JP4825974B2 - Fluorescence enhancement element, fluorescence element, and fluorescence enhancement method - Google Patents

Description

The present invention relates to an optical element capable of enhancing the intensity of fluorescence emitted from a fluorescent substance, and a fluorescence enhancement method using the optical element.
The “fluorescent substance” in the present invention is a general term for substances that emit fluorescence by irradiating with predetermined excitation light or by excitation using a field effect. “Fluorescence” includes various types of light emission including “phosphorescence”.

  Fluorescence analysis, which qualitatively and quantitatively analyzes analyte molecules by exciting the analyte molecules and analyzing the fluorescence emitted from the excited molecules, is one of high-sensitivity analysis methods and plays an important role in microanalysis Plays.

  Fluorescence emitted from an excited substance not only reflects the characteristics of the fluorescent substance itself, but is also easily affected by the environment surrounding the fluorescent substance. Therefore, the fluorescent substance is used as a labeling agent (biosensor) to identify tissues and DNA in the body. It is also used in a wide range of fields, including biomedical chemistry.

  In addition, a fluorescent material excited by a field effect is applied to an organic EL element that has been remarkably developed as one of thin display devices.

  Although fluorescence is widely used in this way, the fluorescence intensity varies depending on the substance. Usually, if the fluorescence of a substance having a weak fluorescence intensity can be observed, the application range is expected to be further expanded. For this reason, research aimed at enhancing the fluorescence of substances has been actively conducted.

  A well-known fluorescence enhancement method is based on the phenomenon that fluorescence emitted from a molecule is enhanced by the presence of a fluorescent molecule in the vicinity of a metal colloid or metal island film (for example, , See Patent Document 1).

  However, although the fluorescence enhancement method using the metal colloid or metal island film described above is effective for fluorescence enhancement, there is a limit to enhancement as described below.

There are two types of factors that cause the fluorescence enhancement effect of this type of metal nanoparticles. The first factor is the enhancement of the electric field in the vicinity of the particles that occurs when surface plasmons are excited in the metal nanoparticles by incident light. Since nearby molecules are excited more efficiently under this enhanced electric field, the absorption rate of incident light (molecular excitation efficiency) effectively increases, and the emission intensity increases in proportion to this. The strength of this enhanced electric field and the range (distance) covered by it depend greatly on the size and shape of the metal nanoparticles.
The more important second factor is the action of increasing the quantum yield of luminescence itself, and its qualitative interpretation is as follows. That is, the light-emitting dipole of the excited molecule excites the surface plasmon free electron vibration mode of the adjacent metal (this means that the energy of the excited molecule is transferred to the metal), and induces luminescence in the metal particle. Give a dipole. Since the net emission probability of the system is proportional to the square of the total dipole moment, an increase in luminous efficiency (quantum yield) can be expected if the induced dipole size is larger than the dipole of the original excited molecule.
However, various free electron excitation modes exist in the metal at the same time, and most of them are rapidly lost as Joule heat, so that the luminous efficiency has to remain at most several percent at the most. In other words, the light emission of a molecule having a relatively high quantum yield is strongly quenched even in the vicinity of a rough metal surface where the enhancement effect can be expected. Therefore, the net enhancement has been limited to molecules with significantly lower quantum yields.

  For this reason, the fluorescence enhancement net obtained by various conventional fluorescence enhancement methods including the fluorescence enhancement device described in Patent Document 1 is not so great, and the luminous efficiency (quantum efficiency) is at most several percent. It was staying at.

Non-Patent Document 1 presents an important inequality for understanding this problem from a more quantitative viewpoint. If the speed at which collective vibration energy of free electrons in a metal fine particle having an arbitrary shape is emitted as light is Γ _r and the speed at which it is lost as Joule heat is Γ _nr , the luminous efficiency of the vibration is φ = Γ _r / (Γ _r + Γ _nr ). In this case, the following equation (1) holds.
Here, V is the volume of the particle, λ is the wavelength of light, ε is the complex permittivity of the metal, and Im is the imaginary part of the complex number. When this is applied to, for example, silver and calculated near the center wavelength (˜600 nm) of the visible portion, the following equation (2) is obtained.

