Red Microalgal Sulfated Polysaccharide-CuO Complexes: Characterization and Bioactivity.

The anion-exchange capacity of the cell-wall sulfated polysaccharide of the red microalga sp. can be exploited for the complexation of metal ions (e.g., Cu, Zn, Ag) to produce novel materials with new bioactivities. In this study, we investigated this algal polysaccharide as a platform for the incorporation of copper as CuO. Chemical and rheological characterization of the CuO-polysaccharide complex showed that the copper is covalently bound to the polysaccharide and that the complex exhibits higher viscosity and conductivity than the native polysaccharide. Examination of the complex's inhibitory activity against the bacteria , , , , and and the fungus revealed a relatively high antimicrobial activity, especially against (92% growth inhibition) as compared to the polysaccharide and to CuO alone. The antibiofilm activity was also found against PA14 and biofilms. An atomic force microscopy examination of the surface morphology of the complex revealed needle-like structures (spikes), approximately 10 nm thick, protruding from the complex surface to a maximum height of 1000 nm, at a density of about 5000/μm, which were not detected in the native polysaccharide. It seems that the spikes on the surface of the CuO-polysaccharide complex are responsible for the antimicrobial activities of the complex, that is, for disruption of microbial membrane permeability, leading to cell death. The study thus indicates that the superior qualities of the novel material formed by complexion of CuO to the polysaccharide should be studied further for various biotechnological applications.