Electrochemical Imaging of Dopamine Release from Three-Dimensional-Cultured PC12 Cells Using Large-Scale Integration-Based Amperometric Sensors

Bipolar electrochemical sensor with perylene diimide-based cathodic luminophore for dopamine detection and imaging

Bipolar electrochemical microscopy (BEM), which visualizes the concentration distribution of molecular species in biological systems by electrochemiluminescence (ECL), is expected to be applied to the high-spatiotemporal-resolution imaging of biomolecules, enabling the analysis of cellular functions. In the past, the molecular species that could be imaged by BEM were generally restricted to oxidized molecules due to the limitation derived from the ECL mechanism of the luminophore. Recently, the imaging of dopamine (DA), a reduced molecule, was achieved using Ru (bpy)32+/glutathione disulfide (GSSG) as a cathodic luminophore. However, a large driving voltage was required for ECL generation, resulting in a low S/N ratio. In this study, we employed N,N'-dimethyl-3,4,9,10-perylenetetracarboxylic diimide (PDI-CH3)/potassium peroxodisulfate (K2S2O8), which is a cathodic luminophore that can be reduced at a nobler potential to produce ECL than [Ru(bpy)3]2+/GSSG. First, the ECL mechanism of PDI-CH3/K2S2O8 was elucidated by using a PDI-CH3 drop-cast glassy carbon electrode (GCE) immersed in K2S2O8 solution as the working electrode in a 3-electrode system. The PDI-CH3 drop-casted GCE, a single closed bipolar electrode (c-BPE), was used as the cathode in the successful quantification of 50-500 μmol L-1 DA in a sample chamber in which a c-BPE anode was immersed, resulting in a high S/N. The selective detection of DA in the presence of ascorbic acid was achieved by modifying the anode with Nafion. Finally, DA imaging was demonstrated using a commercially available anisotropic conducting film with PDI-CH3 coating on the cathode surface as a c-BPE array. The change in the concentration distribution in the inflow of DA was successfully imaged based on the change in the ECL intensity at the c-BPE cathode. This BEM system is expected to be useful for DA imaging of the brain.

Sensor-integrated brain-on-a-chip platforms: Improving the predictive validity in neurodegenerative research

Affecting millions of individuals worldwide, neurodegenerative diseases (NDDs) pose a significant and growing health concern in people over the age of 60 years. Contributing to this trend are the steady increase in the aging population coupled with a persistent lack of disease-altering treatment strategies targeting NDDs. The absence of efficient therapeutics can be attributed to high failure rates in clinical trials and the ineptness of animal models in preceding preclinical studies. To that end, in recent years, significant research effort has been dedicated to the development of human cell-based preclinical disease models characterized by a higher degree of predictive validity. However, a key requirement of any in vitro model constitutes the precise knowledge and replication of the target tissues' (patho-)physiological microenvironment. Herein, microphysiological systems have demonstrated superiority over conventional static 2D/3D in vitro cell culture systems, as they allow for the emulation and continuous monitoring of the onset, progression, and remission of disease-associated phenotypes. This review provides an overview of recent advances in the field of NDD research using organ-on-a-chip platforms. Specific focus is directed toward non-invasive sensing strategies encompassing electrical, electrochemical, and optical sensors. Additionally, promising on- and integrable off-chip sensing strategies targeting key analytes in NDDs will be presented and discussed in detail.

In vitro drug screening models derived from different PC12 cell lines for exploring Parkinson's disease based on electrochemical signals of catecholamine neurotransmitters

Gold nanostructures and a Nafion modified screen-printed carbon electrode (Nafion/AuNS/SPCE) were developed to assess the cell viability of Parkinson's disease (PD) cell models. The electrochemical measurement of cell viability was reflected by catecholamine neurotransmitter (represented by dopamine) secretion capacity, followed by a traditional tetrazolium-based colorimetric assay for confirmation. Due to the  capacity to synthesize, store, and release catecholamines as well as their unlimited homogeneous proliferation, and ease of manipulation, pheochromocytoma (PC12) cells were used for PD cell modeling. Commercial low-differentiated and highly-differentiated PC12 cells, and home-made nerve growth factor (NGF) induced low-differentiated PC12 cells (NGF-differentiated PC12 cells) were included in the modeling. This approach achieved sensitive and rapid determination of cellular modeling and intervention states. Notably, among the three cell lines, NGF-differentiated PC12 cells displayed the enhanced neurotransmitter secretion level accompanied with attenuated growth rate, incremental dendrites in number and length that were highly resemble with neurons. Therefore, it was selected as the PD-tailorable modeling cell line. In short, the electrochemical sensor can be used to sensitively determine the biological function of neuron-like PC12 cells with negligible destruction and to explore the protective and regenerative impact of various substances on nerve cell model.

