Carbon oxide quantum dot antimicrobial agent

Abstract

The purpose of the present invention is to provide: an antimicrobial agent which is based on carbon-based quantum dots and for which there are no concerns in terms of health and safety; and a method for more efficiently producing carbon-based quantum dots which can be used in such an antimicrobial agent, etc. Provided is an antimicrobial agent containing carbon oxide quantum dots. Also provided is a method for producing the antimicrobial agent, the method comprising a step for producing carbon oxide quantum dots. The step for producing the quantum dots comprises: a step for obtaining nanofiber cellulose by nanofiberizing a cellulose-containing raw material; and a step for heating the obtained nanofiber cellulose in water to a temperature of 100-350°C at a pressure of 200 kPa-20 MPa.

Description

Oxidized Carbon Quantum Dot Antimicrobial Agent

[0001] The present invention relates to antimicrobial agents, particularly to antimicrobial agents containing oxidized carbon quantum dots, and methods for making the same.

[0002] Carbon-based quantum dots have been attracting attention in recent years. Quantum dots are nanoscale materials that conform to quantum chemistry and quantum mechanics and are typically microparticles with an average diameter of approximately 0.5 to 100 nm. Because of their unique optical properties, they are being investigated as fluorescent materials and other applications (Patent Documents 1 and 2). Carbon-based quantum dots, in particular, are compatible with living organisms and are cheaper and safer than metal compound quantum dots. Therefore, their application is being considered not only in electronics applications such as displays, but also in various other fields, including bioimaging, protein analysis, and biomedical applications such as cell tracking (Patent Documents 3 and 4, Non-Patent Document 1).

[0003] Republished WO2016 / 129441 Patent Publication No. 2017-43539 Republished WO2019 / 193910 Patent Publication No. 2022-529223

[0004] A. Kundu, et al. , ACS Omega, 2023, 8, 22178

[0005] Furthermore, as an example of application in the biomedical field, Patent Document 4 discloses a technology using carbon quantum dots as an antibacterial agent. However, such carbon quantum dot-based antibacterial agents are in the early stages of research, and there are currently many areas that need improvement. For example, the antibacterial agent described in Patent Document 4 contains a diamine compound and a halogen, which raises concerns about its safety to living organisms. The antibacterial agent also inhibits bacterial growth using a halogen component, and it is difficult to say that it utilizes the properties of carbon-based quantum dots themselves. Furthermore, these antibacterial agents have room for improvement in terms of the manufacturing efficiency of carbon-based quantum dots.

[0006] In order to solve the above-mentioned problems, the present invention aims to provide an antimicrobial agent based on carbon-based quantum dots that does not pose safety and hygiene concerns, and a method for more efficiently producing carbon-based quantum dots that can be used in such antimicrobial agents, etc.

[0007] As a result of intensive research to solve the above-mentioned problems, the inventors of the present invention discovered that oxidized carbon quantum dots, which are carbon-based quantum dots containing oxygen atoms, exhibit excellent antimicrobial activity even though they do not contain halogen components, and that when producing carbon-based quantum dots that can be used in such antimicrobial agents, etc. from raw materials containing cellulose, the production efficiency can be improved by first converting the raw materials into nanofibers, thereby completing the present invention.

[0008] That is, the present invention provides the following (1) to (8): (1) An antimicrobial agent containing oxidized carbon quantum dots. (2) The antimicrobial agent of (1) above, wherein the oxidized carbon quantum dots are graphene-based quantum dots having carbonyl groups. (3) The antimicrobial agent of (1) or (2) above, wherein the amount of oxygen atoms contained in 100 parts by mass of the oxidized carbon quantum dots is 2 to 80 parts by mass. (4) The antimicrobial agent of (3) above, wherein the oxidized carbon quantum dots further contain nitrogen atoms, and the amount of the nitrogen atoms contained in 100 parts by mass of the oxidized carbon quantum dots is 2 to 80 parts by mass. (5) The antimicrobial agent of (1) or (2) above, wherein the oxidized carbon quantum dots are halogen-free. (6) A method for producing the antimicrobial agent of (1) above, comprising a quantum dot production step of producing the oxidized carbon quantum dots, the quantum dot production step comprising: nanofiberizing a cellulose-containing raw material to obtain nanofiber cellulose, and heating the obtained nanofiber cellulose in water at a temperature of 100 to 350°C under a pressure of 200 kPa to 20 MPa. (7) A method for producing oxidized carbon quantum dots, comprising: nanofiberizing a cellulose-containing raw material to obtain nanofiber cellulose, and heating the obtained nanofiber cellulose in water at a temperature of 100 to 350°C under a pressure of 200 kPa to 20 MPa. (8) The production method of (6) or (7) above, wherein the nanofiber cellulose is a fibrous material having a diameter of 2 to 200 nm and a length of 50 nm to 500 μm.

