JP5154346B2 - Sensor electrodes and sensors - Google Patents

Description

  The present invention relates to a surface treated material. The invention also relates to a method for producing such a surface-treated material, an electrode for a sensor having such a surface-treated material, and a sensor having such an electrode.

  In various sensors such as a molecular sensor, a DNA sensor, and a solution sensor that detect dioxin and bisphenol A, it is required to develop an electrode (detection unit) that exhibits high sensitivity to a detection target.

  A general sensor electrode has a structure for quantitatively detecting a detection target substance by specifically adsorbing the detection target substance on the electrode surface and detecting a change in a minute physical property value (for example, current value) generated thereby. Yes. Therefore, the sensitivity of the sensor greatly depends on the degree of adsorption of the detection target substance on the electrode surface.

On the other hand, it is conventionally known that zinc oxide exhibits a good specific adsorptivity for a specific substance. Therefore, a technique for improving the sensitivity of the sensor by surface-treating the electrode surface with zinc oxide has been reported (Non-Patent Document 1).
Matt Law, Lori E. Greene, Justin C. Johnson, Richard Saykally, Peidong Yang, Nature Materials, vol. 4, "Nanowire dye-sensitized solar cells", June, 2005

  However, as described in Non-Patent Document 1, when the electrode surface is modified with zinc oxide in order to increase the sensitivity of the sensor, the specific adsorptivity to the detection target substance is improved. The adsorptivity of the detection target substance is also improved. Therefore, when such a sensor electrode is used for a sensor, the signal-to-noise ratio S / N ratio of the sensor electrode may be reduced due to undesired adsorption of a non-detection target substance, which may reduce sensitivity. is there.

  In addition, in order to increase the sensitivity of the sensor, for example, by installing a porous film of zinc oxide as described above on the surface to increase the surface area of the sensor electrode, due to the electric resistance of the film itself, As a result, the electrical resistance increases, which causes a problem that proper current detection cannot be performed when a detection target is detected.

  The present invention has been made in view of such a background, and provides a material that can detect an appropriate current when used as an electrode of a sensor, has a high S / N ratio, and provides high sensitivity. For the purpose. Moreover, it aims at providing the manufacturing method of such a material.

In the present invention,
A substrate,
A tin oxide nanocrystal placed on the surface of the substrate;
A surface-treated material is provided.

  Here, in the material of the present invention, the tin oxide nanocrystal may have an average length of 3 nm to 50 nm.

  The material of the present invention may further have a strip-sheet tin oxide crystal on the surface of the substrate.

  Moreover, the material of this invention WHEREIN: The said strip-shaped tin oxide crystal | crystallization may have an average length of 10 nm-1000 nm.

  In the material of the present invention, the substrate may be a transparent substrate.

  In the material of the present invention, the substrate may be a conductive substrate.

  In the material of the present invention, the substrate may be a tin oxide substrate doped with fluorine.

  The present invention also provides an electrode for a sensor comprising a surface-treated material having the aforementioned characteristics.

  The present invention also provides a molecular sensor, DNA sensor, solution sensor or gas sensor having such an electrode.

Furthermore, in the present invention, a method for producing a surface-treated material,
(1) preparing a substrate;
(2) adding a tin compound in the liquid to prepare a solution containing tin ions;
(3) immersing the substrate in a solution containing the tin ions, thereby precipitating tin oxide nanocrystals on the surface of the substrate;
A method for producing a surface-treated material is provided.

  Here, in the manufacturing method according to the present invention, the tin oxide nanocrystal may have an average length of 3 nm to 50 nm.

  In the production method of the present invention, in the step (3), a strip-sheet tin oxide crystal may be further deposited on the surface of the substrate.

  In this case, the strip-shaped tin oxide crystals may have an average length of 10 nm to 1000 nm.

  In the manufacturing method of the present invention, the substrate may be a transparent substrate.

  In the manufacturing method of the present invention, the substrate may be a conductive substrate.

  In the production method of the present invention, the substrate may be a tin oxide substrate doped with fluorine.

Further, in the production method of the present invention, the substrate has one treated surface on which tin oxide nanocrystals are deposited, and a non-treated surface opposite to the treated surface,
In the step of (3), the substrate in the solution containing tin ions is arranged so that the liquid surface, the non-treated surface, and the treated surface are in this order from the liquid surface side of the solution containing tin ions. You may arrange | position in the solution containing.

  In the production method of the present invention, the liquid may be water.

In the production method of the present invention, the tin compound may be SnF ₄ (tin fluoride), SnCl ₄ (tin tetrachloride), SnCl ₂ (tin dichloride), SnCl ₂ .2H ₂ O (tin chloride dihydrate). Product), SnCl ₄ .5H ₂ O (tin chloride pentahydrate), SnBr ₂ (tin bromide), SnI ₂ (tin iodide), SnI ₄ (tin iodide), tin acetate, tin oxalate, stearin At least one compound selected from the group consisting of tin oxide, tin sulfate, tin tartrate, tin tetrafluoroborate, tin trifluoromethanesulfonate, and tin metal alkoxide may be included.

