Controlling the Antimicrobial Action of Surface Modified Magnesium Hydroxide Nanoparticles

Magnesium hydroxide nanoparticles (Mg(OH)₂NPs) have recently attracted significant attention due to their wide applications as environmentally friendly antimicrobial nanomaterials, with potentially low toxicity and low fabrication cost. Here, we describe the synthesis and characterisation of a range of surface modified Mg(OH)₂NPs, including particle size distribution, crystallite size, zeta potential, isoelectric point, X-ray diffraction (XRD), dynamic light scattering (DLS), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), energy dispersive X-ray analysis (EDX), Fourier transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM). We explored the antimicrobial activity of the modified Mg(OH)₂NPs on the microalgae (C. reinhardtii), yeast (S. cerevisiae) and Escherichia coli (E. coli). The viability of these cells was evaluated for various concentrations and exposure times with Mg(OH)₂NPs. It was discovered that the antimicrobial activity of the uncoated Mg(OH)₂NPs on the viability of C. reinhardtii occurred at considerably lower particle concentrations than for S. cerevisiae and E. coli. Our results indicate that the antimicrobial activity of polyelectrolyte-coated Mg(OH)₂NPs alternates with their surface charge. The anionic nanoparticles (Mg(OH)₂NPs/PSS) have much lower antibacterial activity than the cationic ones (Mg(OH)₂NPs/PSS/PAH and uncoated Mg(OH)₂NPs). These findings could be explained by the lower adhesion of the Mg(OH)₂NPs/PSS to the cell wall, because of electrostatic repulsion and the enhanced particle-cell adhesion due to electrostatic attraction in the case of cationic Mg(OH)₂NPs. The results can be potentially applied to control the cytotoxicity and the antimicrobial activity of other inorganic nanoparticles.