Real-time selective detection of dopamine and serotonin at nanomolar concentration from complex in vitro systems

Electrochemical sensors provide means for real-time monitoring of neurotransmitter release events, which is a relatively easy process in simple electrolytes. However, this does not apply to in vitro environments. In cell culture media, competitively adsorbing molecules are present at concentrations up to 350 000-fold excess compared to the neurotransmitter-of-interest. Because detection of dopamine and serotonin requires direct adsorption of the analyte to electrode surface, a significant loss of sensitivity occurs when recording is performed in the in vitro environment. Despite these challenges, our single-walled carbon nanotube (SWCNT) sensor was capable of selectively measuring dopamine and serotonin from cell culture medium at nanomolar concentration in real-time. A primary midbrain culture was used to prove excellent biocompatibility of our SWCNT electrodes, which is a necessity for brain-on-a-chip models. Most importantly, our sensor was able to electrochemically record spontaneous transient activity from dopaminergic cell culture without altering the culture conditions, which has not been possible earlier. Drug discovery and development requires high-throughput screening of in vitro models, being hindered by the challenges in non-invasive characterization of complex neuronal models such as organoids. Our neurotransmitter sensors could be used for real-time monitoring of complex neuronal models, providing an alternative tool for their characterization non-invasively.

Effects of Curcumin on Axon Growth and Myelin Sheath Formation in an In Vitro Model

Although the beneficial effects of curcumin, extracted from rhizomes of the ginger family genus Curcuma, on the repair and regeneration of nerves have been evaluated in vitro, there are few studies concerning its effects on axon myelination. Here, we used pheochromocytoma cells as an in vitro model of peripheral nerves. Pheochromocytoma cells were cultured alone or cocultured with Schwann cells and treated with increasing concentrations of curcumin. Cell growth was observed, and the expression levels of growth-associated protein 43 (GAP-43), microtubule-associated protein 2 (MAP-2), myelin basic protein (MBP), myelin protein zero (MPZ), Krox-20, and octamer binding factor 6 (Oct-6) were quantified. We found a significant increase in expression of all six proteins following curcumin treatment, with a corresponding increase in the levels of MBP, MPZ, Krox-20, and Oct-6 mRNA. Upregulation was greater with increasing curcumin concentration, showing a concentration-dependent effect. The results suggested that curcumin can promote the growth of axons by upregulating the expression of GAP-43 and MAP-2, stimulate synthesis and secretion of myelin-related proteins, and facilitate formation of the myelin sheath in axons by upregulating the expression of Krox-20 and Oct-6. Therefore, curcumin could be widely applied in future strategies for the treatment of nerve injuries.

Biosensors integrated 3D organoid/organ-on-a-chip system: A real-time biomechanical, biophysical, and biochemical monitoring and characterization

As a full-fidelity simulation of human cells, tissues, organs, and even systems at the microscopic scale, Organ-on-a-Chip (OOC) has significant ethical advantages and development potential compared to animal experiments. The need for the design of new drug high-throughput screening platforms and the mechanistic study of human tissues/organs under pathological conditions, the evolving advances in 3D cell biology and engineering, etc., have promoted the updating of technologies in this field, such as the iteration of chip materials and 3D printing, which in turn facilitate the connection of complex multi-organs-on-chips for simulation and the further development of technology-composite new drug high-throughput screening platforms. As the most critical part of organ-on-a-chip design and practical application, verifying the success of organ model modeling, i.e., evaluating various biochemical and physical parameters in OOC devices, is crucial. Therefore, this paper provides a logical and comprehensive review and discussion of the advances in organ-on-a-chip detection and evaluation technologies from a broad perspective, covering the directions of tissue engineering scaffolds, microenvironment, single/multi-organ function, and stimulus-based evaluation, and provides a more comprehensive review of the progress in the significant organ-on-a-chip research areas in the physiological state.

