Dioxythiophene/Nafion Polymer Composite Membranes for Tunable Size-Based Selectivity in the Voltammetric Detection of Small Neuropeptides.

Carbon-fiber microelectrodes are proven and powerful sensors for electroanalytical measurements in a variety of environments, including complex systems such as the brain. They are used to detect and quantify a range of biological molecules, including neuropeptides, which are of broad interest for understanding physiological function. The enkephalins (met- and leu-) are endogenous opioid peptides that are involved in both pain and motivated behavior. Each is comprised of only five amino acids including tyrosine, an electroactive species. Electroanalytical measurements targeting tyrosine can reveal the dynamics of endogenous enkephalin transients in live tissue. However, when using electrochemistry in a biological system, selectivity is always a concern. Many larger neuropeptides also contain tyrosine. As such, they could generate a redox signature similar to that of the enkephalins, potentially confounding the measurement. In this work, three distinctly sized dioxythiophene monomers were mixed with Nafion and electrodeposited onto cylindrical carbon-fiber microelectrodes to form composite polymer films that allow for the tunable, size-based exclusion of larger molecules. The dioxythiophene monomers 3,4-ethylenedioxythiophene (EDOT), 3,4-propylenedioxythiophene (ProDOT), and 3,4-(2',2'-diethylpropylene) dioxythiophene (ProDOT-Et2) were used to create nanostructured pores of increasing size. The dioxythiophene/Nafion modified electrodes were characterized in the voltammetric detection of dopamine, a classic small molecule neurotransmitter, and a series of tyrosine containing neuropeptides of increasing size: met-enkephalin (M-ENK; 5 residues), oxytocin (OXY; 9 residues), neurotensin (NT; 13 residues), and neuropeptide Y (NPY; 36 residues). The modified electrodes exhibited enhanced selectivity for smaller peptide species over larger peptides in a manner consistent with the size of the dioxythiophene monomer incorporated into the polymeric film, allowing for tunability in terms of size-based selective detection.

A PEDOT: PSS/GO fiber microelectrode fabricated by microfluidic spinning for dopamine detection in human serum and PC12 cells.

Rapid and accurate in situ determination of dopamine is of great significance in the study of neurological diseases. In this work, poly (3,4-ethylenedioxythiophene): poly (styrenesulfonic acid) (PEDOT: PSS)/graphene oxide (GO) fibers were fabricated by an effective method based on microfluidic wet spinning technology. The composite microfibers with stratified and dense arrangement were continuously prepared by injecting PEDOT: PSS and GO dispersion solutions into a microfluidic chip. PEDOT: PSS/GO fiber microelectrodes with high electrochemical activity and enhanced electrochemical oxidation activity of dopamine were constructed by controlling the structure composition of the microfibers with varying flow rate. The fabricated fiber microelectrode had a low detection limit (4.56 nM) and wide detection range (0.01-8.0 µM) for dopamine detection with excellent stability, repeatability, and reproducibility. In addition, the PEDOT: PSS/GO fiber microelectrode prepared was successfully used for the detection of dopamine in human serum and PC12 cells. The strategy for the fabrication of multi-component fiber microelectrodes is a new and effective approach for monitoring the intercellular neurotransmitter dopamine and has high potential as an implantable neural microelectrode.

Application of a Carbon Fiber Microelectrode as a Sensor for Apocynin Electroanalysis.

In this study, a carbon fiber microelectrode (CF) was applied for the investigation of the electrochemical behavior of the natural antioxidant, apocynin (APO). Given the limited solubility of APO in water, a mixture of anhydrous acetic acid (AcH) with 20%, v/v acetonitrile (AN) and 0.1 mol L-1 sodium acetate (AcNa) was used. The electrochemical properties of APO were examined through linear sweep voltammetry (LSV), differential pulse voltammetry (DPV), and cyclic voltammetry (CV). The anodic oxidation of APO, which is the basis of the method used, proved to be diffusion-controlled and proceeded with a two-electron and one proton exchange. Both radicals and radical cations, arising from the first and second step of electrode reactions, respectively, underwent subsequent chemical transformations to yield more stable final products (EqCiEiCi mechanism). Using optimized DPV conditions, the anodic peak current of APO at a potential of 0.925 V vs. Ag/AgCl showed a good linear response within the concentration range of 2.7 × 10-6-2.6 × 10-4 mol L-1. The detection and quantification limits were determined as 8.9 × 10-7 and 2.7 × 10-6 mol L-1, respectively. The developed DPV method enabled the successful determination of APO in herbal extracts and in dietary supplements. It should be noted that this is the first method to be used for voltammetric determination of APO.

