Abstract
Chitosan-capped stable silver sols (Chit/AgNPs) were fabricated using a chemical reduction method. Chit/AgNPs exhibited a sharp surface plasmon resonance (SPR) peak at 420 nm. The resulting orange-colored sols became colorless after the addition of ferric (Fe3+) ions at room temperature. Chitosan formed a stable complex with Fe3+ ions. The relative viscosity measurements revealed that the chitosan was stable in the presence of hydrogen peroxide at room temperature for ca. 1 h. Hydrogen peroxide catalyzed the Fe3+ sensing activity of the Chit/AgNPs, and the mechanism proceeded through a Fenton-like reaction. The AgNPs were oxidized by Fe3+ ions into silver ions. The Al3+, Ba2+, Ca2+, Cu2+, Co2+, Mg2+, Ni2+, Pb2+, Zn2+, Na+, and K+ did not act as sensors for AgNPs. The plasmonic colorimetric detection limit of Fe3+ ions was found to decrease (from 20 to 100 mu M) with the pH of the working solution. The microbial growth of chitosan and Chit/AgNPs was evaluated against S. aureus and C. albicans human pathogens using optical density measurements. Chitosan prevented electrolyte exchange on the surface of the bacterial cell walls and disturbed the cells' physiological functions.