  In the present invention, when used as an electrode of a sensor, it is possible to provide a material that can detect an appropriate current, has a high S / N ratio, and can obtain high sensitivity. Moreover, it becomes possible to provide the manufacturing method of such a material.

  Hereinafter, features of the present invention will be described in more detail.

  In general, when increasing the sensitivity of a sensor, the sensor electrode (detection unit) has (i) a high specific adsorptivity to a substance to be detected, and (ii) a structure that increases the number of reaction sites as much as possible. It is necessary to do.

  Of these, for item (i), it is conventionally known that zinc oxide has a high specific adsorptivity with respect to a predetermined substance to be detected. Therefore, a material whose surface is modified with zinc oxide is used. It has been proposed. However, zinc oxide has a feature that it has high adsorptivity not only for detection target substances but also for non-detection target substances. Therefore, when a material having a zinc oxide film on the surface is used for the sensor electrode, both the detection target substance and the non-detection target substance are trapped by the zinc oxide, thereby reducing the S / N ratio. As a result, there may arise a problem that the sensitivity cannot be sufficiently increased.

  On the other hand, for item (ii), a porous coating film made of a material having specific adsorptivity is provided on the surface of the substrate material to increase the surface area of the electrode, thereby increasing the reaction site and improving the sensitivity. It is possible. However, such a porous coating film has a significantly increased electrical resistance, especially when it becomes thicker. Therefore, even if the substrate material is conductive, the electrical resistance of the entire electrode is increased by providing such a coating film. Such an increase in the electric resistance of the electrode has a problem that it leads to a decrease in measurement efficiency of the sensor and a decrease in sensitivity of the sensor.

  On the other hand, the material according to the present invention is characterized in that a large number of tin oxide nanocrystals are provided on the surface of the substrate. Due to such characteristics, both the above-mentioned items (i) and (ii) are satisfied. Therefore, when the material according to the present invention is used for, for example, an electrode of a sensor, an appropriate current can be detected, and the conventional method is used. It is possible to obtain an electrode having significantly higher sensitivity than that of the electrode.

  More specifically, in the present invention, with regard to item (i), the adsorptivity to the non-detection target substance is suppressed by using tin oxide instead of zinc oxide as the substance that captures the detection target substance. . In the experience of the inventors of the present application, tin oxide has a tendency to be somewhat inferior in specific adsorption to the detection target substance as compared with zinc oxide. However, tin oxide has a significantly lower adsorptivity to non-detection target substances than zinc oxide, and still has significance over zinc oxide even in consideration of the above-mentioned drawbacks.

  In addition, the material of the present invention has a high surface area because a large number of nano-level irregularities (generated by the tin oxide nanocrystals) are formed on the surface of the substrate. Therefore, the above item (ii) is satisfied by such a characteristic structure. Further, such unevenness on the surface is not constituted by installing a high electrical resistance material such as an oxide or a semiconductor material as a so-called “film”. That is, in the present invention, the unevenness of the surface is formed by dispersing nano-order crystals of tin oxide over the entire substrate surface, and the tin oxide does not cover the entire substrate surface as a “film”. Not in. Therefore, in this invention, the problem that the electrical resistance of the whole material increases by surface treatment can be suppressed significantly. And by these effects, in this invention, appropriate electric current detection is attained, the measurement efficiency is high, and the material for sensors which has high sensitivity can be provided.

In the present application, it should be noted that “tin oxide” is a term including one or both of SnO and SnO ₂ .

  Hereinafter, the structure of the material according to the present invention will be described in more detail with reference to the drawings. FIG. 1 shows a SEM picture of the material according to the invention. 1, (a) to (c) are surface SEM photographs having different magnifications, and (d) is a cross-sectional SEM photograph of the extreme surface of the material according to the present invention.

  The material according to the invention comprises a substrate 10 and a number of tin oxide nanocrystals placed on the substrate 10. In FIG. 1A, the surface of the substrate 10 is a portion composed of polygonal crystals 15 having relatively uniform dimensions throughout the photograph. In the example of the figure, the dimension of the polygonal crystal 15 is about 100 to 300 nm. Further, as shown in FIGS. 1B and 1C, whitish thread-like substances that appear to be slightly attached to the surface of the polygonal crystals 15 constituting the substrate surface are formed of nano-sized tin oxide. Crystal 30. Although not clear from the direction of the photograph, each of the tin oxide nanocrystals 30 has an elongated plate-like form, and the single length thereof is about 10 to 30 nm.

  As shown in FIG. 1D, a large number of these tin oxide nanocrystals 30 are formed on the surface of a polygonal crystal 15 constituting the surface of the substrate. As a result, a large number of extremely fine irregularities at the nano level are formed on the surface (of the polygonal crystals 15 constituting the surface) of the substrate.

