JP4970477B2 - Cationic curdlan derivative / gold nanowire composite - Google Patents

Description

  The present invention belongs to the technical field of nanotechnology, and particularly relates to a composite comprising a cationic polysaccharide derivative and gold nanowire, a method for producing the same, and application of the composite.

  In recent years, the characteristic electronic, optical, and magnetic properties of nanostructures of various metals including gold have attracted attention. Since examples of the optical properties of gold depend on the shape and size of the gold nanostructure, research on controlling the shape and size of the structure has been actively conducted. Among them, one-dimensional gold nanostructures such as nanorods, nanowires, and nanoribbons have been studied for application to nanowiring (Non-Patent Documents 1 to 3). So far, template methods, photoreduction methods, seed methods, and electrochemistry Various synthesis methods such as a manual method have been reported (Non-Patent Documents 4 to 6). Among them, the method using a biomolecule as a template is one of the methods that are attracting attention from the viewpoint of ease and green chemistry. Many methods using DNA and proteins as templates have been reported so far, but most of them are one-dimensional arrangements of gold nanoparticles, and from the reduction of gold ions to the formation of structures in one molecule. There is almost no method to bear. In addition, it is difficult to freely impart a function to the surface of the formed gold nanostructure by conventional methods, and establishment of a new method is required.

JP 2005-20532 A JP 2007-290045 A WO 03101972 JP2008-208294

E. Ozbay, Science, 2006, 311, 189. N. R. Jana, Small, 2005, 1, 875. T. Soejima and N. Kimizuka, Chem. Lett., 2005, 34, 1234. W. A. Lopesand H. M. Jaeger, Nature, 2001, 414, 735. D. Aili, K. Enander, J. Rydberg, I. Nesterenko, F. Bjorefors, L. Baltzer and B. Liedberg, J. Am. Chem. Soc., 2008, 130, 5780. T. O. Hutchinson, Y.-P. Liu, C. J. Kiely and M. Brust, Adv. Mater., 2001, 13, 1800. G. Borjihan, G. Zhong, H. Baigude, H. Nakashima and T. Uryu, Polym. Adv. Technol., 14, 326-329 (2003) V. V. Rostovtsev, L. G. Green, V. V. Fokinand K. B. Sharpless, Angew. Chem. Int. Ed., 41, 2596-2599 (2002) T. Hasegawa, M. Umeda, M. Numata, T. Fujisawa, S. Haraguchi, K. Sakurai and S. Shinkai, Chem. Lett., 35, 82-83 (2006). T. Hasegawa, M. Umeda, M. Numata, C. Li, A.-H. Bae, T. Fujisawa, S. Haraguchi, K. Sakurai and S. Shinkai, Carbohydrate Res., 341,35-40 (2006 ) H. -Y.Wu, W.-L.Huang and M. H. Huang, Crystal Grouth & Design, 2007, 7, 831. J. Zhang, J. Du, B. Han, Z. Liu, T. Jiang and Z. Zhang, Angew. Chem. Int. Ed., 2006, 45, 1116. B. Nikoobakht and M. A. El-Sayed, Chem. Mater., 2003, 15, 1957. T. Soejimaand N. Kimiduka, Chem. Lett., 2005, 34, 1234. N. Mackiewicz, G. Surendran, H. Remita, B. Keita, G. Zhang, L. Nadio, A. Hagege, E. Doris and C. Mioskowski, J. Am. Chem. Soc., 2008, 130, 8110 . D. Aili, K. Enander, J. Rydberg, I. Nesterenko, F. Bjorefors, L. Baltzer and B. Liedberg, J. Am. Chem., Soc. 2008, 130, 5780. W. A. Lopes, and H. M. Jaeger, Nature 2001, 414, 735. D. -M. Chen, T. He, D. -F. Cong, Y. -H. Zhang and F. -C. Liu, J. Phys. Chem., A 2001, 105, 3981.

  The present inventors have found that the internal hydrophobic field of schizophyllan (SPG) or curdlan (CUR), which is a kind of polysaccharide β-1,3-glucan, acts as a one-dimensional host and includes various guest molecules. Yes. In recent years, by using gold nanoparticles as SPG guest molecules, one-dimensional arrangement of gold nanoparticles and formation of nanowires by subsequent processing have been achieved (Patent Documents 1 and 2). However, even with this method, it is only possible to arrange pre-made gold nanoparticles, and it cannot be said that it is a template molecule responsible for metal ion reduction, shape control, and surface functionalization.