The meaning of the above formula (2) is clear. For example, for typical silver nanoparticles with a particle size of about 20 nm, Γ _r ≦ ˜0.02 × Γ _nr , which means φ ≦ ˜0.02. That is, it is clear in principle that a large effect cannot be expected even when general silver nanoparticles are used as a fluorescence enhancer. On the other hand, for particles having a particle size of about 100 nm or more, the restriction by the above formula (2) is greatly relaxed. However, this is only an inequality and shows that it is advantageous to increase the particle volume as much as possible as a necessary condition for increasing the luminous efficiency φ, while what particle size and form are actually sufficiently large Nothing is suggested as to whether the efficiency φ can be realized. For example, in the case of a true spherical silver particle having a particle size of about 500 nm, the inequality (2) is Γ _r ≦ ˜200 × Γ _n , such as Γ _r = 0.99 and Γ _nr = 0.01 (that is, φ˜1). The present inventor has already confirmed that such a silver particle actually has little action to enhance fluorescence, while allowing the desired situation.

JP 2005-524084 Publication ([0045], Fig. 1) Joel Gersten and one other, "Spectroscopic properties of molecules interacting with small dielectric particles", The Journal of Chemical Physics, 1981, 75, 1139

  As a result of researches to solve the problems of the conventional fluorescence enhancement methods as described above, the present inventor has come up with a fluorescence enhancement element capable of dramatically improving the light emission efficiency.

The fluorescence enhancing element according to the present invention formed as described above,
An optical element that enhances light emission of a fluorescent material carried on the element surface,
A large number of flat metal particles having a cross-sectional particle size of 100 to 800 nm and a thickness of 30 to 50 nm, which are formed independently of each other, are provided on a predetermined substrate.

  In the present invention, silver can be suitably used for the metal particles.

  The fluorescence enhancement element of the present invention greatly reduces the strong quenching action of metals, increases the emission rate of molecules at a close distance of about 1 nm from the surface, and brings about a very great fluorescence enhancement effect. In addition, since this fluorescence enhancement element has a very simple configuration, it is easy to handle and is advantageous in terms of cost.

  When silver is used for the metal particles, the effective light emission quantum yield of the fluorescent molecules supported in a single layer near the surface of the particles is improved up to 50% or more.

  Hereinafter, the fluorescence enhancement element according to the present invention will be described in detail. The fluorescence enhancement element of the present invention includes a short-range fluorescence enhancement element that enhances the fluorescence of a fluorescent substance carried near the surface of the element, and a long-range fluorescence enhancement that enhances the fluorescence of a fluorescent substance that is not directly carried on the element surface. It can be roughly divided into elements. In the present invention, the latter element is also referred to as a “fluorescent element”.

≪Short range fluorescence enhancement≫
FIG. 1 shows a cross-sectional view of a fluorescence enhancement element (short-range fluorescence enhancement element) according to the present invention.

  The substrate 1 is a member for providing flat metal particles on the surface thereof. The material is not particularly limited, and a metal may be used. Further, the shape of the substrate 1 is arbitrary such as a flat type, a curved surface type, and a small spherical type. Further, as will be described later, since the fluorescence enhancing element of the present invention emits fluorescence also on the back side of the element, the material of the substrate 1 may be light transmissive.

  The flat metal particles 2 are metal particles having a cross-sectional particle size of about 100 nm or more, a visible light wavelength (about 800 nm) or less, and a thickness of about 30 to 50 nm, and are independent on the surface of the substrate 1 without contacting each other. It is arranged densely in the state. Although it is desirable that all metal particles have a uniform size and shape, there may be some variation in size and shape (see FIGS. 2d and e).

  As the metal of the flat metal particle 2, silver can be preferably used. The reason why silver can be suitably used in the fluorescence enhancement element of the present invention is also explained from the above formula (2). That is, since silver is the metal with the smallest light absorption, in the case of the above-described particle shape, a large coefficient (˜600) is given in equation (2), and as a result, a value of φ = 0.5 to 1 is allowed. Because. As will be described later, by using silver, a large value of φ = 0.5 or more is obtained in actual measurement. In addition to silver, aluminum, gold, copper, or the like can also be used.

  The flat metal particles 2 can be produced by performing, for example, sputtering processing, resist processing, or etching processing on the surface of the substrate 1.

