Methylene blue dye coated silver–silica nanoparticles with dual functionality fabricated by injection pump and ultrasonochemistry

Silver nanoparticles, with diameters of 10 ± 5 nm embedded in silica nanoparticles (∼90 nm), were fabricated at the gram scale using an injection pump and ultrasonication strategy in a single reaction process. The size of the silver and silica nanoparticles was effectively controlled by injection pump-assisted precursors and the catalyst flow rate. Conjunction of in situ ultrasonication lead to better dispersion of the composite in solution to form a relatively uniform suspension, which resulted in maximum exposure of each particle within the reactant solution and an overall pseudo-homogeneous reduction and nucleation within a short period of time compared to other methods. Electrostatic repulsion (silica and silica) and attraction (silica and silver) among the nanoparticles formed the organized particle structure. The morphological properties, optical absorbance, crystallinity and chemical structure of the prepared particles were extensively studied. The resulting silver–silica nanoparticles were coated with methylene blue dye, which not only provided a significant fluorescent property but also positively enhanced the anti-bacterial activity of the simple silver–silica nanoparticles. Minimum inhibitory concentration analyses were performed against three Gram-positive and Gram-negative bacteria to ensure the anti-bacterial properties of the nanoparticles.