Methods for detecting antimicrobial surface coatings using fluorescent indicators

Disclosed are methods for detecting a presence or absence of an antimicrobial surface coating including applying at least one detectable fluorophoric dye compound to a substrate, irradiating the surface of the substrate with ultraviolet radiation in the 100-415 nm wavelength range to excite the detectable fluorophoric dye compound, observing fluorescence of the excited fluorophoric dye compound, and determining the presence or absence of the antimicrobial surface coating based on the observed fluorescence. Further disclosed are antimicrobial surface coating solutions, methods for their application, and methods for confirming the presence and coverage of antimicrobial surface coatings.

TECHNICAL FIELD

The present disclosure is directed generally to antimicrobials and more particularly to antimicrobial surface coatings and methods for detecting a presence or absence of an antimicrobial surface coating using a fluorescent indicator.

BACKGROUND

It is well known that various surfaces can harbor microbes. It is also well known that contact with contaminated surfaces can spread infectious agents such as bacteria and viruses. For example, high-contact interior surfaces in a conveyance such as a passenger aircraft have a high potential to transfer microbes between passengers. While these high-contact surfaces can be disinfected during regular cleanings, comprehensive cleaning and sterilization solutions can be time-consuming. Further, there remains the potential for microbe transfer between cleanings. This potential can be alleviated using antimicrobial surface coatings. While effective, antimicrobial surface coatings can degrade and wear away over time and therefore must be checked to ensure their continued presence and reapplied, as necessary.

Quaternary ammonium compounds (QACs) are commonly used in antimicrobial surface coatings due to their ability to neutralize microbes. That same ability can also be used to bond anionic dyes, for instance bromophenol blue (BPB), to detect the presence of antimicrobial coatings via dye bonding and visual inspection. While effective, the process of bonding visible dyes to surface coatings can permanently stain the surface under test and are reliant on absorbance, which is not inherently sensitive.

Therefore, what is needed are methods for detecting the presence or absence of antimicrobial surface coatings without the need for complicated procedures and without any negative effect on the cosmetic appearance of the coated surface, while having the sensitivity to detect even monolayers of coating.

BRIEF SUMMARY

To achieve the foregoing and other advantages, in a first aspect the present disclosure provides a method for detecting the presence or absence of an antimicrobial surface coating. In embodiments, the method includes providing a substrate to be tested, applying a detectable fluorophoric dye compound to a surface of the substrate, irradiating the surface of the substrate with ultraviolet radiation in the 100-415 nm wavelength range to excite the detectable fluorophoric dye compound, observing fluorescence corresponding to the excited, detectable fluorophoric dye compound, and determining, based on the observed fluorescence, a presence or absence of an antimicrobial surface coating.

In some embodiments, the method may further include the step of pre-treating the substrate with an antimicrobial surface coating solution comprising an antimicrobial component configured to covalently bond to the substrate.

In some embodiments, the step of applying the detectable fluorophoric dye compound to the surface of the substrate may include the steps of depositing the detectable fluorophoric dye compound on the surface of the substrate, allowing the detectable fluorophoric dye compound to stand on the surface of the substrate for at least 30 seconds, removing excess detectable fluorophoric dye compound, and drying the substrate.

In some embodiments, the detectable fluorophoric dye compound may be provided as a water-based or alcohol-based solution.

In some embodiments, the substrate may be associated with a passenger cabin of a conveyance, for instance an aircraft, train, subway, bus, automobile, or vessel.

In some embodiments, the substrate may be an element of a passenger seat, a passenger suite, a passenger amenity, a control unit, a closet or stowage/luggage bin, a lavatory, a self-serve bar or kiosk, or a galley.

In some embodiments, the substrate may be a mechanism for actuating an element in a passenger cabin environment.

The present disclosure further provides a method of coating a substrate with an antimicrobial coating including a detectable fluorescent indicator. In embodiments, the method includes providing a substrate, providing an antimicrobial coating solution comprising an antimicrobial component configured to covalently bond to a surface of the substrate and a detectable, water-soluble fluorescent indicator configured to absorb ultraviolet radiation in the 100-415 nm wavelength range and emit radiation in the 100-1000 nm wavelength range, preferably in the 380-740 nm wavelength range, applying the antimicrobial coating solution to the surface of the substrate, and allowing the antimicrobial coating solution to dry on the surface of the substrate to form the antimicrobial coating.

In some embodiments, the method may further include the steps of irradiating the surface of the antimicrobial coated substrate with ultraviolet radiation in the 100-415 nm wavelength range to excite the detectable fluorescent indicator, observing fluorescence corresponding to the excited detectable fluorescent indicator, and confirming, based on the observed fluorescence, at least one of a presence and coverage of the antimicrobial surface coating.

In some embodiments, the step of allowing the antimicrobial solution to dry on the surface of the substrate may include allowing the antimicrobial coating solution to stand on the surface of the substrate for a time duration of at least 6 hours.

