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Electrochemical methods with tissue-implantable microelectrodes provide an excellent platform for real-time monitoring the neurochemical dynamics in vivo due to their superior spatiotemporal resolution and high selectivity and sensitivity. Nevertheless, electrode implantation inevitably damages the brain tissue, upregulates reactive oxygen species level, and triggers neuroinflammatory response, resulting in unreliable quantification of neurochemical events. Herein, we report a multifunctional sensing platform for inflammation-free in vivo analysis with atomic-level engineered Fe single-atom catalyst that functions as both single-atom nanozyme with antioxidative activity and electrode material for dopamine oxidation. Through high-temperature pyrolysis and catalytic performance screening, we fabricate a series of Fe single-atom nanozymes with different coordination configurations and find that the Fe single-atom nanozyme with FeN4 exhibits the highest activity toward mimicking catalase and superoxide dismutase as well as eliminating hydroxyl radical, while also featuring high electrode reactivity toward dopamine oxidation. These dual functions endow the single-atom nanozyme-based sensor with anti-inflammatory capabilities, enabling accurate dopamine sensing in living male rat brain. This study provides an avenue for designing inflammation-free electrochemical sensing platforms with atomic-precision engineered single-atom catalysts.

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The sensitivity of zinc (Zn(II)) detection using fast-scan cyclic voltammetry (FSCV) with carbon fiber microelectrodes (CFMEs) is low compared to other neurochemicals. We have shown previously that Zn(II) plates to the surface of CFME's and we speculate that it is because of the abundance of oxide functionality on the surface. Plating reduces sensitivity over time and causes significant disruption to detection stability. This limited sensitivity and stability hinders Zn(II) detection, especially in complex matrices like the brain. To address this, we developed plasma-treated gold fiber microelectrodes (AuMEs) which enable sensitive and stable Zn(II) detection with FSCV. Typically, gold fibers are treated using corrosive acids to clean the surface and this step is important for preparing the surface for electrochemistry. Likewise, because FSCV is an adsorption-based technique, it is also important for Zn(II) to adsorb and desorb to prevent irreversible plating. Because of these requirements, careful optimization of the electrode surface was necessary to render the surface for Zn(II) adsorption yet strike a balance between attraction to the surface vs. irreversible interactions. In this study, we employed oxygen plasma treatment to activate the gold fiber surface without inducing significant morphological changes. This treatment effectively removes the organic layer while functionalizing the surface with oxygen, enabling Zn(II) detection that is not possible on untreated gold surfaces. Our results demonstrate significantly improved Zn(II) detection sensitivity and stability on AuME compared to CFME's. Overall, this work provides an advance in our understanding of Zn(II) electrochemistry and a new tool for improved metallotransmitter detection in the brain.

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DNA-aptamer-functionalized electrode arrays can provide an intriguing method for detecting pathogen-derived exometabolites. This work addresses the limitations of previous aptamer-based pathogen detection methods by introducing a novel surface design that bridges the gap between initial efforts in this area and the demands of a point-of-care device. Specifically, the use of a diblock copolymer coating on a high-density microelectrode array and Cu-mediated cross coupling reactions that allow for the exclusive functionalization of that coating by any electrode or set of electrodes in the array provides a device that is stable for 1 year and compatible with the multiplex detection of small-molecule targets. The new chemistry developed allows one to take advantage of a large number of electrodes in the array with one experiment described herein capitalizing on the use of 960 individually addressable electrodes.