  Here, it should be noted that in the case of the present invention, the tin oxide nanocrystals 30 exist not as a general film form but as a large number of fine precipitates dispersed on the surface of the substrate 10. There is. By such an installation mode of the nanocrystal 30 of tin oxide, the material of the present invention can suppress a significant increase in electric resistance and can significantly increase the surface area of the surface.

  Further, in FIG. 1, a plurality of strip-like precipitates 40 are recognized on the surface of the substrate 10 in addition to the tin oxide nanocrystals 30. The strip-shaped precipitate 40 is made of tin oxide, and also looks like a plate when viewed from different directions. Therefore, hereinafter, this strip-like precipitate 40 will be referred to as a strip-sheet-like tin oxide crystal 40. Depending on the surface treatment conditions, the strip-shaped tin oxide crystal 40 may not be formed.

  As described above, in the present invention, a large amount of nano-level irregularities are formed on the substrate surface by placing tin oxide having a lower adsorptivity to the non-detection target substance than zinc oxide on the substrate surface in a nanocrystal state. be able to. This also significantly increases the surface area of the material surface, suppresses a significant increase in the electrical resistance of the material, enables appropriate current detection, and provides a highly sensitive sensor electrode material.

  Furthermore, tin oxide nanocrystals can be directly nucleated and grown on the substrate surface. Therefore, in the present invention, it is not necessary to interpose a third substance such as a seed layer or an intermediate layer between the substrate and the tin oxide nanocrystal.

  Such a material according to the present invention can be used, for example, for an electrode (detection unit) such as a molecular sensor, a DNA sensor, a solution sensor, and a gas sensor. When the material according to the present invention is used for the electrode of such a sensor, the S / N ratio is high due to the high surface area due to surface irregularities caused by the nanocrystals of tin oxide and the low specific adsorption properties of the tin oxide itself for non-detectable substances. A highly sensitive sensor with a high ratio can be obtained.

  In addition, the material according to the present invention can also be used for gas sensors, dye-sensitized solar cells, filters, catalysts, and the like.

  In the present invention, the substrate on which the tin oxide nanocrystals are placed is not particularly limited, and may be of any material, form and structure. For example, when the material according to the present invention is used for an electrode of a molecular sensor or the like, the substrate needs to be made of a transparent material, but when used for other purposes (for example, when used for a detection part of a gas sensor). The substrate may be composed of an opaque material. Similarly, the substrate may be made of a conductive material or a non-conductive material. For example, the material of the substrate may be glass, FTO (fluorine-doped tin oxide), silicon, indium tin oxide (ITO), or the like. Alternatively, a heat-sensitive material such as a polymer film, paper, or rubber may be used. Speaking of strength, the substrate preferably contains tin oxide. In this case, since tin oxide is contained in both the nanocrystal and the substrate, the adhesion of the nanocrystal to the substrate can be further improved.

  The form of the substrate may be a flat shape, a particle shape, a fiber shape, or the like, or may have another complicated shape. The surface state of the substrate is not particularly limited. The substrate surface may be hydrophilic or hydrophobic, for example.

  In the present invention, the size of the tin oxide nanocrystal 30 is not particularly limited. The average length of the tin oxide nanocrystals 30 may be, for example, in the range of about 1 nm to 100 nm. Similarly, in the present invention, the average length of the strip-shaped tin oxide crystals 40 is not particularly limited. The average length of the strip-shaped tin oxide crystals 40 may be, for example, in the range of about 10 nm to 1000 nm.

  In the present application, the “average length” of the tin oxide nanocrystals 30 was determined as an average of 10 points of the length of the tin oxide nanocrystals 30 having typical dimensions in the SEM photograph. Similarly, the “average length” of the strip-sheet-shaped tin oxide crystals 40 was determined as an average of 10 points of the length of the strip-sheet-shaped tin oxide crystals 40 having typical dimensions in the SEM photograph.

(Method for producing material according to the present invention)
Next, a method for producing a material according to the present invention having the above-described features will be described with reference to FIG. FIG. 2 is a flow diagram illustrating a material manufacturing process according to the present invention.

(1. Substrate)
First, in step S110, a substrate for installing a tin oxide nanocrystal is prepared. As described above, the substrate is not particularly limited, and may be any material, form, or structure. In a normal case, the substrate surface is cleaned by washing with an organic solvent such as acetone or ethanol, ultraviolet irradiation, or the like.

  The substrate may be masked with a masking tape or the like except for the surface treatment region.

(2. Solution)
Next, in step S120, a solution for depositing tin oxide nanocrystals on one substrate is prepared. The solution is preferably an aqueous solution from the viewpoint of ease of handling, but may be a non-aqueous solvent such as an organic solvent as long as tin oxide is precipitated. A hydrothermal reaction can also be used.

