JPH08261925A - Substance information detecting system by optical method - Google Patents

Abstract

PURPOSE: To detect the electromagnetic line absorption quantity of a surface layer at high sensitivity by feeding the electromagnetic line at the prescribed incidence angle in the region of the critical angle or above with the medium layer optimized to obtain the optimum light wave guide mode between the medium layer and a subject substance, and using the reflection factor of the electromagnetic wave. CONSTITUTION: A medium layer 10 has a multi-layer structure (dielectric films 4, 5, 6) formed with at least one or more light wave guide layers, an electromagnetic line absorbing substance is contained in one of a transparent film and dielectric films 4, 5, 6, and the medium layer 10 is optimized to obtain the optimum light wave guide mode. A sample having the known refraction factor estimated for a subject substance 7 is kept in contact with the film 6. The electromagnetic line is fed to an optical prism 1 from an electromagnetic line source 8 at the incidence angle of the crirical angle or above determined by the optical prism 1 and the substance 7. When the wave guide mode is optimized, the reflection factor is made extremely small. When the reflection factor change is observed by a photodiode 9, the refraction factor change of the substance 7 can be detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a substance information detection system using an optical method, and more particularly, to a system for measuring the refractive index, the film thickness, and the amount of electromagnetic radiation absorbed by a surface layer of a substance to be detected. The present invention relates to a substance information detection system that is highly sensitive and can be easily detected.

[0002]

2. Description of the Related Art Conventionally, various methods have been used as a method of measuring a change in refractive index, a film thickness distribution, an absorption amount, etc. in the vicinity of a surface of a substance. Attention has been paid to a method using a wave path.

The method using surface plasmon resonance utilizes the fact that the vibration of plasma on a metal surface is affected by the refractive index of a substance adjacent to the metal surface. This can be achieved by using an evanescent wave (attenuated wave) generated when the light is made incident. That is, a sensor in which a metal thin film is provided on a prism is manufactured, a test substance is brought into contact with the metal thin film of the sensor, and electromagnetic radiation is applied at a specific incident angle in a region equal to or greater than a critical angle determined by the prism and the test substance. Upon incidence, a portion of the light seeps into the metal interface, producing an evanescent wave. When this wave number matches the wave number of a surface wave (surface plasmon) generated on the surface of the metal thin film, resonance occurs and the reflected light intensity decreases. To be observed. Since the wave number of this surface plasmon is affected by the change in the refractive index of the surface of the medium in contact with the metal, the change in the refractive index of the surface of the test substance adjacent to the metal thin film is monitored by monitoring the change in the intensity of the reflected light. It can be detected.

On the other hand, in the method using an optical waveguide, when an electromagnetic wave propagates through a core portion in an optical waveguide including a core portion (optical waveguide portion) having a high refractive index and a clad portion having a low refractive index, the electromagnetic radiation is This is based on the fact that it is attenuated by the influence of absorption by a substance in contact with the clad portion. Specifically, for example, an incident light prism is provided at one end of the optical waveguide, and an emission light prism is provided at the other end, and the electromagnetic radiation incident on the incident light prism is guided to the optical waveguide portion. The electromagnetic radiation attenuated and propagated through the prism for emission light is emitted from the other end side, and a test substance is brought into contact with the clad portion. Then, the state of the test substance is detected from the degree of the attenuation by utilizing the fact that the electromagnetic radiation is attenuated in the optical waveguide section through the cladding section in accordance with the change in the absorption amount of the test substance by the electromagnetic radiation. That is.

[0005]

However, in the method using surface plasmon resonance, since a metal thin film is used, the width of the dip in the reflectance curve is limited by the refractive index of the metal used. Therefore, the optimization of the dip shape can only be achieved by adjusting the metal film thickness, and it is difficult to optimize the dip shape to an extent sufficient to obtain highly sensitive detection. Furthermore, in the method using surface plasmon resonance, since no optical waveguide is provided, the light propagation length is short, so that a sharp dip cannot be obtained in the reflectance curve, and it is difficult to detect with high sensitivity. There is also. In order to increase the light propagation length, for example, one dielectric film is provided between the prism and the metal thin film, the refractive index is set to be equal to the refractive index of the test substance, and the light propagation length is increased. There are methods, but the work becomes complicated,
Problems such as limitation of the selection of the test substance occur.