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The synchronization of the electrical and mechanical coupling assures the physiological pump function of the heart, but life-threatening pathologies may jeopardize this equilibrium. Recently, human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) have emerged as a model for personalized investigation because they can recapitulate human diseased traits, such as compromised electrical capacity or mechanical circuit disruption. This research avails the model of hiPSC-CMs and showcases innovative techniques to study the electrical and mechanical properties as well as their modulation due to inherited cardiomyopathies. In this work, hiPSC-CMs carrying either Brugada syndrome (BRU) or dilated cardiomyopathy (DCM), were organized in a bilayer configuration to first validate the experimental methods and second mimic the physiological environment. High-density CMOS-based microelectrode arrays (HD-MEA) have been employed to study the electrical activity. Furthermore, mechanical function was investigated via quantitative video-based evaluation, upon stimulation with a ß-adrenergic agonist. This study introduces two experimental methods. First, high-throughput mechanical measurements in the hiPSC-CM layers (xy-inspection) are obtained using both a recently developed optical tracker (OPT) and confocal reference-free traction force microscopy (cTFM) aimed to quantify cardiac kinematics. Second, atomic force microscopy (AFM) with FluidFM probes, combined with the xy-inspection methods, supplemented a three-dimensional understanding of cell-cell mechanical coupling (xyz-inspection). This particular combination represents a multi-technique approach to detecting electrical and mechanical latency among the cell layers, examining differences and possible implications following inherited cardiomyopathies. It can not only detect disease characteristics in the proposed in vitro model but also quantitatively assess its response to drugs, thereby demonstrating its feasibility as a scalable tool for clinical and pharmacological studies.

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Implantable devices for brain-machine interfaces and managing neurological disorders have experienced rapid growth in recent years. Although functional implants offer significant benefits, issues related to transient trauma and long-term biocompatibility and safety are of significant concern. Acute inflammatory reaction in the brain tissue caused by microimplants is known to be an issue but remains poorly studied. This study presents the use of titanium oxynitride (TiNO) nanofilm with defined surface plasmon resonance (SPR) properties for point-of-care characterizing of acute inflammatory responses during robot-controlled micro-neuro-implantation. By leveraging surface-enriched oxynitride, TiNO nanofilms can be biomolecular-functionalized through silanization. This label-free TiNO-SPR biosensor exhibits a high sensitivity toward the inflammatory cytokine interleukin-6 with a detection limit down to 6.3 fg ml-1 and a short assay time of 25 min. Additionally, intraoperative monitoring of acute inflammatory responses during microelectrode implantation in the mice brain has been accomplished using the TiNO-SPR biosensors. Through intraoperative cerebrospinal fluid sampling and point-of-care plasmonic biosensing, the rhythm of acute inflammatory responses induced by the robot-controlled brain microelectrodes implantation has been successfully depicted, offering insights into intraoperative safety assessment of invasive brain-machine interfaces.

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In order to investigate the changes in the properties of the cell culture solution in the effect of cell synchronization via cell starvation (for 12, 24, and 36 h), a new spiral-interdigital pattern of microelectrode as a biosensor has been proposed. Then, to test its superiority, the results of this spiral-interdigital pattern with the results of the commercial pattern have been compared. The cells were selected from breast cancer standard lines (MDA-MB-231). Changes in CV peaks of the secretions were recorded by the spiral-interdigital pattern, in which increasing the interactive surface with homogenous electric paths had been considered by simulation before fabrication. The results of the simulation and experimental procedures showed a meaningful correlation. The occurrence of CV oxidative peaks at about 0.1-0.4 V and reductive peaks at approximately 0 V in the spiral-interdigital biosensor in the starved MDA-MB-231 cell line has been observed. The starvation situation resembles one that does not cause meaningful cell apoptosis or necrosis, and this method is only used to make the cells synchronized. Also, no peak is observed in normal cell growth conditions. In addition, by using the commercial design of the electrodes, no peak is observed in any of the conditions of normal and synchronized growth of the cells. Therefore, it seems that the observed peaks are caused by the agents that are secreted in the cell culture solution in a synchronized situation. Moreover, the design of the new spiral-interdigital electrode can significantly increase the sensitivity of the sensor to receive these peaks due to more space and a uniform electric field.

