JP2015102455A - Sensor device and measurement method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sensor device capable of detecting a change in the intensity of light due to surface plasmon resonance without being affected by the intensity of a light source, the degree of optical coupling, and a fluctuation in an external environment.SOLUTION: A sensor device (1) has: a light source (7); an optical waveguide (3, 3') including a core for wave-guiding light from the light source and a clad for covering the core; a metal layer (40) which is disposed so as to contact the core and in which surface plasmon resonance occurs due to the light from the light source; a sensor film (41) formed on the surface of the metal layer and specifically bonded with a substance to be measured by dripping a solution containing the substance to be measured onto the sensor film; an emitted light detection part (8) for detecting the intensity distribution of an emitted light from the optical waveguide; and a control part (11) for quantifying the substance to be measured in the solution dripped onto the sensor film on the basis of relationship between the emission angle and the intensity of the emitted light obtained from the intensity distribution detected by the emitted light detection part.

Description

  The present invention relates to a sensor device and a measurement method.

  An optical waveguide type SPR sensor using multiple reflection is known (see, for example, Patent Documents 1 and 2). The SPR sensor is a refractive index sensor using a surface plasmon resonance phenomenon, and is used for chemical analysis and biochemical analysis such as measurement of the concentration of a sample solution and detection of an immune reaction. Surface plasmon resonance is a phenomenon in which light having a wavelength corresponding to the refractive index of the sample solution is absorbed when light is incident on the inner surface of the metal layer in contact with the sample solution at a total reflection angle or more.

  FIG. 16 is a schematic diagram of a conventional optical waveguide type SPR sensor 100. The SPR sensor 100 includes an optical waveguide 103, a metal layer 140, a sensor film 141, a light source 107, and an optical sensor 108. The optical waveguide 103 is an optical fiber having a circular cross section, for example, and includes a core 130 and a clad 131. The metal layer 140 and the sensor film 141 are formed so as to surround a part of the surface of the core 130. A sample solution 106 is dropped around the optical waveguide 103 so as to be in contact with the sensor film 141.

  At the time of measurement, light is incident on the optical waveguide 103 from the light source 107. When incident light propagates in the optical waveguide 103 while repeating total reflection, surface plasmon resonance is generated in the metal layer 140 by light of a specific wavelength. The sensor film 141 is an antibody film that recognizes the substance to be measured contained in the sample solution 106 as an antigen, has a property of specifically binding to the substance to be measured, and is an area where the evanescent wave oozes out on the surface of the metal layer. To change the refractive index. At this time, the metal layer 140 absorbs light in an amount determined by the refractive index of the core 130, the refractive index of the sample solution 106, and the wavelength of light. Hereinafter, the amount of light absorbed by the metal layer 140 due to surface plasmon resonance is referred to as “SPR absorption”. The light passing through the optical waveguide 103 is attenuated by the SPR absorption at the metal layer 140, finally emitted from the emission surface, and detected by the optical sensor 108.

  FIG. 17A is a graph showing the relationship between the wavelength λ of incident light and the transmittance T of the optical waveguide. The wavelength for generating surface plasmon resonance varies depending on the refractive index of the sample solution. As shown in FIG. 17A, when the refractive index n of the sample solution increases, the peak wavelength of SPR absorption shifts to the long wavelength side.

  FIG. 17B is a graph showing the relationship between the refractive index n and the transmittance T of the sample solution measured with incident light having a wavelength of 660 nm. As shown in FIG. 17A, the wavelength 660 nm is light having a shorter wavelength than the peak wavelength of SPR absorption. When light having a wavelength shorter than the peak wavelength of SPR absorption is incident on the optical waveguide, when the refractive index n of the sample solution increases, the transmittance T increases and the intensity of light emitted from the optical waveguide increases.

  For this reason, the change in the refractive index due to the sample solution is measured by detecting the emitted light from the optical waveguide with an optical sensor and looking at the transmitted light amount and the spectral change of the emitted light with respect to the incident light. Further, since the refractive index of the sample solution depends on its concentration, the concentration of the sample solution can be obtained from the refractive index of the sample solution. That is, the amount of the substance to be measured contained in the sample solution can be obtained from the transmittance value by measuring the intensity of the emitted light when light of a specific wavelength is incident with an optical sensor.

  In general, when measuring with an SPR sensor, first, the intensity of the emitted light is measured in a state before the sample solution is dropped, and the measured value is used as a reference. Thereafter, the sample solution is dropped on the sensor film, and the intensity of the emitted light is measured. Then, the SPR absorption amount based on the sample solution is obtained by obtaining the difference between the measured value of the sample solution and the reference, and a calibration curve measured in advance, that is, the relationship between the amount of the substance to be measured in the sample solution and the SPR absorption amount. Is used to quantify the substance to be measured.

  On the other hand, a method for measuring a substance to be measured from a spectral difference using a reference value obtained in a state where the substance to be measured is present is known. For example, in Patent Document 3, infrared rays are incident on a substrate such as a wafer whose surface state is to be measured under conditions where the number of internal reflections is different, multiple internal reflection spectra are measured for each condition, and internal multiplexing with a small number of internal reflections is performed. A surface state measuring device is described in which an absorbance spectrum is obtained using a reflection spectrum as a reference spectrum and a sample spectrum having a large number of internal reflections.

  In the apparatus of Patent Document 3, light is incident at two different incident angles, and the relative intensity changes of the emitted light are compared. In this apparatus, since the reference is acquired in real time, it is possible to cancel the fluctuation factors that occur during the measurement. The device of Patent Document 3 is configured with an SPR sensor using a silicon wafer as an optical waveguide in order to grasp a contamination state due to an organic substance adhering to the silicon wafer, but the silicon wafer is replaced with a glass or polymer optical waveguide. For example, it is considered to be an optical waveguide type SPR sensor used in a liquid.

