FULL PA PER © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1 wileyonlinelibrary.com www.particle-journal.com www.MaterialsViews.com Silver nanoparticles (NPs) encapsulated in amorphous silica shells are syn- thesized and evaluated for their antibacterial action using the Gram-negative Escherichia coli bacterium. These inorganic capsules are synthesized using a new approach that comprises the use of oil-in-water-in-oil (O/ W/ O) multiple emulsions to fabricate SiO 2 capsules incorporating organically capped Ag NPs. This strategy is explored as a mean to promote the bioadhesion of the microorganisms to the silica rough surfaces while still keeping the system with a high surface area for the active metal. The results have shown that the hybrid capsules enable a slow release of cationic silver from the interior of the silica microsphere to the external medium probably through the pore channels in the shell. The antibacterial activity against E. coli is mainly deter- mined by the Ag + ion release rate, suggesting that these particulates can be employed as a robust system for prolonged used as an antimicrobial material. or micelles, [13] and emulsion droplets. [14] Several reports on the preparation of hollow capsules based on polyelectro- lyte multilayers have also appeared as this approach enables the fabrication of morphological well-defined core–shell materials. [15,16] These approaches can be adapted to the fabrication of capsules con- taining functional inorganic NPs. Thus, Anandhakumar et al. [17] incorporated Ag NPs in shells of polyelectrolytes for the photoinduced release of substances of biological interest. In addition, Katagiri et al., [18] using colloidal-templating tech- niques fabricated magneto-responsive capsules formed with polyelectrolytes, lipid bilayers, and magnetite NPs. More recently, highly uniform double emulsions were used as templates in microfluidic techniques to produce polylactic acid and SiO 2 capsules. [19,20] Magnetic microspheres have been fabricated through directly employing magnetic particles (e.g., Fe 3 O 4 , CoFe 2 O 4 ) as emul- sifiers to stabilize Pickering emulsions, instead of common organic surfactants. [21] Miesch et al. [22] demonstrated that two distinct types of NPs, Au NPs with tetra(ethylene glycol) ligands and CdSe quantum dots protected with their native alkane- based ligands, can be used as surfactants to generate both oil-in-water-in-oil (O/ W/ O) and water-in-oil-in-water (W/ O/ W) double-emulsion droplets. In fact, the use of (W/O/W) or (O/W/O) double emulsions has been exploited to produce a number of inorganic/polymer hybrid systems, which include capsules of Fe 3 O 4 , Au, and Ag. [11,23–25] The antimicrobial activity of silver and its compounds have been exploited since a long time. [26,27] In fact, common silver- based objects, such as coins and liquid containers, were empiri- cally used in ancient civilizations to prevent infectious diseases and for water disinfection, for example. Also modern pharma- cology has developed various compounds containing this metal for antimicrobial applications, such as the well-known complex Ag (I) sulfadiazine, which is used in topical creams. Although the use of silver for these applications lost some importance with the advent of modern pharmacochemical antibiotics, there is currently a renewed interest in its application namely because certain strains of microorganisms have became resistant to conventional antibiotics. [28,29] The effect of silver as a broad- spectrum antibiotic has been explained on the basis of different mechanisms, which are still matter of debate. However, the release of cationic silver from an oxidized surface seems to have a relevant role. [30–32] Thus, recent literature offers a myriad of materials based on Ag NPs in which their high specific surface Dr F. L. Sousa, Dr A. V. Girão, Dr. S. Fateixa, Prof. T. Trindade Department of Chemistry-CICECO Aveiro Institute of Nanotechnology University of Aveiro Campus de Santiago 3810-193 Aveiro, Portugal E-mail: tito@ua.pt Prof. A. Almeida Department of Biology-CESAM University of Aveiro Campus de Santiago 3810-193 Aveiro, Portugal DOI: 10.1002/ ppsc.201400168 Multiple Emulsion Templating of Hybrid Ag/ SiO 2 Capsules for Antibacterial Applications Filipa L. Sousa, Adelaide Almeida, Ana V. Girão, Sara Fateixa, and Tito Trindade* 1. Introduction Colloidal nanoparticles (NPs) possess unique chemical/phys- ical properties and can self-assemble into hierarchically organ- ized structures. The use of colloidal NPs as building blocks to design and fabricate functional materials is of both techno- logical and fundamental interest, as it offers control over size and shape-dependent properties of the final materials. [1,2] For example, the controlled fabrication of capsules integrating inor- ganic NPs has attracted considerable attention. [3–5] Depending upon the functionalities of the NPs, these capsules have appli- cations in diverse fields such as in drug delivery, optical bio- sensing, catalysis, among others. [6–10] At present, a diversity of methods has been reported for the fabrication of capsules using either soft or hard templates. These include poly(styrene) beads, [11] SiO 2 colloids, [12] vesicles Part. Part. Syst. Charact. 2014, DOI: 10.1002/ ppsc.201400168