Tungsten Microwires Research Articles

Selective Detection of Escherichia coli K12 and Staphylococcus aureus in Mixed Bacterial Communities Using a Single-Walled Carbon Nanotube (SWCNT)-Functionalized Electrochemical Immunosensor with Dielectrophoretic Concentration

An electrochemical immunosensor has been developed for the rapid detection and identification of potentially harmful bacteria in food and environmental samples. This study aimed to fabricate a microwire-based electrochemical immunosensor (MEI sensor) for selective detection of Escherichia coli and Staphylococcus aureus in microbial cocktail samples using dielectrophoresis (DEP)-based cell concentration. A gold-coated tungsten microwire was functionalized by coating polyethylenimine, single-walled carbon nanotube (SWCNT) suspension, streptavidin, biotinylated antibodies, and then bovine serum albumin (BSA) solutions. Double-layered SWCNTs and 5% BSA solution were found to be optimized for enhanced signal enhancement and nonspecific binding barrier. The selective capture of E. coli K12 or S. aureus cells was achieved when the electric field in the bacterial sample solution was generated at a frequency of 3 MHz and 20 Vpp. A linear trend of the change in the electron transfer resistance was observed as E. coli concentrations increased from 5.32 × 102 to 1.30 × 108 CFU/mL (R2 = 0.976). The S. aureus MEI sensor fabricated with the anti-S. aureus antibodies also showed an increase in resistance with concentrations of S. aureus (8.90 × 102-3.45 × 107 CFU/mL) with a correlation of R2 = 0.983. Salmonella typhimurium and Listeria monocytogenes were used to evaluate the specificity of the MEI sensors. The functionalization process developed for the MEI sensor is expected to contribute to the sensitive and selective detection of other harmful microorganisms in food and environmental industries.

Electrodeposition of PEDOT:ClO4 on non-noble tungsten microwire for nerve and brain recordings

A novel simple and inexpensive methodology based on electrodeposition of PEDOT is presented to improve the properties of tungsten microwires, making them a safe and accessible tool in electrophysiology studies.

Enhanced tensile ductility of tungsten microwires via high-density dislocations and reduced grain boundaries

• W microwires with designed microstructure were microfabricated under EBSD guidance. • High-density dislocations were introduced in W with reduced grain boundaries. • Ultrahigh strength and ductility were achieved in engineered W microwires. • The motion of pre-existing high-density dislocations produces high ductility of W. Despite being strong with many outstanding physical properties, tungsten is inherently brittle at room temperature, restricting its structural and functional applications at small scales. Here, a facile strategy has been adopted, to introduce high-density dislocations while reducing grain boundaries, through electron backscatter diffraction (EBSD)-guided microfabrication of cold-drawn bulk tungsten wires. The designed tungsten microwire attains an ultralarge uniform tensile elongation of ~10.6%, while retains a high yield strength of ~2.4 GPa. in situ TEM tensile testing reveals that the large uniform elongation of tungsten microwires originates from the motion of pre-existing high-density dislocations, while the subsequent ductile fracture is attributed to crack-tip plasticity and the inhibition of grain boundary cracking. This work demonstrates the application potential of tungsten microcomponents with superior ductility and workability for micro/nanoscale mechanical, electronic, and energy systems.

PHAIR: a biosensor for pH measurement in air\u2013liquid interface cell culture

In many biological systems, pH can be used as a parameter to understand and study cell dynamics. However, measuring pH in live cell culture is limited by the sensor ion specificity, proximity to the cell surface, and scalability. Commercially available pH sensors are difficult to integrate into a small-scale cell culture system due to their size and are not cost-effective for disposable use. We made PHAIR—a new pH sensor that uses a micro-wire format to measure pH in vitro human airway cell culture. Tungsten micro-wires were used as the working electrodes, and silver micro-wires with a silver/silver chloride coating were used as a pseudo reference electrode. pH sensitivity, in a wide and narrow range, and stability of these sensors were tested in common standard buffer solutions as well as in culture media of human airway epithelial cells grown at the air–liquid interface in a 24 well cell culture plate. When measuring the pH of cells grown under basal and challenge conditions using PHAIR, cell viability and cytokine responses were not affected. Our results confirm that micro-wire-based sensors have the capacity for miniaturization and detection of diverse ions while maintaining sensitivity. This suggests the broad application of PHAIR in various biological experimental settings.

