阅读说明：本技术 生物传感器 (Biosensor and method for measuring the same ) 是由 竹知和重 岩松新之辅 阿部泰 矢作彻 今野俊介 加藤睦人 于 2016-09-18 设计创作，主要内容包括：本发明涉及一种生物传感器。该生物传感器包括：半导体活性层；第一栅极绝缘膜,所述第一栅极绝缘膜设置在所述半导体活性层的第一表面上并且使所述半导体活性层和第一栅极电极相互绝缘；第二栅极绝缘膜,所述第二栅极绝缘膜设置在所述半导体活性层的第二表面上；第二栅极电极,所述第二栅极电极设置在所述第二栅极绝缘膜上,并延伸到与和所述半导体活性层重叠的区域以二维方式间隔开的位置；以及酶,所述酶固定于所述第二栅极电极的延伸端侧,并与溶液内的材料反应以调制施加于所述第二栅极电极的电压,其中,所述第二栅极绝缘膜的每单位面积的静电电容比所述第一栅极绝缘膜的每单位面积的静电电容大。(The present invention relates to a biosensor. The biosensor includes: a semiconductor active layer; a first gate insulating film that is provided on a first surface of the semiconductor active layer and insulates the semiconductor active layer and a first gate electrode from each other; a second gate insulating film provided on a second surface of the semiconductor active layer; a second gate electrode provided on the second gate insulating film and extending to a position spaced two-dimensionally apart from a region overlapping with the semiconductor active layer; and an enzyme that is immobilized on an extended end side of the second gate electrode and reacts with a material in a solution to modulate a voltage applied to the second gate electrode, wherein an electrostatic capacitance per unit area of the second gate insulating film is larger than an electrostatic capacitance per unit area of the first gate insulating film.)

1. A biosensor, comprising:

a semiconductor active layer;

a first gate insulating film that is provided on a first surface of the semiconductor active layer and insulates the semiconductor active layer and a first gate electrode from each other;

a second gate insulating film provided on a second surface of the semiconductor active layer;

a second gate electrode provided on the second gate insulating film and extending to a position spaced two-dimensionally apart from a region overlapping with the semiconductor active layer; and

an enzyme immobilized on an extension end side of the second gate electrode and reacting with a material in a solution to modulate a voltage applied to the second gate electrode,

wherein an electrostatic capacitance per unit area of the second gate insulating film is larger than an electrostatic capacitance per unit area of the first gate insulating film.

2. A biosensor, comprising:

a semiconductor active layer;

a first gate insulating film that is provided on a first surface of the semiconductor active layer and insulates the semiconductor active layer and a first gate electrode from each other;

a second gate insulating film provided on a second surface of the semiconductor active layer;

a second gate electrode provided on the second gate insulating film and extending to a position spaced two-dimensionally apart from a region overlapping with the semiconductor active layer;

an ion-sensitive insulating film disposed on the second gate electrode; and

an enzyme immobilized on the ion-sensitive insulating film and reacting with a material in a solution to cause a potential change in the ion-sensitive insulating film,

wherein an electrostatic capacitance per unit area of the second gate insulating film is larger than an electrostatic capacitance per unit area of the first gate insulating film.

3. A biosensor, comprising:

a semiconductor active layer;

a first gate insulating film that is provided on a first surface of the semiconductor active layer and insulates the semiconductor active layer and a first gate electrode from each other;

a second gate insulating film provided on a second surface of the semiconductor active layer;

a second gate electrode provided on the second gate insulating film and extending to a position spaced two-dimensionally apart from a region overlapping with the semiconductor active layer;

an ion-sensitive insulating film disposed on the second gate electrode; and

a plurality of enzymes immobilized on the ion-sensitive insulating film and reacting with a material in a solution to cause a potential change in the ion-sensitive insulating film,

wherein the plurality of enzymes are provided on the ion-sensitive insulating film at regular intervals or in a random manner so that the surface of the ion-sensitive insulating film is brought into contact with the solution, and

the second gate insulating film has a larger electrostatic capacitance per unit area than the first gate insulating film.

