WO2024147001A1

WO2024147001A1 - Disinfectant formulation

Info

Publication number: WO2024147001A1
Application number: PCT/GB2023/052698
Authority: WO
Inventors: Davy STOKER
Original assignee: Micronclean Ltd
Current assignee: Micronclean Ltd
Priority date: 2023-01-06
Filing date: 2023-10-18
Publication date: 2024-07-11
Anticipated expiration: 2025-07-06
Also published as: GB202315915D0; GB2626064A; GB2626064B

Abstract

An aqueous disinfectant formulation suitable for sterilisation by exposure to ionising radiation to enable use of the disinfectant formulation in sterile environments. The disinfectant formulation comprises at least one biocidal active; a pH modifier (or buffer) and an antimicrobial metal active. The antimicrobial metal active is more resistant to degradation as a result of ionising radiation and in some cases shows enhanced biocidal activity following irradiation.

Description

Disinfectant Formulation

Field of invention

The present invention relates to disinfectant formulations, methods for preparing disinfectant formulations, and methods for preparing sterile disinfectant formulations and sterile cleaning articles containing disinfectant formulations. In particular the present invention relates to disinfectant formulations suitable for irradiation sterilisation, and irradiation sterilised disinfectant formulations for cleanroom disinfectants and the preparation of sterile cleaning articles for use in cleanrooms.

Background art

Cleanrooms are widely used in scientific research in life sciences and electronics as well as in the production of electronic components such as semiconductor devices, battery technology, aerospace engineering and other products which are highly sensitive to contamination. A constant airflow of highly filtered, clean and (in some cases) sterile air with a very low concentration of airborne particulate matter is typically provided within the cleanroom to prevent damage or contamination of sensitive work within the room. Depending on the application, exhaust air may also be cleaned, filtered and disinfected to prevent or limit the escape of hazardous material e.g. radioactive material or harmful microbes) from the cleanroom. Cleanrooms are - dependent on application - typically maintained at either positive pressure (to prevent any leaks causing an ingress of untreated air) or negative pressure (to prevent any leaks causing egress of potentially contaminated air).

Staff working within a cleanroom are often required to wear protective clothing to prevent micro-organisms present on human skin and hair from contaminating the cleanroom environment. Staff, materials and equipment typically enter and leave through airlocks and may be subjected on entry/exit to an air shower to remove any contaminants.

Providing a sterile environment within a cleanroom is particularly important where the cleanroom is utilised in biotechnology or pharmaceutical research or production. UV light can be used to disinfect air within the cleanroom, but chemical disinfectants also play an important role, particularly for maintaining sterile surfaces. A variety of chemical disinfectants are available for use in cleanrooms, with more common disinfectants including alcohol-based disinfectants (e.g. aqueous solutions of ethanol or isopropyl alcohol), diamine-based disinfectants, quaternary ammonium based disinfectants and sporicides. Different disinfectants are often rotated to prevent the build-up of resistant organisms. Different disinfectants have different breadths of biocidal activity and rotation also ensures that all target micro-organisms can be effectively destroyed.

Given the different breadth of different disinfectants and the requirement for a sterility to be maintained at all times within the cleanroom, it is often necessary to ensure that disinfectant products (e.g. solutions or wipes) themselves are sterile so that they do not inadvertently contaminate the cleanroom. Sterile disinfectants are produced either using a completely aseptic production method (which is expensive and challenging to maintain for high-volume production) or more commonly by subjecting disinfectants to ionising radiation (such as gamma, x-ray or electron beam radiation) after production.

However ionising radiation can have a negative impact on the efficacy of biocidal actives within the disinfectant. For example, gamma irradiation of aqueous solutions leads to the formation of hydroxyl radicals which can then attack and degrade biocidal actives. For example, quaternary ammonium based biocidal actives may be susceptible to damage from hydroxyl radicals through hydrogen abstraction from the beta carbon to yield an alkene decomposition product, or hydroxyl radicals may directly attack the alpha carbon in an SN2 mechanism.