Direct growth of single crystalline ReO3 nanorods on a tungsten (W) microwire for enhanced electron-transfer reaction kinetics

We report the direct growth of highly single crystalline rhenium trioxide (ReO3) nanorods on a tungsten (W) microwire electrode via the physical vapor transport process without any catalyst. In our growth mode, ReO3 nanocubes were initially formed on the surface of a tungsten (W) microwire electrode and further they were anisotropically grown along the [001] crystallographic direction. Furthermore, we performed the fundamental electrochemical experiments so that from cyclic voltammetric measurements, ReO3 nanorods on a W microwire exhibit a good capacitance and Nernstian behavior for a Fe(CN)63−/Fe(CN)64− redox couple in 1 M KNO3 aqueous solution, indicating a promising electrode material for electrochemical applications.

Lactic Acid Biosensor Based on Lactate Dehydrogenase Immobilized on Au Nanoparticle Modified Microwire Electrode

Lactate, a key metabolite of the anerobic metabolic pathway serves as a biomarker for lactic acidosis in clinical diagnostics. A variety of electrochemical biosensors have been exploited for the determination of lactate. Here we describe an improved electrochemical lactic acid biosensor that utilizes self-assembled monolayers (SAMs) of cysteamine-modified gold nanoparticles (AuNPs) on flexible tungsten microwire electrode to immobilize lactate dehydrogenase (LDH) to the microwire electrode. The fabricated AuNP-cysteamine-LDH electrode showed excellent behavior towards lactic acid at pH 6 and at 35 °C at an applied potential of +0.4 V (vs Ag/AgCl reference electrode). The biosensor exhibited a linear dynamic range of $500~\mu \text{M}$ to 7 mM with a very high sensitivity of $31.40~\mu \text{A}$ /mM cm2. The biosensor demonstrated good selectivity towards lactic acid, wherein a nafion layer was utilized to screen out interfering species. The AuNP-cysteamine-LDH electrode remained stable up to 18 days. The practicality of the AuNP-cysteamine-LDH electrode was assessed by determining lactic acid concentrations in sera and a sensitivity of $73.16~\mu \text{A}$ / mM cm2 was observed up to 5 mM.

Micro-Slit Cutting in an Aluminum Foil Using an Un-Traveling Tungsten Wire

Microslit cutting in aluminum foils is considered to be difficult as aluminum foils have low hardness and deformability. In this study, a novel cutting method is proposed where a tungsten microwire is utilized as the tool to cut aluminum foil without tool traveling or spinning. A statics simulation is first performed to analyze the cutting mechanism. Further, a tungsten wire with a diameter of 50 μm is utilized as the tool and a series of experiments are carried to discuss how the feeding rate influences slit width and roughness. With optimal parameters, it takes only 100 s to fabricate a 5 mm long microslit with an average width of 48.75 μm, width standard deviation of 1.48 μm, and surface roughness of 0.110 μm when applying initial/secondary velocity of 50/50 μm·s−1.

Parallel, minimally-invasive implantation of ultra-flexible neural electrode arrays

Objective. Implanted microelectrodes provide a unique means to directly interface with the nervous system but have been limited by the lack of stable functionality. There is growing evidence suggesting that substantially reducing the mechanical rigidity of neural electrodes promotes tissue compatibility and improves their recording stability in both the short- and long-term. However, the miniaturized dimensions and ultraflexibility desired for mitigating tissue responses preclude the probe’s self-supported penetration into the brain tissue. Approach. Here we demonstrate the high-throughput implantation of multi-shank ultraflexible neural electrode arrays with surgical footprints as small as 200 µm2 in a mouse model. This is achieved by using arrays of tungsten microwires as shuttle devices, and bio-dissolvable adhesive polyethylene glycol (PEG) to temporarily attach a shank onto each microwire. Main results. We show the ability to simultaneously deliver electrode arrays in designed patterns, to adjust the implantation locations of the shanks by need, to target different brain structures, and to control the surgical injury by reducing the microwire diameters to cellular scale. Significance. These results provide a facile implantation method to apply ultraflexible neural probes in scalable neural recording.

