Miniaturized probe on polymer SU-8 with array of individually addressable microelectrodes for electrochemical analysis in neural and other biological tissues

An SU-8 probe with an array of nine, individually addressable gold microband electrodes (100 μm long, 4 μm wide, separated by 4-μm gaps) was photolithographically fabricated and characterized for detection of low concentrations of chemicals in confined spaces and in vivo studies of biological tissues. The probe's shank (6 mm long, 100 μm wide, 100 μm thick) is flexible, but exhibits sufficient sharpness and rigidity to be inserted into soft tissue. Laser micromachining was used to define probe geometry by spatially revealing the underlying sacrificial aluminum layer, which was then etched to free the probes from a silicon wafer. Perfusion with fluorescent nanobeads showed that, like a carbon fiber electrode, the probe produced no noticeable damage when inserted into rat brain, in contrast to damage from an inserted microdialysis probe. The individual addressability of the electrodes allows single and multiple electrode activation. Redox cycling is possible, where adjacent electrodes serve as generators (that oxidize or reduce molecules) and collectors (that do the opposite) to amplify signals of small concentrations without background subtraction. Information about electrochemical mechanisms and kinetics may also be obtained. Detection limits for potassium ferricyanide in potassium chloride electrolyte of 2.19, 1.25, and 2.08 μM and for dopamine in artificial cerebral spinal fluid of 1.94, 1.08, and 5.66 μM for generators alone and for generators and collectors during redox cycling, respectively, were obtained.

Carbon Anode in Carbon History

This study examines how the several major industries, associated with a carbon artifact production, essentially belong to one, closely knit family. The common parents are the geological fossils called petroleum and coal. The study also reviews the major developments in carbon nanotechnology and electrocatalysis over the last 30 years or so. In this context, the development of various carbon materials with size, dopants, shape, and structure designed to achieve high catalytic electroactivity is reported, and among them recent carbon electrodes with many important features are presented together with their relevant applications in chemical technology, neurochemical monitoring, electrode kinetics, direct carbon fuel cells, lithium ion batteries, electrochemical capacitors, and supercapattery.

Electrochemically Active Thin Carbon Films with Enhanced Adhesion to Silicon Substrates

Thin carbon films deposited on technologically relevant substrates, such as silicon wafers, can be easily implemented in miniaturized electrochemical devices and used for sensing applications. However, a major issue in most carbon films is the weak film/substrate adhesion that shortens the working device lifetime. This paper describes the facile preparation of robust thin carbon films on silicon substrates by one-pot sol-gel synthesis. The improved adherence of these carbon films is based on the incorporation of silica through the controlled synthesis of a resorcinol/formaldehyde gel modified with aminopropyltriethoxysilane. The films demonstrate excellent adhesion to the silicon substrate, good homogeneity, excellent electrical conductivity and superior electrochemical performance. Moreover, this approach opens the door to the fabrication of carbon thin-film electrodes by photolithographic techniques.

Vertically Aligned Carbon Nanofiber based Biosensor Platform for Glucose Sensor

Vertically aligned carbon nanofibers (VACNFs) have recently become an important tool for biosensor design. Carbon nanofibers (CNF) have excellent conductive and structural properties with many irregularities and defect sites in addition to exposed carboxyl groups throughout their surfaces. These properties allow a better immobilization matrix compared to carbon nanotubes and offer better resolution when compared with the FET-based biosensors. VACNFs can be deterministically grown on silicon substrates allowing optimization of the structures for various biosensor applications. Two VACNF electrode architectures have been employed in this study and a comparison of their performances has been made in terms of sensitivity, sensing limitations, dynamic range, and response time. The usage of VACNF platform as a glucose sensor has been verified in this study by selecting an optimum architecture based on the VACNF forest density.