A Microfluidic System for Investigating Anticipatory Medication Effects on Dopamine Homeostasis in Dopaminergic Cells

Dopamine (DA) homeostasis influences emotions, neural circuit development, cognition, and the reward system. Dysfunctions in DA regulation can lead to neurological disorders, including depression, developmental disorders, and addiction. DA homeostasis disruption is a primary cause of Parkinson's Disease (PD). Therefore, understanding the relationship between DA homeostasis and PD progression may clarify the mechanisms for pharmacologically treating PD. This study developed a novel in vitro DA homeostasis platform which consists of three main parts: (1) a microfluidic device for culturing DAergic neurons, (2) an optical detection system for reading DA levels, and (3) an automatic closed-loop control system that establishes when and how much medication to infuse; this uses a microfluidic device that can cultivate DAergic neurons, perfuse solutions, perform in vitro PD modeling, and continuously monitor DA concentrations. The automatically controlled closed-loop control system simultaneously monitors pharmacological PD treatment to support long-term monitoring of DA homeostasis. SH-SY5Y neuroblastoma cells were chosen as DAergic neurons. They were cultivated in the microfluidic device, and real-time cellular DA level measurements successfully achieved long-term monitoring and modulation of DA homeostasis. When applied in combination with multiday cell culture, this advanced system can be used for drug screening and fundamental biological studies.

Thermally Drawn CNT-Based Hybrid Nanocomposite Fiber for Electrochemical Sensing

Nowadays, bioelectronic devices are evolving from rigid to flexible materials and substrates, among which thermally-drawn-fiber-based bioelectronics represent promising technologies thanks to their inherent flexibility and seamless integration of multi-functionalities. However, electrochemical sensing within fibers remains a poorly explored area, as it imposes new demands for material properties-both the electrochemical sensitivity and the thermomechanical compatibility with the fiber drawing process. Here, we designed and fabricated microelectrode fibers made of carbon nanotube (CNT)-based hybrid nanocomposites and further evaluated their detailed electrochemical sensing performances. Carbon-black-impregnated polyethylene (CB-CPE) was chosen as the base material, into which CNT was loaded homogeneously in a concentration range of 3.8 to 10 wt%. First, electrical impedance characterization of CNT nanocomposites showed a remarkable decrease of the resistance with the increase in CNT loading ratio, suggesting that CNTs notably increased the effective electrical current pathways inside the composites. In addition, the proof-of-principle performance of fiber-based microelectrodes was characterized for the detection of ferrocenemethanol (FcMeOH) and dopamine (DA), exhibiting an ultra-high sensitivity. Additionally, we further examined the long-term stability of such composite-based electrode in exposure to the aqueous environment, mimicking the in vivo or in vitro settings. Later, we functionalized the surface of the microelectrode fiber with ion-sensitive membranes (ISM) for the selective sensing of Na+ ions. The miniature fiber-based electrochemical sensor developed here holds great potential for standalone point-of-care sensing applications. In the future, taking full advantage of the thermal drawing process, the electrical, optical, chemical, and electrochemical modalities can be all integrated together within a thin strand of fiber. This single fiber can be useful for fundamental multi-mechanistic studies for biological applications and the weaved fibers can be further applied for daily health monitoring as functional textiles.

PC-12 Cell Line as a Neuronal Cell Model for Biosensing Applications

PC-12 cells have been widely used as a neuronal line study model in many biosensing devices, mainly due to the neurogenic characteristics acquired after differentiation, such as high level of secreted neurotransmitter, neuron morphology characterized by neurite outgrowth, and expression of ion and neurotransmitter receptors. For understanding the pathophysiology processes involved in brain disorders, PC-12 cell line is extensively assessed in neuroscience research, including studies on neurotoxicity, neuroprotection, or neurosecretion. Various analytical technologies have been developed to investigate physicochemical processes and the biosensors based on optical and electrochemical techniques, among others, have been at the forefront of this development. This article summarizes the application of different biosensors in PC-12 cell cultures and presents the modern approaches employed in neuronal networks biosensing.

Fabrication of High-Density Vertical Closed Bipolar Electrode Arrays by Carbon Paste Filling Method for Two-Dimensional Chemical Imaging

