KR100948177B1 - Gas sensor for determining freshness of meat products and Method thereof - Google Patents

Abstract

The present invention relates to a meat freshness sensor and a manufacturing method thereof. More specifically, by coating a mixture of carbon nanotubes and a conductive polymer on the oxide film formed on the substrate and forming an electrode on the mixture layer to measure the resistance change of the sensor according to the amount of harmful gas generated from the meat, it is easy and accurate It is possible to determine the freshness, excellent stability, excellent performance at room temperature, gas desorption to the sensing material is more rapid, and relates to a meat freshness sensor and its manufacturing method with improved reaction speed.

Meat Freshness, Carbon Nanotubes, Conductive Polymers, Polyaniline, Resistance Changes

Description

Sensor sensor for determining freshness of meat products and Method

The present invention relates to a meat freshness sensor and a manufacturing method thereof. More specifically, by coating a mixture of carbon nanotubes and a conductive polymer on the oxide film formed on the substrate and forming an electrode on the mixture layer to measure the resistance change of the sensor according to the amount of harmful gas generated from the meat, it is easy and accurate It is possible to determine the freshness, excellent stability, excellent performance at room temperature, gas desorption to the sensing material is more rapid, and relates to a meat freshness sensor and its manufacturing method with improved reaction speed.

In the age of mass distribution of food, consumers' desire to find safe food is increasing by measuring the freshness of food and responding promptly according to the result.

In particular, meat is a food that requires careful attention in the distribution process because it is easily deteriorated or decayed outside of frozen state due to the presence of various kinds of harmful microorganisms and bacteria. Moreover, as the Free Trade Agreement (FTA) with the United States is recently concluded, it is becoming more important to screen beefs with high safety as beefs of various nationalities other than Korean beef begin to be distributed.

Korean Laid-Open Patent Publication No. 2003-0096077 discloses an invention related to a "freshness indicator of food" which grasps the freshness of a food through a phase change of a pH sensitive polymer material. According to the above patent, a hole is formed so that ions or solvents in the food, which are changed according to the quality of the food, may come into contact with the pH-sensitive polymer material, and the semi-permeable membrane is provided so that only the ions or the solvent may pass through the hole. The contact was made. As a pH-sensitive polymer material, sulfonamide is reacted with methacryloyl chloride to obtain ionized sulfonamide groups, and then N, N-dimethylacrylamide, which is an acryrylamide group, is obtained. And synthesized by reacting with various molar ratios.

The food freshness indicator has the advantage of easily measuring the stability of the food using a polymer sensitive to acidity, but has a problem in that it is very poor in terms of stability.

On the other hand, in addition to the method of determining the freshness of food by observing the phase change of the substance, there is a gas measurement sensor that measures the amount of harmful gas generated in the food by using the characteristic that the electrical conductivity changes according to the adsorption of gas molecules. The material used as the gas measuring sensor includes a metal oxide semiconductor such as SnO ₂ , a solid electrolyte material, various organic materials, a composite of carbon black and organic materials, and the like.

However, in the case of a gas measurement sensor made of such a material, the following problems exist. When using a metal oxide semiconductor or a solid electrolyte material, there is a problem in that the operation of the sensor is normally performed only when heated to a temperature of 200 to 600 degrees Celsius or higher. In addition, in the case of an organic material, the electrical conductivity is low, and in the case of the composite of carbon black and an organic material, there is a problem that the sensitivity is significantly low.

With the rapid increase in meat supply and consumption, there is a need to develop a sensor that can quickly and accurately determine the freshness of meat.

The present invention has been made to solve the above problems, and in particular, it is possible to determine the freshness of meat easily and accurately, excellent stability, excellent performance at room temperature, gas desorption to the sensing material more quickly It is an object of the present invention to provide a meat freshness sensor and a method for manufacturing the same, which have improved reaction speed.

Meat freshness sensor for determining the freshness of meat according to the present invention devised to achieve the above object is a substrate in which an oxide film is laminated; A mixture layer of carbon nanotubes and a conductive polymer laminated on an upper surface of the oxide film; And a source electrode and a drain electrode formed spaced apart from each other on both sides of the upper surface of the mixture layer.

In addition, the conductive polymer is preferably polyaniline.

In addition, the conductive polymer may be any one of polypyrrole and polythiophene.

In addition, the source electrode or the drain electrode may be made of any one of platinum (Pt), gold (Au), nickel (Ni), chromium (Cr).