  The object of the present invention is to provide a new technology that can obtain a composite that is dispersed and stable in an aqueous solution by reducing gold ions to form a nanowire, and that further increases the functionality of the resulting composite. Is to develop.

The present inventors have found that the above object can be achieved by utilizing the characteristics of the cationic curdlan, and have derived the present invention.
Thus, according to the present inventor, a composite comprising a cationic curdlan derivative and gold nanowire is provided.
Furthermore, according to the present invention, there is provided a method for producing the complex, which comprises photoreducing chloroaurate in an aqueous solution under basic conditions in the presence of a cationic curdlan derivative. Is provided.

  Further, the present invention is a method for detecting an anionic compound using the complex as an application of the complex, wherein (1) a step of mixing the complex and the anionic compound in an aqueous solution, and (2) A method comprising drying the obtained solution and measuring its Raman scattering is provided.

  Furthermore, the present invention provides a salt characterized in that an anionic compound is bonded to the complex by electrostatic interaction as a further use of the complex.

The conceptual diagram of this invention. CUR-N ^+, which is a cationic curdlan, is considered to function as an excellent template molecule due to its molecular recognition site and guest inclusion ability. Structure of anionic porphyrin (TPPS). 4 is a TEM image obtained from Sample 1 of Example 1. FIG. A structure in which gold was crystallized randomly was observed. 4 is a TEM image obtained from Sample 2 of Example 1. FIG. A wire-like structure was observed. It was shown that a one-dimensional gold nanostructure using CUR-N ⁺ as a template can be constructed by controlling the pH. An AFM image obtained from Sample 2 of Example 1. A wire-like structure having a uniform height was observed. The TEM image after performing the refinement | purification by centrifugation performed in Example 2. FIG. It became clear that CUR-N ⁺ / Au nanostructures could be isolated by centrifugation. The result of the HRTEM image, electron beam diffraction pattern, and EDX spectrum measurement by HRTEM performed in Example 3. The change of the absorption spectrum of the reaction solution when the light irradiation time performed in Example 4 is changed. Since the absorbance in the near-infrared region increased with the light irradiation time, the formation of gold nanostructures was confirmed. The result of the absorption spectrum measurement of the reaction solution obtained by shortening the light irradiation time obtained in Example 4. Absorption peaks characteristic of gold nanostructures were confirmed. TEM image of the reaction solution obtained by shortening the light irradiation time obtained in Example 4. It was clarified that nano-particles were organized in a one-dimensional shape, and they grew and fused to form a one-dimensional nano-structure. The result of the zeta potential measurement performed in Example 4. It was shown that the surface of the structure was cationic and CUR-N ⁺ was present on the surface of the CUR-N ⁺ / Au nanostructure. The result of the absorption spectrum and CD spectrum measurement of anionic porphyrin (TPPS) in the presence of CUR-N ⁺ / Au nanostructure performed in Example 5. TPPS it was confirmed that interacts with ^{CUR-N +} present in ^CUR-N + / Au nanostructures surface. The result of SERS measurement performed in Example 6. It was confirmed that the Raman scattering of porphyrin was enhanced by the presence of TPPS, which is an anionic porphyrin, on the surface of the CUR-N ⁺ / Au nanostructure. 4 is a TEM image of a gold structure obtained by photoreduction of gold ions in the presence of a CUR-N ⁺ / SWNT complex performed in Comparative Example 1. FIG. No wire-like structure was observed, and only nanoparticles were observed. From this result, it can be said that a hydrophobic space of CUR-N ⁺ is necessary to obtain a one-dimensional gold nanostructure. 4 is a TEM image of a gold nanostructure obtained by photoreduction of gold ions in the presence of PDDA, which is a cationic polymer in Comparative Example 2. FIG. It became clear that a one-dimensional structure was not synthesized even when a cationic polymer other than CUR-N ⁺ was used. 4 is a TEM image of a gold structure obtained by photoreduction of gold ions in the presence of chitosan, which is a reducing polysaccharide, in Comparative Example 3. FIG. A one-dimensional structure was not observed, and it was confirmed that the guest inclusion ability of CUR-N ⁺ is important for obtaining a one-dimensional nanostructure.

