JPH02183145A - Optical fiber sensor - Google Patents

Abstract

PURPOSE:To achieve a rise in sensitivity and a higher response speed by forming a tip part curved in an optical fiber sensor in which light is introduced to a reagent layer through an optical fiber to measure a nature of an object to be measured by light obtained from the reagent layer. CONSTITUTION:An optical fiber 100 comprises a long-sized core 101, a clad 102 and a jacket 103 and the tip part 110 thereof is formed so curved as to make a part of a ball. A reagent layer 104 and a permselective film 105 covering the layer is formed on a spherical face of the tip 110. Here, the reagent layer 104 contains a material which causes a sort of optical change in reaction with a material to be measured and the permselective film 105 has functions to block material other than that to be measured and a reaction interfering substance from reaching the reagent layer 104 from outside and to prevent the reagent layer from spilling out. In this manner, a surface curved to hold the reagent allows a coating of a larger surface area with an even thickness for the reagent layer 104 and the permselective film 105, thereby realizing a higher sensitivity and a higher response speed.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a sensor that measures the properties of an object to be measured.

More specifically, the present invention relates to an optical fiber sensor that optically measures the properties of a substance using an optical fiber.

[Prior Art] In recent years, various optical fiber sensors have been devised mainly for the purpose of remote measurement. In particular, advances in photometry methods and optical fibers have made it possible to miniaturize sensors.

Optical fiber sensors are those that directly obtain optical information (e.g., absorbance, fluorescence intensity, etc.) of the substance to be measured located at the tip of the optical fiber, and those that directly obtain optical information (e.g., absorbance, fluorescence intensity, etc.) of the substance to be measured located at the tip of the optical fiber. It can be classified as a method in which information on the substance to be measured is obtained indirectly by fixing a reagent that undergoes some change to the tip of an optical fiber and obtaining optical information about the reagent. In the former, the object to be measured is limited to a substance having optical information (for example, a dye).

The latter method can be applied to a wider range of substances to be measured. Measurements can be made by taking advantage of the weakened extinction phenomenon. For example, taking advantage of the fact that the intensity of fluorescence from a fluorescent substance such as pyrene is reduced by oxygen, it is possible to fix the fluorescent substance as a reagent at the tip of a five-optical fiber and detect the intensity of the fluorescence emitted from the fluorescent substance, thereby detecting the surrounding oxygen. There are ways to measure concentration. In these cases, separate or single optical fibers transmit the light from the light source for exciting the fluorescent substance and the fluorescence emitted from the fluorescent substance. To enable actual oxygen concentration measurements, the layer containing the reagent is required to have a high oxygen permeability coefficient, and therefore various methods for immobilizing the reagent have been proposed. For example, (1) a method of dissolving a fluorescent substance in a silicone polymer (Patent Publication No. 59-24379).

(2) A method of dissolving a fluorescent substance in a polymer containing a plasticizer (Austrian Patent Publication A4248/82), (3
) A method of adsorption and immobilization on a porous support (Kokusai Shi 1jlp
Hl:T US82101418) There is a nato.

(4) Also, by creating a specific angle between the light from the light source (e.g., transmitted by an optical fiber) and the surface of the reagent layer, the light from the light source can be directed to the reagent layer and the material that fixes it. A device that prevents reflection from entering the photodetector at the interface with
There is.

(5) In order to further increase the surface area, a method can be considered in which the tip of the optical fiber is cut obliquely to the longitudinal direction of the optical fiber and a reagent layer is provided on the cross section.

In the measurement of target substances other than oxygen, various optical fiber sensors have been devised for measuring ion concentrations such as pH. For example, (6) there is a method in which a dye whose fluorescence spectroscopic properties change depending on the ion concentration is fixed to the tip of an optical fiber and the surrounding ion concentration is measured.