  When the fluorescence enhancing element of the present invention is used, the fluorescent material 3 is supported on the surface of the fluorescence enhancing element having the above-described configuration, that is, on the surface of the flat metal particles 2. However, when the concentration of the fluorescent material 3 supported on the surface increases, the excitation energy moves between the fluorescent materials, the probability of a non-radiation process increases, and the intensity of the fluorescence decreases (self-quenching effect). Therefore, in order to reduce the self-quenching effect as much as possible, it is desirable that the fluorescent material be supported at the lowest possible concentration (thin).

As shown in FIG. 1A, the fluorescent material 3 can be directly supported on the surface of the tabular metal particle 2, but may be supported at a predetermined distance from the surface of the tabular metal particle 2. . The method for supporting the fluorescent material 3 separately from the surface of the flat metal particles 2 is not particularly limited, and the fluorescent material 3 may not be fixed.
As shown in FIG. 1B, a configuration may be adopted in which spacers 4 are provided on the surface of the flat metal particles 2 and the fluorescent material 3 is supported on the surfaces of the spacers 4. By providing the spacer 4, the fluorescent material 3 can be fixed at a certain distance from the surface of the metal particles. The spacer 4 only needs to be nonconductive, and the configuration thereof is not limited.

In order to obtain the fluorescence enhancement effect, the distance from the surface of the metal particle to the fluorescent substance 3 is desirably 10 nm or less, and when it is about 1 nm, the fluorescence enhancement effect is maximized.
Until now, in order to obtain a fluorescence enhancement effect, the fluorescent material 3 is present at a position at least 3 nm or more, preferably 10 nm or more away from the metal surface, in order to avoid direct energy transfer to the non-light emitting mode in metal as much as possible. However, in the fluorescence enhancing element of the present invention, 10 nm or less, preferably about 1 nm is suitable as described above, and sufficient fluorescence enhancing effect can be obtained even if it is directly supported on the metal surface. Is obtained.

  In the fluorescence enhancing element according to the present invention, when the light absorption rate of the fluorescent substance to be enhanced in fluorescence is small or the fluorescence quantum yield is low, in order to increase the enhancement effect, FIG. As shown, two different fluorescent materials can be supported.

  In this configuration, two types of fluorescent materials are mixedly supported, and each plays the role of donor 3a and acceptor 3b (FIG. 1C). It should be noted that the emission wavelength range of the donor must overlap with the absorption wavelength range of the acceptor, and the larger the overlap, the better. Further, it is desirable that the donor 3a is advantageous in terms of the ratio of the donor 3a to the acceptor 3b (molecular number ratio) in order to increase the light absorption rate as much as possible.

  In the fluorescence enhancing element having this configuration, the donor 3a absorbs the excitation light, and the excitation energy moves to the acceptor 3b very quickly through the mediation of the metal particles. In this way, the light emission of the indirectly-accepted acceptor 3b is enhanced. In addition, this configuration also brings about an effect that the self-quenching effect decreases due to the increase in the distance between the acceptors 3b due to the presence of the donor 3a, and thus the emission enhancement effect of the acceptor 3b is high.

  Theoretically, it has been shown that the energy transfer rate between two types of light-emitting molecules (donor and acceptor) increases by several orders of magnitude near the surface of the metal. In order to avoid this, it is necessary to provide the fluorescent molecules at a distance of several nanometers or more from the surface, and it is difficult to observe even if this surface enhanced energy transfer is used. However, in the fluorescence enhancement element according to the present invention, this limitation is removed, and strong light emission from the acceptor is obtained through enhanced energy transfer from the donor 3a to the acceptor 3b.

≪Long-range fluorescence enhancement≫
FIG. 2 shows a cross-sectional view of a fluorescent element according to the present invention, which is a long-range fluorescence enhancing element.

The basic configuration of the fluorescent element according to the present invention is similar to the configuration of the short-range fluorescence enhancing element described above,
A substrate,
A large number of tabular metal particles having a cross-sectional particle size of 100 to 800 nm and a thickness of 30 to 50 nm, formed independently of each other on the substrate,
A fluorescent material supported in a thin film on the surface of the flat metal particles;
A holding medium which is provided on the fluorescent material and has a thickness of 100 nm or less and in which the same type of fluorescent material as the fluorescent material is dispersed and held.

