Nanoelectrode Arrays Research Articles

Dielectrophoretic capture of Escherichia coli and boar sperms using ULSI-fabricated three-dimensional protruding TiN nano-electrode arrays.

In recent years, dielectrophoresis has become widely recognized as a highly suitable method for creating good tools for particle separation, with significant successes achieved in a variety of areas. Expanding upon this, we adopted a semiconductor CMOS process, instead of a MEMS process, which allowed for the following: 1) wire insulation to mitigate Joule heat and prevent thermal fluctuation interference with the dielectrophoretic force; 2) isolation of harmful materials from biological samples, making the chip biocompatible; and, 3) the ability to employ nano-electrodes capable of generating a stronger electric field than conventional electrodes, thus allowing chip capture at lower voltages. Additionally, our chip is scalable, enabling multiplied throughput based on sample processing requirements. These features make our chip more widely applicable and suitable for capturing bacteria and sperm. In this study, we focused on optimizing the parameters of dielectrophoresis and employed 3-D protruding TiN nano-electrode arrays to facilitate the capture of Escherichia coli and boar sperms. The experimental data demonstrates that the capture efficiency of this chip for E. coli was approximately 79.25% ± 2.66%, and the highest capture efficiency for sperms was approximately 39.2% ± 3.9%.

Closed Bipolar Nanoelectrode Array for Ultra-Sensitive Detection of Alkaline Phosphatase and Two-Dimensional Imaging of Epidermal Growth Factor Receptors.

The combination of closed bipolar electrodes (cBPE) with electrochemiluminescence (ECL) imaging has demonstrated remarkable capabilities in the field of bioanalysis. Here, we established a cBPE-ECL platform for ultrasensitive detection of alkaline phosphatase (ALP) and two-dimensional imaging of epidermal growth factor receptor (EGFR). This cBPE-ECL system consists of a high-density gold nanowire array in anodic aluminum oxide (AAO) membrane as the cBPE coupled with ECL of highly luminescent cadmium selenide quantum dots (CdSe QDs) luminophores to achieve cathodic electro-optical conversion. When an enzyme-catalyzed amplification effect of ALP with 4-aminophenyl phosphate monosodium salt hydrate (p-APP) as the substrate and 4-aminophenol (p-AP) as the electroactive probe is introduced, a significant improvement of sensing sensitivity with a detection limit as low as 0.5 fM for ALP on the cBPE-ECL platform can be obtained. In addition, the cBPE-ECL sensing system can also be used to detect cancer cells with an impressive detection limit of 50 cells/mL by labeling ALP onto the EGFR protein on A431 human epidermal cancer cell membranes. Thus, two-dimensional (2D) imaging of the EGFR proteins on the cell surface can be achieved, demonstrating that the established cBPE-ECL sensing system is of high resolution for spatiotemporal cell imaging.

Probe Beam Deflection study of Au Nanoparticles Supported into TiO2 Mesoporous Films

Mesoporous thin films modified with nanoparticles of metal (Au) have been used for the fabrication of an ultra‐microelectrode array (UMEA). For the first time, UMEAs were studied using probe beam deflection (PBD) and cyclic voltammetry. The study was carried out using the [Fe(CN)6]3‐/ [Fe(CN)6]4‐ couple as a redox probe. The electrochemical response is that of an array of nanoelectrodes. The effects of scan rate on the current and PBD signal profiles are discussed in the context of mass transport within the pores and at the solution‐electrode interface. The study suggests that the combination of PBD and CV allows a better understanding on the mass transport phenomena in this type of UMEAs of complex architecture.

