JP2012073226A - Probe for fiber and manufacturing method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a probe for fiber for measuring infrared absorption with a very high sensitivity that can carry out measurement of an infrared absorption signal even when a liquid or gas 4 of measurement object is apart from a spectrometer 1.SOLUTION: The probe for fiber 3 is constructed by forming a metal nano-structural film exhibiting an electromagnetic field enhancing effect on a surface of a probe material for fiber that transmits infrared light. The probe is not limited to a fiber shape. The probe is only required to receive the infrared light from an infrared fiber 2, reflect the infrared light at the surface of the probe material, and return it to the infrared fiber 2, and required to be attachable/detachable.

Description

  The present invention relates to a probe for fibers for measuring an infrared absorption signal such as an infrared absorption spectrum in which a metal nanostructure film is coated on the surface. In the present application, the term “infrared” is used in a broad sense including mid-infrared and near-infrared.

  As shown in Non-Patent Document 1 and Non-Patent Document 1, surface enhanced Raman scattering (SERS) and surface enhanced infrared absorption (SEIRA) effects are highly sensitive and simple chemistry. Energetic research is being conducted as a phenomenon that can be applied to sensors and biosensors. In particular, unlike a dielectric sensor such as a surface plasmon sensor or a resistance measurement type gas sensor, a SEIRA sensor can measure a signal due to molecular vibration. Therefore, detection and status of components of molecular species, such as detection and identification of components such as biomolecules and macromolecules, high-sensitivity monitoring of their state changes, or monitoring of reaction processes of chemical species on the electrode surface of fuel cells, etc. -Demonstrates power in environmental monitoring.

  Non-Patent Document 1 is a study on high-sensitivity Raman scattering using metal nanoparticles, Non-Patent Document 2 is a study on surface-enhanced infrared absorption by a metal nanostructure film, and Non-Patent Document 3 is an adsorption of a fine particle film in a solution.・ Research on kinetics and molecular processes in desorption, Non-patent document 4 is research on adsorption / desorption monitoring of metal fine particles in solution, Non-patent document 5 is grown after adsorbing gold nanoparticles. This is a research paper on creating a structural film.

  Metal films consisting of island-like metal nanostructures and continuous metal films with rough surface morphology exhibit high infrared activity, and nanothin films obtained by growing such metal films on semiconductor / insulator substrates are used as sensor materials. It is often done. When such a sensor material is used for highly sensitive in-situ measurement, for example, a material obtained by growing a film on a silicon prism crystal in a liquid flow cell has been used. However, in such measurement, it is necessary to accurately incorporate and adjust the flow cell in the spectroscope, and the target that can be further measured is limited to a liquid sample having a small volume of about 1.0 ml or less. . In addition, in order to grow the prism film by controlling the metal film, it is necessary to take out and set the cell once and it takes time to manufacture the film.

  On the other hand, let infrared light pass through an optical fiber material that transmits or transmits light in the infrared band and irradiate the specimen placed outside the spectrograph and analyze the reflected light, or animal, human body, paint, liquid sample For example, a method for measuring the absorption spectrum of infrared light totally reflected at the interface between a specimen and a fiber or a fiber probe by directly contacting the specimen with elasticity and fluidity has been established.

  However, these methods use infrared light directly reflected from the far field or evanescent light at the fiber probe-sample interface to obtain an infrared absorption spectrum of the portion in contact with the probe surface. The penetration length is on the order of about 1 μm or more, and it is difficult to obtain an absorption signal from a thin film at a molecular layer level or a trace amount of sample.

  In view of such circumstances, the present invention provides a highly sensitive surface for a probe for a flexible infrared fiber that can be applied to on-site environmental measurement, in-situ chemical reaction measurement, in-situ biological / medical measurement, and the like. The purpose of this is to realize a highly sensitive probe by coating with a metal nanostructure film for the purpose, and to simplify highly sensitive measurement. Here, the fiber probe in the present invention is placed in direct contact with the sample solution / sample to be measured in the tip of the infrared fiber or in the optical path, has a function of enhancing the signal, and the incident infrared light is used as the sample. A replaceable part that reflects off the interface between the solution / sample and the probe and returns to the spectrometer. If such a probe can be used, biological samples that cannot be set inside the spectrometer, samples during chemical reactions, and environmental measurements such as water quality measurements in fields such as rivers and lakes can be easily measured. It becomes possible. Further, the coating process of the probe material with the metal nanostructure film can be simplified because a flow cell is not used, and a manufacturing method suitable for mass production on a manufacturing line is desired.