In some embodiments, the method may further include the steps of rinsing and drying the surface of the antimicrobial coated substrate.

In some embodiments, the method may further include the step of, in the absence of fluorescence or due to inadequate coverage, reapplying the antimicrobial coating solution to the surface of the substrate.

In some embodiments, the substrate may be associated with a passenger cabin of a conveyance, for instance an aircraft.

In some embodiments, the substrate may be an element of a passenger seat, a passenger suite, a passenger amenity, a control unit, a closet or stowage/luggage bin, a lavatory, a self-serve bar or kiosk, or a galley and/or may correspond to a mechanism for actuating an element in a passenger cabin environment.

This brief summary is provided solely as an introduction to subject matter that is fully described in the detailed description and illustrated in the drawings. This brief summary should not be considered to describe essential features nor be used to determine the scope of the claims. Moreover, it is to be understood that both the foregoing summary and the following detailed description are exemplary and explanatory only and are not necessarily restrictive of the subject matter claimed.

DETAILED DESCRIPTION

Before explaining one or more embodiments of the disclosure in detail, it is to be understood that the embodiments are not limited in their application to the details of construction and the arrangement of the components or steps or methodologies set forth in the following description or illustrated in the drawings. In the following detailed description of embodiments, numerous specific details may be set forth to provide a more thorough understanding of the disclosure. However, it will be apparent to one of ordinary skill in the art having the benefit of the instant disclosure that the embodiments disclosed herein may be practiced without some of these specific details. In other instances, well-known features may not be described in detail to avoid unnecessarily complicating the instant disclosure.

Broadly speaking, the present disclosure provides embodiments of methods for detecting antimicrobial surface coatings, detectable antimicrobial surface coating solutions, and methods for forming detectable antimicrobial surface coatings.

FIG.1illustrates a first method100according to the present disclosure. In a step102, a substrate is provided and an antimicrobial surface coating solution is applied to at least a portion of a surface of the substrate via, for example, a conventional coating process including but not limited to electrostatic spray application, dipping, wiping, or other common application methods. In a step104, the antimicrobial solution may stand on the surface of the substrate until dry to form the antimicrobial surface coating. In some embodiments, the antimicrobial coating solution may stand on the surface of the substrate for a predetermined time duration, for example, about 30 minutes to about 6 hours to form the antimicrobial surface coating. Excess (e.g., unbonded) antimicrobial surface coating solution may be removed in one or more optional rinsing steps and the coated substrate may be dried in one or more optional drying steps.

In one or more of the embodiments of the present disclosure, the substrate may be any substrate type, for instance a high-contact substrate located in a passenger cabin of a conveyance such as an aircraft. Examples of substrates include, but are not limited to, synthetic or natural fabric surfaces, plastics, metals, composites and composite finishes, wood, glass, leather, and other non-cationic substrates. Substrate environments may include, but are not limited to, passenger cabins, crew quarters, lavatories, and galleys. Other environments may include schools, hospitals, public buildings, etc. In the case of a passenger conveyance, the substrate may be an element of, for example, a passenger seat, a passenger suite, interior panels, luggage bins, doors, walls, passengers amenities, control panels, passenger service units, lavatory fixtures, galley equipment, and beverage carts. In some embodiments, a substrate may be a mechanism operable for manipulating an element, for example, a handle, lock, latch, switch, control panel, etc.

In one or more embodiments of the present disclosure, the antimicrobial coating solution may include a quaternary ammonium compound (QACs, “quats) or other static/non-leachable compound (e.g., silane-functionalized QACs, “SiQuat” or “silquat”) configured to attract negatively-charged microorganisms to the surface where the microorganisms are neutralized. To an extent, QACs and other such static compounds may covalently bond to the substrates to which they are applied, resulting in sustainable layers of antimicrobial coatings that may persist for extended periods of time (e.g., 12 months or longer). In some embodiments, the antimicrobial layers may be of no more than nanometer-level thickness, which means that while such antimicrobial or antiviral coatings are invisible under normal conditions, they may be susceptible to wear or erosion due to physical contact.

In a step106, a tester, for instance a crewmember or maintenance staff, may perform a field assessment of the substrate under test by applying a detectable fluorophoric compound to the substrate surface. For example, the substrate under test (e.g., or a control portion thereof) may be fully or partially immersed in one or more fluorophore-containing solutions (e.g., a solution of 0.05 to 0.28 volume percent in water or alcohol). Alternatively or additionally, the fluorophore-containing solution may be applied to the substrate by a process such as spraying, wiping, and via a pen-type applicator for direct application to the surface. Alternatively, application of a detectable fluorophoric compound may occur within minutes of application of the antimicrobial coating, rather than during field assessment. In a step108, the fluorophore-containing solution may stand on the surface of the substrate for a predetermined time duration, for example, about 30 seconds up to about 5 minutes, more preferably about 30 seconds up to about 6 hours or more. In a step110, the substrate surface may be rinsed to remove excess fluorophore-containing solution and then dried. In embodiments, fluorophoric solutions applied to the substrate under test may bond to QACs or other static antimicrobial compounds. In some embodiments, fluorophores may be applied to a control portion of the substrate under test.

