Sequential laser and ultrasonic wave generation of TiO2-Ag core-shell nanoparticles and their anti-bacterial properties.

Core-shell nanoparticles have unusual physical, chemical and biological properties. Until now, for the Ag and TiO₂ combination, only Ag core and TiO₂ shell nanoparticles have been practically demonstrated. In this investigation, novel TiO₂@Ag core-shell (TiO₂ core and Ag shell) nanoparticles were produced via ultrasonic vibration of Ag-TiO₂ compound nanoparticles. A bulk Ti/Ag alloy plate was used to generate colloidal Ag-TiO₂ compound nanoparticles via picosecond laser ablation in deionised water. The colloidal nanoparticles were then sonicated in an ultrasonic bath to generate TiO₂@Ag core-shell nanoparticles. They were characterised using a UV-VIS spectrometer, transmission electron microscopy (TEM), high-angle annular dark-field-Scanning transmission electron microscopy (HAADF-STEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The Ag-TiO₂ compound and the TiO₂@Ag core-shell nanoparticles were examined for their antibacterial activity against Escherichia coli (E. coli) JM109 strain bacteria and compared with those of Ag and TiO₂ nanoparticles. The antibacterial activity of the core-shell nanoparticles was slightly better than that of the compound nanoparticles at the same concentration under standard laboratory light conditions and both were better than the TiO₂ nanoparticles but not as good as the Ag nanoparticles.