Patent ID: 12222309

BEST MODE FOR CARRYING OUT THE INVENTION

[Preliminary Experiment 1]

In this preliminary experiment, conductivity and film formation continuity when a conductive thin film was formed on an insulating substrate having a fine uneven structure formed on a surface were checked.

Au was sputtered to form an Au thin film having a thickness of 5 to 200 nm on the surface of the insulating substrate having the fine uneven structure in which a plurality of bumps schematically illustrated inFIGS.2aand3awere arranged. The results of checking the conduction between two smooth regions separated by the fine uneven structure are shown in Table 1. More specifically, the fine uneven structure formed on the surface of the insulating substrate is configured to include substantially circular columns having a diameter of 10 to 50 nm and a height of 100 to 2000 nm arranged at regular intervals of 50 to 200 nm.

TABLE 1Au thin film thickness (nm)Conduction5Absence20Absence50Absence100Absence150Presence200Presence

When the thickness of the Au thin film was 100 nm or less, there was no conduction, and when the thickness was 150 to 200 nm, there was conduction.FIG.6illustrates a schematic view of an image obtained by observing a cross section of a state in which (a) Au thin films having a thickness of 50 nm and (b) a thickness of 150 nm are formed on the insulating fine uneven structure with an electron microscope (the schematic view was used for improving visibility). It was checked that the Au thin film having a thickness of 50 nm was formed on the tip of each bump forming the fine uneven structure but was discontinuous, and the Au thin film having a thickness of 150 nm was continuously formed over the entire fine uneven structure. This result is consistent with the results of the conductivity test described above.

It has been checked that when an appropriately designed fine uneven structure (for example, the fine uneven structure schematically illustrated inFIG.3a) is formed on one insulating substrate, even when a conductive thin film having a thickness of 5 to 100 nm usually used in producing an electrode substrate is formed, the conductive thin film formed on the upper bottom surface of each bump constituting the fine uneven structure is not connected, and two smooth regions separated by such a fine uneven structure are electrically insulated.

[Preliminary Experiment 2]

In this preliminary experiment, the visibility when a conductive thin film was formed on an insulating substrate having a fine uneven structure formed on a surface were checked.

FIG.7is a photomicrograph of an upper surface in a state where an Au thin film having a thickness of 50 nm is formed on an insulating substrate having fine uneven structure regions schematically illustrated inFIG.3aformed, on a surface of the insulating substrate while leaving a plurality of linear regions with a line/space of about 0.2 mm.

It was visually checked that the plurality of linear regions where the fine uneven structure region was not formed were colored with the color of the formed material, and the fine uneven structure region had a lower light reflectance than that of the linear region and was dark in color.

That is, according to the present disclosure, it has been checked that a fine circuit formed by the fine uneven structure can be visually inspected at a stage of forming the conductive thin film.

Based on the findings obtained in the above preliminary experiment, according to a first aspect of the present disclosure, there is provided an electrode substrate including an insulating substrate having, on a surface thereof, a region where at least one fine uneven structure is formed and a plurality of smooth regions separated by the fine uneven structure; and a conductive thin film formed on an entire at least one surface of the insulating substrate where the fine uneven structure is formed, wherein the conductive thin film formed on the region where the fine uneven structure is formed is discontinuous.

In a more specific aspect, the present disclosure provides a probe for a biosensor, including an insulating substrate having, on a surface thereof, a region where at least one fine uneven structure is formed and a plurality of smooth regions separated by the fine uneven structure; a conductive thin film formed on an entire at least one surface of the insulating substrate where the fine uneven structure is formed; and at least one electrode formed in the smooth region separated by the fine uneven structure, wherein the conductive thin film formed on the region where the fine uneven structure is formed is discontinuous, and each of two or more smooth regions separated by the region where the fine uneven structure is formed is electrically insulated.

The fine uneven structure region includes a plurality of protrusions discontinuous in at least one direction in a top view of the insulating substrate. In one aspect, the plurality of protrusions discontinuous in the at least one direction is formed of a columnar body (substantially circular column or a substantially prismatic column) having a diagonal dimension of 10 to 50 nm and a height of 100 to 2000 nm and disposed at intervals of 50 to 200 nm. In another aspect, a substantial cone or a substantial pyramid having a bottom surface having the same shape as the upper bottom surface or a bottom surface having an area smaller than the upper bottom surface is coupled to the upper bottom surface of each of the protrusions.