In this study, a carbon paste filling method was proposed as a simple strategy for fabricating high-density bipolar electrode (BPE) arrays for bipolar electrochemical microscopy (BEM). High spatiotemporal resolution imaging was achieved using the fabricated BPE array. BEM, which is an emerging microscopic system in recent years, achieves label-free and high spatiotemporal resolution imaging of molecular distributions using high-density BPE arrays and electrochemiluminescence (ECL) signals. We devised a simple method to fabricate a BPE array by filling a porous plate with carbon paste and succeeded in fabricating a high-density BPE array (15 μm pitch). After a detailed observation of the surface of the BPE array using a scanning electron microscope, the basic electrochemical and ECL emission characteristics were evaluated using potassium ferricyanide solution as a sample solution. Moreover, inflow imaging of the sample molecules was conducted to evaluate the imaging ability of the prepared BPE array. In addition, Prussian Blue containing carbon ink was applied to the sample solution side of the BPE array to provide catalytic activity to hydrogen peroxide, and the quantification and inflow imaging of hydrogen peroxide by ECL signals was achieved. This simple fabrication method of the BPE array can accelerate the research and development of BEM. Furthermore, hydrogen peroxide imaging by BEM is an important milestone for achieving bioimaging with high spatiotemporal resolution such as biomolecule imaging using enzymes.

Integrated electrochemical microfluidic sensor with hierarchically porous nanoarrays modified graphene fiber microelectrode for bioassay

The development of high-efficient biosensing systems for rapid and sensitive detection of disease-related biomarkers in human samples is of great significance for disease diagnosis and treatment in clinical practice. In this work, we develop an integrated electrochemical microfluidic sensing platform based on freestanding graphene fiber (GF) microelectrode for bioassay. In order to improve the electrocatalytic activity of GF microelectrode, it has been modified by unique 3D well-ordered hierarchically porous nickel-cobalt phosphide (NiCoP) nanosheet arrays (NSAs). Benefiting from the excellent electrochemical properties and structural merits, the resultant NiCoP-NSAs modified GF microelectrode shows excellent sensing performances towards neurotransmitter dopamine (DA), with a high sensitivity of 5.56 μA cm^-2 μM^-1, a low detection limit of 14 nM, as well as good selectivity, reproducibility and stability. Furthermore, in virtue of the miniaturized size and good mechanical properties, the nanohybrid GF microelectrode can be embedded into a home-made microfluidic chip to construct an integrated electrochemical microfluidic sensing device, which has been used for sensitive analysis of DA in minimal volume of human serum and urine samples, and in situ tracking DA released from neuroblastoma cells SHSY-5Y under the stimulation for physio-pathological and pharmacological study of nervous system-related diseases.

Lab-In-A-Syringe: A Novel Electrochemical Biosensor for On-Site and Real-Time Monitoring of Dopamine in Freely Behaving Mice

There is a growing demand for real-time analysis and sampling of biofluids on a single low-cost platform in ultralow fluid volumes with robustness. In this study, a microfluidic sensor was developed, manufactured through an additive manufacturing technique, and used for dopamine (DA) measurements. We implemented a biosensing system using pencil graphites (PGEs) integrated into a three-dimensional (3D) printed microfluidic syringe-type device (μSyringe). The amperometry technique was used to monitor the current changes associated with the electrooxidation of DA. The sensing signal was stable and linear in a concentration range of DA between the limit of quantification (0.1 nM) and the upper limit of linearity (500 nM). The μSyringe sensing device is simple, robust, and stable, making it suitable for real-time measurement of DA in cerebrospinal fluid (CSF) from freely moving mice.

Electrochemical Imaging of Endothelial Permeability Using a Large-Scale Integration-Based Device

It is important to clarify the transport of biomolecules and chemicals to tissues. Herein, we present an electrochemical imaging method for evaluating the endothelial permeability. In this method, the diffusion of electrochemical tracers, [Fe(CN)₆]^4-, through a monolayer of human umbilical vein endothelial cells (HUVECs) was monitored using a large-scale integration-based device containing 400 electrodes. In conventional tracer-based assays, tracers that diffuse through an HUVEC monolayer into another channel are detected. In contrast, the present method does not employ separated channels. In detail, a HUVEC monolayer is immersed in a solution containing [Fe(CN)₆]^4- on the device. As [Fe(CN)₆]^4- is oxidized and consumed at the packed electrodes, [Fe(CN)₆]^4- begins to diffuse through the monolayer from the bulk solution to the electrodes and the obtained currents depend on the endothelial permeability. As a proof-of-concept, the effects of histamine on the monolayer were monitored. Also, an HUVEC monolayer was cocultured with cancer spheroids, and the endothelial permeability was monitored to evaluate the metastasis of the cancer spheroids. Unlike conventional methods, the device can provide spatial information, allowing the interaction between the monolayer and the spheroids to be monitored. The developed method is a promising tool for organs-on-a-chip and drug screening in vitro.