On the other hand, in the above-described method using the conventional optical waveguide, the light propagation length must be increased in order to enhance the detection accuracy, and therefore, the optical waveguide length itself must be increased. Further, it is necessary to provide separate prisms for the incident light and the outgoing light, and the apparatus cannot be made compact and simple.

The present invention has been made in view of the above circumstances, and has as its object to provide a system which can detect information on a test substance with extremely high sensitivity and can be easily detected as compared with the conventional method. It is in.

[0008]

Means for Solving the Problems In order to solve the above-mentioned conventional problems, the present inventors have conducted intensive studies, and as a result, have found that the refractive index, the film thickness of the test substance, and the amount of electromagnetic radiation absorbed by the surface layer portion. Detection,
The present invention has been completed by developing a new technique that can be easily detected with a single system at a higher accuracy than any of the conventional methods and is different from any of the conventional methods.

That is, according to the present invention, electromagnetic waves are incident on the test substance via the optical coupling member and the medium layer, and the characteristics of the reflected light from the test substance are changed via the medium layer and the optical coupling member. In a substance information detection system by an optical method of detecting information on the test substance by monitoring, the medium layer includes at least two or more dielectric film layers, and at least one or more of the dielectric film layers Is an optical waveguide layer, and the dielectric film layer is transparent or at least one layer contains an electromagnetic radiation absorbing substance and has a predetermined extinction coefficient (imaginary part of complex refractive index). At a predetermined incident angle in a region equal to or greater than a critical angle determined by the optical coupling member and the test substance, an optimal optical waveguide mode is established between the medium layer and the test substance. The refractive index, thickness, and extinction coefficient of the medium layer are optimized, and by using the optimized medium layer, the reflectivity of the electromagnetic radiation incident near the predetermined angle of incidence is used. Provided is a substance information detection system using an optical method, which detects a refractive index, a film thickness, and an electromagnetic radiation absorption amount of a surface layer portion of a test substance with high sensitivity.

Here, the detection of the refractive index or the film thickness of the test substance is performed by using a multilayer dielectric film having at least one layer containing an electromagnetic radiation absorbing substance as the optimized medium layer. The detection is performed by detecting the reflectance of the electromagnetic radiation incident on the medium layer in the vicinity of the predetermined incident angle.

Further, the detection of the amount of electromagnetic radiation absorption at the surface layer of the test substance is performed by using a transparent dielectric film as the medium layer, and comparing the dielectric film with the test substance containing the electromagnetic radiation absorbing substance. Perform the above optimization so that an optimal optical waveguide mode is obtained between
The detection is performed by detecting the reflectance of the electromagnetic radiation incident on the optimized medium layer in the vicinity of the predetermined incident angle.

The medium layer used in the present invention comprises at least two or more dielectric films, and at least one of the dielectric films forms an optical waveguide layer. As used herein, the term "optical waveguide" is intended to include any transmission path for electromagnetic radiation in or near the optical range, where light waves are transmitted through the waveguide by repeated internal reflection at the waveguide wall. The dielectric film is not particularly limited as long as it is made of a dielectric material. Specifically, polytetrafluoroethylene, polymethyl methacrylate (PMMA), SiO
₂ , polystyrene, MgF _{2 and the} like, but are not limited thereto.

Next, this dielectric film layer is transparent, or at least one layer contains an electromagnetic radiation absorbing substance and has a predetermined extinction coefficient (imaginary part of complex refractive index). Electromagnetic radiation absorbing materials
Any substance can be used without particular limitation as long as it is a substance that absorbs the type of electromagnetic radiation used for detection, but one having good compatibility with the solvent used for forming the dielectric film can be suitably used. Would. Specific examples include dyes such as methylene blue, methyl red, methyl orange, and rhodamine, but are not limited thereto. Further, the dielectric material itself may have electromagnetic radiation absorption.

