Iron(III) and aluminium(III) based mixed nanostructured hydroxyphosphates as potential vaccine adjuvants: Preparation and physicochemical characterization

Adjuvants are substances that, when combined with an antigen in a vaccine formulation, potentiate the immune response against that antigen. Aluminium hydroxyphosphate is among the currently used adjuvants in vaccines, while studies on its iron analogue, ferric hydroxyphosphate, are quite limited. In this article we report on the preparation and physicochemical characterization of novel nanostructured iron and aluminium based mixed hydroxyphosphates as potential vaccine adjuvants, prepared by controlled co-precipitation from mixed solutions of Fe(III) and Al(III) chlorides with sodium phosphate and sterilized by autoclaving. The obtained hydroxyphosphates consisted of a network of platy nanoparticles (20-40 nm in size), which aggregated in aqueous medium to form secondary micron-sized particles. The obtained nanostructured hydroxyphosphates were characterized by energy dispersive X-ray spectroscopy for elemental composition, X-ray powder diffraction, infrared spectroscopy, zeta-potential measurements for determination of isoelectric point, protein adsorption, and dissolution rate in sodium citrate solution.