Suppression of Resistive Coupling in Nanogap Electrochemical Cell: Resolution of Dual Pathways for Dopamine Oxidation.

A nanogap cell involves two working electrodes separated by a nanometer-wide solution to enable unprecedented electrochemical measurements. The powerful nanogap measurements, however, can be seriously interfered with by resistive coupling between the two electrodes to yield erroneous current responses. Herein, we employ the nanogap cell based on double carbon-fiber microelectrodes to suppress resistive coupling for the assessment of intrinsic current responses. Specifically, we modify a commercial bipotentiostat to compensate the Ohmic potential drop shared by the two electrodes through the common current pathway with a fixed resistance in the solution. Resistive coupling through both non-Faradaic and Faradaic processes is suppressed to eliminate erroneous current responses. Our approach is applied to investigate the mechanism of dopamine oxidation at carbon-fiber microelectrodes as important electrochemical sensors for the crucial neurotransmitter. Resistive coupling is suppressed to manifest the intrinsic current responses based on the oxidation of both adsorbed and non-adsorbed forms of dopamine to the respective forms of dopamine-o-quinone. The simultaneous dual oxidation pathways are observed for the first time and can be mediated through either non-concerted or concerted mechanisms of adsorption-coupled electron transfer. The two mechanisms are not discriminated for the two-electron oxidation of dopamine because it can not be determined whether the intermediate, dopamine semi-quinone, is adsorbed on the electrode surface. Significantly, our approach will be useful to manifest intrinsic current responses without resistive coupling for nanogaps and microgaps, which are too narrow to eliminate the common solution resistance by optimizing the position of a reference electrode.

Measurement of neuropeptide Y with molecularly imprinted polypyrrole on carbon fiber microelectrodes.

The measurement of neuropeptides using small electrodes for high spatial resolution would provide us with localized information on the release of neuromolecules. The release of Neuropeptide Y (NPY) is related to different neurological diseases such as stress, obesity, and PTSD, among others. In this conference paper, we electrodeposited polypyrrole on carbon fiber microelectrodes in the presence of NPY to develop a molecularly imprinted polypyrrole sensitive to NPY. Optimization of the electrodeposition process resulted in the full coverage of the polymer with nucleation sites on the carbon fiber ridges, achieving completion by the seventh cycle. Electrodeposition was performed for five cycles, and using cyclic voltammetry (CV), we studied the change in the oxidation current peak for polypyrrole due to the presence of NPY. We also observed a change in capacitance due to the presence of NPY, which was studied by electrochemical impedance spectroscopy (EIS). A linear correlation was found between the oxidation peak and the concentration of NPY between 50 ng/mL and 1000 ng/mL. In addition, a linear correlation was also found between microelectrode capacitance and the concentration of NPY between 50 ng/mL and 1000 ng/mL at 100 kHz.

Amperometric bio-sensing of lactate and oxygen concurrently with local field potentials during status epilepticus.

Epilepsy is a prevalent neurological disorder with a complex pathogenesis and unpredictable nature, presenting limited treatment options in >30 % of affected individuals. Neurometabolic abnormalities have been observed in epilepsy patients, suggesting a disruption in the coupling between neural activity and energy metabolism in the brain. In this study, we employed amperometric biosensors based on a modified carbon fiber microelectrode platform to directly and continuously measure lactate and oxygen dynamics in the brain extracellular space. These biosensors demonstrated high sensitivity, selectivity, and rapid response time, enabling in vivo measurements with high temporal and spatial resolution. In vivo recordings in the cortex of anaesthetized rats revealed rapid and multiphasic fluctuations in extracellular lactate and oxygen levels following neuronal stimulation with high potassium. Furthermore, real-time measurement of lactate and oxygen concentration dynamics concurrently with network electrical activity during status epilepticus induced by 4-aminopyridine (4-AP) demonstrated phasic changes in lactate levels that correlated with bursts of electrical activity, while tonic levels of lactate remained stable during seizures. This study highlights the complex interplay between lactate dynamics, electrical activity, and oxygen utilization in epileptic seizures.

Simultaneous detection of norepinephrine and 5-hydroxytryptophan using poly-alizarin/multi-walled carbon nanotubes-graphene modified carbon fiber microelectrode array sensor.

