this work, we report on the design and fabrication of nanocarbon-based bioFETs for DNA hybridization detection. Employing a combination of microfluidics and real-time electrical measurements, we investigated the response of bioFETs to single-stranded DNA (ssDNA) probe tethering and hybridization with complementary target ssDNA in saline buffer solution. The bioFETs were assembled from individual carbon nanotubes or graphene nanoribbons connected by pairs of metallic electrodes using photolithography techniques. Transfer curves of bioFETs in saline buffer were measured using an immersed pseudo-reference electrode. We obtained transfer curves showing current modulation with high OFF-current at the charge-neutrality point. Probe and target ssDNA were chosen as 22-nucleotide-long complementary sequences. Probe tethering on nanocarbon was obtained using diazonium chemistry followed by EDC/NHS coupling of an amine moiety placed at the extremity of the DNA probe [1]. Transfer characteristics were measured before/after probe and target injection. Moreover, to further characterize the bioFETs response, probe immobilization and probe-target hybridization were recorded in real-time using electrical readout. The development of highly selective and ultra-sensitive sensors for DNA will open novel technological avenues to improve the detection of genetic biomarkers for various diseases. [1] Bouilly, D. et al. Nano Letters 16, 4679–4685 (2016)

Ultrathin Alumina Membranes as Scaffold for Epithelial Cell Culture from the Intestine of Rainbow Trout.

Permeable membranes are indispensable for in vitro epithelial barrier models. However, currently available polymer-based membranes are low in porosity and relatively thick, resulting in a limited permeability and unrealistic culture conditions. In this study, we developed an ultrathin, nanoporous alumina membrane as novel cell culture interface for vertebrate cells, with focus on the rainbow trout (Onchorynchus mykiss) intestinal cell line RTgutGC. The new type of membrane is framed in a silicon chip for physical support and has a thickness of only 1 μm, with a porosity of 15% and homogeneous nanopores (Ø = 73 ± 21 nm). Permeability rates for small molecules, namely lucifer yellow, dextran 40, and bovine serum albumin, exceeded those of standard polyethylene terephthalate (PET) membranes by up to 27 fold. With the final goal to establish a representative model of the fish intestine for environmental toxicology, we engineered a simple culture setup, capable of testing the cellular response toward chemical exposure. Herein, cells were cultured in a monolayer on the alumina membranes and formed a polarized epithelium with apical expression of the tight junction protein ZO-1 within 14 days. Impedance spectroscopy, a noninvasive and real time electrical measurement, was used to determine cellular resistance during epithelial layer formation and chemical exposure to evaluate barrier functionality. Resistance values during epithelial development revealed different stages of epithelial maturity and were comparable with the in vivo situation. During chemical exposure, cellular resistance changed immediately when barrier tightness or cell viability was affected. Thus, our study demonstrates nanoporous alumina membranes as promising novel interface for alternative in vitro approaches, capable of allowing cell culture in a physiologically realistic manner and enabling high quality microscopy and sensitive measurement of cellular resistance.

Characterization of intrinsic hysteresis of pentacene-based organic thin-film transistor through in-situ real-time electrical measurement

The intrinsic hysteresis of a pentacene-based organic thin-film transistor was characterized through home-designed in-situ real-time electrical measurement. The device exhibited intrinsic hysteresis after the device fabrication without breaking the vacuum, which has not been observed previously. Similar behavior was observed when introducing the nitrogen gas. Compared with the measurement condition of vacuum or nitrogen gas, exposure to the ambient air resulted in a severe hysteresis. It was attributed to both the acceptor-like traps at the organic/dielectric interface and the donor-like traps in the transport channel. When the chamber was vacuumed out again, a significantly reduced hysteresis was obtained almost the same as that measured just after device fabrication, indicating the reversibility of the extrinsic hysteresis. We also related the hysteresis to the morphological change under different deposition rates of pentacene. The smoother surface at higher deposition rate caused reduced hysteresis because of the elimination of vacancies near the pentacene/dielectric interface.

Strain rate-dependent tensile properties and dynamic electromechanical response of carbon nanotube fibers

This investigation into the rate-dependent tensile behavior of carbon nanotube (CNT) fibers provides insight into the role of strain rate and specimen gage length on tensile strength. Chemical vapor produced CNT continuous fibers made of single and dual wall CNTs are evaluated and the potential for fiber improvement by post-process stretching to improve alignment is explored. Post-processed CNT fibers exhibit significantly higher strengths (3–5GPa) and moduli (80–200GPa) than untreated fibers. During dynamic tension evaluation, real-time electrical measurements provide correlations between high rate deformation/damage mechanical behavior and electrical resistance of the fiber specimens. Furthermore, this first look into the dynamic tensile behavior of CNT fibers demonstrates their potential to serve as sensors in high rate applications.

Real-time electrical measurement of L929 cellular spontaneous and synchronous oscillation.

Nonexcitable cell types, fibroblasts of heart muscle or astrocytes, are well known for their spontaneous Ca2+ oscillations. On the other hand, murine fibroblast (L929) cells are known to be deficient in cell–cell adhesive proteins and therefore lack gap junctions for cellular communication. However, these cells exhibit a unique property of collectively synchronized and spontaneous oscillation, as revealed by real-time monitoring of cells cultured on a 250-μm diameter microelectrode for more than 3 days using an electrical cell-substrate impedance-sensing system (ECIS). Live-cell imaging is a widely used technique for oscillation detection, but it has limitations relating to cellular physiological environment maintenance for microscopic analysis and for prolonged periods of study. The present research emphasizes an electrical-sensing technique (ECIS) capable of overcoming the most important issues inherent in live-cell imaging systems for the detection of L929 cellular spontaneous and synchronized oscillation in real-time for longer periods. Possible mechanisms involved in L929 oscillation were elucidated to be periodic extension/contraction of lamellipodia continued as blebbing, which is produced by signals from the actomyosin complex initiated by connexin hemichannel opening and adenosine triphosphate (ATP) release. By applying the connexin hemichannel inhibitor, flufenamic acid, the hindrance of ATP release and calcium transients were analyzed to elucidate this hypothesis.