JP 2013-007687 A JP 2012-122915 A Japanese Patent No. 4792267

  In an optical waveguide type SPR sensor, the intensity of emitted light is affected by changes in the light source intensity, fluctuations in the optical coupling between the light source, the optical waveguide, and the optical sensor (alignment misalignment), and changes in the external environment such as temperature and humidity. Change, which becomes a measurement error. Originally, the measurement of the reference and the measurement of the sample need to be performed at the same time, but in reality, they are performed at different times, so fluctuations that occurred between the measurement of the reference and the measurement of the sample, Variations that occur during measurement become measurement errors.

  Even when the reference value is acquired in a state where there is a sample as in the apparatus of Patent Document 3, in order to measure two optical paths alternately, strictly speaking, fluctuations are canceled using two spectra at different times, Eventually, measurement errors may be included. In order to obtain spectra in the two optical paths at the same time, two sets of light sources and an infrared analyzer installed in advance in the target optical path are required, which increases costs and increases the size of the apparatus.

  Accordingly, an object of the present invention is to provide a sensor device capable of detecting a change in light intensity due to surface plasmon resonance without being affected by variations in light source intensity, optical coupling degree, external environment, and the like. Another object of the present invention is to provide a lower-cost and smaller sensor device.

  The sensor device according to the present invention is disposed so as to be in contact with a light source, a core for guiding light from the light source and a clad covering the core, and the surface plasmon resonance is generated by the light from the light source. A metal layer, a sensor film that is formed on the surface of the metal layer and in which a solution containing the substance to be measured is dropped and specifically binds to the substance to be measured, and outgoing light detection that detects the intensity distribution of the outgoing light from the optical waveguide And a control unit for quantifying the substance to be measured in the solution dropped on the sensor film based on the relationship between the emission angle and intensity of the outgoing light obtained from the intensity distribution detected by the outgoing light detection unit It is characterized by that.

  In the sensor device according to the present invention, the control unit determines, from the intensity distribution, a parameter of a theoretical formula that describes the relationship between the emission angle and intensity of the emitted light, whereby the light in the metal layer with respect to the emission angle of the emitted light is determined. It is preferable to determine the change in absorption.

  In the sensor device according to the present invention, the outgoing light detector is preferably a two-dimensional image sensor that receives the outgoing light on the outgoing surface of the optical waveguide.

  In the sensor device according to the present invention, the optical waveguide is an optical fiber, and the control unit correlates the emission angle and intensity of the emitted light from the radial intensity distribution in the circularly symmetric pattern acquired by the two-dimensional image sensor. It is preferable to acquire the attached data.

  In the sensor device according to the present invention, the optical waveguide is an optical waveguide having a square cross section formed on the surface of the substrate, and the control unit has a pattern perpendicular to the metal layer in the pattern obtained by the two-dimensional image sensor. It is preferable to acquire data in which the emission angle and intensity of the emitted light are associated with each other from the intensity distribution.

  In the sensor device according to the present invention, the light source is preferably an LED light source having an outgoing light intensity with a Lambertian distribution.

  The measurement method according to the present invention includes a light source, an optical waveguide including a core that guides light from the light source and a cladding that covers the core, and a surface plasmon resonance caused by the light from the light source. A measurement method using a sensor device having a metal layer and a sensor film formed on the surface of the metal layer and in which a solution containing the substance to be measured is dropped and specifically binds to the substance to be measured. Detecting the intensity distribution of the emitted light, and quantifying the substance to be measured in the solution dropped on the sensor film based on the relationship between the emission angle and intensity of the emitted light obtained from the detected intensity distribution It is characterized by having.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the sensor apparatus which can detect the light intensity change by surface plasmon resonance, without being influenced by light source intensity | strength, optical coupling degree, and the external environment fluctuation | variation. Further, according to the present invention, it is possible to provide a lower-cost and smaller sensor device.

1 is a schematic diagram of a sensor device 1. FIG. 4 is a cross-sectional view illustrating an example of a detection unit 4. FIG. It is a schematic diagram of a flow cell type sensor chip 2A. It is a schematic diagram of a sensor chip 2B having an optical waveguide 3 'having a square cross section. It is a figure for demonstrating the measurement principle by the sensor apparatus. Change in outgoing light intensity Po from the optical waveguide with respect to the wavelength λ of incident light, and outgoing light intensity with respect to the outgoing angle ψ from the optical waveguide when using a light source having a wavelength λ _S shorter than the peak wavelength λ _{0 of} SPR absorption It is the graph which showed the change of Po. It is a figure which shows the light which guides the core 30, totally reflecting by angle (theta). It is a figure which shows light source intensity distribution I ((psi)) which is a Lambert distribution. A graph showing an example of the light source intensity distribution I (ψ), the number of times of light reflection N (ψ), the transmittance Tm (ψ) of the SPR portion, and the emitted light intensity Po (ψ) when a light source having a Lambertian distribution is used. It is. It is a graph which shows the change of the emitted light intensity Po ((psi)) when the peak wavelength of SPR absorption shifts to the long wavelength side, and the transmittance | permeability Tm increases, and when the light source intensity | strength I increases. It is a figure which shows the example of the pattern acquired with the image sensor 10 when the optical waveguide 3 which is an optical fiber of a circular section is used. 4 is a flowchart illustrating an example of a method for obtaining parameters I ₀ and α of emitted light intensity Po (ψ) from a pattern acquired by the image sensor 10. It is a figure which shows the pattern of the emitted light intensity acquired with the image sensor 10 when using the sensor chip 2B. 6 is a graph showing a change in intensity in the y direction in a pattern of emitted light intensity acquired by the image sensor 10. It is a graph which shows the relationship between the inclination (alpha) calculated | required by linear approximation of each graph of the emitted light intensity _Pref (y) of _FIG.14 (C), and the density | concentration of a sample solution. 1 is a schematic diagram of a conventional optical waveguide type SPR sensor 100. FIG. 4 is a graph showing the relationship between the wavelength λ of incident light and the transmittance T of the optical waveguide, and the graph showing the relationship between the refractive index n and the transmittance T of the sample solution measured with incident light having a wavelength of 660 nm.

