JPH09250981A - Surface plasmon resonance sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sensor which effectively functions even with a molecule of sample matrix for calculating concentration of substance by providing a semiconductor thin film to at least a part of a metal thin film of translucent light transparent medium which reflects light, under the condition of geometric total reflection, in a light reflecting surface provided with the metal thin film. SOLUTION: A surface plasmon resonance sensor 1 is constituted in such a way that a light transparent medium 2 is provided with a metal thin film 3 and a semiconductor thin film 4 is so provided as to cover at least a part of the thin film 3. The semiconductor thin film 4 is brought into contact with sample matrix in sample solution, and it interacts with molecules to-be-detected, to cause variation in band structure and carrier concentration in the semiconductor. Continuously, an incident plane 2a of the medium 2 is irradiated with light from a light source unit 5, and the light is so converged that the focus is placed on a light reflecting surface 2b. Change of evanescent wave formed with the medium 2 and the thin film 3 is detected with a photodetecting unit 6 comprising a CCD image pickup element provided on a light-emitting surface 2c, etc., and converted into an electric signal with a control means, as an output signal of the sensor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface plasmon resonance sensor utilizing an evanescent wave of light for measuring a substrate to be measured in a solution to be measured using an optical system.

[0002]

2. Description of the Related Art Generally, in a biosensor, a substrate to be measured, which is a blood component such as a specific protein or antigen in blood, or a urine component such as glucose or ascorbic acid in urine, has a function of discriminating these substrates. A biological substance that has a biochemical reaction with the substrate is used. Then, various physicochemical displacements associated with the progress of this biochemical reaction are detected by the physicochemical device, and the specification of the measurement target substrate, its concentration, etc. are detected. For example, one that detects the substrate concentration through the electrode reaction of an electrode active substance that is consumed or produced by a biochemical reaction, or one that detects the enthalpy change that occurs with the progress of the biochemical reaction with a thermistor to detect the substrate concentration. These biosensors have been put to practical use since early on.

On the other hand, in recent years, attention has been paid to changes in the dielectric constant with the progress of biochemical reactions, and biosensors have been proposed for measuring a substrate to be measured in a solution to be measured using an optical device. (JP-A-1-138443). In this biosensor, as an optical system, a light-transmitting light-transmitting medium that reflects light under a geometrical total reflection condition is provided on a light-reflecting surface provided with a metal thin film. An optical system that forms an evanescent wave coupling is used. The measuring principle is as follows.

When the p-polarized light is irradiated on the light-reflecting surface of the optical transmission medium of the optical system for forming the evanescent wave coupling at various incident angles satisfying the condition of total reflection, it is advantageous when the incident angle has a certain value. The phenomenon occurs. That is, when the p-polarized light is applied to the light reflecting surface, an evanescent wave having a wave number having an incident angle θ as a variable is generated on the light transmitting medium side film surface of the metal thin film. Since the metal can be regarded as a solid plasma, a surface plasmon wave as a wave of quantum charge density is generated by the light tunnel effect on the film surface of the metal thin film on the anti-light transmission medium side. The surface plasmon wave is generated as a wave between the metal thin film and the medium in contact with the film surface on the side opposite to the light-transmitting medium as a boundary surface.

When the incident angle θ has a certain value, a surface plasmon resonance phenomenon occurs in which the wave numbers of the evanescent wave and the surface plasmon wave coincide with each other, and the light energy is used as the excitation energy of the surface plasmon wave. Be seen. At this time, in terms of energy, there is a relationship that the energy of the light incident on the light reflecting surface is equal to the sum of the energy used to excite the surface plasmon wave and the energy of the reflected light from the reflecting surface. Therefore, by measuring the state of changes in the reflection angle and the energy (light amount), it is possible to determine the presence or absence of the surface plasmon resonance phenomenon, and consequently the incident angle when the phenomenon occurs. On the other hand, there is a correlation between the incident angle and the refractive index of the medium when the surface plasmon resonance phenomenon occurs, and this refractive index can be defined by the permittivity of the medium from Maxwell's equation, and the biochemical reaction by biological substances. Is correlated with the dielectric constant. Therefore, the angle of incidence at that time is determined from the angle of reflection when the amount of reflected light suddenly decreases, and the degree of progress of the biochemical reaction by the biological substance, that is, the substrate concentration is calculated from the above correlations.

