JP2009103643A - Device for surface enhanced raman spectroscopy - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure a Raman spectrum highly accurately in a short time. <P>SOLUTION: A substrate 110 for enhancing optical field is vibrated at 1 kHz by a stage 116, and light L1 is irradiated to a sample 111 placed on the substrate 110. Light L2 comprising Raman scattered light emitted from the sample 111 and background light emitted from the substrate 110 is spectrally diffracted by a diffraction grating 155, and a spectrum intensity signal is measured by a photodiode 157, and a signal synchronized with 1 kHz is detected from the spectrum intensity signal by a lock-in amplifier 160. The signal, wherein a signal component of the background light having a small change of light intensity is suppressed, even when an irradiation position of the light L1 and a relative position with the substrate 110 are changed, includes many signal components of the Raman scattered light emitted from the sample 111 whose light intensity is fluctuated synchronously with a periodical change of the relative position. The Raman spectrum is acquired based on the signal. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a surface-enhanced Raman spectroscopic device including a photoelectric field enhancement substrate that enhances a photoelectric field upon receiving light irradiation.

  The Raman measurement method is a method for obtaining a spectrum of Raman scattered light (Raman spectrum) by dispersing scattered light obtained by irradiating a single wavelength light to a substance, and is used for identification of a substance contained in a sample. Yes. Since the Raman scattered light is weak light, a photoelectric field enhancing substrate in which the Raman scattered light is enhanced on the surface has been developed. As a photoelectric field enhancing substrate, for example, a substrate using localized plasmon resonance as shown in Patent Document 1 is known.

When a sample is placed on a metal body, particularly a metal body having nano-order irregularities on the surface, the electric field enhancement due to the local plasmon resonance occurs in the substrate using the localized plasmon resonance, and the surface of the metal body is increased. That is, the Raman scattered light intensity of the contacted sample is enhanced. On the other hand, when performing Raman measurement using such a photoelectric field enhancement substrate, the Raman scattered light and fluorescence emitted from this photoelectric field enhancement substrate itself are also enhanced by the substrate and superimposed on the measurement light as background light, There is a problem that the measurement accuracy decreases. In Patent Document 2, first, the Raman measurement is performed in a state where the sample is not placed, and only the background light emitted from the substrate is measured. Then, the sample is placed, the Raman measurement is performed, and the measurement spectrum is measured. Discloses a measurement apparatus that improves the measurement accuracy of the Raman spectrum by subtracting the spectrum of the background light from the spectrum.
JP 2005-172569 A US 6888629

  However, in the Raman measuring apparatus described in Patent Document 2, it is necessary to measure the spectrum of the background light emitted from the substrate before placing the sample on the photoelectric field enhancing substrate, and the labor and time required for the measurement are required. There is a problem of increasing.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a surface-enhanced Raman spectroscopic device capable of performing Raman spectrum measurement in a short time and with high accuracy.

The surface-enhanced Raman spectroscopic device of the present invention irradiates a sample placed on a photoelectric field enhancement substrate with light, and measures the spectrum of Raman scattered light emitted from the sample and enhanced by the photoelectric field enhancement substrate. In the surface-enhanced Raman spectrometer,
A light irradiating means for irradiating the sample placed on the photoelectric field enhancing substrate with the light;
Moving means for periodically moving a relative position between the irradiation position of the light and the photoelectric field enhancement substrate;
Spectral intensity signal measuring means for spectrally measuring the Raman scattered light emitted from the sample and the background light emitted from the photoelectric field enhancement substrate by the light irradiation and measuring a spectral intensity signal;
Synchronization detection means for detecting a signal synchronized with a movement cycle of the relative position from the spectrum intensity signal.

  Here, the “sample placed on the photoelectric field enhancement substrate” specifically refers to a sample that is in contact with or adjacent to the surface of the photoelectric field enhancement substrate, a sample that exists in the vicinity of the substrate surface, or the like. .

  The moving means may vibrate a relative position between the irradiation position of the light and the photoelectric field enhancement substrate.

The moving means may vibrate the photoelectric field enhancement substrate in a plane perpendicular to the optical axis of the light.