  The cationic curdlan derivative constituting the complex of the present invention is one in which various cationic functional groups or atomic groups are introduced into the side chain of the curdlan belonging to the β-1,3-glucan which is a polysaccharide. However, preferred examples include those composed of repeating units represented by the following formula (I).

  In formula (I), R represents a cationic substituent. A preferred example of the cationic substituent is a quaternary ammonium group (for example, trimethylammonium group), but is not limited thereto.

The above cationic curdlan derivatives used in the present invention can be synthesized by combining known reactions. For example, curdlan can be azide (Non-Patent Document 7), and then an ionic substituent can be introduced by the technique of Click Chemistry (Non-Patent Document 8 and Patent Document 3) (Non-Patent Documents 9 and 10).
For example, the details of the synthesis conditions when -N ⁺ (CH ₃ ) ₃ (trimethylammonium) is used as the cationic substituent are described in Patent Document 4, but in brief, the azide curdlan of the raw material is Dissolve in a solvent such as DMSO, add distilled water, propylamine, CuBr ₂ , ascorbic acid, add 1-propynyl-trimethylammonium, and stir at room temperature for 1-10 hours. It is obtained by dialysis and lyophilization.
The molecular weight of curdlan used as a raw material is not particularly limited, but a weight average molecular weight of about 1,000,000 is relatively easily available.

The composite comprising the cationic curdlan derivative of the present invention and the gold nanowire is produced (prepared) by photoreducing chloroaurate in an aqueous solution in the presence of the cationic curdlan derivative as described above. Is done.
Various methods have been proposed in the past for reducing gold ions to obtain a gold nanostructure. For example, first, a reducing agent or an electron source for carrying out the reduction is necessary. Reduction with a reducing agent such as NaBH ₄ or ascorbic acid (Non-patent Document 11), or heat / light as an electron source such as sugars or amines. Reduction is performed by acting ultrasonic waves or the like (Non-patent Document 12). On the other hand, there is a need for a system that allows gold produced by reduction to exist stably in a solution, and many methods using the cationic surfactant Cetyltrimethylammonium Bromide (CTAB) as a stabilizer have been reported (Non-patent Documents 11 and 11). 13). CTAB is said not only as a gold stabilizer but also has an effect of concentrating reduced gold ions (Non-patent Document 13). That is, in order to efficiently construct a gold nanostructure whose shape is controlled by reduction, (1) a molecule responsible for the effect of concentrating gold ions, (2) an electron source that efficiently reduces gold ions, (3) Although it is thought that a stabilizer that allows the reduced gold to exist stably is necessary, there is no method for producing a gold nanostructure by simple reduction in which a single substance plays these roles.

In the present invention, a cationic curdlan derivative (hereinafter sometimes abbreviated as CUR-N ⁺ ) can be expected from (1) a concentration effect of gold ions because many cationic sites are localized, (2) Since it is a saccharide, the hydroxyl group acts as an electron source for reduction (Non-patent Document 13), (3) the reduced gold is included in the interior of the helix (hydrophobic space) and acts as a stabilizer. Therefore, it is considered that it is an optimal compound for reducing gold ions without requiring a reducing agent or a stabilizer additive.

FIG. 1 schematically shows the action of the cationic curdlan derivative and the structure of the resulting complex in the formation of the complex according to the present invention. The composite of the present invention comprising a cationic curdlan derivative (CUR-N ⁺ ) and a gold nanowire has a CUR-N ⁺ functioning as a one-dimensional host, and the gold nanostructure (gold nanowire) is formed in its spiral interior. In addition to being stabilized by inclusion in (hydrophobic space), there is a cationic substituent derived from the side chain of CUR-N ^{+ on} the surface. The width of the gold nanowire is generally about 10 to 200 nm, but preferably about 20 to 50 nm. It has been confirmed by various analytical means that the CUR-N ⁺ / gold nanowire composite according to the present invention exhibits such a structure (see Examples described later).

It is known that gold is produced when chloroaurate is reduced in an aqueous solution. However, when producing a CUR-N ⁺ / gold nanowire composite according to the present invention, pH conditions in the reduction reaction are essential. . In other words, a characteristic gold nanostructure is not formed even if photoreduction of gold ions is performed under acidic or neutral conditions, but only after performing photoreduction under basic conditions, is a wire-like gold nanostructure Is formed. It is understood that this is because the structure of chloroauric acid changes with pH, and the interaction with CUR-N ⁺ changes accordingly.