[0009] According to the present invention, an antimicrobial agent based on carbon-based quantum dots is provided that is free from safety and hygiene concerns. Furthermore, according to the manufacturing method of the present invention, oxidized carbon quantum dots that can be used in such antimicrobial agents can be more efficiently manufactured.

[0010] FIG. 2 is a photograph showing the results of an antibacterial test in Example 1.

[0011] Representative embodiments of the present invention will be described in detail below, but the present invention is not limited to these.

[0012] <Antimicrobial Agent> The antimicrobial agent of this embodiment is characterized by containing oxidized carbon quantum dots. Here, the antimicrobial agent is a chemotherapeutic agent that suppresses the growth, activity, development, proliferation, etc. of microorganisms. Note that examples of microorganisms include prokaryotes such as bacteria and archaea, unicellular eukaryotes such as fungi including mold and protozoa, viruses such as pathogenic viruses and phages, cell colonies such as lichens, and even spores that are parts of these. In other words, the antimicrobial agent of this embodiment includes antibacterial agents, antifungal agents, antiviral agents, etc.

[0013] <Oxidized Carbon Quantum Dots> Oxidized carbon quantum dots themselves are known. They are fine particles composed mainly of carbon atoms and containing small amounts of oxygen atoms, etc., with an average diameter of about 0.5 to 100 nm, particularly about 1.0 to 10 nm. The inventors have discovered that these fine particles exhibit antimicrobial effects, including antibacterial effects.

[0014] Carbon oxide quantum dots can be produced by existing top-down and bottom-up methods (see Patent Document 1). The top-down method involves decomposing bulk materials with graphite structures, such as carbon fiber, coke, and graphene oxide, to the nano-level using physical and chemical techniques. The bottom-up method involves chemically synthesizing carbon quantum dots by calcining or hydrothermal reaction using low-molecular-weight compounds as carbon sources.

[0015] The bottom-up method can be carried out by hydrothermal reaction or by using oxygen-containing organic compounds such as cellulose as low molecular weight compounds, thereby incorporating oxygen atoms into quantum dots, and oxidized carbon quantum dots can be easily produced. Recently, hydrothermal synthesis methods using waste cellulose materials such as orange peels and waste agricultural materials, as well as wood flour, have also been investigated (Non-Patent Document 1).

[0016] Oxidized carbon quantum dots may also be produced by oxidizing commercially available carbon-based quantum dots, such as those available from Sigma-Aldrich Corporation, Fuji Pigment Co., Ltd., GS Alliance Co., Ltd., Funakoshi Co., Ltd., and Kishida Chemical Co., Ltd., with an oxidizing agent. Carbon-based quantum dots are typically SP ２ It is composed of graphene, which has a hexagonal lattice structure mainly composed of bonded carbon. Examples include, but are not limited to, graphene (in the narrow sense), carbon nanotubes (CNTs), fullerenes, carbon nanohorns, and carbon nanofibers. Note that all of these carbon materials have a graphene structure and are therefore included in the broad definition of graphene. Hereinafter, unless otherwise specified, "graphene" will be used in the broad sense to include CNTs, fullerenes, and the like.