    If the light irradiating means includes an objective lens that condenses the light onto the sample, the moving means vibrates the objective lens in a plane perpendicular to the optical axis of the light. There may be.

  The moving means rotates the photoelectric field enhancement substrate in a plane perpendicular to the optical axis of the light. Alternatively, it may be moved in parallel.

  Usually, since the photoelectric field enhancement substrate is formed so that the structure of the surface is regularly arranged, the light intensity of the background light emitted from the photoelectric field enhancement substrate when the substrate is irradiated with light, Even if the irradiation position of light changes, it does not fluctuate greatly. On the other hand, since the sample is not uniformly distributed on the photoelectric field enhancement substrate, the light intensity of the Raman scattered light emitted from the sample 111 varies greatly when the light irradiation position changes.

  The surface-enhanced Raman spectroscopic device of the present invention irradiates a sample placed on a photoelectric field enhancement substrate with light, and measures the spectrum of Raman scattered light emitted from this sample and enhanced by the photoelectric field enhancement substrate In the enhanced Raman spectroscopic device, when irradiating the sample placed on the photoelectric field enhancement substrate with light, the relative position between the light irradiation position and the photoelectric field enhancement substrate is periodically moved. The spectral intensity signal is measured by spectroscopic analysis of the Raman scattered light emitted from the sample and the background light emitted from the photoelectric field enhancement substrate. From the spectral intensity signal, the relative position between the light irradiation position and the photoelectric field enhancement substrate is measured. Since a signal synchronized with the movement period is detected, the signal component of the background light with little change in light intensity is suppressed even if the relative position changes, and is synchronized with the periodic change of the relative position. As a result, it is possible to detect signals containing many Raman scattered light signal components emitted from samples with varying light intensity, eliminating the need for prior background light spectrum measurement, which was necessary in the past. In addition, the Raman spectrum can be measured with high accuracy.

  If the relative position between the light irradiation position and the photoelectric field enhancement substrate is vibrated, it is not necessary to secure a space for moving the relative position. Further, if the photoelectric field enhancement substrate is vibrated in a plane perpendicular to the optical axis of light, the relative position can be moved with a simple configuration such as a stage.

  If an objective lens for condensing light onto the sample is provided and the objective lens is vibrated in a plane perpendicular to the optical axis of the light, it is not necessary to secure a space for moving the relative position. .

  A surface-enhanced Raman spectroscopic device according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of a surface-enhanced Raman spectroscopic device 100.

  As shown in FIG. 1, the surface-enhanced Raman spectroscopic device 100 includes a photoelectric field enhancement substrate 110 on which a sample 111 is placed and a photoelectric field enhancement substrate 110 placed on the photoelectric field enhancement substrate 110 in the XY direction. A stage unit 115 including a stage 116 to be moved and a stage control unit 117 for controlling the operation of the stage 116, and a sine wave generation unit for outputting a 1 kHz sine wave signal to the stage control unit 117 and a lock-in amplifier 160 described later. 139, a light irradiation unit 140 for condensing and irradiating the light L1 onto the photoelectric field enhancement substrate 110, a Raman scattering light emitted from the sample 111, a Raman scattering light or a fluorescence emitted from the photoelectric field enhancement substrate 110 A spectral intensity measuring unit 150 for measuring the spectral intensity by splitting the light L2 including the ground light; And a lock-in amplifier 160 that receives a 1 kHz sine wave signal and detects a B signal that is synchronized with the 1 kHz sine wave signal input from the spectrum intensity signal, and a sample from the output signal of the lock-in amplifier 160 A control unit 170 that includes a spectrum generation unit 171 that generates a Raman spectrum of the device and is connected to each part and controls the operation of the entire apparatus, and a display unit 180 that is connected to the control unit 170 are provided.

  The light irradiation unit 140 is a semiconductor laser 141 that emits light L1 having a wavelength of 780 nm at 30 mW, a lens 142 that collimates the light L1 emitted from the semiconductor laser 141, and reflects light at 780 nm in a right angle direction. The notch filter 143 that transmits light of the wavelength and the objective lens 144 that condenses the light L1 reflected by the notch filter 143 onto the sample 111 of the photoelectric field enhancement substrate 110 are included. The stage 116 has a vibration function by piezo in addition to the movement function of moving in the XY directions. Under the control of the stage controller 117, the stage 116 vibrates at a high speed in the left-right direction shown in FIG.