Lighting up ATP in cells and tissues using a simple aptamer-based fluorescent probe

Extracellular ATP as a purinergic signaling molecule, together with ATP receptor, are playing an important role in tumor growth, therapy resistance, and host immunity suppression. Meanwhile ATP is a crucial indicator for cellular energy status and viability, thus a vital variable for tissue regeneration and in vitro tissue engineering. Most recent studies on COVID-19 virus suggest infection caused ATP deficit and release as a major characterization at the early stage of the disease and major causes for disease complications. Thus, imaging ATP molecule in both cellular and extracellular contexts has many applications in biology, engineering, and clinics. A sensitive and selective fluorescence “signal-on” probe for ATP detection was constructed, based on the base recognition between a black hole quencher (BHQ)-labeled aptamer oligonucleotide and a fluorophore (Cy5)-labeled reporter flare. The probe was able to detect ATP in solution with single digit µM detection limit. With the assistance of lipofectamine, this probe efficiently entered and shined in the model cells U2OS within 3 h. Further application of the probe in specific scenery, cardio-tissue engineering, was also tested where the ATP aptamer complex was able to sense cellular ATP status in a semi-quantitative manner, representing a novel approach for selection of functional cardiomyocytes for tissue engineering. At last a slight change in probe configuration in which a flexible intermolecular A14 linker was introduced granted regeneration capability. These data support the application of this probe in multiple circumstances where ATP measurement or imaging is on demand.

Light in Electrochemistry

Electrochemistry represents an important analytical technique used to acquire and assess chemical information in detail, which can aid fundamental investigations in various fields, such as biological studies. For example, electrochemistry can be used as simple and cost-effective means for bio-marker tracing in applications, such as health monitoring and food security screening. In combination with light, powerful spatially-resolved applications in both the investigation and manipulation of biochemical reactions begin to unfold. In this article, we focus primarily on light-addressable electrochemistry based on semiconductor materials and light-readable electrochemistry enabled by electrochemiluminescence (ECL). In addition, the emergence of multiplexed and imaging applications will also be introduced.

Bio-inspired Incrustation Interfacial Polymerization of Dopamine and Cross-linking with Gelatin toward Robust, Biodegradable Three-Dimensional Hydrogels

In nature, laccase enzymatically catalyzes the reaction of phenolic compounds with oxygen to produce hardened surfaces known as cuticles on insects and plants. Inspired by this natural process, the present work investigated a robust, biodegradable hydrogel synthesized from dopamine and gelatin. This gel is obtained by the oxidation of dopamine dissolved in water, after which the resulting quinone compound automatically undergoes self-polymerization. The oxidized dopamine subsequently undergoes Schiff base and Michael addition reactions with gelatin, such that the exposed gelatin surface cross-links to generate a continuous hardened hydrogel film. Because gelatin transitions between sol and gel states with changes in temperature, two- and three-dimensional structures could be obtained from the gel state. This bio-inspired interfacial cross-linking reaction provides a simple means of forming complex morphologies and represents a promising technique for bio-applications.

Solid-phase microextraction integrated nanobiosensors for the serial detection of cytoplasmic dopamine in a single living cell

Dopamine participates in many physiological and pathological processes. Dynamic monitoring of dopamine levels in the cytoplasm of a single living cell reflects not only the functional state of dopamine synthesis factors but also the processes of related neurodegenerative diseases. Due to the low content of cytoplasmic dopamine and the difficulty to keep cells alive during the operating process, the detection of cytoplasmic dopamine is still challenging. Herein, a solid-phase microextraction (SPME) technique integrated nanobiosensor was employed to trace and quantify dopamine concentration fluctuations in the cytoplasm of a single living cell. We designed a polypyrrole modified carbon fiber nanoprobe as a bifunctional nanoprobe that can extract cytoplasmic dopamine and then perform electrochemical detection. This bifunctional nanoprobe can detect 10 pmol/L extracted dopamine and detected a 60% decrease of the cytoplasmic dopamine concentration in a single living cell by K⁺ stimulation. This study allowed for the first time serially detecting cytoplasmic dopamine while keeping the target cell alive, which might yield a new method for research on dopamine neurotoxicity and the related drug action mechanisms for neurodegenerative disease.