[0017] The oxidized carbon quantum dots of this embodiment also preferably have the graphene structure described above. When some of the carbon atoms in this graphene bond with oxygen to form, for example, a carbonyl group or a hydroxyl group, the oxidized carbon quantum dots are generated. In the antimicrobial agent of this embodiment, the oxidized carbon quantum dots are preferably graphene-based quantum dots having a carbonyl group. Here, the carbonyl group broadly means a group having a double bond between oxygen and carbon, and includes, in addition to a -C(=O)- group or a -C(=O)-H group, -C(=O)-NH- or -C(=O)-NH ２ The groups include amide groups, carboxy groups, ester groups, acid anhydride groups, and the like.

[0018] The oxidized carbon quantum dots in this embodiment preferably contain 2 to 80 parts by mass, preferably 3 to 40 parts by mass, and particularly preferably 5 to 25 parts by mass of oxygen atoms per 100 parts by mass of total mass (including the remaining raw materials and moisture contained in the oxidized carbon quantum dots). Oxidized carbon quantum dots with such an oxygen content can exhibit more pronounced antimicrobial properties.

[0019] Although the present invention is not limited by any particular theory, it is believed that the effectiveness of the antimicrobial agent of this embodiment is due to the carbon-based quantum dots becoming more compatible with cells and the surrounding environment upon oxidation. Carbon-based quantum dots are known to exhibit antibacterial activity (see, for example, Patent Document 4). When carbonyl groups or hydroxyl groups are generated by oxidation, they become more likely to come into contact with the cell surface of microorganisms, potentially making the antimicrobial activity more readily apparent. Furthermore, depending on the type and synthesis method of carbon-based quantum dots, polyphenols used as raw materials for the hydrothermal reaction may remain, potentially contributing to the antimicrobial activity. In particular, when the raw materials contain nitrogen, nitrogen-containing functional groups such as amino groups or amide groups may be formed on the carbon-based quantum dots, which may then adhere to and penetrate the cell membranes of microorganisms, potentially resulting in genetic mutations or the generation of reactive oxygen species.

[0020] The oxidized carbon quantum dots of this embodiment further contain nitrogen atoms, and the amount of nitrogen atoms contained in the oxidized carbon quantum dots per 100 parts by mass of their total mass (including the remaining raw materials contained in the oxidized carbon quantum dots) is preferably 2 to 80 parts by mass, more preferably 3 to 40 parts by mass, and even more preferably 5 to 25 parts by mass. The form of the nitrogen contained is not particularly limited, and may be, for example, an amino group, an imino group, an amide group, or the like. Nitrogen-containing oxidized carbon quantum dots are commercially available from Fuji Dye Co., Ltd., GS Alliance Co., Ltd., and the like.

[0021] The antimicrobial agent of this embodiment is believed to exhibit antimicrobial properties due to the oxygen-containing functional group as described above, and does not require halogen components, which are essential for the antibacterial composition described in, for example, Patent Document 4. Therefore, it can be used without concerns about safety and hygiene. The antimicrobial agent of this embodiment preferably contains halogen-free oxidized carbon quantum dots, and more preferably contains halogen- and heavy metal-free oxidized carbon quantum dots.

[0022] There are no particular limitations on the average particle size (diameter) of the oxidized carbon quantum dots, and they can be, for example, about 0.5 to 100 nm, particularly about 1.0 to 10 nm, which is the average size of typical carbon quantum dots. The term "diameter" refers to the distance from one end of the oxidized carbon quantum dot particle to the other, not from the center. In other words, the oxidized carbon quantum dots do not have to be spherical, and may be, for example, disk-shaped, spheroidal, or even irregular polygonal.

[0023] <Form of Antimicrobial Agent> The antimicrobial agent of this embodiment may be in any form as long as it contains the oxidized carbon quantum dots described above. For example, the oxidized carbon quantum dots themselves can be used in the form of a fine powder or formed into tablets, etc. They can also be used by dispersing them in water, ethanol, glycerin, or even gels such as agar. The antimicrobial agent of this embodiment may also contain components other than the oxidized carbon quantum dots, such as dispersants, pH adjusters, nutrients, herbicides, insecticides, recombinant genes, and even other antibacterial agents such as silver ions and zinc pyrithione, antifungal agents, antiviral agents, etc.

