Oxygen radical activated aqueous solution generating device and sterilization method

Abstract

To maintain a sterilization effect of an oxygen radical activated aqueous solution generated by irradiation with an oxygen plasma.SOLUTION: An apparatus for generating an oxygen radical activated aqueous solution comprises a chamber 110, a holding unit 120, a gas supply unit 130, a gas discharge unit 140, a plastic cover 150, a radical irradiation unit 200, and a cooler 300. The holding unit 120 is a container for holding an aqueous solution to be irradiated with plasma, and is a container for holding an oxygen radical activated aqueous solution generated after plasma irradiation. The radical irradiation unit 200 is used for irradiation with oxygen radicals. The cooler 300 cools holding unit 120.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an apparatus for generating an oxygen radical activated aqueous solution and a sterilization method. [Background technology]

[0002] Plasma technology is applied in the fields of electricity, chemistry, and materials. In addition to charged particles such as electrons and ions, plasma generates neutral particles such as atoms and molecules, as well as ultraviolet rays. Among the products generated within plasma, particles with unpaired electrons (including atoms, molecules, and ions) are called radicals. Such ultraviolet rays and radicals are known to have a sterilizing effect.

[0003] Patent Document 1 describes that by irradiating an aqueous solution containing a cyclic organic compound having at least one of a benzene ring, a pyrrole ring, and a pyridine ring with oxygen plasma, it is possible to produce an oxygen radical activated aqueous solution that can be used as a sterilizing aqueous solution capable of killing Escherichia coli and the like.

[0004] Patent Document 2 describes a sterilization method in which plasma is irradiated onto water such as tap water, pure water, physiological saline, aqueous solutions, and various other liquids to generate a plasma-treated sterilizing liquid whose pH is adjusted to 4.8 or less, and the resulting liquid is kept at 10°C or less. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2020-33294 [Patent Document 2] Republished Publication No. 2013-161327 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the inventors' investigations revealed that the sterilizing effect of the oxygen radical activated aqueous solution prepared by the method of Patent Document 1 decreases in a short period of time. Therefore, it was found that the sterilizing effect cannot be expected if the solution is used after being kept for a certain period of time after being irradiated with oxygen plasma.

[0007] It was also found that a pH close to neutral is desirable for use in sterilizing various objects.

[0008] The inventors have conducted extensive research into the cause of the short-term decrease in the bactericidal effect of the oxygen radical activated aqueous solution prepared by the method of Patent Document 1, and have discovered that there is a relationship between the temperature of the oxygen radical activated aqueous solution and the bactericidal effect. The present disclosure utilizes this finding and aims to maintain the bactericidal effect when an aqueous solution containing a cyclic organic compound having a pyrrole ring is irradiated with oxygen plasma to produce an oxygen radical activated aqueous solution. [Means for solving the problem]

[0009] The present disclosure relates to an oxygen radical activated aqueous solution generating apparatus characterized by having a holding unit that holds an aqueous solution containing a cyclic organic compound having a pyrrole ring in a liquid state at 15°C or below, and an oxygen radical irradiation device that irradiates the aqueous solution held in the holding unit with oxygen radicals to generate an oxygen radical activated aqueous solution.

[0010] The present disclosure also provides a sterilization method characterized by maintaining an aqueous solution containing a cyclic organic compound having a pyrrole ring in a liquid state at 15°C or below, irradiating the aqueous solution with oxygen radicals to generate an oxygen radical activated aqueous solution, sterilizing an object while maintaining the oxygen radical activated aqueous solution at 15°C or below, and heating the oxygen radical activated aqueous solution to 20°C or above to complete sterilization of the object. [Effects of the Invention]

[0011] According to the present disclosure, the bactericidal effect of the oxygen radical activated aqueous solution can be enhanced and the bactericidal effect can be maintained for a long period of time. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram showing the configuration of a sterilization device. [Figure 2] FIG. [Figure 3] FIG. 2 is a diagram showing the internal structure of the radical irradiation unit 200. [Figure 4] FIG. 10 is a diagram showing the configuration of a modified example of the sterilization device. [Figure 5] Graph showing the relationship between the temperature of the aqueous solution and the number of colonies. [Figure 6] Graph showing the relationship between tryptophan concentration and colony number. [Figure 7] Graph showing the relationship between storage time and colony count. [Figure 8] Graph showing the bactericidal effect of aqueous solutions containing a mixture of benzene, pyrrole, or indole. DETAILED DESCRIPTION OF THE INVENTION

[0013] Specific embodiments of the present disclosure will be described below with reference to the drawings.

