Modification of algae with zinc, copper and silver ions for usage as natural composite for antibacterial applications

Nanometer sized metal particles are used in many applications as antimicrobial materials. However in public discussion nanoparticular materials are a matter of concern due to potential health risks. Hence there is a certain demand for alternative antimicrobial acting materials. For this, the aim of this work is to realize an antimicrobial active material based on the release of metal ions from a natural depot. By this, the use of elemental metal particles or metal oxide particles in nanometer or micrometer scale is avoided. As natural depot four different algae materials (gained from Ascophyllum nodosum, Fucus vesicolosus, Spirulina platensis and Nannochloropsis) are used and loaded by bioabsorption with metal ions Ag(+), Cu(2+) and Zn(2+). The amount of metal bound by biosorption differs strongly in the range of 0.8 to 5.4 mg/g and depends on type of investigated algae material and type of metal ion. For most samples a smaller release of biosorbed Ag(+) and Cu(2+) is observed compared to a strong release of Zn(2+). The antibacterial activity of the prepared composites is investigated with Escherichia coli. Algae material without biosorbed metal has only a small effect on E. coli. Also by modification of algae with Zn(2+) only a small antibacterial property can be observed. Only with biosorption of Ag(+), the algae materials gain a strong bactericidal effect, even in case of a small amount of released silver ions. These silver modified algae materials can be used as highly effective bactericidal composites which may be used in future applications for the production of antimicrobial textiles, papers or polymer materials.