By the way, in such a biosensor, the metal thin film is located in the vicinity of the film surface on the side opposite to the light-transmitting medium, specifically, in the evanescent region (about 10) which causes the tunnel effect.
At 0 nm), a biochemical reaction between the substrate and the biological substance needs to occur. Therefore, the patent application publication No. 4-50
As proposed in 1605, it is common practice to immobilize a so-called ligand layer on which a biological substance is immobilized on the above-mentioned film surface of a metal thin film.

As described above, the biosensor for measuring the substrate to be measured in the solution to be measured using the optical system for forming the evanescent wave bond is not affected by the degree of coloring or opacity of the solution to be measured, or Since it has the advantage that it is only necessary to fix a biological substance that causes a biochemical reaction with a substrate on the surface of the metal thin film on the side of the anti-light transmission medium, it is rapidly spreading.

[0008]

However, when the concentration of the molecule of the substrate to be measured in the solution to be measured is low or when the molecule has a small molecular weight, it is difficult for the molecule to directly affect the evanescent wave. From the above-mentioned correlations, it was not possible to calculate the degree of progress of the biochemical reaction by the biological substance, that is, the substrate concentration.

Therefore, an object of the present invention is to provide a surface plasmon resonance sensor that functions effectively even for molecules of a substrate to be measured, which has been conventionally difficult to affect the evanescent wave, and can calculate the concentration of the substrate. To provide.

[0010]

The surface plasmon resonance sensor of the present invention is characterized in that a semiconductor thin film is arranged on a metal thin film where an evanescent wave is generated. The metal thin film is provided on a light-transmitting light-transmitting medium and reflects light on the light-reflecting surface under a geometric total reflection condition. The semiconductor thin film interacts with the molecule to be detected and changes the band structure and carrier concentration in the semiconductor. As described above, the semiconductor and the molecule directly or indirectly interact with each other to change carriers (charges) in the semiconductor. The evanescent wave formed by the light transmission medium and the metal thin film is affected by the change of carriers in the semiconductor. The change in the evanescent wave is converted into an electric signal by the means of the prior art and becomes an output signal of the sensor.

Since the refractive index of the semiconductor thin film is smaller than that of the light transmitting medium, it is possible to sufficiently satisfy the excitation condition of the surface plasmon wave.

The material of the semiconductor thin film is a fluorine compound, preferably polytetrafluoroethylene formed by a sputtering method.

The above-mentioned features and effects of the present invention, as well as other features and advantages, will be made clear by the description of the following embodiments.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a structure in which an embodiment of the present invention is applied to a surface plasmon resonance sensor. Reference numeral 1 is a surface plasmon resonance sensor of the present invention, in which a light transmitting medium 2 is provided with a metal thin film 3, and further a semiconductor thin film 4 is provided so as to cover at least a part of the metal thin film 3.

The light transmitting medium 2 is made of glass having a refractive index of 1.52, and has a light incident surface 2a, a light reflecting surface 2b and a light emitting surface 2
c. The metal thin film 3 is made of gold and has a film thickness of 50.
The thing of mm is fixed to the light reflecting surface 2b of the light transmitting medium 2 by utilizing the vacuum deposition method.

The semiconductor thin film 4, which is a feature of the present invention, is provided on the metal thin film 3 which excites surface plasmon waves. Specifically, it is formed by a sputtering method using PTFE (polytetrafluoroethylene) as a target. There is. The film thickness is about 300 nm. The composition ratio of carbon and fluorine of this film is about 1: 1. By the way, the composition ratio of simple PTFE is 1: 2. The film is dense and AF
No porous portion was found even by measurement with M (atomic force microscope). When the electrical characteristics of this film were measured, it showed the characteristics of an N-type semiconductor.