  That is, the difference between the two is that, in this fluorescent element, the holding medium 5 having a thickness of about several tens to 100 nm is on the substrate 1, that is, on the flat metal particles carrying the fluorescent material 3 on or near the surface. It is a point provided in. In the holding medium 5, the same fluorescent material 3 that is supported on the flat metal particles 2 is dispersed. The holding medium 5 may be anything as long as the fluorescent material 3 can be held in a dispersed state, and may be a polymer or a liquid film as long as it is transparent at the absorption and emission wavelengths of the fluorescent material 3.

  In this configuration, most of the fluorescent material 3 exists in the holding medium 5 and is located at a distance that is not directly enhanced by the tabular metal particles 2, but the fluorescence carried near the surface of the tabular metal particles 2. The enhanced fluorescence of the substance 3 indirectly enhances the fluorescence of the entire fluorescent substance 3 present in the holding medium 5, and as a result, strong emission enhancement occurs.

  According to the present fluorescent element, as long as a significant amount of the fluorescent material 3 is supported at a distance within about 10 nm from the flat metal particles, the range of enhancement can be expanded to a distance of about 100 nm. Become. Therefore, this element can be used for detection of a molecule having such a low luminous efficiency that sufficient detection sensitivity cannot be obtained with a single-layer support, for example. In addition, the fact that the holding medium 5 may be a liquid film has the effect of greatly expanding the target sample for high-sensitivity analysis using enhanced fluorescence.

  In this fluorescent element, as in the case of the short-range fluorescence enhancing element, two types of fluorescent substances that serve as donors and acceptors can be used as the fluorescent substance 3. In this case, a donor and an acceptor are mixed and supported on the surface of the fluorescent element or in the vicinity of the surface, and only the fluorescent substance serving as the acceptor is dispersed in the holding medium 5. Further, a fluorescent material in which a donor and an acceptor are mixed may be dispersed in the holding medium 5.

≪Enhanced lasing≫
In a configuration similar to the above-described long-range fluorescence enhancing element (FIG. 2), the thickness of the holding medium 5 in which the fluorescent material 3 is dispersed is set to 1000 nm or more, and the intensity is enhanced by pumping the element with a pulse laser. Laser emission occurs (details will be described later).

  Hereinafter, in order to confirm the effect of the fluorescence enhancement element according to the present invention, various experiments conducted by the present inventor will be described.

≪Short range fluorescence enhancement≫

[Fabrication of fluorescence enhancement element]
Mica was used as the substrate 1. Mica is suitable as a substrate 1 for a fluorescence enhancing element because it has not only high insulation but also a smooth surface. Mica is light transmissive. Using a DC sputtering method, silver particles were deposited at a relatively slow film deposition rate of 1-2 nm / min on the peeled surface of mica having an atomically smooth surface. The temperature of the mica during the deposition process was adjusted to about 200 to 300 ° C. FIG. 3 is an AFM image showing how the film grows as the deposition time increases (ad in FIG. 3).

  In the initial stage of film deposition, a typical silver island film is formed in which silver nanoparticles of several tens of nm or less are densely packed as shown in FIG. Such a state occurs even under other film forming conditions and methods, but the island films are usually grown into a continuous film state immediately after being fused and united with each other. Under this condition, several adjacent particles grow together but do not become a continuous film, but grow into larger independent particles, each of which is completely separated from other particles. (The state of d after passing through b and c). The deposition process was completed in the state of d in FIG. E in FIG. 3 is a three-dimensional image of d. As observed from the three-dimensional image shown in e of FIG. 3, the particles at this time were tabular, with a width of several hundred nm and an average thickness of about 50 nm.

  In the state of FIG. 3a, the fluorescence enhancement effect was very small. This is in agreement with the result of consideration based on the above-described equation (2). In the state of FIG. 3b, the grains already show a tabular morphology and the grain size reaches close to 50 nm. At this point, the fluorescence enhancement effect appeared remarkably, but not yet the maximum, and the maximum enhancement effect was obtained in the state of d in FIG.

  If the deposition process was not completed in the state of d in FIG. 3 and this was continued, the silver particles began to contact each other, and conductivity appeared in the film. At this time, although a significant fluorescence enhancement effect was still obtained, the effect was greatly reduced. This is not because the shape or size of individual silver particles changes, but because the continuous film is formed. In fact, a completely continuous silver film exhibits such a strong quenching action that it completely quenches the fluorescence of molecules in the vicinity thereof.

