JP2732878B2 - Optical fiber sensor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a sensor for measuring properties of an object to be measured, and more specifically, an optical fiber for optically measuring properties of a substance using an optical fiber. Related to sensors.

[Related Art] In recent years, various optical fiber sensors mainly for remote measurement have been devised. In particular, the miniaturization of sensors has become possible due to the development of photometric methods and optical fibers themselves. The optical fiber sensor directly obtains optical information (for example, absorbance, fluorescence intensity, etc.) of the substance to be measured located at the tip of the optical fiber directly through the optical fiber,
A reagent that undergoes some change, such as a reaction with the substance to be measured, is fixed to the tip of the optical fiber, and the information on the substance to be measured can be obtained indirectly by obtaining the optical information of the reagent. In the former, the object to be measured is limited to a substance having optical information (for example, a dye).

The latter can be applied to a wider range of substances to be measured. For example, in the measurement of the oxygen concentration in a liquid or a gas, since oxygen has poor optical information, the measurement can be performed by utilizing the quenching phenomenon in which the intensity of light emission such as fluorescence is weakened by oxygen. For example, taking advantage of the fact that the intensity of fluorescence from a fluorescent substance such as pyrene is reduced by oxygen, the fluorescent substance is fixed at the tip of an optical fiber as a reagent, and the intensity of the fluorescent light emitted from the reagent is detected to detect the surrounding oxygen. There is a method of measuring the concentration. In these cases, the light from the light source for exciting the fluorescent substance and the fluorescent light emitted from the fluorescent substance are transmitted by different or single optical fibers. In order to enable actual oxygen concentration measurement, the layer containing the reagent is required to have a high oxygen permeability coefficient, and various methods for fixing the reagent have been proposed. For example, (1) a method of dissolving a fluorescent substance in a silicone polymer (Patent Publication No. 59-24379), and (2) a method of dissolving a fluorescent substance in a polymer containing a plasticizer (Austrian Patent Publication A4248 / 82) (3) A method of adsorbing and fixing on a porous support (international application PC
T US82 / 01418).

(4) In addition, by giving a specific angle between the light from the light source (for example, transmitted by an optical fiber) and the surface of the reagent layer, the light from the light source can be used to fix the reagent layer and the material for fixing the same. (Austrian Patent Publication A2955 / 84) to prevent the light from being reflected at the interface with the photodetector and entering the photodetector.

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

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

The method of fixing a dye such as a phosphor in an optical sensor targeting hydrogen ion concentration (pH) is listed as follows. (7) Using cellulose as a carrier film, a monomer copolymerizable with a phosphor and a monomer copolymerizable with the phosphor are used. (8) a method of copolymerizing in a network to form a so-called interpenetrating network structure in which the cellulose, the copolymer of the phosphor and the monomer are not chemically bonded to each other (US Pat. No. 4,568,518), A method in which a fluorescent substance is bound to a substance having a functional group formed on cellulose by covalent bond (German Patent Publication 334363)
6, "Analytical Chemistry", Vol. 54, No. 82, 1982
Pages 1 to 823, "IEEE Transactions on Biomedical Engineering", 1986, BME 33, 117-1
(9) a method of bonding a fluorescent substance to an ion exchange membrane by ionic bonding (Japanese Patent Application Laid-Open No. 60-86449); and (10) a method of converting a fluorescent substance to an optical fiber or the like with a covalent bond via a silane coupling agent. There is a method of directly bonding to a glass surface (Japanese Patent Application Laid-Open No. 60-100037, "Analytical Science", 1987, Vol. 3, pp. 7-9).

[Problems to be Solved by the Invention] In the above proposals (1) and (2), there is no description of the sensor shape, and no specification is made. Proposal (3)
In the above, a void is generated between the optical fiber and the reagent layer due to the use of the porous support, which causes a large loss in the amount of light due to reflection and scattering, and the sensor shape is regulated by the need for a tube-shaped envelope. Is done. If the miniaturization of the sensor is intended, it is desirable that the light from the light source and the fluorescent light are transmitted by the same optical fiber. In the method (3) using two (a pair of) optical fibers, the miniaturization is required. There is a limit.