Towards a dual in-line electrochemical biosensor for the determination of glucose and hydrogen peroxide

Herein, we report the development of a sensitive and selective dual mode electrochemical platform for the detection of glucose and H2O2. The platform is based on tungsten and gold microwire electrodes decorated with gold nanoparticles (AuNPs) and colloidal platinum (colloidal-Pt), respectively. The nanostructured AuNPs electrode was used as a support matrix for the immobilization of horseradish peroxidase (HRP) and the colloidal-Pt served as the non-enzymatic glucose biosensor in the construction of a dual in-line electrochemical biosensor that provides a microenvironment for HRP and a pathway for analyte diffusion via the high surface area. The dual-mode approach allows for the simultaneous detection of glucose and H2O2. The glucose biosensor exhibited a dynamic linear range of 0.5 mM to 8 mM glucose. Linearity for H2O2 was up to 70 μM. Operational stability resulted in 75% of the initial biosensor response after 27 days. The dual in-line biosensor showed good sensitivity of 0.403 mA mM−1 cm−2 for glucose and 0.193 mA mM−1 cm−2 for H2O2 in addition to good anti-interference ability. Thus, the low-cost and simple dual in-line biosensor can be used for the real-time detection of glucose and H2O2 in the clinical, biological and environmental fields.

A high-density carbon fiber neural recording array technology

Objective. Microwire and Utah-style neural recording arrays are the predominant devices used for cortical neural recording, but the implanted electrodes cause a significant adverse biological response and suffer from well-studied performance degradation. Recent work has demonstrated that carbon fiber electrodes do not elicit this same adverse response, but these existing designs are not practically scalable to hundreds or thousands of recording sites. We present technology that overcomes these issues while additionally providing fine electrode pitch for spatial oversampling. Approach. We present a 32-channel carbon fiber monofilament-based intracortical neural recording array fabricated through a combination of bulk silicon microfabrication processing and microassembly. This device represents the first truly two-dimensional carbon fiber neural recording array. The density, channel count, and size scale of this array are enabled by an out-of-plane microassembly technique in which individual fibers are inserted through metallized and isotropically conductive adhesive-filled holes in an oxide-passivated microfabricated silicon substrate. Main results. Five-micron diameter fibers are spaced at a pitch of 38 microns, four times denser than state of the art one-dimensional arrays. The fine diameter of the carbon fibers affords both minimal cross-section and nearly three orders of magnitude greater lateral compliance than standard tungsten microwires. Typical impedances are on the order of hundreds of kiloohms, and successful in vivo recording is demonstrated in the motor cortex of a rat. 22 total units are recorded on 20 channels, with unit SNR ranging from 1.4 to 8.0. Significance. This is the highest density microwire-style electrode array to date, and this fabrication technique is scalable to a larger number of electrodes and allows for the potential future integration of microelectronics. Large-scale carbon fiber neural recording arrays are a promising technology for reducing the inflammatory response and increasing the information density, particularly in neural recording applications where microwire arrays are already used.

Acquisition of Neural Action Potentials Using Rapid Multiplexing Directly at the Electrodes.

Neural recording systems that interface with implanted microelectrodes are used extensively in experimental neuroscience and neural engineering research. Interface electronics that are needed to amplify, filter, and digitize signals from multichannel electrode arrays are a critical bottleneck to scaling such systems. This paper presents the design and testing of an electronic architecture for intracortical neural recording that drastically reduces the size per channel by rapidly multiplexing many electrodes to a single circuit. The architecture utilizes mixed-signal feedback to cancel electrode offsets, windowed integration sampling to reduce aliased high-frequency noise, and a successive approximation analog-to-digital converter with small capacitance and asynchronous control. Results are presented from a 180 nm CMOS integrated circuit prototype verified using in vivo experiments with a tungsten microwire array implanted in rodent cortex. The integrated circuit prototype achieves <0.004 mm2 area per channel, 7 µW power dissipation per channel, 5.6 µVrms input referred noise, 50 dB common mode rejection ratio, and generates 9-bit samples at 30 kHz per channel by multiplexing at 600 kHz. General considerations are discussed for rapid time domain multiplexing of high-impedance microelectrodes. Overall, this work describes a promising path forward for scaling neural recording systems to numbers of electrodes that are orders of magnitude larger.

