Electroanalysis of ascorbate and dopamine at a gold electrode modified with a positively charged self-assembled monolayer

In Situ Ratiometric Determination of Cerebral Ascorbic Acid after Ischemia Reperfusion

Ascorbic acid (AA) is significant in protecting the brain from further damage and maintaining brain homeostasis after ischemia stroke (IS); however, the dynamic change of cerebral AA content after different degrees of ischemic stroke is still unclear. Herein, carboxylated single-walled carbon nanotube (CNT-COOH)- and polyethylenedioxythiophene (PEDOT)-modified carbon fiber microelectrodes (CFEs) were proposed to detect in situ cerebral AA with sensitivity, selectivity, and stability. Under differential pulse voltammetry scanning, the CFE/CNT-COOH/PEDOT gave a ratiometric, electrochemically responsive signal. The internal standard peak at -310 mV was from the reversible peak of O2 reduction and the deprotonation and protonation of quinone groups, while AA was oxidized at -70 mV. In vivo experimental results indicated that the cerebral AA level gradually increased with the ischemic time increasing in different middle cerebral artery occlusion (MCAO) model mice. This work implies that the increasing cerebral AA level may be highly related to the glutamate excitotoxicity and ROS-led cell apoptosis and paves a new way for further understanding the release and metabolic mechanisms of AA during ischemia reperfusion and IS.

Electrochemically Activatable Liquid Organic Hydrogen Carriers and Their Applications

Hydrogen has been chosen as an environmentally benign energy source to replace fossil-fuel-based energy systems. Since hydrogen is difficult to store and transport in its gaseous phase, thermochemical liquid organic hydrogen carriers (LOHCs) have been developed as one of the alternative technologies. However, the high temperature and pressure requirements of thermochemical LOHC systems result in huge energy waste and impracticality. This Perspective proposes electrochemical (EC)-LOHCs capable of more efficient, safer, and lower temperature and pressure hydrogen storage/utilization. To enable this technology, several EC-LOHC candidates such as isopropanol, phenolic compounds, and organic acids are described, and the latest research trends and design concepts of related homo/hetero-based electrocatalysts are discussed. In addition, we propose efficient fuel-cell-based systems that implement electrochemical (de)hydrogenation of EC-LOHCs and present prospects for relevant technologies.

Environment-Friendly Ascorbic Acid Fuel Cell

Recently, ascorbic acid (AA) has been studied as an environment-friendly fuel for energy conversion devices. This review article has deliberated an overview of ascorbic acid electrooxidation and diverse ion exchange types of AA-based fuel cells for the first time. Metal and carbon-based catalysts generated remarkable energy from environment-friendly AA fuel. The possibility of using AA in a direct liquid fuel cell (DLFC) without emitting any hazardous pollutants is discussed. AA fuel cells have been reviewed based on carbon nanomaterials, alloys/bimetallic nanoparticles, and precious and nonprecious metal nanoparticles. Finally, the obstacles and opportunities for using AA-based fuel cells in practical applications have also been incorporated.

Microelectrode Sensor for Real-Time Measurements of Nitrite in the Living Brain, in the Presence of Ascorbate

The impaired blood flow to the brain causes a decrease in the supply of oxygen that can result in cerebral ischemia; if the blood flow is not restored quickly, neuronal injury or death will occur. Under hypoxic conditions, the production of nitric oxide (^●NO), via the classical L-arginine–^●NO synthase pathway, is reduced, which can compromise ^●NO-dependent vasodilation. However, the alternative nitrite (NO₂⁻) reduction to ^●NO, under neuronal hypoxia and ischemia conditions, has been viewed as an in vivo storage pool of ^●NO, complementing its enzymatic synthesis. Brain research is thus demanding suitable tools to probe nitrite’s temporal and spatial dynamics in vivo. In this work, we propose a new method for the real-time measurement of nitrite concentration in the brain extracellular space, using fast-scan cyclic voltammetry (FSCV) and carbon microfiber electrodes as sensing probes. In this way, nitrite was detected anodically and in vitro, in the 5–500 µM range, in the presence of increasing physiological concentrations of ascorbate (100–500 µM). These sensors were then tested for real-time and in vivo recordings in the anesthetized rat hippocampus; using fast electrochemical techniques, local and reproducible transients of nitrite oxidation signals were observed, upon pressure ejection of an exogenous nitrite solution into the brain tissue. Nitrite microsensors are thus a valuable tool for investigating the role of this inorganic anion in brain redox signaling.