When carrying out the measurement using the surface plasmon resonance sensor 1 of the present invention, the semiconductor thin film 4 is brought into contact with the substrate to be measured in the solution to be measured, and interacts with the molecule to be detected to cause the band in the semiconductor to be detected. It causes changes in structure and carrier concentration. As described above, the semiconductor and the molecule directly or indirectly interact with each other to change carriers (charges) in the semiconductor.

Subsequently, light is emitted from a light source unit 5 including a light emitting diode or a semiconductor laser, which emits light of a single wavelength, toward the incident surface 2a of the light transmitting medium 2, and a lens or the like (not shown) is used. The light is reflected so that it is focused on the light reflecting surface 2b. Thus, the evanescent wave formed by the light transmitting medium 2 and the metal thin film 3 is affected by the change of carriers in the semiconductor. The change of the evanescent wave is caused by the light emitting surface 2c.
It is detected by the light receiving unit 6 including a CCD image pickup device provided on the side, converted into an electric signal by a control means (not shown), and becomes an output signal of the sensor.

Next, an example of measuring humidity using the surface plasmon resonance sensor 1 of the present invention will be described with reference to FIG. Here, standard air of 20 ° C and humidity of 50% RH at 20 ° C
The time-dependent change of the resonance angle when the air is alternately switched and flowed is measured. In the figure, the two mountains are 2
This is where air with 0 ° C. and 50% RH was flowed.

Although specific embodiments of the present invention have been described above, the present invention is not limited to these. For example, in the case of a combination in which a semiconductor and a target molecule do not directly interact, Means such as fixing a selectively acting catalyst on the semiconductor surface may be taken. Further, the present invention can be applied not only to a surface plasmon resonance sensor but also to a sensor using an evanescent wave such as a sensor using an optical fiber.

[0021]

As described above, according to the present invention, the metal thin film of the light-transmissive light-transmitting medium which reflects light on the light reflecting surface provided with the metal thin film under the geometrical total reflection condition. Since a semiconductor thin film is provided on at least a part, it is possible to measure the concentration even when the concentration of the molecule of the substrate to be measured in the solution to be measured, which was difficult to measure in the past, is low or when the molecule has a small molecular weight. Became.

In a preferred embodiment of the present invention, a semiconductor thin film formed by sputtering with PTFE (polytetrafluoroethylene) as a target is employed, so that the humidity in the atmosphere can be measured. .

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a surface plasmon resonance sensor of the present invention.

FIG. 2 is a graph showing the results of measurement using the surface plasmon resonance sensor of the present invention.

[Explanation of symbols]

 1: Surface plasmon resonance sensor 2: Light transmission medium 3: Metal thin film 4: Semiconductor thin film 5: Light source unit 6: Light receiving unit

Claims (5)

[Claims] 1. A semiconductor thin film provided on a metal thin film,
The light-reflective surface on which the metal thin film is provided has a light-transmissive light-transmissive medium that reflects light under geometric total reflection conditions,
A surface plasmon resonance sensor for measuring a substrate to be measured in a solution to be measured, which is in contact with the semiconductor thin film, by using an optical system that forms an evanescent wave bond between the light transmitting medium and the metal thin film. 2. The surface plasmon resonance sensor according to claim 1, wherein the semiconductor thin film has a refractive index smaller than that of the light transmitting medium. 3. The surface plasmon resonance sensor according to claim 1, wherein the semiconductor thin film is made of a fluorine compound. 4. The surface plasmon resonance sensor according to claim 1, wherein the semiconductor thin film is formed of polytetrafluoroethylene by a sputtering method. 5. An incident-side optical system in which the optical system condenses and irradiates light from a light source on the light reflecting surface, and reflected light reflected by the light reflecting surface and emitted from the light transmitting medium to the outside. 5. The surface plasmon resonance sensor according to claim 1, further comprising: an emission side optical system that receives the light and detects the light amount of the reflected light for each reflected light.