Here, an aqueous solution will be described as an example. A tin compound is added to the aqueous solution to prepare a solution containing tin ions. The tin compound may contain any valent tin, and the tin may be divalent or tetravalent. Examples of the tin compound include SnF ₄ (tin fluoride), SnCl ₄ (tin tetrachloride), SnCl ₂ (tin dichloride), SnCl ₂ · 2H ₂ O (tin chloride dihydrate), SnCl ₄ · 5H. ₂ O (tin chloride pentahydrate), SnBr ₂ (tin bromide), SnI ₂ (tin iodide), SnI ₄ (tin iodide), tin acetate, tin oxalate, tin stearate, tin sulfate, tartaric acid Tin metal alkoxides such as tin, tin tetrafluoroborate, tin trifluoromethanesulfonate, and tin methoxide can be used.

  The concentration of tin ions contained in the solution is not particularly limited. The concentration of tin ions may be in the range of 0.1 mM to 100 mM, for example. If the concentration of tin ions is higher than 100 mM, the time for the precipitation reaction is significantly shortened, so that the control becomes relatively difficult. Further, when the tin ion concentration is less than 0.1 mM, the time for the precipitation reaction is significantly increased. However, even if the concentration of tin ions is outside the range of 0.1 mM to 100 mM, there is no significant change in the properties of the resulting tin oxide nanocrystals, and such a concentration may be adopted if necessary. .

(3. Processing)
Next, in step S130, one substrate is immersed in the second solution, and tin oxide nanocrystals are deposited and grown on the substrate. FIG. 3 schematically shows a state where the substrate 10 is immersed in a solution 60 containing tin ions. The substrate 10 has a surface-treated surface 70 that is surface-treated with tin oxide and a non-treated surface 80 on the opposite side.

  Here, when the substrate 10 is immersed in the solution 60, it is preferable to install the substrate 10 so that the surface to be treated 70 of the substrate 10 is so-called “downward”. When the surface-treated surface 70 of the substrate 10 is so-called “upward”, tin oxide floating in the solution after deposition stays on the surface-treated surface 70 of the substrate 10 and interferes with subsequent deposition and growth of tin oxide. Because there is a risk of doing. Note that “downward” means that the surface to be treated 70 of the substrate 10 is disposed in a downward direction in parallel with the liquid surface 90 of the solution 60, as shown in FIG. It should be noted that the state in which the surface 70 is inclined downward with respect to the liquid surface 90 of the solution 60 at an angle other than 90 ° is also included. When the surface-treated surface 70 of the substrate 10 is facing downward, the floating tin oxide does not stay on the surface-treated surface 70 and falls toward the bottom of the solution 60 to form a precipitate.

  The temperature of the solution and the treatment time during the treatment are not particularly limited. However, when the temperature is low, it is necessary to immerse and hold the substrate for a longer time. The processing temperature is, for example, in the range of room temperature to 99 ° C., for example, 90 ° C. Further, the processing time is not particularly limited, but is, for example, in the range of 1 minute to 24 hours, for example, 20 minutes.

  After the immersion treatment, the substrate is taken out of the solution and washed with water. Thereafter, when the masking process is performed, the masking material is removed.

  Through the above steps, a substrate on which tin oxide nanocrystals are deposited can be obtained. The size of the tin oxide nanocrystal varies depending on the processing conditions, and is, for example, about 1 nm to 100 nm. In addition, as described above, the size (full length) of the strip-shaped tin oxide crystals that can be present simultaneously with the tin oxide nanocrystals varies depending on the processing conditions, but is, for example, about 10 nm to 300 nm.

  Thus, in the present invention, high-temperature treatment is not required for the formation of tin oxide nanocrystals. Therefore, there is an advantage that the degree of freedom in selecting the substrate material is widened, and a material that is weak against heat can be used for the substrate.

  Examples will be described below.

(Production of substrate surface-treated with tin oxide)
First, for surface cleaning, an FTO substrate (length 26 mm × width 50 mm × thickness 1.1 mm, 9.3-9.7Ω / □, manufactured by Asahi Glass Co., Ltd.) was irradiated with ultraviolet rays (UV). For UV irradiation, a low-pressure mercury lamp (PL16-110) manufactured by Sen Special Light Source was used. The main wavelengths of light from this light source are 184.9 nm and 253.7 nm. The irradiation time was 10 minutes.

  Note that the contact angle of the FTO surface changes (decreases) depending on the UV irradiation time. For example, the initial FTO substrate surface has a contact angle with water of 96 ° and is a hydrophobic surface, whereas the contact angle becomes 70 ° by 30 seconds of UV irradiation. Further, the contact angles were changed to 54 °, 30 °, 14 ° and 5 ° by UV irradiation for 1 minute, 2 minutes, 3 minutes and 4 minutes, respectively. In the irradiation for 5 minutes or more, the contact angle on the FTO surface showed superhydrophilicity of almost 0 ° below the measurement limit.

  Next, the masking tape was installed in the surface treatment area | region of the FTO board | substrate, and the masking process was performed. Here, among the surfaces that have been subjected to UV irradiation, from the respective sides at both ends of the width of the FTO substrate to the inner region of 14 mm, and the surface side that has not been subjected to UV irradiation, non-surface-treated regions (that is, masking regions) ).

