Antimicrobial properties of a multi-component alloy

Abstract

High traffic touch surfaces such as doorknobs, countertops, and handrails can be transmission points for the spread of pathogens, emphasizing the need to develop materials that actively self-sanitize. Metals are frequently used for these surfaces due to their durability, but many metals also possess antimicrobial properties which function through a variety of mechanisms. This work investigates metallic alloys comprised of several metals which individually possess antimicrobial properties, with the target of achieving broad-spectrum, rapid sanitation through synergistic activity. An entropy-motivated stabilization paradigm is proposed to prepare scalable alloys of copper, silver, nickel and cobalt. Using combinatorial sputtering, thin-film alloys were prepared on 100 mm wafers with ≈50% compositional grading of each element across the wafer. The films were then annealed and investigated for alloy stability. Antimicrobial activity testing was performed on both the as-grown alloys and the annealed films using four microorganisms-Phi6, MS2, Bacillus subtilis and Escherichia coli-as surrogates for human viral and bacterial pathogens. Testing showed that after 30 s of contact with some of the test alloys, Phi6, an enveloped, single-stranded RNA bacteriophage that serves as a SARS-CoV-2 surrogate, was reduced up to 6.9 orders of magnitude (> 99.9999%). Additionally, the non-enveloped, double-stranded DNA bacteriophage MS2, and the Gram-negative E. coli and Gram-positive B. subtilis bacterial strains showed a 5.0, 6.4, and 5.7 log reduction in activity after 30, 20 and 10 min, respectively. Antimicrobial activity in the alloy samples showed a strong dependence on the composition, with the log reduction scaling directly with the Cu content. Concentration of Cu by phase separation after annealing improved activity in some of the samples. The results motivate a variety of themes which can be leveraged to design ideal antimicrobial surfaces.

Figure 1

(a) Compositional map of Ni, Cu, Ag and Co. (b) X-ray diffraction patterns, taken at positions 1–17, identified in panel c. (c) Contour plot of the two FCC phases in the as-grown system.

Figure 2

X-ray diffraction patterns captured at positions 1–17 after the anneal.

Figure 3

(a) Contour plot showing the relative XRD peak intensity for the FCC phases after the anneal, A(50°) / (A(47°) + A(50°)), where A is the peak area. (b) SEM and EDX images of positions 3, 8, and 1, identified in the contour plot. The scale bar in the SEM image corresponds to 1000 nm.

Figure 4

Antimicrobial activity of single component (left) and multicomponent (right) surfaces, tested on (a, e) Phi6, (b, f) MS2, (c, g) E. coli, and (d, h) B. subtilis. No B. subtilis was recovered on the metal Cu.

Figure 5

Heat map of log-reduction on the thin film chips of (a) Phi6, (b) MS2, (c) E. coli, and (d) B. subtilis; log-reduction on the annealed chips of (e) Phi6, (f) MS2, (g) E. coli, and (h) B. subtilis.

Figure 6

Line-cuts of the antimicrobial activity for (a) Phi6, (b) MS2, (c) E. coli, and (d) B. subtilis, taken across the equatorial ray of the wafers between Cu and Ni.