[0014] (First embodiment) The first embodiment is a device for generating an oxygen radical activated aqueous solution that can be used as a sterilizing aqueous solution capable of sterilizing an object. The oxygen radical activated aqueous solution is generated by irradiating an aqueous solution containing a cyclic organic compound having a pyrrole ring with oxygen radicals. The temperature of the oxygen radical activated aqueous solution is maintained at 15°C or less from the time of oxygen radical irradiation until it is used to sterilize an object.

[0015] Examples of cyclic organic compounds having a pyrrole ring include tryptophan, indole, pyrrole, etc. The aqueous solution may contain two or more types of cyclic organic compounds.

[0016] Oxygen radicals are neutral particles with an unpaired electron. Although, strictly speaking, triplet oxygen atoms do not have an unpaired electron, in this specification, oxygen radicals are intended to include triplet and singlet oxygen atoms.

[0017] The pH of the oxygen radical activation aqueous solution is, for example, 5 to 8, and can also be 6 to 8. In other words, it is neutral or weakly acidic. Therefore, it is particularly effective for sterilizing agricultural products. For example, if the oxygen radical activation aqueous solution of the first embodiment is used on agricultural products being hydroponically grown, the pH of the water will not change, and therefore the agricultural products can be sterilized without affecting the growth of the crops. In addition, tryptophan is an essential amino acid, so it is also safe.

[0018] The mechanism by which an oxygen radical-activated aqueous solution with bactericidal properties is produced by irradiating an aqueous solution containing a cyclic organic compound with a pyrrole ring with oxygen radicals is unknown, but it is thought that the oxygen radicals induce some kind of chemical reaction to produce an active substance capable of sterilization.

[0019] The reason why the temperature of the oxygen radical activated aqueous solution is kept below 15°C from the time of oxygen radical irradiation until it is used to sterilize the object is because the sterilizing effect is reduced if the temperature of the oxygen radical activated aqueous solution is higher than 15°C. This is thought to be because the active substances generated by the irradiation of oxygen radicals are decomposed. Since the sterilizing effect can be maintained at 15°C or below, the oxygen radical activated aqueous solution can be stored after it is created.

[0020] Furthermore, when irradiated with oxygen radicals, the solution should be in a liquid state at 15°C or below, but a lower temperature is preferable. After irradiation with oxygen radicals, the oxygen radical activated aqueous solution may be frozen by cooling it to a temperature below its freezing point, which allows the solution to be stored for a longer period of time. In this case, the oxygen radical activated aqueous solution can be thawed before use for sterilization.

[0021] The temperature of the aqueous solution rises due to the irradiation of oxygen radicals, so it is preferable to measure the temperature of the aqueous solution during irradiation with oxygen radicals and perform feedback control so that the temperature of the aqueous solution does not exceed 15°C.

[0022] It is more preferable to maintain the temperature of the oxygen radical activated aqueous solution at 10°C or below. This can further prevent a decrease in the bactericidal effect. The lower limit of the temperature is arbitrary as long as it is higher than the freezing point of the aqueous solution.

[0023] The sterilizing effect of the oxygen radical activated aqueous solution disappears when its temperature is raised above 20° C. Therefore, sterilization may be terminated by raising the temperature of the oxygen radical activated aqueous solution to above 20° C. The end time of sterilization can be controlled with high precision by controlling the temperature.

[0024] The concentration of the cyclic organic compound in the aqueous solution is preferably 10 mM (M=mol / L) or more, which can further improve the bactericidal effect.