According to one aspect of the present invention, the surface of a probe material made of a material that transmits or transmits infrared light is coated with a metal nanostructure film, and an absorption signal is enhanced by an electromagnetic field enhancement effect of the metal nanostructure film. A fiber probe for measuring external absorption signals is provided.
Here, the fiber probe material may be a polycrystalline infrared (PIR) fiber.
Alternatively, the fiber probe material may be a crystal of an infrared light transmitting material such as silicon, germanium, diamond, ZnSe, KBr, NaCl, or the like.
The metal nanostructure film may include a plurality of metal islands spaced apart from each other.
According to the other aspect of this invention, the manufacturing method of the said probe for fibers provided with the following steps is given.
(A) The surface of the probe material made of a material that transmits or transmits infrared light is surface-treated with a silane coupling agent.
(B) Adsorbing metal nanoparticles on the surface of the probe material surface-treated with the silane coupling agent.
(C) Growing the adsorbed metal nanoparticles.
Here, the step of growing the metal nanoparticles may be performed by electroless plating.
The metal may be gold.
Here, the electroless plating may be performed using an AuCl ₄ / hydroxylamine solution.
According to still another aspect of the present invention, a PIR fiber probe containing Ag is selected from the group consisting of a chemical surface treatment, an electrochemical surface treatment, and a physical surface treatment that irradiates an electron beam. A method for producing the fiber probe is provided, in which the Ag nanoparticle deposited on the surface by performing at least one surface treatment is used as the metal nanostructure film.
According to still another aspect of the present invention, metal nanorods or metal nanodisks having a plasmon resonance frequency in the infrared band, or metal nanorods, metal nanodisks or metal nanoparticles are connected to increase the plasmon resonance frequency in the infrared band. Fabrication of the fiber probe, wherein the metal nanostructure film is formed by immobilizing the metal film formed on the fiber surface made of a material that transmits or transmits infrared light directly or via a coupling agent A method is given.
Here, the metal nanostructure film may be coated with a substance having affinity for both the object to be detected by the fiber probe and the metal nanostructure film.

  By using the fiber probe of the present invention, a much higher sensitivity can be obtained compared to the case of using a conventional similar probe not having the metal nanostructure film of the present invention. This sensitivity is higher than that of the single reflection type total reflection attenuation measurement probe reported by the inventor of the present application, in which the gold nanostructure film is coated on the Si prism surface. Rather, it is easier to use than a probe with such a reported configuration.

The schematic diagram of the structural example of the measurement system using the probe for fibers of this invention. The schematic diagram of the growth of the gold | metal nanostructure film | membrane on the highly sensitive probe surface for infrared absorption signal measurement in the Example of this invention. The figure which shows the infrared absorption spectrum measured while growing the gold nanostructure film | membrane on the probe surface for fibers in the Example of this invention. The scanning electron micrograph of the probe for fibers after gold nanostructure film coating in the example of the present invention, and a partial enlarged photograph. Results of recording an absorption signal of 32% CH stretching vibration in a performance evaluation spectrum prepared by adsorbing monodecane octadecanethiol to a fiber probe coated with a gold nanostructure film manufactured in an example of the present invention FIG. In the Example of this invention, the scanning electron micrograph of the probe surface for the fibers made from PIR before electron beam irradiation. A scanning electron microscope on the surface of a probe for a PIR fiber shown in FIG. 6 in which an electron beam accelerated by 25 kV is irradiated with a current of 58 microamperes in a range of about 500 microns in diameter for 2.6 hours to deposit Ag. Photo. Scanning electron micrograph of the surface of a probe for a PIR fiber in FIG. 6 in which Ag was deposited by irradiating an electron beam accelerated at 25 kV with a current of 58 microamperes in a range of about 500 microns in diameter for 7.5 hours. . Schematic which shows the example of the shape of the probe for fibers of this invention.