  Spectral intensity measurement unit 150 emits light L2 emitted from pinhole plate 152 having pinhole 151 for removing noise light and sample 111 or photoelectric field enhancement substrate 110 and transmitted through lens 144 and notch filter 143. , A lens 153 for condensing into the pinhole 151, a lens 154 for collimating the light L2 passing through the pinhole 151, a diffraction grating 155 for dispersing the light L2, and a predetermined one of the dispersed light L2 It has an objective lens 156 that condenses light of a wavelength and a photodiode 157 that measures the light intensity of the condensed light of a predetermined wavelength. A rotating unit 158 that rotates the diffraction grating 155 is attached to the diffraction grating 155. The rotation unit 158 is connected to the control unit 170, rotates the diffraction grating 155 under the control of the control unit 170, and sequentially makes light of different wavelengths in the light L2 enter the photodiode 157. The photodiode 157 sequentially outputs the detected light intensity to the lock-in amplifier 160.

The photoelectric field enhancement substrate 110 is obtained by anodizing a part of an anodized metal body such as Al to form a metal oxide body (Al ₂ O ₃ or the like), and a large number of fine metal oxide bodies formed in the process of anodization. It is a device obtained by growing a metal in each hole by plating or the like.

  Hereinafter, a method for manufacturing the photoelectric field enhancement substrate 110 will be briefly described with reference to FIGS. The photoelectric field enhancing substrate 110 can be manufactured by various methods. Here, as an example, a manufacturing method using an aluminum substrate is shown. (A)-(c) shows roughly the shape of the board | substrate cross section in the preparation process of the optical enhancement board | substrate 110. FIG.

  First, (a) shows the base 121 before entering the manufacturing process of the photoelectric field enhancement substrate 110. In the present embodiment, an aluminum layer thinned by rolling is used as the base 121. When an anodizing process is performed on the surface of the aluminum layer 122 using an anodizing device, an alumina layer 124 having a large number of fine holes 123 opened in the substrate surface 122 is formed as shown in FIG. The fine holes 123 are regularly arranged over almost the entire surface 122 of the substrate. The hole diameter, depth, and interval of the fine holes 123 vary depending on the conditions of anodization (for example, the concentration and temperature of the electrolyte used for anodization, the method of applying voltage, the voltage value, time, etc.).

Next, gold (Au) is filled by electroplating into the fine holes 123 naturally formed by the anodizing treatment. In the case of performing electroplating, the plating process is continued even after the gold is filled to the same position as the substrate surface 122. For this reason, as shown in (c), the head protrudes above the substrate surface 122, and the diameter of the head is larger than the diameter of the fine hole 123 (so-called mushroom type) gold fine particles 125 are formed. Is done. The diameter of the metal particle 125 can be designed to an arbitrary value, but is designed to be smaller than the wavelength of the light L1 so that the enhancement effect of the Raman scattered light is increased.

  FIG. 3 is a perspective view showing a part of the photoelectric field enhancement substrate 110. As shown in this figure, the gold fine particles 125 are arranged with a period of 63 nm over the entire surface 122 of the photoelectric field enhancement substrate 110. As described above, when a metal body having an uneven structure smaller than the wavelength of the light L1 is formed on the device surface 122, localized plasmons are induced when the device surface 122 is irradiated with the light L1. For this reason, the Raman scattered light emitted from the sample 111 is enhanced by the irradiation of the light L1.

  Note that the photoelectric field enhancement substrate is not limited to the above configuration, and devices such as those shown in FIGS. 4 and 5 can also be used. 4 is a cross-sectional view, and FIG. 5 is a perspective view and a top view.

  The photoelectric field enhancement substrate 110a shown in FIG. 4A is subjected to anodic oxidation as shown in FIGS. 2A and 2B, and the metal oxide body 124 formed by anodic oxidation is removed. This is a device in which only the non-anodized portion 121 of the metal oxide body is left (see Japanese Patent Laid-Open No. 2006-250924). Such a device is constituted by a non-anodized portion 121 having a plurality of dimple-like recesses 126 on the device surface.