Method of manufacturing a meat freshness sensor for determining the freshness of meat according to the present invention is (a) a doped silicon substrate, a silicon oxide film formed on the upper surface of the silicon substrate, carbon nanotube powder, and hydrochloric acid, DBSA (Dodecyl Benzene) Preparing a polyaniline powder doped with any one of Sulfonic Acid), CSA (Camphor Sulfonic Acid), BSA (Benzene Sulfonic Acid) and TSA (Toluene Sulfonic Acid); (b) dispersing the carbon nanotube powder and the doped polyaniline powder in a liquid phase to prepare a mixture; (c) spin coating the mixture on a silicon oxide film of the doped silicon substrate at a rotation speed of 3000 rpm or more and 5000 rpm or less; (d) baking and annealing the mixture layer; And (e) forming a source electrode formed of chromium (Cr) material and a drain electrode formed of gold (Au) material on the coated mixture layer through step (d). It is characterized by.

In addition, the number of repetitions of the spin coating is preferably 3 to 5 times.

delete

delete

delete

According to the present invention, the stability is improved, the conductivity is high at room temperature, and the time taken for the gas molecules to desorb at room temperature is reduced, so that the gas generated in the meat can be detected by changing the resistance in a wide range. It is effective to obtain a gas measuring sensor.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. First of all, in adding reference numerals to the components of each drawing, it should be noted that the same reference numerals have the same reference numerals as much as possible even if displayed on different drawings. In addition, in describing the present invention, when it is determined that the detailed description of the related well-known configuration or function may obscure the gist of the present invention, the detailed description thereof will be omitted. In addition, the following will describe a preferred embodiment of the present invention, but the technical idea of the present invention is not limited thereto and may be variously modified and modified by those skilled in the art.

First, a meat freshness sensor according to a preferred embodiment of the present invention will be described.

1 is a vertical cross-sectional view of a meat freshness sensor according to a preferred embodiment of the present invention.

In the meat freshness sensor according to the preferred embodiment of the present invention, referring to FIG. 1, the substrate 10 having the oxide film 20 stacked thereon, the mixture layer 30, the source electrode 40, and the drain electrode 50. It is formed to include.

As the substrate 10, a general semiconductor device substrate may be used, and a silicon substrate is preferably used. As the silicon substrate, either an p-type silicon substrate doped with an acceptor or an n-type silicon substrate doped with a donor may be selectively used.

The oxide film 20 is formed on the upper surface of the substrate 10, and a silicon oxide film SiO ₂ may be used. At this time, the thickness of the oxide film 20 may be formed to about 200nm, it is preferable to form the same or similar area as the substrate 10.

The mixture layer 30 is coated on the top surface of the oxide film 20. The mixture layer 30 is made of a mixture of carbon nanotubes (CNT) and a conductive polymer.

Carbon nanotubes are a tube-shaped molecule formed by rounding a graphite plate made of carbon (C) connected by hexagonal rings, and have a nanostructure of only a few nanometers to several tens of nm in diameter. Due to these structural features, carbon nanotubes can operate at room temperature unlike metal oxide semiconductors or solid electrolyte materials.In contrast to carbon black and organic compounds, carbon nanotubes have high sensitivity to electrical conductivity when reacting with harmful gases. It is good and the reaction speed is excellent. In addition, the carbon nanotubes are excellent in strength but well bent and are not substantially damaged or abraded even after repeated use, and have a property of returning to their original electrical conductivity when heated to 200 ° C. In addition, carbon nanotubes have excellent electron emission characteristics and chemical reactivity, and have a high surface reactivity due to their large specific surface area. Therefore, carbon nanotubes have an advantage of being able to easily detect even a small amount of harmful gases.

However, when the carbon nanotube alone is used for the sensing material of the noxious gas sensor, the energy required for the desorption is greater than that of the thermal energy at room temperature, so the desorption of gas molecules is not easy. These limitations increase the time required for the hazardous gas sensor to return to its original conductivity. The present invention overcomes these limitations by preparing a sensing material by mixing conductive polymers with carbon nanotubes.

