Bare Carbon Fiber Microelectrode Research Articles

In Vivo Monitoring of Oxygen in Rat Brain by Carbon Fiber Microelectrode Modified with Antifouling Nanoporous Membrane.

Oxygen (O2) is involved in many life activities, and its in vivo monitoring is of vital importance. In vivo electrochemistry with carbon fiber microelectrode (CFME) has been proven to be a suitable technique, but the surface fouling propensity poses a great challenge to its current stability and reliability. Herein we electro-grafted silica nanoporous membrane (SNM) consisting of uniform, closely packed, and vertically aligned nanochannels on the CFME surface, which was capable of protecting the surface effectively from biofouling and, meanwhile, preserving the permeability to O2. In comparison with a bare CFME, the SNM/CFME after implantation in the brain of a live rat maintained its analytical sensitivity to O2. Moreover, the implanted electrode could monitor O2 continuously under the in vivo condition, exhibiting an excellent current stability, as well as a fast response, up to 2 h. Further considering the high permeability, selectivity, and biocompatibility of SNM, we believe the modified CFME is a highly reliable sensor for long-term in vivo monitoring of O2, as well as other neurochemicals, with promise in physiological, ethological, and neurological studies.

(Invited) Carbon Nanotube-Based Microelectrodes for Enhanced Neurochemical Detection

Carbon-fiber microelectrodes (CFMEs) have been traditionally used with fast scan cyclic voltammetry (FSCV) to detect neurochemicals in vivo. However, there are several challenges in detecting neurochemical changes using bare CFMEs. First and foremost, fouling has been shown to significantly decrease sensitivity through the formation of biopolymers from serotonin and other analytes that block sites for analyte absorption. The loose sheets of graphene that make up the carbon fiber also have relatively low conductivities, which result in slow electron transfer for electrode materials and low temporal resolution. Carbon Nanotubes (CNTs) have shown to be promising for use as electrode materials. Carbon nanotubes (CNTs) are highly sp2 hybridized, which is very advantageous for measuring fast neurochemical changes in vivo. The CNTs also contain a high percentage of edge-plane carbon that is the catalytic site for neurotransmitter oxidation, which is fouling resistant. Furthermore, the cylindrical structure of CNTs provide a high aspect ratio, which allows for more sites for analyte adsorption and high sensitivity to detect low basal levels of neurochemicals. Several methods have been developed to incorporate CNTs onto CFMEs such as dipcoating; however, the method is highly variable and produces noise. Wetspinning CNTs with polymers or acids to form CNT fiber has been shown to be highly efficacious in developing novel electrode materials. For example, poly(ethyleneimine) CNT fiber microelectrodes were fouling resistant to both serotonin and 5-hydroxyindoleacetic acid (5-HIAA). They were also able to detect exogenously applied serotonin onto brain slices. Acid spun CNT fiber microelectrodes were formed with either sulfuric acid or chlorosulfonic acid that preclude the use of sonication, polymers, or surfactants, which act as impurities that reduce sensitivity.

Investigation of dilution agent effect onto interactions between methylene blue and DNA using carbon fiber based DNA biosensor

This paper focuses on the dilution agent effect onto interactions between methylene blue (MB) and DNA using carbon fiber microelectrode (CFME) based DNA biosensor. In this study, designed CFME based DNA biosensor was successfully carried out considering the effect of probe dilution agent (e.g. 3-mercaptopropionic acid) against proposed hybridization mechanism types. The voltammetric signals of MB were measured at bare CFME, single-stranded DNA (ssDNA)-modified CFME and double-stranded DNA (dsDNA)-modified CFME by means of square wave voltammetry (SWV). The electrochemical parameters for MB on binding to DNA onto single CFME in the solution and at the electrode surface were described. This study shows that probe dilution agent is a significant factor to determine the type of DNA hybridization mechanisms.

The Electrochemical Behavior of Carbon Fiber Microelectrodes Modified with Carbon Nanotubes Using a Two-Step Electroless Plating/Chemical Vapor Deposition Process.

Carbon fiber microelectrode (CFME) has been extensively applied in the biosensor and chemical sensor domains. In order to improve the electrochemical activity and sensitivity of the CFME, a new CFME modified with carbon nanotubes (CNTs), denoted as CNTs/CFME, was fabricated and investigated. First, carbon fiber (CF) monofilaments grafted with CNTs (simplified as CNTs/CFs) were fabricated in two key steps: (i) nickel electroless plating, followed by (ii) chemical vapor deposition (CVD). Second, a single CNTs/CF monofilament was selected and encapsulated into a CNTs/CFME with a simple packaging method. The morphologies of as-prepared CNTs/CFs were characterized by scanning electron microscopy. The electrochemical properties of CNTs/CFMEs were measured in potassium ferrocyanide solution (K4Fe(CN)6), by using a cyclic voltammetry (CV) and a chronoamperometry method. Compared with a bare CFME, a CNTs/CFME showed better CV curves with a higher distinguishable redox peak and response current; the higher the CNT content was, the better the CV curves were. Because the as-grown CNTs significantly enhanced the effective electrode area of CNTs/CFME, the contact area between the electrode and reactant was enlarged, further increasing the electrocatalytic active site density. Furthermore, the modified microelectrode displayed almost the same electrochemical behavior after 104 days, exhibiting remarkable stability and outstanding reproducibility.