As a second aspect of the present disclosure, there is provided a method for producing a probe for a biosensor described above. This producing method includes: a step of forming a conductive thin film of a conductive material selected from carbon, gold, silver, copper, platinum, palladium, or the like on the entire surface of an insulating substrate having, on a surface thereof, a region where at least one fine uneven structure is formed and a plurality of smooth regions separated by the fine uneven structure; and a step of forming an electrode in the plurality of smooth regions separated by the fine uneven structure, wherein the fine uneven structure region includes a plurality of protrusions discontinuous in at least one direction in a surface direction (top view) of the insulating substrate, and the conductive thin film formed on the region where the fine uneven structure is formed is discontinuous. As a result, the conductive thin film formed on the upper bottom surface of one protrusion constituting the fine uneven structure region and the conductive thin film formed on the upper bottom surface of another adjacent protrusion are electrically insulated.

As a third aspect of the present disclosure, there is provided a biosensor including the probe for a biosensor described above.

EXAMPLES

An example in which a probe of an in vivo electrochemical glucose sensor is prepared using the above-described technique for forming a fine uneven structure region in a desired pattern will be described below. However, the technology of the present disclosure is not applied only to a glucose sensor, and is useful for producing all electrode substrates in which it is necessary to form a plurality of electrodes on one insulating base material.

1. Method for Producing Probe for Implantable Biosensor

A method for producing a probe11of an implantable biosensor1according to one embodiment of the present disclosure will be described. The following structure and producing method are one specific example of the present disclosure, and are not limited to the following configuration and producing steps as long as a desired fine uneven structure region having the features of the present disclosure is formed.

Example 1

<Production of Probe>

(1) Preparation of Insulating Substrate

An implantable biosensor1includes a main body10and a probe11, and the probe11is schematically formed in a key shape including a sensing portion inserted into a living body and a terminal portion electrically connected to an internal circuit of the biosensor main body10. The sensing portion is formed thin so as to be inserted into the body, and the terminal portion has a constant size so as to be inserted into the biosensor main body10to form an electrical connection. First, an insulating substrate111is prepared (FIG.8a,FIG.11a). The insulating substrate is not particularly limited as long as it is a material and has a thickness that can be used as a probe to be inserted into a living body, and for example, polyethylene terephthalate (PET) having a thickness of about 200 μm can be used. Here, a polyethylene terephthalate (PET) sheet (LUMIRROR R 20 #188 produced by TORAY INDUSTRIES, INC.; 189 μm thick) was used.

(2) Formation of Fine Uneven Structure Region

An insulating fine uneven structure region112for forming an outer frame for forming the key-shaped probe11is formed on the insulating substrate111, and an insulating fine uneven structure region113for forming an electrode lead for electrically insulating a working electrode lead and a reference electrode lead is formed (FIG.8b,FIG.11b). The insulating fine uneven structure region113for forming an electrode lead is essential, but the insulating fine uneven structure region112for forming an outer frame may not be formed as desired. The fine uneven structure regions112and113are of an insulating type.

Such a fine uneven structure region was formed by a nanoimprinting technique in which hot pressing is performed using a mold on which a corresponding fine uneven structure is formed.

(3) Formation of Conductive Thin Film

The conductive thin film114is formed on the insulating substrate111on which the fine uneven structure region is formed by depositing a conductive material selected from the group consisting of carbon or a metal such as gold, silver, platinum, or palladium by sputtering, vapor deposition, ion plating, or the like. A preferred thickness of the conductive thin film is 5 to 100 nm. In this example, the conductive thin film114having a thickness of 100 nm was formed on the insulating substrate111by direct gold (Au) sputtering (FIG.9c,FIG.11c).

The conductive thin film114is divided into a working electrode lead114aand a reference electrode lead114bdue to the presence of the insulating fine uneven structure region113for forming an electrode lead.