4. The biosensor of claim 2 or 3, further comprising:

a detection unit that detects a potential on the ion-sensitive insulating film after amplifying the potential by a value of a ratio obtained by dividing the capacitance per unit area of the second gate insulating film by the capacitance per unit area of the first gate insulating film.

5. The biosensor of any one of claims 1 to 3, wherein the semiconductor active layer is an oxide semiconductor or an organic semiconductor.

6. A biosensor, comprising:

a semiconductor active layer;

a first gate insulating film that is provided on a first surface of the semiconductor active layer and insulates the semiconductor active layer and a first gate electrode from each other;

a second gate insulating film provided on a second surface of the semiconductor active layer;

a second gate electrode provided on the second gate insulating film and extending to a position spaced two-dimensionally apart from a region overlapping with the semiconductor active layer;

an ion-sensitive insulating film disposed on the second gate electrode and including a region in contact with a solution; and

an enzyme immobilized at a position spatially separated from the ion-sensitive insulating film and reacting with a material in the solution to cause a potential change in the region of the ion-sensitive insulating film,

wherein an electrostatic capacitance per unit area of the second gate insulating film is larger than an electrostatic capacitance per unit area of the first gate insulating film.

7. The biosensor of claim 6, further comprising:

a detection unit that detects a potential on the ion-sensitive insulating film after amplifying the potential by a value of a ratio obtained by dividing the capacitance per unit area of the second gate insulating film by the capacitance per unit area of the first gate insulating film.

8. The biosensor of claim 6, further comprising:

a mechanism that controls a flow of a sensing target material between the ion-sensitive insulating film and the enzyme fixed at the position spatially separated from the ion-sensitive insulating film.

9. The biosensor of claim 6, further comprising:

a first substrate on which the first gate electrode, the first gate insulating film, the semiconductor active layer, the second gate insulating film, the second gate electrode, and the ion-sensitive insulating film are formed; and

a second substrate in which the enzyme is immobilized,

wherein the second substrate includes a groove in one surface, the enzyme is immobilized on an inner surface of the groove, and

the first substrate and the second substrate are disposed in a state where the ion-sensitive insulating film and the enzyme face each other.

10. The biosensor of claim 6,

the first gate electrode, the first gate insulating film, the semiconductor active layer, the second gate insulating film, the second gate electrode, and the ion-sensitive insulating film are formed in this order on a substrate, and

the enzyme that reacts with the material in the solution to cause the potential change in the region of the ion-sensitive insulating film is immobilized on the substrate.

11. The biosensor of any one of claims 6 to 10, wherein the semiconducting active layer is an oxide semiconductor or an organic semiconductor.

Technical Field

The present invention relates to a biosensor and a detection device using the same.

Background

In recent years, biosensors using biomaterial recognition mechanisms of biopolymers have been used in the fields of medical and environmental analysis. The biosensor is obtained by combining a biomaterial-recognizing mechanism of a biopolymer, an interface potential detecting mechanism on the interface (also referred to as a solid-liquid interface) of a solution and an insulating film, and an electrical measuring device.

As the biomaterial-recognizing mechanism, substrate specificity of enzymes, antibody-antigen reaction, interaction between deoxyribonucleic acid (DNA) and DNA, interaction between ribonucleic acid (RNA) and RNA, binding of lectins to physiologically active sugar chains, affinity of proteins to specific biomaterials, and the like have been used.

As the interface potential detecting means, for example, an ion sensitive FET (FET sensor) having a basic structure of a Metal Oxide Semiconductor Field Effect Transistor (MOSFET) has been used. The FET sensor measures the electric double layer potential by detecting a potential change of the electric double layer formed on the solid-liquid interface as a threshold voltage (Vth) shift of a reference electrode potential-drain current characteristic (Vref-Id characteristic).