  A self-assembled monolayer of linear mercaptocarboxylic acid molecules was used as a spacer for adjusting the distance between the flat metal particles 2 and the fluorescent material 3. When adjusting the thickness of the spacer 4, the monomolecular film having a single layer thickness (the length of a linear mercaptocarboxylic acid molecule) of about 1.4 nm was laminated by passing copper ions. The structure of such a spacer is schematically shown in FIG.

  In addition, as a simple method that can provide spacers of any thickness in a single treatment, the spacer layer is diluted to 1 nm or less by diluting a spin-on-glass (SOG) solution with ethanol and spin-coating it. Therefore, this method was also used as appropriate.

[Supporting fluorescent material]
Rhodamine B dye (FIG. 5) was used as the fluorescent material 3. In order to make the loading amount thin and uniform, a diluted ethanol solution of rhodamine B was spin-coated at 3000 rpm on the surface of the fluorescence enhancement element.

[Measurement of fluorescence]
The fluorescence enhancing element (spacer thickness: 1.4 nm) carrying rhodamine B obtained as described above is irradiated with excitation light having a wavelength of 532 nm from the front side (metal particle side) of the substrate 1 and the resulting fluorescence is measured. did. The shape of the silver particles was the shape shown in FIG. The fluorescence spectrum thus measured is shown by a solid line in FIG. The chain line indicates the fluorescence spectrum when the same loading amount of rhodamine B is supported on the glass surface. The graph on the left side of FIG. 6 is a spectrum when the loading amount of rhodamine B is relatively large and the fluorescence quantum yield on the glass surface is about 1%, and the graph on the right side of FIG. It is a spectrum when the amount is relatively small and the fluorescence quantum yield on the glass surface is about 40%.

  From the graph of FIG. 6, by using the fluorescence enhancement element of the present invention, the fluorescence enhancement rate is about 40 times in the former case (left of FIG. 6), and the fluorescence enhancement rate is 6 times in the latter case (right of FIG. 6). It was confirmed that the degree was reached.

However, since the fluorescence enhancement rate obtained above does not consider the following two points, it does not quantitatively represent the fluorescence enhancement effect (due to the quantum yield enhancement).
1) Absorption rate of excitation light that varies depending on the element (substrate) is not taken into consideration.
2) The angle dependence of fluorescence is not considered.
Therefore, the present inventor conducted an experiment for quantitatively evaluating the fluorescence enhancement rate as follows.

[Consideration of light absorption rate]
In order to take into account the light absorption rate of 1) above, the light absorption rate of the fluorescence enhancement element of the present invention itself (FIG. 7 chain line) and the light absorption rate of the fluorescence enhancement element carrying rhodamine B (solid line of FIG. 7) were measured. did. In the latter, the loading amount of rhodamine B was the same as that shown in the left graph of FIG.

From the chain line in FIG. 7, it was found that the absorptance of the fluorescence enhancing element (metal particles: silver) of the present invention monotonously increased on the short wavelength side, and had a low absorptance of about 20% or less in the region of 500 nm or more. . This is different from a normal silver island film that shows a wide absorption band due to dipole surface plasmon excitation around 500 nm.
After loading Rhodamine B (solid line), the shape is simply the absorption of the silver island film and the dye. Therefore, in the graph of FIG. 7, the difference between the solid line and the chain line is nothing but absorption by rhodamine B. This size was almost five times larger than the value obtained with the same loading amount of rhodamine B by the glass reference substrate.
That is, this absorption amplification effect contributes to the fluorescence enhancement rate in the left graph of FIG. 6, and the enhancement rate of the fluorescence quantum yield is about 10 times.

[Consideration of fluorescence angle dependency]
In order to take into account the fluorescence angle dependency of 2) above, the fluorescence intensity change with the measurement angle was measured in the fluorescence enhancement element carrying rhodamine B (FIG. 8).

  As shown in FIG. 8, a phenomenon was observed in which the fluorescence intensity was stronger on the back side than on the front side of the substrate 1. The property shown in this phenomenon can naturally be observed only when the substrate 1 is light transmissive. However, when the fluorescence enhancing element of the present invention is used for a biosensor or the like, the property of fluorescence is not observed. This means that the degree of freedom of the measurement location is high.