The conductive polymer is a polymer material and has a metal property. Examples of the conductive polymer include polyaniline, polypyrrole, and polythiophene. In particular, polyaniline is stable in air, has high electrical conductivity at room temperature, and has a property of increasing solubility and electrical conductivity in general organic solvents by a functional dopant. In the case of polypyrrole, thermal stability, solubility, electrical conductivity, etc. are superior to polyaniline, but when the device is manufactured, the contact surface between the substrate and the sensing object is poor, and the coating on the substrate is also disadvantageous. On the other hand, polyaniline has an optimal feature to be used as an element because it has a very good adhesion (adhension) to the substrate. Therefore, in the present invention, it is most preferable to apply polyaniline as the conductive polymer.

Conductive polymers are not easy to process because of their strong intermolecular attraction due to Van der Waals interactions between unlocalized π electrons along the chain. In order to overcome this, processability may be improved while maintaining the electrical conductivity by chemical modification such as substituting a long alkyl group instead of hydrogen of the monomer. In addition, when an organic acid having a large molecule size is used as a admixture in the conductive polymer, the intermolecular attraction is reduced, so that it can be dissolved in an organic solvent while maintaining electrical conductivity.

There are three types of conductive polymers: an ion-polymer solid electrode system, a composite having an electrically conductive material in a non-conductive material, and a conductive polymer by an electric carrier. In addition, the conductive polymer may be classified into an ion conductive polymer and an electron conductive polymer according to the type of the charge carrier. In addition, the ion conductive polymer is classified into a form of a polymer salt in which an ionic group is covalently bonded to the polymer, and a polymer solid electrolyte capable of dissociating a salt like a liquid electrolyte. Electronically conductive polymers are classified into a method of providing conductivity by mixing carbon black, metal powder, or fiber, which is a conductor, with a polymer, which is an insulator (conductive composite), and a polymer that is essentially conductive.

In order to improve the electrical conductivity of such a conductive polymer, it is preferable that the anion is doped. Dopants include electron acceptors (oxidants) and electron donors (reducing agents) .Oxidizing a polymer with an oxidizing agent forms delocalized positive charges in the polymer backbone (p-doping). It will form a negative charge (n-doped). As the dopant, hydrochloric acid, DBSA (Dodecyl Benzene Sulfonic Acid), CSA (Camphor Sulfonic Acid), BSA (Benzene Sulfonic Acid), TSA (Toluene Sulfonic Acid) and the like are preferably used.

The mixture layer 30 may be formed by, for example, dispersing a polyaniline polymer powder in carbon nanotube powder using an organic solvent and then coating the oxide film 20. The mixture layer 30 may be irregularly provided in the horizontal direction on the upper surface of the oxide film 20. Oxide semiconductors function as sensors through adsorption and desorption with gas only at high temperatures, but polyaniline, which is a conductive polymer, can be used at room temperature.

Polypyrrole and polyaniline, which are conductive polymers used as sensors, are generally synthesized by electropolymerization, but this method has the following limitations.

In order to apply the conductive polymer as a sensor, an electrode having an electrode gap of several micrometers or less is required. If the gap between the electrodes is wide, the thickness of the conductive polymer film to be synthesized is so thick that the sensitivity to the gas is not well expressed, and once synthesized in the solution, once synthesized, the conditions in the solution change, so that mass synthesis is impossible. In addition, the conductive polymer synthesized by chemical polymerization is insoluble in the organic solvent because of the intermolecular interaction and crosslinking, and thus it is impossible to make a uniform film.

Polyaniline has a general pattern of sensor elements according to dopants, and can form a uniform and thin film so that the gas can be accurately measured by recognizing the change in conductivity with respect to the gases generated from meat decay.

The source electrode 40 is formed on one side of the upper surface of the mixture layer 30, and is preferably formed to a thickness of about 30 ~ 50nm. The source electrode 40 may be formed of platinum (Pt), gold (Au), nickel (Ni), chromium (Cr), or other metal material, and is preferably formed of chromium material.

The drain electrode 50 is formed on the other side of the upper surface of the mixture layer 30, and is similarly formed to have a thickness of about 30 to 50 nm. The drain electrode 50 may be formed of platinum (Pt), gold (Au), nickel (Ni), chromium (Cr), or other metal material, and is preferably formed of gold material. Preferably, the distance between the source electrode 40 and the drain electrode 50 is approximately 50 mu m.

Next, a method of manufacturing a meat freshness sensor according to a preferred embodiment of the present invention will be described.

2 is a flowchart illustrating a method of manufacturing a meat freshness sensor according to a preferred embodiment of the present invention. 3 is a photograph taken of a carbon nanotube and polyaniline mixture through a scanning electron microscope, and FIG. 4 is a photograph taken of a carbon nanotube and polyaniline mixture coated on a silicon oxide film in a film form through a scanning electron microscope.