Microelectrode arrays with overlapped diffusion layers as electroanalytical detectors: theory and basic applications

This contribution contains a survey of basic literature dealing with arrays of microelectrodes with overlapping diffusion layers as prospective tools in contemporary electrochemistry. Photolithographic thin layer technology allows the fabrication of sensors of micrometric dimensions separated with a very small gap. This fact allows the diffusion layers of single microelectrodes to overlap as members of the array. Various basic types of microelectrode arrays with interacting diffusion layers are described and their analytical abilities are accented. Theoretical approaches to diffusion layer overlapping and the consequences of close constitution effects such as collection efficiency and redox cycling are discussed. Examples of basis applications in electroanalytical chemistry such as amperometric detectors in HPLC and substitutional stripping voltammetry are also given.

Electrocatalytic Reduction of Hydrogen Peroxide on Palladium-Gold Codeposits on Glassy Carbon: Applications to the Design of Interference-Free Glucose Biosensor

Following our previous studies on the catalytic activity electrochemically codeposited on graphite Pd-Pt electrocatalysts for hydrogen peroxide electroreduction, a series of glassy carbon electrodes were modified with Pd or (Pd+Au) deposits aiming at the development of even more efficient electrocatalysts for the same process. The resulting electrodes were found to be very effective at low applied potentials (−100and−50 mV versus Ag/AgCl, 1 M KCl). The surface topography of the electrode modified with Pd+Au mixed in proportions 90% : 10%, exhibiting optimal combination of sensitivity and linear dynamic range towards hydrogen peroxide electrochemical reduction, was studied with SEM and AFM. The applicability of the same electrode as transducer in an amperometric biosensor for glucose assay was demonstrated. At an applied potential of−50 mV, the following were determined: detection limit (S/N=3) of6×10−6 M glucose, electrode sensitivity of 0.15 μAμM−1, and strict linearity up to concentration of3×10−4 M.

Newly developed chemical probes and nano-devices for cellular analysis

A cellular analyzing system including a "real-time cellular imaging system" and a "comprehensive analyzing system for cellular responses" was developed. A "real-time cellular imaging system" is a system used to measure real-time imaging of multiple phenomena of a single cell with high special and temporal resolutions for the purpose to understand the pathology and physiology in a single cell and realize to single cell level diagnosis. A "real-time cellular imaging system" includes multi-probe imaging with AFM (atomic force microscopy), optical and SECM (scanning electrochemical microscopy) modes, which provides us with topological information and biochemical reactions at the local area of the interior and exterior of a cell. Scanning electrochemical/optical microscopy was applied to image PC12 cells. On the other hand, cells respond to their specific substances via their ligands. Therefore, the comprehensive analysis of protein-protein interaction is the important issue to determine the functions of cells. For this purpose, a "comprehensive analysis system for cellular responses" was developed. This system is based on SPR (surface plasmon resonance) and MS (mass spectrometry) using a nano-fabricated substrate. The interaction between IL-1 beta and anti-IL-1 beta antibodies was detected.

Additive route to lithographically defined nanoporous silica, polymer, and carbon films

A facile method was investigated for patterning microporous and mesoporous silica, polymer, and carbon films using a combination of lithography and solid-state chemistry. This process exploits the difference in chemical reactivity between the lithographically exposed and unexposed regions to control the reaction of a target precursor from the vapor phase. A block copolymer film loaded with a photoacid generator is utilized as a preformed template, and tetraethylorthosilicate (TEOS) and furfuryl alcohol (FA) are the silica and carbon precursors, respectively. Following UV exposure and reaction with vaporized precursors, thermal decomposition of the polymeric template yields a mesoporous film in the exposed regions. Dense line-space patterns down to 1.5 microm features were resolved with I-line lithography. Sharper features were formed using FA; this behavior is attributed to the requirement for water in the system during TEOS condensation. Moisture in the system appears to lead to enhanced diffusion of the photoacid and a small decrease in the feature resolution. This methodology provides a simple etch-free route to patterning mesoporous films using commercially available materials.