Summary of the Invention

The present invention seeks to provide disinfectant formulations which are suitable for sterilisation by exposure to ionising radiation and retain their biocidal activity following ionising irradiation, and in certain cases even exhibit increased biocidal activity following ionising irradiation.

Viewed from a first aspect the present invention provides an aqueous disinfectant formulation suitable for sterilisation by exposure to ionising radiation (e.g. gamma radiation), comprising 0.05 wt.% to 60 wt.% of at least one biocidal active; 0.1 wt.% to 20 wt.% of a pH modifier/buffer; and up to 5% of an antimicrobial metal active.

In this context, “aqueous disinfectant formulation” should be interpreted to mean that the formulation contains water as a solvent, although water may not be the only solvent in the formulation. For example, other water miscible solvents may be present with a wt.% less than, equal to or greater than that of water.

Preferably the formulation comprises between 0.001% wt.% and 2.5% wt.% inclusive of the antimicrobial metal active. Particularly preferably the formulation comprises between 1 wt.% and 2 wt.% inclusive of the antimicrobial metal active.

The antimicrobial metal active may be selected from a group consisting of aluminium, bismuth, cobalt, copper, gold, iron, manganese, molybdenum, nickel, platinum, silver, titanium, zirconium and zinc, or combinations thereof. Preferably the antimicrobial metal is selected from the group consisting of copper, silver, and zinc, or combinations thereof. The antimicrobial metal or each antimicrobial metal may be present in the formulation either in a colloidal form (i.e. solid particles of a metal or a water insoluble metal oxide (e.g. titanium(IV) oxide)) or in an ionic form (e.g. as a soluble metal salt or compound). Alternatively the antimicrobial metal or each antimicrobial metal may be present in a mixture of colloidal form and ionic form (e.g. both solid particles of the metal and dissolved as a soluble metal salt).

Colloidal particles of an antimicrobial metal or metal oxide show biocidal activity within formulations, but the level of activity is often lower at comparable concentrations compared to other biocidal actives such as quaternary ammonium compounds. However, when the colloidal particles of an antimicrobial metal or metal oxide are subjected to ionising radiation such as gamma radiation (which would be expected during the production of a sterile formulation), the biocidal activity of the colloidal metal increases post-irradiation. This is likely due to the ionising radiation breaking down larger particles and increasing available surface area of the active. Thus by including colloidal particles of an antimicrobial metal or metal oxide, loss in biocidal activity as a result of irradiation of biocidal actives can be at least partially offset by the increase in biocidal activity of the colloidal antimicrobial metal or metal oxide.

Where an antimicrobial metal is present in a colloidal form, the particles preferably have an average size of between 1 nm and 250 nm ( “average size ” in the context of this application should be taken to be the mean size of 1000 random particles observed within an SEM or TEM image taken of the formulation).

Particularly preferably the particles have an average size of between 100 nm and 200 nm. This particle size range advantageously offers the greatest enhancement of biocidal activity as a result of ionising irradiation.

Where an antimicrobial metal is present in a colloidal form, the antimicrobial metal is preferably in a metallic form i.e. particles of substantially pure metal). Alternatively (or additionally) the antimicrobial metal or each antimicrobial metal may be in an ionic form (/.<?. dissolved within the formulation as a soluble metal salt. For example, where the antimicrobial metal or one of the antimicrobial metals is silver, the formulation may comprise a silver (I) halide (AgX) (e.g. silver fluoride (AgF), silver chloride (AgCl), silver bromide (AgBr), or silver iodide (Agl)), silver (I) sulfide (AgS), silver (II) sulfate (Ag₂SO₄), silver (I) nitrate (AgNO), silver (I) acetate (CFFCChAg) or another silver salt of an organic acid, or silver (I) carbonate (Ag₂CO3), or a combination thereof. Preferably where one or more antimicrobial is present in an ionic form then the formulation includes silver (I) nitrate (AgNO).