  Hereinafter, a sensor device and a measurement method according to the present invention will be described in detail with reference to the accompanying drawings. However, it should be noted that the technical scope of the present invention is not limited to these embodiments, but extends to the invention described in the claims and equivalents thereof.

  FIG. 1 is a schematic diagram of the sensor device 1. The sensor device 1 is an SPR sensor that quantifies a substance to be measured by using localized surface plasmon resonance (Localized Surface Plasmon Resonance). The sensor device 1 includes a sensor chip 2, a light source 7, an optical sensor 8, a control unit 11, a light source driving circuit 12, and a display device 13. In the following, the direction from the light source 7 toward the optical sensor 8 is defined as the z direction, and the x, y, and z axes are defined as shown in FIG.

  The sensor chip 2 includes an optical waveguide 3 and a sample solution holding unit 5. FIG. 1 shows a cross section of the sensor chip 2 in the yz plane. The optical waveguide 3 is an optical fiber made of glass or polymer. A part of the clad of the optical waveguide 3 is removed, and the detection unit 4 is formed in that part. The sample solution holding unit 5 holds the sample solution 6 therein.

  2A to 2C are cross-sectional views illustrating examples of the detection unit 4. 2A to 2C also show a part of the optical waveguide 3. The optical waveguide 3 includes a core 30 and a clad 31 that covers the core 30 and has a refractive index lower than that of the core 30. The optical waveguide 3 has a circular cross section and confines light in the core 30.

  First, referring to FIG. 2A, the detection unit 4 includes a metal layer 40 and a sensor film 41, and is formed rotationally symmetric with respect to a central axis extending in the z direction.

  The metal layer 40 is a layer in which surface plasmon resonance occurs when light enters, and is formed on the core 30 exposed by removing a part of the clad 31 by etching or the like. The metal layer 40 is a layer (metal particle layer) composed of metal particles such as gold, silver, platinum, copper, aluminum, or alloys thereof. In the detection unit 4, localized surface plasmon resonance occurs in the fine metal particles included in the metal layer 40. In the metal layer 40, it is preferable that the metal particles are not stacked on each other in the thickness direction, and are arranged at a slight interval so as not to contact each other in the plane direction. Moreover, in order to make the detection accuracy of the detection part 4 favorable, it is preferable that the particle diameter of each metal particle is about 5-300 nm.

  The sensor film 41 is formed of an antigen, an antibody, a receptor, or the like that specifically binds to the substance to be measured. The sensor film 41 is formed on the surface of the metal particles that constitute the metal layer 40.

  FIG. 2B is a cross-sectional view illustrating another example of the detection unit 4. 2B includes a metal layer 40A composed of metal particles and a sensor film 41. The difference from the detection unit 4 in FIG. 2A is that a sensor film 41 is also formed on the core 30 between the metal particles. The detection unit 4 in FIG. 2A has a metal layer 40 composed of metal particles having a sensor film 41 provided on the surface in advance. However, like the detection unit 4A in FIG. After forming the metal layer 40A including the sensor layer 41, the sensor film 41 may be formed on the metal layer 40A.

  FIG. 2C is a cross-sectional view showing still another example of the detection unit 4. 2C includes a very thin island-shaped metal layer 40B formed on the surface of the core 30 and a sensor film 41 formed on the metal layer 40B. The thickness of the metal layer 40B is preferably about several nm to several tens of nm, for example. In the detection unit 4B, localized surface plasmon resonance occurs in each minute island included in the metal layer 40B.

  For example, an LED light source is used as the light source 7. The distance between the light source 7 and the optical waveguide 3 is preferably as close as possible to increase the light utilization efficiency, and may be brought into contact as necessary. The size of the light emitting surface of the light source 7 is preferably larger than the core diameter of the optical waveguide 3 so that the incident light intensity does not easily fluctuate even if a positional shift occurs. In addition, the distribution of the emitted light intensity of the light source 7 with respect to the emission angle is preferably a Lambertian distribution.

  The optical sensor 8 is a two-dimensional optical sensor that detects outgoing light from the optical waveguide 3 (measures transmittance) in order to measure the SPR absorption amount. The optical sensor 8 includes a lens 9 and an image sensor 10. The lens 9 converts the light emitted from the optical waveguide 3 into parallel light. However, instead of the lens 9, an optical element such as a holographic element may be used. The image sensor 10 is a two-dimensional image sensor such as a CCD or CMOS sensor, and detects a two-dimensional intensity distribution of light emitted from the optical waveguide 3 as a two-dimensional pattern. The image sensor 10 is an example of an outgoing light detection unit.