Bioelectronic properties of DNA, protein, cells and their applications for diagnostic medical devices

From a couple of centuries ago, understanding physical properties of biological material, their interference with their natural host and their potential manipulation for employment as a conductor in medical devices, has gathered substantial interest in the field of bioelectronics. With the fast-emerging technologies for fabrication of diagnostic modalities, wearable biosensors and implantable devices, which electrical components are of essential importance, a need for developing novel conductors within such devices has evolved over the past decades. As the possibility of electron transport within small biological molecules, such as DNA and proteins, as well as larger elements such as cells was established, several discoveries of the modern charge characterization technologies were evolved. Development of Electrochemical Scanning Tunneling Microscopy and Nuclear Magnetic Resonance among many other techniques were of vital importance, following the discoveries made in sub-micron scales of biological material. This review covers the most recent understandings of electronic properties within different scale of biological material starting from nanometer range to millimeter-sized organs. We also discuss the state-of-the-art technology that's been made taking advantage of electronic properties of biological material for addressing diseases like Parkinson's Disease and Epilepsy.

True Picomolar Neurotransmitter Sensor Based on Open-Ended Carbon Nanotubes

Neurotransmitters are important chemicals in human physiological systems for initiating neuronal signaling pathways and in various critical health illnesses. However, concentration of neurotransmitters in the human body is very low (nM or pM level) and it is extremely difficult to detect the fluctuation of their concentrations in patients using existing electrochemical biosensors. In this work, we report the performance of highly densified carbon nanotubes fiber (HD-CNTf) cross-sections called rods (diameter ∼ 69 μm, and length ∼ 40 μm) as an ultrasensitive platform for detection of common neurotransmitters. HD-CNTf rods microelectrodes have open-ended CNTs exposed at the interface with electrolytes and cells and display a low impedance value, i.e., 1050 Ω. Their fabrication starts with dry spun CNT fibers that are encapsulated in an insulating polymer to preserve their structure and alignment. Arrays of HD-CNTf rods microelectrodes were applied to detect neurotransmitters, i.e., dopamine (DA), serotonin (5-HT), epinephrine (Epn), and norepinephrine (Norepn), using square wave voltammetry (SWV) and cyclic voltammetry (CV). They demonstrate good linearity in a broad linear range (1 nM to 100 μM) with an excellent limit of detection, i.e., 32 pM, 31 pM, 64 pM, and 9 pM for DA, 5-HT, Epn, and Norepn, respectively. To demonstrate practical application of HD-CNTf rod arrays, detection of DA in human biological fluids and real time monitoring of DA release from living pheochromocytoma (PC12) cells were performed.

Electrochemical Micropyramid Array-Based Sensor for In Situ Monitoring of Dopamine Released from Neuroblastoma Cells

Abnormal dopamine neurotransmission is associated with several neurological and psychiatric disorders such as Parkinson's disease, schizophrenia, attention deficiency and hyperactivity disorder, and addiction. Developing highly sensitive, selective, and fast dopamine monitoring methods is of high importance especially for the early diagnosis of these diseases. Herein, we report a new ultrasensitive electrochemical sensing platform for in situ monitoring of cell-secreted dopamine using Au-coated arrays of micropyramid structures integrated directly into a Petri dish. This approach enables the monitoring of dopamine released from cells in real-time without the need for relocating cultured cells. According to the electrochemical analyses, our dopamine sensing platform exhibits excellent analytical characteristics with a detection limit of 0.50 ± 0.08 nM, a wide linear range of 0.01-500 μM, and a sensitivity of 0.18 ± 0.01 μA/μM. The sensor also has remarkable selectivity toward DA in the presence of different potentially interfering small molecules. The developed electrochemical sensor has great potential for in vitro analysis of neuronal cells as well as early diagnosis of different neurological diseases related to abnormal levels of dopamine.

Bioimaging using bipolar electrochemical microscopy with improved spatial resolution

In this study, we developed bipolar electrochemical microscopy (BEM) using a closed bipolar electrode (cBPE) array with an electrochemiluminescence (ECL) detecting system.

Electric and Electrochemical Microfluidic Devices for Cell Analysis

Microfluidic devices are widely used for cell analysis, including applications for single-cell analysis, healthcare, environmental monitoring, and organs-on-a-chip that mimic organs in microfluidics. Moreover, to enable high-throughput cell analysis, real-time monitoring, and non-invasive cell assays, electric and electrochemical systems have been incorporated into microfluidic devices. In this mini-review, we summarize recent advances in these systems, with applications from single cells to three-dimensional cultured cells and organs-on-a-chip. First, we summarize microfluidic devices combined with dielectrophoresis, electrophoresis, and electrowetting-on-a-dielectric for cell manipulation. Next, we review electric and electrochemical assays of cells to determine chemical section activity, and oxygen and glucose consumption activity, among other applications. In addition, we discuss recent devices designed for the electric and electrochemical collection of cell components from cells. Finally, we highlight the future directions of research in this field and their application prospects.