Examples of the main factors that change the electric double layer potential include: change in the pH of the solution, physical and chemical adsorption to the interface of the insulating film, and the like. For example, the relationship between pH and electrical double layer potential is understood by the nernst theory of electrochemistry. For example, at 25 ℃, the pH changes by 1 (which means that the hydrogen ion concentration in the solution changes by 1 order of magnitude). Due to this change, the electrical double layer potential changes by about 59 mV. This means that 59mV/pH is the theoretical limit for sensor sensitivity in pH sensors based on the electrical double layer potential.

The value of pH is a useful indicator of biosensing. Biosensors decompose biological materials by enzymatic reactions and generate hydrogen ions as a byproduct, causing pH changes in solution. In addition, the biosensor measures the concentration of the biomaterial by detecting the pH change using the FET sensor. The biosensor has both a molecular recognition function using an enzyme and a substrate decomposition function, and a pH measurement function using an FET sensor. Therefore, it is necessary that the molecular recognition and substrate decomposition functions and the pH measurement function do not inhibit each other. In addition, the change in the concentration of hydrogen ions generated by the enzyme reaction becomes lower than that of the original biomass material. Therefore, in order to realize biosensing using pH change as an index, it is necessary to have a function capable of accurately detecting an extremely minute pH change.

In the field of clinical examination, it is expected that the need for point of care testing (POCT) for performing detection near a subject at a medical site will increase in the future. Such clinical examination is performed to grasp the concentration of a specific biomaterial. In addition, in this clinical examination, it is considered that the demand for measurement of a low concentration material that cannot be detected in the prior art will increase. In order to meet such a demand, a biosensor capable of performing highly sensitive measurement is required.

Next, a technique related to the present invention (hereinafter, referred to as "related art") will be explained.

As for the TFT biosensor, there are reports on Label-free detection of DNA molecules and horseradish peroxidase molecules using amorphous silicon TFTs (D. Goncales and others, "Label-free electronic detection of biomolutes using a-Si: H field-effect devices", "Journal of Non-Crystalline Solids", ELSEVIER, 2006, 6/15, 352, 2007) -2010). In addition, the TFT is an abbreviation of a thin film transistor. Linear Vth shifts were obtained up to 0.4. mu.M in DNA molecules and up to 0.1. mu.M in horseradish peroxidase molecules.

Among TFT biosensors using carbon nanotubes in the active layer, an acetylcholine sensor (Wei Xue and another, "a thin-film sensor based on estimated cholesterol sensor using self-associated carbon nanotubes and SiO) in which acetylcholinesterase is immobilized to the upper part of the active layer is disclosed₂nanoparticles "," Sensors and actors B: Chemical ", ELSEVIER, 9/25.2008, Vol.134, p.981-. As sensitivity, resolution and response time, 378.2 μ A/decade, 10nM and 15 sec values were obtained, respectively.

As a known example of utilization of enzymatic reactions, a report on a penicillin sensor having An ion sensitive membrane in which penicillin oxidase is immobilized on An FET sensor (A. Poghessian and Others, "An ISFET-based pen sensor with high sensitivity, low detection limit and low lifetime", "Sensors and directors B: Chemical", ELSEVIER, 6.1.2001, volume 76, page 519) was made. The penicillin sensor has a structure in which penicillin is decomposed by using an enzyme and pH is changed by generating hydrogen ions as a by-product and the change in pH is detected by an FET sensor. As the detection sensitivity, 120. + -.10 mV/mM was obtained, confirming continuous operation for 1 year or more.

In addition, as a biosensor including a field effect transistor, there are the following report examples. Specifically, a reaction field to which a detection target material-recognizing molecule is fixed on one surface of a silicon substrate and a field-effect element formed as a detection unit on the other surface of the silicon substrate are provided, thereby achieving an improvement in detection sensitivity (japanese patent application laid-open No. 2013-148456).