  The control unit 11 includes a video interface and an information processing circuit inside. The control unit 11 takes in the two-dimensional pattern detected by the image sensor 10 from the video interface to the information processing circuit. And the control part 11 calculates | requires SPR absorption amount based on the relationship between the emission angle and intensity | strength of the emitted light from the optical waveguide obtained from a two-dimensional pattern by the procedure mentioned later using an information processing circuit, Quantify the substance to be measured in the sample solution. Quantification means, for example, obtaining the concentration and refractive index of the substance to be measured in the sample solution. Further, the control unit 11 controls operations of the light source driving circuit 12 and the display device 13.

  The light source driving circuit 12 is a circuit for driving the light source 7. The display device 13 displays the measurement result obtained by the control unit 11.

  FIG. 3 is a schematic diagram of a flow cell type sensor chip 2A. In the sensor device 1, instead of the sensor chip 2 in FIG. 1, a flow cell type sensor chip 2A shown in FIG. 3 may be used.

  The sensor chip 2 </ b> A has a flow cell 50. In the flow cell 50, an inflow port 51 and an outflow port 52 are provided in the sample solution holding unit 5 of FIG. The sample solution 6 is sent to the sample solution holding unit 5 by the syringe pump 53, and after contacting and reacting with the sensor film 41, the sample solution 6 is discharged to the reservoir 54.

  FIG. 4 is a schematic diagram of a sensor chip 2B having an optical waveguide 3 'having a square cross section. In the sensor device 1, a sensor chip 2B shown in FIG. 4 may be used instead of the sensor chip 2 of FIG.

  In the sensor chip 2 of FIG. 1, an optical fiber having a circular cross section is used as the optical waveguide 3. However, the sensor chip 2B has an optical waveguide 3 'having a square cross section instead of the optical fiber. The optical waveguide 3 ′ has a core 30 ′, a clad 31 ′, and a base substrate 32 ′. The base substrate 32 ′ is a flat substrate that also serves as a clad, on which a core 30 ′ and a clad 31 ′ are formed. The core 30 ′ is embedded in the base substrate 32 ′ so that the upper surface is exposed, and is disposed parallel to the longitudinal direction (z direction) of the base substrate 32 ′ at the center in the width direction (x direction) of the base substrate 32 ′. Yes. The core 30 ′ has a rectangular cross section along the xy plane. The clad 31 'is disposed on both sides of the core 30' so as to cover the upper surface of the base substrate 32 '.

  The detection unit 4 is formed by removing a part of the clad 31 ′, and is arranged so as to cover the upper surface of the base substrate 32 ′ where the clad 31 ′ is removed and the upper surface of a part of the core 30 ′. Has been. In the detection unit 4, a metal layer 40 and a sensor film 41 similar to those of the sensor chip 2 are formed. In the sensor chip 2B, the detection unit 4A in FIG. 2B or the detection unit 4B in FIG. 2C may be used.

  The sensor chip 2B in FIG. 4 may be a flow cell type sensor chip as shown in FIG.

  An outline of a method for quantifying a substance to be measured in a sample solution using the sensor device 1 will be described. First, a required amount of a sample solution containing an unknown amount of a substance to be measured is dropped on the sample solution holding unit 5 with a syringe or the like, and the detection unit 4 is covered with the sample solution 6. Then, the light source 7 is caused to emit light using the light source driving circuit 12 and light is incident on the optical waveguide. The incident light propagates through the optical waveguide while repeating and gradually attenuated total reflection, causes the detection unit 4 to generate SPR absorption according to the refractive index of the sample solution, and finally exits from the exit surface of the optical waveguide. .

  The intensity distribution of the emitted light is detected by the image sensor 10 of the optical sensor 8. Then, the two-dimensional pattern detected by the image sensor 10 is taken into the control unit 11 and the SPR absorption amount is obtained by a method described later. Thereby, the refractive index of a sample solution and the density | concentration of the to-be-measured substance in a sample solution are calculated | required. In the measurement using the sensor device 1, the reference measurement before dropping the sample solution is not necessary.

  Below, the measurement principle by the sensor apparatus 1 is demonstrated. The description is made using the optical waveguide 3 which is an optical fiber having a circular cross section, but the same applies to the case where the optical waveguide 3 'having a square cross section is used.

  FIG. 5 is a diagram for explaining the principle of measurement by the sensor device 1. In FIG. 5, three light beams having different incident angles from the light source 7 are indicated by thick solid lines, thin solid lines, and thin dashed arrows. These three light beams are light beams having different incident angles to the optical waveguide 3 instead of having different wavelengths. It can be seen that the number of reflections at the detection unit 4 and the exit angle from the optical waveguide 3 differ depending on the incident angle. The greater the incident angle, the greater the number of reflections and the greater the SPR absorption.

6 (A) and 6 (B) show the case where a light source having a wavelength λ _S shorter than the peak wavelength λ ₀ of the SPR absorption and the change in the emitted light intensity Po from the optical waveguide with respect to the wavelength λ of the incident light is used. Is a graph showing the change of the outgoing light intensity Po with respect to the outgoing angle ψ from the optical waveguide.

  The graph on the left side of FIG. 6A shows the relationship between the wavelength λ of incident light and the emitted light intensity Po. The three solid line graphs having different thicknesses indicate the intensity of the emitted light when a sample solution (for example, pure water) not containing the substance to be measured is dropped.