Amperometric glucose sensor based on catalytic reduction of dissolved oxygen at soluble carbon nanofiber

This work shows excellent catalytic activity of soluble carbon nanofiber (CNF), which was obtained with a simple nitric acid treatment, toward the electroreduction of dissolved oxygen at a low operating potential. Thus the CNF was applied in the construction of amperometric biosensors for oxidase substrates using glucose oxidase as a model. The good dispersion of CNF led to convenient preparation and acceptable repeatability of the proposed sensors. UV-vis spectra, Fourier transform infrared spectra, X-ray photoelectron spectra and titration curves demonstrated that the good dispersion resulted from the large numbers of surface oxygen-rich groups produced in the treatment process. The membrane of CNF showed good stability and provided fast response to dissolved oxygen with a linear range from 0.1 to 78 microM and detection limit of 0.07 microM. The proposed glucose biosensor could monitor glucose ranging from 10 to 350 microM with detection limit of 2.5 microM and sensitivity of 36.3 nA cm(-2) microM(-1). The coefficients of variation for intra-assay were 4.7 and 3.2% at glucose concentrations of 20 and 210 microM, respectively. The use of a low operating potential (-0.3 V) and Nafion membrane produced good selectivity toward the glucose detection. CNF-based biosensors would provide wide range of bioelectrochemical applications in different fields.

Structure and Electrochemical Properties of Carbon Films Prepared by a Electron Cyclotron Resonance Sputtering Method

This paper describes the characterization, electrochemical properties, and applications of carbon films prepared by the electron cyclotron resonance (ECR) sputtering method. The ECR-sputtered carbon film was deposited within several minutes at room temperature. The optimized sputtering conditions significantly change the film structure, which includes many more sp3 bonds (sp3/sp2 = 0.702) than previously reported film (sp3/sp2 = 0.274)1 with an extremely flat surface (0.7 A). The ECR-sputtered carbon films exhibit excellent electrochemical properties. For example, they have nearly the same potential window in the positive direction as that of high-quality, boron-doped diamond (moderately doped, 10(19)-10(20) boron atoms/cm3)2 and an even wider potential window in the negative direction with a low background current, high stability, and suppression of fouling by electroactive species without pretreatment. The electron-transfer rates at ECR-sputtered carbon films are similar to those of glassy carbon (GC) for Ru(NH3)(6)(2+)/(3+) and Fe(CN)(6)(3-)/(4-), whereas they are much slower than those of GC for Fe2+/3+, dopamine oxidation, and O2 reduction due to weak interactions between electroactive species and the ECR-sputtered carbon film surface. Such a response can be attributed to the ultraflat surface and low surface O/C ratios of ECR-sputtered carbon films. ECR-sputtered carbon film is advantageous for measuring biochemicals with high oxidation potentials because of its wide potential window and high stability. Highly reproducible and well-defined cyclic voltammograms were obtained for histamine and azide ions with a peak potential at 1.25 and 1.12 V vs Ag/AgCl, respectively. The film is very stable for continuous voltammetry measurements in 10 microM bisphenol A, which usually fouls the electrode surface with oxidation products.

Continuous On-Line Monitoring of Extracellular Ascorbate Depletion in the Rat Striatum Induced by Global Ischemia with Carbon Nanotube-Modified Glassy Carbon Electrode Integrated into a Thin-Layer Radial Flow Cell

This study describes a novel analytical system integrating in vivo microdialysis sampling with a radial thin-layer flow cell with a single-walled carbon nanotube (SWNT)-modified glassy carbon electrode as working electrode for continuous and on-line monitoring of ascorbate depletion in the rat striatum induced by global ischemia. The SWNTs, especially those after vacuum heat treatment at 500 degrees C, are found to be able to enhance the electron-transfer kinetics of ascorbate oxidation at a low potential (ca. -50 mV) and possess a strong ability against electrode fouling. These properties essentially make it possible to determine ascorbate with a good stability and high selectivity against catecholamines and their metabolites and other electroactive species of physiological levels. While being integrated with in vivo microdialysis to assemble an on-line analytical system, the electrode is proved useful for continuous and sensitive monitoring of the basal dialysate level of ascorbate and its depletion in the rat striatum induced by global ischemia. The basal dialysate level of ascorbate is determined to be 5.0 +/- 0.5 microM (n = 5) and a 50 +/- 10% (n = 3) depletion is recorded for the basal ascorbate after 4 h of global ischemia.