Poly(lactic acid)/Carbon Nanotube Composite Microneedle Arrays for Dermal Biosensing

Minimally invasive, reliable and low-cost in vivo biosensors that enable real-time detection and monitoring of clinically relevant molecules and biomarkers can significantly improve patient health care. Microneedle array (MNA)-based electrochemical sensors offer exciting prospects in this respect, as they can sample directly from the skin. However, their acceptability is dependent on developing a highly scalable and cost-effective fabrication strategy. In this work, we evaluated the potential for poly(lactic acid)/carboxyl-multiwalled carbon nanotube (PLA/ f-MWCNT) composites to be developed into MNAs and their effectiveness for dermal biosensing. Our results show that MNAs are easily made from solvent-cast nanocomposite films by micromolding. A maximum carbon nanotube (CNT) loading of 6 wt % was attained with the current fabrication method. The MNAs were mechanically robust, being able to withstand axial forces up to 4 times higher than necessary for skin insertion. Electrochemical characterization of these MNAs by differential pulse voltammetry (DPV) produced a linear current response toward ascorbic acid, with a limit of detection of 180 μM. In situ electrochemical performance was assessed by DPV measurements in ex vivo porcine skin. This showed active changes characterized by two oxidative peaks at 0.23 and 0.69 V, as a result of the diffusion of phosphate-buffered saline. The diagnostic potential of this waveform was further evaluated through a burn wound model. This showed an attenuated oxidative response at 0.69 V. Importantly, the impact of the burn could be measured at progressive distances from the burn site. Overall, alongside the scalable fabrication strategy, the DPV results promise efficient electrochemical biosensors based on CNT nanocomposite MNAs.

Cost-effective synthesis of three-dimensional nitrogen-doped nanostructured carbons with hierarchical architectures from the biomass of sea-tangle for the amperometric determination of ascorbic acid

In this work, the three-dimensional nitrogen-doped nanostructured carbons with hierarchical architectures (3D-NNCsHAs) with high density of defective sites, high surface area and pluralities of pore size distributions was prepared through the pyrolysis of sea-tangle (Laminaria japonica), an inexpensive, eco-friendly and abundant precursor. Benefitting from their structural uniqueness, a selective and sensitive ascorbic acid (AA) sensor based on 3D-NNCsHAs was developed. Compared to the glassy carbon electrode (GCE) and the carbon nanotubes modified GCE (CNTs/GCE), the 3D-NNCsHAs modified GCE (3D-NNCsHAs/GCE) presents higher performance towards the electrocatalysis and detection of AA, such as lower detection limit (1 μM), wider linear range (10-4410 μM) and lower electrooxidation peak potential (-0.02 V vs. Ag/AgCl). In addition, 3D-NNCsHAs/GCE also exhibits high anti-interference and anti-fouling abilities for AA detection. Particularly, the fabricated 3D-NNCsHAs/GCE is able to determine AA in real samples and the results acquired are satisfactory. Therefore, the 3D-NNCsHAs can be considered as a kind of novel electrode nanomaterial for the fabrication of selective and sensitive AA sensor for the extensive practical applications ranging from food analysis, to pharmaceutical industry and clinical test.

