## 4 Discussion  
Amorphous silicon dioxides are known to confer desirable attributes upon incorporation with active ingredients including enhanced biocompatibility, improved chemical stability, and improved thermal stability [7; 9; 37; 38; 39]. Modified Stober methodologies employed by [PERSON] et al. afford silica coatings on fluorescent dye-doped polymeric nanoparticles towards obtaining an insulating layer with improved physical stability [37]. Silver-silica core-shell structures, successfully prepared by [PERSON] et al., use a modified Stober process to confer chemical stability to metallic silver nanoparticles without hindering antimicrobial efficacy [9]. These methods are conducive to conventional organic drugs or weak oxidizing agents such as metallic silver, affording control over polymerization and deposition of silicon dioxide. However, in the presence of strong oxidizing agents such as silver oxynitrate, chemical incompatibilities restrict the successful application of these methodologies. Acid-catalyzed polymerization or deposition of alkali silicates are also known to generate amorphous silica [5; 24; 25; 27]. Similar to the aforementioned silica-shell strategies, conventional acid-precipitated silicate methodologies are reliant upon the use of surfactants and organic precursors as structure-directing agents and therefore pose challenges for use with highly oxidizing materials. In the present work, alternate methods for the in-situ polymerization  
Figure 8: Antimicrobial efficacy of silver oxynitrate (Ag\({}_{7}\)NO\({}_{11}\)) and Ag\({}_{7}\)NO\({}_{11}\):SiO\({}_{2}\) containing 0.1:1, SiO\({}_{2}\):Ag. (**A**) Single-time log reduction for 1-h treatment period against _P. aeruginosa_ and 4-h treatment period against _S. aureus_ challenged at \(1\times 10^{6}\) CFU/mL; (**B**) Biofilm log reduction values for 2-h treatment period against _P. aeruginosa_ and 4-h treatment period against _S. aureus_ established 3D biofilm. Results representing the average of triplicate data (\(n=3\)), error bars indicated represent standard deviations of the triplicate measurements. of silica with higher oxidation state silivers are presented wherein the formation of the silica structure is self-directed through acidic by-products of silver oxynitrate synthetic reactions. Silicate ions will polymerize to form silica in solutions having pH of less than about 10 (H4 SiO4, pK\({}_{\text{a1}}\) = 9.8) [40]. In the preparation of silver oxynitrate, Equation (3), it is known that sulfuric and nitric acids are generated as by-products of the silver oxidation reaction resulting in the reduction of pH of the solution from neutral to pH 1-2 (data not shown). These acids, as shown previously, are suitable to effect protonation of silicic acid at room temperature and formation of oligomeric silicic acids resulting in the precipitation of amorphous silica [24; 25; 40]. In the methodologies presented herein alkali silicates at various concentrations relative to silver are dispersed into an oxidizing solution of potassium persulfate to which a soluble silver solution is added resulting in the oxidation of silver and chemical deposition of silver oxynitrate, as verified by XRD in Figure 1. Finite nucleation locus of silver oxynitrate, a crystalline compound with the cubic space group Fm3m, generate an acid gradient in the immediate vicinity of silver oxynitrate nucleation sites, directing the spatial polymerization or precipitation of silica [41]. As observed in Figures 2 and 3, silver oxynitrate solids are observed to be impregnated in a silica framework. Absence of AgO or other degradation products of silver oxynitrate, as seen in in Figure 1, indicates that the co-deposition process does not impair the formation of silver oxynitrate. Formation of silver sulfate does not occur as a by-product of the reaction, as seen in Equation (3). Rather silver sulfate is an impurity forming due to incomplete conversion of soluble silver to silver oxynitrate.