Listing methods for identifying dyes such as fluorescent substances in optical sensors that target hydrogen ion concentration (pH) are as follows: (7) Cellulose is used as the carrier film, and a monomer that can be copolymerized with the fluorescent substance is mixed with cellulose. A method in which cellulose, a copolymer of a phosphor, and a monomer are copolymerized in a network to form a so-called interpenetrating network structure in which they are not chemically bonded to each other (U.S. Pat. No. 4,588,5
18), (8) A method of bonding a phosphor with a covalent bond to cellulose with a functional group (German Patent Publication 334383B, "Analytical Chemistry, 1982, Vol. 54, pp. 821-823,"
“IEEE) Transactions on Φ Biomedical Φ Engineering’ 19B! 3rd Year BNE 3
3, pp. 117-132).

(8) Method of bonding a phosphor to an ion exchange membrane through ionic bonding (Japanese Unexamined Patent Publication No. 130-88449), (10)
A method of directly bonding a phosphor to the glass surface of an optical fiber through a covalent bond via a silane coupling agent, etc. (Japanese Patent Application Laid-Open No. 130-100037, "Analytical Science °', 1987, No. 3 @ No. 7 to 9) page) etc.

[Problems to be solved by the invention] In the above-mentioned proposals (1) and (2), the shape of the sensor is neither described nor specified, and in proposal (3), since a porous support is used, light A void is created between the fiber and the reagent layer, which increases the loss of light quantity due to reflection-scattering, and requires a tubular envelope, which limits the sensor shape. If miniaturization of the sensor is planned, it is desirable that the light from the light source and the fluorescence be transmitted through the same optical fiber. There is a limit.

In proposal (4), the surface on which the reagent layer is fixed is just a flat surface, and when used as an optical fiber sensor, it is difficult to fix the reagent layer uniformly and with sufficient strength on such a small flat surface. Alternatively, it is not possible to increase the surface area of the reagent layer, which is an effective means for improving sensitivity.

In proposal (5), not only does the light reflection at the interface become larger and the loss of light quantity increases, but it is extremely difficult to form a uniform reagent layer in a minute area. Furthermore, a selectively permeable membrane or a protective membrane may be provided between the reagent layer and the medium to be measured. It is difficult to provide a uniform film. Also,
Since the tip of the optical fiber has an acute angle, the membrane is likely to be torn when the fiber sensor is guided to the measurement site.

The sensor of proposal (6) also has the same problems as the aforementioned oxygen sensor.

Regarding proposals (7) to (lO), none of the methods specifies the shape of the reagent layer.

The present invention has been made in consideration of the problems of the prior art, and provides a microscopic optical fiber sensor for measuring the properties of substances, which has high sensitivity, fast response speed, and excellent reproducibility. The purpose is to provide

[Means for Solving the Problems] According to the present invention, the present invention includes a reagent layer containing a reagent that is affected by an object to be measured, and an optical fiber having the reagent layer at its tip, and transmits light to the reagent layer through the optical fiber. In an optical fiber sensor that is used to measure the properties of an object to be measured by guiding the light obtained from the reagent layer through an optical fiber, the tip portion is formed with at least one curved surface. It is possible.

According to one feature of the invention, the curved surface includes an optical fiber sensor formed of substantially the same material as the core of the optical fiber.

Another feature of the invention includes an optical fiber sensor characterized in that the material forming the curved surface and the optical fiber have substantially the same refractive index.

Here, the term "r-reagent layer" refers to a layer in which a reagent that can react with the substance to be measured in the medium to be measured and cause a change in optical information is distributed in the form of a thin film or multilayer;
For example, this includes a layer in which fine particles such as microcapsules containing a reagent are dispersed. Roughly speaking, the term "curved surface" includes not only geometric curved surfaces such as spherical surfaces, ellipsoidal surfaces, and paraboloid surfaces, but also curved surfaces that are composites of these geometric surfaces.

Moreover, one curved surface may be formed not only in a convex shape but also in a concave shape.