Multi-walled carbon nanotubes, graphene and alizarin polymer composites coated carbon fiber microelectrode array sensor (p-AZ/MWCNT-GR/CFMEA) was constructed and used for the simultaneous detection of norepinephrine (NE) and 5-hydroxytryptophan (5-HT). The morphology and structural characteristics of sensor are characterized using scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. Its electrochemical behavior has been studied with cyclic voltammetry and electrochemical impedance spectroscopy. The sensor exhibits excellent electrochemical activity for the oxidation of NE and 5-HT, two well separated oxidation peaks with the peak potential difference of 220 mV are observed on the cyclic voltammogram. NE and 5-HT both show two electrons and two protons electrochemical reaction on the p-AZ/MWCNT-GR/CFMEA. Under the optimized experiment conditions, the linear ranges of the sensor for NE and 5-HT are 0. 08- 8 µM and 0. 1-20 µM with detection limits of 4. 22 nM and 14. 2 nM (S/N = 3), respectively. In addition, the microsensor array show good reproducibility, stability and selectivity for the determination of NE and 5-HT. Finally, the p-AZ/MWCNT-GR/CFMEA is applied to the simultaneous detection of NE and 5-HT in human serum samples and macrophages.

Simultaneous, Real-Time Detection of Glutamate and Dopamine in Rat Striatum Using Fast-Scan Cyclic Voltammetry.

Glutamate and dopamine (DA) represent two key contributors to striatal functioning, a region of the brain that is essential to motor coordination and motivated behavior. While electroanalytical techniques can be utilized for rapid, spatially resolved detection of DA in the interferent-rich brain environment, glutamate, a nonelectroactive analyte, cannot be directly detected using electroanalytical techniques. However, it can be probed using enzyme-based sensors, which generate an electroactive reporter in the presence of glutamate. The vast majority of glutamate biosensors have relied on amperometric sensing, which is an inherently nonselective detection technique. This approach necessitates the use of complex and performance-limiting modifications to ensure the desired single-analyte specificity. Here, we present a novel glutamate microbiosensor fabricated on a carbon-fiber microelectrode substrate and coupled with fast-scan cyclic voltammetry (FSCV) to enable the simultaneous quantification of glutamate and DA at single recording sites in the brain, which is impossible when using typical amperometric approaches. The glutamate microbiosensors were characterized for sensitivity, stability, and selectivity by using a voltammetric waveform optimized for the simultaneous detection of both species. The applicability of these sensors for the investigation of neural circuits was validated in the rat ventral striatum. Electrically evoked glutamate and DA release were recorded at single-micrometer-scale locations before and after pharmacological manipulation of glutamatergic signaling. Our novel glutamate microbiosensor advances the state of the art by providing a powerful tool for probing coordination between these two species in a way that has previously not been possible.

In Vivo Electrochemical Measurement of Glucose Variation in the Brain of Early Diabetic Mice.

Diabetes is a chronic disease caused by a decrease in insulin level or insulin resistance. Diabetes also has detrimental effects on the brain, which can lead to the injury of the blood-brain barrier and influence the glucose transport. In this study, we use in vivo electrochemical measurement to explore the glucose variation in the brain of early diabetic mice. The glucose level in mice brain is measured using a carbon fiber microelectrode modified with the osmium-derivatized polymer and glucose oxidase. The electrode shows an excellent electrochemical performance, antibiofouling ability, and high stability, which can work stably in the mice brain for 2 h. By monitoring the glucose level in the brain of normal and diabetic mice after injection of concentrated glucose solution into the abdominal cavity, it is found that the variation of cerebral glucose decreases by ∼2 fold for diabetic mice. It is proposed that diabetes can downregulate the activity of glucose transporter in the brain and finally inhibit the brain glucose uptake.

Exploiting Microelectrode Geometry for Comprehensive Detection of Individual Exocytosis Events at Single Cells.

Carbon fiber microelectrodes are commonly used for real-time monitoring of individual exocytosis events at single cells. Since the nature of an electrochemical signal is fundamentally governed by mass transport to the electrode surface, microelectrode geometry can be exploited to achieve precise and accurate measurements. Researchers traditionally pair amperometric measurements of exocytosis with a ∼10-µm diameter, disk microelectrode in an "artificial synapse" configuration to directly monitor individual release events from single cells. Exocytosis is triggered, and released molecules diffuse to the "post-synaptic" electrode for oxidation. This results in a series of distinct current spikes corresponding to individual exocytosis events. However, it remains unclear how much of the material escapes detection. In this work, the performance of 10- and 34-µm diameter carbon fiber disk microelectrodes was directly compared in monitoring exocytosis at single chromaffin cells. The 34-µm diameter electrode was more sensitive to catecholamines and enkephalins than its traditional, 10-µm diameter counterpart, and it more effectively covered the entire cell. As such, the larger sensor detected more exocytosis events overall, as well as a larger quantal size, suggesting that the traditional tools underestimate the above measurements. Both sensors reliably measured l-DOPA-evoked changes in quantal size, and both exhibited diffusional loss upon adjustment of cell-electrode spacing. Finite element simulations using COMSOL support the improved collection efficiency observed using the larger sensor. Overall, this work demonstrates how electrode geometry can be exploited for improved detection of exocytosis events by addressing diffusional loss─an often-overlooked source of inaccuracy in single-cell measurements.