Further, when the medium layer is irradiated with an electromagnetic ray at a predetermined incident angle at a predetermined incident angle in a region equal to or more than a critical angle defined by the optical coupling member and the test substance, the medium layer may be in contact with the test substance. It is necessary to optimize the refractive index, the thickness and the extinction coefficient of the medium layer so that the optimum optical waveguide mode is obtained between them. The refractive index of the medium layer can be determined by selecting the material of each dielectric film to be used, and the extinction coefficient can be determined by adjusting the content of the electromagnetic radiation absorbing substance. Further, since the depth of the dip is affected by the thickness of each dielectric film, optimization is necessary. In the case of the present invention, as parameters for the optimization, many options such as the incident angle, the refractive index of the medium layer, the thickness, and the extinction coefficient can be used. And detection with high sensitivity becomes possible.

Hereinafter, the detection system of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited by this.

[0016]

FIG. 1 is a diagram for explaining an example of the outline of a detection system according to the present invention.

FIG. 2 shows an example in which the medium layer has three layers, and the first dielectric thin film 4, the second dielectric thin film 5, and the third dielectric film 6 are formed on one surface of the transparent substrate 3. Are respectively formed to form the medium layer 10. An optical prism (optical coupling member) 1 is provided on the other surface of the transparent substrate 3 via a matching oil 2. In the drawing, reference numeral 7 denotes a test substance, 8 denotes an electromagnetic radiation source, 9 denotes a photodiode, 11 denotes an XY stage, and 12 denotes an optical prism fixing member.

The medium layer 10 has at least one medium therein.
A multilayer structure is formed in which more than one layer forms an optical waveguide layer.
For example, the refractive index of the first dielectric film 4 is n ₄ , the refractive index of the second dielectric film 5 is n ₅ , and the refractive index of the third dielectric film is n.
_6. Assuming that the refractive index of the test substance is n ₇ and the refractive index of the optical prism 1 is n ₁ , the material of the dielectric film is selected so that n ₅ , n ₆ > n ₄ , n ₇ . 2 dielectric film 5
The third dielectric film 6 forms an optical waveguide, but is not limited to these examples. In the case of a multilayer, a cladding layer may be formed between a plurality of optical waveguide layers.

In order for the incident electromagnetic radiation to couple the optical waveguide mode, the refractive index of the optical prism 1 needs to be higher than the refractive index of the cladding layer. For example, in the above example, n
_1> a n _4, n _7.

The medium layer 10 may be transparent or a first dielectric thin film 4, a second dielectric thin film 5, and a third dielectric thin film 6.
At least one layer contains an electromagnetic radiation absorbing substance. By changing the content of the electromagnetic radiation absorbing substance, the extinction coefficient can be adjusted in the optimization of the medium layer described later. When the refractive index and the film thickness of the test substance 7 are to be detected, the medium layer containing the electromagnetic radiation absorbing substance is placed on the test substance 7.
In order to detect the amount of electromagnetic radiation absorption of the surface layer, a transparent medium layer is used.

Further, in the present invention, the medium layer 10 needs to be optimized so that an optimum optical waveguide mode is obtained.
The “optimal optical waveguide mode” means a mode in which the propagation length is long and the real part of the propagation constant changes sensitively to the change in the refractive index of the test substance. About optimization of the medium layer 10,
This will be described below together with the procedure for detecting the refractive index of the test substance.

The detection of the refractive index of the test substance 7 is performed, for example, in the following procedure.

First, the medium layer 10 is optimized. A sample having a known refractive index n _s within a range including the refractive index estimated to be possessed by the test substance 7 to be detected is brought into contact with the third dielectric film 6. In this state, the electromagnetic radiation from the electromagnetic radiation source 8 is incident on the optical prism 1 at an incident angle in a region equal to or greater than the critical angle determined by the optical prism 1 and the test substance 7. Here, the incident angle at which the dip at which the reflectance at the interface of the optical prism 1 sharply drops is obtained using the incident angle of the electromagnetic radiation, the refractive index, the film thickness, and the extinction coefficient of the dielectric film as parameters. Such a dip occurs in the region equal to or larger than the critical angle because the wave vector of the waveguide mode existing depending on the material, thickness, etc. of each dielectric film is the amount of the interface direction component of the wave vector of the incident light beam. When it becomes equal to, the incident light that has leaked into the medium layer 10 from the interface of the optical prism 1 excites the optical waveguide mode into the medium layer 10 and propagates while attenuating in the waveguide.
When the waveguide mode is optimized, all the energy of the incident light is given to the waveguide mode, and the reflectance becomes extremely small. On the other hand, when optimization is not performed, part of the energy of the waveguide mode is emitted again as reflected light. If the refractive index of the test substance 7 placed in contact with the third dielectric film 6 of the medium layer 10 changes, this change in the refractive index affects the optical waveguide mode, which also affects the emitted light. It will be. Therefore, by observing the change in the reflectance with the photodiode 10, the change in the refractive index of the test substance 7 can be detected.