Method for manufacturing a meat freshness sensor according to a preferred embodiment of the present invention, referring to Figure 2, the substrate, carbon nanotube powder, polyaniline powder preparation step (S10), mixture preparation step (S20), mixture coating step (S30) And a source electrode and a drain electrode forming step (S40).

Step 10 is a step of preparing a substrate on which the oxide film is laminated, and carbon nanotube powder and polyaniline powder. The substrate on which the oxide film is stacked may be a silicon substrate, and the carbon nanotube powder may be formed of carbon nanotubes having a length of about 4 μm and a diameter of 20 nm. The polyaniline powder is preferably chemically synthesized using an acid as a doping material, and the doping material is hydrochloric acid, dodecyl benzene sulfate acid (DBSA), camphor sulfate sulfonic acid (CSA), benzene sulfide acid (BSA), toluene sulfate compound (TSA). It is preferable that it is either.

Step 20 is to prepare a mixture by dispersing the carbon nanotube powder and polyaniline powder in a liquid phase. In this case, the weight ratio of the carbon nanotube powder and the polyaniline powder may be 1: 100. The liquid in which the carbon nanotube powder and the polyaniline powder are dispersed is preferably an organic solvent. A scanning electron micrograph of the mixture is shown in FIG. 3.

Step 30 is a step of coating the mixture prepared in step 20 on the oxide film of the substrate. The mixture coated on the oxide film is shown in FIG. 4. At this time, the coating of the mixture is preferably made of a spin-coating (spin-coating) method, it is preferable that the number of repetitions of the spin coating is about 3 to 5 times. If the number of coatings is less than 3 times, the thickness of the mixture layer becomes too thin to measure the sufficient electrical conductivity, and if it exceeds 5 times, the metal properties become excessively predominant and the freshness of the meat is changed due to the change in electrical conductivity according to the degree of adsorption of harmful gas molecules. The purpose of the invention to determine the will not be achieved. In addition, the rotational speed of the spin coating is preferably about 3000 to 5000rpm. If the rotational speed is less than 3000rpm, the mixture is not sufficiently coated on the oxide film, and if the speed exceeds 5000rpm, there is a problem that the metal properties become large. Although not shown, after the coating of the mixture through step 30, it is preferable to dry and fix the mixture layer by baking, and to stabilize it by annealing. Baking is carried out at 150 degrees Celsius for 30 seconds, and annealing may be performed at 200 degrees Celsius for 2 hours.

In step 40, a source electrode and a drain electrode are formed on the coated mixture layer through step 30. The source electrode and the drain electrode may be formed by depositing chromium and gold, respectively. At this time, the source electrode and the drain electrode may be formed to a thickness of about 30 ~ 50nm, the interval between both electrodes is preferably approximately 50㎛.

Hereinafter, the experimental results of the meat freshness sensor manufactured by the manufacturing method of the meat freshness sensor according to a preferred embodiment of the present invention.

5 is a graph showing the change of the source-drain current and the resistance value before gas measurement. FIG. 6 is a graph illustrating a change in resistance of a sensor to a gas generating meat for at least 15 hours at room temperature using carbon nanotubes as a sensing material. FIG. 7 is a graph illustrating a change in resistance of a sensor to a gas generating meat for at least 15 hours at room temperature using carbon nanotubes and polyaniline as sensing materials. FIG. 8 is a graph illustrating a change in resistance of a sensor to a gas generating meat for at least 50 hours at room temperature using carbon nanotubes and polyaniline as sensing materials.

EXAMPLE

A silicon substrate having a silicon oxide film having a thickness of 200 nm was prepared under 1000 ° C., atmospheric pressure, and wet oxidation conditions to form a carbon nanotube and polyaniline mixture layer. The silicon substrate was a 4-inch p-type silicon wafer manufactured by Silicon Material Inc. of the United States. Subsequently, under the pressure of 1 × 10 ^-4 Pa, a photoresist film was formed on the upper surface of the mixture layer in addition to the portion where the source electrode and the drain electrode were to be formed, and chromium (CERAC, USA) and gold (MKE, Korea) were deposited on the top surface of the photoresist film. Thereafter, the photoresist film and the metal thereon were removed together to form a source electrode and a drain electrode.