  The high-sensitivity probe for measuring an infrared absorption signal of the present invention has an infrared absorption signal on the surface of an optical fiber or other material (that is, the side surface in the case of a fiber shape) that transmits or transmits light in the infrared band. It is a probe formed by coating a metal nanostructure film that enhances the resistance. The probe of this configuration has both high enhancement effect of infrared absorption signal and high surface sensitivity at the same time, and it is easy to set biological samples, liquid samples during chemical reaction, and samples such as rivers and soils without setting them inside the spectrometer. In-situ monitoring can be performed. Furthermore, the part which touches a measurement sample directly can be made detachable, and the detachable probe which attached the probe of this invention to the said detachable part can be comprised. Thus, the probe of the present invention is characterized by high sensitivity, simplicity, and versatility. In addition, as a material of the high-sensitivity probe for measuring the infrared absorption signal used here, the absorption of infrared light is small, and the infrared light from the fiber is passed through the water-probe material interface and the atmosphere-probe material interface. Any device that totally reflects the light may be used.

  In addition, although the term “film” is used in the present application, this is not limited to a continuous structure that completely covers a certain surface. A “film” in the present application partially covers the target surface by collecting a large number of fine particles and minute flats that are at least partially discontinuous with each other (that is, a part of the gap is opened). It is a concept that includes a structure that is coated in such a manner.

  Further, the configuration of the measurement system using the probe of the present invention as described below with reference to FIG. 1 can be directly applied to the production of the fiber probe of the present invention as described in the section of the examples. Therefore, the coating process on the surface of the probe material (fiber etc.) with the metal nanostructure film can be simplified without using a flow cell or the like, and a method suitable for mass production on the production line can be realized.

  FIG. 1 shows a schematic diagram of an example of a measurement system using the probe of the present invention. In FIG. 1, the coated infrared fiber 2 is extended from the infrared spectrometer 1 and pulled out to the vicinity of the liquid specimen sample 4 to be measured. A high-sensitivity probe 3 for measuring infrared absorption is detachably attached to the tip of the infrared fiber 2. The fiber measuring probe of the present invention is provided in a portion of the probe 3 that contacts the sample. In this example, the probe is in the form of an optical fiber. As can be seen from FIG. 1, infrared spectrometer 1 → infrared fiber 2 → high sensitivity probe 3 for infrared absorption measurement (infrared light passes through the fiber probe of the present invention) → infrared fiber 2 → Infrared spectrometer 1 is formed, an infrared light loop starting from infrared spectrometer 1 and returning to infrared spectrometer 1 again. An infrared absorption spectrum can be obtained by normalizing the spectrum of infrared light returning through this loop with a certain reference value. The reference value for normalization may be, for example, the spectrum of infrared light that has returned to the infrared spectrometer 1 when the probe 3 is immersed in a pure solvent of the liquid specimen 4. Alternatively, when the analyte molecules in the solution are adsorbed on the probe, the measured value R0 of the spectrum at the moment when the probe is attached to the solution (that is, in the state where the analyte molecules are not substantially adsorbed) is used as a reference value, and the time At the same time, the measured value R of the spectrum at each time point when the analyte molecule has advanced to the probe can be normalized by the reference value. Furthermore, when detecting gas molecules in the atmosphere, the place described as “solution” in the above description is read as “atmosphere”. Further, when the infrared fiber 2 and the probe 3 are provided as a set, an infrared light spectrum as the reference value can be provided for the set.