[0024] <Method of Use of Antimicrobial Agent> There are no particular limitations on the method of use of the antimicrobial agent of this embodiment. For example, fine particles of oxidized carbon quantum dots may be sprinkled on an object to be treated to which antimicrobial properties are to be imparted, or a paint or ink containing oxidized carbon quantum dots may be applied to the object to be treated. Furthermore, objects against which microbial growth should be prevented, such as tableware or medical instruments, may be stored in a dispersion of the antimicrobial agent of this embodiment. It is believed that the antimicrobial agent of this embodiment also exhibits further antimicrobial activity by irradiating the oxidized carbon quantum dots with light, which causes electron excitation and the generation of active oxygen. Therefore, the antimicrobial agent of this embodiment is also suitable for applications exposed to sunlight, such as agricultural materials and building materials.

[0025] <<Method for Producing Antimicrobial Agent>> The antimicrobial agent of the above embodiment can be produced by the bottom-up method using hydrothermal reaction described above, etc. Specifically, the antimicrobial agent can be obtained by a production method that has a quantum dot production process for producing oxidized carbon quantum dots, and the quantum dot production process includes a step of nanofiberizing a cellulose-containing raw material to obtain nanofiber cellulose, and a step of heating the obtained nanofiber cellulose in water at a temperature of 100 to 350°C under a pressure of 200 kPa to 20 MPa.

[0026] <Cellulose-Containing Raw Material> The first requirement for the manufacturing method of this embodiment is that a raw material containing cellulose be used for the hydrothermal reaction. There are no particular limitations on the cellulose-containing raw material, and general-purpose plant materials can be used. For example, grasses such as straw, wood, seaweed, and even waste agricultural materials such as fruit bark, food waste, waste paper, and used clothing may be used. In particular, the use of waste wood, waste agricultural materials, waste paper, and the like leads to waste reduction and reuse, which is beneficial from the perspective of environmental conservation. Furthermore, since carbon dioxide quantum dots can be synthesized relatively easily and production costs can be reduced, the use of waste materials is also advantageous from a cost perspective. Furthermore, seaweed contains a large amount of nitrogen compounds such as amino acids, and depending on the variety, it also has a high nitrogen uptake capacity, making it useful as a raw material for producing nitrogen-containing carbon dioxide quantum dots.

[0027] <Nanofiber Formation> The second requirement in the production method of this embodiment is to form the cellulose-containing raw material into nanofibers. By forming the cellulose-containing raw material into nanofibers, it becomes possible to produce oxidized carbon quantum dots more efficiently.

[0028] There are no particular limitations on the method of nanofiberization, and various known methods can be used. Examples include, but are not limited to, physical crushing methods such as mechanical pulverization and grinding using a mill-type ultrafine grinder such as the Supermass Colloider manufactured by Masuko Sangyo Co., Ltd., and chemical crushing methods using Schweitzer solution, etc. Furthermore, either a wet method or a dry method can be used. However, nanofiberization of cellulose-containing raw materials is preferably carried out using a wet method. Furthermore, high pressure may be applied during nanofiberization.

[0029] When forming nanofibers, it is preferable to form the cellulose-containing raw material into a fibrous substance having a diameter of 2 to 200 nm and a length of 50 nm to 500 μm, and particularly a diameter of 20 to 800 nm and a length of 100 nm to 200 μm. Nanofiber cellulose of such sizes further improves the efficiency of producing oxidized carbon quantum dots by hydrothermal reaction.

[0030] <Hydrothermal Reaction> In the production method of this embodiment, the nanofiber cellulose obtained as described above is then subjected to a hydrothermal reaction. The hydrothermal reaction may be carried out in water using a general-purpose apparatus such as an autoclave under a pressure of about 200 kPa to 20 MPa, particularly about 500 kPa to 10 MPa, and at a temperature of about 100 to 350°C, preferably about 200 to 300°C, particularly about 220 to 280°C. There are no particular restrictions on the reaction time, but it is preferable to react for, for example, 1 minute to 72 hours, particularly about 1 to 12 hours.