FIG. 2 shows a result of a simulation performed by the present inventors as a specific example of the optimization of the medium layer.

FIG. 2 shows that n _S = 1.330 as a test substance.
7 is a reflectance curve obtained by optimizing a medium layer in the case of (liquid substance). As the first dielectric film 4, a polytetrafluoroethylene film (700 nm thick, n ₃ =
1.303); as the second dielectric film 5, a polymethyl methacrylate (PMMA) containing a dye (methylene blue) containing a dye (methylene blue) (film thickness 600 nm, n ₄ = 1.49)
0 + 0.001i); SiO ₂ as the third dielectric film
Simulation was performed using each of the films (thickness: 10 nm, n ₆ = 1.459). As shown in line A, a deep and narrow dip was obtained at an incident angle of 62.0 °.

On the other hand, when optimization was performed using a metal thin film (silver) using surface plasmon resonance, a dip was obtained at an incident angle of 67.5 ° as shown by a line B. It is understood that the width of the dip is inferior to that of the dielectric film (line A) in comparison with the case of the above dielectric film, and that the use of the dielectric film has lower detection sensitivity than that of the present invention.

Therefore, when the test substance is a liquid substance,
Using a medium layer optimized like the above dielectric layers,
If the light is incident at an incident angle of about 62.0 °, a change in the refractive index of the test substance can be detected with extremely high sensitivity just by knowing the change in the incident angle at which the dip occurs.

Further, if a calibration curve indicating the relationship between the incident angle at which dip occurs and the refractive index is prepared, the value of the refractive index of the test substance can be known. FIG. 3 is a calibration curve showing an incident angle at which a dip occurs when the refractive index is changed in increments of 0.01 using the optimized medium layer. By using this, for example, if the angle at which the dip occurs with respect to the test substance is 62.5 °, it can be read that the refractive index of the test substance is 1.342.

The detection of the film thickness of the test substance can be performed in accordance with the above-mentioned refractive index. That is, using the optimized medium layer, a calibration curve of the incident angle-film thickness at which a dip occurs is prepared using a plurality of samples of known thickness.

After that, a test substance having an unknown thickness is brought into contact with the dielectric film 6 and the incident angle at which the dip occurs is obtained, whereby the film thickness can be obtained from the calibration curve. Note that if it is only necessary to detect the presence or absence of a change in the thickness of the test substance, it is sufficient to know that the incident angle at which the dip occurs has changed without creating a calibration curve.

When the amount of electromagnetic radiation absorption of the surface layer of the test substance is detected, the medium layer does not contain the electromagnetic radiation absorbing substance, and is substantially the same as the above case except that a transparent material is used. It can be carried out.

That is, first, the transparent medium layer film is optimized. A known extinction coefficient (for example, 0.00) in a range including the electromagnetic radiation absorption amount estimated to be possessed by the test substance to be detected.
The sample having 1) is brought into contact with the third dielectric film 6. In this state, an electromagnetic ray is incident. Here, the incident angle, the thickness of the transparent dielectric film, and the extinction coefficient of the sample are taken as parameters, and the incident angle at which the dip at which the reflectance falls sharply is obtained. Then, when it is confirmed that the sharpest dip occurs at a certain predetermined incident angle θ, using the transparent medium layer, a calibration curve of the reflectance-extinction coefficient is created using a plurality of samples having known absorption amounts. deep.

Thereafter, a test substance having an actually unknown extinction coefficient is brought into contact with the dielectric film 6 and irradiated with electromagnetic radiation at an incident angle near the incident angle θ in the range including the incident angle θ. , The extinction coefficient of the test substance in the surface layer can be obtained from the above-mentioned calibration curve.

