Optochemical sensor and method for production

Abstract

An optochemical sensor for measuring concentrations of analytes is provided with a reactive matrix preferably made of polymeric material capable of swelling. Further provided are a mirror layer and a layer of a plurality of discrete islands that are electrically conductive, between which layers the reactive matrix is positioned, the diameter of the islands being smaller than the wavelength of the light employed for monitoring and evaluation.

Description

BACKGROUND OF THE INVENTIONThis invention relates to an optochemical sensor for measuring concentrations of substances by means of a reactive sensor film, and a method for preparing such an optochemical sensor.Optochemical sensors are based on the fact that a chemical reaction between the sensor material and the analyte leads to a change in the optical properties of the sensor. Such a change may involve optical properties such as absorption or fluorescence, in which instance the reaction may be detected by means of spectroscopic methods.Optochemical sensors for measuring concentrations of chemical species are met with growing interest for several reasons; compared to conventional measuring devices they are characterized by much shorter response times, greater mechanical robustness, and insensitivity to electromagnetic interferences in addition to other advantages. To ensure a short response time, however, it is essential for such optochemical sensors that the sensor material be suff...

AI Technical Summary

Benefits of technology

It is an object of the invention to provide an optochemical sensor of the above kind, which will permit a concentration of an analyte, such as pH value or ionic strength, to be determined in a simple and reproducible manner, where no electrodes are needed and the result of the measurement can be obtained rapidly and most acutely, even if the changes in the concentration to be measured are very small.

In a preferred embodiment wherein the mirror layer is metallic, the metal chosen for mirror and island film should be gold. Basically it would be possible to use other metals, such as aluminum or silver, for preparation of the mirror and the island film. Such other metals are more sensitive to chemical attack, however, than the island film of gold preferred by the invention. In addition, gold is characterized by excellent absorption properties and thus a high sensitivity and strong spectral shift of the reflection minima.

Due to the thin film and short response time, and the clearly visible strong spectral shift of the reflection minima, a change in color can be detected rapidly and reliably. At the same time, the relatively simple design of the optochemical sensor will give a high degree of mechanical stability. To ensure sufficiently short response times and distinct spectral shifts of the reflection minimum of the film structure, it is proposed in a preferred embodiment that the optical thickness of the polymer matrix be less than 1,000 nm, in particular, less than 600 nm. To increase the rate of response the optical thickness may be less than 100 nm; in principle, film thicknesses of slightly greater than 10 nm to 15 nm are possible if suitable polymers are selected.

The optochemical sensor described by the invention can be prepared in a simple manner, by vapor-depositing the island film on the polymer matrix, or rather, on the metal layer and the polymer layer. By means of this technique of vapor deposition the extremely small mass thickness and the formation of discrete islands required by the invention may be obtained, which will produce the typical strong spectral shift of the reflection minima. As an alternative, the island film may be prepared or modified by the attachment of metallic particles or islands to the polymer matrix, or by removing excess metal from the polymer film, thereby producing islands or changing their number or size, in which way the desired mass thickness may be accurately obtained.

Basically, the use of different optical densities and different wavelengths will serve to find an optimum response rate for the measurement of certain analytes. Tests have shown that color changes can be reliably detected for visual discrimination between different thicknesses in increments of some 10 to 30 nm change in optical thickness; this change in optical thickness is due to a change in ionic strength and ensuing swelling of the polymer matrix, and may be calibrated in a simple way. It has been found especially that sulphonic acid groups in a polymer may cause shrinking at high ionic strength, and that these processes are fully reversible if a chemical environment is maintained that does not destroy the matrix or the island film.

Problems solved by technology

With conventional interferometric methods it is hardly possible, however, to detect small changes in the thickness of thin layers.

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