[0031] In addition, during the hydrothermal reaction, components (auxiliary materials) other than nanofiber cellulose can also be used as raw materials for oxidized carbon quantum dots. These auxiliary materials include, but are not limited to, organic acids such as aliphatic hydroxycarboxylic acids, aromatic hydroxycarboxylic acids, polycarboxylic acids, ascorbic acid, and sugars such as monosaccharides and disaccharides. These compounds are useful as auxiliary materials in this embodiment because they are not harmful to the human body and are low-cost. When producing nitrogen-containing oxidized carbon quantum dots, nitrogen compounds such as urea, ammonia, and sodium nitrate may also be used in combination. Preferred nitrogen compounds include organic amine compounds and amino acids.

[0032] The hydrothermal reaction can be carried out without a catalyst, or may be carried out with the addition of an acid catalyst. Examples of acid catalysts include, but are not limited to, inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid; organic acids such as sulfonic acids including p-toluenesulfonic acid; and solid acid catalysts such as cationic ion exchange resins and ion exchange membranes. However, from the standpoint of safety and hygiene, a hydrothermal reaction without a catalyst is preferred.

[0033] <Post-treatment> By the hydrothermal reaction described above, oxidized carbon quantum dots are usually obtained in the form of an aqueous dispersion. This aqueous dispersion can be used as an antimicrobial agent, fluorescent material, or electronic material as is, but it may also be subjected to post-treatment such as purification or mixing with other components. Preferably, the dispersion is filtered using a glass filter or the like to remove reaction residues and impurities.

[0034] <Method for Producing Oxidized Carbon Quantum Dots> The oxidized carbon quantum dots obtained by the manufacturing method of the above embodiment can be used for various purposes other than antimicrobial agents. For example, they can be used for biomedical analytical reagents such as bioimaging, protein analysis, and cell tracking, as well as agricultural applications such as plant disease prevention, soil revitalization, fermentation promotion of compost, and insect repellent. Furthermore, by taking advantage of their unique optical properties, they can also be used as fluorescent materials, electronic materials such as display and battery materials, photocatalysts, etc.

[0035] The present invention also encompasses a method for producing oxidized carbon quantum dots, which includes the steps of nanofiberizing a cellulose-containing raw material to obtain nanofiber cellulose, and heating the obtained nanofiber cellulose in water at a temperature of 100 to 350°C under a pressure of 200 kPa to 20 MPa. The type of cellulose-containing raw material and the details of the hydrothermal synthesis conditions in this method for producing oxidized carbon quantum dots can be the same as those used in the method for producing antimicrobial agents described above. The production method of this embodiment makes it possible to obtain oxidized carbon quantum dots, which are useful as electronics materials, photocatalysts, and the like, with a higher quantum yield.

[0036] The present invention will be described in more detail below with reference to examples. These examples are provided solely for the purpose of illustrating specific aspects and embodiments, in order to facilitate understanding of the concept and scope of the present invention as disclosed herein and as set forth in the appended claims, and the present invention is not limited to these examples in any way.

[0037] <Preparation of Antimicrobial Agent and Evaluation of Antibacterial Properties> [Example 1] Waste wood was cut into small pieces with scissors, and 1 g of these small pieces was mixed with 50 g of water. This mixture was converted into nanofibers with a size of approximately 100 nm in diameter and 5000 nm in length using a physical disintegrator (Supermass Colloider, manufactured by Masuko Sangyo Co., Ltd.), yielding a gel-like substance. The resulting gel-like substance was placed in an autoclave and reacted at 250°C (pressure: approximately 4 MPa) for 6 hours. After cooling, the contents were removed from the autoclave and filtered through a glass filter to remove solid reaction residues. The resulting filtrate was irradiated with violet light at a wavelength of 405 nm using a Quantaurus-QY Plus Expanded Absolute PL Quantum Yield Spectrometer C13534-11 manufactured by Hamamatsu Photonics. Luminescence was observed, demonstrating the production of quantum dots. It should be noted that previous studies using Raman spectroscopy, infrared absorption spectroscopy, etc. have confirmed that oxidized carbon quantum dots can be produced from purified cellulose under similar conditions.

[0038] Saliva was dropped onto the agar medium in a petri dish, and then five drops (approximately 1.5 ml) of the filtrate obtained above were dropped onto it, and the dish was kept at 37° C. for 36 hours. Photographs of the dish after the holding period and a petri dish kept under the same conditions without the drop of the oxidized carbon quantum dot-containing filtrate are shown in FIG.