Generally speaking, it is desirable that the material of the curved surface to which the reagent layer is fixed is substantially the same as the material of the core of the optical fiber.

Here, the term ``r-material'' refers to the properties of each material at their mutual interface, mainly optical properties such as refractive index, surface energy, etc., and ``r-materials are substantially the same'' means that each material is This also includes cases where they are the same.

C Effect J First, in an optical sensor having two reagent layers, the reagent layer and the selectively permeable membrane provided between it and the medium to be measured have high uniformity, and the thinner the membrane, the higher the sensitivity and the faster the response speed. . Furthermore, the large surface area of the reagent layer (or selectively permeable membrane) in contact with the medium to be measured is a factor that increases sensitivity. Here, the selected f1 membrane is a substance that can react with a reagent other than the substance to be measured, or a factor that inhibits this reaction.
The selectively permeable membrane plays the role of preventing substances from reaching the reagent layer and improving the selectivity of the sensor. At the same time, the permselective membrane also plays the role of protecting the reagent layer and preventing reagent flow.

In addition, in a minute optical fiber sensor, the loss of the amount of light is minimized as the reagent layer is placed closer to the tip of the optical fiber. Therefore, a method can be considered in which the reagent layer is directly coupled to the tip of the optical fiber. Also,
The simplest and most reliable method for forming a reagent layer is to dissolve the matrix that forms the reagent layer (usually a polymer) together with the reagent in an appropriate solvent, apply this solution to the tip of the optical fiber, and apply the solution as necessary. This method involves drying and removing the solvent.

Next, the tip of the optical fiber is cut in a plane perpendicular to the length direction of the fiber, and this cross section is directly immersed in a solution of an appropriate viscosity of the matrix forming the reagent layer as described above, or this solution is cut into a cross section. When the reagent is dropped onto a surface, a reagent layer with a spherical outer surface can be formed due to surface tension. therefore,
Although the surface area exposed by 11i becomes larger in practice, the thickness of the reagent layer has a convex lens-like distribution, resulting in extremely slow response speed and lack of reproducibility.

As a result of extensive studies, the inventors discovered that by making the surface that binds and holds the reagent layer curved, the reagent layer and/or selectively permeable membrane can be coated with a uniform thickness and a large surface area. It has sensitivity, fast response speed, and excellent reproducibility. It has been found that it is possible to form an optical fiber sensor in which the reagent layer is resistant to destruction.

[Embodiment] FIG. 1 is a cross-sectional view showing an embodiment of the present invention, in which the tip of the optical fiber lOO is made spherical. As shown in the figure, the optical fiber 100 has a long core 10 made of an optically transparent material! and a cladding 1 surrounding the peripheral surface and made of a material having a refractive index different from that of the core 101.
02 and a jacket 103 surrounding the peripheral surfaces thereof.

The tip portion 110 is formed into a curved surface so as to form part of a sphere as a whole, as shown in the figure. As shown, a reagent layer 104 is formed on the spherical surface of the tip 110, and a selective permeation layer 111105 is formed to clean the reagent layer 104.

In order to prevent malfunctions caused by ambient light and damage caused by external forces, the peripheral surface of the clad 1G2 is surrounded by a jacket 103 as shown in the figure except for the tip.

The reagent layer 104 contains a material that can react with the analyte to produce a certain optical change, which is uniformly distributed in the tip 110, but may also be non-uniformly distributed. In addition, it may be formed in a thin film form, not necessarily in a single layer but in a multilayer form, or in which microcapsules are dispersed, and the radius of curvature is also equal to the radius of the optical fiber 101. The selectively permeable membrane 105 prevents substances other than the target substance to be measured that can react with the reagent and factors or substances that inhibit the reaction from reaching the reagent layer 104 from the outside, thereby improving selectivity as a sensor. It also has the function of preventing the reagent layer 104 from flowing out or adhering to other substances.