Nafion-Radical Hybrid Films on Carbon Nanotube Transistors for Monitoring Antipsychotic Drug Effects on Stimulated Dopamine Release

We developed floating electrode-based carbon nanotube biosensors for the monitoring of antipsychotic drug effects on the dopamine release from PC12 cells under potassium stimulation. Here, carbon nanotube field-effect transistors with floating electrodes were functionalized with 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS^•) radicals by Nafion films. This method allows us to build selective biosensors for dopamine detection with a detection limit down to 10 nM even in the presence of other neurotransmitters such as glutamate and acetylcholine, resulting from the selective interaction between ABTS^• radicals and dopamine. The sensors were also utilized to monitor the real-time release of dopamine from PC12 cells upon the stimulation of high-concentrated potassium solutions. Significantly, the antipsychotic effects of pimozide on the dopamine release from potassium-stimulated PC12 cells could also be evaluated in a concentration-dependent manner by using the sensors. The quantitative and real-time evaluation capability of our strategy should provide a versatile tool for many biomedical studies and applications.

Micro/nanoelectrochemical probe and chip devices for evaluation of three-dimensional cultured cells

Herein, we present an overview of recent research progress in the development of micro/nanoelectrochemical probe and chip devices for the evaluation of three-dimensional (3D) cultured cells. First, we discuss probe devices: a general outline, evaluation of O₂ consumption, enzyme-modified electrodes, evaluation of endogenous enzyme activity, and the collection of cell components from cell aggregates are discussed. The next section is focused on integrated chip devices: a general outline, electrode array devices, smart electrode array devices, droplet detection of 3D cultured cells, cell manipulation using dielectrophoresis (DEP), and electrodeposited hydrogels used for fabrication of 3D cultured cells on chip devices are discussed. Finally, we provide a summary and discussion of future directions of research in this field.

Real-time characterization of uptake kinetics of glioblastoma vs. astrocytes in 2D cell culture using microelectrode array

Extracellular measurement of uptake/release kinetics and associated concentration dependencies provides mechanistic insight into the underlying biochemical processes. Due to the recognized importance of preserving the natural diffusion processes within the local microenvironment, measurement approaches which provide uptake rate and local surface concentration of adherent cells in static media are needed. This paper reports a microelectrode array device and a methodology to measure uptake kinetics as a function of cell surface concentration in adherent 2D cell cultures in static fluids. The microelectrode array simultaneously measures local concentrations at five positions near the cell surface in order to map the time-dependent concentration profile which in turn enables determination of surface concentrations and uptake rates, via extrapolation to the cell plane. Hydrogen peroxide uptake by human astrocytes (normal) and glioblastoma multiforme (GBM43, cancer) was quantified for initial concentrations of 20 to 500 μM over time intervals of 4000 s. For both cell types, the overall uptake rate versus surface concentration relationships exhibited non-linear kinetics, well-described by a combination of linear and Michaelis-Menten mechanisms and in agreement with the literature. The GBM43 cells showed a higher uptake rate over the full range of concentrations, primarily due to a larger linear component. Diffusion-reaction models using the non-linear parameters and standard first-order relationships are compared. In comparison to results from typical volumetric measurements, the ability to extract both uptake rate and surface concentration in static media provides kinetic parameters that are better suited for developing reaction-diffusion models to adequately describe behavior in more complex culture/tissue geometries. The results also highlight the need for characterization of the uptake rate over a wider range of cell surface concentrations in order to evaluate the potential therapeutic role of hydrogen peroxide in cancerous cells.

Electrochemicolor Imaging Using an LSI-Based Device for Multiplexed Cell Assays

Multiplexed bioimaging systems have triggered the development of effective assays, contributing new biological information. Although electrochemical imaging is beneficial for quantitative analysis in real time, monitoring multiple cell functions is difficult. We have developed a novel electrochemical imaging system, herein, using a large-scale integration (LSI)-based amperometric device for detecting multiple biomolecules simultaneously. This system is designated as an electrochemicolor imaging system in which the current signals from two different types of biomolecules are depicted as a multicolor electrochemical image. The mode-selectable function of the 400-electrode device enables the imaging system and two different potentials can be independently applied to the selected electrodes. The imaging system is successfully applied for detecting multiple cell functions of the embryonic stem (ES) cell and the rat pheochromocytoma (PC12) cell aggregates. To the best of our knowledge, this is the first time that a real-time electrochemical mapping technique for multiple electroactive species, simultaneously, has been reported. The imaging system is a promising bioanalytical method for exploring complex biological phenomena.

