A procedure for the preparation of ZnO nanocubes in an alginate biopolymer was introduced. The obtained nanocubes were used for the preparation of ZnO/Ag heterostructures. High resolution scanning electron microscopy showed that reduction of silver salts in the presence of nanocubes results in the formation of spherical silver nanoparticles at their edges and vertices. UV-vis and photoluminescence spectroscopy revealed that alginate-ZnO/Ag nanostructures exhibit different optical properties compared to the starting alginate-ZnO system. The surface plasmon resonance peak of the silver nanoparticles dominates the absorption spectra of the ZnO/Ag hybrid particles, while at the same time the Ag nanoparticles quench the ZnO emission. The photocatalytic activity of the ZnO/Ag heterostructure was faster than that of the pure ZnO and further improved with increasing the concentration of silver. Both the alginate-ZnO and alginate-ZnO/Ag nanocomposites showed strong antimicrobial activities against gram-positive (Staphylococcus aureus) and gram-negative (Escherichia coli) bacteria. (C) 2014 Elsevier B.V. All rights reserved.