  In order to produce a cationic curdlan derivative / gold nanowire composite according to the present invention, the solution obtained by photoreduction is usually subjected to an appropriate separation means (preferably centrifugation) to recover the precipitate. To do.

  The operating conditions such as the amount of light and light irradiation time in the photoreduction process, and the number of rotations of the centrifugation in the separation process depend on the concentration (amount) of the raw material, but the desired gold nanowire can be obtained by observation with a TEM or AFM. The operating conditions can be defined to generate (see examples below).

The present invention makes it possible to form a composite including a stable gold nanostructure (gold nanowire) by using CUR-N ⁺ as a template. In that case, CUR-N ⁺ functions as an ideal template molecule that satisfies all of the requirements for reducing gold (gold ions) to obtain gold nanostructures, and this effect can be achieved with other substances. It cannot be obtained even if it is tried as a template (see the comparative example below).

Complexes of the present invention comprising a cationic curdlan derivatives and gold nanowires are the cationic exist cationic substituent on its surface, usually in water Cl ^- Medium with monoatomic anion such as It has been summed up. However, it is conceivable to replace the anion with a more complex anionic compound having a higher function. In fact, it has been found that when the complex of the present invention is mixed with a specific anionic compound and subjected to Raman scattering measurement, it exhibits SERS (surface enhanced Raman scattering). Thus, according to the present invention, the step of mixing the complex of the present invention and an anionic compound (specifically, a sample that may contain an anionic compound) in an aqueous solution, and drying the resulting solution And a method for detecting an anionic compound comprising the step of measuring Raman scattering. The anionic compound to be detected is theoretically possible as long as it has Raman scattering, but examples of particularly preferred anionic compounds include cyanine dye compounds and porphyrin compounds. Specific examples include tetrakis (4-sulfonatophenyl) porphyrin (TPPS).

SERS is a very sensitive sensing method, but it is difficult to detect impurities present in the system because of the high sensitivity. However, in the method for detecting an anionic compound according to the present invention, only CUR-N ⁺ is used without using an additive, and only the target anionic compound such as TPPS can be detected with high sensitivity.

  Furthermore, according to the present invention, as another viewpoint, an anionic compound is bound to the cationic curdlan derivative / gold nanowire composite of the present invention as detected by the above detection method by electrostatic interaction. The salt comprising Such a salt is expected to be useful as an element that exhibits a function derived from an anionic compound by binding an anionic compound having a high function to the surface of the cationic complex of the present invention. The

For example, TPPS is considered as a model body for photosynthesis, and uses such as a light collecting antenna and a light response (sensing) element are expected. In order to exert these functions, it is necessary to strictly control the association state of porphyrin molecules. The fact that SERS was confirmed by reacting the complex of the present invention with TPPS was understood that the association state of TPPS on the surface of the complex was strictly controlled and sensed (see Examples below), Applications to light collection antennas and light response elements are expected. Like the porphyrin compound, the cyanine dye is known to have photoresponsiveness, and as a salt bound to the CUR-N ⁺ / gold nanowire composite of the present invention by electrostatic interaction, its photoresponsive function Applications are expected as materials.

Hereinafter, details of the present invention will be described by way of examples.
[Example 1]
(PH dependence in photoreduction of gold ion by CUR-N ⁺ )
NaOH aqueous solution (1.0 M) was added to HAuCl ₄ aqueous solution (40 mM) to prepare pH values of 3.4, 6.8 and 10.3. Next, according to Table 1, HAUCl4 aqueous solution and CUR-N ⁺ [wherein R in formula (I) is a methylammonium group] aqueous solution (5 mg / mL) are mixed and irradiated with a high pressure mercury lamp (USHIO Optical Modulex, 100W). Photoreduction of gold ions in samples 1 to 3 having different pHs (light quantity: 15 mW, total light, 1 h) was performed. As a result, only sample 3 having a pH of 10.3 changed from pale yellow to black-green, and the reduction from Au (III) to Au (0) proceeded. The aggregates of Samples 1 and 3 were collected and washed by centrifugation (2000 rpm, 10 min). The aggregate obtained from Sample 2 has a metallic luster, and it is considered that bulk gold was formed. On the other hand, the aggregate obtained from Sample 3 was blackish green. Each obtained aggregate was redispersed in distilled water, and TEM and AFM observations were performed.