Quantitation of Hydrogen Peroxide Fluctuations and Their Modulation of Dopamine Dynamics in the Rat Dorsal Striatum Using Fast-Scan Cyclic Voltammetry

The dopaminergic neurons of the nigrostriatal dopamine (DA) projection from the substantia nigra to the dorsal striatum become dysfunctional and slowly degenerate in Parkinson's disease, a neurodegenerative disorder that afflicts more than one million Americans. There is no specific known cause for idiopathic Parkinson's disease; however, multiple lines of evidence implicate oxidative stress as an underlying factor in both the initiation and progression of the disease. This involves the enhanced generation of reactive oxygen species, including hydrogen peroxide (H2O2), whose role in complex biological processes is not well understood. Using fast-scan cyclic voltammetry at bare carbon-fiber microelectrodes, we have simultaneously monitored and quantified H2O2 and DA fluctuations in intact striatal tissue under basal conditions and in response to the initiation of oxidative stress. Furthermore, we have assessed the effect of acute increases in local H2O2 concentration on both electrically evoked DA release and basal DA levels. Increases in endogenous H2O2 in the dorsal striatum attenuated electrically evoked DA release, and also decreased basal DA levels in this brain region. These novel results will help to disambiguate the chemical mechanisms underlying the progression of neurodegenerative disease states, such as Parkinson's disease, that involve oxidative stress.

Oxidation-State Speciation of [ReI(DMPE)3]+/[ReII(DMPE)3]2+ by Voltammetry with a Chemically Modified Microelectrode

The analytical utility of chemically modified microelectrodes for oxidation-state speciation of redox couples by cyclic voltammetry has been explored. [Re(I)(DMPE)3]+/[Re(II)(DMPE)3]2+, where DMPE = 1,2-bis(dimethylphosphino)ethane, was studied at carbon-fiber microelectrodes of approximately 5 microm in radius coated with Nafion-entrapped solgel-derived silica (Nafion-silica) composite. The results are compared with cyclic voltammetry of [Fe(CN)6]3-/[Fe(CN)6]4- at bare carbon-fiber microelectrodes. At both microelectrodes, the cathodic and anodic limiting currents are linearly proportional to the concentrations of the reducible and oxidizable species of a redox couple, respectively. The shape of the cyclic voltammogram and the magnitude of the steady-state limiting current are not affected by the potential at which the scan starts. Speciation of both forms of a redox couple could be achieved voltammetrically at the microelectrodes. However, a considerably slower scan rate was required to achieve steady state at the modified electrode because of the smaller diffusion coefficients of [Re(I)(DMPE)3]+ and [Re(II)(DMPE)3]2+ in the Nafion-silica composite. The detection limit at the modified electrode was considerably lower (5 x 10(-9) M for [Re(I)(DMPE)3]+) than at the bare electrode (6 x 10(-5) M for [Fe(CN)6]3- and [Fe(CN)6]4-) because of the substantial preconcentration of [Re(I)(DMPE)3]+ by the Nafion-silica composite.

Unidirectional current flow of reversible redox couples on a MoO3 film-modified microelectrode

In this paper, we have investigated the reactivity of the molybdenum oxide film toward some standard redox systems (e.g., ferrocene (Fc) and its derivatives) and observed a few interesting phenomena. The results demonstrate that the electrochemical behaviour of Fc and its derivatives at the oxide-modified carbon fiber (CF) microelectrode differs from that at a bare CF microelectrode, The conductivity of the molybdenum oxide film is seriously affected by the range and the direction of the potential scan, which influences the electrochemical behaviour of these redox systems at the film electrode. If the cycling potential is more positive than the reduction potential of the molybdenum oxide film, the reduction and oxidation peak currents of Fc and its derivatives could not be observed. The result indicates that the molybdenum oxide film on a microelectrode surface cannot transfer electrons between the surface of the electrode and Fc or its derivatives due to the existence of a high resistance between the interface in these potential ranges. On the other hand, if the lower limit of the scan potential was extended to a potential more negative than the reduction peak potential of the film, the oxidation peak of Fc or its derivatives appeared at about the potential relative to E-0 of Fc or its derivatives on the bare electrode, and the peak current is proportional to the concentration of these couples in the electrolyte. To our surprise, the peak height on the modified electrode is much larger than that on the bare CF microelectrode under the same conditions in the range of low concentration of these couples, and the oxidation peak potential of these couples is more negative than that on the bare CF microelectrode. On the basis of the experimental observation, we propose that these redox couples may undergo an interaction with the reduction state of the molybdenum oxide film. The new phenomena that we observed have been explained by using this interaction. (C) 1997 Elsevier Science S.A.