Optochemical sensor

Details Optochemical sensor Optochemical sensor

1998-09-28

2001-07-03

Warden, Jill (Department: 1743)

Chemical apparatus and process disinfecting, deodorizing, preser

Analyzer, structured indicator, or manipulative laboratory...

Means for analyzing liquid or solid sample

C422S068100, C422S082050, C422S082090, C422S082110, C422S083000, C436S127000, C436S136000, C436S068000, C436S172000

Reexamination Certificate

active

06254829

ABSTRACT:

The invention relates to an optochemical sensor including a matrix containing a luminescence indicator whose luminescence may be extinguished or quenched by oxygen.
BACKGROUND OF THE INVENTION
Optochemical sensors (optodes), in the following referred to as “optical sensors” or “sensors” for reasons of simplicity, these days are widely employed, preferably in the form of membranes, in sensor configurations in order to quantify particular substances such as, e.g., oxygen or glucose in a sample. Optical sensors are used, for instance, in environmental measuring technology and in emergency medicine (blood gas analysis). The mode of functioning of optical sensors and the basic structure of a sensor configuration generally comprising an optical sensor formed of several layers, an excitation light source and an optoelectronic detection system has been described in the literature (e.g., Sensors and Actuators B 11 (1993), pp. 281-289; Sensors and Actuators B 29 (1995), pp. 169-173).
There has already been known a plurality of indicator substances and sensors which respond to the chemical substances mentioned and, in particular, oxygen by changing an optical characteristic of the indicator. In U.S. Pat. No. 3,612,866, for instance, Stevens describes an optical sensor capable of being calibrated and sensitive to oxygen, which contains the dye pyrene, the luminescence of which is extinguished by diffusing-in oxygen in a concentration-dependent manner. At the same time, the sensor includes a reference sensor on a neighboring site, which reference sensor is masked by an additional oxygen-impermeable membrane. The concentration of oxygen is determined by the ratio of the signals of the two areas.
Furthermore, Lüibbers in U.S. Reissue Pat. No. RE 31,879 describes a luminescence-optical oxygen sensor including the indicator pyrene butyric acid, optionally stirred into a silicone matrix having a high permeability for oxygen, whose sensitive layer is embedded between a light-permeable covering layer and an oxygen-permeable base layer contacted by the analyzed liquid.
In another U.S. Pat. No. 4,657,736 Marsoner describes an oxygen sensor comprising modified dyes that are readily soluble in silicone, thus offering an enhanced stability of the sensor against the aggregation of dye molecules. The sensor is prepared by stirring the dye into a prepolymer and subsequent polymerization to silicone.
In U.S. Pat. No. 4,752,115 Murray describes an oxygen-sensitive layer of a transition metal complex in a plasticized organic polymer matrix (e.g., PVC), which is applied as a layer onto a fiber optic conductor element via which the excitation light is launched. Those complexes, in general, are more photostable than organic dyes. Again, the luminescence intensity is measured as a function of the concentration of oxygen in the layer.
In U.S. Pat. No. 4,775,514 Barnikol describes a luminescent surface for determining oxygen in gases, liquids and tissues. The sensitive layer on the surface is comprised of a homogenous mixture of an organic dye (pyrene, coronene, etc.) with silicone.
Khalil in U.S. Pat. Nos. 4,810,655 and 5,043,286 describes measurements of the decay times of phosphorescent dyes having long decay times readily accessible by measuring techniques, instead of luminescence intensity measurements. The fluorinated porphyrins used exhibit relatively high photostabilities. In addition, the parameter decay time is less prone to photodecomposition effects as compared to luminescence intensity.
The same technique is employed by Bacon in U.S. Pat. No. 5,030,420, which describes an oxygen sensor comprised of a ruthenium(II) complex immobilized in a silicone that is impermeable to many liquids such as, e.g., acids and bases, complexing agents, oxidizing and reducing liquids, yet is highly permeable for oxygen and other gases. However, that sensor contains the indicator electrostatically bound to filler particles (silica gel) in the silicone, a fact the author's attention is drawn to only at a later point of time (e.g., Sacksteder, et al., Anal. Chem. 65, p. 3480). This provides for a good stability against washing out of the dye in the first place.
The stability of a sensor against washing out of the indicator also is the topic of proposals in U.S. Pat. No. 5,070,158 to Holloway and U.S. Pat. No. 5,128,102 to Kaneko, which disclose the possibility of chemically binding indicator molecules to a polymer matrix.
Another way of improving the stability of a sensor against the loss of its indicator and hence the deterioration of the photophysical properties of the membrane is set forth by
Markle in U.S. Pat. No. 5,511,547. A special silicone matrix comprising polar carbinol groups serves to enhance the interaction between indicator (e.g., tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) chloride) and matrix in order to reduce the washing out, and also the aggregation, of the indicator molecules. Those measures are, however, not suitable for substantially enhancing the photostability of the membrane per se.
Finally, Jensen in U.S. Pat. No. 5,242,835 describes a method for determining the concentration of oxygen in a sample by detecting the emission of the singlet oxygen itself, which is excited by energy transmission during the extinction of the luminescence, occuring at a wavelength of approximately 1270 nm. Also that method is prone to photodecomposition of the indicator or the matrix by exactly that reactive singlet oxygen, the latter returning into its ground state without radiation during a photochemical reaction, thus causing also the sensitizer molecules (indicators) serving the production of the singlet oxygen to be attacked.
As already mentioned, optochemical sensors, in general, contain dyes which respond to a change in the concentration of the substance to be analyzed within the sensitive layer by changing their photophysical properties. The intensity and decay time of the luminescence of oxygen sensors will, for instance, decrease with the concentration of oxygen increasing in the sensitive layer.
A problem faced by many sensors and, in particular, oxygen sensors is their proneness to decomposition, which is triggered by the irradiated excitation light (Anal. Chem. 1991, 63, pp. 337-342). Both the luminescence indicator itself and the matrix are susceptible to decomposition. The problem of photoinduced decomposition occurs, in particular, if radiation occurs at a high intensity in order to enhance the signal quality and reduce the measuring error or if a single sensor is operated over a very long period of time as happens in the monitoring of chemical substances. Since the intensity of luminescence is a direct function of the concentration of dyes, the photodecomposition of these dyes in sensors of that kind is undesired.
The decay time of the luminescence of a sensor with dyes immobilized therein is a function of the concentration of the luminophores, in particular, if and when
firstly, an overlay background luminescence (of sources other than the dye) occurs,
secondly, luminescent degradation products are again formed by the photodecomposition of the dyes, the decay time of which degradation products differs from the decay time of the luminescence of the starting dyes, and
thirdly, a decomposition of the matrix (environment) of the dye changes the photophysical properties of the latter.
Thus, the decomposition of the luminophore or of the matrix (for instance, by the action of singlet oxygen) of typical sensor systems is undesirable for the following reasons:
On the one hand, the mere decrease of the luminescence intensity (at a constant decay time) results in a relative increase of the background fluorescence and hence in a change of the calibration curves. The decrease of the luminescence intensity constitutes a problem to all sensor systems if the radiation quantity to be measured is thereby lowered to such an extent that the dynamic range of the receiver electronics is left. A decrease of the luminescence intensity causes particular problems to sensor systems based on the measurement of the

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