Comparative study of antimicrobial activity of silica-based nanohybrids functionalized with 5-aminosalicylic acid: toward reduced silver usage

Abstract

In this study, we report the synthesis, characterization, and antimicrobial evaluation of two silica-based hybrid nanocomposites: SiO<inf>2</inf> functionalized with 5-aminosalicylic acid (5-ASA), and its silver-decorated counterpart, SiO<inf>2</inf>/5-ASA/Ag. The organic ligand 5-ASA was covalently anchored onto the surface of amorphous silica nanoparticles, forming interfacial charge-transfer (ICT) complexes capable of visible-light absorption, as confirmed by UV–Vis diffuse reflectance spectroscopy and supported by DFT/TD-DFT calculations. The subsequent deposition of silver nanoparticles resulted in the formation of plasmonic nanohybrids with enhanced light-harvesting properties. The materials were extensively characterized using FTIR, TGA/DTA, XRD, HRTEM/EDX, and DRS techniques. Their antimicrobial activities were assessed against Escherichia coli, Staphylococcus aureus, and Candida albicans using time-resolved CFU assays at multiple concentrations. Both hybrids demonstrated significant antimicrobial performance; however, notably, the silver-free SiO<inf>2</inf>/5-ASA sample exhibited potent bactericidal activity, particularly against S. aureus, even at low concentrations. This finding suggests that the presence of –NH<inf>2</inf> groups from the 5-ASA ligand contributes to antimicrobial action via interactions with bacterial cell walls, highlighting the potential for silver-free nanomaterials in antimicrobial applications. The results support the development of multifunctional ICT-based nanohybrids with reduced reliance on metallic silver, addressing growing environmental and regulatory concerns.