As a result of TEM observation, in addition to the large aggregates of several tens of μm or more, a large number of hexagonal structures in which gold crystal was grown were observed from Sample 2 (FIG. 3). On the other hand, a large number of wire-like structures were observed from sample 3, although the width varied from about 10 to 100 nm (FIG. 4). When the wire-like image was examined in detail, a very thin contrast was confirmed around the strong contrast that seems to be gold. In addition, a structure having a height of about 10 nm is also confirmed from AFM observation (FIG. 5), and it is understood that the structure obtained from this also has a wire shape.
As a reference experiment, photoreduction of an aqueous solution of HAuCl ₄ (pH 10.3) not containing CUR-N ⁺ was performed, but almost no reduction of gold ions was confirmed. From this, it is considered that the reduction reaction of gold ions progressed using CUR-N ⁺ as an electron source. Gold ions are mostly present in the state of Au (OH) ₄ ⁻ in an aqueous solution at pH 10.3, and are said to be more likely to interact with cations than AuCl ₄ ⁻ (Non-patent Document 14). For this reason, it is considered that the concentration effect by CUR-N ⁺ is enhanced and the reduction is promoted.

[Example 2]
(Separation of structures by centrifugation)
From the examples, it was shown that a wire-like gold nanostructure was constructed by CUR-N ⁺ . However, even under conditions where the structure was confirmed with good reproducibility, the structures present in the solution varied in width from several tens of nm to several hundreds of nm. Therefore, an attempt was made to separate the size of the structure by centrifugation. HAuCl ₄ aqueous solution (40 mM, pH 10.4, 150 μL), distilled water (300 μL), CUR-N ⁺ aqueous solution (5 mg / mL, 150 μL) were mixed in this order, and photoreduction of Au ions (light amount: 15 mW, water filter, 1 h) ) The obtained solution was subjected to centrifugation at 500 rpm, 1000 rpm, and 3000 rpm (both for 10 min) in order, and a precipitate 500, a precipitate 1000, and a precipitate 3000 corresponding to the respective rotation speeds were collected. Each precipitate was redispersed in distilled water and observed by TEM.
As a result of TEM observation, a large number of large structures close to a sheet shape rather than a wire shape or aggregates thereof were observed from the precipitate 500 (FIG. 6A). In addition, a wire-like structure having a width of about 80 nm to 200 nm or an aggregate thereof was confirmed from the precipitate 1000 (FIG. 6B). On the other hand, a large number of wire-like gold nanostructures having a width of 20-50 nm were observed from the precipitate 3000, and almost no large aggregates were confirmed (FIG. 6C).

Example 3
(Structural analysis of photoreduction products by high-resolution TEM observation)
The solution was mixed under the same conditions as in Example 2, and Au ion photoreduction (light amount: 15 mW, water filter, 1 h) was performed. The target product was collected and washed by centrifugation (2000 G, 10 min), redispersed in distilled water, and subjected to HRTEM observation and EDX spectrum measurement. As a result (FIG. 7), lattice stripes having different orientations were observed from one structure. This indicates that the gold nanostructure is formed of a plurality of nanoparticles. Moreover, when the electron beam diffraction measurement of the gold nanostructure was performed, the scattering pattern attributed to the (111) plane, the (200) plane, the (220) plane, the (311) plane, and the (420) plane was confirmed. It was. This is a result showing that the gold nanowire is formed of a large number of nanoparticles, which is consistent with the result of HRTEM observation. Furthermore, a thin layer having a thickness of about 1-2 nm was observed on the side surface of the wire-like gold nanostructure. Further, when EDS spectrum measurement was performed on this region, in addition to the peak indicating the presence of Au, peaks attributed to C, N, and O were confirmed, and CUR-N ⁺ was present in the structure. Was recognized. As a result of EDX line analysis of this structure, it was confirmed that N atoms and O atoms were present more on the side surface than the central portion, and CUR-N ⁺ was found to exist on the surface of the structure.

