JPH07229829A - Total reflection prism cell - Google Patents

Abstract

PURPOSE:To measure the infrared absorption spectrum of a liquid sample with high sensitivity by disposing a mesh metal carrying a sample under a prism. CONSTITUTION:A gold mesh 3(mesh metal) of 100pm thick is set under a semicylindrical total reflection prism 1 through an air gap of 20mum. A liquid sample 5 is then injected through an injection port 6 into the gold mesh 3 using a syringe 7. Infrared light 8 enters the end face of the prism 1 and partially reflected on the interface of the prism 1 and the air gap 2 while partially transmits the interface. The light impinging directly on the gold mesh 3 through the air gap 2 excites the local field on the surface of gold and increases the infrared absorption of the sample 5 at a part in contact with the excited part of gold mesh 3. The light impinging on the gold mesh 3 through the sample 5 is confined within a cavity defined by the gold mesh 3 and produces an interference field thus increasing infrared absorption of the sample 5 in the cavity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical cell for measuring an infrared absorption spectrum with high sensitivity.

[0002]

2. Description of the Related Art A high-sensitivity infrared spectrum measuring method using a total reflection prism and a metal is described in Spectroscopic Research (1992) No. 41.
Vol. 164 to 173 and Spectroscopic Research (1993) Vol. 42, 127 to 139. Here, a high-sensitivity infrared sensor with an Otto arrangement in which a sample is sandwiched between a total reflection prism and a metal plate or a metal thin film, or a Kretschmann arrangement in which a metal thin film is vapor-deposited on the prism and the sample is introduced onto the prism. The principle model of the spectrum measurement method is described in detail.

In the Otto arrangement, assuming that the space between the total reflection prism and the metal thin film is one cavity, total reflection is repeated between the prism and the metal, and the interference electric field is excited by confining light in the cavity. In the Kretschmann arrangement, light is incident on the metal particles forming the metal thin film,
Plasma vibrations of the metal particles are excited to form a local electric field near the particles. It is said that the interference electric field and the localized electric field are the causes of the increase in infrared absorption.

An example of highly sensitive measurement of molecules in a liquid is described in Surface Science (1985), Volume 158, pp. 616 to 623. Here, high-sensitivity detection of mercaptobenzothiazole (MBT) dissolved in an acidic aqueous solution is performed using a total reflection prism on which silver is vapor-deposited, and measurement is performed in the Kretschmann arrangement. M
The peak of C = S stretching vibration of BT disappeared, and instead Ag
(I) Since the peak of MBT is increased, Kret
It has been suggested that the local electric field in the schmann configuration extends over distances of only a few molecular layers.

[0005]

The conventional high-sensitivity infrared absorption spectrum measurement method using a metal thin film and a total reflection prism mainly targets a solid sample and a liquid sample. The measurement examples in this case were limited to the Kretschmann arrangement. In the measurement of this Kretschmann configuration, it is highly likely that the molecule to be measured exists near the metal where the local electric field is generated due to the formation of a complex by the chemical interaction between the metal thin film deposited on the prism and the molecules in the liquid. It was essential for increasing sensitivity. On the other hand, the Otto arrangement is a method in which metal is vapor-deposited or a metal plate is pressure-bonded onto a thin film of an ultrathin solid sample usually formed on a total reflection prism for measurement. Could not be measured.

[0006]

In order to solve the above problems, the present invention provides a total reflection prism surface with a mesh metal or a metal in which grooves are formed so that a viscous or liquid sample can be carried in the metal. .

[0007]

The above means operates as follows. That is,
The infrared light enters the total reflection prism from the light source, and is emitted to the detector while being reflected in the total reflection prism. At this time, light incident on the prism-sample (metal) interface from the prism side is divided into light reflected on the prism side and light transmitted on the sample side. Light incident on the prism-sample (metal) interface at a critical angle or more is totally reflected on the prism side.
As an evanescent wave, it penetrates the sample side by about 1 to 2 μm. At this time, a localized electric field is excited in the vicinity of a portion of the metal plate in which the mesh metal or the groove is formed in contact with the prism by the incidence of light on the metal from the prism side. This localized electric field increases the infrared absorption of the sample near the metal. Further, an extremely small cavity made of metal is formed on the prism side of the mesh-shaped metal or the metal plate having the groove formed, and the cavity is filled with the sample. Therefore, the light incident on the metal from the prism side is totally reflected by the metal, but since the cavity is extremely small compared to the normal Otto arrangement, the light is not absorbed by the sample and is confined in the cavity of the metal and interferes. The electric field is excited. Therefore, this interference electric field increases the infrared absorption of the sample in the cavity.