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Subcellularly amperometric analysis in situ is crucial for understanding intracellular redox biochemistry and subcellular heterogeneity. Unfortunately, the ultra-small size and complex microenvironment inside the cell pose a great challenge to achieve this goal. To address the challenge, a minimized living microbial sensor has been fabricated in this work for amperometric analysis. Here, by fabricating the dimidiate microelectrode as the working electrode, while fitting a living electroactive bacterium (EAB) as the transducer, outward extracellular electron transfer (EET) of the sensory EAB is correlated with the concentration of lactic acid, which is electrochemically recorded and thus displays an electrical signal output for detection. In specific, the S. oneidensis modified dimidiate microelectrode (S.O.@GNE-NPE) acts as an integrated electroanalytical device to generate the electrical signal in situ. The established microcircuit provides unprecedented precision and sensitivity, contributing to subcellular amperometric measurement. The microbial sensor shows a linear response in the concentration range of 0-60 mM, with a limit of detection (LOD) at 0.3 mM. The microsensor also demonstrates good selectivity against interferences. Additionally, intracellular analysis of lactic acid provides direct evidence of enhanced lactic metabolism in cancer cells as a result of "Warburg Effect". This work shows an example of nano-, bio- and electric technologies that have been integrated on the EAB-modified dimidiate microelectrode, and achieves intracellular biosensing application through such integration. It may give a new strategy on the combination of micro/nanotechnologies with sensory EAB for the necessary development of bioelectronic devices.

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BACKGROUND: Brain-computer interfaces can enable communication for people with paralysis by transforming cortical activity associated with attempted speech into text on a computer screen. Communication with brain-computer interfaces has been restricted by extensive training requirements and limited accuracy. METHODS: A 45-year-old man with amyotrophic lateral sclerosis (ALS) with tetraparesis and severe dysarthria underwent surgical implantation of four microelectrode arrays into his left ventral precentral gyrus 5 years after the onset of the illness; these arrays recorded neural activity from 256 intracortical electrodes. We report the results of decoding his cortical neural activity as he attempted to speak in both prompted and unstructured conversational contexts. Decoded words were displayed on a screen and then vocalized with the use of text-to-speech software designed to sound like his pre-ALS voice. RESULTS: On the first day of use (25 days after surgery), the neuroprosthesis achieved 99.6% accuracy with a 50-word vocabulary. Calibration of the neuroprosthesis required 30 minutes of cortical recordings while the participant attempted to speak, followed by subsequent processing. On the second day, after 1.4 additional hours of system training, the neuroprosthesis achieved 90.2% accuracy using a 125,000-word vocabulary. With further training data, the neuroprosthesis sustained 97.5% accuracy over a period of 8.4 months after surgical implantation, and the participant used it to communicate in self-paced conversations at a rate of approximately 32 words per minute for more than 248 cumulative hours. CONCLUSIONS: In a person with ALS and severe dysarthria, an intracortical speech neuroprosthesis reached a level of performance suitable to restore conversational communication after brief training. (Funded by the Office of the Assistant Secretary of Defense for Health Affairs and others; BrainGate2 ClinicalTrials.gov number, NCT00912041.).

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Hericium erinaceus is a basidiomycetes fungus with previously uncharacterised extracellular electrophysiology. Here, we present results of recordings of the electrical potentials of fungal biofilms of this species using microelectrode arrays (MEAs). In particular, we focused on modelling the temporal and spatial progression of the low frequency (≤ 1 Hz) potentials. Culture media control studies showed that the electrical potential activity results from the growth and subsequent spiking behaviours of the mycelium extracellular matrices. An antifungal assay using nystatin suspension, 10,000 unit/mL in DPBS, provided evidence for the biological origin of electrical potentials due to targeting of the selective permeability of the cell membrane and subsequent cessation of electrical activity. Conversely, injection of L-glutamic acid increased the combined multi-channel mean firing rate from 0.04 Hz to 0.1 Hz. Analysis of bursting and spatial propagation of the extracellular signals are also presented.

