Silica Spheres Functionalized with Silver and Bismuth Nanoparticles—Antibacterial Activity Against Clinically Relevant Bacterial Pathogens

The aim of the study was to develop hybrid nanomaterials based on monodisperse silica spheres as carriers for silver nanoparticles (AgNPs) or bismuth nanoparticles (BiNPs) and to evaluate their antimicrobial properties. Silica spheres were synthesized using a modified Stöber method, either unmodified or functionalized with (3-aminopropyl)triethoxysilane (APTES), prior to AgNP or BiNP deposition. The materials were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), inductively coupled plasma optical emission spectroscopy (ICP-OES), and zeta potential measurements, while antimicrobial activity was assessed by microdilution against Gram-positive (<i>Staphylococcus aureus</i>, <i>Staphylococcus epidermidis</i>, <i>Enterococcus faecalis</i>, <i>Enterococcus faecium</i>) and Gram-negative bacteria (<i>Escherichia coli</i>, <i>Pseudomonas aeruginosa</i>), with <i>Helicobacter pylori</i> as a clinical model. The results show that both SiO₂-AgNP and SiO₂-BiNP composites completely inhibited <i>H. pylori</i> and showed high activity against other pathogens, although <i>P. aeruginosa</i> remained less susceptible. Functionalization of AgNP-coated samples with APTES promoted uniform distribution of AgNPs, with the minimum bactericidal concentration (MBC) to minimum inhibitory concentration (MIC) ratios ranging from 1 to 4, confirming a bactericidal rather than bacteriostatic effect. In contrast, BiNP-coated samples without APTES exhibited lower MIC values from 74 to 595 μg mL^-1, consistent with increased Bi³⁺ release from amorphous phases. This indicates the antimicrobial potential, highlighting the role of surface functionalization in regulating ion release and biological performance, and suggesting applications in the biomedical and food industries.