  According to the present invention, a sensitivity higher by one digit to two digits or more with respect to an absorption signal of molecular vibration in the vicinity of the probe surface is realized as compared with a normal infrared fiber probe not using a metal nanostructure. Remote sensing is possible because a fiber optical system that can freely route infrared light is used, and measurement can be performed easily and quickly by placing the probe directly in contact with the biological sample without setting the sample inside the spectrometer. Is possible. Also, in the measurement of a liquid sample, since the measurement can be performed simply by immersing the probe directly inside the fluid sample without pouring the sample into a liquid flow cell or the like, it is possible to easily monitor river contamination and chemical quality. By using such a probe, it is possible to easily perform high-sensitivity measurement such as a sample (biological specimen, solution during chemical reaction, outdoor environment measurement) that cannot be set inside the spectrometer. The manufacturing process is also simplified because no flow cell is used, and a manufacturing method suitable for mass production can be realized. Such a merit is not found in a conventional measurement method using an Attenuated Total Reflection prism installed inside a spectrometer.

  Hereinafter, a method for producing the probe of the present invention and specific examples of characteristics of the produced probe will be described, but the present invention is not limited to this. For example, in FIG. 1 and the following embodiments, an infrared fiber is used as a fiber probe, and in the embodiment, a PIR fiber is specifically used. However, the material and shape of the fiber probe of the present invention are the same. The material is not limited, and any material that can transmit or transmit infrared light can be used, and the shape is suitable for measurement, probe fabrication, and other handling. It can take any shape that reflects internally at the interface and returns to the spectrometer. For example, as a material, a crystal of an infrared light transmitting material such as silicon, germanium, diamond, KBr, NaCl, ZnSe or the like can be used, and the shape thereof is triangular, hemisphere, semi-cylinder, plate, You can take various things such as. For example, FIG. 9 schematically illustrates a fiber probe Pa, a triangular prism-like fiber probe Pb, and a plate-like fiber probe Pc that are shaped like a fiber folded back on a loop as shown in FIG. . Note that the upward and downward arrows drawn along the fiber leading to each fiber probe in FIG. 9 are the corresponding fibers from a measuring device (not shown) such as an infrared spectrometer as shown in FIG. The direction of the measurement infrared light that is sent to the probes Pa to Pc and returns to the measuring device is shown.

  As a method for producing a probe for measuring infrared absorption signals in the present invention, a PIR fiber (Polycrystalline Infra-Red Fiber; an infrared optical fiber made of a metal halide such as polycrystalline silver chloride / silver bromide) is used as an infrared fiber. ), And an island-shaped gold nanostructure film is grown on the surface by electroless plating.

  A schematic diagram showing an example of the growth of the gold nanostructure film on the surface of the fiber probe is shown in FIG. First, the surface of the infrared fiber probe is covered with a silane coupling agent (such as aminopropyltriethoxysilane), and then the fiber probe is immersed and adsorbed in a colloidal solution of gold nanoparticles prepared by a citrate reduction method or the like. The amino group of aminopropyltriethoxysilane and gold nanoparticles are bonded by Coulomb force or the like to form a uniformly adsorbed gold nanoparticle film (FIG. 2A). The amount of gold nanoparticles to be adsorbed is determined in advance by associating an infrared absorption spectrum with a scanning electron microscopic observation, etc., and determining the amount of adsorption by judging the spectrum and the signal of infrared light. Using this result, the amount of adsorbed particles is controlled with good reproducibility while measuring infrared absorption. In FIG. 2A, the layer of the silane coupling agent on the surface of the fiber probe is not shown because this layer is so thin that it cannot be seen on the scale of FIG. Actually, a very thin silane coupling layer of about one molecular layer exists here.

After that, an infrared fiber probe is immersed in an AuCl ₄ / hydroxylamine solution, and gold nanoparticles are formed on the fiber probe by an electroless plating so as to form a plurality of flat island regions having gaps therebetween. Growing (FIGS. 2B to 2C). The growth progress of such a structure is judged from the infrared absorption signal as in the case of gold nanoparticle adsorption, and the growth time is adjusted. Such in-situ monitoring is described in more detail in Patent Document 1 and Non-Patent Document 5, although it relates to growth on a substrate. In addition, as an index other than the infrared absorption spectrum for characterizing the optimum island-shaped nanostructure, the nanogap size is about 1 to 10 nm, or the two-dimensional coverage on the flat surface of the flat island-shaped particles Is 80% or more.