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Flexible fiber-based microelectrodes allow safe and chronic investigation and modulation of electrically active cells and tissues. Compared to planar electrodes, they enhance targeting precision while minimizing side effects from the device-tissue mechanical mismatch. However, the current manufacturing methods face scalability, reproducibility, and handling challenges, hindering large-scale deployment. Furthermore, only a few designs can record electrical and biochemical signals necessary for understanding and interacting with complex biological systems. In this study, we present a method that utilizes the electrical conductivity and easy processability of MXenes, a diverse family of two-dimensional nanomaterials, to apply a thin layer of MXene coating continuously to commercial nylon filaments (30-300 µm in diameter) at a rapid speed (up to 15 mm/s), achieving a linear resistance below 10 Ω/cm. The MXene-coated filaments are then batch-processed into free-standing fiber microelectrodes with excellent flexibility, durability, and consistent performance even when knotted. We demonstrate the electrochemical properties of these fiber electrodes and their hydrogen peroxide (H2O2) sensing capability and showcase their applications in vivo (rodent) and ex vivo (bladder tissue). This scalable process fabricates high-performance microfiber electrodes that can be easily customized and deployed in diverse bioelectronic monitoring and stimulation studies, contributing to a deeper understanding of health and disease.

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BACKGROUND: The local pH change mediated by the pathogenic bacterial species Streptococcus mutans plays a significant role in the corrosion of hydroxyapatite (HA) present in the tooth in the dynamic oral cavity. The acid produced by the bacteria decreases the local pH and releases Ca2+ ions from the HA. We studied the bacteria-mediated demineralization of HA by scanning electrochemical microscopy (SECM) after growing S. mutans biofilm on HA for 7 days. RESULTS: We notably developed a triple-function SECM-compatible tip that could be positioned above the biofilm. It can also measure the pH and [Ca2+] change simultaneously above the biofilm-HA substrate. The triple-function SECM tip is a combination of a potentiometric pH sensor deposited with iridium oxide and a dual-function carbon-based Ca2+ ion-selective membrane electrode with a slope of 67 mV/pH and 34.3 mV/log [Ca2+], respectively. The distance-controlled triple-function SECM tip monitored real-time pH and [Ca2+] changes 30 µm above the S. mutans biofilm. The high temporal resolution pH data demonstrated that after approximately 20 min of sucrose addition, S. mutans started to produce acid to titrate the solution buffer, causing a pH change from 7.2 to 6.5 for HA and from 7.2 to 5 for the glass substrate. We observed that, after 30 min of acid production, ∼300 µM of Ca2+ ions were increased at pH 6.5 above the biofilm surface as a result of the pH change in the local microenvironment. After the release of Ca2+ from HA, the pH environment again shifted toward the neutral side, from 6.5 to 7.2. Therefore, precipitation of Ca2+ happens at the top of the biofilm, thus corroding the HA from underneath. For a glass substrate, in contrast, no Ca2+ ions were released, and the pH did not change back to 7.2. We were able to observe the dynamics of the HA demineralization-remineralization process simultaneously with our newly developed triple-function SECM tip or microprobe. SIGNIFICANCE: This technique could notably advance the study of similar complex processes, such as bacteria-mediated corrosion in biomedical and environmental contexts.

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Temperature has a profound influence on various neuromodulation processes and has emerged as a focal point. However, the effects of acute environmental temperature fluctuations on cultured cortical networks have been inadequately elucidated. To bridge this gap, we have developed a brain-on-a-chip platform integrating cortical networks and electrodeposited Pt/Ir modified microelectrode arrays (MEAs) with 3D-printed bear-shaped triple chambers, facilitating control of temperature transients. This innovative system administers thermal stimuli while concurrently monitoring neuronal activity, including spikes and local field potentials, from 60 microelectrodes (diameter: 30 µm; impedance: 9.34 ± 1.37 kΩ; and phase delay: -45.26 ± 2.85°). Temperature transitions of approximately ±10 °C/s were applied to cortical networks on MEAs via in situ perfusion within the triple chambers. Subsequently, we examined the spatiotemporal dynamics of the brain-on-a-chip under temperature regulation at both the group level (neuronal population) and their interactions (network dynamics) and the individual level (cellular activity). Specifically, we found that after the temperature reduction neurons enhanced the overall information transmission efficiency of the network through synchronous firing to compensate for the decreased efficiency of single-cell level information transmission, in contrast to temperature elevation. By leveraging the integration of high-performance MEAs with perfusion chambers, this investigation provides a comprehensive understanding of the impact of temperature on the spatiotemporal dynamics of neural networks, thereby facilitating future exploration of the intricate interplay between temperature and brain function.