Where the antimicrobial metal or one of the antimicrobial metals is copper, the formulation may comprise a copper (I) halide (CuX) or a copper(II) halide (CuX₂) e.g. copper (I) chloride (CuCl) or copper(II) chloride (CuCl₂)), copper (II) benzoate, copper(II) acetate or another copper salt of an organic acid, or copper (II) sulfate (CuSO₄), or a combination thereof.

Where the antimicrobial metal or one of the antimicrobial metals is zinc, the formulation may comprise a zinc halide ZnX₂ e.g. zinc chloride (ZnCl₂)), zinc acetate (Zn(CH3CO₂)₂), zinc nitrate (Zn(NO)₂), or zinc sulfate (ZnSO₄), or a combination thereof.

Dissolved compounds of antimicrobial metals may show some biocidal activity within formulations, but the level of activity is often lower at comparable concentrations compared to other biocidal actives such as quaternary ammonium compounds. However, when formulations containing antimicrobial metals dissolved in an ionic form are exposed to ionising radiation such as gamma radiation (which would be expected during the production of a sterile formulation), the biocidal activity of the ionic metal increases postirradiation. In contrast to the increase in activity observed for colloidal metal particles, the increase in biocidal activity of ionic metals is likely due to the ionising radiation causing metal atoms to agglomerate into particles, thus facilitating biocidal activity. In addition to this, the anions of certain metal salts (e.g. nitrate salts) may provide a radical scavenging effect. Therefore by including an antimicrobial metal in an ionic form, the loss in biocidal activity as a result of ionising irradiation of biocidal actives can advantageously be at least partially offset by the increase in biocidal activity of the biocidal metal.

The formulation may comprise one biocidal active, two biocidal actives, or three or more biocidal actives. Preferably the formulation comprises one or two biocidal actives.

The one or more biocidal actives may each be a quaternary ammonium compound (QAC/Quat), a quaternary ammonium salt or a triamine. The one or more biocidal actives may be independently selected from a group consisting of benzalkonium chloride (BAC) or other halide salts, didecyldimethylammonium chloride (DDAC) or other halide salts, alkyldimethylbenzylammonium chloride (ADBAC) or other halide salts, alkyl dimethyl ethylbenzyl ammonium chloride (ADEBAC) or other halide salts, dimethyloctadecyl[3- (trimethoxysilyl)propyl]ammonium chloride or other halide salts, benzyl-C12-18- alkyldimethyl, salts with l,2-benzisothiazol-3(2H)-one 1,1-dioxide (1: 1) (ADBAS), and N- (3-aminopropyl)-N-dodecylpropane-l,3-diamine).

Preferably the formulation comprises between 0.1 wt.% and 50 wt.% of the one or more biocidal actives. Particularly preferably the formulation comprises between 5 wt.% and 25 wt.% of the one or more biocidal actives.

The formulation may further comprise between 0.1 wt.% and 20 wt.% alcohol. The formulation preferably comprises between 1 wt.% and 20 wt.% alcohol. Particularly preferably the formulation comprises between 2 wt.% and 10 wt.% alcohol. Even more preferably the formulation comprises between 4 wt.% and 6 wt.% alcohol.

The alcohol may be a simple monoalcohol (i.e. have a general formula of CnEEn+iOEl). The alcohol may be selected from a group consisting of methanol, ethanol, isopropanol and n- butanol. Preferably the alcohol is ethanol.

The alcohol advantageously enhances solubility of other components within the formulation, which may have low solubility in water alone. The amount and type of alcohol within the formulation can be tailored for optimum solubility of different biocidal actives and/or colloidal or ionic biocidal metals. The alcohol itself may also provide a small additional biocidal effect.

The formulation may further comprise a complexing agent. The complexing agent can advantageously improve the solubility of antimicrobial metals. The complexing agent can also act to sequester deactivating ions, such as iron and calcium, which can negatively impact the efficacy of active biocides, such as quaternary ammonium salts. The complexing agent may be a chelating agent such as ethylenediaminetetraacetic acid (EDTA). The formulation may comprise between 0. 1% and 5% of the complexing agent. Preferably the complexing agent is selected from a group consisting of ethylenediaminetetraacetic acid, trisodiumnitrilotriacetate, phosphates, citrates, zeolites, diethylenetriamine pentaacetate and egtazic acid.

