Chemistry: electrical and wave energy – Apparatus – Electrolytic
Patent
1990-04-11
1991-08-13
Niebling, John F.
Chemistry: electrical and wave energy
Apparatus
Electrolytic
204416, 357 25, G01N 2730
Patent
active
050393901
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to a chemically sensitive transducer for the selective detection of the chemical properties of a fluid, and more specifically, to a transducer with a measuring electrode overlaid with a membrane that is sensitive to the chemical properties. This electrode is coupled to the gate of a field-effect transistor. The transducer has an encapsulation which isolates the entire transducer except for the membrane from the fluid.
The term "chemically sensitive" refers to an ion or gas sensitive property, a sensitivity to enzyme substrates, to antibodies/antigens or to hydride-forming DNA/RNA groups. Depending on their sensitivity, transducers can be utilized in medicine, for example in blood analysis, in clinical chemistry, for therapy control, hormone determination, infection and tumor diagnoses, as well as in fermentation control, food and environment analyses and process control.
A chemically sensitive transducer is known from EP-B-0 065 350, in which the gate of a field-effect transistor is connected via a laterally abutting conductor to an allocated measuring electrode disposed on the same side of the substrate. The field-effect transistor is provided in a semiconductor substrate. The measuring electrode is provided with a membrane, (i.e., a coating) which is sensitive to the chemical property to be determined and which is applied by electroplating, sputtering or vapor deposition. The field-effect transistor is encapsulated against the fluid that is to be examined by a protective layer composed of an epoxin resin or rubber.
Immersing a transducer of this design in the fluid to be examined yields, due to the ion exchange reactions between the electro-active substance of the membrane and the fluid at the gate electrode of the field-effect transistor, a potential which influences the channel conductivity of the field-effect transistor. Potentiometric or ammetric measurement permits obtaining a corresponding output signal proportional to the concentration of the parameter to be measured.
Other chemically sensitive transducers are known from EP-A-0 302 228, EP-B 0 078 590 and U.S. Pat. No. 4,514,276.
Although the voltage produced by the ion exchange reaction lies in the mV range, the non-reactive load capacity of the membrane, however, lies in the pA to fA range. When working with such low charge quantities, it is important that all interfering influences, in particular those of an electric or thermal nature, be prevented, a point for which the above-cited publications provide no measures. Another problem with the known transducers is that they can only be utilized for the determination of those chemical properties to which the membranes, which can be applied onto the measuring electrode with the aforementioned processes, are sensitive.
An object of the present invention is to provide a chemically sensitive transducer featuring higher sensitivity in comparison to known chemically sensitive transducers and which, at the same time, is insensitive to electric influences and temperature fluctuations. The transducer should also be able to be designed to be sensitive to properties that can be detected only with membrane substances of little stability.
These and other objects are provided by the present invention which provides a chemically sensitive transducer for selectively determining a chemical property of a fluid and providing a measurement signal to an amplifying circuit. The transducer has a measuring electrode coupled to the amplifying circuit and provides a measurement signal to the amplifying circuit. A membrane covers the measuring electrode, this membrane being sensitive to a specified chemical property. A carrier plate, with first and second sides, has the measuring electrode arranged on its first side and the amplifying circuit on its second side. The carrier plate has a conductor extending between the first and second sides which electrically couples the measuring electrode and the amplifying circuit.
The arrangement of the measuring elect
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Brauchle Christoff
Hampp Norbert
Niebling John F.
Phasge Arun S,.
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