In Proposal (4), the surface on which the reagent layer is fixed is merely a flat surface, and when used as an optical fiber sensor,
Not only is it difficult to fix the reagent layer uniformly and with necessary and sufficient strength on such a minute plane, but also 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 the light reflection at the interface becomes larger and the loss of light amount increases, but also it is extremely difficult to form a uniform reagent layer on a minute portion. Further, even when a permselective film or a protective film is provided between the reagent layer and the medium to be measured, it is also difficult to provide a uniform film. Further, since the shape of the tip portion of the optical fiber is an acute angle, this film is easily broken when the fiber sensor is guided to the measurement site.

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

Regarding proposals (7) to (10), none of the methods specifies the shape of the reagent layer.

The present invention has been made in view of such problems of the related art, and has a high sensitivity, a fast response speed, and excellent reproducibility, and is a minute optical fiber sensor for measuring a property of a substance. The purpose is to provide.

[Means for Solving the Problems] According to the present invention, there is provided a reagent layer containing a reagent affected by an object to be measured, and an optical fiber having the reagent at its tip, and light is transmitted to the reagent layer through the optical fiber. By guiding the light obtained from the reagent layer again through the optical fiber, the tip portion and the reagent layer covering the tip portion of the optical fiber sensor used for measuring the property of the object to be measured are both curved. It can be measured by being formed.

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.

According to another feature of the invention, there is provided an optical fiber sensor, wherein the material forming the curved surface and the optical fiber have substantially the same refractive index.

Here, the `` reagent layer '' is a layer in which a reagent capable of causing a change in optical information by causing some correspondence with a substance to be measured in a medium to be measured is a layer in which a thin film or a multilayer is distributed. This includes a layer in which fine particles such as microcapsules containing a reagent are dispersed. Furthermore, "curved surface"
The term includes not only a geometrically curved surface such as a spherical surface, an ellipsoidal surface, and a paraboloid, but also a curved surface obtained by combining these geometrical surfaces.

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

Furthermore, it is desirable that the material of the curved surface on which the reagent layer is fixed and the material of the core of the optical fiber are substantially the same.

As used herein, the term “material” refers mainly to optical properties such as refractive index of each material and properties at an interface such as surface energy, and “materials are substantially the same” means that each material is substantially the same. This includes the case where they are the same as each other.

[Operation] First, in an optical sensor having a reagent layer, the reagent layer and the permselective membrane provided between the reagent layer and the medium to be measured have higher uniformity, and the thinner the film, the higher the sensitivity and the faster the response speed. . In addition, a large surface area of the reagent layer (or the permselective membrane) in contact with the medium to be measured is a factor for increasing the sensitivity. Here, the permselective membrane prevents substances that can react with a reagent other than the substance to be measured or factors / substances inhibiting this reaction from reaching the reagent layer, and plays a role of improving selectivity as a sensor. . At the same time, the permselective membrane also plays a role in protecting the reagent layer and preventing outflow of the reagent.

In the case of a minute optical fiber sensor, the loss of the light amount is minimized as the distance between the reagent layer and the tip of the optical fiber is shorter. Therefore, a method of directly coupling the reagent layer to the tip of the optical fiber is conceivable. The simplest and most reliable method of providing a reagent layer is to dissolve the matrix (usually polymers) forming the reagent layer in a suitable solvent together with the reagent, apply this solution to the end of the optical fiber, This is a method of removing the solvent by drying according to the following conditions.

Next, the tip of the optical fiber is cut along a plane perpendicular to the longitudinal direction of the fiber, and this section is directly immersed in a solution having a suitable viscosity of the matrix for forming the reagent layer as described above, or the solution is sectioned. , A reagent layer having a spherical outer surface can be formed by surface tension. Therefore, the exposed surface area is actually large, but the thickness of the reagent layer has a convex lens-like distribution, the response speed is extremely slow, and the reproducibility is lacking.

As a result of intensive studies, the inventor has made it possible to apply a uniform thickness and a large surface area to the reagent layer and / or the permselective membrane by making the surface holding and holding the reagent layer curved, so that a high surface area can be obtained. It has been found that it is possible to form a fiber optic sensor with high sensitivity, fast response speed, and excellent reproducibility, in which the reagent layer is hard to break.