A thin solid line extending in the horizontal direction indicates the intensity of emitted light when the emission angle ψ from the optical waveguide is zero. When the emission angle ψ is 0, the light travels approximately linearly along the optical waveguide, so that reflection from the metal layer does not occur. For this reason, the emitted light intensity Po is constant regardless of the wavelength λ. A slightly thick solid curve indicates the intensity of the emitted light when the emission angle ψ is relatively small ψ ₁ . In this case, the curve of the emitted light intensity Po has a downwardly convex shape having a depth peak proportional to the number of reflections at the metal layer at the wavelength λ ₀ due to SPR absorption. The thickest solid curve indicates the intensity of emitted light when the emission angle ψ is relatively large ψ ₂ (> ψ ₁ ). When the ψ = ψ _2, than when the ψ = ψ _1, peak only SPR absorption exit angle [psi greater amount also increases.

In addition, the broken line shows the intensity of the emitted light when the sample solution containing the substance to be measured is dropped, the substance to be measured binds to the sensor film, and the peak wavelength of SPR absorption shifts from λ ₀ to λ ₁ on the long wavelength side. It is. When the output angle ψ is 0, the intensity of the output light does not change even if there is a wavelength shift. However, when the output angle ψ is ψ ₁ and ψ ₂ , as indicated by the arrow b in the figure, The emitted light intensity changes from a curved line to a broken curve.

The graph on the right side of FIG. 6A shows the relationship between the outgoing angle ψ and the outgoing light intensity Po when a light source having a wavelength λ _S shorter than the peak wavelength λ _{0 of} SPR absorption is used. The solid line and broken line graphs respectively correspond to the solid line and broken line graphs on the left side of FIG. As shown in the graph, the outgoing light intensity Po decreases as the outgoing angle ψ increases. When there is a wavelength shift, the emitted light intensity Po changes from a solid line graph to a broken line graph as indicated by an arrow c in the figure. Light having an emission angle ψ of 0 does not change the intensity of the emitted light, but the amount of change in the emitted light intensity increases as the emission angle ψ increases.

  Further, the graph on the left side of FIG. 6B shows the relationship between the wavelength λ of the light source and the emitted light intensity Po, as in FIG. 6A. The solid line graph is the same as that in FIG. 6A, but the broken line graph indicates the emitted light intensity when the light source intensity increases for some reason. In this case, as indicated by the arrow f in the figure, the emitted light intensity increases uniformly from the solid curve to the broken curve, regardless of the emission angle.

The graph on the right side of FIG. 6B shows the emission angle ψ and the emitted light intensity Po when using a light source having a wavelength λ _S shorter than the peak wavelength λ _{0 of} SPR absorption, as in FIG. 6A. Show the relationship. The solid line and broken line graphs respectively correspond to the solid line and broken line graphs on the left side of FIG. The solid line graph is the same as that in FIG. 6A, but the broken line graph indicates the emitted light intensity when the light source intensity increases. When the light source intensity increases, the emission light intensity increases regardless of the emission angle, and the entire curve moves upward as indicated by the arrow g in the figure.

  As described above, it can be distinguished from the graph shape of the emission angle dependency of the emission light intensity whether the change in the emission light intensity is caused by the wavelength shift or the change in the light source intensity or the optical coupling.

  The amount of change in outgoing light intensity with respect to the outgoing angle is as follows: light source intensity and its angular distribution, optical coupling with optical waveguide, optical fiber characteristics (numerical aperture, core and cladding refractive index, etc.) It is theoretically determined from the SPR absorption amount for each reflection. As will be described later, the emission angle dependence of the emitted light intensity is expressed by a theoretical formula including a parameter for changing the SPR absorption amount and a parameter for changing the light source intensity. In the sensor device 1, the output angle dependency of the output light intensity from the optical waveguide is acquired using a two-dimensional image sensor, and the data obtained by associating the output angle with the output light intensity is fitted to a theoretical formula to obtain the theory. Parameters included in the expression can be obtained with high accuracy. For this reason, even if the light source intensity fluctuates during the measurement, it is possible to obtain the change in the SPR absorption amount independently of that and to quantify the substance to be measured with high accuracy.

  Below, the theoretical formula describing the output angle dependence of the emitted light intensity will be described.

  FIG. 7 is a diagram showing light guided through the core 30 while being totally reflected at an angle θ. The core diameter of the optical waveguide is D, and the length of the detection unit 4 in the z direction is L. An incident angle from a light source (not shown in FIG. 7) to the optical waveguide is ψ, and an angle when light propagating in the optical waveguide is reflected at the core-cladding interface is θ. The incident angle ψ defines a direction perpendicular to the end face of the optical waveguide (z direction) as 0, and the reflection angle θ defines the longitudinal direction (z direction) of the optical waveguide as 0.

Since light incident on the optical waveguide from the light source is refracted at the end face of the optical waveguide, assuming that the refractive index of air is n1 and the refractive index of the core is n2, the relationship between θ and ψ is expressed by equation (1).

When the number of times of light reflection is N (ψ) and the SPR absorption amount for each reflection is a, a portion of the optical waveguide 3 where the detection unit 4 is provided and SPR absorption occurs (referred to as “SPR portion”). The transmittance Tm (ψ) of is expressed by equation (2).

Since the number of reflections N (θ) with respect to θ is expressed by equation (3), when θ is replaced with ψ using equation (1), the number of reflections N (ψ) with respect to ψ is expressed by equation (4). .

Therefore, when the angle dependency of the light source intensity is I (ψ), the emitted light intensity Po (ψ) from the optical waveguide is expressed by the following equation (5).

Any light source intensity distribution may be used. For example, a Lambert distribution is generally used in a chip-mounted LED. In the case of Lambert distribution, as shown in the equation (6), the light source intensity distribution I (ψ) is expressed by cos of the emission angle ψ.