(4) Formation of Insulating Film

On the front side of the insulating substrate111, an insulating film115ahaving an opening is formed by a sputtering method, a screen printing method, or the like at a portion excluding regions used as the working electrode116and the reference electrode117, and a working electrode terminal116aand a reference electrode terminal117afor electrical connection with the main body10(FIG.9d). A preferred thickness of the insulating film is 0.1 to 40 μm. Here, an insulating film having a thickness of 10 to 20 μm was formed by a screen printing method. As a substitute for the insulating film, an insulating film having the same shape as the insulating film115amay be attached.

(5) Formation of Sensing Layer

An aqueous solution of a redox mediator and an aqueous solution of an analyte-responsive enzyme are mixed on the conductive thin film114aof the sensing portion of the probe, which is not covered with the insulating film115a, and the mixed aqueous solution is applied and dried to form a sensing layer116bcontaining at least the redox mediator and the analyte-responsive enzyme (FIG.10e,FIG.11e).

In the present disclosure, the sensing layer may be a multilayer film containing at least a redox mediator and an analyte-responsive enzyme, and formed of a mediator layer containing the redox mediator and an enzyme layer containing the analyte-responsive enzyme by sequentially applying and drying an aqueous solution of the redox mediator and an aqueous solution of the analyte-responsive enzyme. A preferred thickness of the sensing layer is 0.1 to 80 μm.

In addition, in order to improve the conductivity of the sensing layer, conductive particles such as a carbon particle suspension may be applied and dried first before the mixed aqueous solution of the redox mediator and the analyte-responsive enzyme.

In the present disclosure, the “analyte-responsive enzyme” means a biochemical substance capable of specifically catalyzing oxidation or reduction of an analyte. Any biochemical substance may be used as long as it can be used for the sensing purpose of the biosensor. For example, in a case where glucose is used as an analyte, a suitable analyte-responsive enzyme is glucose oxidase (GOx), glucose dehydrogenase (GDH), or the like. The “redox mediator” means an oxidation-reduction substance that mediates electron transfer, and is responsible for transfer of electrons generated by an oxidation-reduction reaction of an analyte in a biosensor. For example, a phenazine derivative and the like are included, but not limited thereto, and any oxidation-reduction substance may be used as long as it can be used for the sensing purpose of a biosensor.

In addition, an example of synthesis of a redox mediator is shown below.

Synthesis Example: Synthesis of Phenazine Derivative Having Carboxyl Group

For example, 5-(4-carboxybutyl)-1-methoxyphenazinium nitrate is synthesized by acting an N-alkylating agent on 1-methoxyphenazine. Furthermore, 5-{[(2,5-dioxopyridin-1-yl) oxy]-5 oxopentyl}-1-methoxyphenazinium nitrate in which N-hydroxysuccinimide is added to the terminal carboxyl group to improve the reactivity of the carboxyl group is synthesized. The corresponding N-alkylating agent can be selected to synthesize a desired N-alkylcarboxyphenazinium salt.

0.6 mg of 5-{[(2,5-dioxopyridin-1-yl) oxy]-5 oxopentyl}-1-methoxyphenazinium nitrate (Ph-C5-Su) obtained in the synthesis example was weighed and dissolved in a 120 μL of 100 mM 2-morpholinoethanesulfonic acid (MES) buffer solution (pH 6.0).

Separately, 5 mg of poly (L-lysine) hydrochloride (Peptide Research Institute Code 3075; M.W.>12000, cut-off by dialysis) was weighed out and dissolved in a 1 mL of 100 mM MES buffer solution (pH 6.0). The two solutions were mixed and reacted at room temperature for 4 hours with stirring.

A reaction solution was subjected to gel filtration chromatography with a PD-10 column (GE Healthcare) using PBS as an elution buffer. The solution after gel filtration was filtrated through a centrifugal ultrafiltration filter (Amicon Ultra-4 30 k; Merck Millipore).

According to the above procedure, a high molecular weight polymer (PLL-05-Ph_1) in which phenazine was covalently bonded to poly (L-lysine) hydrochloride was obtained.

The obtained PLL-05-Ph_1 solution was adjusted to have an absorbance of about 11 at 386 nm with PBS while being measured by a microplate (greiner bio-one UV-STAR MICROPALLETE 96 WELL F-BODEN) and a plate reader (TECAN infinite M 200 PRO). As the absorbance, a value obtained by subtracting the measured absorbance of PBS as a blank value was used.

