Chemistry: molecular biology and microbiology – Apparatus – Including measuring or testing
Patent
1998-05-01
2000-02-29
Redding, David A.
Chemistry: molecular biology and microbiology
Apparatus
Including measuring or testing
4352875, 4352887, 435808, 435817, 204403, 204415, 356317, 356345, 356432, C12M 300
Patent
active
060308281
DESCRIPTION:
BRIEF SUMMARY
INTRODUCTION TO THE DESCRIPTION
The present invention relates to a microsensor for measuring the concentration of a primary substrate in the surrounding environment which can be a fluid, a gas or a matrix, which microsensor comprises a first casing with an opening, which opening is in contact with a first barrier and a reaction space which borders on the first barrier, in which reaction space a catalytic material is located, a material intended to catalyse a conversion of the primary substrate with the concomitant conversion of a secondary substrate, and which microsensor furthermore comprises a transducer for the secondary substrate, which transducer is located at a distance from the first barrier.
Different types of biosensors for measuring the concentration and partial pressures of different primary substrates are known. J. Chem. Tech. Biotechnol. 44, 85-106 (1989) describes different methods and different sensors. However, the sensors described have various disadvantages. For measuring the concentration of the primary substrate, for instance methane, in an environment, it is necessary that the secondary substrate, for instance oxygen, is present in the environment in which the primary substrate is to be measured. Consequently, if the concentration of the secondary substrate is unknown or zero, it is not possible to measure the concentration of the primary substrate. Furthermore, it has been shown that in sensors depending on several substrates which are initially added to the reaction space, these substrates can be depleted or degraded. Finally, the sensors described are not miniaturised, which leads to extensive diffusive distances and response times, and in-situ measurements is difficult.
European Journal of Applied Microbiology and Biotechnology 10, 235-243 (1980) describes a biosensor, comprising a first vessel containing a microbiological fluid in which measurements are to be made and a second vessel containing an electrolyte and cathodes and an anode submerged in the electrolyte. Between the first and the second vessel two Teflon.RTM. membranes are placed, between which agar with immobilised Clostridium butyricum is deposited.
However, this sensor has several disadvantages. Measurements are very sensitive to whether sufficient stirring is established in the fluid, in which the measurements are to be made. Thus it is necessary to provide a constant stirring of the fluid. Furthermore, it is not possible to make in-situ measurements, as samples have to be taken for the measurement. Consequently, precise measurements over time are difficult to make and so are measurements with high spatial resolution. The necessity of stirring and the sensor construction in general makes the sensor unsuited for measurements at the location in question, for instance a bio-gas reactor.
Electroanalysis, 1 (1989) 305-309 describes a sensor type, comprising a silicon core, plated with silicon oxide on an outer and on an inner surface. The silicon core is furnished with gold electrodes and a chamber containing alginate. A gas permeable membrane is covering the gold electrodes and contains a reservoir containing immobilised bacteria. The gas permeable membrane makes a barrier between the chamber containing the alginate and the reservoir with the immobilised bacteria.
Due to the physical design of this sensor and other macroscopic sensors that consume an analyte in the process of measuring with a one-dimensional direction of diffusion, the role of a diffusive boundary layer will be significant, making such sensors very sensitive to the degree of stirring and thus unsuited for in-situ measurements. The sensor described above needs both the primary substrate, which is to be measured, and the secondary substrate to be present in the environment. The nutrition in the alginate in the sensor will further limit the use of the sensor as the bacteria will die, and CO.sub.2, which is the primary substrate for this sensor, will be released by the bacteria, affecting the measurement when the bacteria die, as the nutrition in the algina
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Damgaard Lars Riis
Revsbech Niels Peter
Redding David A.
Unisense APS.
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