After heat treatment at 120 ° C. for 10 minutes to remove water molecules adhered to the mixture layer of the gas measurement sensor thus manufactured, source-drain voltage of -1V to 1V was supplied to the gas measurement sensor in a vacuum gas atmosphere. The change of the source-drain current was observed. At this time, the source-drain voltage was fixed at 1V. The results are shown in FIG. Moreover, the result of having observed the resistance value is also shown in FIG.

[Comparative Example]

The same conditions as in Example were maintained except that the sensing material was formed of carbon nanotubes alone instead of the mixture layer. The results are shown in FIG.

Referring to the comparative example of FIG. 6 and the embodiment of FIG. 7, polyaniline, which is a conductive polymer, is mixed with carbon nanotubes, thereby showing an excellent resistance change.

Gas measurement of the sensor used Equation 1 below.

S (%) = (RR ₀ ) / R × 100

(R ₀ is the device resistance value before gas measurement, and R is the device resistance value when exposed to meat gas.)

The above description is merely illustrative of the technical idea of the present invention, and various modifications, changes, and substitutions may be made by those skilled in the art without departing from the essential characteristics of the present invention. will be. Accordingly, the embodiments disclosed in the present invention and the accompanying drawings are not intended to limit the technical spirit of the present invention but to describe the present invention, and the scope of the technical idea of the present invention is not limited by the embodiments and the accompanying drawings. . The scope of protection of the present invention should be interpreted by the following claims, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present invention.

The present invention enables a simple and accurate measurement of the freshness of meat in large quantities in the reality that meat consumption is increasing, it can be widely used in a sensor for measuring meat rot.

1 is a vertical cross-sectional view of a meat freshness sensor according to a preferred embodiment of the present invention,

2 is a flow chart of a meat freshness sensor manufacturing method according to a preferred embodiment of the present invention,

3 is a photograph taken through a scanning electron microscope of a carbon nanotube and a polyaniline mixture,

4 is a photograph taken through a scanning electron microscope a state in which a carbon nanotube and a polyaniline mixture is coated on a silicon oxide film in a film form;

5 is a graph showing the change of the source-drain current and the resistance value before gas measurement;

Figure 6 is a graph showing the change in resistance of the sensor to the gas generating meat for more than 15 hours at room temperature as a carbon nanotube sensing material,

FIG. 7 is a graph illustrating a change in resistance of a sensor to a gas generating meat for at least 15 hours at room temperature using carbon nanotubes and polyaniline as sensing materials;

FIG. 8 is a graph illustrating a change in resistance of a sensor to a gas generating meat at room temperature for 50 hours or more using carbon nanotubes and polyaniline as sensing materials.

<Description of the symbols for the main parts of the drawings>

10-substrate 20-oxide film

30-mixture layer 40-source electrode

50-drain electrode

Claims (9)

In the meat freshness sensor for determining the freshness of meat, A silicon substrate doped with an acceptor or donor; A silicon oxide film formed on an upper surface of the silicon substrate; Polyaniline powder doped with any one of carbon nanotubes and hydrochloric acid, DBSA (Dodecyl Benzene Sulfonic Acid), CSA (Camphor Sulfonic Acid), BSA (Benzene Sulfonic Acid) and TSA (Toluene Sulfonic Acid) stacked on the silicon oxide layer A mixture layer formed of; And Meat freshness sensor comprising a source electrode formed of a chromium (Cr) material and a drain electrode formed of a gold (Au) material spaced apart from each other on both sides of the upper surface of the mixture layer. delete delete delete In the manufacturing method of the meat freshness sensor for determining the freshness of meat, (a) a doped silicon substrate, a silicon oxide film formed on an upper surface of the silicon substrate, carbon nanotube powder, and hydrochloric acid, dodecyl benzene sulfate sulfate (CSA), camphor sulfate sulfonic acid (CSA), benzene sulfide acid (BSA), and TSA Preparing a polyaniline powder doped with any of Toluene Sulfonic Acid; (b) dispersing the carbon nanotube powder and the doped polyaniline powder in a liquid phase to prepare a mixture; (c) forming a mixture layer by spin coating the mixture on a silicon oxide film of the doped silicon substrate at a rotation speed of 3000 rpm or more and 5000 rpm or less; (d) baking and annealing the mixture layer; And (e) forming a source electrode formed of chromium (Cr) material and a drain electrode formed of gold (Au) material on the coated mixture layer through step (d). Method of manufacturing a meat freshness sensor characterized in that. delete delete delete delete

Images