Development of an electrochemical biosensor with TiN nano-electrode arrays for IL-6 detection

In this study, we developed a novel electrochemical biosensor for detecting IL-6 that uses a nano-electrode array (NEA) fabricated via standard CMOS processing. Miniaturizing the electrodes to the nanoscale and arranging them in an array to form an NEA facilitated the creation of a higher electric field magnitude, compared to that available via the use of microelectrodes, that could be used to improve biosensor sensitivity. Additionally, the array configuration of the NEA aided in providing sufficient reaction sites. Each nano-electrode in the NEA was cylindrically shaped, with a radius of 0.1 µm, and a top layer formed by TiN physical vapor deposition. Each NEA biosensor was divided into four independent banks, with each bank including a set of WE, CE and RE. These banks were capable of independently inputting and outputting electrical signals. This design allowed the NEA biosensor to undergo selective modification by CV input. In this study, we discuss and address material and contamination issues associated with CMOS-produced NEAs and their uses as biosensors. To ameliorate these issues, we stored materials and products in a nitrogen-controlled cabinet and conducted pretreatment cleaning on the electrodes. Both steps had a noticeable impact on the cleanliness of the electrode surfaces. These optimized conditions resulted in a remarkable 96.6 % reduction in Rct. The NEA surface was functionalized by electrochemically grafting diazonium salts subsequently immobilized with anti-IL-6 antibodies via EDC/NHS chemistry. The resulting NEA biosensor demonstrated sufficient sensitivity to rapidly distinguish inflammatory conditions and disease severity. This showcases the potential for using NEA devices mass-produced via standard CMOS processing as electrodes for biosensors.

High-Throughput Single-Entity Electrochemistry with Microelectrode Arrays.

We describe micro- and nanoelectrode array analysis with an automated version of the array microcell method (AMCM). Characterization of hundreds of electrodes, with diameters ranging from 100 nm to 2 μm, was carried out by using AMCM voltammetry and chronoamperometry. The influence of solvent evaporation on mass transport in the AMCM pipette and the resultant electrochemical response were investigated, with experimental results supported by finite element method simulations. We also describe the application of AMCM to high-throughput single-entity electrochemistry in measurements of stochastic nanoparticle impacts. Collision experiments recorded 3270 single-particle events from 671 electrodes. Data collection parameters were optimized to enable these experiments to be completed in a few hours, and the collision transient sizes were analyzed with a U-Net deep learning model. Elucidation of collision transient sizes by histograms from these experiments was enhanced due to the large sample size possible with AMCM.

A Bifunctional Wearable Sensor Based on a Nanoporous Membrane for Simultaneous Detection of Sweat Lactate and Temperature.

Wearable sensors for non-invasive, real-time detection of sweat lactate have far-reaching implications in the fields of health care and exercise physiological responses. Here, we propose a wearable electrochemical sensor with gold nanoelectrode arrays fabricated on the nanoporous polycarbonate (PC) membrane by encapsulating lactate oxidase (LOx) in chitosan (CS) hydrogel for detecting body temperature and sweat lactate concurrently. Flexible gold nanoporous electrodes not only enhance electrode area but also offer a nanoconfined space to accelerate the catalytic reaction of LOx and control substrate concentration on the surface of LOx to decrease substrate inhibition. The proposed sensor has a long durability of 13 days and better selectivity for the detection of sweat lactate over a wide linear range (0.01-35 mM) with a low detection limit (0.144 μM). Furthermore, temperature-dependent transmembrane currents passing through the sensor are used to estimate body temperature. We then use multiple linear regression to adjust the effect of temperature on lactate detection and succeed in monitoring lactate molecules in sweat and body temperature during exercise.

Microelectrode Set Made of Carbon Nanotubes for the Detection of Biomolecules and Neurotransmitters