  A photoelectric field enhancement substrate 110b shown in FIG. 4B is obtained by forming a metal layer 127 along the uneven shape on the surface of the photoelectric field enhancement substrate 110a (see JP-A-2006-250924). ).

  In the photoelectric field enhancement substrate 110c shown in FIG. 4C, the metal layer 127 of the photoelectric field enhancement substrate 110b is formed into particles by annealing treatment to form metal particles 128 on the non-anodized portion 121 of the metal to be anodized. (See Japanese Patent Application No. 2006-198009 (not disclosed at the time of filing this patent application)).

  5A is a device in which a plurality of metal particles 132 are fixed in an array on a conductor 130 and a flat dielectric 131. The photoelectric field enhancement substrate 110e shown in FIG. The arrangement pattern of the metal particles 132 can be appropriately designed and is preferably substantially regular. In such a configuration, the average diameter and pitch of the metal particles 132 are designed to be smaller than the wavelength of the light L1.

  The photoelectric field enhancement substrate 110f shown in FIG. 5B is a device in which a metal pattern layer 134 in which fine metal wires 133 are formed in a lattice pattern on a conductor 130 and a flat dielectric 131 is formed. The pattern of the metal pattern layer 134 can be appropriately designed and is preferably substantially regular. In such a configuration, the average line width and pitch of the fine metal wires 133 are designed to be smaller than the wavelength of the light L1.

  A photoelectric field enhancement device 110g shown in FIG. 5C is composed of a plurality of metal nanorods 136 disposed on a plate 135 (see Japanese Patent Application Laid-Open No. 2007-139612). The metal nanorods have a minor axis length of about 3 nm to 50 nm and a major axis length of about 25 nm to 1000 nm, and the major axis length is smaller than the wavelength of the excitation light.

  Further, the surface of the photoelectric field enhancing substrate may be constituted by a metal layer having a roughened surface. Examples of the roughening method include an electrochemical method using oxidation reduction and the like. In addition, as the photoelectric field enhancing substrate, a known device having a surface electric field enhancing effect can be used.

It should be noted that hot spots that increase the intensity of the photoelectric field are distributed on the surface of these photoelectric field enhancement substrates.

  Next, a Raman spectroscopy method for measuring the Raman spectrum of the sample 111 using the above-described surface-enhanced Raman spectrometer 100 will be described. First, prior to measurement, the photoelectric field enhancement substrate 110 on which the sample 111 is placed is placed on the stage 116.

  Hereinafter, the measurement of the Raman spectrum of the sample 111 is performed under the control of the control unit 170. First, the stage 116 moves, and the photoelectric field enhancement substrate 110 moves to a position where the light L1 can be irradiated onto the sample 111.

  Light L1 having an output of 30 mW and a wavelength of 780 nm is emitted from the semiconductor laser 141 of the light irradiation unit 140 and is collimated by the lens 142. The light L1 is reflected by the notch filter 143, condensed by the objective lens 144, and irradiated to the sample 111 on the photoelectric field enhancement substrate 110 as a spot having a diameter of 1 μm. By the irradiation of the light L1, Raman scattered light is emitted from the sample 111, and Raman scattered light and fluorescence are emitted from the photoelectric field enhancement substrate 110.

  The light L2 including the Raman scattered light emitted from the sample 111 and the Raman scattered light emitted from the photoelectric field enhancement substrate 110 or the background light made of fluorescence is shifted from 780 nm, and therefore passes through the notch filter 143. The light is condensed by the lens 153, passes through the pinhole 151, is collimated again by the lens 154, and enters the diffraction grating 155. Note that Rayleigh scattered light or the like has a wavelength of 780 nm, which is the same as that of the light L1, and is reflected by the notch filter 143, so that it does not enter the diffraction grating 155. The light L <b> 2 is dispersed by the diffraction grating 155, and light having a predetermined wavelength dispersed in the direction of the photodiode 157 is collected by the lens 156 and enters the photodiode 157. The output of the photodiode 157 is output to the lock-in amplifier 160.