  FIG. 8 is a diagram showing a light source intensity distribution I (ψ) that is a Lambertian distribution. FIG. 9 shows the light source intensity distribution I (ψ), the number of light reflections N (ψ), the transmittance Tm (ψ) of the SPR portion, and the emitted light intensity Po (ψ) when a light source having a Lambertian distribution is used. It is a graph which shows an example.

  The light source intensity distribution I (ψ) decreases by cos with respect to the emission angle ψ according to the equation (6). Since the number of reflections N (ψ) is an integer, it increases stepwise as shown in FIG. 9 with respect to the emission angle ψ. Along with this, the transmittance Tm (ψ) decreases exponentially while drawing a step-like curve with respect to the emission angle ψ. As a result, the emitted light intensity Po (ψ) decreases almost linearly while drawing a stepped curve with respect to the emission angle ψ.

  If the number of reflections N (ψ) is treated as a real number for better visibility, the emitted light intensity Po (ψ) that has changed in a staircase pattern in FIG. 9 is substantially represented by a straight line. Therefore, in the following, in order to reduce the amount of calculation, the output light intensity Po (ψ) is linearly approximated.

When the outgoing light intensity Po (ψ) of equation (5) using the Lambert distribution of equation (6) as the light source intensity distribution I (ψ) is expanded to the first order term of ψ, equation (7) is obtained. Is obtained.

Since L, D, n1, n2, and a are all constants, if the coefficient of the first-order term of ψ is α as shown in equation (8), the emitted light intensity Po (ψ) is expressed by equation (9). The

α is a parameter indicating a change in SPR absorption, and I ₀ is a parameter indicating a change in light source intensity. The emitted light intensity Po (ψ) is represented by a straight line determined by these parameters I ₀ and α.

  FIG. 10 is a graph showing changes in the emitted light intensity Po (ψ) when the peak wavelength of SPR absorption is shifted to the longer wavelength side to increase the transmittance Tm and when the light source intensity I is increased. In FIG. 10, the equation (9) in which the outgoing light intensity Po (ψ) is linearly approximated is plotted.

The thick solid line is a graph of the emitted light intensity Po (ψ) before the peak wavelength shift or the light source intensity fluctuation occurs. As described in FIGS. 6A and 6B, the outgoing light intensity Po (ψ) when the peak wavelength of SPR absorption is shifted has a gentle slope as shown by a thin solid line graph. When the intensity I increases, the emitted light intensity Po (ψ) increases regardless of the emission angle ψ as shown by the broken line graph (translated in the vertical direction). From the graph of FIG. 10, it can be seen that the shift of the peak wavelength corresponds to the change in the parameter α in the equation (9), and the change in the light source intensity I corresponds to the change in the parameter I _{0 in} the equation (9).

Next, a method for obtaining the parameters I ₀ and α of the emitted light intensity Po (ψ) from the pattern acquired by the image sensor 10 will be described.

  FIG. 11 is a diagram illustrating an example of a pattern acquired by the image sensor 10 when the optical waveguide 3 which is an optical fiber having a circular cross section is used. When an optical fiber having a circular cross section is used for the optical waveguide, the emission pattern is also approximately circularly symmetric, and pixels having the same emission angle are distributed concentrically.

  In the case of using the optical waveguide 3 ′ having a rectangular cross section, the metal layer is formed only on the surface of the substrate, so light traveling while reflecting on the front and back surfaces of the core 30 ′ (the traveling direction has a y component). SPR absorption occurs only in (light). Therefore, although not shown, in the pattern of the image sensor when the optical waveguide 3 ′ having a square cross section is used, the emission angle dependency of the emission light intensity appears only in the y direction.

FIG. 12 is a flowchart illustrating an example of a method for obtaining the parameters I ₀ and α of the emitted light intensity Po (ψ) from the pattern acquired by the image sensor 10. The flow shown in FIG. 12 is executed by the CPU in the control unit 11 according to a program stored in advance in the memory in the control unit 11.

  First, the origin O on the pattern is obtained (S1). The origin O is a position where light emitted straight from the optical waveguide hits the pattern. In order to obtain the origin O, a position where the intensity of the emitted light is the highest should be searched. In that case, it is preferable to perform a spatial averaging process in advance to remove noise.

  When the origin O is obtained, the emission angle corresponding to each pixel on the pattern is obtained (S2). The emission angle from the optical waveguide is proportional to the spatial distance from the origin O on the pattern. Therefore, in order to obtain the emission angle corresponding to each pixel on the pattern, the distance from the origin O to that pixel may be obtained.

In general, pixel coordinates of a two-dimensional image sensor have an origin at the upper left of the screen, an x axis in the horizontal right direction, and a y axis in the vertical direction downward. When the pixel coordinates of the origin O are (x ₀ , y ₀ ) and the pixel coordinates of the point p _i are (x _i , y _i ), the inter-pixel distance d _i can be obtained by equation (10).

Since the inter-pixel distance d _i and the emission angle are in a proportional relationship, the proportional coefficient is included in the parameter α in the equation (9). Therefore, a relative value may be used as the value of the emission angle ψ _{i at} the point p _i .

Even when the inter-pixel distance d _i and the spatial distance on the emission pattern are not proportional, it is easy to make the two proportional to each other by calibrating in advance. In addition, there may be a case where the relationship between the distance and the emission angle is not proportional, but in this case as well, the relationship between the two is obtained from the optical design of the optical sensor 8, so that if both are corrected as necessary, the relationship is made proportional. It is easy.