In addition, an example of a biosensor in which a longitudinal transistor is used as a transducer and an enzyme and an antibody having a molecular recognition function are immobilized on porous alumina is disclosed, which shows the possibility of a high-speed response operation (japanese patent application laid-open No. 2010-151540).

Disclosure of Invention

As described above, examples of the biosensor are disclosed. However, all of the above documents have the following structure: the concentration of the measurement target material is measured from the Vth shift of the Vref-Id characteristic by applying a gate voltage to a reference electrode immersed in a solution containing the measurement target material. In this sensor, it is difficult to obtain sensitivity higher than the theoretical sensitivity based on the nernst theory. Therefore, it is difficult to apply the above-described structure to the measurement of a biomaterial at an extremely low concentration.

A pH sensor using the basic structure of a MOSFET has been put to practical use. When attempting to apply to the measurement of biological materials, it is apparent that a higher sensitivity of the pH sensor is required. In the case of pH measurement of a liquid solution, it is considered sufficient that the sensitivity is equal to or less than 59mV/pH based on Nernst theory.

When attempting to apply to the measurement of biological materials, it is apparent that a highly sensitive pH sensor is required. For example, the biological material to be measured by the biosensor is about 10^－7mol/L to 10^－9The concentration in mol/L is present in a solution of about pH 7. When the biological material is decomposed using the enzyme, it is necessary to detect a change in the concentration of hydrogen ions generated due to the decomposition, a change in pH approximately in the range of 0.001 to 0.01. At this time, in the related art pH sensor, it is necessary to detect a minute voltage change of 0.059mV to 0.59 mV. When the influence of sensor drift, thermal fluctuation, variation in liquid temperature, and the like is taken into consideration, in the biosensor of the related art, it is difficult to achieve measurement with high reliability.

In addition, since the biopolymer is fixed on the insulating film, the disclosed technology has a structure in which the biopolymer-based material discrimination unit and the pH sensing portion of the FET sensor are present at the same site. When the biopolymer film becomes thick, the pH sensing portion does not come into contact with the solution, and therefore there is a concern that this situation causes a decrease in pH sensitivity. In addition, the region in which the enzyme can be immobilized is limited, and thus it is difficult to increase the amount of change in pH due to the enzyme reaction. That is, this causes a problem that it is difficult to improve the detection sensitivity for biological materials.

In the structure of the disclosed technique in which an enzyme is immobilized on an insulating film, it is basically difficult to exchange the enzyme. In general, it is known that a biopolymer such as an enzyme degrades in function with the passage of time. Thus, biopolymers lose function in a very short period of time compared to inorganic structures. Therefore, in the structure of the disclosed technology in which exchange of enzymes is difficult, when the enzymes lose activity, even if the TFT sensor unit operates normally, the function as a biosensor is lost. This leads to a problem that the life of the sensor is shortened and the burden on the user is increased.

In addition, in the structure of the disclosed technology, since the enzyme molecule is disposed at the position closest to the reference electrode, there is also a problem that the activity may be decreased by the application of the gate voltage.

The purpose of the present invention is to provide a biosensor and a detection device capable of detecting an extremely small pH change caused by an enzyme reaction with high sensitivity.

A biosensor according to an aspect of an embodiment includes: a semiconductor active layer; a gate insulating film that is provided on a first surface of the semiconductor active layer and insulates the semiconductor active layer and a gate electrode from each other; an ion-sensitive insulating film disposed on the second surface of the semiconductor active layer and including a region in contact with a solution; and an enzyme immobilized at a position spatially separated from the region and reacting with a material within the solution to cause a potential change within the region. In addition, in the biosensor according to an aspect of the embodiment, an electrostatic capacitance per unit area of the ion-sensitive insulating film is larger than an electrostatic capacitance per unit area of the gate insulating film.

