D. J. Strike

Microreactor and electrochemical detectors fabricated using Si and EPON SU-8

Abstract An electrochemiluminescence (ECL) detector and a microenzymatic reactor (MER) combining Si and SU-8 technologies are described. Both devices were fabricated using standard processing techniques to produce on-wafer sensor elements, which were composed of a platinum or, alternatively, carbon interdigitated electrode array. The platinum array was resting on top of an Si pn photodiode. After these elements were completed, the entire wafer was modified with SU-8, which was structured to form a series of shaped spacers surrounding each device. For the ECL detector, a simple flow-channel was defined whereas for the microreactor a more complex layout defining two chambers separated by a series of SU-8 columns was employed. The upstream chamber of the microreactor was packed with porous glass beads modified with immobilised enzyme glucose oxidase whereas the downstream chamber contained the electrochemical detector. The performance of the ECL detector was assessed by the detection of codeine using ruthenium (II) tris(2,2′-bipyridyl). A detection limit of 100 μM was obtained and pharmaceutical preparations were successfully assayed. The MER was first evaluated by electrochemical determination of glucose and as a next step, a miniature ECL detector was placed on line downstream the MER to perform glucose measurements by ECL. Glucose was determined with detection limits of 2 and 50 μM by electrochemistry and ECL, respectively. This system was found to have a lifetime of at least 1 month when stored at 4°C.

Electrocatalytic oxidation of methanol on platinum microparticles in polypyrrole

The oxidation of methanol on gold electrodes modified with polypyrrole and platinum is reported. These electrodes were characterized by cyclic voltammetry and by 12h polarizations in methanol solutions. They were found to give higher currents and lower rates of drift than electrodes of platinum and platinized gold. The effect of varying the amount of platinum deposited is also discussed.

Reproducible fabrication of an array of gas-sensitive chemo-resistors with commercially available polyaniline

Polyaniline, which was obtained as a dispersion from a commercial supplier, was used to prepare chemo-resistors. The sensors were prepared in a batch process by spin coating on a wafer with Au interdigitated electrode arrays (IDAs). The gas response behaviour of the so-prepared sensors could be modified by a post-treatment with organic solvents to obtain an array of sufficiently different sensors for the successful recognition of five different vapours. The preliminary fabrication procedure showed a good batch-to-batch reproducibility, as well as an excellent stability of the sensor responses.

Electrochemical Techniques for the Modification of Microelectrodes

The deposition of enzymes using electrochemically aided adsorption in the presence of glutaraldehyde allows spatially well controlled protein layers to be formed. By adjusting the deposition parameters (i.e. current, pulse, duration and amplitude) this technique, originally developed for the deposition of glucose oxidase (GOx), can be readily applied to several other enzymes. As an example, and illustrating the potential of this technique in the fabrication of multisensors, a glucose-sarcosine dual analyte sensor is described. | The deposition of enzymes using electrochemically aided adsorption in the presence of glutaraldehyde allows spatially well controlled protein layers to be formed. By adjusting the deposition parameters (i.e. current, pulse, duration and amplitude) this technique, originally developed for the deposition of glucose oxidase (GOx), can be readily applied to several other enzymes. As an example, and illustrating the potential of this technique in the fabrication of multisensors, a glucose-sarcosine dual analyte sensor is described.

Electrodeposition of glucose oxidase for the fabrication of miniature sensors

Abstract Glucose oxidase enzyme electrodes have been prepared by passing a current through an aqueous solution of glucose oxidase and bovine serum albumin, with the working electrode as anode. These electrodes have been found to be highly active. When subsequently modified with a polypyrrole layer the response to two model interferences ascorbate and acetaminophen was considerably reduced.

Miniature Electrochemical Glucose Biosensors

Glucose-oxidase-based sensors were realized using three techniques of immobilizing thin layers of enzyme over a three-thin-film electrode transducer. Sensors with chemically crosslinked membranes, completed by an outer diffusion-limiting membrane, were characterized with consideration of the basic requirements of an implantable device. Thus, e.g. a negligible loss of the activity was observed when the sensors were sterilized by a 2.5 MRad dose of gamma radiation. On the other hand, the sensors with the electrochemically deposited membranes were particularly suitable, e.g. with respect to response time, etc., for flow-injection analysis measurements.

Gas-Dependent Field Effect Transistor with an Electrodeposited Conducting Polymer Gate Contact

Field effect transistor structures with a conducting polymer gate contact have been realized. An electrodeposition technique, suitable for a wide range of conducting polymers, was used. This is illustrated with the deposition of two different types of polypyrroles. The sensors show responses to organic vapors due to partial charge transfer between the sorbed vapor and the conducting polymer, and can be used for electronic nose applications. Due to the measuring principle, based on work function instead of resistance changes, this sensor is also believed to be useful for fundamental research on gas-polymer interactions. ©1999 The Electrochemical Society

Enzymatic microreactor using Si, glass and EPON SU-8

This article describes the design, fabrication and initial testing of an enzymatic microreactor using Si, glass, epoxy and Perspex components. The microreactor geometry was defined by a photostructured EPON SU-8 spacer. This gave two chambers, an upstream chamber (vol. ∼2.7 μl) which was packed with control pore glass (CPG) and a downstream chamber (vol. ∼1.5 μl) which contained the detectors. Eleven EPON SU-8 columns separated the chambers and prevented the CPG from passing. Glucose detection via glucose oxidase immobilized to the CPG was used as a model system. Conversion efficiencies between 15 and 60% at flow rates of 150 and 26 μ1 min−1 respectively were obtained. Overall the system was found to be robust and to have a lifetime of at least one month.

Polymeric Membranes for Silicon Based (Bio)Sensors

During the last decade, chemical and biochemical sensor research has benefited from the availability of new technologies and materials. New embodiments of classical devices have resulted from the use of e.g., solid state technology for the realization of the transducers. In this paper we describe several examples of membrane deposition techniques used in connection with planar, silicon based electrochemical transducers. Casting and electrochemical deposition of glucose oxidase containing membranes are described for the fabrication of glucose enzyme electrodes. Photolithographic patterning of polyacrylamide hydrogel and of siloxane based gas permeable membrane is used for the realization of an amperometric oxygen sensor and an ISFET-based pCO2 device. The last example is that of a free-chlorine sensor for which the photolithographic patterning of the polyHEMA hydrogel layer is described.

Immobilization of Enzymes on Microelectrodes Using Chemical Crosslinking

Note: 160 Reference SAMLAB-ARTICLE-1997-012 Record created on 2009-05-12, modified on 2016-08-08