FIG. 4 is a calibration curve showing the relationship between the reflectance and the extinction coefficient in a simulation performed by the present inventors. If this is used, for example, if it is observed that the reflectance is 0.4, it can be seen from this calibration curve that the extinction coefficient of the test substance is 0.00019.

If it is only necessary to detect the presence or absence of a change in the absorption amount of the test substance, it is sufficient to detect the depth at which the dip occurs, without creating the above calibration curve.

In the above embodiment, the case where the number of the medium layers is three has been described. However, even when the number of the medium layers is four or more, it can be basically considered based on the same principle as described above.
In the case of two layers, for example, assuming that there is no third dielectric film 6 from FIG. 1, n ₅ > n ₄ , n ₇
The second dielectric film 5 forms an optical waveguide by selecting the material of the dielectric film so as to satisfy the same condition as the above-described three-layer case, except for the above. Further, in this case, the medium layer is transparent, or one or both of the first dielectric thin film 4 and the second dielectric thin film 5 contain an electromagnetic radiation absorbing substance.

In the above embodiment, the detection target is a liquid substance. However, the detection target is not limited to this, and the system of the present invention is applicable to a gas (gas) substance, a solid substance, and the like. Of course, it can be detected.

[0038]

As described above in detail, according to the present invention, compared with the conventional method using surface plasmon resonance using a metal thin film, the number of options for optimization according to the detection substance is increased. Optimization becomes easier. Further, since the optical waveguide mode is used, a sharp dip can be obtained in the reflectance curve. In the present invention, 1
With one system, the refractive index, the film thickness, and the amount of electromagnetic radiation absorbed in the surface layer of the test substance can be detected with extremely high sensitivity and easily.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing one embodiment of a detection system of the present invention.

FIG. 2 is a graph showing a relationship between a reflectance and an incident angle at which a dip occurs.

FIG. 3 is a graph showing a relationship between an incident angle at which a dip occurs and a refractive index.

FIG. 4 is a graph showing a relationship between reflectance and extinction coefficient.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical prism (optical coupling member) 2 Matching oil 3 Transparent substrate 4 1st dielectric film 5 2nd dielectric film 6 3rd dielectric film 7 Test substance 8 Electromagnetic radiation source 9 Photodiode 10 Medium layer 11 XY stage 12 Optical prism fixing member

Continued on the front page (72) Inventor Kazuyoshi Goto 6-26-1, Jingumae, Shibuya-ku, Tokyo Kirin Brewery Co., Ltd.

Claims (3)

[Claims] 1. An electromagnetic radiation is incident on a test substance via an optical coupling member and a medium layer, and characteristics of light reflected from the test substance are monitored through the medium layer and the optical coupling member. In a substance information detection system using an optical method for detecting information on a test substance, the medium layer includes at least two dielectric film layers, and at least one of the dielectric film layers forms an optical waveguide layer. The dielectric film layer is set to be transparent or to have at least one layer containing an electromagnetic radiation absorbing substance and having a predetermined extinction coefficient (imaginary part of complex refractive index). At a predetermined incident angle in a region equal to or greater than the critical angle defined by the optical coupling member and the test substance, the medium layer is set such that an optimal optical waveguide mode is established between the medium layer and the test substance. Refractive index, thickness The extinction coefficient and the extinction coefficient have been optimized, and using the optimized medium layer, from the reflectance of the electromagnetic radiation incident near the predetermined incident angle,
A substance information detection system using an optical method, which detects a refractive index, a film thickness, and an electromagnetic radiation absorption amount of a surface layer portion of a test substance with high sensitivity. 2. As the optimized medium layer, at least one or more dielectric film layers containing an electromagnetic radiation absorbing substance are used, and the medium layer is made to enter near the predetermined incident angle. 2. The method according to claim 1, wherein the refractive index or the thickness of the test substance is detected with high sensitivity from the reflectivity of the electromagnetic radiation.
Described substance information detection system. 3. A transparent dielectric film is used as the medium layer, and the optimization is performed so that an optimum optical waveguide mode is established between the dielectric film and a test substance containing an electromagnetic radiation absorbing substance. Detecting the amount of electromagnetic radiation absorbed by the surface layer of the test substance with high sensitivity from the reflectance of the electromagnetic radiation incident on the optimized medium layer in the vicinity of the predetermined incident angle. The substance information detection system according to claim 1.