Abstract
Copper–fluoropolymer (Cu-CFx) nano-composite films are deposited by dual ion-beam sputtering. The extensive analytical characterization of these layers reveals that inorganic nanoparticles composed of Cu(II) species are evenly dispersed in a branched fluoropolymer matrix. In particular, X-ray photoelectron spectroscopy has been employed to study the surface chemical composition of the material and to assess how it changes on increasing the copper loading in the composite. Transmission electron microscopy reveals that the copper nanoclusters have a mean diameter of 2–3 nm and are homogeneously in-plane distributed in the composite films. Electrothermal atomic absorption spectroscopy has been used to study the kinetics of copper release in the solutions employed for the biological tests. The Cu-CFx layers are employed as bioactive coatings capable of inhibiting the growth of target microorganisms such as Saccharomyces cerevisiae, Escherichia coli, Staphylococcus aureus, and Lysteria. The results of the analytical characterization enable a strict correlation to be established among the chemical composition of the material surface, the concentration of copper dissolved in the microorganisms broths, and the bioactivity of the nano-structured layer.
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Acknowledgments
Miss C. Caso, Mr S. Giacummo, and Mr A. Tambone are gratefully thanked for their skilled assistance during biological experiments (C.C.) and XPS analyses (S.G., A.T.). Professor E. Traversa and Dr L. Ghibelli are greatly acknowledged for useful discussions.
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Appendix
Appendix
Curve-fit parameters employed for XPS data treatment
Full width at half maximum values (eV) as a function of spectral region and metal loading
φ | C1s | F1s | O1s | Cu2p3/2a | ||
---|---|---|---|---|---|---|
Photoelectron peaks (1 and 2) | Shake-up (1) | Shake-up (2 and 3) | ||||
0.05 | 2.29 | 2.66 | – | – | – | – |
0.15 | 2.34 | 2.82 | 2.40 | 3.64 | 3.18 | 3.12 |
0.25 | 2.13 | 2.71 | 2.40 | 3.82 | 3.82 | 2.90 |
The curve-fit function (gl) takes into account the mixed Gaussian–Lorentzian character of the peak shape as reported in the following:
The tail function is:
and the total function is:
where x is an energy variable, h the peak height, m the Lorentzian/Gaussian merge factor as Lorentzian percentage center (peak center), b the peak width, CT the tail constant, ETH the exponential tail height, and ET the exponential tail.
Generally speaking, curve-fitting was carried out without the use of tails (CT=0, EHT=0, ET=0), except for the cupric oxide component of the Cu2p3/2 and O1s spectral regions. For these signals, after analysis of a CuO standard, the parameters reported in the table were used.
Tail parameters used for curve-fitting in the O1s and Cu2p3/2 regions
| CT | EHT | ET |
---|---|---|---|
CuO | 0.01 | 0.0384 | 0.2 |
CuO | 0.005 | 0.05 | 0.05 |
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Cioffi, N., Ditaranto, N., Torsi, L. et al. Analytical characterization of bioactive fluoropolymer ultra-thin coatings modified by copper nanoparticles. Anal Bioanal Chem 381, 607–616 (2005). https://doi.org/10.1007/s00216-004-2761-4
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DOI: https://doi.org/10.1007/s00216-004-2761-4