When the emission angle is obtained for each pixel on the pattern, data in which the emission angle ψ _i is associated with the emission light intensity Po _i is created for each pixel (S3). When the optical waveguide 3 which is an optical fiber is used, the emission pattern is circularly symmetric and pixels having the same emission angle are distributed concentrically, so that the emission angle ψ _i is output from the radial intensity distribution centered on the origin O. Data in which the light intensity Po _i is associated is created. In addition, when the optical waveguide 3 ′ having a square cross section is used, data in which the emission angle ψ _i and the emission light intensity Po _i are associated is created from the intensity distribution in the y direction in the pattern acquired by the image sensor 10. To do.

Since the actual intensity of the emitted light and the data obtained from the image sensor are in a proportional relationship, the proportional coefficient is included in the parameter I ₀ in equation (9). Therefore, a relative value may be used for the value of the emitted light intensity Po _{i at} the point p _i .

Then, the parameters I ₀ and α of equation (9) are obtained from the data obtained in step S3 by the least square method (S4). The method for obtaining the parameters I ₀ and α of the emitted light intensity Po (ψ) from the pattern acquired by the image sensor 10 ends here.

  In the sensor device 1, a large amount of data corresponding to the number of pixels of the image sensor 10 is fitted to a theoretical formula by the least square method so that the error is minimized, and a change in the SPR absorption amount is obtained. For this reason, compared with the case where the data of the emitted light intensity measured with the light of two different angles are used, SPR absorption amount change can be calculated | required with high precision.

In the sensor device 1, the change in the emitted light intensity Po with respect to the emission angle is expressed by a linear expression, and the change in the SPR absorption amount and the change in the light source intensity are obtained as different parameters α and I ₀ , respectively. Changes in the source intensity, the influence of variation in emission intensity due to misalignment of the incident side are included in the parameter I _0. Further, the fluctuation of the outgoing light intensity due to the misalignment between the optical waveguide on the outgoing side and the optical sensor is calculated for the angle dependence after obtaining the position of the optical waveguide (origin O) on the pattern acquired by the image sensor 10. This can be countered. For this reason, even if there is a variation in the intensity of the light source or a variation in the intensity of the emitted light due to the misalignment, the sensor device 1 can determine the change in the SPR absorption amount without being affected by the influence.

  Moreover, since the above method is fitting to a linear expression, it is also useful in that the amount of calculation can be reduced.

  Further, the sensor device 1 uses an LED light source as the light source 7, and an optical system such as a beam light source or a lens is not necessary. Since the angle distribution of the light source intensity of the LED light source itself is used, the sensor device 1 does not need to provide a plurality of light sources having different incident angles or a mechanism for changing the incident angle of the light sources. Further, a two-dimensional image sensor is used as the optical sensor 8, and an expensive and large-sized device such as a spectroscope is not necessary. For this reason, the sensor device 1 can reduce the size and the price of the device.

  Using the sensor chip 2B having the optical waveguide 3 'having a square cross section shown in FIG. 4, an experiment was conducted in which the concentration of the sample solution was measured with the sensor device 1 using ethylene glycol as the substance to be measured. The optical waveguide 3 'was made of polymer, and the light source was an LED light source having a wavelength of 660 nm.

  FIG. 13A and FIG. 13B are diagrams showing patterns of emitted light intensity acquired by the image sensor 10 when the sensor chip 2B is used. FIG. 13A shows a pattern before dropping a sample solution, and FIG. 13B shows a pattern after dropping pure water not containing a substance to be measured as a sample solution. The black dots in the figure correspond to positions where the emitted light intensity is strong.

  The pattern in FIG. 13A is isotropic, and the intensity decreases in the same manner in both the x and y directions as the distance from the center increases. On the other hand, the pattern of FIG. 13B has a lower emission light intensity as a whole than the pattern of FIG. 13A, and the emission light intensity in the y direction is particularly the pattern of FIG. It turns out that it has fallen greatly compared with. This corresponds to SPR absorption of light that travels while being reflected by the front and back surfaces of the core 30 ′ (light whose traveling direction has a y component).

  FIG. 14A to FIG. 14C are graphs showing the intensity change in the y direction in the pattern of the emitted light intensity acquired by the image sensor 10.

  First, FIG. 14A shows the intensity of emitted light Po when there is no sample solution (AIR) and when a sample solution containing 0%, 1%, 3%, and 5% of ethylene glycol is dropped as a substance to be measured. The graph of (y) is shown. Here, 0% corresponds to the case where pure water is added as a sample solution. The emitted light intensity Po (y) is a change in the emitted light intensity with respect to the pixel position in the y direction on a straight line in the y direction passing through the origin O on the pattern of the image sensor. However, since noise (variation) is generated in the data of only one line passing through the origin O, a total of 21 lines parallel to the y direction centering on the origin O (for each of the 10 pixels in the ± x directions and the line passing through the origin O). Data averaged for a line parallel to the y direction) was plotted.

  In the case of no sample solution, the metal layer is in contact with air having a refractive index smaller than that of the sample solution through the sensor film, so the peak wavelength of SPR absorption is greatly shifted to the short wavelength side, and almost no SPR absorption occurs at the light source wavelength of 660 nm. Does not happen. On the other hand, when the sample solution is in contact with the sensor film, the peak of SPR absorption occurs near 700 nm, so that large SPR absorption occurs at the light source wavelength of 660 nm, and the transmittance decreases. In the sample solution to which ethylene glycol is added, the peak wavelength shifts to the long wavelength side with the concentration, and thus the transmittance increases. For this reason, the emitted light intensity Po (y) increases as the ethylene glycol concentration increases to 0%, 1%, 3%, and 5%.