Embodiment FIG. 1 is a cross-sectional view showing an embodiment of the present invention, in which an optical fiber 100 has a spherical tip. As shown in the figure, the optical fiber 100 has a long core 101 made of an optically transparent material, a clad 102 surrounding the peripheral surface and made of a material having a refractive index different from that of the core 101, and a peripheral part thereof. It consists of a jacket 103 surrounding the surface.

The tip portion 110 is formed in a curved shape so as to form a part of a sphere as a whole as shown. A reagent layer 104 is formed on the spherical surface of the distal end portion 110 as shown, and a permselective membrane 105 is formed so as to cover the reagent layer 104. Further, in order to prevent malfunction due to disturbance light and prevent damage due to external force, the outer surface of the clad 102 is surrounded by a jacket 103 as shown in FIG.

The reagent layer 104 includes a material that can react with a substance to be measured and cause some optical change. It is uniformly distributed on the tip 110, but may be unevenly distributed. Further, it may be formed in a thin film shape, and may be formed not in a single layer but in a multilayer shape. Further, microcapsules may be dispersed. Further, the radius of curvature may be equal to or larger than the radius of the optical fiber 101. Permselective membrane 1
05 indicates that a substance other than the substance to be measured, which can react with the reagent, or a factor or substance that inhibits the reaction is externally supplied to the reagent layer 104
To the sensor to give it selectivity as a sensor,
Further, it has a function of preventing the reagent layer 104 from flowing out and adhering to other substances.

FIG. 2 shows a case where the radius of curvature of the spherical portion at the distal end of the optical fiber 100 is larger than the radius of the optical fiber 100, and FIG.

The material that forms the curved surface is the core 101 of the optical fiber 100.
It is desirable that the material is the same as that of. Because if there is a difference in optical properties such as refractive index between these materials,
This is because light is reflected at the interface and light amount loss occurs. Further, a difference in surface energy or the like impairs the adhesiveness between the two materials, and tends to cause a problem of a decrease in strength.

The reagent layer 104 is fixed to the tip (curved surface) of the optical fiber 100 manufactured as described above, and if necessary, the substance to be measured is placed between the reagent layer 104 and the medium to be measured 510 (FIG. 4). However, in such a case, the reagent layer 104 and the permselective membrane 105 can have a uniform thickness and a large application area. In addition, the reagent layer 104 and / or the permselective membrane 105 applied in this manner are difficult to have a sharp portion, and thus are not easily destroyed by an external impact.

Example PMMA plastic optical fiber (cladding diameter 0.5m)
m) was cut to a length of 2 m with a sharp knife, and one end was immersed in a dimethylformamide solution of PMMA and dried, and this was repeated several times to make the end surface substantially spherical. This spherical surface is tris (2,2'-bipyridine) ruthenium (II) chloride 20m
M, immersed in a 10% aqueous solution of polyvinylpyrrolidone and dried to form a thin layer having a substantially uniform thickness. Furthermore, a thin layer of silicone was formed from a 10% toluene solution of silicone RTV (made by Toray Silicone) so that the polyvinylpyrrolidone layer was not exposed. This example had a shape as shown schematically in FIG. After the silicone was cured, it was immersed in water for one week, but there was no significant change in shape such as film thickness. The thus prepared optical fiber probe for measuring oxygen concentration is used, for example, by connecting to an optical measuring device as shown in FIG. FIG. 4 is a diagram showing an example of the optical measuring device used in this embodiment. Light emitted from a light source 502 such as a xenon lamp driven by a power supply 501 is focused by an aspheric lens 503, and only light near a wavelength of 440 nm is transmitted by an interference filter 504. Further, the light around the wavelength of 440 nm is focused by the convex lens 505 and totally reflected by the dichroic mirror 506. The totally reflected light is focused by the objective lens 507, and the optical fiber 1
It is incident on the core 101 of 00. The incident light is optical fiber 1
The probe 509 of 00 is reached. The light that has reached the probe 509 irradiates the reagent layer 104, for example, through the core 101 in FIG. The irradiated reagent layer 104 emits light at a wavelength of 610 nm in this example, and diverges from the opening end. The divergent light is converged by the objective lens 507 in the same optical path as before, and the dichroic mirror 5
The light passes through 06, is focused by the convex lenses 511 and 512, and passes through the interference filter 513. Only the transmitted light having a wavelength of 610 nm is incident on the photomultiplier tube 514. The incident light is converted into photoelectrons by a photomultiplier tube 514 and multiplied in the photomultiplier tube 514. The electric signal by this is amplified by the preamplifier 516, and A
It is converted to a digital signal by the / D converter 517. The converted digital signal is further processed by an arithmetic unit (computer) 51
It is processed at 8 and displayed on the display device (CRT) 519.