[0025] As described above, the sterilization method of the first embodiment can maintain the sterilizing effect of the oxygen radical activated aqueous solution. Therefore, it is not necessary to use the oxygen radical activated aqueous solution generated by irradiation with oxygen radicals for sterilization immediately after generation, but the generated oxygen radical activated aqueous solution can be stored and taken out as needed for sterilization.

[0026] Next, the configuration of the oxygen radical activation aqueous solution generating device of the first embodiment will be described.

[0027] Figure 1 shows the configuration of an apparatus for generating an oxygen radical activated aqueous solution. As shown in Figure 1, the sterilization apparatus has a chamber 110, a holding unit 120, a gas supply unit 130, a gas exhaust unit 140, a plastic cover 150, a radical irradiation unit 200, and a cooler 300. It may also have an injector that irradiates the oxygen radical activated aqueous solution onto the object to be sterilized.

[0028] The chamber 110 accommodates the radical irradiation unit 200 and also accommodates a gas that is shielded from the atmosphere.

[0029] The holder 120 is a container for holding the aqueous solution to be irradiated with plasma, and is a container for holding the oxygen radical activated aqueous solution generated after plasma irradiation. The aqueous solution contains a cyclic organic compound having a pyrrole ring. The holder 120 is also slidable in a direction perpendicular to the direction of plasma irradiation. Therefore, when the aqueous solution is irradiated with plasma products, the aqueous solution can be uniformly irradiated with the plasma products.

[0030] The gas supply unit 130 is for supplying an inert gas such as argon into the interior of the chamber 110. The gas exhaust unit 140 is for exhausting gas from the interior of the chamber 110. The plastic cover 150 is for preventing the atmosphere of the chamber 110 from entering the interior of the plastic cover 150 while the radicals are being irradiated. The holder 120 is disposed inside the plastic cover 150. Therefore, the radicals can be suitably irradiated onto the aqueous solution while excluding the influence of the external atmosphere.

[0031] The radical irradiation unit 200 irradiates radicals among plasma products generated in the plasma generation region. Here, plasma products refer to chemical species and the like generated in the plasma generation region. In other words, plasma products include ions, electrons, radicals, light, and the like. The radical irradiation unit 200 irradiates oxygen radicals among these plasma products. Specifically, the radical irradiation unit 200 irradiates triplet oxygen atoms and singlet oxygen molecules. The radical irradiation unit 200 may also irradiate ozone. Note that, as will be described later, the radical irradiation unit 200 does not irradiate light such as ultraviolet light. The radical irradiation unit 200 also does not irradiate electrons or ions.

[0032] As shown in Fig. 1, the radical irradiation unit 200 has an irradiation port 210, a plasma gas supply unit 220, a power supply unit 230, and a robot arm 240. The irradiation port 210 is for irradiating the aqueous solution with radicals. The plasma gas supply unit 220 is for supplying plasma gas to the radical irradiation unit 200. The plasma gas is a mixed gas of oxygen and an inert gas (e.g., argon). The power supply unit 230 is for supplying power to each unit of the radical irradiation unit 200. The robot arm 240 is for moving the radical irradiation unit 200.

[0033] 2 is a perspective view showing the irradiation port 210. The irradiation port 210 has two slits 211. The slits 211 are openings with a length of 16 mm and a width of 0.5 mm. Radicals are irradiated from the slits 211. The irradiation port 210 can be moved in the width direction of the slits 211. This is to irradiate the radicals evenly into the aqueous solution.

[0034] Next, the internal structure of the radical irradiation part 200 will be described with reference to Fig. 3. The radical irradiation part 200 further includes a discharge part 250, an intermediate structure part 260, and a nozzle part 270.

[0035] The discharge unit 250 has a plasma generation region therein. Therefore, the discharge unit 250 has a pair of opposing electrodes. Plasma is generated in the space between the pair of electrodes. The plasma contains ions, electrons, radicals, ultraviolet rays, etc.