Electrode miniaturization is an alternative path for the development of sensitive electrochemical sensors. The low charging current, enhanced mass transport and their suitability to be employed in resistive mediums has made microelectrodes attractive for detection of biomolecules. Carbon nanotubes (CNTs) are unique nanomaterials with high electrical conductivity and mechanical strength. They are known for their chemical stability and the ability to assemble them into nano and microelectrodes makes them an appealing alternative electrode material compared to metals. This talk will report the fabrication of an electrochemical-set that has CNT microelectrode assemblies as working, reference, and counter electrode components and have been tested for the detection of heavy metals (Pb2+), neurotransmitters (dopamine), and other biomolecules (nicotinamide adenine dinucleotide (NADH), furosemide). Limits of detection of 0.5 nM for dopamine, 18 nM for NADH, 2 nM for Furosemide, and 0.4 ppt for Pb2+ have been achieved. Different voltammetric techniques were employed during the study: cyclic voltammetry (CV), square wave voltammetry (SWV), amperometry, and square wave anodic stripping voltammetry (SWASV). The robustness of the electrodes and the simplicity of its fabrication have been demonstrated. Furthermore, a simple method for the fabrication nanoelectrode arrays that can be employed as working electrodes will be presented. The background and key components that are considered important to achieve this performance will be reported.

Elevating intracellular action potential recording in cardiomyocytes: A precision-enhanced and biosafe single-pulse electroporation system

Action potentials play a pivotal role in diverse cardiovascular physiological mechanisms. A comprehensive understanding of these intricate mechanisms necessitates a high-fidelity intracellular electrophysiological investigative approach. The amalgamation of micro-/nano-electrode arrays and electroporation confers substantial advantages in terms of high-resolution intracellular recording capabilities. Nonetheless, electroporation systems typically lack precise control, and commonly employed electroporation modes, involving tailored sequences, may escalate cellular damage and perturbation of normal physiological functions due to the multiple or higher-intensity electrical pulses. In this study, we developed an innovative electrophysiological biosensing system customized to facilitate precise single-pulse electroporation. This advancement serves to achieve optimal and uninterrupted intracellular action potential recording within cardiomyocytes. The refinement of the single-pulse electroporation technique is realized through the integration of the electroporation and assessment biosensing system, thereby ensuring a consistent and reliable means of achieving stable intracellular access. Our investigation has unveiled that the optimized single-pulse electroporation technique not only maintains robust biosafety standards but also enables the continuous capture of intracellular electrophysiological signals across an expansive three-day period. The universality of this biosensing system, adaptable to various micro/nano devices, furnishes real-time analysis and feedback concerning electroporation efficacy, guaranteeing the sustained, secure, and high-fidelity acquisition of intracellular data, thereby propelling the field of cardiovascular electrophysiological research.

Crater-like nanoelectrode arrays for electrochemical detection of dopamine release from neuronal cells

Stem cell therapy has shown great potential in treating various incurable diseases using conventional chemotherapy. Parkinson’s disease (PD)—a neurodegenerative disease—has been reported to be caused by quantitative loss or abnormal functionality of dopaminergic neurons (DAnergic neurons). To date, stem cell therapies have shown some potential in treating PD through ex vivo engraftment of stem-cell-derived neurons. However, accurately identifying the differentiation and non-invasively evaluating the functionality and maturity of DAnergic neurons are formidable challenges in stem cell therapies. These strategies are important in enhancing the efficacy of stem cell therapies. In this study, we report a novel cell cultivation platform, that is, a nanocrater-like electrochemical nanoelectrode array (NCENA) for monitoring dopamine (DA) release from neurons to detect exocytotic DA release from DAnergic neurons. In particular, the developed NCENA has a nanostructure in which three-dimensional porous gold nanopillars are uniformly arranged on conductive electrodes. The developed NCENA exhibited great DA sensing capabilities with a linear range of 0.39–150 μM and a limit of detection of 1.16 μM. Furthermore, the nanotopographical cues provided by the NCENA are suitable for cell cultivation with enhanced cellular adhesion. Finally, we successfully analysed the functionality and maturity of differentiated neurons on the NCENA through its excellent sensing ability for exocytotic DA.