The formulation may comprise between 1 wt.% and 20 wt.% of a pH modifier/buffer. The pH modifier/buffer advantageously ensures that the pH of the formulation remains within an acceptable range for safe use and to ensure that biocidal actives remain soluble and in a usable (z.e. active) form. Preferably the pH of the formulation is between pH 7 and pH 13. Even more preferably the pH of the formulation is between pH 8 and pH 10. Preferably the composition comprises between 2 wt.% and 10 wt.% of a pH modifier/buffer. Even more preferably the formulation comprises between 4 wt.% and 6 wt.% pH modifier/buffer.

The pH modifier/buffer may be any pH modifier/buffer which is soluble in aqueous solutions and is capable of adjusting the pH of the formulation to the required range and/or acting as a pH buffer within the required pH range. Preferably the pH modifier/buffer is selected from a group consisting of ethanolamine, diethanolamine, triethanolamine, lecithin and morpholine.

The formulation may further comprise between 0.1 wt.% and 10 wt.% of a surfactant. Preferably the formulation comprises between 2 wt.% and 8 wt.% (e.g. 5 wt.%) of a surfactant. The surfactant is preferably a non-ionic surfactant. The surfactant may be selected from a group consisting of alcohol ethoxylates (e.g. 2-((l-((2-ethylhexyl)poly-oxy)poly-propan-2- yl)oxy)ethanol) and fatty alcohol ethoxylates.

The formulation may further comprise up to 1 wt.% of a radical scavenger.

Reactive oxygen species formed within the solution as a result of exposure to ionising radiation during the sterilisation process may include water radiolysis products such as hydrogen peroxide, hydrogen radicals, hydroxyl radicals and hydrogen superoxide. These reactive oxygen species readily react with organic compounds including many biocidal actives. The radical scavenger advantageously quenches free radicals and other reactive oxygen species formed within the solution as a result of exposure to ionizing radiation. This prevents or limits degradation of the biocidal active(s) by the free radicals, thus preventing (or limiting) loss in the biocidal activity of the formulation as a result of the sterilisation process.

Due to the nature of radical quenching mechanisms, the minimum quantity of the radical scavenger required is very low (<0.01 wt.%) to be effective. Thus the formulation may comprise between 0.001 wt.% and 1 wt.% of a radical scavenger. Preferably the formulation comprises between 0.01 wt.% and 0.1 wt.% of a radical scavenger.

Any compound capable of scavenging radicals and other reactive oxygen species (e.g. superoxide) which is stable under ambient conditions and is at least partially soluble in aqueous solutions may be used as a radical scavenger. The radical scavenger may be selected from a group consisting of nitrate salts (e.g. sodium nitrate, potassium nitrate, or silver nitrate), nitrite salts, t-butanol, hydrochloric acid, sodium hydroxide, ascorbic acid, cysteine, thiourea, glutathione, N-2-hydroxyethylpiperazine-N’ -2 -ethanesulfonic acid (HEPES), tris(hydroxymethyl)aminoethane (Tris), ethylene glycol, melatonin, and 2- mercaptoethanol.

Certain alcohols (including simple monoalcohols such as methanol and ethanol) can themselves act as weak radical scavengers. The formulation may thus comprise an alcohol in addition to a radical scavenger (i.e. the radical scavenger is different to the alcohol, although the radical scavenger may also be an alcohol). Thus reference within this specification to “radical scavenger” should be interpreted to exclude any simple monoalcohol (i.e. alcohols having the general formula CnThn+iOH; for example methanol (n=l); ethanol (n=2); isopropanol (n=3) and n-butanol (n=4)) which is present in an amount greater than 1 wt.%, regardless of whether the alcohol has radical scavenging capability.

Viewed from a second aspect the present invention provides a sterile aqueous disinfectant formulation comprising an aqueous disinfectant formulation as hereinbefore described, wherein the aqueous disinfectant formulation has been sterilised by exposure to ionising radiation.