  In addition, the measurement of the infrared absorption in the manufacturing process mentioned above is realizable by the completely same structure as the system structure at the time of measuring an actual object as shown, for example in FIG. That is, in FIG. 1, the amount of gold nanoparticles adsorbed or grown as described above can be monitored in situ by using a colloidal solution of gold nanoparticles or an electroless plating solution instead of a liquid specimen. . This makes it possible to manufacture a high-performance fiber probe with a narrow variation in performance without preparing a specially configured device or jig dedicated to the manufacturing process.

  FIG. 3 shows an absorption spectrum obtained by growing a gold nanoparticle film through an infrared fiber probe being fabricated. The time course of the spectrum is shown from top to bottom. Along with the growth of the gold nanostructure, it can be confirmed that the absorption signal of the bending vibration of water molecules in the solution near 1620 1 / cm is enhanced. Here, FIG. 3 shows a spectrum obtained by dividing the spectrum at each growth time by the reference spectrum using the spectrum at the growth start time 0 as a standard for normalization. FIG. 4 shows an SEM photograph of the island-shaped gold nanostructure film thus grown on the surface of the fiber. On the surface of the fiber probe, a plurality of island-like regions, that is, island-like nanostructures that have grown flat in the direction parallel to the surface, not spherical, can be confirmed. It is expected that an island-shaped gold nanostructure film having a flat shape deviating from such a spherical shape causes high infrared absorption (Non-Patent Document 5).

  An infrared absorption spectrum after adsorbing octadecanethiol on the surface of the prepared infrared probe is shown in FIG. By bonding the thiol group to the gold surface, a monolayer thick film is formed on the gold nanostructure surface. It was observed that a huge absorption signal of 32% was generated at the frequency of the stretching vibration of CH (29201 / cm) regardless of the thickness of the monolayer. This is about twice as high as that of a single reflection type total reflection attenuation measurement when the gold nanostructure film is coated on the surface of the Si prism (see Patent Document 1). This is a result that could not be predicted from Non-Patent Document 5, indicating that effects other than the gold nanostructure are effective. For example, since the nature of the substrate is different from that of silicon, an effect that the morphology of the grown Au nanostructure is different can be considered. In addition, since the PIR fiber used here is a polycrystalline material, the surface of the portion covered with the gold nanostructure film is rough and the area of the film is increased compared to a single crystal prism or the like. Compared to single-reflection ATR measurement on a flat surface, infrared light is reflected in the fiber probe multiple times, and high signal enhancement is expected. In the measurement results shown in FIG. 5, the spectrum at the start of octadecanethiol adsorption is used as a standard for normalization.

  Here, the spectrum of FIG. 5 corresponds to the SEM of FIG. 4 and the bottom spectrum of FIG. However, the growth of the Au film at this point was still insufficient, and the sensitivity increased as the growth continued.

  In the measurement under the same conditions without the gold nanostructure film, the octadecanethiol signal was buried in the noise level and was hardly observed. From the above results, it was confirmed that a very high infrared absorption signal enhancement effect was produced by coating the fiber surface with a gold nanostructure film. Although the results shown here do not optimize the growth time, growth temperature, solution concentration, and the like of the gold nanostructure, it is possible to enhance the signal even higher by optimizing these growth parameters. Here, an example was shown in which an octadecanethiol molecule that directly adsorbs to gold was used as a sample. However, in the case of a sample that is difficult to adsorb directly to gold, it has affinity for the target sample and affinity for gold. The surface of the gold nanostructure can be coated with a film that has a structure that can be applied to a wide range of analyte molecules.

  Such a metal nanostructure can also be realized by depositing silver on the surface of the fiber by electrochemical surface treatment or by directly irradiating a PIR fiber using silver halide with an electron beam. Compared to the chemical growth method shown above, there is an advantage that it is not necessary to grow in two stages, the gold nanoparticle adsorption process and the gold nanoparticle growth process, and it can be manufactured by a single electron beam irradiation. . FIGS. 6 to 8 show the results of irradiating the surface of the PIR fiber with a 58 microampere electron beam at 25 kiloelectron volts and having a diameter of about 500 microns. It can be seen that the amount of nanoparticles on the fiber surface is increased by the surface precipitation of Ag from the inside as the irradiation amount of the electron beam is increased. The PIR fiber used in this example is Polycrystalline InfraRed (PIR-) Fibers (registered trademark) manufactured by A.R.T. Photonics GmbH.