  When the optical waveguide 3 ′ having a rectangular cross section is used, the light reflected from the side surface of the optical waveguide on which the metal layer is not formed (the light traveling in the xz plane) does not cause SPR absorption, and thus has a transmittance. Should not decrease. However, polymer optical waveguides have poor dimensional accuracy and surface roughness characteristics compared to glass optical waveguides, so that it is easy to make fine irregularities on the end face of the optical waveguide, and fluctuations and scattering at the core-clad interface. The light travel direction changes randomly. For this reason, when a polymer optical waveguide is used, SPR absorption occurs even in the light emitted in the xz plane and the intensity distribution is seen not only in the y direction but also in the x direction in the pattern of the image sensor. Even with light having an emission angle of 0, the transmittance is reduced due to SPR absorption. This phenomenon is called a mixing phenomenon here. In order to remove the influence of this mixing phenomenon, processing for aligning the peak positions of each graph of the emitted light intensity Po (y) in FIG.

FIG. 14B shows the output light intensity so that the intensity of light that goes straight in the z direction and peaks at the origin in the y direction (the output light intensity at the peak position) is 1 for each graph in FIG. shows a graph of Po relative the (y) the output light intensity _{P ref} (y). Since this process is considered to be a change in the emitted light intensity I ₀ , it is clear from the equation (9) that the relative processing may be performed in this way.

FIG. 14C is a partially enlarged view of FIG. In FIG. 14B, it appears that the slope of the graph of the output light intensity P _ref (y) corresponding to the parameter α representing the output angle dependence of the output light intensity hardly changes depending on the concentration of the sample solution. However, in the partially enlarged view of FIG. 14C, it can be seen that as the concentration of the sample solution increases, the slope of the graph of the emitted light intensity P _ref (y) corresponding to the parameter α changes.

FIG. 15 is a graph showing the relationship between the slope α obtained by linearly approximating each graph of the emitted light intensity P _ref (y) of FIG. 14C by the least square method and the concentration of the sample solution. The horizontal axis represents the ethylene glycol concentration C (%) in the sample solution, and the vertical axis represents the value of the slope α for each concentration.

  Since the y pixel position 520 in FIG. 14C corresponds to the emission angle 0 and the inclination is obtained in a region where the y pixel position on the left side is small, the inclination α is a positive value. As shown in FIG. 15, the slope α decreases as the concentration C of the sample solution increases. That is, it can be seen that the SPR absorption amount is relatively decreased, which is the same as the theory. By using the relationship of the parameter α to the concentration C of the sample solution thus obtained as a calibration curve, it is possible to quantify a substance to be measured having an unknown concentration.

Regarding the optical waveguide 3 ′ having a rectangular cross section, in particular, when a polymer optical waveguide is used, a so-called mixing phenomenon occurs. Therefore, in general, the parameter I ₀ shown in the equation (9) greatly varies depending on the concentration of the sample solution, and The emission angle dependent parameter α becomes a small value. However, in the measurement method of the sensor device 1, since the variation of the light source intensity I ₀ is canceled, even if the parameter I ₀ varies greatly, it is possible to quantify the SPR absorption from the parameter alpha.

DESCRIPTION OF SYMBOLS 1 Sensor apparatus 2, 2A, 2B Sensor chip 3, 3 'Optical waveguide 4, 4A, 4B Detection part 6 Sample solution 7 Light source 8 Optical sensor 11 Control part 30, 30' Core 31, 31 'Cladding 40, 40A, 40B Metal Layer 41 Sensor membrane

Claims (7)

A light source;
An optical waveguide including a core that guides light from the light source and a cladding that covers the core;
A metal layer disposed in contact with the core and causing surface plasmon resonance by light from the light source;
A sensor film that is formed on the surface of the metal layer and in which a solution containing a substance to be measured is dropped to specifically bind to the substance to be measured;
An outgoing light detector for detecting an intensity distribution of outgoing light from the optical waveguide;
A control unit that quantifies the substance to be measured in the solution dropped on the sensor film, based on the relationship between the emission angle and intensity of the emission light obtained from the intensity distribution detected by the emission light detection unit;
A sensor device.   The control unit determines a parameter of a theoretical formula describing a relationship between an emission angle and an intensity of the emitted light from the intensity distribution, thereby determining a light absorption amount in the metal layer with respect to the emission angle of the emitted light. The sensor device according to claim 1, wherein a change is obtained.   The sensor device according to claim 2, wherein the emission light detection unit is a two-dimensional image sensor that receives the emission light on an emission surface of the optical waveguide. The optical waveguide is an optical fiber;
The said control part acquires the data which matched the output angle and intensity | strength of the said emitted light from the intensity distribution of the radial direction in the circularly symmetric pattern acquired by the said two-dimensional image sensor. Sensor device. The optical waveguide is an optical waveguide having a square cross section formed on the surface of a substrate,
The said control part acquires the data which matched the output angle and intensity | strength of the said emitted light from the intensity distribution of the direction perpendicular | vertical to the said metal layer in the pattern acquired by the said two-dimensional image sensor. The sensor device according to 1.   The sensor device according to claim 1, wherein the light source is an LED light source having an emitted light intensity with a Lambertian distribution. A light source, an optical waveguide including a core that guides light from the light source and a clad that covers the core, and a metal layer that is disposed in contact with the core and causes surface plasmon resonance by the light from the light source; A measurement method using a sensor device having a sensor film formed on the surface of the metal layer and having a sensor film that specifically binds to the substance to be measured by dropping a solution containing the substance to be measured,
Detecting an intensity distribution of light emitted from the optical waveguide;
Quantifying the substance to be measured in the solution dropped on the sensor film based on the relationship between the emission angle and intensity of the emitted light obtained from the detected intensity distribution;
Measuring method.