The ionising radiation may be gamma radiation, electron beam radiation or x-ray radiation. Preferably the ionising radiation is gamma radiation. A dosage level of ionising radiation may be up to 75 kGy. Preferably a dosage level of ionising radiation is in the range of 15 to 60 kGy. Even more preferably a dosage level of ionising radiation is in the range of 25 to 50 kGy (e.g. about 35 kGy).

Viewed from a third aspect the present invention provides a method for preparing an aqueous disinfectant formulation suitable for sterilisation by exposure to ionising radiation, comprising the steps of: adding one or more biocidal actives to water to form a concentrated aqueous biocidal solution; adding a pH modifier/buffer to the concentrated aqueous biocidal solution; adding an antimicrobial metal active to the concentrated aqueous biocidal solution; and diluting the concentrated aqueous biocidal solution to the required concentration.

The at least one biocidal active, pH modifier/buffer and antimicrobial metal active may be as hereinbefore defined.

The concentrated aqueous biocidal solution may be diluted with water, one or more water miscible alcohols, or a mixture of water and one or more water miscible alcohols. The method may further comprise the step of adding an alcohol as hereinbefore defined to the concentrated aqueous biocidal solution.

The method may further comprise the step of adding a surfactant as hereinbefore defined to the concentrated aqueous biocidal solution.

The method may further comprise the step of adding a radical scavenger as hereinbefore defined to the concentrated aqueous biocidal solution.

The method may further comprise the step of adding a complexing agent as hereinbefore defined to the concentrated aqueous biocidal solution.

Viewed from a fourth aspect the present invention provides a method for preparing a sterile aqueous disinfectant formulation, comprising the steps of: preparing an aqueous disinfectant formulation as hereinbefore described; then placing the aqueous disinfectant formulation inside a container and hermetically sealing the resultant filled container; then sterilising the filled container by exposure to ionising radiation.

Viewed from a fifth aspect the present invention provides a method for preparing a sterile cleaning article (e.g for use in a cleanroom), comprising the steps of: preparing a disinfectant formulation as hereinbefore described; then assembling a cleaning article and treating it with the disinfectant formulation; then placing the treated cleaning article in a packaging and hermetically sealing the packaging to maintain its integrity; then sterilising the packaged cleaning article by exposure to ionising radiation.

The cleaning article may be any article which may be used to apply or dispense the disinfectant formulation. For example the cleaning article may be a bottle, a spray bottle, a wipe or a mop.

The ionising radiation may be gamma irradiation, electron beam radiation or x-ray irradiation. Preferably the ionising radiation is gamma radiation. A dosage level of ionising radiation may be up to 75 kGy. Preferably a dosage level of ionising radiation is in the range of 15 to 60 kGy. Even more preferably a dosage level of ionising radiation is in the range of 25 to 50 kGy (e.g. about 35 kGy).

Viewed from a sixth aspect the present invention provides a sterile cleaning article comprising: a storage medium; a disinfectant formulation as hereinbefore described provided in or on the storage medium; wherein the sterile cleaning article is contained within a hermetically sealed packaging; wherein the storage medium; the disinfectant formulation and the hermetically sealed packaging have together been sterilised by exposure to ionising radiation.

The storage medium may be a container (e.g. a bottle) or may be an absorbent material such as a wipe, mop, pad or other fabric, cloth or paper material.

The disinfectant formulation in the storage medium may have undergone a physical and/or chemical alteration as a result of exposure to ionising radiation. For example, where the disinfectant formulation includes colloidal particles of an antimicrobial metal or metal oxide, the particles may have a smaller size (i.e. have been broken down) as a result of exposure to ionising radiation, thus increasing available surface area of the antimicrobial metal active. Where the disinfectant formulation includes dissolved salts of an antimicrobial metal then the metal may have agglomerated into larger particles or colloidal structures as a result of exposure to ionising radiation.