Here, 0.18 μl of a solution obtained by suspending Ketjen Black EC 600 JD (Lion Specialty Chemicals Co., Ltd.) as a carbon particle suspension at 2 mg/ml with a 0.2% aqueous tetradecyltrimethylammonium bromide (Wako Pure Chemical Industries, Ltd.) solution was applied by an inkjet apparatus (Labojet 3000: produced by Microjet) and dried. Thereafter, 0.12 μl of a mixed aqueous solution of the synthesized PLL-05-Ph_1 as a redox mediator, glucose dehydrogenase (FAD-dependent) (BBI international GDH GLD1) as an analyte-responsive enzyme, and a glutaraldehyde solution (Wako Pure Chemical Industries, Ltd.) was similarly applied by an inkjet apparatus and dried to form a sensing layer116bhaving a two-layer structure.

(6) Formation of Reference Electrode

Ag/AgCl is deposited on the reference electrode opening of the insulating film115aformed on the front side of the insulating substrate111by a screen printing method, a dispenser method, or the like to form a reference electrode117(FIG.10f). A preferred thickness of the reference electrode is 5 to 40 μm. Here, Ag/AgCl was deposited by a screen printing method to form a reference electrode (thickness: 10 to 15 μm).

(7) Formation of Counter Electrode

Although not illustrated inFIGS.8to11, a conductive thin film is also formed on the back side of the insulating substrate111in the same step as a case of the front side, an insulating film115bhaving an opening is formed by a sputtering method, a screen printing method, or the like in a portion excluding a region used as the counter electrode terminal118afor electrical connection with the counter electrode118and the main body10, and the conductive thin film114cof the sensing portion of the probe, which is not covered with the insulating film115b, is used as the counter electrode118(FIG.12g). In the case of forming a plurality of electrodes on the back side, a desired fine uneven structure is formed in the same step as a case of the front side.

(8) Separation into Individual Probes

Individual probes are separated from the insulating substrate111on which the plurality of probes are formed along the insulating fine uneven structure region112for forming an outer frame. The probe is separated by cutting the insulating substrate, but a cutting method is not particularly limited, and the probe can be cut by a method known in the art such as laser cutting or die cutting using a pinnacle (registered trademark) die.

One of the isolated probes is shown inFIG.12. The key-shaped probe11is illustrated in a top view as viewed from the front side in an upper part and in a top view as viewed from the back side in a lower part.

(9) Formation of Protective Film

The sensing portion of the probe is immersed in a solution containing a biocompatible resin for sensor protection to form a protective film119on both surfaces, side surfaces, and end surfaces of the sensing portion (FIG.12h). The protective film119covers at least the working electrode116, the reference electrode117, and the counter electrode118without covering the working electrode terminal116a, the reference electrode terminal117a, and the counter electrode terminal118a, and is formed to have a length equal to or longer than the length to be inserted into the living body. A preferred thickness of the protective film is 5 to 200 μm. As the biocompatible resin for sensor protection, although not limited, poly (4-vinylpyridine) can be used, and the poly (4-vinylpyridine) may be crosslinked with a crosslinking agent such as polyethylene glycol diglycidyl ether (PEGDGE), and examples thereof include poly (tert-butyl methacrylate)-b-poly (4-vinylpyridine), polystyrene-co-4-vinylpyridine-co-oligo [propylene glycol methyl ether] methacrylate, and the like.

Here, the sensing portion was immersed in an ethanol solution containing a crosslinking agent and a polymer for a protective film to form a protective film (thickness: 5 to 60 μm) on both surfaces, side surfaces, and end surfaces of the sensing portion. More specifically, a solution obtained by dissolving poly (tert-butyl methacrylate)-b-poly (4-vinylpyridine) (GENERAL SCIENCE CORPORATION) in ethanol so as to be 10% (weight/volume), a solution obtained by dissolving polystyrene-co-4-vinylpyridine-co-oligo [propylene glycol methyl ether] methacrylate) and random (GENERAL SCIENCE CORPORATION) in ethanol so as to be 10% (weight/volume), a solution obtained by dissolving them in poly (ethylene glycol) diglycidyl ether, and a water/ethanol (5/95 volume %) solution of 200 mM 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid as a buffer solution were prepared, the probe prepared above was immersed in a protective film solution prepared by mixing the solutions, and the probe was repeatedly immersed again 5 to 15 times after drying for 10 minutes and dried for 24 hours or more, so that a crosslinked protective film was formed to obtain a probe.