Electrospun γ-Fe2O3 nanofibers as bioelectrochemical sensors for simultaneous determination of small biomolecules

Nanofibers of α-Fe₂O₃ and γ-Fe₂O₃ have been obtained after the controlled calcination of precursor nanofibers synthesized by electrospinning. α-Fe₂O₃ nanofibers showed an irregular toruloid structure due to the decomposition of poly (4-vinyl) pyridine in air while γ-Fe₂O₃ nanoparticles decorated nanofibers were observed after the calcination under N₂ atmosphere. Electrochemical measurements showed that different electrochemical behaviors were observed on the glassy carbon electrodes modified by α-Fe₂O₃ and γ-Fe₂O₃ nanofibers. The electrode modified by γ-Fe₂O₃ nanofibers exhibited high electrocatalytic activities toward oxidation of dopamine, uric acid and ascorbic acid while α-Fe₂O₃ nanofibers cannot. Furthermore, the γ-Fe₂O₃ modified electrode can realize the selective detection of biomolecules in ternary electrolyte solutions. The synthesis of nanofibers of α-Fe₂O₃ and γ-Fe₂O₃ and their electrochemical sensing properties relationship have been discussed and analyzed based on the experimental results.

Simultaneous measurements of ascorbate and glutamate in vivo in the rat brain using carbon fiber nanocomposite sensors and microbiosensor arrays

Nanocomposite sensors consisting of carbon fiber microelectrodes modified with Nafion® and carbon nanotubes, and ceramic-based microelectrode biosensor arrays were used to measure ascorbate and glutamate in the brain with high spatial, temporal and chemical resolution. Nanocomposite sensors displayed electrocatalytic properties towards ascorbate oxidation, translated into a negative shift from +0.20V to -0.05V vs. Ag/AgCl, as well as a significant increase (10-fold) of electroactive surface area. The estimated average basal concentration of ascorbate in vivo in the CA1, CA3 and dentate gyrus (DG) sub regions of the hippocampus were 276±60μM (n=10), 183±30μM (n=10) and 133±42μM (n=10), respectively. The glutamate microbiosensor arrays showed a high sensitivity of 5.3±0.8pAμM^-1 (n=18), and LOD of 204±32nM (n=10), and t_50% response time of 0.9±0.02s (n=6) and high selectivity against major interferents. The simultaneous and real-time measurements of glutamate and ascorbate in the hippocampus of anesthetized rats following local stimulus with KCl or glutamate revealed a dynamic interaction between the two neurochemicals.

Simultaneous voltammetric detection of dopamine, ascorbic acid and uric acid using a poly(2-(N-morpholine)ethane sulfonic acid)/RGO modified electrode

A poly(2-(N-morpholine) ethane sulfonic acid)/reduced graphene oxide (RGO) modified glassy carbon electrode (GCE) was prepared using an electropolymerization method, and was characterized by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The electrochemical behaviors and simultaneous detection of ascorbic acid (AA), dopamine (DA) and uric acid (UA) at this electrode were studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Tests showed that this electrode exhibited excellent electrocatalytic activity towards the oxidation of AA, DA and UA. The oxidation peak currents of AA, DA and UA were proportional with their concentrations in the ranges 1.0 μM-30 μM (30 μM-100 μM), 0.05 μM-100 μM and 0.1 μM-100 μM, with detection limits of 0.43 μM, 0.0062 μM and 0.056 μM, respectively. In addition, this electrode exhibited an excellent selectivity, reproducibility and stability, and has been successfully used to determine real samples with satisfactory results.

Synthesis of carbon nanoparticle embedded graphene for sensitive and selective determination of dopamine and ascorbic acid in biological fluids

We have prepared carbon nanoparticle embedded graphene (CNEG) by carbonizing a ternary composite of GO/melamine-formaldehyde resin/Zn(OAc)₂.