Observing the change in luminescence intensity while changing the oxygen concentration in the blood with the oxygenator using this device, the Stern-Volmer equation was established between the luminescence intensity and the oxygen concentration, and the response speed was within 20 seconds. And it was very fast.

Comparative Example On the other hand, FIG. 5 shows a conventional example. A plastic optical fiber 120 is cut sharply, a permselective film 105 is formed so as to include the indicator layer 104 with a transparent or translucent material having a different refractive index, and the same procedure as in the embodiment is performed without forming a spherical surface. When the optical fiber probe was prepared, the polyvinylpyrrolidone layer and the silicone layer did not become uniform in thickness, but became partially swollen by immersion in water for one week.

The optical fiber probe for measuring oxygen concentration thus prepared was connected to an optical measuring device as shown in FIG. 4, and while changing the oxygen concentration in the blood with an oxygenator,
Observation of the change in the luminescence intensity showed that the Stern-Volmer equation was established between the luminescence intensity and the oxygen concentration, but the slope was about half that of the example. The response speed was as slow as 30 seconds.

 Here, the Stern-Volmer equation is expressed as Fo / F = 1 + Kqτo [Q] = 1 + Ko [Q]. Where Fo is the emission intensity when no quenching substance is present F is the emission intensity Kq is the quenching reaction rate coefficient τo is the emission lifetime when no quenching substance is present [Q] is the concentration of the quenching substance Ko is the extinction coefficient of Stern-Volmer is there.

[Effects of the Invention] As described above in detail, the present invention provides a reagent layer at the tip of an optical fiber, and detects the intensity, spectrum, emission life, and the like of light generated from the reagent layer, thereby making contact with the reagent layer. An optical fiber sensor for measuring gas concentration, pH, various ion concentrations, temperature, etc. in a medium to be measured, characterized in that a surface on which a reagent layer is fixed comprises at least one curved surface. Therefore, the reagent layer and / or the permselective membrane on the outer side, that is, the side in contact with the medium to be measured can be formed with a uniform thickness and thinner, and the surface area thereof can be increased. Therefore, not only an increase in sensitivity and an improvement in response speed can be obtained, but also damage to the distal end portion becomes difficult.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of an optical fiber sensor according to the present invention, FIGS. 2 and 3 are sectional views showing another embodiment of the present invention, and FIG. 4 is an optical system used in the embodiment. FIG. 5 is a schematic view of a measuring device, and FIG. 5 is a cross-sectional view showing a comparative example according to the prior art. Description of Signs of Main Parts 100 Optical Fiber 101 Core 102 Cladding 103 Jacket 104 Reagent Layer 105 Permselective Membrane 401 Optical Fiber Bundle 402 Hemisphere 501 Xenon Lamp Power supply 502 xenon lamp 503 aspheric lens 504 interference filter (440 nm) 505 convex lens 506 dichroic mirror 507 objective lens 509 probe 510 medium to be measured (blood) 511 …… Convex lens 512 …… Convex lens 513 …… Interference filter (610nm) 514 …… Photomultiplier tube 515 …… High voltage power supply 516 …… Preamplifier 517 …… A / D converter 518 …… Computing unit (computer) 519 …… Display Equipment (CRT)

Claims (3)

(57) [Claims] An optical fiber having a reagent layer containing a reagent affected by an object to be measured and an optical fiber having the reagent layer at a distal end thereof, light is guided to the reagent layer through the optical fiber, and the light is guided from the reagent layer to the reagent layer. In the optical fiber sensor used for measuring the property of the object to be measured by guiding the obtained light through the optical fiber, the tip portion and the reagent layer covering the tip portion are both formed in a curved surface shape. An optical fiber sensor, comprising: 2. The optical fiber sensor according to claim 1, wherein a curved surface of a tip portion of said optical fiber is formed of substantially the same material as a core of said optical fiber. 3. The optical fiber sensor according to claim 1, wherein the material forming the curved surface of the tip of the optical fiber has substantially the same refractive index as the core of the optical fiber.