2. Internal Structure of Probe of Implantable Biosensor

An internal structure of the probe11of the implantable biosensor1according to one embodiment of the present disclosure will be further described.

FIG.13is a top view of the probe11completed up to formation of the protective film as viewed from the front side.FIG.14is a cross-sectional view taken along cut line IV-IV′ inFIG.13. The conductive thin films114are formed on both sides of the insulating substrate111. The conductive thin film114on the front side is separated into two electrode leads, that is, the working electrode lead114aand the reference electrode lead114bby the insulating fine uneven structure region113for forming an electrode lead, and is electrically insulated. The sensing layer116bis formed on a partial region of the working electrode lead114a. In addition, the reference electrode117is formed in the opening portion of the insulating film115a, and is electrically connected to the reference electrode lead114b. The conductive thin film114on the back side serves as a counter electrode lead114c, and a part thereof functions as the counter electrode118.

FIG.15is a cross-sectional view taken along cut line V-V′ inFIG.14. The working electrode lead114ais formed on the front side of the insulating substrate111, and the sensing layer116bis formed thereon. A counter electrode lead114cis formed on the back side of the insulating substrate111. Furthermore, it can be seen that the entire periphery of the sensing portion is covered with the protective film119.

FIG.16is a cross-sectional view taken along cut line VI-VI′ inFIG.14. On the front side of the insulating substrate111, the working electrode lead114aand the reference electrode lead114belectrically separated by the insulating fine uneven structure region113for forming an electrode lead are formed, and an insulating film115ais formed thereon. The reference electrode117is formed in the opening of the insulating film115a. The counter electrode lead114cis formed on the back side of the substrate111, and the insulating film115bis formed thereon. Furthermore, it can be seen that the entire periphery of the sensing portion is covered with the protective film119of the present disclosure.

3. Preparation of Biosensor

The completed probe11was attached to the biosensor main body10to produce an implantable biosensor.

INDUSTRIAL APPLICABILITY

According to the present disclosure, since the insulating substrate on which the fine uneven structure region appropriately designed in a nanosize is formed is used, it is possible to produce an electrode substrate including a very fine circuit having a wiring width and a wiring interval (line/space) on the order of several hundreds of nm. The miniaturization can also contribute to downsizing of the sensor. In addition, it is also possible to arrange a plurality of electrodes in a conventional size, which can also contribute to producing of a multifunctional sensor. Regarding the producing method, since the circuit patterning is performed on the insulating substrate in advance using the nanoimprinting technology, the number of producing steps is reduced, and thereby the producing cost can be reduced. In addition, since the fine uneven structure is patterned by transferring a mold, dimensional variations in producing are small, and mass production with stable circuit dimensions is possible. Further, when the conductive thin film having a thickness of 5 to 100 nm is formed on the fine uneven structure region, the reflectance of light is different between the fine uneven structure region and the smooth region where the fine uneven structure is not formed, so that a fine circuit can be checked using a camera or the like at a stage of forming the conductive thin film. With this feature, a circuit failure can be found before proceeding to a subsequent step, and thus the yield is improved.

REFERENCE SIGNS LIST

1Implantable biosensor10Main body11Probe111Insulating substrate112Insulating fine uneven structure region for forming outer frame113Insulating fine uneven structure region for forming electrode lead114Conductive thin film114aWorking electrode lead114bReference electrode lead114cCounter electrode lead115Insulating film116Working electrode116aWorking electrode terminal116bSensing layer117Reference electrode117aReference electrode terminal118Counter electrode118aCounter electrode terminal119Protective film2Living bodyA First smooth regionB Second smooth regionC1Fine uneven structure region of first embodimentC2Fine uneven structure region of second embodimentD Smooth region of insulating substrateE Upper bottom surface of protrusion (upper side in longitudinal sectional view)F Side surface of protrusion (side in longitudinal sectional view)G Lower bottom surface of protrusion (lower side in longitudinal sectional view)H Bottom portion of fine uneven structure