The radius of curvature of the spherical part at the tip of the optical fiber 100 is the optical fiber! The case where the radius is larger than 00 is shown in FIG. 2, and the case where it is equal is shown in FIG.

FIG. 4 shows a bundle of a plurality of optical fibers 100, whose tips are aligned and a spherical portion of the same quality as in the previous example is provided by the same means.

Next, we will discuss the processing of the tip of the sensor.

For example, materials such as quartz fiber and glass fiber have high heat resistance, but are difficult to process.

If the material can be melted at high temperatures, a curved surface can be created by locally heating the area where the curved surface is desired. Also, P
In the case of a plastic optical fiber whose core is made of thermoplastic resin such as MMA (poly(methyl methacrylate)), the optical fiber 100 is cut with a cutting tool such as a sharp knife, and the material forming the curved surface is melted. It can be produced by fixing a solution prepared on the tip of the optical fiber 100 and drying it, or by fixing a melt obtained by keeping this material at a high temperature on the tip of the optical fiber 100 and cooling it.

The material forming the curved surface is the core 1 of the optical fiber 00.
It is desirable that the material is the same as 01, because
This is because if there is a difference in optical properties such as refractive index between these materials, light will be reflected at the interface, resulting in loss of light amount. Further, differences in surface energy, etc. impair the adhesion between the two materials, which tends to cause a problem of weakening in strength.

A reagent layer 104 is fixed to the tip (curved surface) of the optical fiber 00 produced in this way, and if necessary, a selection for the substance to be measured is made between the reagent layer 104 and the medium to be measured 51O (FIG. 5). Although the permeation layer 105 is interposed, even in such a case, the reagent layer 104 and the selectively permeable membrane 105 can be made to have a uniform thickness and have a large coating area.

In addition, the reagent layer 1G4 and/or the selectively permeable membrane 105 coated in this manner do not have sharp parts and are therefore difficult to be destroyed by external impact.

Example: PMMA plastic optical fiber (cladding diameter 0.
5mm) to a length of 2m with a sharp knife, and one end is marked with P.
immersed in dimethylformamide solution of MMA and dried;
This was repeated several times to make the end surface almost spherical. This spherical surface is defined as tris(2,2°-bipyridine)ruthenium(I)
I) Immersed in an aqueous solution of 20 N chloride and 10% polyvinylpyrrolidone and dried to form a thin layer with a fairly uniform thickness. Furthermore, from above, silicone R was applied to prevent the polyvinylpyrrolidone layer from being exposed.
A thin layer of silicone was formed from a 10% toluene solution of TV (Resilicone). This example had a shape as shown schematically in FIG. After the silicone had hardened, it was immersed in water for one week, but there was no significant change in the film thickness or shape. The thus prepared optical fiber probe for # elementary concentration measurement is used by being connected to an optical measuring device as shown in FIG. 5, for example.

FIG. 5 is a diagram showing an example of the optical measuring device used in this example. Light emitted from a light source 502 such as a xenon lamp driven by a power source 501 is focused by an aspherical lens 503, and only light having a wavelength of around 440n layer is transmitted through an interference filter 5G4. Further, the light having a wavelength of around 440n is focused by the convex lens 505 and totally reflected by the dichroic mirror 508. Is the totally reflected light the objective lens 50? The light is focused at and input into the core 101 of the optical fiber 100. The incident light passes through the probe 509 of the optical fiber 100.
reach. The light that has reached the probe 509 passes through the core 101 in FIG. 1, for example, and irradiates the reagent layer 104. The irradiated reagent layer 104 emits light at a wavelength of 1110 ns in this example, and the zero-divergent light that diverges from its opening end follows the same optical path as before, is focused by an objective lens 507, and is focused by a dichroic mirror 506. The light passes through, is focused by convex lenses 511 and 512, and passes through the interference filter 5!3. Only the transmitted light with a wavelength of 810 nm is incident on the photomultiplier tube 514. The incident light is converted into photoelectrons by the photomultiplier tube 514 and multiplied within the open tube 514 . The electrical signal resulting from this is amplified by a preamplifier 518.

