Optical fiber sensor arrangement for determining an analyte, in particular glucose.

p0001The invention relates to a fiber-optic sensor system for determining an analyte, in particular from glucose, comprising an optical fiber arrangement with frontally arranged sensor.

p0002For continuous determination of glucose fiber optic sensor arrays have become known which comprise a light fiber bundle with a flat sensor structure on its front side. The flat sensor structure affects in measurements in a flow-measurement with respect to the hydrodynamic properties adversely. For example, it comes to adhesion of air bubbles in the measuring chamber under which the glucose measurement is difficult and an accurate measurement is not possible.

p0003The invention is based on the object to determine an analyte to provide a fiber optic sensor array, the versatile, for measurements in Durchflußmeßkammern is hydrodynamically low and is particularly suitable for continuous glucose determination.

p0004This object is inventively achieved in a fiber-optic sensor system with the features of claim 1. Advantageous designs of the fa seroptischen inventive sensor assembly are the subject of the dependent claims.

p0005The behavior of the fiber optic sensor system according to the invention is extremely low. The response time of the sensor until a stable signal is about 1 to 3 minutes. The lifetime of the sensors is more than a week, and after one week, no decrease in signal in respect to the initial signal level is measured.

p0006An inventive fiber optic sensor system for determining an analyte, in particular glucose thus comprises an optical fiber arrangement with the front side arranged sensor, as the light guide arrangement comprises a light-conducting monofilament is provided on the front end of the light conducting single fiber a silicone rubber layer having dissolved therein a fluorescent indicator is applied, the silicone rubber layer with is a light-absorbing material coated on it an enzyme is immobilized, and a protective membrane arranged on the enzyme layer.

p0007The inventive fiber optic sensor assembly thus comprises only a single fiber, thus affecting the hydrodynamic properties of the sensor system very advantageous effect. A fiber assembly according to the invention for the determination of glucose can be used as miniaturized Glucosebiosensor directly into solutions (eg food or invasive in the bloodstream) or in solid samples (meat, fish, etc.) and in Durchflußmeßkammern.

p0008The measuring principle of the optical fiber sensor assembly according to the invention is based upon the determination of glucose in the fluorimetric determination of oxygen via dynamic fluorescence quenching of an indicator by triplet oxygen. As support material, the sensor assembly includes a layer of silicone rubber in which a fluorescence indicator is a dependent on the oxygen concentration fluorescence is dissolved and immobilized. Here, the property of silicone is used, that this has a high permeability and solubility for oxygen. The silicone rubber layer is coated with a light absorbing material in order to achieve optical isolation of the sensor from the environment and eliminate a possible influence of a self fluorescence of the sample liquid. This structure thus represents an oxygen sensor. Another function of the light-absorbing material is that it serves as a bonding agent between the silicone rubber layer and the immobilized enzyme or enzyme gel. The immobilized enzyme uses oxygen during a catalyzed reaction. For example, changing the formula used to determine glucose glucose glucose and oxygen into gluconolactone and hydrogen peroxide. The success while decrease in the oxygen concentration is measured by the oxygen sensor. The amount of oxygen consumed is proportional to the measured glucose concentration. On the enzyme layer a protective membrane is finally positioned, which protects the enzyme layer against the effects of the sample liquid.

p0009It has proved to be expedient to remove the sheath at the front end of the single fiber over a length of about 0.0 to 1.0 mm, preferably 0.5 to 1.0 mm. In this way the applied silicone rubber layer can be certainly coupled to the single fiber and at the same time, an optical isolation of the single fiber is ensured against ambient light. Very advantageous is a teardrop-shaped application of the silicone rubber layer on the end of the single fiber.

p0010As a fluorescence indicator decacyclene is preferably used. However, it can be any fluorescent dye may be used which shows a change of the fluorescence intensity with the concentration of oxygen.

p0011In a preferred embodiment of the fiber optic sensor system according to the invention of the light-absorbing material is activated carbon. However, it can also be used other substances that are used as binders between enzyme and silicone rubber, as a substrate for enzyme immobilization.

p0012In a preferred embodiment of the invention the enzyme is glucose oxidase. Alternatively, the enzyme may be for example one of oxidases, oxygenases or oxidoreductases. This allows the determination of other analytes in addition to the determination of glucose.

p0013Advantageously, the enzyme is immobilized by crosslinking with glutaraldehyde. However, also other Enzymimmobilisierungstechniken be used.