Next, a solution for surface treatment was prepared. The solution was prepared by adding SnF ₂ (mass number 156.71 g, purity 90.0%, manufactured by Wako Pure Chemical Industries, Ltd.) to distilled water at a concentration of 5 mM.

  Next, the FTO substrate masked as described above was completely immersed in the solution so as to have an inclination of about 45 ° with respect to the solution surface. At this time, the FTO substrate was completely immersed in the solution so that the surface treatment region was on the lower side. The temperature of the solution was 90 ° C. The immersion time was 20 minutes.

  Thereafter, the FTO substrate was taken out of the solution and washed with running water. The adhesion between the FTO substrate and the tin oxide nanocrystals was extremely good, and the nanocrystals did not fall off even in the treatment with running water.

  Finally, the masking tape was removed to obtain an FTO substrate in which tin oxide was installed in a predetermined area.

(Evaluation of surface-treated substrate 1: X-ray diffraction measurement)
Next, XRD measurement was performed on the surface-treated FTO substrate. RINT-2100V manufactured by Rigaku Corporation was used as the measuring device. The measurement results are shown in FIG. 2θ = 26.5 °, 33.8 °, 37.9 °, 42.6 °, 51.6 °, 54.6 °, 61.7 °, 65.8 °, 71.0 °, 78.6 Diffraction peaks were observed at °, 80.9 °, 89.5 °, 90.6 ° and 93.0 °. This peak position coincides with the diffraction peak position of tin oxide (SnO and SnO ₂ ). In this example, tin oxide is contained in both the FTO substrate and the nanocrystal, and it is unclear which one the peak obtained in FIG. Therefore, when the surface treatment with tin oxide is performed, the particles that do not adhere to the FTO substrate but fall off and settle in the solution are collected by a centrifuge (model 8920, manufactured by Kubota Corporation). Then, XRD measurement was performed again. The rotational speed of the centrifuge was 4000 rpm, and the centrifugation time was 10 minutes.

FIG. 4 (b) shows the measurement results of the particles thus recovered. Diffraction peaks were observed at 2θ = 18.3 °, 29.9 °, 33.3 °, 37.2 °, 44.0 °, 48.1 °, 50.8 ° and 57.5 °. These peak positions correspond to SnO peaks. In addition, diffraction peaks were also observed at positions of 2θ = 27 °, 34 °, 38 °, 52 °, and 57.5 °. These peak positions correspond to SnO ₂ peaks. Therefore, in this example, it is expected that nanocrystals containing both SnO and SnO ₂ were obtained.

The diffraction peak of SnO ₂ was broader than the diffraction peak of SnO. From this, it is considered that the SnO ₂ precipitate has a smaller crystallite size and lower crystallinity than the SnO precipitate.

Generally, the crystal size d is expressed as follows using the diffraction angle θ, the incident X-ray wavelength λ (1.54051１．５), and the half-value width β (Scherrer's formula):

d = kλ / βcos θ Formula (1)

Here, k is 0.9.

Using this equation (1), the crystallite size in the direction perpendicular to the (200) plane of SnO was found to be d = 24.2 nm (see FIG. 4 (C1)). Similarly, when the crystallite size in the direction perpendicular to the (211) plane of SnO ₂ was obtained, d = 2.9 mm was obtained (see FIG. 4 (C2)). From this, it was found that both the SnO precipitate and the SnO ₂ precipitate were crystalline in this example.

The ratio of the intensity of the (200) diffraction peak of SnO to the (211) diffraction peak of SnO ₂ (height intensity ratio) was 0.537. The ratio of the integrated intensities of both was 4.65. The ratio of the intensity intensity of the diffraction peak and the ratio of the integrated intensity correlate with the abundance of the substance, and these results indicate that the sample contains more SnO ₂ than SnO. .

(Surface treatment substrate evaluation 2: SEM observation results)
FIG. 1 described above shows an SEM photograph of the obtained surface-treated substrate. (A)-(c) is the surface SEM photograph from which magnification differs, (d) is a cross-sectional SEM photograph. For reference, FIG. 5 shows a surface SEM photograph of an FTO substrate not subjected to surface treatment.

  1A to 1D show that tin oxide nanocrystals are uniformly formed on the surface of the FTO substrate. In particular, it can be seen from the center of the photograph in FIG. 5D that irregularities of about 5 to 10 nm are formed on the surface of the FTO due to the nanocrystals of tin oxide. It was also observed that strip sheet-like tin oxide crystals were dispersed on the entire surface of the FTO substrate surface. The strip-shaped tin oxide crystals had a width of 10-20 nm, a length of 100 nm, a thickness of about 5 nm, and an aspect ratio of about 5-10.