A/D converter 51? Convert it to a digital signal.

The converted digital signal is further processed by an arithmetic unit (computer) 518 and displayed on a display device (CRT) 519.

When we observed changes in luminescence intensity using this device while changing the oxygen concentration in the blood using an artificial lung device, we found that the Stern-Volmer equation was established between luminescence intensity and oxygen concentration, and the response speed was within 20 seconds. It was very fast.

salt! 1 On the other hand, FIG. 6 is a diagram showing a conventional example. The plastic optical fiber 120 is sharply cut, and the selective transmission film 105 is made so as to wrap the indicator layer 104 with a transparent or translucent material having different refractive indexes, without making it spherical.
When an optical fiber probe was prepared using the same technique as in the example, both the polyvinylpyrrolidone layer and the silicone layer did not have uniform thickness, and some parts swelled after being immersed in water for one week.

The optical fiber probe for oxygen concentration measurement prepared in this way was connected to an optical measurement device as shown in Figure 5, and changes in luminescence intensity were observed while the oxygen concentration in the blood was changed by an artificial lung device. Although the Stern-7-Wolmer equation was established between the emission intensity and the oxygen concentration, the slope was about half that of the example. Furthermore, the response speed was slow at 30 seconds.

Here, the Stern-Volmer equation is Fo/F=1
It is expressed as +Kqτo [Q] ±1+Ko [Q]. However, Fo is the emission intensity in the absence of a quencher F is the emission intensity KQ is the quenching reaction rate coefficient τ0 is the emission lifetime [Q] in the absence of a quencher is the concentration of the quencher Ko is the Stern-Volmer extinction coefficient be.

[Effects of the Invention] As detailed above, the present invention provides a reagent layer at the tip of an optical fiber, and detects the intensity, spectrum, luminescence lifetime, etc. of light generated from this reagent layer. An optical fiber sensor intended for measuring gas concentration, pH, various ion concentrations, temperature, etc. in a medium to be measured, characterized in that the surface to which the reagent layer is fixed consists of at least one curved surface. Therefore, the reagent layer and/or the selectively permeable membrane on the outside thereof, that is, on the side in contact with the medium to be measured, can be formed to have a uniform thickness and be thinner, and its surface area can also be increased. Therefore, not only the sensitivity and the response speed are improved, but also the tip part is less likely to be damaged.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of an optical fiber sensor according to the present invention. 12 to 4 are cross-sectional views showing another embodiment of the present invention, and FIG. 5 is a schematic diagram of an optical measuring device used in the embodiment. FIG. 6 is a sectional view showing a comparative example according to the prior art. Explanation of the symbols for the ' part...Optical fiber...Core...Clad...Jacket...Reagent layer...Selective transmission membrane...Optical fiber bundle...Hemisphere...For xenon lamps Power source...Xenon lamp...Aspherical lens...Interference filter (440nm)...Convex lens...Dichroic mirror...Objective lens...Probe...Measurement medium (blood)・Convex lens ・Convex lens ・Interference filter (810nm) ・Photomultiplier tube ・High voltage power supply ・Preamplifier ・A/D converter ・Arithmetic unit (computer) ・Display Device (CRT) Figure 1

Claims (1)

[Claims] 1. A reagent layer containing a reagent that is affected by an object to be measured, and an optical fiber having the reagent layer at its tip, which guides light to the reagent layer through the optical fiber, and An optical fiber sensor used for measuring the properties of the object to be measured by guiding light obtained from the reagent layer through the optical fiber, characterized in that the tip portion is formed into at least one curved surface. optical fiber sensor. 2. The optical fiber sensor according to claim 1, wherein the curved surface is made of substantially the same material as the core of the optical fiber. 3. The optical fiber sensor according to claim 1 or 2, wherein the material forming the curved surface has substantially the same refractive index as the core of the optical fiber.