Therefore, by exciting a sample on a surface of a prism by supporting a sample on a metal mesh or a metal plate having grooves, a local electric field and an interference electric field, which are two electric fields that increase infrared absorption, are excited. Therefore, compared to the Otto configuration and the Kretschmann configuration, which use a vapor-deposited metal film in which either the localized electric field or the interference electric field must be selected, a larger increase in infrared absorption can be performed.

[0009]

1 is a sectional view of a total reflection prism cell according to a first embodiment of the present invention. Below the semi-cylindrical total reflection prism cell 1, there is an air gap 2 of 20 μm and a thickness of 10
A 0 μm gold mesh 3 is installed. Below the gold mesh 3 is a pool-shaped sample introduction part 4, and at the bottom is a sample injection port 6 for injecting the sample 5 from the bottom side of the mesh 3. The liquid sample is injected from the injection port 6 with the syringe 7 so as to enter the mesh of the gold mesh. The infrared light 8 enters from the end surface of the prism 1, and is partially reflected and partially transmitted at the prism-air gap interface. The light that is directly incident on the gold mesh 3 through the air gap excites a localized electric field on the gold surface and increases the infrared absorption of the sample in contact with the gold mesh site where the electric field is excited. Further, the light incident on the gold mesh 3 via the sample is confined in the cavity formed by the gold mesh, forms an interference electric field, and increases the infrared absorption of the sample in the cavity.

FIG. 2 is a sectional view of a total reflection prism cell which is a second embodiment of the present invention. The structure is almost the same as that of the first embodiment, but the prism 1 and the gold mesh 3 are directly adhered to each other without an air gap. Since the strength of the interference electric field tends to depend on the distance of the air gap, it is necessary to change the gap distance according to the sample in this way.

FIG. 3 is a sectional view of a total reflection prism cell which is a third embodiment of the present invention. Under the prism 1, a silver plate 9 having a groove formed directly and a silver plate holding portion 10 are arranged, and the sample 5 is introduced into the groove of the silver plate.

FIG. 4 is a plan view of the silver plate 9 and the silver plate holder 10 of the third embodiment as seen from the prism side. A plurality of grooves 11 are formed on the silver plate 9, and the width of the grooves 11 is equal to or smaller than the diameter of the infrared light flux incident on the prism 1. Further, there is a sample reservoir 12 in which no groove is formed, which is a silver plate holding portion 10.
The sample injected from the sample injection port 6 formed in 1 is pooled, and the sample is sent into the groove 11 by the capillary phenomenon.

FIG. 5 is a sectional view of a total reflection prism cell according to a fourth embodiment of the present invention. The prism 1 is held by the prism holding plate 13, and the gold mesh 3 and the sample 5 are absorbed on the surface thereof.
Is pressure-bonded to the surface of the prism 1 so that is on the prism side.
The sample 5 absorbed by the water absorbing material 14 is pressed into the prism, so that the sample 5 permeates into the gold mesh 3, and the excess sample is discharged from the gap 16 onto the holding plate 13.

FIG. 6 is a sectional view of a total reflection prism cell according to a fifth embodiment of the present invention. Fourth Embodiment Prism-
A transparent optical material film 17 having a refractive index lower than that of the prism, for example, sapphire which is insoluble in water and has a refractive index of 1.6 is formed on the mesh interface, and the distance between the prism and the mesh is adjusted.

FIG. 7 is a block diagram of a blood measuring apparatus using the second embodiment of the present invention. This blood measuring device
The spectroscope section 18 and the computer section 19 can be roughly divided into
The spectroscope unit 18 measures the infrared absorption of blood, and the computer unit 19 performs calculation processing such as Fourier transform of signals measured by the spectroscope and concentration measurement. The measuring method is outlined below.
The infrared light 21 emitted from the infrared light source 20 enters the sample chamber 22. The total reflection prism cell of the second embodiment of the present invention is installed in this sample chamber, and the infrared light 21 absorbs the light of a specific wavelength by the blood in the cell, and the infrared light 21 is absorbed by the Michelson interferometer 23. Incident. Michelson interferometer 23
Amplitude-modulates the incident light to an intermittent frequency proportional to its wave number. The modulated light is converted into an electric signal by the detector 24, and is taken into the computer unit 19 by the AD converter 25.

