Magnetic Poly(N-isopropylacrylamide) Nanocomposites: Effect of Preparation Method on Antibacterial Properties

The most challenging task in the preparation of magnetic poly(N-isopropylacrylamide) (Fe(3)O(4)-PNIPAAm) nanocomposites for bio-applications is to maximise their reactivity and stability. Emulsion polymerisation, in situ precipitation and physical addition were used to produce Fe(3)O(4)-PNIPAAm-1, Fe(3)O(4)-PNIPAAm-2 and Fe(3)O(4)-PNIPAAm-3, respectively. Their properties were characterised using scanning electron microscopy (morphology), zeta-potential (surface charge), thermogravimetric analysis (stability), vibrating sample magnetometry (magnetisation) and dynamic light scattering. Moreover, we investigated the antibacterial effect of each nanocomposite against Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus. Both Fe(3)O(4)-PNIPAAm-1 and Fe(3)O(4)-PNIPAAm-2 nanocomposites displayed high thermal stability, zeta potential and magnetisation values, suggesting stable colloidal systems. Overall, the presence of Fe(3)O(4)-PNIPAAm nanocomposites, even at lower concentrations, caused significant damage to both E. coli and S. aureus DNA and led to a decrease in cell viability. Fe(3)O(4)-PNIPAAm-1 displayed a stronger antimicrobial effect against both bacterial strains than Fe(3)O(4)-PNIPAAm-2 and Fe(3)O(4)-PNIPAAm-3. Staphylococcus aureus was more sensitive than E. coli to all three magnetic PNIPAAm nanocomposites.