Machine learning and data augmentation methods for multispectral capacitance images of nanoparticles with nanoelectrodes array biosensors

A large number of technology applications still remain where Artificial Intelligence techniques, carefully tailored to the specific application needs, could provide performance benefits to hardware technologies. One such area is biosensing with innovative complementary-metal–oxide–semiconductor nanocapacitor arrays. These sensors operate as powerful imaging platforms but, despite the advancements in the field, the knowledge necessary for precise and robust interpretation of their response to analytes is still largely lacking.In this work, we leverage the ability of Machine Learning methods for computer vision to construct precise and robust models in different operation scenarios. By recognizing the similarity between multifrequency capacitance maps and multispectral images, we identified optimal Machine Learning algorithms to accurately estimate the size of analytes measured by the nanoelectrode array biosensor.As a relevant case study, we focus on measurements of the radius of dielectric spherical nano-particles dispersed in deionized water and phosphate buffer saline. The performance of large, established image-processing neural networks is compared to that of less complex, purposely developed ones. Sizable training data sets are generated by accurate finite element simulations of the sensor response combined with measured data. An excellent accuracy, comparable to traditional sizing technology, is achieved for the task of providing a quantitative measure of the nano-particle radius when the latter is comparable to the pitch of the pixels in the array. We report a size median error below 15% in all scenarios when a few percent of measured data samples is added to the simulation-based training data set.

Toward Continuous Nano-Plastic Monitoring in Water by High Frequency Impedance Measurement With Nano-Electrode Arrays

Toward Continuous Nano-Plastic Monitoring in Water by High Frequency Impedance Measurement With Nano-Electrode Arrays

A miniaturized organic photoelectrochemical transistor aptasensor based on nanorod arrays toward high-sensitive T-2 toxin detection in milk samples

Detection of T-2 toxin is of great significance to environment and human health, as T-2 toxin is one of the main toxins that contaminate crops, stored grain and other food. Herein, a zero-gate-bias organic photoelectrochemical transistor (OPECT) sensor was proposed based on nanoelectrode arrays as gate photoactive materials which can result in the accumulation of photovoltage and preferable capacitance leading to better sensitivity of the OPECT. For comparison, the channel current of OPECT was 100 times higher than photocurrent of conventional photoelectrochemical (PEC) attributing to remarkable signal amplification of OPECT. It was also found that the detection limit of OPECT aptasensor was as low as 28.8 pg/L, lower than 0.34 ng/L of the conventional PEC method, further indicating the advantage of the OPECT devices in T-2 toxin determination. This research has been successfully applied in real sample detection which provided a general platform of OPECT for food safety analysis.

Catalytic activity of glucose oxidase after dielectrophoretic immobilization on nanoelectrodes.

Dielectrophoresis (DEP) is an AC electrokinetic effect that is proven to be effective for the immobilization of not only cells, but also of macromolecules, e.g., antibodies and enzyme molecules. In our previous work, we have already demonstrated the high catalytic activity of immobilized horseradish peroxidase after DEP. To evaluate the suitability of the immobilization method for sensing or research in general, we want to test it for other enzymes, too. In this study, glucose oxidase (GOX) from Aspergillus niger was immobilized on TiN nanoelectrode arrays by DEP. Fluorescence microscopy showed the intrinsic fluorescence of the immobilized enzymes flavin cofactor on the electrodes. The catalytic activity of immobilized GOX was detectable, but a fraction of less than 1.3% of the maximum activity that was expected for a full monolayer of immobilized enzymes on all electrodes was stable for multiple measurement cycles. Therefore, the effect of DEP immobilization on the catalytic activity strongly depends on the used enzyme. This article is protected by copyright. All rights reserved.