Since the effective light transmittance of the metal particles 2 used in this example is only about 10%, if the light emission originates from the excited rhodamine B itself, it is observed on the back side of the substrate 1. The fluorescence intensity is observed on the front side and should be significantly lower than that. In practice, however, light is not shielded by the layer of metal particles 2 but rather is enhanced.
This is because the enhanced fluorescence is not generated from the fluorescent material 3 (rhodamine B), but the metal particles (silver particles) that have received energy from the excited fluorescent material 3 as shown in the schematic diagram of FIG. ). This is consistent with the qualitative interpretation of the above-described enhanced fluorescence (due to enhanced quantum yield).

  Based on the above points, the inventor of the present application quantitatively evaluates the luminous efficiency of the silver particles receiving energy from the excited rhodamine B, taking into account the above-mentioned light absorption rate and fluorescence angle dependency, and observation. The net fluorescence quantum yield for the resulting fluorescence was determined as a function of dye (rhodamine B) loading. FIG. 10 shows the result.

  From the graph of FIG. 9, although the quantum yield is relatively low due to the self-quenching effect in the region where the amount of rhodamine B supported is large, the quantum yield of 10% or more in the region of 1% or less on the glass reference substrate. The rate is obtained. As the load of rhodamine B decreased, the quantum yield further increased, and showed a value of 50% or more in the limit of the low load. As described above, equation (2) for silver particles allows such a large luminous efficiency, but does not guarantee it. This experiment demonstrated that silver particles actually have such a large luminous efficiency.

[Consideration of spacer thickness]
Next, the relationship between the spacer thickness and the fluorescence quantum yield was examined by changing the length of the spacer (FIG. 11). The loading amount of rhodamine B was about 5 × 10 ¹³ / cm ² . From this result,
1. A significant fluorescence enhancement effect can be obtained even when rhodamine B is directly supported on the silver surface without using a spacer.
2. The fluorescence enhancement effect increases rapidly as the spacer thickness increases within a close range of 1 nm or less, and becomes maximum at a thickness of about 1 nm.
3. The fluorescence enhancement effect is observed up to a thickness of about 10 nm.
The three points became clear.

[Fluorescence enhancement by donor / acceptor]
Rhodamine 110 dye (FIG. 12A) is used as the donor fluorescent substance (3a in FIG. 1C), and rhodamine B dye (FIG. 5) or basic fuchsin is used as the acceptor fluorescent substance (3b in FIG. 1C). A dye (FIG. 12B) was used. Both mixed dilute ethanol solutions were spin-coated at 3000 rpm on the surface of the fluorescence enhancement element.

  FIG. 13 shows a graph showing the dependence of the fluorescence spectrum on the spacer thickness when the ratio of the number of donor to acceptor molecules is 2: 1 and rhodamine B dye is used as the acceptor. The emission of the acceptor that gains energy from the donor is dominant under all conditions, but its intensity is maximum at a close distance of about 1 nm.

  Next, FIG. 14 shows the fluorescence spectrum of the acceptor when rhodamine 110 dye is used as the donor and fuchsin dye is used as the acceptor and both are mixed and supported at a ratio of donor: acceptor = 2: 1. FIG. 14 also shows the fluorescence spectrum of the donor when only the donor is supported for comparison. The acceptor fuchsin dye is a typical dye with a very low fluorescence quantum yield (1% or less). In the apparatus used by the present inventor, it is possible to observe fluorescence when only the fuchsin dye is adsorbed on the glass surface. could not. Further, when the fuchsin dye was supported on the surface of the silver particle in the form as shown in FIGS. 1A and 1B, the fluorescence was greatly enhanced and became observable, but the intensity was still insufficient. there were. However, in this configuration, as shown in the graph of FIG. 14, the fluorescence of the fuchsin dye is observed with an integrated intensity comparable to the fluorescence intensity when the donor is supported alone, and the effectiveness of the fluorescence enhancement method of this configuration is confirmed. confirmed.

≪Long-range fluorescence enhancement≫
For the basis of the fluorescent element that is a long-range fluorescence enhancing element, a fluorescence enhancing element prepared by the same method as the short-range fluorescence enhancing element described above was used.