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Microglia are important players in surveillance and repair of the brain. Implanting an electrode into the cortex activates microglia, produces an inflammatory cascade, triggers the foreign body response, and opens the blood-brain barrier. These changes can impede intracortical brain-computer interfaces performance. Using two-photon imaging of implanted microelectrodes, we test the hypothesis that low-intensity pulsed ultrasound stimulation can reduce microglia-mediated neuroinflammation following the implantation of microelectrodes. In the first week of treatment, we found that low-intensity pulsed ultrasound stimulation increased microglia migration speed by 128%, enhanced microglia expansion area by 109%, and a reduction in microglial activation by 17%, indicating improved tissue healing and surveillance. Microglial coverage of the microelectrode was reduced by 50% and astrocytic scarring by 36% resulting in an increase in recording performance at chronic time. The data indicate that low-intensity pulsed ultrasound stimulation helps reduce the foreign body response around chronic intracortical microelectrodes.

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High-throughput sensors are valuable tools for enabling massive, fast, and accurate diagnostics. To yield this type of electrochemical device in a simple and low-cost way, high-density arrays of vertical gold thin-film microelectrode-based sensors are demonstrated, leading to the rapid and serial interrogation of dozens of samples (10 µL droplets). Based on 16 working ultramicroelectrodes (UMEs) and 3 quasi-reference electrodes (QREs), a total of 48 sensors were engineered in a 3D crossbar arrangement that devised a low number of conductive lines. By exploiting this design, a compact chip (75 × 35 mm) can enable performing 16 sequential analyses without intersensor interferences by dropping one sample per UME finger. In practice, the electrical connection to the sensors was achieved by simply switching the contact among WE adjacent fingers. Importantly, a short analysis time was ensured by interrogating the UMEs with chronoamperometry or square wave voltammetry using a low-cost and hand-held one-channel potentiostat. As a proof of concept, the detection of Staphylococcus aureus in 15 samples was performed within 14 min (20 min incubation and 225 s reading). Additionally, the implementation of peptide-tethered immunosensors in these chips allowed the screening of COVID-19 from patient serum samples with 100% accuracy. Our experiments also revealed that dispensing additional droplets on the array (in certain patterns) results in the overestimation of the faradaic current signals, a phenomenon referred to as crosstalk. To address this interference, a set of analyses was conducted to design a corrective strategy that boosted the testing capacity by allowing using all on-chip sensors to address subsequent analyses (i.e., 48 samples simultaneously dispensed on the chip). This strategy only required grounding the unused rows of QRE and can be broadly adopted to develop high-throughput UME-based sensors. In practice, we could analyze 48 droplets (with [Fe(CN)6]4-) within ∼8 min using amperometry.

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Oocyte selection is a crucial step of assisted reproductive treatment. The most common approach relies on the embryologist experience which is inevitably prone to human error. One potential approach could be the use of an electrical-based approach as an ameliorative alternative. Here, we developed a simple electrical microsensor to characterize mouse oocytes. The sensor is designed similarly to embryo culture dishes and is familiar to embryologists. Different microelectrode models were simulated for oocyte cells and a more sensitive model was determined. The final microsensor was fabricated. A differential measuring technique was proposed based on the cell presence/absence. We predicted oocyte quality by using three electrical characteristics, oocyte radii, and zona thicknesses, and also these predictions were compared with an embryologist evaluation. The evaluation of the oocyte membrane capacitance, as an electrophysiological characteristic, was found to be a more reliable method for predicting oocytes with fertilization and blastocyst formation success competence. It achieved 94% and 58% prediction accuracies, respectively, surpassing other methods and yielding lower errors. This groundbreaking research represents the first of its kind in this field and we hope that this will be a step towards improving the accuracy of the treatment.