Single Cell Electrochemiluminescence Imaging: From the Proof-of-Concept to Disposable Device-Based Analysis

We report here the development of coreactant-based electrogenerated chemiluminescence (ECL) as a surface-confined microscopy to image single cells and their membrane proteins. Labeling the entire cell membrane allows one to demonstrate that, by contrast with fluorescence, ECL emission is only detected from fluorophores located in the immediate vicinity of the electrode surface (i.e., 1-2 μm). Then, to present the potential diagnostic applications of our approach, we selected carbon nanotubes (CNT)-based inkjet-printed disposable electrodes for the direct ECL imaging of a labeled plasma receptor overexpressed on tumor cells. The ECL fluorophore was linked to an antibody and enabled to localize the ECL generation on the cancer cell membrane in close proximity to the electrode surface. Such a result is intrinsically associated with the unique ECL mechanism and is rationalized by considering the limited lifetimes of the electrogenerated coreactant radicals. The electrochemical stimulus used for luminescence generation does not suffer from background signals, such as the typical autofluorescence of biological samples. The presented surface-confined ECL microscopy should find promising applications in ultrasensitive single cell imaging assays.

Unique Configurations of Compression and Truncation of Neuronal Activity Underlie l-DOPA-Induced Selection of Motor Patterns in Aplysia

A key issue in neuroscience is understanding the ways in which neuromodulators such as dopamine modify neuronal activity to mediate selection of distinct motor patterns. We addressed this issue by applying either low or high concentrations of l-DOPA (40 or 250 μM) and then monitoring activity of up to 130 neurons simultaneously in the feeding circuitry of Aplysia using a voltage-sensitive dye (RH-155). l-DOPA selected one of two distinct buccal motor patterns (BMPs): intermediate (low l-DOPA) or bite (high l-DOPA) patterns. The selection of intermediate BMPs was associated with shortening of the second phase of the BMP (retraction), whereas the selection of bite BMPs was associated with shortening of both phases of the BMP (protraction and retraction). Selection of intermediate BMPs was also associated with truncation of individual neuron spike activity (decreased burst duration but no change in spike frequency or burst latency) in neurons active during retraction. In contrast, selection of bite BMPs was associated with compression of spike activity (decreased burst latency and duration and increased spike frequency) in neurons projecting through specific nerves, as well as increased spike frequency of protraction neurons. Finally, large-scale voltage-sensitive dye recordings delineated the spatial distribution of neurons active during BMPs and the modification of that distribution by the two concentrations of l-DOPA.

Electrochemical Motion Tracking of Microorganisms Using a Large-Scale-Integration-Based Amperometric Device

Motion tracking of microorganisms is useful to investigate the effects of chemical or physical stimulation on their biological functions. Herein, we describe a novel electrochemical imaging method for motion tracking of microorganisms using a large-scale integration (LSI)-based amperometric device. The device consists of 400 electrochemical sensors with a pitch of 250 μm. A convection flow caused by the motion of microorganisms supplies redox species to the sensors and increases their electrochemical responses. Thus, the flow is converted to electrochemical signals, enabling the electrochemical motion tracking of the microorganisms. As a proof of concept, capillary vibration was monitored. Finally, the method was applied to monitoring the motion of Daphnia magna. The motions of these microorganisms were clearly tracked based on the electrochemical oxidation of [Fe(CN)₆ ]^4- and reduction of O₂ .

Microfabricated, Massive Electrochemical Arrays of Uniform Ultramicroelectrodes

We report the preparation and electrochemical characterization of massive electrochemical arrays containing as many as 110,000 highly uniform ultramicroelectrodes (UMEs). These arrays were microfabricated using conventional photolithography techniques on a gold-coated silicon chip in a simple three-step method. Photoresist polymer was used as an effective insulating matrix to define 2 μm, 3 μm, and 4 μm diameter circular UMEs across a 1 × 1 mm² area. The UME arrays are high uniform and contain tens of thousands of active disk-shape UMEs slightly recessed in thin films of photoresist. These arrays were tested with cyclic voltammetry and copper electrodeposition to assess the adhesion of photoresist to the gold surface as well as to examine their electrochemical activity. Numerical simulations were performed to further validate their electrochemical response. These UME arrays can be a useful platform for fundamental understanding molecular transport in uniform electrochemical arrays and designing highly-sensitive electroanalytical sensors.