According to one aspect of the embodiment, an extremely small pH change caused by an enzyme reaction can be detected with high sensitivity.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed.

Drawings

Fig. 1 is a sectional view showing a TFT biosensor of a first embodiment;

FIG. 2 is a graph showing Vg-Id characteristics of the TFT biosensor of example 1;

fig. 3 is a sectional view showing a TFT biosensor of a second embodiment;

FIG. 4 is a schematic diagram of a portion of the TFT biosensor of FIG. 3;

FIG. 5 is a sectional view showing a TFT biosensor of example 3;

fig. 6 is a sectional view showing a TFT biosensor of a third embodiment;

fig. 7 is a sectional view showing a TFT biosensor of a fourth embodiment;

FIG. 8 is a sectional view showing a TFT biosensor of example 6;

fig. 9 is a sectional view showing a TFT biosensor of a fifth embodiment;

fig. 10A and 10B are sectional views showing a TFT biosensor of a sixth embodiment;

fig. 11 is a schematic view showing a TFT biosensor of a sixth embodiment;

fig. 12A and 12B are sectional views showing a TFT biosensor of a seventh embodiment;

fig. 13 is a cross-sectional view showing a TFT biosensor using an organic semiconductor as a semiconductor active layer;

fig. 14 is a circuit diagram of a TFT biosensor device of the eighth embodiment;

fig. 15 is a diagram showing a configuration example of a microprocessor of the TFT biosensor device;

fig. 16 is an explanatory view showing a measurement principle in the TFT biosensor device of the eighth embodiment;

fig. 17 is a diagram showing a table storing correspondence between hydrogen ion concentration and gate electrode voltage; and

fig. 18 is an explanatory view of a measurement method in the TFT biosensor device in example 12.

Detailed Description

Hereinafter, embodiments for carrying out the present invention (hereinafter, referred to as "embodiments") will be described with reference to the drawings. In addition, in the present specification and the drawings, substantially the same constituent elements will be given the same reference numerals. The shapes in the drawings are shown for ease of understanding by those skilled in the art and do not necessarily match exactly the actual dimensions and ratios.

In each of the following embodiments, a biosensor configured using a TFT will be described, and thus the biosensor will be referred to as a TFT biosensor.

(first embodiment)

Fig. 1 is a sectional view showing a TFT biosensor 101 of the first embodiment.

The TFT biosensor 101 includes a semiconductor active layer 12 connected to a source electrode 13s and a drain electrode 13 d. On one surface (first surface, lower surface in fig. 1) of the semiconductor active layer 12, a thermally oxidized film 10 as a gate insulating film and a silicon substrate 11 as a gate electrode are provided. Further, an ion-sensitive insulating film 14 and a protective insulating film 15 are provided on the other surface (second surface, upper surface in fig. 1) of the semiconductor active layer 12. In addition, the TFT biosensor 101 includes a reference electrode 17 at a position spatially separated from the ion-sensitive insulating film 14 and the protective insulating film 15.

The capacitance per unit area of the ion-sensitive insulating film 14 is set to be larger than the capacitance per unit area of the gate insulating film (thermal oxide film 10). Further, the TFT biosensor 101 includes a second insulating substrate 18 provided with an enzyme 19 having substrate specificity on one surface thereof at a position spatially separated from the ion-sensitive insulating film 14 and the protective insulating film 15. At this time, regarding a structure, it is preferable that the silicon substrate 11 on which the TFTs are formed and the second insulating substrate 18 (enzyme 19) are opposed to each other as shown in fig. 1, but may be disposed in a two-dimensional manner, such as the same plane.

The space between the silicon substrate 11 and the second insulating substrate 18 is filled with a solution including the object-to-be-sensed material 16. The protective insulating film 15 covers a region other than a region overlapping with the channel region of the semiconductor active layer 12 on the upper surface of the ion-sensitive insulating film 14. The ion-sensitive insulating film 14 includes a region not covered with the protective insulating film 15. On this region, the ion-sensitive insulating film 14 is in contact with a solution including a sensing object material 16.