[0039] As shown in Figure 1, bacterial growth was significantly suppressed in the petri dish into which the oxidized carbon quantum dot-containing filtrate was dropped. Note that in this example, no catalysts or raw materials containing halogens or heavy metals were used. It was revealed that the agent containing oxidized carbon quantum dots according to the present invention exhibits antibacterial effects even without the inclusion of halogen components. It was also demonstrated that oxidized carbon quantum dots can be produced without a catalyst from waste wood, a harmless cellulose-based raw material.

[0040] <<Study on the manufacturing method of antimicrobial agent>> [Example 1] The quantum yield of the entire filtrate of the oxidized carbon quantum dots manufactured by the method of Example 1, which includes a nanofiber manufacturing process, was measured from the light emission upon irradiation with violet light, and was found to be 6.9%.

[0041] Comparative Example 1: An attempt was made to prepare a filtrate containing oxidized carbon quantum dots under the same conditions as in Example 1, except that the amount of water per gram of waste wood chips was 20 g and nanofiberization was not performed. In this comparative example, carbonized raw material remained on the filter during filtration. The obtained filtrate emitted light when irradiated with violet light at a wavelength of 405 nm. However, the quantum yield was 3.2%, a lower value than in Example 1, in which the cellulose raw material was nanofiberized, even though the raw material concentration was approximately 2.5 times that of Example 1.

[0042] [Examples 2 to 4 and Comparative Examples 2 to 4] Instead of waste wood, old newspapers were used as raw materials, and the same operations as in Example 1, including nanofiber formation, hydrothermal synthesis, filtration, and measurement, were carried out (Example 2). Furthermore, the same operations as in Example 2 were carried out, except that tangerine peel or waste seaweed was used instead of old newspapers (Examples 3 to 4). Furthermore, the same operations as in Examples 2 to 4 were carried out, except that the amount of water per gram of raw material piece was 20 g and nanofiber formation was not carried out (Comparative Examples 2 to 4). The quantum yield measurement results for each of the obtained liquid samples are shown in Table 1 below, along with the results for Example 1 and Comparative Example 1.

[0043]

[0044] As shown in Table 1, in Examples 1 to 4, in which the cellulose-containing raw material was nanofiberized according to the present invention, the quantum yield was improved compared to Comparative Examples 1 to 4, in which nanofiberization was not performed. It was also revealed that oxidized carbon quantum dots can be produced from old newspapers, agricultural waste, etc.

Claims

1. An antimicrobial agent containing oxidized carbon quantum dots.

2. The antimicrobial agent according to claim 1, wherein the oxidized carbon quantum dots are graphene-based quantum dots having carbonyl groups.

3. The antimicrobial agent according to claim 1 or 2, wherein the amount of oxygen atoms contained in 100 parts by mass of the oxidized carbon quantum dots is 2 to 80 parts by mass.

4. The antimicrobial agent according to claim 3, wherein the oxidized carbon quantum dots further contain nitrogen atoms, and the amount of the nitrogen atoms contained in 100 parts by mass of the oxidized carbon quantum dots is 2 to 80 parts by mass.

5. The antimicrobial agent according to claim 1 or 2, wherein the oxidized carbon quantum dots are halogen-free.

6. A method for producing the antimicrobial agent according to claim 1, comprising a quantum dot production process for producing the oxidized carbon quantum dots, the quantum dot production process comprising: a process for nanofiberizing a raw material containing cellulose to obtain nanofiber cellulose; and a process for heating the obtained nanofiber cellulose in water at a temperature of 100 to 350°C under a pressure of 200 kPa to 20 MPa.

7. A method for producing oxidized carbon quantum dots, comprising: a step of nanofiberizing a raw material containing cellulose to obtain nanofiber cellulose; and a step of heating the obtained nanofiber cellulose in water at a temperature of 100 to 350°C under a pressure of 200 kPa to 20 MPa.

8. The method of claim 6 or 7, wherein the nanofiber cellulose is a fibrous material having a diameter of 2 to 200 nm and a length of 50 nm to 500 μm.

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