Plasma-Assisted Atomic Layer Deposition of IrO2 for Neuroelectronics

In vitro and in vivo stimulation and recording of neuron action potential is currently achieved with microelectrode arrays, either in planar or 3D geometries, adopting different materials and strategies. IrO2 is a conductive oxide known for its excellent biocompatibility, good adhesion on different substrates, and charge injection capabilities higher than noble metals. Atomic layer deposition (ALD) allows excellent conformal growth, which can be exploited on 3D nanoelectrode arrays. In this work, we disclose the growth of nanocrystalline rutile IrO2 at T = 150 °C adopting a new plasma-assisted ALD (PA-ALD) process. The morphological, structural, physical, chemical, and electrochemical properties of the IrO2 thin films are reported. To the best of our knowledge, the electrochemical characterization of the electrode/electrolyte interface in terms of charge injection capacity, charge storage capacity, and double-layer capacitance for IrO2 grown by PA-ALD was not reported yet. IrO2 grown on PtSi reveals a double-layer capacitance (Cdl) above 300 µF∙cm-2, and a charge injection capacity of 0.22 ± 0.01 mC∙cm-2 for an electrode of 1.0 cm2, confirming IrO2 grown by PA-ALD as an excellent material for neuroelectronic applications.

Nanoimprinted arrays of glassy carbon nanoelectrodes for improved electrochemistry of enzymatic redox-mediators

In the present study, the preparation and electrochemical application of perfectly ordered arrays of glassy carbon nanoelectrodes (GC-NEAs) is presented. After careful morphological characterization, we examined the voltammetric behaviour on GC-NEAs of some redox mediators commonly used in enzymatic electrochemical biosensors. GC-NEAs were fabricated by using nanoimprint lithography to generate ordered arrays of nanoholes, with average radius of 145 nm, onto a polycarbonate thin film deposited on a glassy carbon plate. The redox mediators examined were (ferrocenylmethyl)trimethylammonium (FA+) as typical redox mediator for oxidase enzymes and Azure A and B as examples of mediators used for reductase enzymes. The voltammetric signals recorded indicate that the here prepared GC-NEAs operate under total overlap diffusion conditions, with an accessible potential window significantly wider than the one typical of arrays of gold nanoelectrodes. Interestingly, the electrochemical behaviour of the GC-NEAs perfectly fits with what expected on the basis of the geometrical features of the array demonstrating the role of these parameters in ruling the contribution of capacitive and faradic currents of the array which reflect in improved detection capabilities.

Low-density Pt nanoarray-based hydrogen peroxide sensing platform and its application in trace sarcosine detection

Hydrogen peroxide (H2O2) is an important signaling molecule that regulates many biological processes. It is of great value to realize rapid, accurate, highly sensitive and low-cost H2O2 detection in the immediate detection of trace disease markers. Low-density nanoelectrode arrays have a high signal-to-noise ratio and are advantageous for trace detection. In this paper, low-density Pt nanoelectrode arrays were successfully prepared by a simple method of ion sputtering combined with electrodeposition based on a track-etched polycarbonate membrane template. The arrays had a detection limit as low as 0.03 μM for H2O2 at a constant potential, a sensitivity of 125.9 μA mM−1, and a linear range spanning nearly four orders of magnitude (0.1–655 μM). The developed sarcosine sensors based on these arrays had a very low detection limit (0.08 μM) and wide linear range (0.5–64.5 μM) for the rapid detection of trace amounts of sarcosine in serum. With a wide linear range and low detection limits, this hydrogen peroxide sensing platform has great potential for use in the rapid electrochemical detection of trace substances.

Scalable and Robust Hollow Nanopillar Electrode for Enhanced Intracellular Action Potential Recording.

Electrophysiology is a unique biomarker of the electrogenic cells that can perform a disease investigation or drug assessment. In the recent decade, vertical nanoelectrode arrays can successfully achieve a high-quality intracellular electrophysiological study in electrogenic cells and their networks. However, a high success rate and high-quality and long-term intracellular recording using low-cost nanostructures is still a considerable challenge. Herein, we develop a scalable and robust hollow nanopillar electrode to achieve enhanced intracellular recording of cardiomyocytes. The template-based synthesis of vertical hollow nanopillars is compatible with large-scale and efficient microfabrication processes and is convenient to regulate the geometry of hollow nanopillars. Compared with the conventional same-size planar electrode, the regulating height of a hollow nanopillar can achieve high-quality and prolonged intracellular recordings, which can improve the cell-electrode interface for tight coupling and effective electroporation. It is demonstrated that the geometry regulation of a nanostructure is a powerful strategy to enhance intracellular recording.

