Equal contributions by the last two authors
Evaluation of biocidal efficacy of copper alloy coatings in comparison with solid metal surfaces: generation of organic copper phosphate nanoflowers
Article first published online: 11 JAN 2013
© 2012 The Society for Applied Microbiology
Journal of Applied Microbiology
Volume 114, Issue 3, pages 680–687, March 2013
How to Cite
Gutierrez, H., Portman, T., Pershin, V. and Ringuette, M. (2013), Evaluation of biocidal efficacy of copper alloy coatings in comparison with solid metal surfaces: generation of organic copper phosphate nanoflowers. Journal of Applied Microbiology, 114: 680–687. doi: 10.1111/jam.12094
- Issue published online: 18 FEB 2013
- Article first published online: 11 JAN 2013
- Accepted manuscript online: 10 DEC 2012 06:33PM EST
- Manuscript Accepted: 21 NOV 2012
- Manuscript Revised: 12 NOV 2012
- Manuscript Received: 10 OCT 2012
- biocidal efficacy;
- copper alloys;
- Escherichia coli ;
- organic copper phosphate crystals;
- phosphorus bronze;
- Staphylococcus epidermidis ;
- thermal spray
To analyse the biocidal efficacy of thermal sprayed copper surfaces.
Methods and Results
Copper alloy sheet metals containing >60% copper have been shown to exhibit potent biocidal activity. Surface biocidal activity was assessed by epifluorescence microscopy. After 2-h exposure at 20°C in phosphate-buffered saline (PBS), contact killing of Gram-negative Escherichia coli and Gram-positive Staphylococcus epidermidis by brass sheet metal and phosphor bronze was 3–4-times higher than that by stainless steel. SEM observations revealed that the surface membranes of both bacterial strains were slightly more irregular when exposed to brass sheet metal than stainless steel. However, when exposed to phosphor bronze coating, E. coli were 3–4 times larger with irregular membrane morphology. In addition, the majority of the cells were associated with spherical carbon-copper-phosphate crystalline nanostructures characteristic of nanoflowers. The membranes of many of the S. epidermidis exhibited blebbing, and a small subset was also associated with nanoflowers.
Our data indicate that increasing the surface roughness of copper alloys had a pronounced impact on the membrane integrity of Gram-positive and, to a lesser degree, Gram-negative bacteria. In the presence of PBS, carbon-copper-phosphate-containing nanoflowers were formed, likely nucleated by components derived from killed bacteria. The intimate association of the bacteria with the nanoflowers and phosphor bronze coating likely contributed to their nonreversible adhesion.
Significance and Impact of the Study
Thermal spraying of copper alloys provides a strategy for the rapid coating of three-dimensional organic and inorganic surfaces with biocidal copper alloys. Our study demonstrates that the macroscale surface roughness generated by the thermal spray process enhances the biocidal activity of copper alloys compared with the nanoscale surface roughness of copper sheet metals. Moreover, the coating surface topography provides conditions for the rapid formation of organic copper phosphate nanocrystals/nanoflowers.