Long-term stability of neural signals from microwire arrays implanted in common marmoset motor cortex and striatum

Current neuroprosthetics rely on stable, high quality recordings from chronically implanted microelectrode arrays (MEAs) in neural tissue. While chronic electrophysiological recordings and electrode failure modes have been reported from rodent and larger non-human primate (NHP) models, chronic recordings from the marmoset model have not been previously described. The common marmoset is a New World primate that is easier to breed and handle compared to larger NHPs and has a similarly organized brain, making it a potentially useful smaller NHP model for neuroscience studies. This study reports recording stability and signal quality of MEAs chronically implanted in behaving marmosets. Six adult male marmosets, trained for reaching tasks, were implanted with either a 16-channel tungsten microwire array (five animals) or a Pt-Ir floating MEA (one animal) in the hand-arm region of the primary motor cortex (M1) and another MEA in the striatum targeting the nucleus accumbens (NAcc). Signal stability and quality was quantified as a function of array yield (active electrodes that recorded action potentials), neuronal yield (isolated single units during a recording session), and signal-to-noise ratio (SNR). Out of 11 implanted MEAs, nine provided functional recordings for at least three months, with two arrays functional for 10 months. In general, implants had high yield, which remained stable for up to several months. However, mechanical failure attributed to MEA connector was the most common failure mode. In the longest implants, signal degradation occurred, which was characterized by gradual decline in array yield, reduced number of isolated single units, and changes in waveform shape of action potentials. This work demonstrates the feasibility of long-term recordings from MEAs implanted in cortical and deep brain structures in the marmoset model. The ability to chronically record cortical signals for neural prosthetics applications in the common marmoset extends the potential of this model in neural interface research.

AuNPs‐HRP microneedle biosensor for ultrasensitive detection of hydrogen peroxide for organ preservation

AbstractThe preservation of tissues and organs for transplantation has garnered considerable attention due to the oxidative stress that arises from the excess of reactive oxygen species produced upon the removal of an organ from its native environment. Herein, gold nanoparticles (AuNPs)‐horseradish peroxidase (HRP) ultrasensitive microneedle biosensor is developed using a simple electrochemical method for the determination of H2O2. Tungsten microwire was homogenously modified with AuNPs via electrodeposition and 3‐mercaptopropionic acid (MPA) to form self‐assembled monolayers (SAMs) for the immobilization of HRP. The prepared AuNPs‐MPA electrode exhibited high electrocatalytic activity towards the reduction of H2O2. At an applied potential of −300 mV, the AuNPs‐HRP electrode yielded a linear ranges of 5 nM to 5 µM H2O2 (R = 0.999) and 1–5 mM H2O2 (R = 0.985) with a low detection limit of 800 pM and a sensitivity of 490.59 Ma/mM/cm2 on average as the result of the strong synergistic effect between HRP and AuNPs. Common interfering species such as ascorbic acid, acetaminophen, glucose and uric acid were effectively eliminated. In addition, the fabricated biosensor exhibited high electrocatalytic activity for the determination of H2O2 in real time from rat abdominal wall perfused with histidine–tryptophan–ketoglutarate solution.

Electrode impedance analysis of chronic tungsten microwire neural implants: understanding abiotic vs. biotic contributions.

Changes in biotic and abiotic factors can be reflected in the complex impedance spectrum of the microelectrodes chronically implanted into the neural tissue. The recording surface of the tungsten electrode in vivo undergoes abiotic changes due to recording site corrosion and insulation delamination as well as biotic changes due to tissue encapsulation as a result of the foreign body immune response. We reported earlier that large changes in electrode impedance measured at 1 kHz were correlated with poor electrode functional performance, quantified through electrophysiological recordings during the chronic lifetime of the electrode. There is a need to identity the factors that contribute to the chronic impedance variation. In this work, we use numerical simulation and regression to equivalent circuit models to evaluate both the abiotic and biotic contributions to the impedance response over chronic implant duration. COMSOL® simulation of abiotic electrode morphology changes provide a possible explanation for the decrease in the electrode impedance at long implant duration while biotic changes play an important role in the large increase in impedance observed initially.