[Supporting fluorescent material]
Using a fuchsin dye (FIG. 12B) as a fluorescent substance, a solution obtained by dissolving this in a polyvinyl alcohol (PVA) aqueous solution was spin-coated on the surface of the fluorescence enhancement element at 3000 rpm. At this time, due to the interaction between the amino group of the fuchsin dye and the carboxyl group on the spacer surface, a relatively high density fuchsin monolayer is automatically supported on the spacer surface (distance where the direct enhancement effect is strongest), and the fuchsin dye Most of the remaining was dispersed in the polymer layer (thickness: about 100 nm). Note that the fluorescence quantum yield of the fuchsin dye retained in the polymer medium increases to several tens of percent due to the restriction of the degree of freedom of molecular motion.

[Measurement of fluorescence]
A spectrum A shown in FIG. 15 is a fluorescence spectrum at this time, and a compared spectrum B is obtained in the absence of a spacer, that is, in a state where there is almost no fluorescent substance at a distance where direct enhancement is strongest. . Most of the fluorescent substances A and B are dispersed in a polymer medium that is not directly enhanced, and the observed fluorescence intensity should be essentially the same, but the actual intensity of A is 3 It is more than doubled. This indicates that the enhanced fluorescence of the fluorescent substance present at a short distance from the surface of the silver particle is a result of indirectly enhancing the light emission from the thick polymer layer that is not directly enhanced.

≪Enhanced lasing≫

[Supporting fluorescent material]
A rhodamine B dye was used as a fluorescent substance, and a solution obtained by dissolving this in a polyvinyl alcohol (PVA) aqueous solution was applied thickly (several μm or more) on the surface of the fluorescence enhancement element (short-range fluorescence enhancement element).

[Confirmation of enhanced lasing]
The sample pulse YAG laser (pulse width ～5Ns, wavelength 532 nm) was irradiated with, when the thickness of the spacer is 2nm or less, or when not provided at all spacers, dyes dispersed polymer by the number mJ / cm ² about excitation energy Strong lasing occurred from the layer, and a strong and sharp emission spectrum (laser emission) as shown in FIG. 16A was obtained. FIG. 16B shows an emission spectrum when the thickness of the spacer is 3 nm or more. With this slight difference, lasing is almost lost. This can be interpreted as a result of avalanche amplification of the enhanced fluorescence of a very small amount of the fluorescent substance existing within a distance of several nanometers from the surface of the silver particle.

  The fluorescence enhancing element according to the present invention can be directly applied to, for example, a selective biosensor or bioprobe using a molecular recognition reaction of a biomolecule. Further, the long-distance enhancement effect and enhancement lasing of the fluorescent element according to the present invention can be effectively applied to the improvement of the light emission efficiency of the organic EL element and the development of an organic laser.

  Although the fluorescence enhancement element, the fluorescence element, and the fluorescence enhancement method according to the present invention have been described above, it goes without saying that the use is not limited to the above-described ones, and appropriate modifications and corrections are made within the spirit of the present invention. Obviously it may be.

In order to obtain the fluorescence enhancement effect, the flat metal particles according to the present invention do not necessarily have to be arranged on the substrate, and can be used in various forms as fluorescence enhancement particles as long as they can be arranged in the vicinity of the fluorescent substance. Is possible. For example, it is possible to easily enhance the fluorescence of the fluorescent material by uniformly dispersing the flat metal particles in the medium containing the fluorescent material.