In addition, in order to diffuse the hydrogen ions generated by the enzyme reaction rapidly and to improve the responsiveness of the TFT sensor, it is preferable that the interval between the ion-sensitive insulating film 14 and the second insulating substrate 18 is as narrow as possible. On the interface where the ion-sensitive insulating film 14 is in contact with the solution including the sensing target material 16, the ion-sensitive insulating film 14 has a property of causing the potential on the interface to change in response to predetermined ions. The ion-sensitive insulating film 14 is also referred to as an "ion-sensitive insulator", or "pH-sensitive transducer".

The TFT biosensor 101 further includes any one of a voltage detection unit 20 that reads a potential difference between the source electrode 13s and the gate electrode (silicon substrate 11), and a current detection unit 21 that reads a current flowing in the source electrode 13s or the drain electrode 13 d. In fig. 1, the voltage detection means 20 and the current detection means 21 are both shown.

(example 1)

Next, example 1 in which the first embodiment is further embodied will be described with reference to fig. 1. First, a method for manufacturing the TFT biosensor 101 of example 1 will be described.

A manufacturing apparatus (hereinafter, referred to as "manufacturing apparatus") of the TFT biosensor 101 forms the thermal oxide film 10 to a film thickness of 200nm on the silicon substrate 11. Instead of the thermal oxide film 10, a silicon oxide film, a silicon nitride film, or the like formed by a plasma Chemical Vapor Deposition (CVD) method or a sputtering method may be used. In addition, the term "manufacturing apparatus" is used as a general term for each apparatus necessary for manufacturing biosensors, such as a film forming apparatus for sputtering or CVD, an organic material coating apparatus, and an annealing furnace.

In addition, a thermal oxide film 10 is formed on a silicon substrate 11, and an oxide semiconductor film (hereinafter, simply referred to as In-Ga-Zn-O) composed of indium-gallium-zinc-oxygen is deposited by a sputtering method using a metal mask. The thickness of the In-Ga-Zn-O film was set to 50 nm. In the film formation process, a Direct Current (DC) sputtering method In a mixed gas atmosphere of argon and oxygen was used using a sintered body target composed of In-Ga-Zn-O without heating the substrate. After the film formation, the substrate was annealed at 400 ℃ for 1 hour in air. By patterning the oxide semiconductor film, the semiconductor active layer 12 having an island shape is formed.

Next, the source electrode 13s and the drain electrode 13d are formed by DC sputtering of molybdenum (Mo) using a metal mask. The film thicknesses of the source electrode 13s and the drain electrode 13d are set to 50 nm. In addition, the ion-sensitive insulating film 14 as a tantalum oxide (Ta) film having a film thickness of 200nm was sputtered and patterned using a metal mask. In the film formation, a sintered target composed of Ta — O was used, and a Radio Frequency (RF) sputtering method in a mixed gas atmosphere of argon and oxygen was used without heating the substrate.

Thereafter, the manufacturing apparatus was annealed at 300 ℃ for 1 hour in air. The thermal oxide film 10 has a relative dielectric constant of about 4, and the tantalum oxide (ion-sensitive insulating film 14) formed as a film by sputtering has a relative dielectric constant of about 20. The thicknesses of the thermal oxide film 10 and the ion-sensitive insulating film 14 were set to 200nm, respectively. Therefore, the difference in the relative dielectric constant value is reflected in the electrostatic capacitance per unit area, and therefore the size of the electrostatic capacitance per unit area of the ion-sensitive insulating film 14 composed of tantalum oxide is about 5 times the electrostatic capacitance per unit area of the gate insulating film composed of the thermally oxidized film 10.