Robust deep brain stimulation functional MRI procedures in rats and mice using an MR-compatible tungsten microwire electrode.

To develop a series of robust and readily adoptable protocols for the application of deep brain stimulation (DBS)-functional MRI (fMRI) in rodents. DBS-fMRI procedures were conducted in rat and mouse under varying anesthetic conditions (isoflurane in rat and mouse, α-chloralose in rat). A homemade two-channel tungsten microwire electrode was used to minimize magnetic susceptibility artifacts, and was targeted to the ventral posteromedial (VPM) thalamus for DBS-fMRI scanning procedures. Compared with a commercially available MR-compatible electrode, the tungsten microwire generated greatly reduced magnetic-susceptibility artifacts. In the rat, VPM-DBS using the microwire electrode resulted in robust positive blood-oxygen-level-dependent signal changes in somatosensory cortex that were relatively independent of anesthetic type. In the mouse, VPM-DBS similarly generated large, positive neurovascular responses in somatosensory cortex that were detected using cerebral blood volume measurements. Collectively, this work describes reasonable and easily adoptable procedures for conducting DBS-fMRI studies in rodent models. The protocols developed herein may be extended to study DBS effects under numerous experimental conditions and at varying stimulation targets.

Insulated Conducting Cantilevered Nanotips and Two-Chamber Recording System for High Resolution Ion Sensing AFM

Biological membranes contain ion channels, which are nanoscale pores allowing controlled ionic transport and mediating key biological functions underlying normal/abnormal living. Synthetic membranes with defined pores are being developed to control various processes, including filtration of pollutants, charge transport for energy storage, and separation of fluids and molecules. Although ionic transport (currents) can be measured with single channel resolution, imaging their structure and ionic currents simultaneously is difficult. Atomic force microscopy enables high resolution imaging of nanoscale structures and can be modified to measure ionic currents simultaneously. Moreover, the ionic currents can also be used to image structures. A simple method for fabricating conducting AFM cantilevers to image pore structures at high resolution is reported. Tungsten microwires with nanoscale tips are insulated except at the apex. This allows simultaneous imaging via cantilever deflections in normal AFM force feedback mode as well as measuring localized ionic currents. These novel probes measure ionic currents as small as picoampere while providing nanoscale spatial resolution surface topography and is suitable for measuring ionic currents and conductance of biological ion channels.

Comprehensive characterization and failure modes of tungsten microwire arrays in chronic neural implants

For nearly 55 years, tungsten microwires have been widely used in neurophysiological experiments in animal models to chronically record neuronal activity. While tungsten microwires initially provide stable recordings, their inability to reliably record high-quality neural signals for tens of years has limited their efficacy for neuroprosthetic applications in humans. Comprehensive understanding of the mechanisms of electrode performance and failure is necessary for developing next generation neural interfaces for humans. In this study, we evaluated the abiotic (electrophysiology, impedance, electrode morphology) and biotic (microglial reactivity, blood–brain barrier disruption, biochemical markers of axonal injury) effects of 16-channel, 50 µm diameter, polyimide insulated tungsten microwires array for implant durations that ranged from acute to up to 9 months in 25 rats. Daily electrode impedance spectroscopy, electrophysiological recordings, blood and cerebrospinal fluid (CSF) withdrawals, and histopathological analysis were performed to study the time-varying effects of chronic electrode implantation. Structural changes at the electrode recording site were observed as early as within 2–3 h of electrode insertion. Abiotic analysis indicated the first 2–3 weeks following surgery was the most dynamic period in the chronic electrode lifetime as there were greater variations in the electrode impedance, functional electrode performance, and the structural changes occurring at the electrode recording tips. Electrode recording site deterioration continued for the long-term chronic animals as insulation damage occurred and recording surface became more recessed over time. In general, electrode impedance and functional performance had smaller daily variations combined with reduced electrode recording site changes during the chronic phase. Histopathological studies were focused largely on characterizing microglial cell responses to electrode implantation. We found that activated microglia were present near the electrode tracks in all non-acute animals studied, thus indicating presence of a neuroinflammatory response regardless of post-implantation survival times and electrode performance. Conversely, dystrophic microglia detectable as fragmented cells were found almost exclusively in acute animals surviving only few hours after implantation. While there was no consistent relationship between microglial cell responses and electrode performance, we noticed co-occurrence of high ferritin expression, intraparenchymal bleeding, and microglial degeneration suggesting presence of excessive oxidative stress via Fenton chemistry. Biochemical analysis indicated that these electrodes always caused a persistent release of axonal injury biomarkers even several months after implantation suggesting persistent tissue damage. Our study suggests that mechanisms of electrode failure are multi-factorial involving both abiotic and biotic parameters. Since these failure modes occur concurrently and cannot be isolated from one another, the lack of consistent relationship between electrode performance and microglial responses in our results suggest that one or more of the abiotic factors were equally responsible for degradation in electrode performance over long periods of time.