  With the output of the photodiode 157 being output to the lock-in amplifier 160, the control unit 170 inputs the 1 kHz sine wave output from the sine wave generation unit 139 to the stage control unit 117. The stage control unit 117 vibrates the stage 116 at a high speed between the position a and the position c as shown in FIG. Note that the hot spot 112 shown in FIG. 6 has a particularly high photoelectric field enhancement.

  The light L2 includes Raman scattered light emitted from the sample 111 and background light made of Raman scattered light and fluorescence emitted from the photoelectric field enhancement substrate 110. The light L2 is condensed on the photoelectric field enhancement substrate 110 by the objective lens 144, and the diameter of the condensed spot is about 1 μm.

  Since a large number of fine metal particles 125 are regularly arranged on the surface of the photoelectric field enhancement substrate 110, the background light emitted from the photoelectric field enhancement substrate 110 is moved even if the position of the condensing spot is moved. The light intensity does not change greatly. On the other hand, since the sample 111 is not uniformly distributed on the photoelectric field enhancing substrate 110, the light intensity of the Raman scattered light emitted from the sample 111 varies greatly when the position of the focused spot changes. In particular, as shown in FIG. 6, when hot spots 112 having a large enhancement intensity are distributed on the surface of the photoelectric field enhancement substrate 110, the emission from the sample 111 depends on whether or not the sample 111 exists on the hot spot. Since the enhancement of the Raman scattered light to be changed changes, the fluctuation of the light intensity is particularly large when the position of the focused spot is changed.

  For example, if the spectrum of the background light is as shown in FIG. 7 and the irradiation position of the light L1 moves to ac, the spectrum of the light L2 is as shown in FIG. 8 (a) to FIG. 8 (c). Will change as follows.

  On the other hand, the light intensity signal output from the photodiode 157 is a light intensity signal of one wavelength, and includes a signal component of background light and a signal component of Raman scattered light emitted from the sample 111. For this reason, the light intensity signal output from the photodiode 157 is input to the lock-in amplifier 160, and by detecting a signal synchronized with 1 kHz input as the reference signal, The signal component of the background light with a small change in light intensity is suppressed, and a signal containing a large amount of the signal component of the Raman scattered light emitted from the sample 111 whose light intensity varies in synchronization with the change in the focused spot position is detected. be able to.

  The output of the lock-in amplifier 160 is input to the control unit 170 and stored in the spectrum generation unit 171. When the signal detection at the predetermined wavelength is completed, the rotating unit 158 rotates the diffraction grating 155. The wavelength of light dispersed in the direction of the photodiode 157 changes, and light having the next wavelength enters the photodiode 157. By sequentially rotating the diffraction grating 155, light having different wavelengths in the light L2 sequentially enters the photodiode 157, and the output of the photodiode 157 is input to the lock-in amplifier 160 and detected by the lock-in amplifier 160. The signal is output to the spectrum generator 171 and stored. The spectrum generation unit 171 stores the signal detected by the lock-in amplifier 160 over time, thereby suppressing the spectrum of the background light as shown in FIG. 9 and the Raman scattered light emitted from the sample 111. A spectrum containing a lot of spectra is acquired and output to the display unit 180.

  As apparent from the above description, in the surface-enhanced Raman spectroscopic device according to the present embodiment, the sample is irradiated with the light L1 while the photoelectric field enhancement substrate 110 is vibrated at a frequency of 1 kHz, and the Raman scattered light emitted from the sample 111. And a spectral intensity signal of the light L2 including background light composed of Raman scattered light and fluorescence emitted from the photoelectric field enhancement substrate 110, and the photoelectric field enhancement substrate 110 is detected from the spectrum intensity signal using the lock-in amplifier 160. Since the signal synchronized with 1 kHz which is the oscillation period of the light is detected, even if the irradiation position of the light L1 is changed, the signal component of the background light with little change in light intensity is suppressed, and the periodic change of the irradiation position of the light L1 is suppressed. Can detect a signal containing a lot of signal components of Raman scattered light emitted from the sample 111 whose light intensity fluctuates in synchronization with Since, it is possible to spectral measurement of the prior background light has been conventionally required becomes unnecessary to measure the Raman spectrum in a short time and with high precision.