Carbon Electrode Sensor for the Measurement of Cortisol with Fast-Scan Cyclic Voltammetry.

Cortisol is a vital steroid hormone that has been known as the "stress hormone", which is elevated during times of high stress and anxiety and has a significant impact on neurochemistry and brain health. The improved detection of cortisol is critically important as it will help further our understanding of stress during several physiological states. Several methods exist to detect cortisol; however, they suffer from low biocompatibility and spatiotemporal resolution, and they are relatively slow. In this study, we developed an assay to measure cortisol with carbon fiber microelectrodes (CFMEs) and fast-scan cyclic voltammetry (FSCV). FSCV is typically utilized to measure small molecule neurotransmitters by producing a readout cyclic voltammogram (CV) for the specific detection of biomolecules on a fast, subsecond timescale with biocompatible CFMEs. It has seen enhanced utility in measuring peptides and other larger compounds. We developed a waveform that scanned from -0.5 to -1.2 V at 400 V/s to electro-reduce cortisol at the surface of CFMEs. The sensitivity of cortisol was found to be 0.87 ± 0.055 nA/µM (n = 5) and was found to be adsorption controlled on the surface of CFMEs and stable over several hours. Cortisol was co-detected with several other biomolecules such as dopamine, and the waveform was fouling resistant to repeated injections of cortisol on the surface of the CFMEs. Furthermore, we also measured exogenously applied cortisol into simulated urine to demonstrate biocompatibility and potential use in vivo. The specific and biocompatible detection of cortisol with high spatiotemporal resolution will help further elucidate its biological significance and further understand its physiological importance and impact on brain health.

Aptamer functionalized cell membrane for brain and nerve cell sensing with high sensitivity and stability.

Accurate dopamine (DA) monitoring with high stability is essential for investigating the chemical basis of brain function and pathology. Electrochemical-based tissue-implantable carbon fiber electrodes (CFEs) show great potential in sensing the dynamics of neurochemicals at a sub-second timescale. However, their anti-fouling property, selectivity, and stability pose challenges. Here, we presented a novel strategy to enhance electrode biocompatibility and stability by modifying CFE with a chitosan (CS) film, brain cell membrane (M), and aptamer cholesterol amphiphiles (DNA-cho). We found that CFE was uniformly covered by a cicada-like membrane after being modified. Electrochemical characterizations indicated that DNA-cho-M-CS-CFE exhibited a wide linear range of DA concentration and showed high sensitivity, specificity, and stability. The electrode also presented excellent fouling resistance and biocompatibility. Moreover, the biosensor was used to detect DA in K+-induced brain slices and PC12 cells with a satisfactory stability and sensitivity and to prove that LPS treatment leads to the delayed and decreased release of DA. DNA-cho-M-CS-CFE showed excellent electrochemical performance and unique advantages for long-term in vivo sensing of living cells, thus providing a new feasible scheme for studying neurochemical kinetics and brain diseases.

Editors' Choice-Review-The Future of Carbon-Based Neurochemical Sensing: A Critical Perspective.

Carbon-based sensors have remained critical materials for electrochemical detection of neurochemicals, rooted in their inherent biocompatibility and broad potential window. Real-time monitoring using fast-scan cyclic voltammetry has resulted in the rise of minimally invasive carbon fiber microelectrodes as the material of choice for making measurements in tissue, but challenges with carbon fiber's innate properties have limited its applicability to understudied neurochemicals. Here, we provide a critical review of the state of carbon-based real-time neurochemical detection and offer insight into ways we envision addressing these limitations in the future. This piece focuses on three main hinderances of traditional carbon fiber based materials: diminished temporal resolution due to geometric properties and adsorption/desorption properties of the material, poor selectivity/specificity to most neurochemicals, and the inability to tune amorphous carbon surfaces for specific interfacial interactions. Routes to addressing these challenges could lie in methods like computational modeling of single-molecule interfacial interactions, expansion to tunable carbon-based materials, and novel approaches to synthesizing these materials. We hope this critical piece does justice to describing the novel carbon-based materials that have preceded this work, and we hope this review provides useful solutions to innovate carbon-based material development in the future for individualized neurochemical structures.