Evaluation of a microwire sensor functionalized to detect Escherichia coli bacterial cells

A functionalized microwire sensor based on dielectrophoresis (DEP) and antigen–antibody reaction was initially developed for sensitive and selective detection of E. coli O157:H7. The dynamics of gold–tungsten microwires were manipulated using an automated X–Y–Z stage and the sensing process included antibody immobilization and bacterial detection, and cell quantification. Antibodies were first immobilized on surface of the microwire to improve sensing specificity, and then coupled with DEP for capture of E. coli cells in a mixture of E. coli cells and non-conductive polystyrene beads. Afterward, fluorescein-conjugated secondary antibodies were applied to the wire for quantification of captured bacteria. Field Emission Scanning Electron Microscope (FESEM) figures and fluorescence intensities of bacteria on the wire validated the sensing mechanism. The entire immobilization and detection procedure could be completed within 30min with simple operations. Performance of the microwire sensor was not significantly affected when conducted in orange juice. In addition, the detection limit of this sensor was about 5 bacterial cells per microwire in 1000CFU/mL bacterial suspensions when the electric field generated at 3MHz and 20 peak to peak voltage (Vpp), and only targeted E. coli cells were concentrated and captured.

Quantifying long-term microelectrode array functionality using chronic in vivo impedance testing

Long-term acquisition of high-quality neural recordings is a cornerstone of neuroprosthetic system design. Mitigating the experimental variability of chronically implanted arrays has been a formidable task because the sensor recording sites can be influenced by biotic and abiotic responses. Several studies have implicated changes in electrical interface impedance as a preliminary marker to infer electrode viability. Microelectrode impedance plays an important role in the monitoring of low amplitude and high-resolution extracellular neural signals. In this work, we seek to quantify long-term microelectrode array functionality and derive an impedance-based predictor for electrode functionality that correlates the recording site electrical properties with the functional neuronal recordings in vivo. High temporal resolution metrics of this type would allow one to assess, predict, and improve electrode performance in the future. In a large cohort of animals, we performed daily impedance measurements and neural signal recordings over long periods (up to 21 weeks) of time in rats using tungsten microwire arrays implanted into the somatosensory cortex. This study revealed that there was a time-varying trend in the modulation of impedance that was related to electrode performance. Single units were best detected from electrodes at time points when the electrode entered into the 40–150 KΩ impedance range. This impedance trend was modeled across the full cohort of animals to predict future electrode performance. The model was tested on data from all animals and was able to provide predictions of electrode performance chronically. Insight from this study can be combined with knowledge of electrode materials and histological analysis to provide a more comprehensive predictive model of electrode failure in the future.

Characterization of the Electrical Properties of Individual p-Si Microwire/Polymer/n-Si Microwire Assemblies

The electrical properties of individual p- and n-type silicon microwires have been investigated using a direct contact formation technique, in which an Ohmic contact between the tungsten probe and microwire was produced by applying mechanical force to the probe/microwire junction. This method alleviated the need for lithography or a high-temperature process to form a metal/Si ohmic contact. The technique was also used to characterize the Si microwire/conducting polymer junctions in a single cell of a membrane-supported bilayer Si microwire structure that is of interest for the direct production of fuels from sunlight. The data indicate that the combination of PEDOT–PSS–Nafion and highly doped Si microwires is suitable, from an electrical resistance perspective, to be used in a solar fuels generation device.