In a step112, the substrate under test having the applied fluorophoric solution is irradiated with ultraviolet radiation in the 100-415 nm wavelength range, more preferably in the 365-415 nm wavelength range, to excite the at least one detectable fluorophoric dye compound. For example, the tester may apply long-wave ultraviolet (UV) light (e.g., “blacklight”) to the treated substrate under test. In a step114, the fluorescence corresponding to the excited fluorophoric dye compound is observed. For example, while the applied fluorophores may be imperceptible under normal visible light (e.g., and therefore may not present as a “stain”), the fluorophores may fluoresce under UV light. In a step116, a presence or absence, or coverage, of the antimicrobial surface coating is determined based on the observed fluorescence.

For example, areas of the substrate under test where the fluorophores have bonded to antimicrobial QACs fluoresce and therefore are clearly visible under UV light, indicating areas where the antimicrobial coating is present. Similarly, a lack of fluorescence under UV light indicates the absence of an antimicrobial surface coating, for example, attenuated by wear or erosion. In an optional additional step118, the substrate under test may be flagged for further action, for instance reapplication of the antimicrobial surface coating, servicing, or replacement of the associated substrate, element or component. In an optional step120, the substrate under test may be washed with an aqueous solution containing sufficient concentrations of cationic species, such as cetyltrimethylammonium chloride or ammonium bicarbonate, to remove the detectable fluorophoric dye compound to ‘reactivate’ the antimicrobial properties of the underlying QACs or coatings.

In embodiments, the detectable fluorophoric dye compounds may be anionic dye compounds capable of bonding to QACs or other static antimicrobial coatings, e.g., via sulfonate or carboxylic acid functional groups. For example, anionic dye compounds of λex<500 nm and λem>400 nm may be ideally invisible under normal visible light and fluoresce under UV light (e.g., Tetrasodium 4,4′-bis[[4-[bis(2-hydroxyethyl)amino]-6-(4-sulphonatoanilino)-1,3,5-triazin-2-yl]amino]stilbene-2,2′-disulphonate], Disodium;5-[[4-anilino-6-[2-hydroxyethyl(methyl)amino]-1,3,5-triazin-2-yl]amino]-2-[2-[4-[[4-anilino-6-[2-hydroxyethyl(methyl)amino]-1,3,5-triazin-2-yl]amino]-2-sulfonatophenyl]ethenyl]benzenesulfonate, Disodium 4,4′-bis(4-anilino-6-morpholino-s-triazin-2-ylamino)-2,2′-stilbenedisulfonate, Disodium;5-[[4-(2-methylanilino)-6-morpholin-4-yl-1,3,5-triazin-2-yl]amino]-2-[2-[4-[[4-(2-methylanilino)-6-morpholin-4-yl-1,3,5-triazin-2-yl]amino]-2-sulfonatophenyl]ethenyl]benzenesulfonate, Hexasodium;2-[[4-[(3-amino-3-oxopropyl)-(2-hydroxyethyl)amino]-6-[4-[2-[4-[[4-[(3-amino-3-oxopropyl)-(2-hydroxyethyl)amino]-6-(2,5-disulfonatoanilino)-1,3,5-triazin-2-yl]amino]-2-sulfonatophenyl]ethenyl]-3-sulfonatoanilino]-1,3,5-triazin-2-yl]amino]benzene-1,4-disulfonate, and related, as well as fluorescein-SA, Lucifer yellow, sulforhodamine-B or sulforhodamine-101, pyranine, HPTS or HPTS(Lys)3, MPTS, CTR, TSPP, TCPP, PTCA).

While the first method100is disclosed including both coating formation steps coating detection/identification steps, it is envisioned and intended that the detection/identification steps can be practiced alone in the case of a substrate under test considered to already include an antimicrobial surface coating or a substrate under in which the presence or absence of an antimicrobial surface coating is unknown. For instance, the detection steps can be practiced alone to determine antimicrobial coating presence, coverage area, wear, etc., for the purpose of determining the need for coating, recoating, spot-coating, replacement, etc. Further, the recited rinsing, washing and drying steps can be optional or additional rinsing, washing and drying steps can be performed. Coating application, dye compound application, rinsing, washing and drying procedures may vary depending on the substrate type, coating type, fluorophoric dye compound type, substrate location, and testing environment, among other factors. The foregoing is applicable to the recited method100and methods discussed further below.