Next, the manufacturing apparatus exposes the surface of the ion-sensitive insulating film 14 located immediately above the channel region of the semiconductor active layer 12, and covers the remaining portion of the surface of the ion-sensitive insulating film 14 with the protective insulating film 15. It is preferable to use a silicone resin as the protective insulating film 15, but a photoresist, an epoxy resin, or the like may be used as long as appropriate water resistance and insulation properties can be obtained.

The TFT having the above-described structure is immersed in phosphate buffered saline including the sensor object material 16. At this time, the exposed region of the ion-sensitive insulating film 14 is in contact with phosphate buffered saline. Phosphate buffered saline is an example of the solution. In addition, an Ag/AgCl electrode filled with a saturated KCL solution was used as the reference electrode 17, and immersed in phosphate buffered saline including the sensing object material 16.

For example, the main component of the enzyme 19 is glucose oxidase. Specifically, the enzyme 19 is a mixture of 10% glucose oxidase, 10% bovine serum albumin, and 8% glutaraldehyde. The manufacturing apparatus dropwise adds the enzyme 19 to one surface of the second insulating substrate 18, and dries the enzyme at room temperature for 192 hours. By drying, the enzyme 19 is immobilized on the second insulating substrate 18.

The immobilized enzyme 19 was immersed in a phosphate buffer adjusted to pH 6.5 and 0.1mol/L and maintained at 4 ℃. The manufacturing apparatus immerses the second insulating substrate 18 on which the enzyme 19 is immobilized in phosphate buffered saline containing the material to be sensed 16. Here, the second insulating substrate 18 faces the silicon substrate 11 on which the TFTs are formed. At this time, the second insulating substrate 18 and the silicon substrate 11 can be bonded to each other with a spacer interposed therebetween, thereby controlling the distance between the two substrates. Phosphate buffered saline was adjusted to pH 6.8 and a liquid temperature of 37 ℃ as the optimal environment for enzyme 19.

In the TFT biosensor 101 configured as described above, the present inventors first applied a constant potential of 0.5V to the drain electrode 13d of the TFT biosensor 101, set the source electrode 13s and the reference electrode 17 to the ground potential (0V), and varied the gate voltage Vg in the range of 0V to +7V, thereby measuring the Vg-Id characteristic (characteristic of the drain current Id with respect to the gate voltage Vg).

Fig. 2 is a graph showing the Vg-Id characteristics of the TFT biosensor 101 of example 1. The upper graph of FIG. 2 shows the measurement of the Vg-Id characteristic in air, and the lower graph shows the measurement of the Vg-Id characteristic in phosphate buffered saline. It can be appreciated that the Vg-Id characteristic drifts to the positive side due to immersion in the liquid. Next, the present inventors added an aqueous glucose solution to phosphate buffered saline, wherein the aqueous glucose solution was adjusted so that the final concentration was a predetermined value. In addition, the TFT biosensor 101, the reference electrode 17, and the enzyme 19 immobilized on the second insulating substrate 18 are immersed in phosphate buffered saline. At this time, to maintain the pH of the phosphate buffered saline, the added glucose was dissolved in the same phosphate buffered saline.

Here, the following reaction is performed between the added glucose and glucose oxidase (enzyme 19).

β -D-glucose + O₂→ D-glucono-lactone + H₂O₂(catalyst: glucose oxidase)

At this time, D-glucono-lactone is converted into gluconic acid by hydrolysis, and the pKa (acid dissociation constant) of gluconic acid is about 3.8, thereby causing a change in pH of the solution. This pH change increases in proportion to the glucose concentration in the solution. Therefore, the TFT biosensor 101 can measure the glucose concentration based on the Vg-Id characteristic drift caused by the pH change.

In the present embodiment, a desired value is detected from the Vth drift of the Vg-Id characteristic (characteristic between the gate electrode voltage and the drain current). This is different from the related art of detection of an interface potential or ion concentration or the like according to Vth drift based on the Vref-Id characteristic.