FIG. 6 shows a cross-sectional TEM photograph of the surface-treated FTO substrate. In the figure, the FTO substrate looks dark. A flat surface and a polycrystalline surface having a sharp angle are mixed on the surface of the FTO substrate. In addition, nanocrystals with nano-order dimensions are observed on the FTO surface. The crystal was about 10 nm in size and rounded. Moreover, a lattice image was observed in a part of this crystal, and the lattice spacing was about 0.33 nm to 0.37 nm. This was consistent with the interval of the SnO ₂ (110) plane.

(Surface Treatment Substrate Evaluation 3: Optical Property Measurement)
Next, the optical characteristics of the FTO substrate surface-treated with tin oxide were evaluated.

  First, as a result of visual observation of the FTO substrate, the region surface-treated with tin oxide showed the same color and gloss as the region not surface-treated, and the boundary between both regions was unclear. From this, it was found that the surface treatment of tin oxide according to the present invention can be performed without changing the color of the substrate.

  Next, on the surface of the FTO substrate, the transmittance was evaluated in each of the surface-treated region and the non-surface-treated region. For the measurement, a UV-Vis UV-visible spectrophotometer (UV-VIS-NMR V670, manufactured by Jusco) was used. FIG. 7 shows UV-Vis spectra of both surface regions. A solid line is a result in a region surface-treated with tin oxide, and a broken line is a result in a non-surface-treated region. From this figure, it was found that the transmission characteristics of the two were almost the same, and the transmittance of the FTO substrate hardly decreased even when the surface treatment was performed with tin oxide. In particular, since the scattering is sufficiently suppressed in the visible light region, it can be seen that the tin oxide deposited by the surface treatment has a size not larger than the visible light wavelength (that is, 300 nm or less).

  In general, in a dye-sensitized solar cell or a dye-sensitized sensor, a device is driven by photoexcitation, so that a high visible light transmittance is required for an electrode. From the result of FIG. 7, the material formed according to the present invention can be sufficiently used for a device that requires such a high visible light transmittance.

  Next, fluorescence intensity was evaluated by the following method using the obtained surface-treated substrate.

  A polyvinyl chloride (PVC) tape (thickness: 0.1 mm) having a total of nine holes (three pieces × three steps) opened in three steps was installed in the surface treatment region of the FTO substrate treated with tin oxide. FIG. 8 shows a top view of such a substrate. The FTO substrate 105 has a surface-treated area 125 on the center side and unsurface-treated areas 130 on both ends. The tape 110 installed in the surface-treated region 125 has nine holes 120. As shown in FIG. 8, these holes 120 are three in each of an upper stage, an interruption, and a lower stage, and a pitch M = 5 mm. Is provided. Moreover, the pitch N of each step is 5 mm. The diameter of each hole is 3 mm.

  Next, dye-labeled DNA: ssDNA-Cy5 (cy5-DP53-t: Cy5-GCGGCATGAACCTGAGGCCCCATCCT) was dissolved in water to prepare solutions with dye concentrations of 1 μM and 100 nM (hereinafter referred to as A solution and B solution, respectively). ). In addition, a dye-free DNA: ssDNA (lamda-gt10: TTGAGCAAGTTCAGCCTGTGTAG) was dissolved in water to prepare a solution having a DNA concentration of 1 μM (hereinafter referred to as “C solution”).

  The above three types of solutions were collected with a pipette (collected amount: 0.1 ml) and dropped into each hole 120 provided in the tape 110 described above. At this time, the liquid A was dropped into the upper three holes, the liquid B was dropped into the three interrupted holes, and the liquid C was dropped into the lower three holes.

Next, the FTO substrate was air-dried at 95 ° C. for 10 minutes, and then rinsed three times for 15 minutes each using a sodium dodecyl sulfate (SDS, NaC ₁₂ H ₂₅ SO ₄ ) solution. Rinse 3 times with water. Thereafter, the FTO substrate was boiled in pure water for 2 minutes, immersed in absolute ethanol at 4 ° C. for 1 minute, and then dried by air blow.

  The FTO substrate thus obtained was irradiated with a He / Ne laser (Taihuntri scanner, GE Healthcare UK) with excitation light of 633 nm, and the fluorescence characteristics from each hole were evaluated.

  Table 1 shows the intensity of fluorescence obtained from the FTO substrate.

Table 1 also shows the results obtained with an unsurface-treated FTO substrate for comparison. The rightmost column shows the ratio of the fluorescence intensity of the surface-treated FTO substrate to the fluorescence intensity of the non-surface-treated FTO substrate. From this result, it can be seen that 16 times the intensity of fluorescence is detected from the surface-treated FTO substrate that has been dye-adsorbed with the liquid A, compared to the non-surface-treated FTO substrate that has been subjected to the same dye adsorption. It can also be seen that 16 times the intensity of fluorescence is detected from the surface-treated FTO substrate that has been dye-adsorbed with the B liquid, compared to the non-surface-treated FTO substrate that has been subjected to the same dye adsorption. This indicates that the amount of dye adsorbed on the FTO substrate was improved 16 times by the surface treatment with tin oxide. That is, the surface treatment increased the surface area of the FTO substrate, and the dye adsorption amount was improved accordingly.