Interfacial Janus gold nanoclusters as excellent phase- and orientation-specific dopamine sensors

This investigation, following our recent report on the one-pot hemi-micellar interfacial synthesis of Janus gold nanoclusters and the inter-cluster electron coupling establishing insulator-metal transition in the oriented Janus monolayers [Langmuir, 2010, 26(17), 14047], was to fabricate modified electrodes for sensing dopamine, the neurotransmitter. With a detection limit in the sub-nanomolar range, the apparent electron transfer rate constants for dopamine detection signified an intricate Janus cluster 2D phase dependency. Surface pressure as a thermodynamic variable controlled the electronic communication between the clusters as a result of varied inter-cluster distance and size, ultimately reflecting on the sensitivity and detection limit for dopamine sensing. The non-covalent nature of the ligands on the core metal clusters facilitated the overall electro-catalytic oxidation of dopamine. The notable feature of this precise work was that it established a more effective phase- and orientation-specific Janus cluster sensing than those reported through patterned gold nanowire based sensors.

Determination of dopamine in pharmaceutical formulation using enhanced luminescence from europium complex

Biologically important compound dopamine plays an important role in the central and peripheral nervous systems. Insufficient dopamine level due to the loss of dopamine producing cells may lead to disease called Schizophrenia and Parkinson's disease. Hence, a simple and fast detection of dopamine is necessary to study in the fields of neurophysiology and clinical medicine. An enhanced fluorimetric determination of dopamine in the presence of ascorbic acid is achieved using photoluminescence of europium complex, Eu(III)-dipicolinic acid. In order to obtain better responses, several operational parameters have been investigated. Under the optimum conditions, the method showed good stability and reproducibility. The application of this method for the determination of dopamine neurotransmitters was satisfactory. Linear response was found down to 3.0 × 10(-7)M with limit of detection 1.0 × 10(-8)M. The relative standard deviation was found to be 3.33% from 20 independent measurements for 1.0 × 10(-5)M of dopamine.

Sensitivity and selectivity determination of bisphenol A using SWCNT-CD conjugate modified glassy carbon electrode

In this study, we demonstrated a highly sensitive electrochemical sensor for the determination of bisphenol A (BPA) in aqueous solution by using single-walled carbon nanotubes (SWCNTs)/β-cyclodextrin (β-CD) conjugate (SWCNT-CD) modified glassy carbon electrode (GCE). The cyclic voltammetry results show that the modified GCE exhibits strong catalytic activity toward the oxidation of BPA with a well-defined cyclic voltammetric peak at 0.543 V. The response current exhibits a linear range between 10.8 nM and 18.5 μM with a high sensitivity (1256 μA mM(-1)). The detection limit of BPA is 1.0 nM (S/N=3). The enhanced performance of the fabricated sensor can be attributed to the combination of the excellent electrocatalytic properties of SWCNTs and the molecular recognition ability of β-CD. The sensor was successfully applied to determine BPA leached from real plastic samples with good recovery, ranging from 95% to 103%.

The simultaneous electrochemical detection of ascorbic acid, dopamine, and uric acid using graphene/size-selected Pt nanocomposites

In this study, a graphene/Pt-modified glassy carbon (GC) electrode was created to simultaneously characterize ascorbic acid (AA), dopamine (DA), and uric acid (UA) levels via cyclic voltammetry (CV) and differential pulse voltammetry (DPV). During the preparation of the nanocomposite, size-selected Pt nanoparticles with a mean diameter of 1.7 nm were self-assembled onto the graphene surface. In the simultaneous detection of the three aforementioned analytes using CV, the electrochemical potential differences among the three detected peaks were 185 mV (AA to DA), 144 mV (DA to UA), and 329 mV (AA and UA), respectively. In comparison to the CV results of bare GC and graphene-modified GC electrodes, the large electrochemical potential difference that is achieved via the use of the graphene/Pt nanocomposites is essential to the distinguishing of these three analytes. An optimized adsorption of size-selected Pt colloidal nanoparticles onto the graphene surface results in a graphene/Pt nanocomposite that can provide a good platform for the routine analysis of AA, DA, and UA.