Combining Ag and γ-Fe₂O₃ properties to produce effective antibacterial nanocomposites

The antibacterial activity of hybrid γ-Fe₂O₃/Ag nanocomposites against the bacterial pathogens E. coli (Gram-negative) and S. aureus (Gram-positive) has been studied. Silver is a well-known bactericidal agent and γ-Fe₂O₃ nanoparticles release heat when they are exposed to alternating magnetic fields. The combination of both properties to fight infections has not been previously explored. The nanocomposites were synthesized through reduction of silver nitrate in the presence of pre-synthesized superparamagnetic γ-Fe₂O₃ nanoparticles. Changing systematically the ratio of γ-Fe₂O₃ and silver precursor and the temperature of the reaction allowed obtaining superparamagnetic nanocomposites with different Ag contents and particle sizes. The antibacterial activity of the samples was tested, and the minimum inhibitory concentrations and minimum bactericidal concentrations of the nanocomposites were determined to compare the microbicidal activity of the samples. It was found that it is related with the release of silver ions from the nanocomposites. Finally, we studied the combination of the bactericidal effect of silver and magnetic hyperthermia finding a synergetic effect between them when plates containing E. coli or S. aureus bacteria with γ-Fe₂O₃/Ag nanocomposites were subjected to an alternating magnetic field. This effect is related with an increase in the release of silver ions due to that heat dissipation.