FIG.2illustrates a second method200according to the present disclosure. Broadly speaking, the second method200includes the steps of preparing an antimicrobial surface coating solution including a detectable fluorescent indicator component, coating a substrate with the prepared solution to form an antimicrobial surface coating, and detecting the presence or absence of the applied antimicrobial surface coating. In some embodiments, the antimicrobial surface coating solution may include an antimicrobial component and a detectable, water-soluble fluorescent indicator provided as a mixture to be coated on a substrate to impart antimicrobial properties to the coated substrate. In some embodiments, the solution may be a water-based or alcohol-based solution.

In a step202, an antimicrobial surface coating solution is prepared including at least a quaternary ammonium compound or other static/non-leachable compound and a detectable fluorescent indicator. In some embodiments, fluorescent indicators according to the present disclosure may include any fluorescent compound capable of absorption in the UV spectrum and emission in the visible spectrum. For example, the fluorescent compound may absorb radiation in the 100-415 nm wavelength range, more preferably in the 300-415 nm wavelength range, and most preferably in the 365-415 nm wavelength range, and emit radiation in the 100-1000 nm wavelength range, more preferably emit visible light in the 380-740 nm wavelength range. Suitable fluorescent compounds may be transparent in the presence of visible light and uncolored so as not to alter the color and/or transparency of the coating. Suitable fluorescent compounds can include, but are not limited to, commercially available fluorescent dyes, pigments, colorants and brighteners. A specific, non-limiting example of a suitable fluorescent compound can include 5-[[4-[bis(2-hydroxyethyl)amino]-6-(4-sulfonatoanilino)-1,3,5-triazin-2-yl]amino]-2-[(E)-2-[4-[[4-[bis(2-hydroxyethyl)amino]-6-(4-sulfonatoanilino)-1,3,5-triazin-2-yl]amino]-2-sulfonatophenyl]ethenyl]benzenesulfonate.

In a step204, the prepared solution is applied to the predetermined substrate and allowed to stand on the surface of the substrate until dry to form the antimicrobial surface coating. In some embodiments, the antimicrobial coating solution may be allowed to stand on the surface of the substrate for a predetermined time duration, for example, at least about 6 hours to form the antimicrobial surface coating. In an optional step206, the coated substrate may be rinsed or wiped to remove excess surface coating solution and subsequently dried.

In a step208, the substrate under test having the formed surface coating is irradiated with ultraviolet radiation, for example, in the 100-415 nm wavelength range, more preferably in the 365-415 nm wavelength range, to excite the detectable fluorescent indicator. For example, UV light may be directed to the substrate under test. In a step210, the fluorescence corresponding to the excited fluorescent indicator is observed. In a step212, a presence or absence, or coating coverage, of the antimicrobial surface coating is determined based on the observed fluorescence. For example, areas of the substrate that fluoresce are indicative of bonded antimicrobial surface coating, while areas of the substrate that do not fluorescence are indicative of uncoated substrate.

In some embodiments, the determination step212may include comparing the intensity of fluoresce to a predetermined threshold value and/or compared to a control area known to be coated or known to lack a coating. In some embodiments, intensity level data for a particular substrate may be saved for comparison against future data to track wear and/or coating performance. In some embodiments, the methods disclosed herein can be used to determine the level of coating wear between areas of a substrate by comparing the level of fluorescent intensity between different predetermined areas. For example, obtained data can be used to determine frequent touchpoints that may require more frequent recoating, more robust coating, and/or additional coating layers. In an optional additional step214, the substrate under test may be flagged for further action, for instance reapplication of antimicrobial surface coating, servicing or replacement of the associated substrate, element or component.

Methods according to the present disclosure can be used to verify the presence or absence of an antimicrobial coating, for example, to verify the application and quality of the coating during manufacturing, and/or detect wear in the coating during service. In some embodiments, the method includes providing a substrate coated with an antimicrobial surface coating containing a fluorescent indicator, exposing the coated substrate to UV light to excite the fluorescent indicator, and observing the presence or absence of fluorescence to detect coating presence and wear. In further embodiments, the method may include measuring the intensity of fluorescence across a coated substrate exposed to UV light and comparing the measured intensity to predefined threshold values corresponding to predefined wear indicators. Collected data may be analyzed to determine coating performance, compare performance between substrates, measure usage and wear, etc.

FIG.3shows schematically a substrate300under test, a detectable fluorescent indicator302(e.g., provided as an applied fluorophoric compound according to the first method100or as a component of the formed antimicrobial surface coating according to the second method200), application of the appropriate radiation304to be absorbed by the fluorescent indicator302, and emission of light in the visible spectrum306indicating the presence of an antimicrobial surface coating.

Antimicrobial surface coatings according to the present disclosure find widespread application in the field of antimicrobials and may be used to surface treat any substrate benefitting from the advantages of an antimicrobial surface coating.