  In dye-sensitized solar cells and dye-sensitized sensors, high dye adsorption characteristics are required for high efficiency. It can be seen that the material according to the invention can be applied significantly to these devices.

  Next, the photocurrent was evaluated by the following method using the surface-treated FTO substrate obtained as described above.

  The surface-treated FTO substrate was irradiated with 0.7 mW red laser excitation light (wavelength 632 nm) or 97 mW red laser excitation light (wavelength 650 nm), and the resulting photocurrent value was measured.

  Table 2 shows the measurement results.

In Table 2, IPCE means photoelectric conversion efficiency, which is calculated from the following formula:

_{IPCE (%) = 1250I sc (} μA / cm 2) / λ (nm)
/ P _in (W / m ² ) × 100 Formula (2)

Here, I _sc : current density, λ: wavelength, P _in : excitation light irradiation intensity (Nazeeruddin, MK; Kay, A .; Rodicio, I .; Humprybaker, R .; Muller, E .; Liska, P .; Vlachopoulos, N .; Gratzel, M. Journal of the American Chemical Society, 115, 6382-6390 (1993)).

  As shown in this table, 4.0% and 1.5% photoelectric conversion efficiencies are obtained from the surface-treated FTO substrate subjected to dye adsorption with the liquid A and liquid B under the irradiation of 0.7 mW laser. It was. On the other hand, the surface-treated FTO substrate subjected to DNA adsorption with C solution showed a photoelectric conversion efficiency of 0.3%. Similarly, under the irradiation of 97 mW laser, photoelectric conversion efficiencies of 1.1%, 0.3%, and 0.04% were obtained when the liquid A, liquid B, and liquid C were used, respectively.

  In the column of S / N ratio in Table 2, the ratio of the photocurrent value obtained with the A liquid to the photocurrent value obtained with the C liquid, that is, the signal-to-noise ratio is shown. From Table 2, it was found that the signal-to-noise ratio was 14 under the irradiation of 0.7 mW laser, and the signal-to-noise ratio was 29 under the irradiation of 97 mW laser.

  Thus, in the surface treatment substrate according to the present invention, the signal-to-noise ratio is sufficiently large, and it was shown that the material of the present invention can be applied as an electrode for a high-sensitivity sensor.

  Next, a surface-treated FTO substrate was produced in the same manner as in Example 1. However, in this example, the surface treatment was performed by changing the immersion time of the FTO substrate in the solution.

  9 to 10 show surface SEM photographs of FTO substrates that have been surface-treated at different immersion times. 9 (1a) and (1b) are FTO substrates surface-treated with a dipping time of 5 minutes, and FIGS. 9 (2a) and (2b) are FTO substrates surface-treated with a dipping time of 10 minutes. 9 (3a) and (3b) are FTO substrates that have been surface-treated with an immersion time of 20 minutes (same as Example 1), and FIGS. 10 (4a) and (4b) are immersions for 30 minutes. FIGS. 10 (5a) and (5b) are FTO substrates that have been surface-treated with an immersion time of 1 hour, and FIGS. 10 (6a) and (6b) are 2 hours. It is the FTO board | substrate surface-treated by soaking time.

  From these figures, it can be seen that the average length of tin oxide nanocrystals tends to increase with increasing immersion time. That is, the immersion time increased to 5 minutes, 10 minutes, 20 minutes, 30 minutes, 1 hour, and 2 hours, and the average lengths of the tin oxide nanocrystals on the surface of the FTO substrate were 3 nm, 5 nm, 10 nm, 20 nm, and 50 nm, respectively. And grown to 100 nm. Moreover, the average length of the strip-shaped tin oxide crystals also increased, and when the immersion time was 1 hour, the average length grew to about 100 to 150 nm. In addition, when the immersion time was 5 minutes or less, strip-sheet tin oxide crystals were not recognized.

  Next, using each surface-treated FTO substrate produced by changing the immersion time in this way, a fluorescence intensity evaluation test was performed by the method described above.

  FIG. 11 shows the relationship between the average length of tin oxide nanocrystals deposited on the surface-treated FTO substrate and the fluorescence intensity when the liquid A and liquid B were dropped. In addition, since the fluorescence intensity was hardly obtained in the experiment in which the liquid C was dropped, this result is not shown in FIG. It can be seen that the fluorescence intensity increases with an increase in the average length of the nanocrystals regardless of the dye concentration in the solution.

  As a result, the average length of the nanocrystals increases, the fine irregularities on the surface of the FTO substrate become remarkable, and the surface area of the FTO substrate increases. Therefore, the amount of dye adsorbed on the FTO substrate increases, thereby increasing the fluorescence. It shows that the strength is improved.