Viewed from a seventh aspect the present invention provides a method for disinfecting a surface in a cleanroom, comprising the steps of: cleaning the surface, for example using a neutral detergent; treating the surface with a first disinfectant formulation as hereinbefore described one or more times over a first time period; then treating the surface with a second disinfectant formulation as hereinbefore described one or more times over a second time period; wherein the first and second disinfectant formulations each contain a different set of one or more biocidal actives.

The first time period is preferably between 1 week and 2 weeks. The second time period is preferably between 1 week and 2 weeks.

There may be a gap between the first and second time periods. The gap may be up to 1 week, between 1 week and 2 weeks or between 1 week and 3 weeks.

Detailed description of preferred embodiment of the invention

Example 1 : DDAC and BAC with colloidal silver disinfectant formulation

Preparation

100 g of a commercially available 50 wt.% solution in water of didecyldimethylammonium chloride (DDAC 50) was added to 100 g of a commercially available 50 wt.% solution in water of benzalkonium chloride (BAC 50). To the resultant mixture was added 10 g 2-((l- ((2-ethylhexyl)poly-oxy)poly-propan-2-yl)oxy)ethanol surfactant, 50 g ethanol, 50 g ethanolamine and 20 g of metallic silver particles having an average size of between 100 nm and 200 nm. The resultant solution was then diluted with 670 ml water to give DDAC and BAC disinfectant formulation 1 suitable for sterilisation by exposure to ionising radiation shown in Table 1. The pH of disinfectant formulation 1 was between pH 8 and pH 9.

Table 1: Composition of Disinfectant Formulation 1

Example 2: DDAC and triamine with colloidal silver disinfectant formulation

Preparation 20 g of dodecyl dipropylene triamine was added to 100 g of a commercially available 50 wt.% solution in water of didecyldimethylammonium chloride (DDAC 50). To the resultant mixture was added 10 g 2-((l-((2-ethylhexyl)poly-oxy)poly-propan-2- yl)oxy)ethanol surfactant, 50 g ethanol, 50 g ethanolamine and 20 g of metallic silver particles having an average size of between 100 nm and 200 nm. The resultant solution was then diluted with 750 ml water to give DDAC and triamine disinfectant formulation 2 suitable for sterilisation by exposure to ionising radiation shown in Table 2. The pH of disinfectant formulation 2 was between pH 8 and pH 9.

Table 2: Composition of Disinfectant Formulation 2

Example 3: DDAC and BAC with ionic silver disinfectant formulation Preparation

100 g of a commercially available 50 wt.% solution in water of didecyldimethylammonium chloride (DDAC 50) was added to 100 g of a commercially available 50 wt.% solution in water of benzalkonium chloride (BAC 50). To the resultant mixture was added 10 g 2-((l- ((2-ethylhexyl)poly-oxy)poly-propan-2-yl)oxy)ethanol surfactant, 50 g ethanol, 50 g ethanolamine and 0.010 g of silver nitrate. The resultant solution was then diluted with

689.99 ml water to give DDAC and BAC disinfectant formulation 3 suitable for sterilisation by exposure to ionising radiation shown in Table 3. The pH of disinfectant formulation 3 was between pH 8 and pH 9.

Table 3: Composition of Disinfectant Formulation 3

Example 4: DDAC and ADBAC with colloidal copper disinfectant formulation

Preparation

120g of a commercially available 50 wt.% solution in water of didecyldimethylammonium chloride (DDAC 50) was added to 20 g of a commercially available 50 wt.% solution in water of alkyldimethylbenzylammonium chloride (ADBAC 50). To the resultant mixture was added 10 g 2-((l-((2-ethylhexyl)poly-oxy)poly-propan-2-yl)oxy)ethanol surfactant, 20 g EDTA, 50 g ethanolamine and 5 g of metallic copper particles having an average size of between 100 nm and 200 nm. The resultant solution was then diluted with 775 ml water to give DDAC and ADBAC disinfectant formulation 4 suitable for sterilisation by exposure to ionising radiation shown in Table 4. The pH of disinfectant formulation 4 was between pH 8 and pH 9. Table 4: Composition of Disinfectant Formulation 4

Efficacy tests In order to test the efficacy of antimicrobial metal, test samples 5 to 8 were prepared. Test samples 5 to 8 were prepared in the same way to formulations 1 to 4 respectively, but with 5% DDAC, ADBAC and BAC solutions used rather than 50% solutions, and 2 g of dodecyl dipropylene triamine used rather than 20 g (with the mass balance being made up with water). The compositions of test samples 5 to 8 are shown in Table 5.