FIG. 4 is a cross-sectional view of the fluorescence enhancing element according to the present invention when (A) no spacer is provided, (B) when a spacer is provided, and (C) two types of fluorescent substances are carried. Sectional drawing of the fluorescent element which concerns on this invention. An AFM image showing the formation process of flat metal particles. The schematic diagram of an example of a spacer. Chemical structure of rhodamine B. The fluorescence spectrum at the time of carrying | supporting rhodamine B on the fluorescence enhancement element (solid line) and glass surface (chain line) of this invention. The absorption spectrum at the time of carrying | supporting the rhodamine B on the fluorescence enhancement element (solid line) and glass surface (chain line) of this invention. The graph which shows the change of the fluorescence intensity by a measurement angle. The schematic diagram which shows that the enhanced fluorescence has arisen from the metal particle. The graph which shows the change of the fluorescence quantum yield by the loading amount of rhodamine B. The graph which shows the relationship between the thickness of a spacer, and a fluorescence quantum yield. (A) Chemical structural formula of rhodamine 110 dye, (B) fuchsin dye. The graph which shows the spacer thickness dependence of the fluorescence intensity of a donor and an acceptor. The graph which shows the fluorescence spectrum of an acceptor at the time of carrying | supporting the fluorescence spectrum of only a donor, and a donor and an acceptor. (A) A graph showing long-range fluorescence enhancement when a spacer is present and (B) when no spacer is present. 6 is a graph showing enhanced lasing when the spacer thickness is (A) 2 nm or less and (B) 3 nm or more.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Flat metal particle 3 ... Fluorescent substance 3a ... Donor 3b ... Acceptor 4 ... Spacer 5 ... Holding medium

Claims (11)

An optical element that enhances light emission of a fluorescent material carried on the element surface,
A plurality of flat metal particles formed independently of each other and having a cross-sectional particle size of 100 to 800 nm and a thickness of 30 to 50 nm are provided on a predetermined substrate,
The surface of said tabular metal particles have a spacer bearing a fluorescent material thereon,
The fluorescence enhancing element, wherein the spacer has a thickness of 10 nm or less .   The fluorescence enhancement element according to claim 1, wherein the flat metal particles are made of silver. A fluorescent element that enhances light emission of a fluorescent substance,
A substrate,
A large number of tabular metal particles having a cross-sectional particle size of 100 to 800 nm and a thickness of 30 to 50 nm, formed independently of each other on the substrate,
A fluorescent material supported in a thin film on the surface of the flat metal particles;
A holding medium which is provided on the fluorescent material and has a thickness of 100 nm or less and holds the same type of fluorescent material as the fluorescent material dispersed therein;
A fluorescent element comprising: The fluorescent element according to claim 3 , wherein the flat metal particles are made of silver. The fluorescent element according to claim 3 or 4 , wherein a spacer is provided on a surface of the flat metal particle, and a fluorescent material supported in a thin film shape is supported on the spacer. The fluorescent element according to claim 5 , wherein the spacer has a thickness of 10 nm or less. 10 nm from the surface of the plate-like metal particles in a fluorescence enhancing element formed independently of each other and having a large number of plate-like metal particles having a cross-sectional particle size of 100 to 800 nm and a thickness of 30 to 50 nm on a predetermined substrate. A fluorescence enhancement method characterized in that a fluorescent substance is carried at positions separated by the following distance and enhanced emission is obtained by irradiating predetermined excitation light. The surface of a fluorescence enhancing element formed by a large number of flat metal particles having a cross-sectional particle size of 100 to 800 nm and a thickness of 30 to 50 nm formed independently of each other on a predetermined substrate, or the surface of the flat metal particles dispersed with supporting the fluorescent substance into a thin film at a position away by a distance of a certain, provided on the fluorescent substance, the fluorescent substance the same type and the fluorescent substance inside the holding medium thickness is 100nm or less from A fluorescence enhancement method characterized in that enhanced fluorescence is obtained by irradiating a predetermined excitation light to a fluorescent element that is held. Claims, characterized in that to the surface or the flat metal thin film on the donor and mixing carrying two different fluorescent substances responsible acceptor spaced a distance of a certain from the surface of the particles of the fluorescence enhancement element Item 9. The fluorescence enhancement method according to Item 7 or 8 . The fluorescence enhancement method according to claim 9 , wherein a larger amount of the fluorescent substance that plays the role of the donor is supported than the fluorescent substance that plays the role of the acceptor. Formed independently of one another, cross-sectional diameter is 100 to 800 nm, in fluorescence enhancement device tabular metal particles having a thickness of 30~50nm comprises provided a number on a given substrate, the surface of the tabular metal particles The fluorescent material is supported in a thin film at a position separated by 2 nm or less, and the fluorescent material of the same type as the fluorescent material is dispersed and held inside a holding medium provided on the fluorescent material and having a thickness of 1000 nm or more. A fluorescence enhancement method for generating laser light emission from a fluorescent material by irradiating a fluorescent element with a pulse laser.