  The infrared absorption signal measurement probe of the present invention has a signal enhancement effect in the infrared band by a metal nanostructure film such as gold. Utilizing this, for example, by combining with a portable infrared absorption spectroscope, it can be applied to detection of trace amounts of environmental hormones in fluid samples, rivers, soils, and the like. By covering the surface of the metal nanostructure with a molecule having affinity for the target molecule, it is possible to have a selection system for the molecule to be measured. By using the probe according to the present invention, it is difficult to set the measurement sample in an apparatus in which a conventional sample chamber and a spectroscope are integrated, such as environmental measurements such as lake water and solutions during reaction. Time observation and highly sensitive trace measurement are possible (see Fig. 1). If this highly sensitive probe is introduced into a living organism, it can be applied to medical diagnosis. It can be applied to chemical sensors, biosensors, gas sensors using the present invention, and medical diagnostic measuring instruments and quality control measuring instruments to which they are applied. It is done.

WO2009 / 031662

K. Kneipp, H. Kneipp, I. Itzkan, R. R. Dasari, and M. S. Feld. Chem. Rev., 99: 2957-2975 (1999). M. Osawa, Bull. Chem. Soc. Jpn. 70, 2681-2880 (1997) D. Enders, T. Nagao, T. Nakayama, and M. Aono, Langmuir 23, 6119 (2007) D. Enders, T. Nagao, A. Pucci and T. Nakayama Surf. Sci., 600, L71 (2006) D. Enders, T. Nagao, T. Nakayama and M. Aono, Jpn. J. Appl. Phys. 49, L1222-L1224 (2007)

Claims (11)

  An infrared absorption signal measuring fiber probe in which a probe material surface made of a material that transmits or transmits infrared light is coated with a metal nanostructure film, and an absorption signal is enhanced by an electromagnetic field enhancement effect of the metal nanostructure film.   The fiber probe of claim 1, wherein the fiber probe material is a polycrystalline infrared (PIR) fiber.   The fiber probe according to claim 1, wherein the fiber probe material is a crystal of an infrared light transmitting material such as silicon, germanium, diamond, ZnSe, KBr, or NaCl.   The fiber probe according to any one of claims 1 to 3, wherein the metal nanostructure film includes a plurality of metal islands spaced apart from each other. The manufacturing method of the probe for fibers in any one of Claim 1 to 4 which provided the following steps.
(A) The surface of the probe material made of a material that transmits or transmits infrared light is surface-treated with a silane coupling agent.
(B) Adsorbing metal nanoparticles on the surface of the probe material surface-treated with the silane coupling agent.
(C) Growing the adsorbed metal nanoparticles.   The method for producing a fiber probe according to claim 5, wherein the step of growing the metal nanoparticles is performed by electroless plating.   The method for producing a fiber probe according to claim 5, wherein the metal is gold. The method for producing a fiber probe according to claim 7, wherein the electroless plating is performed using an AuCl ₄ / hydroxylamine solution.   A PIR fiber probe containing Ag is subjected to at least one surface treatment selected from the group consisting of a chemical surface treatment, an electrochemical surface treatment, and a physical surface treatment that irradiates an electron beam. The method for producing a fiber probe according to any one of claims 1 to 4, wherein Ag nanoparticles deposited on the surface are used as the metal nanostructure film.   Metal nanorods or metal nanodisks with plasmon resonance frequency in the infrared band, or metal films that have metal plasmon resonance frequency in the infrared band by connecting metal nanorods, metal nanodisks or metal nanoparticles with infrared light The method for producing a fiber probe according to any one of claims 1 to 4, wherein the metal nanostructure film is formed by immobilizing directly or via a coupling agent on a fiber surface made of a material to be transmitted or transmitted. . The method for producing a fiber probe according to any one of claims 5 to 10, wherein the metal nanostructure film is coated with a substance having an affinity for both an object to be detected by the fiber probe and the metal nanostructure film. .