A Platinized Carbon Fiber Microelectrode-Based Oxidase Biosensor for Amperometric Monitoring of Lactate in Brain Slices.

BACKGROUND: Direct and real-time monitoring of lactate in the extracellular space can help elucidate the metabolic and modulatory role of lactate in the brain. Compared to in vivo studies, brain slices allow the investigation of the neural contribution separately from the effects of cerebrovascular response and permit easy control of recording conditions. METHODS: We have used a platinized carbon fiber microelectrode platform to design an oxidase-based microbiosensor for monitoring lactate in brain slices with high spatial and temporal resolution operating at 32 °C. Lactate oxidase (Aerococcus viridans) was immobilized by crosslinking with glutaraldehyde and a layer of polyurethane was added to extend the linear range. Selectivity was improved by electropolymerization of m-phenylenediamine and concurrent use of a null sensor. RESULTS: The lactate microbiosensor exhibited high sensitivity, selectivity, and optimal analytical performance at a pH and temperature compatible with recording in hippocampal slices. Evaluation of operational stability under conditions of repeated use supports the suitability of this design for up to three repeated assays. CONCLUSIONS: The microbiosensor displayed good analytical performance to monitor rapid changes in lactate concentration in the hippocampal tissue in response to potassium-evoked depolarization.

Improved Serotonin Measurement with Fast-Scan Cyclic Voltammetry: Mitigating Fouling by SSRIs.

Selective serotonin reuptake inhibitors (SSRIs) have been used for decades to treat disorders linked to serotonin dysregulation in the brain. Moreover, SSRIs are often used in studies aimed at measuring serotonin with fast-scan cyclic voltammetry (FSCV) in living tissues. Here, we show that three different SSRIs - fluoxetine, escitalopram, and sertraline - significantly diminish the faradaic oxidation current of serotonin when employing the commonly used Jackson waveform. Coating carbon-fiber microelectrodes (CFMs) with Nafion resulted in further degradation of peak current, increased response times, and decreased background charging currents compared to bare CFMs. To decrease fouling, we employed a recently published extended serotonin waveform, which scans to a maximum positive potential of +1.3 V, rather than +1.0 V used in the Jackson waveform. Use of this waveform with bare CFMs alleviated the decrease in faradaic current, indicating decreased electrode fouling. Collectively, our results suggest that fouling considerations are important when designing FSCV experiments that employ SSRIs and that they can be overcome by using the appropriate waveform.

Spatial Transcriptomics as a Novel Approach to Redefine Electrical Stimulation Safety.

Current standards for safe delivery of electrical stimulation to the central nervous system are based on foundational studies which examined post-mortem tissue for histological signs of damage. This set of observations and the subsequently proposed limits to safe stimulation, termed the "Shannon limits," allow for a simple calculation (using charge per phase and charge density) to determine the intensity of electrical stimulation that can be delivered safely to brain tissue. In the three decades since the Shannon limits were reported, advances in molecular biology have allowed for more nuanced and detailed approaches to be used to expand current understanding of the physiological effects of stimulation. Here, we demonstrate the use of spatial transcriptomics (ST) in an exploratory investigation to assess the biological response to electrical stimulation in the brain. Electrical stimulation was delivered to the rat visual cortex with either acute or chronic electrode implantation procedures. To explore the influence of device type and stimulation parameters, we used carbon fiber ultramicroelectrode arrays (7 µm diameter) and microwire electrode arrays (50 µm diameter) delivering charge and charge density levels selected above and below reported tissue damage thresholds (range: 2-20 nC, 0.1-1 mC/cm2). Spatial transcriptomics was performed using Visium Spatial Gene Expression Slides (10x Genomics, Pleasanton, CA, United States), which enabled simultaneous immunohistochemistry and ST to directly compare traditional histological metrics to transcriptional profiles within each tissue sample. Our data give a first look at unique spatial patterns of gene expression that are related to cellular processes including inflammation, cell cycle progression, and neuronal plasticity. At the acute timepoint, an increase in inflammatory and plasticity related genes was observed surrounding a stimulating electrode compared to a craniotomy control. At the chronic timepoint, an increase in inflammatory and cell cycle progression related genes was observed both in the stimulating vs. non-stimulating microwire electrode comparison and in the stimulating microwire vs. carbon fiber comparison. Using the spatial aspect of this method as well as the within-sample link to traditional metrics of tissue damage, we demonstrate how these data may be analyzed and used to generate new hypotheses and inform safety standards for stimulation in cortex.