Table 5: Composition of test samples 5 to 8

Test samples 5 to 8 were prepared with lower levels of the organic biocidal actives (10% compared to formulations 1 to 4). This was to enable the effect of the antimicrobial metal has on antimicrobial efficacy before and after samples were exposed to gamma radiation to be clearly seen. For formulations 1 to 4, the relatively high concentration of biocidal actives means that efficacy is very high, beyond the detection limit of the test procedure. This means that the effect of the antimicrobial metal on efficacy, whilst present in formulations 1 to 4, cannot be clearly measured.

Test samples 5 to 8 were tested both before and after 25-50 kGy gamma irradiation for their fungicidal activity against Aspergillus brasiliensis according to the EN13697:2015+Al :2019 test protocol. Comparative test samples 9 and 10 (which are the same as test samples 5 and 6 respectively with the exception that they do not contain any antimicrobial metal particles) were also tested according to the same protocol before and after gamma irradiation.

A. brasiliensis was added to 0.3 g/1 bovine albumin and the resultant solution was applied onto a stainless steel metal surface. The sample surface was left to air-dry and then the test substance (i.e. one of test samples 5 to 10) was applied to the sample surface and left for 15 minutes. The sample was then submerged in a neutraliser solution of lecithin and Tween 80 (polysorbate 80). A sample of the neutraliser solution was then taken, plated and incubated for 3 days. A temperature of between 18 °C and 25 °C was maintained throughout the test. The number of A. brasiliensis microbes recovered from the plate was then measured and compared to a control sample (following the same procedure but with water applied to the sample surface rather than the test substance). The log reduction (extent to which the formulation is capable of reducing the number of microbes, where >Log 6 kill corresponds to a loss of > 99.9999 %) of each sample was then determined and is shown in Table 6, both before and after irradiation.

Table 6: results of efficacy tests (EN13697:2015+Al :2019) of test samples 5 to 8 and comparative test samples 9 and 10 before and after gamma irradiation

As shown in Table 6, when a formulation containing particles of an antimicrobial metal (colloidal silver or copper) is subjected to gamma irradiation, activity increases post irradiation (test samples 5, 6 and 8). The same is true for the formulation containing an antimicrobial metal in an ionic form (silver nitrate, test sample 7). In comparison, comparative samples 9 and 10 (with no antimicrobial metal present) show a decrease in efficacy upon gamma irradiation.

Thus the presence of an antimicrobial metal within formulations can reduce or counteract the loss in biocidal activity from gamma irradiation, and can even lead to an increase in antimicrobial efficacy following gamma irradiation. Thus, where disinfectant formulations 1 to 4 are added to a cleaning article such as a wipe, bottle, spray bottle, or mop, the cleaning article can be packaged in hermetically sealed packaging and sterilised using ionising radiation such as gamma radiation without leading to a loss in antimicrobial activity.

Claims

1. An aqueous disinfectant formulation suitable for sterilisation by exposure to ionising radiation comprising:

0.05 wt.% to 60 wt.% of at least one biocidal active;

0.1 wt.% to 20 wt.% of a pH modifier/buffer; and up to 5% of an antimicrobial metal active.

2. The aqueous disinfectant formulation of claim 1, wherein the formulation comprises between 1 wt.% and 2 wt.% inclusive of the antimicrobial metal active.

3. The aqueous disinfectant formulation of claim 1 or 2, wherein the antimicrobial metal active is selected from a group consisting of copper, silver, and zinc, or combinations thereof.

4. The aqueous disinfectant formulation of any preceding claim, wherein the antimicrobial metal active is present in the formulation as solid particles of a metal or a water insoluble metal oxide.

