FIELD

The present disclosure generally relates to analytical measurements using X-ray fluorescence (XRF) spectrometry, and more specifically to systems and methods for analyzing antimicrobial coatings on surfaces using a handheld XRF analyzer.

BACKGROUND

In general, it is inherently difficult to quantify thickness and composition of thin films coated on surfaces. For example, a large or permanently fixed surface (e.g., a countertop) cannot be physically brought to an analytical laboratory for surface analysis. In other examples, the difference in weight between an uncoated and coated surface may be undetectable or statistically unreliable, particularly if the surface is considerably heavy in weight and the thin film coating is correspondingly miniscule in weight, which is often the situation.

Various analytical methods such as atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), Auger Electron Spectroscopy (AES), Fourier Transform Infrared Spectroscopy (FTIR), and Raman spectroscopy are useful for thin film quantification and characterization. However, of these methods, only FTIR and Raman are sufficiently portable to be taken into the field to analyze thin film coatings on fixed surfaces. Further, and depending on the substances to be analyzed, some of these analytical methods do not have sufficient detection sensitivity for quantitative analysis of thin films. See, for example,Encyclopedia of Materials Characterization, Butterworth-Heinemann, Stoneham, MA Publishers, C. Brundle, et al., editors, ISBN-13: 978-0-7506-9168-0.

Various antimicrobial coatings applied to surfaces are in the form of thin films, so the coatings are often difficult or impossible to quantify and characterize out in the field where the coated surfaces are located, such as in hospitals and other institutions. Such films may have thicknesses in the several monolayers to micron range, with weights per unit area of less than about 1 mg/in2. For some antimicrobial coatings (e.g., comprising a silane and/or a titanium species), the weight of the antimicrobial coating per unit of area may relate to residual antimicrobial efficacy of the coating. As such, knowing how much antimicrobial coating has been disposed on a surface, or that remains on the surface after a period of time and wear, is important in estimating the antimicrobial efficacy of the coating. Further, such coatings may be worn off by frequent handling of the surface or from various environmental exposures or cleaning protocols, and thus it is important to have a portable quantification method able to track the amount of antimicrobial coating remaining on a surface over time.

In spite of the vast knowledge in thin film analysis, there still exists a need for new portable analytical methods for quantifying antimicrobial coatings in the field, applicable on a diverse set of surfaces such as plastics and metals, non-destructive, rapid and inexpensive, in order to predict antimicrobial efficacy of a coated surface as the coating is worn off over time. In particular, a portable analytical method for quantifying antimicrobial coatings in a healthcare setting, such as a coating comprising a silane or titanium species, is needed.

SUMMARY

Contaminated surfaces are a critical risk factor for transmitting infectious disease. Current disinfection products provide short-term antimicrobial action; however, these surfaces can be re-contaminated within hours after cleaning. To address this limitation, long-lasting antimicrobial polymer coatings have been developed, as an adjunct to traditional disinfecting and cleaning protocols. Due to the microscale thickness and transparency of such polymer coatings, confirmation of the presence of a coating on a surface is difficult with conventional methods. To solve this problem, this disclosure provides a novel approach to measuring durable polymer coatings on glass, plastics, stainless steel and other surfaces to validate their presence and relative antimicrobial activity.

In various embodiments, a hand-held X-Ray Fluorescence Spectroscopy (XRF) analyzer is utilized to quantitatively evaluate the amount of antimicrobial polymer coating deposited on test surfaces and remaining after mechanical abrasion and washing. Additionally, the relationship between the XRF spectra and antimicrobial activity was evaluated using a modified version of an existing sanitization protocol for hard surfaces usingStaphylococcus epidermidisas the test organism. The analytic method using XRF is simple, inexpensive, rapid, portable, quantifiable, and provides direct proof of the presence of an antimicrobial coating.

In various embodiments, a method of quantifying antimicrobial silane and/or titanium thin films using portable X-ray fluorescence spectroscopy (XRF) has now been discovered. In various embodiments, an XRF14Si and/or22Ti peak intensity becomes a predictor of antimicrobial efficacy and durability of antimicrobial thin films comprising a silane and/or a titanium species. In various embodiments, an antimicrobial coating comprises a silane having a quaternary ammonium chloride substituent, allowing for analysis of the coating and prediction of antimicrobial efficacy by assessing14Si and/or17Cl content in the coating by XRF.

The method comprises using a handheld XRF analyzer for quantifying an amount of silicon atoms (14Si), titanium atoms (22Ti), and/or chlorine (17Cl) atoms present in an antimicrobial thin film coating, and relating the quantity of14Si,22Ti and/or17Cl to an expected antimicrobial efficacy of the coating by using a calibration curve. In various embodiments, a calibration curve allows for interpolation of expected residual antimicrobial efficacy of an antimicrobial coating given a measured photon count of an element known to be present in the coating, such as silicon, titanium or chloride. In various embodiments, a calibration curve of antimicrobial efficacy versus elemental photon counts is specific to a particular organism, such as a bacteria or virus species.

In various embodiments, a method of estimating an expected level of residual antimicrobial efficacy for an antimicrobial coating comprising silicon and/or titanium comprises: obtaining14Si or22Ti photon counts from the antimicrobial coating using XRF spectroscopy; and converting the obtained14Si or22Ti photon counts to the expected level of residual antimicrobial efficacy using a calibration curve.

In various embodiments, a method of measuring a thickness of an antimicrobial coating comprising silicon and/or titanium comprises: obtaining14Si or22Ti photon counts from the antimicrobial coating using XRF spectroscopy; and converting the obtained14Si or22Ti photon counts to the thickness using a calibration curve.

In various embodiments, a method of measuring the weight per unit of surface area of an antimicrobial coating comprising silicon and/or titanium comprises: obtaining14Si or22Ti photon counts from the antimicrobial coating using XRF spectroscopy; and converting the obtained14Si or22Ti photon counts to the weight per unit of surface area using a calibration curve.

In various embodiments, the antimicrobial coating comprises a silane selected from the group consisting of 3-(trimethoxysilyl) propyl dimethyl octadecyl ammonium chloride, 3-(trihydroxysilyl) propyl dimethyl octadecyl ammonium chloride, 3-chloropropyltrimethoxysilane, 3-chloropropyltriethoxysilane, 3-chloropropylsilanetriol, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropylsilanetriol, homopolymers therefrom, and mixtures thereof. In certain aspects, XRF analysis of antimicrobial coatings comprising 3-(trimethoxysilyl) propyl dimethyl octadecyl ammonium chloride or 3-(trihydroxysilyl) propyl dimethyl octadecyl ammonium chloride may comprise obtaining17Cl photon counts, or photon counts from another halide associated with the ammonium substituent if not chloride. In various embodiments, the antimicrobial coating comprises nanoparticulate TiO2.

In various embodiments, the step of obtaining the14Si or22Ti photon counts comprises irradiation of the antimicrobial coating with X-rays emanating from a handheld XRF analyzer and detecting X-ray emissions from the coating.

In various embodiments, the calibration curve comprises an x/y plot of the expected level of residual antimicrobial efficacy for a desired microorganism versus the14Si or22Ti photon counts.