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.

An integrated electrochemical POCT platform for ultrasensitive circRNA detection towards hepatocellular carcinoma diagnosis.

Hepatocellular carcinoma (HCC) is the fourth leading cause of cancer-related death. Circ-CDYL, one of the circular RNAs (circRNAs), is recognized as an independent marker for HCC early diagnosis. Point-of-care testing (POCT) of circRNA is essential and in great demand for clinical applications. Herein, we report a fully integrated electrochemical POCT platform for circRNA detection based on Au nanoflowers (AuNFs)/peptide nucleic acid (PNA) modified carbon-fiber microelectrode (CFME). PNA is applied as the recognition element, highly specified for a back-splice junction of circRNA. AuNFs increased active site for PNA probes, improving target-capturing efficiency at an ultralow level. The platform provides a linear range of 10 fM to 1 µM, with a detection limit as low as 3.29 fM. This biosensor demonstrates high specificity towards one-base mismatch and is stable for up to 24 days. The analytical performance has also been verified in human serum samples, demonstrating the potential utility in clinical POCT applications for HCC.

3D nitrogen-doped carbon nanofoam arrays embedded with PdCu alloy nanoparticles: Assembling on flexible microelectrode for electrochemical detection in cancer cells.

In this work, we developed a novel and facile strategy for the synthesis of a highly active and stable electrocatalyst based on PdCu alloy nanoparticles (PdCu-ANPs) embedded in 3D nitrogen-doped carbon (NC) nanofoam arrays (NFAs), which were assembled on flexible carbon fiber (CF) microelectrode for in situ sensitive electrochemical detection of biomarker H2O2 in cancer cells. Our results showed that NC-NFAs support possessed a unique hierarchically porous architecture by integrating the macrospores in arrays scaffold within mesopores in individual NC nanofoam, which offered exceptionally large surface area for embedding high-density PdCu-ANPs in it as well as facilitated the mass transfer and molecular diffusion during the electrochemical reaction. Taking the advantages of the unique structural merit of NC-NFAs support and excellent electrocatalyitc properties of PdCu-ANPs that embedded in it, the resultant PdCu-ANPs/NC-NFAs modified CF microelectrode exhibited good electrochemical sensing performances towards H2O2 including a wide linear range from 2.0 µM to 3.44 mM, a low detection limit of 500 nM, as well as good reproducibility, stability and anti-interference ability. When used in real-time in situ tracking H2O2 secreted from different types of human colorectal cancer cells, i.e., HCT116, HT29, SW48 and LoVo, it can distinguish the types of cancer cells by measuring the number of extracellular H2O2 molecules released per cell, which demonstrates its great promise in cancer diagnose and management.

Plasmodium chabaudi Affects Mast Cell Degranulation as Measured by Carbon-Fiber Microelectrode Amperometry.

Mast cells (MCs) are effector cells of the immune system commonly known for their role in asthma and allergy. They are present throughout biological systems in various tissues, serving as an interface between the biological system and environment. Previous work characterizing the impact of malaria on MCs revealed contradictory results, showing minimal to strong correlation between MC degranulation and disease progression. This work seeks to reveal how MC degranulation is impacted in the presence of malaria, induced by Plasmodium chabaudi, using a mouse model and a single cell measurement technique that reveals exquisite biophysical detail about any impacts to the degranulation process. It was hypothesized that the malaria parasites would impact MC degranulation response during live infection, and the differences would be revealed via carbon-fiber microelectrode amperometry. In fact, the data collected show that different stages of malaria infection affect MC degranulation differently, affirming the importance of considering different infection stages in future studies of malarial immune response. Furthermore, a comparison of MC degranulation response to that measured from platelets under similar circumstances shows similar trends in quantitative degranulation, suggesting that MC and platelet exocytosis machinery are affected similarly despite their distinct biological roles. However, based on the small number of mouse replicates, the studies herein suggest that there should be further study about cellular and disease processes. Overall, the work herein reveals important details about the role of MCs in malaria progression, relevant during treatment decisions, as well as a potentially generalizable impact on chemical messenger secretion from cells during malarial progression.