Electro-Sorption of Hydrogen by Platinum, Palladium and Bimetallic Pt-Pd Nanoelectrode Arrays Synthesized by Pulsed Laser Ablation.

Sustainable and renewable production of hydrogen by water electrolysers is expected to be one of the most promising methods to satisfy the ever-growing demand for renewable energy production and storage. Hydrogen evolution reaction in alkaline electrolyte is still challenging due to its slow kinetic properties. This study proposes new nanoelectrode arrays for high Faradaic efficiency of the electro-sorption reaction of hydrogen in an alkaline electrolyte. A comparative study of the nanoelectrode arrays, consisting of platinum or palladium or bimetallic nanoparticles (NPs) Pt80Pd20 (wt.%), obtained by nanosecond pulsed laser ablation in aqueous environment, casted onto graphene paper, is proposed. The effects of thin films of perfluoro-sulfonic ionomer on the material morphology, nanoparticles dispersion, and electrochemical performance have been investigated. The NPs-GP systems have been characterized by field emission scanning electron microscopy, Rutherford backscattering spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, cyclic voltammetry, and galvanostatic charge-discharge cycles. Faradaic efficiency up to 86.6% and hydrogen storage capacity up to 6 wt.% have been obtained by the Pt-ionomer and Pd/Pt80Pd20 systems, respectively.

High-density individually addressable platinum nanoelectrodes for biomedical applications

3-D vertical nanoelectrode arrays (NEAs) have found applications in several biomedical and sensing applications, including high-resolution neuronal excitation and measurement and single-molecule electrochemical biosensing. There have been several reports on high-density nanoelectrodes in recent years, with the filling ratio of electrodes reaching close to 0.002 (assuming the electrode diameter of 200 nm and pitch of 4 μm). Still, it is well below the nanowire filling ratio required to form interconnected neuronal networks, i.e., more than 0.14 (assuming the electrode diameter of 200 nm and pitch of 1.5 μm). Here, we employ a multi-step, large-area electron beam lithography procedure along with a targeted, focused ion beam based metal deposition technique to realize an individually addressable, 60-channel nanoelectrode chip with a filling ratio as high as 0.16, which is well within the limit required for the formation of interconnected neuronal networks. Moreover, we have designed the NEA chip to be compatible with the commercially available MEA2100-System, which can, in the future, enable the chip to be readily used for obtaining data from individual electrodes. We also perform an in-depth electrochemical impedance spectroscopy characterization to show that the electrochemical behavior and the charge transfer mechanism in the array are significantly influenced by changing the thickness of the SU-8 planarization layer (i.e., the thickness of the exposed platinum surface). In addition to neural signal excitation and measurement, we propose that these NEA chips have the potential for other future applications, such as high-resolution single-molecule level electrochemical and bio-analyte sensing.

AC electrokinetic immobilization of influenza virus.

The use of alternating current (AC) electrokinetic forces, like dielectrophoresis and AC electroosmosis, as a simple and fast method to immobilize sub-micrometer objects onto nanoelectrode arrays is presented. Due to its medical relevance, the influenza virus is chosen as a model organism. One of the outstanding features is that the immobilization of viral material to the electrodes can be achieved permanently, allowing subsequent handling independently from the electrical setup. Thus, by using merely electric fields, we demonstrate that the need of prior chemical surface modification could become obsolete. The accumulation of viral material over time is observed by fluorescence microscopy. The influences of side effects like electrothermal fluid flow, causing a fluid motion above the electrodes and causing an intensity gradient within the electrode array, are discussed. Due to the improved resolution by combining fluorescence microscopy with deconvolution, it is shown that the viral material is mainly drawn to the electrode edge and to a lesser extent to the electrode surface. Finally, areas of application for this functionalization technique are presented.