[0036] The intermediate structure 260 is a structure that removes ions, electrons, and ultraviolet rays from the plasma, and therefore, neutral particles including radicals generated from the plasma are supplied to the nozzle 270.

[0037] The nozzle unit 270 is for sending neutral particles containing radicals to the slit 211 of the irradiation port 210. That is, the radical irradiation unit 200 of this embodiment sprays neutral particles, which are plasma products, onto the aqueous solution. These neutral particles contain radicals and argon atoms.

[0038] The cooler 300 cools the holding unit 120. As long as the cooler 300 can cool the holding unit 120, it may be disposed inside or outside the chamber 110. The aqueous solution held in the holding unit 120 is maintained in a liquid state at 15°C or below by the cooler 300. After the aqueous solution is irradiated with oxygen plasma to generate the oxygen radical activated aqueous solution, it may remain in a liquid state at 15°C or below, or may be frozen into a solid state.

[0039] 4, in addition to the cooler 300, a heater 500 may be provided to heat the holding unit 120. By heating the oxygen radical activated aqueous solution held in the holding unit 120 by the heater 500 to 20°C or higher, the sterilizing effect can be eliminated.

[0040] As described above, in the apparatus for generating an oxygen radical activated aqueous solution according to the first embodiment, it is not necessary to use the oxygen radical activated aqueous solution for sterilization immediately after it is generated, but it can be used for sterilization at any timing. [Example]

[0041] (Experiment 1) A sterilized dish was placed in a copper dish containing tryptophan. The copper dish was then placed on a Peltier element. A thermocouple temperature sensor was placed in contact with the solution and the Peltier element. The Peltier element and thermocouple temperature sensor were connected to a temperature controller, which controlled the temperature of the solution to a predetermined level.

[0042] Next, the aqueous solution was irradiated with oxygen plasma for 1 minute using the plasma irradiation unit 200 of the first embodiment. The total gas flow rate was 5 slm, the Ar gas flow rate was 4.97 slm, the volume fraction of oxygen was 0.6%, and the density of triplet oxygen atoms was 2×10 15 / cm 3 The irradiation distance was set to 10 mm.

[0043] Next, 0.3 mL of the aqueous solution was removed from the sterilized dish and added to the E. coli suspension (solvent: phosphate buffer). The density of the E. coli in the E. coli suspension was 1 × 10 8 The tryptophan concentration in the aqueous solution was adjusted to 1 mM. 0.3 mL of the E. coli suspension was then removed and placed back into a sterilized dish, which was then allowed to stand for 1 minute.

[0044] Next, the aqueous solution was removed from the sterilized dish and 100 μL was dropped onto the culture dish, and after culturing at 37° C. for 24 hours, the number of colonies was counted.

[0045] Figure 5 is a graph showing the relationship between the temperature of the aqueous solution (temperature before plasma irradiation) and the number of colonies. The temperature of the aqueous solution was varied in 5°C increments from -5 to 20°C. For comparison, the number of colonies was measured in the same manner when the aqueous solution was not irradiated with oxygen plasma and the temperature was set to -5°C. Note that due to freezing point depression, the aqueous solution remains in a liquid state even at -5°C.

[0046] As shown in Figure 5, at temperatures between -5 and 10°C, the number of colonies was below the detection limit. This indicates that a strong bactericidal effect can be maintained by maintaining the temperature of the aqueous solution between -5 and 10°C. On the other hand, when oxygen plasma was not irradiated, the number of colonies was approximately 1 x 10 7 CFU / mL. It was confirmed that no bactericidal components were produced without oxygen plasma irradiation. In addition, at 15°C, the colony count was approximately 1 x 10 5 CFU / mL, indicating a reduced bactericidal effect. At 20°C, the number of colonies was approximately 4 × 10 6The CFU / mL was not significantly different from that without oxygen plasma irradiation. In other words, the bactericidal effect almost disappeared at 20°C. From these results, it was found that the temperature of the aqueous solution must be kept below 15°C to maintain the bactericidal effect, and that a temperature of 10°C or below is preferable to ensure sufficient bactericidal effect.