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Electrical stimulation (ES) techniques, such as deep brain and transcranial electrical stimulation, have shown promise in alleviating the symptoms of depression and other neurological disorders in vivo. A new noninvasive ES method called temporal interference stimulation (TIS), possesses great potential as it can be used to steer the stimulation and possibly selectively modulate different brain regions. To study TIS in a controlled environment, we successfully established an in vitro 'TIS on a chip' setup using rat cortical neurons on microelectrode arrays (MEAs) in combination with a current stimulator. We validated the developed TIS system and demonstrated the spatial steerability of the stimulation by direct electric field measurements in the chip setup. We stimulated cultures of rat cortical neurons at 28 days in vitro (DIV) by two-channel stimulation delivering 1) TIS at 653 Hz and 643 Hz, resulting in a 10 Hz frequency envelope, 2) low-frequency stimulation (LFS) at 10 Hz and 3) high-frequency stimulation (HFS) at 653 Hz. Unstimulated cultures were used as control/sham. We observed the differences in the electric field strengths during TIS, HFS, and LFS. Moreover, HFS and LFS had the smallest effects on neuronal activity. Instead, TIS elicited neuronal electrophysiological responses, especially 24 hours after stimulation. Our 'TIS on a chip' approach eludicates the applicability of TIS as a method to modulate neuronal electrophysiological activity. The TIS on a chip approach provides spatially steerable stimuli while mitigating the effects of high stimulus fields near the stimulation electrodes. Thus, the approach opens new avenues for stimulation on a chip applications, allowing the study of neuronal responses to gain insights into the potential clinical applications of TIS in treating various brain disorders.

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Interdigitated electrodes (IDEs) enable electrochemical signal enhancement through repeated reduction and oxidation of the analyte molecule. Porosity on these electrodes is often used to lower the impedance background. However, their high capacitive current and signal interferences with oxygen reduction limit electrochemical detection ability. We present utilization of alkanethiol modification on nanoporous gold (NPG) electrodes to lower their background capacitance and chemically passivate them from interferences due to oxygen reduction, while maintaining their fast electron transfer rates, as validated by lower separation between anodic and cathodic peaks (ΔE) and lower charge transfer resistance (Rct) values in comparison to planar gold electrodes. Redox amplification based on this modification enables sensitive detection of various small molecules, including pyocyanin, p-aminophenol, and selective detection of dopamine in the presence of ascorbic acid. Alkanethiol NPG arrays are applied as a multiplexed sensor testbed within a well plate to screen binding of various peptide receptors to the SARS COV2 S-protein by using a sandwich assay for conversion of PAPP (4-aminophenyl phosphate) to PAP (p-aminophenol), by the action of AP (alkaline phosphatase), which is validated against optical ELISA screens of the peptides. Such arrays are especially of interest in small volume analytical settings with complex samples, wherein optical methods are unsuitable.

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Electrophysiological recordings are vital in assessing biological functions, diagnosing diseases, and facilitating biofeedback and rehabilitation. The applications of conventional wet (gel) electrodes often come with some limitations. Microneedle array electrodes (MAEs) present a possible solution for high-quality electrophysiological acquisition, while the prior technologies for MAE fabrication have been either complex, expensive, or incapable of producing microneedles with uniform dimensions. This work employed a projection stereolithography (P µ SL) 3D printing technology to fabricate MAEs with micrometer-level precision. The MAEs were compared with gel and flat electrodes on electrode-skin interface impedance (EII) and performances of EMG and ECG acquisition. The experimental results indicate that the P µ SL 3D printing technology contributed to an easy-to-perform and low-cost fabrication approach for MAEs. The developed MAEs exhibited promising EII and enabled a stable EMG and ECG acquisition in different conditions without inducing skin allergies, inflammation, or injuries. This research lies in the development of a type of customizable MAE with considerable biomedical application potentials for ultra-minimally invasive or non-invasive electrophysiological acquisition.

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A W-doped Pt modified graphene oxide (Pt-W-GO) electrochemical microelectrode was developed to detect hydrogen peroxide (H2O2) in real time at a subcellular scale. Interestingly, results showed that the concentration of H2O2 in the nucleus of HeLa cells was 2.68 times and 0.51 times that in the extracellular membrane and cytoplasm, respectively.

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