5. The aqueous disinfectant formulation of claim 4, wherein the particles have an average size of between 100 nm and 200 nm.

6. The aqueous disinfectant formulation of claims 1 to 3, wherein the antimicrobial metal active is dissolved within the formulation as one or more metal salts or compounds.

7. The aqueous disinfectant formulation of claims 4 or 5, wherein the antimicrobial metal active further comprises one or more metal salts or compounds dissolved within the formulation.

8. The aqueous disinfectant formulation of any preceding claim, wherein the one or more biocidal actives are independently selected from a group consisting of benzalkonium chloride (BAC) or other halide salts, didecyldimethylammonium chloride (DDAC) or other halide salts, alkyldimethylbenzylammonium chloride (ADBAC) or other halide salts, alkyl dimethyl ethylbenzyl ammonium chloride (ADEBAC) or other halide salts, dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride or other halide salts, benzyl-C12-18-alkyldimethyl, salts with l,2-benzisothiazol-3(2H)-one 1,1 -dioxide (1 :1) (ADBAS), and N-(3-aminopropyl)-N-dodecylpropane-l,3-diamine).

9. The aqueous disinfectant formulation of any preceding claim, wherein the formulation comprises between 5 wt.% and 25 wt.% of the one or more biocidal actives.

10. The aqueous disinfectant formulation of any preceding claim, wherein the formulation further comprises between 0. 1 wt.% and 20 wt.% alcohol.

11. The aqueous disinfectant formulation of claim 10, wherein the alcohol is selected from a group consisting of methanol, ethanol, isopropanol and //-butanol.

12. The aqueous disinfectant formulation of any preceding claim, wherein the pH modifier/buffer is selected from a group consisting of ethanolamine, diethanolamine, triethanolamine, lecithin and morpholine.

13. The aqueous disinfectant formulation of any preceding claim, wherein the formulation further comprises between 0.1 wt.% and 10 wt.% of a surfactant.

14. The aqueous disinfectant formulation of claim 13, wherein the surfactant is selected from a group consisting of alcohol ethoxylates and fatty alcohol ethoxylates.

15. A sterile aqueous disinfectant formulation, comprising an aqueous disinfectant formulation according to any preceding claim, wherein the aqueous disinfectant formulation has been sterilised by exposure to ionising radiation.

16. The sterile aqueous disinfectant formulation of claim 15, wherein the aqueous disinfectant formulation has been exposed to ionising radiation at a dosage level in the range of 15 to 60 kGy.

17. A method for preparing an aqueous disinfectant formulation suitable for sterilisation by exposure to ionising radiation, comprising the steps of: adding one or more biocidal actives to water to form an aqueous biocidal solution; adding a pH modifier/buffer to the aqueous biocidal solution; and adding an antimicrobial metal active to the aqueous biocidal solution.

18. The method of claim 17, further comprising the step of diluting the aqueous biocidal solution to a required concentration.

19. A method for preparing a sterile aqueous disinfectant formulation, comprising the steps of: preparing an aqueous disinfectant formulation according to the method of claim 17 or 18; placing the prepared aqueous disinfectant formulation inside a container and hermetically sealing the resultant filled container; and sterilising the filled container by exposing the filled container to ionising radiation.

20. The method of claim 19, wherein a dosage level of the ionising radiation is in the range of 15 to 60 kGy.

21. A method for preparing a sterile cleaning article, comprising the steps of: preparing an aqueous disinfectant formulation according to claims 1 to 14; assembling a cleaning article and treating it with the aqueous disinfectant formulation; placing the treated cleaning article in a packaging and hermetically sealing the packaging; sterilising the packaged cleaning article by exposure to ionising radiation.

22. A sterile cleaning article comprising: a storage medium; an aqueous disinfectant formulation according to claims 1 to 14 provided in or on the storage medium; wherein the sterile cleaning article is contained within a hermetically sealed packaging; and wherein the storage medium, the disinfectant formulation and the hermetically sealed packaging have together been sterilised by exposure to ionising radiation.