p0014The protective membrane is suitably made of cellulose acetate, which is advantageously applied by dipping in a solution. This is in the case of cellulose acetate to cellulose acetate in acetonitrile. According to the thickness of the protective membrane, the sensor sensitivity or the analytical range of the sensor can be adjusted.

p0015The Gesamtmeßvorrichtung according to the invention is extremely simple. The photoconductive single fiber is advantageously connected to a conventional fluorometer wherein only instead of a cuvette normally used a rotating mirror arrangement is provided so that light from a light source through a first lens system on the rotating mirror assembly into the light-guiding fiber is coupled. The light-conducting fiber is also connected via a second lens system having a detector of the fluorimeter.

p0016The invention will be further described hereinafter with reference to preferred embodiments and the drawing. In the drawings:<ul><li>Fig. 1 is a cross sectional view of a light-conducting fiber with single end side arranged sensor,</li><li>Fig. 2 shows a schematic arrangement of the overall construction of a fiber optic sensor array coupled to a conventional fluorimeter</li><li>FIG. 3a shows an example for a sensor arrangement for measurement in static solutions,</li><li>Fig. 3b is an example of a built-in a flow-measurement sensor arrangement,</li><li>Fig. 4 is a calibration curve of a sensor system for static measurement,</li><li>Fig. 5 is a calibration curve of a sensor system for measuring a flow-measurement,</li><li>FIGS. 6a and 6b show a plan view and a cross-sectional view of an apparatus for coupling a light conductive single-fiber to a conventional fluorimeter.</li></ul>

p0017In Fig. 1 a cross-sectional view of a fiber optic sensor array according to the invention for the determination of glucose. The front end of a light-conducting single fiber 2 is naked, that is, the cover 4 of the monofilament is removed in a length of about 0.5 to 1.0 mm. In this area, a silicone rubber layer 6 is in ge this area is a silicone rubber layer 6 having dissolved therein decacyclene applied teardrop shape as fluorescent indicator. The silicone rubber layer is coated with charcoal 8 as a light absorbing material. On the activated carbon has a layer of the enzyme glucose oxidase is 10 immobilized by crosslinking with glutaraldehyde. On the enzyme layer, a protective membrane 12 is applied from cellulose acetate by dipping in a cellulose acetate in acetonitrile.

p0018Fig. 2 shows the coupling of the sensor arrangement according to the invention with a conventional fluorimeter. In front of a light source 20, a Anregegungslichtmonochromator 22 and a first lens system 24 are arranged. A mirror 26 is arranged so that it is reflected by the first lens system, light passing in the light-conducting single fiber 2, which enters the Glucosebiosensor 6-12 at the front end of the single fiber.

p0019At the other end of the light conductive individual fibers are a second lens system 28 and a Fluoreszenzlichtmonochromator 30. from the photoconductive single fiber passing focused and filtered light then enters a photomultiplier 32, the electrical output signal to an evaluation unit can be supplied.

p0020In Fig. 3a shows a sensor arrangement of the invention for the static measurement in solutions is schematically illustrated. A light-conducting single fiber 2 is immersed with its front end or the glucose sensor into a 6-12 contained in a tank 40 solution 42 whose glucose content is to be determined.

p0021In Fig. 3b a built-in flow-measurement chamber according to the invention a fiber optic sensor assembly is shown schematically. A photoconductive single fiber 2 extends through the wall of a flow-measurement chamber 50 to a line 52 which is flowed through from top to bottom in Fig. 3b from a liquid to be examined.

p0022In FIG. 4 is a calibration curve of a glucose sensor for a static measuring system, for example, is that illustrated in Fig. 3a measuring arrangement shown. The photomultiplier output signal (fluorescence) is plotted against the glucose concentration. The analytical range of the sensor system is 1 to 10 mM glucose at this static arrangement.

p0023In the calibration curve of Fig. 5 shown in a flow arrangement of the analytical range is 0.05 to 1.5 mM. Through greater thickness of the protective membrane, however, higher concentrations of glucose can be measured.

p0024In Fig. 6a and Fig. 6b schematically the structure of an apparatus for coupling a light-conducting monofilament illustrates a conventional fluorimeter. To the extent that parts are the same as in the illustration of FIG. 2, they are provided with the same reference numerals and will not be described again. In this case, the mirror 26 is a glued piece of aluminum foil that is easily shaped parabolically. The mirror 26 and the end of the light conductive individual fibers 2 are arranged in a block 60 made of plexiglass. By means of a screw 62, the block 60 rotatably connected to the interior of the fluorimeter. Conventionally befände at this point a cuvette.