[0047] (Experiment 2) The temperature of the aqueous solution was set to 0°C, and the tryptophan concentration of the aqueous solution was varied, and the number of colonies was counted in the same manner as in Experiment 1.

[0048] Figure 6 is a graph showing the relationship between tryptophan concentration and colony count. As shown in Figure 6, the colony count decreased significantly when the tryptophan concentration exceeded 2.5 mM, and was below the detection limit at 10 mM or higher. This indicates that in order to maintain bactericidal effect, the tryptophan concentration should be 5 mM or higher, and more preferably 10 mM or higher.

[0049] (Experiment 3) An aqueous solution containing tryptophan was irradiated with oxygen plasma for 3 minutes. The tryptophan concentration was 50 mM, and the temperature of the aqueous solution before oxygen plasma irradiation was 0°C. The aqueous solution was then collected in a container, frozen in liquid nitrogen, and stored at -80°C for a predetermined period of time. An E. coli suspension was then added to the container, and the container was immersed in water at 15°C to thaw the aqueous solution and allow it to react with the E. coli. The number of colonies was then counted in the same manner as in Experiment 1.

[0050] Figure 7 is a graph showing the relationship between storage time and colony count. As shown in Figure 7, after 15 minutes of storage, the number of colonies was approximately 1 x 10 5 CFU / mL, approximately 1 × 10 4 CFU / mL, which is higher than the colony count of 1 × 10 without oxygen plasma irradiation. 7 The number was lower than CFU / mL. As a result, it was found that the bactericidal effect can be maintained for a long time by freezing the aqueous solution after oxygen plasma irradiation.

[0051] (Experiment 4) Instead of tryptophan, an aqueous solution containing benzene, pyrrole, or indole was prepared, and an E. coli suspension was added. The aqueous solution was then irradiated with oxygen plasma for 5 minutes. The number of colonies was then counted in the same manner as in Experiment 1. For comparison, the number of colonies was also counted without oxygen plasma irradiation.

[0052] As shown in Figure 8, benzene had no bactericidal effect even when exposed to oxygen plasma. On the other hand, pyrrole and indole had a bactericidal effect, as the colony counts were reduced to below the detection limit after oxygen plasma exposure. This indicates that the pyrrole ring is closely related to the bactericidal effect. [Industrial Applicability]

[0053] The present disclosure can be used for various types of sterilization. [Explanation of symbols]

[0054] 110: Chamber 120: Holding part 130: Gas supply unit 140: Gas exhaust section 200: Radical irradiation unit 210: Irradiation port 211: Slit 250:Discharge part 260: Intermediate structure part 270: Nozzle section 300: Cooler 500: Heater

Claims

1. a holding unit that holds the aqueous solution containing the cyclic organic compound having a pyrrole ring in a liquid state at 15°C or less; an oxygen radical irradiation device that irradiates the aqueous solution held in the holding unit with oxygen radicals to generate an oxygen radical activated aqueous solution; An apparatus for generating an oxygen radical activated aqueous solution, comprising:

2. 2. The apparatus for generating an oxygen radical activation aqueous solution according to claim 1, wherein the cyclic organic compound is tryptophan, pyrrole, or indole.

3. 3. The oxygen radical activation aqueous solution generating apparatus according to claim 1, wherein the oxygen radical activation aqueous solution has a pH of 5 or more and 8 or less.

4. 4. The oxygen radical activation aqueous solution generating apparatus according to claim 1, wherein the concentration of the cyclic organic compound in the aqueous solution is 10 mM or more.

5. an aqueous solution containing a cyclic organic compound having a pyrrole ring is maintained in a liquid state at 15°C or less, and the aqueous solution is irradiated with oxygen radicals to produce an oxygen radical activated aqueous solution; The oxygen radical activated aqueous solution is kept at a temperature of 15°C or less while sterilizing the object. The oxygen radical activated aqueous solution is heated to 20°C or higher to complete the sterilization of the object. A sterilization method characterized by the above.

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