Recessed microelectrode array for a micro flow-through system allowing on-line multianalyte determination in vivo

Using CMOS-compatible processes, a microelectrode system for use in a micro flow-through cell was manufactured. The electrode was specially designed to enable multianalyte determination with immobilized oxidase enzymes and combines minimal flow dependency with a very small dead volume (< 1 mu L) of the cell. This allows biomedical applications like measurements of glucose and lactate in interstitial fluid, which can be collected by ultrafiltration. Besides a 3-electrode system with 4 individually addressable platinum working electrodes, the sensor contains 2 electrodes that measure the conductivity of the sample as well as a Pt thermoresistor to measure the temperature. The temperature dependence in enzyme reactions can thus be controlled during on-line measurements. The 4 working electrodes comprise multielectrode arrays, each comprising 192 micro-holes with a diameter of 3.6 mu m. They are arranged symmetrically around the central counter electrode, which is surrounded by a circular Ag/AgCl reference electrode. Between the array and the reference electrode are the loops of the Pt thermoresistor. The thermoresistor is electrically insulated from the measurement solution by a Si3N4 layer. A method for the pretreatment of platinum thin-film electrodes that increases the reversibility of the electrode process is described. The chemical modification of the working electrodes by electropolymerization of a resorcinol/1,3-diaminobenzene mixture enables interference-free measurement in blood and plasma as well as protection against electrode fouling

Surface characterization of a silicon-chip-based DNA microarray

The immobilization of DNA (deoxyribonucleic acid) on solid supports is a crucial step for any application in the field of DNA microarrays, It determines the efficacy of the hybridization and influences the signal strength for the detection. We used solid supports made from silicon wafers as an alternative substrate to the commonly used microscope glass slides. The covalent immobilization of thiol-terminated DNA oligonucleotides on self-assembled layers of (3-mercaptopropyl)trimethoxysilane (MPTS) by disulfide bond formation was investigated. Contact angle measurement, variable angle spectral ellipsometry (VASE), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) were used to characterize the changing properties of the surface during the DNA array fabrication. During wafer processing the contact angle changed from 3 degrees for the hydroxylated surface to 48.5 degrees after deposition of MPTS. XPS data demonstrated that all sulfur in the MPTS layer was present in the form of reduced SH or S-S groups. VASE measurements indicated a layer thickness of 57.8 Angstrom for the immobilized 16 base oligonucleotides including a 18 carbon atom spacer located between the disulfide bond and the oligomer. AFM was used to characterize the DNA layer before and after hybridization to a complementary target. The data recorded after hybridization revealed a sharp increase in particle size from 89 nm(2) to a mean value of 363 nm(2). Fluorescence microscopy was used to monitor the hybridization of a fluorescently labeled DNA target to the immobilized probe. The heat stable disulfide-linkage formed during the oligonucleotide immobilization allowed the stripping of complementary DNA targets as well as rehybridization, These data show the advantages and applicability of silicon wafers that have been processed with CMOS (complementary metal oxide semiconductor) compatible processes as solid support in DNA technology. This approach offers the possibility of integration with other silicon-based components such as PCR microreactors and capillary electrophoresis units into a "lab-on-a-chip"

Poisoning influence of cyanide on the catalytic oxygen reduction by cobalt(III) tetra(3-methoxy-4-hydroxylphenyl) porphyrin modified electrode

Cobalt(III) tetra(3-methoxy-4-hydroxylphenyl) porphyrin ((CoTMHPP)-T-III) can be irreversibly bound to a platinum electrode through a sol-gel network. Based on our finding that cobalt metalloporphyrin catalyzes dioxygen reduction near 0 mV (vs. Ag/AgCl), the electrocatalytic kinetics of oxygen reduction has been studied by cyclic voltammetry and rotating disk voltammetric methods. A possible reaction mechanism is suggested for the observed catalysis. In the presence of cyanide, the electrocatalytic reductive current for dioxygen is decreased due to the strong binding of cyanide ions to the cobalt metal center. A simplified model is proposed to describe this poisoning effect based on the Koutecky-Levich theory and coordination equilibrium between cyanide and the electrocatalyst. The model is well supported by the experimental results. The poisoning effect can be used for highly sensitive cyanide detection. (C) 2000 The Electrochemical Society. S0013-4651(99)05-073-9. All rights reserved

Enzyme biosensor for studying therapeutics of Alzheimer's disease

An electrochemical method for the investigation and comparison of anti-Alzheimer medications that is based on the inhibition of the acetylcholinesterase is presented. The developed amperometric biosensor determines the in-vitro inhibition of the acetylcholinesterase that is co-immobilized with choline oxidase on the working electrode surface of a three-electrode system using gel entrapment. The sensor has been applied to determine the IC,, values of two known and one newly developed Alzheimer remedy. A simultaneous measurement with the photometric standard method shows the applicability of our method for fast drug screening. (C) 2000 Elsevier Science S.A. All rights reserved

Investigation of oxygen- and hydrogen peroxide-reduction on platinum particles dispersed on poly(o-phenylenediamine) film modified glassy carbon electrodes

Composite membrane modified electrodes were prepared by electrochemical deposition of platinum particles in a poly(o-phenylenediamine) (PPD) him coated on glassy carbon (GC) electrodes. The modified electrodes showed high catalytic activity towards the reduction of oxygen and hydrogen peroxide. A four-electron transfer process predominated the reduction process. The pH dependence and the stability of the electrodes were also studied

Tone reversal of an AFM lateral force image due to hybridization of oligonucleotides immobilized on polymers

No abstract available

Integrated DNA detection system on silicon substrate with photodiodes

This paper describes the process in developing of a fully integrated approach for Deoxyribo-Nucleic-Acid (DNA) diagnosis and gene mapping with photodiodes. The objectives and methodologies of DNA analysis based on traditional microarrays are briefly reviewed. The issues of material compatibility between DNA materials and silicon-based materials are evaluated. Reasons for the selection of covalent attachment of synthetic DNA to self-assembled monolayer films on silicon dioxide as immobilization method are addressed. Atomic force microscopy (AFM) and microscope images are used to verify the efficiency of DNA probe immobilization and the subsequent DNA hybridization. With the consideration of process compatibility between silicon processing and biochemical material handling, necessary process modification in photodiode fabrication is described. Measured signal from photodiodes with the hybridized DNA samples containing fluorescent labeled from the DNA probe microarrays on silicon substrates can be clearly distinguished from those without fluorescent labeled. The result demonstrated that the technique could be used for DNA identification purpose