Example 4
(Influence of irradiation time in photoreduction)
The solution was mixed under the same conditions as in the sample of Example 2, and a part of the solution was taken in an absorption cell having an optical path length of 1 mm and irradiated with light. Absorption spectra were measured before light irradiation, 1 minute, 2 minutes, 4 minutes, 6 minutes, 10 minutes and 15 minutes after light irradiation. The results are shown in FIG.
The whole solution turned black-green after 2 minutes of light irradiation and became darker with the light irradiation time. Aggregation was not confirmed visually until 10 minutes after irradiation with light, but aggregates were confirmed visually after 15 minutes. As a result of the absorption spectrum measurement, broad absorption was confirmed in the near infrared region from the sample after 2 minutes of light irradiation. It is considered as surface plasmon absorption derived from gold nanostructures. The peak is broad because the structure is not uniform or due to scattering by the structure. The absorption in the near-infrared region increased with the lapse of light irradiation time, suggesting the growth of the structure.

Based on the above results, a sample with a light irradiation time of 10 minutes was prepared and examined in detail. A solution was prepared so that the same conditions as in Example 2 were obtained, and gold ions were photoreduced (light amount: 15 mW, water filter, 10 min). The resulting black-green solution was centrifuged (1000 rpm, 10 min) to obtain a black precipitate A. Since the supernatant solution was light green and transparent, when it was further centrifuged (3000 rpm, 10 min), the supernatant became light yellow and transparent, and the precipitate B was recovered. When the precipitates A and B were sufficiently washed by centrifugation and redispersed in distilled water, a light green transparent solution and a light blue transparent solution were obtained, respectively. Absorption spectrum measurement, DLS measurement, zeta potential measurement, and TEM observation of each aqueous dispersion were performed for detailed examination.
As a result of the absorption spectrum measurement, although a slight shoulder was confirmed around 650 nm and 1050 nm from the aqueous dispersion of precipitate A, no clear peak was confirmed. On the other hand, absorption having a maximum absorption wavelength of 598 nm and 1098 nm was confirmed from the aqueous dispersion of the precipitate B (FIG. 9). The former indicates the association of nanoparticles (Non-patent Document 15), and the latter indicates the formation of a gold nanostructure with a high axial ratio (Non-Patent Document 16).

Subsequently, when TEM observation of each dispersion aqueous solution was performed, as shown in FIG. 10 (right), many structures such as gold nanoparticles having a diameter of about 2 nm were organized from the dispersion aqueous solution of the precipitate B. Observed. The width | variety of the structure | tissue is about 50-100 nm, and corresponded with the value of the wire-like gold nanostructure observed so far. This result is consistent with the result of the absorption spectrum measurement.
On the other hand, a wire-like gold nanostructure was confirmed from the dispersed aqueous solution of the precipitate A, and a part where nanoparticles having a diameter of about 5 nm were densely organized was also observed. That is, the observed wire-like gold nanostructure is considered to be formed by closely gathering and fusing small gold nanoparticles (Non-patent Document 17). This result is consistent with the result of HRTEM observation.
Moreover, the absorption considered to originate in CUR-N ⁺ at 400 nm or less was confirmed. If CUR-N ⁺ is present independently, it usually does not fall off by centrifugation at about 3000 rpm. That is, it was suggested that CUR-N ⁺ was present in the recovered structure.

Furthermore, DLS measurement and zeta potential measurement of each dispersion aqueous solution were performed. As a result of the DLS measurement, the precipitate A-dispersed aqueous solution showed the presence of a structure having a hydrodynamic radius of about 1100 nm (intensity). On the other hand, a signal (intensity) having peak tops at about 140 nm and about 1000 nm was confirmed from the dispersed aqueous solution of the precipitate. In other words, it was suggested that a structure of gold nanoparticles as shown in FIG. 9 was formed in the solution although there was a somewhat small structure. This is consistent with the result of the absorption spectrum measurement. In addition, as a result of the zeta potential measurement (FIG. 11), a value of +16.3 to +25.8 mV was obtained from both the aqueous dispersions of precipitates A and B, and the surface of the structure or tissue existing in the solution was a cation. It was suggested that it is sex.
Based on the above results, the observed wire-like gold nanostructures are not grown anisotropically using gold nanoparticles as seeds, but gold nanoparticles with a diameter of several nanometers are organized and fused. It is thought that it is formed by doing. This is considered to be due to the concentration effect of gold ions by CUR-N ⁺ and the guest inclusion ability.