FIG. 8 is a diagram of a sample cell and a sample flow path of this blood measuring apparatus. Gold mesh 3 under the total reflection prism 1
Are arranged in close contact with each other, and the sample channel 26 is provided under the gold mesh. The sample flow path 26 is provided with a sample cup 27 for containing a sample, a washing liquid bottle 28, and a waste liquid bottle 29. When the sample is sucked up by the pump 30 from the sample cup 27 and the flow path 26 under the gold mesh 3 is filled,
The infrared absorption of the sample is measured. When the measurement is completed, the flow path is switched to the cleaning liquid direction by the solenoid valve 31, the cleaning liquid fills the flow path, and the inside of the cell is cleaned. The discharged blood and washing liquid are discarded in the waste liquid bottle 29. The pump 30 and the solenoid valve 31 are controlled by the computer section 19.

9 and 10 are characteristic charts showing the effect of the present invention. FIG. 9 is a comparison of the infrared absorption spectrum measured by the blood measuring apparatus using the present invention and the infrared absorption spectrum measured by the conventional blood measuring apparatus using the total reflection method. When the absorbances are simply compared, the sensitivity of this example is about 30 times higher than that of the conventional method.

FIG. 10 shows the correlation between the value of urea in blood measured by infrared absorption (vertical axis) and the value of urea in blood measured by the urease method. The white data points are the correlation between the urea concentration measured by the blood measuring device using the conventional total internal reflection method and the urea concentration measured by the urease method, and the data points in black are the blood measuring devices using this example. It is a correlation between the measured urea concentration and the urea concentration measured by the urease method. 20 mg because the conventional method has low sensitivity
Although / dl or less cannot be detected, it can be seen from this example that even a low concentration of urea can be accurately measured.

[0019]

According to the present invention, the infrared absorption spectrum of a liquid sample can be measured with high sensitivity.

[Brief description of drawings]

FIG. 1 is a sectional view of a first embodiment of the present invention.

FIG. 2 is a sectional view of a second embodiment of the present invention.

FIG. 3 is a sectional view of a third embodiment of the present invention.

FIG. 4 is a plan view of a sample introducing part according to a third embodiment of the present invention.

FIG. 5 is a sectional view of a fourth embodiment of the present invention.

FIG. 6 is a sectional view of a fifth embodiment of the present invention.

FIG. 7 is a block diagram of a blood measuring device.

FIG. 8 is an explanatory diagram around the sample cell of the blood measurement apparatus.

FIG. 9 is a characteristic diagram showing the effect of the present invention.

FIG. 10 is a characteristic diagram showing the effect of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Total reflection prism cell, 2 ... Air gap, 3 ... Gold mesh, 4 ... Sample introduction part, 5 ... Sample, 6 ... Sample injection port,
7 ... Syringe, 8 ... Infrared light.

Claims (7)

[Claims] 1. A cell for measuring an absorption spectrum of a sample by introducing the sample directly or through a gap into a prism surface of a high refractive index substance and by totally reflecting infrared light in the prism. Directly on or 10
A total reflection prism cell in which a reticulated metal carrying the sample is placed through a gap of 0 μm or less. 2. A cell in which a sample is introduced into a prism surface of a high refractive index material directly or through a gap, and infrared light is totally reflected in the prism to measure an absorption spectrum of the sample. Directly on or 10
A metal plate having a plurality of grooves formed with a gap of 0 μm or less;
A total reflection prism cell, wherein the sample introduced into the groove is installed with the surface of the sample exposed facing the prism surface. 3. The total reflection prism cell according to claim 1, wherein the mesh metal and the metal plate are made of any one of gold, silver, copper and platinum. 4. The total reflection prism cell according to claim 1, wherein the mesh metal has a mesh size equal to or smaller than a diameter of a light beam incident on the total reflection prism. 5. The total reflection prism cell according to claim 1, wherein the gap is transparent to infrared light incident on the total reflection prism and has a refractive index smaller than that of the total reflection prism. 6. The total reflection prism cell according to claim 1, wherein the total reflection prism is zinc selenide, silicon, or germanium. 7. The blood measuring apparatus according to claim 1, comprising an infrared light source, the total reflection prism cell, an interferometer, a detector, and a computer for processing a signal detected by the detector.