  FIG. 10 shows a surface-enhanced Raman spectroscopic device 200 that is a modification of the embodiment. In the surface-enhanced Raman spectroscopic device 200, an objective lens vibrating unit 210 that vibrates the objective lens 144 at 1 kHz in a plane perpendicular to the optical axis direction of the light L1 is provided, and the objective lens 144 is vibrated to irradiate the light L1. The relative position between the position and the photoelectric field enhancement substrate 110 is periodically moved. In this case, a 1 kHz sine wave output from the sine wave generation unit 139 is input to the objective lens vibration unit 210. The stage unit 220 includes a stage 221 that moves the photoelectric field enhancement substrate 110 in the XY directions, and a stage control unit 222 that controls the operation of the stage 221.

  In both the surface-enhanced Raman spectroscopic device 100 and the surface-enhanced Raman spectroscopic device 200, the vibration width of the light L1 on the photoelectric field enhancing substrate 110 is preferably equal to or larger than the diameter of the condensed spot of the light L1.

  In addition, as the photoelectric field enhancement substrate 110, a substrate having a periodic structure and whose optical enhancement intensity changes periodically may be used. In such a case, it is preferable that the diameter of the focused spot is larger than one period width of the periodic structure. Moreover, it is preferable that the position vibration width of the relative position is larger than the diameter of the focused spot.

  In the present embodiment, the relative position between the irradiation position of the light L1 and the photoelectric field enhancement substrate 110 is vibrated, but the present invention is not limited to this. For example, the photoelectric field enhancement substrate 110 may be disposed on the rotation stage and rotated, or the photoelectric field enhancement substrate 110 may be translated.

Surface-enhanced Raman spectroscopic apparatus according to an embodiment of the present invention (A)-(c) is a manufacturing process diagram of a photoelectric field enhancement substrate. Perspective view of the surface of the photoelectric field enhancement substrate Sectional view of a modification of the photoelectric field enhancement substrate A perspective view and a top view of a modification of the photoelectric field enhancement substrate Explanatory drawing of the irradiation position of light L1 Illustration of background light spectrum Explanatory drawing of spectrum of light L2 in each irradiation position Illustration of the spectrum of Raman scattered light Modification of surface-enhanced Raman spectrometer

Explanation of symbols

100, 200 Surface-enhanced Raman spectroscopy device 110 Photoelectric field enhancement substrate 111 Sample 115 Stage unit 116 Stage 117 Stage control unit 139 Sine wave generation unit
140 Light Irradiation Unit 141 Light Source 143 Notch Filter 150 Spectrum Intensity Measurement Unit 151 Pinhole 152 Pinhole Plate 155 Diffraction Grating 157 Photodiode 158 Rotation Unit 160 Lock-in Amplifier 170 Control Unit 171 Spectrum Generation Unit 210 Objective Lens Vibration Unit

Claims (4)

In a surface-enhanced Raman spectroscopic device that measures the spectrum of Raman scattered light emitted from the sample and enhanced by the photoelectric field-enhancing substrate by irradiating the sample placed on the photoelectric field-enhancing substrate,
A light irradiating means for irradiating the sample placed on the photoelectric field enhancing substrate with the light;
Moving means for periodically moving a relative position between the irradiation position of the light and the photoelectric field enhancement substrate;
Spectral intensity signal measuring means for spectrally measuring the Raman scattered light emitted from the sample and the background light emitted from the photoelectric field enhancement substrate by the light irradiation and measuring a spectral intensity signal;
A surface-enhanced Raman spectroscopic apparatus, comprising: synchronization detection means for detecting a signal synchronized with a movement cycle of the relative position from the spectrum intensity signal.   2. The surface-enhanced Raman spectroscopic apparatus according to claim 1, wherein the moving means vibrates a relative position between the irradiation position of the light and the photoelectric field enhancement substrate.   3. The surface-enhanced Raman spectroscopic apparatus according to claim 2, wherein the moving means vibrates the photoelectric field enhancing substrate in a plane perpendicular to the optical axis of the light. The light irradiation means includes an objective lens that condenses the light onto the sample,
The surface-enhanced Raman spectroscopic apparatus according to claim 2, wherein the moving means vibrates the objective lens in a plane perpendicular to the optical axis of the light.

Images