Example 5
(Interaction of CUR-N ⁺ / Au nanostructure and anionic dye)
From the above examples, it was clarified that CUR-N ⁺ exists on the surface of the CUR-N ⁺ / Au nanostructure. Taking advantage of this feature, an attempt was made to try to adsorb an anionic dye on the surface of the CUR-N ⁺ / Au nanostructure by electrostatic interaction. This time, protonated tetrakis (4-sulfonatophenyl) porphyrin (H ₄ TPPS ²⁻ ), which has been attracting attention as a photosynthesis model, was used as an anionic dye.
Gold ions were photoreduced with CUR-N ⁺ under the same conditions as in Example 2. After light irradiation for 1 hour, only the gold nanostructure was collected and washed by centrifugation (3000 rpm, 2times). It was redispersed in distilled water (200 μL) to give a CUR-N + / Au aqueous solution.
According to Table 2, the sample tube was mixed with H ₄ TPPS ^2- water solution, AcOH / AcONa buffer solution (pH 3.4), distilled water and CUR-N ⁺ / Au solution in order, and absorption and CD spectrum measurements were performed.

As a result of the absorption spectrum measurement (FIG. 12), a peak derived from the J-associated species of H ₄ TPPS ² appeared by adding the CUR-N ⁺ / Au aqueous solution. Further, a CD signal having a maximum absorption wavelength derived from the J-associated species as a zero point was also confirmed, and an interaction between CUR-N ⁺ and H ₄ TPPS ^2- was confirmed.

Example 6
(Surface enhanced Raman scattering measurement)
From Example 5, it was confirmed that CUR-N ⁺ / Au nanostructures and H ₄ TPPS ²⁻ interacted with each other to promote the formation of J aggregates of H ₄ TPPS ²⁻ . On the gold nanostructure surface, Raman scattering is enhanced by surface plasmon resonance. In this system, H ₄ TPPS ²⁻ is stably adsorbed on the surface of the CUR-N ⁺ / Au nanostructure by electrostatic interaction, so it is expected that highly efficient surface enhanced Raman scattering (SERS) will be observed. (Non-patent Document 18).
H ₄ TPPS ^2- water solution, AcOH / AcONa buffer solution (pH 3.4), distilled water, and CUR-N ⁺ / Au solution were mixed under the same conditions as in sample 103. This solution was cast on a glass substrate and sufficiently dried. As a reference sample, only an H ₄ TPPS ^2- water solution (in pH 3.4 buffer, 1.3 × 10 ⁻³ M) was cast on a glass substrate and sufficiently dried.
As a result of the Raman scattering measurement, no clear signal was confirmed only from H ₄ TPPS ^2- . On the other hand, ^CUR-N + / Au peak nanostructures were from sample addition derived from porphyrin ^{(1550cm -1, 1450cm -1, 1347cm} -1, 1029cm -1) is detected clearly, SERS is confirmed (FIG. 13).

[Comparative Example 1]
(Reference experiment using CUR-N ⁺ / SWNT complex)
From the experiments so far, it has been clarified that the photoreduction of Au ions by CUR-N ⁺ is promoted and a wire-like gold nanostructure is formed. Among them, it has been considered that the hydrophobic space of CUR-N ⁺ plays an important role in the formation of gold nanostructures. Therefore, (1) if CUR-N ^{+ includes a} guest molecule, reduction of Au ions proceeds, or (2) if it proceeds, what structure is formed to determine CUR-N ⁺ / Photoreduction of Au ions using a SWNT (single-walled carbon nanotube) composite was performed.
Each solution was mixed according to Table 3, and Au ion photoreduction (light quantity: 15 mW, water filter, 1 h) was performed. In sample 27, only the CUR-N ⁺ / SWNT complex was added, and in sample 30, CUR-N ⁺ / SWNT complex and CUR-N ⁺ were added.