  Next, the surface treatment FTO substrate produced by changing the immersion time was irradiated with a red laser having an actually measured output value of 0.7 mW (wavelength 632 nm) and 97 mW (wavelength 650 nm), and a photocurrent value generated from the FTO substrate Was measured. The results are shown in FIGS. 12 and 13, respectively. 12 and 13, the horizontal axis indicates the average length of the nanocrystal, and the vertical axis indicates the obtained photocurrent.

  12 and 13, the photocurrent value showed the maximum value in the surface-treated FTO substrate in which the average length of the tin oxide nanocrystals was 10 nm (immersion time: 20 minutes) in any laser irradiation. (Measurement value with liquid A).

  In the above-described measurement of the fluorescence intensity, as shown in FIG. 11, the fluorescence intensity increased as the average length of the tin oxide nanocrystals increased. However, the result of the measurement of the photocurrent value did not agree with this tendency, and as shown in FIGS. 12 and 13, the maximum value was shown when the average length of the tin oxide nanocrystals was 10 nm. This indicates that the photocurrent is not only dependent on the amount of dye adsorbed on the surface-treated FTO substrate, but also greatly influenced by the conductivity of the surface-treated FTO substrate. That is, as the immersion time increases and the average length of tin oxide nanocrystals increases, the amount of dye adsorption increases, but the electrical resistance of the entire material combining the FTO substrate and the nanocrystals increases, resulting in a photocurrent. Seems to be reduced.

  Therefore, when the material of the present invention is applied to an electrode of a sensor such as a molecular sensor, it is considered most effective to install tin oxide having an average nanocrystal length of about 10 nm. However, as shown in FIGS. 12 and 13, even when the average length of the tin oxide nanocrystals is about 3 nm and 50 nm, the absolute value of the photocurrent is sufficiently large, so that the average length is other than 10 nm. It can be said that the surface-treated substrate on which the tin oxide nanocrystal is installed can be sufficiently used as a sensor electrode.

  The present invention can be used for electrodes of, for example, molecular sensors, DNA sensors, solution sensors, and gas sensors. The material according to the present invention can also be used for electrodes, filters, catalysts and the like of dye-sensitized solar cells.

It is an example of the SEM photograph of the material by this invention. It is a flowchart which shows the manufacturing method of the material by this invention. It is the figure which showed typically the state of a board | substrate at the time of immersing a board | substrate in a solution and depositing a tin oxide nanocrystal on the to-be-processed surface. It is the figure which showed the X-ray-diffraction result of the material by this invention. It is the surface SEM photograph of the FTO board | substrate which is not implementing surface treatment. It is a cross-sectional TEM photograph of a surface-treated FTO substrate. It is the figure which showed the UV-Vis spectrum of the surface treatment FTO board | substrate and the non-surface treatment FTO board | substrate. It is a typical top view of the FTO board | substrate with which the tape which has nine holes was installed in the surface treatment area | region. It is the surface SEM photograph of the surface treatment FTO board | substrate obtained when changing immersion time. It is the surface SEM photograph of the surface treatment FTO board | substrate obtained when changing immersion time. It is the graph which showed the relationship between the average length of the nanocrystal of a tin oxide, and fluorescence intensity. It is the graph which showed the relationship between the average length of the nanocrystal of a tin oxide at the time of irradiating a red laser with an output of 0.7 mW, and a photocurrent. It is the graph which showed the relationship between the average length of the nanocrystal of a tin oxide, and a photocurrent at the time of irradiating the red laser of 97 mW output.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Substrate 15 Polygonal crystal constituting substrate surface 30 Tin oxide nanocrystal 40 Strip sheet tin oxide crystal 60 Solution 70 Surface to be treated 80 Non-treated surface 90 Liquid surface 105 FTO substrate 110 Tape 120 Hole 125 Surface treatment region 130 Unsurfaced treatment area.

Claims (8)

An electrode for a sensor having a surface-treated material ,
The surface-treated material is
A substrate,
A tin oxide nanocrystal placed on the surface of the substrate;
Have
The tin oxide nanocrystals are grown on the surface of the substrate directly in the tin ion-containing solution that does not contain a nitrogen component, instead of a core particle. Arranged in the form of objects,
The electrode according to claim 1, wherein the tin oxide nanocrystal has an average length of 3 nm to 50 nm. Wherein the surface treated material, further, the surface of the substrate, the electrode according to claim 1, characterized in that it comprises a strip sheet of tin oxide crystals. The strip sheet of tin oxide crystals electrode according to claim 2, characterized in that it has an average length of 10 nm to 1000 nm. The substrate electrode according to any one of claims 1 to 3, characterized in that a transparent substrate. The substrate electrode according to any one of claims 1 to 4, characterized in that a conductive substrate. The substrate electrode according to any one of claims 1 to 5, characterized in that fluorine is doped tin oxide substrate. The nanocrystals tin oxide electrode according to any one of claims 1 to 6, characterized in that it comprises both SnO and SnO _2. It has an electrode according to any one of claims 1 to 7 ,
A sensor selected from the group consisting of a molecular sensor, a DNA sensor, a solution sensor, and a gas sensor.