In sample 27, small aggregates were confirmed as soon as the CUR-N ⁺ / SWNT complex aqueous solution was added to the Au ion aqueous solution. On the other hand, in sample 30, no aggregation was confirmed even after addition of the CUR-N ⁺ / SWNT complex aqueous solution. When each sample was irradiated with light and photoreduction of Au ions was performed, in Sample 27, a lump such that small aggregates gathered after several minutes of light irradiation was redispersed when lightly shaken. In addition, a large aggregate was also confirmed 10 minutes after Sample 30, but this was also redispersed when shaken lightly. After light irradiation for 1 hour, black precipitates were collected and washed by centrifugation. Each recovered material was redispersed in distilled water and observed by TEM.
As a result of TEM observation (FIG. 14), it was confirmed that fine particles having a particle diameter of about 1-2 nm were present on the wire considered to be SWNT from any sample. This is because when gold ions are photoreduced using CUR-N ⁺ , first, gold nanoparticles are formed, and the gold-like gold nanostructure is formed by high-density organization and fusion. This is consistent with the idea that it is formed. When this is enlarged, it seems that the fine particles are arranged along the wire. Further, many wire-like structures observed so far were also observed from the sample 30. However, it was not confirmed that SWNT was involved in these wire-like structures.
From the above results, when Au ions were photoreduced using a CUR-N ⁺ / SWNT complex, a gold nanostructure as observed so far when CUR-N ⁺ was used as in the present invention. The body was not confirmed, and an image in which a large number of gold nanoparticles covered the periphery of SWNT was confirmed. This indicates that the internal space of CUR-N ⁺ plays an important role in forming a wire-like gold nanostructure.

[Comparative Example 2]
(Reference experiment using cationic polymer)
As a CUR-N ⁺ reference compound, poly (diallyldimethylammonium chloride) (PDDA), which is a cationic polymer, was used for photoreduction of Au ions. Samples were prepared according to Table 4, and Au ion photoreduction (light quantity: 15 mW, water filter, 1 h) was performed. The concentration of the PDDA stock solution (2.5 mg / mL) was prepared such that the concentration of the cation site was the same as CUR-N ⁺ (5 mg / mL).

After 10 minutes of light irradiation, all samples remained yellow and transparent, and no significant change was observed. After 20 minutes of light irradiation, the solution became cloudy, and after 40 minutes, yellow precipitates were confirmed in all samples. When precipitates were collected by centrifugation (2000 rpm, 10 min), all the precipitates had a metallic luster, and it was predicted that bulk gold was formed. Moreover, the supernatant was yellow and transparent, suggesting that the reduction did not proceed sufficiently. From this, it is considered that CUR-N ⁺ works as an electron source for photoreduction.
As a result of TEM observation (FIG. 15), large aggregates were confirmed from any of the samples, and a wire-like structure as observed when CUR-N ⁺ was used was not observed. This suggests that the ability to reduce CUR-N ⁺ and its specific hydrophobic space are required to construct a wire-like gold nanostructure.

[Comparative Example 3]
(Reference experiment using chitosan)
Photoreduction of gold ions was attempted using chitosan, which is a polysaccharide having an amine moiety. Chitosan is a polysaccharide in which D-glucosamine has a β1 → 4 bond, and has a linear structure unlike β-1,3-glucan. HAuCl ₄ aqueous solution (40 mM, pH 10.4, 150 μL), distilled water (300 μL) and chitosan aqueous solution (2.5 mg / mL, 150 μL) were mixed in order, and photoreduction of gold ions (light amount: 15 mW, water filter, total light) )
Aggregation was not confirmed even when the chitosan aqueous solution was added. The whole solution turned black after several minutes of light irradiation, suggesting the reduction of gold ions. However, no large aggregates were observed even after 1 hour of light irradiation, and the particles were uniformly dispersed. A part of the structure was recovered by centrifugation (6000 rpm, 30 min). As a result of TEM observation (FIG. 14), a large number of images of agglomeration of spherical structures in which fine particles gathered and various shapes of gold structures were observed, and no wire-like structures were observed. From this, it was clarified that no wire was formed even when a polysaccharide having reducing ability was used. That is, it is considered that a wire-like gold nanostructure is formed by the concentration effect of Au ions by the CUR-N ⁺ cation site or the presence of a hydrophobic space.

According to the present invention, gold nanowires that are attracting attention as a novel material in the field of nanodevices can be produced as a complex with a cationic derivative of curdlan, which is a natural polysaccharide. Furthermore, it can be expected to be applied to a nano-sensing element or the like by electrostatically neutralizing the surface portion of the complex with a functional anion compound.

Claims (2)

A composite comprising a cationic curdlan derivative and gold nanowire , wherein the cationic curdlan derivative is a repeating unit represented by the following formula (I) (wherein R represents a cationic substituent): A composite characterized by comprising.
The composite according to claim 1, wherein the cationic substituent R is a quaternary ammonium group.