Au@mSiO₂ nanocomposites with large pores for protein transport

Gold-mesoporous silica (Au@mSiO₂) core-shell nanoparticles (NPs) have shown interesting potential for the loading of molecules to be delivered by plasmonic heating. In this study, we describe the unprecedented synthesis of Au@mSiO₂ NPs with large pores (lp-Au@mSiO₂), aiming at encapsulating large biomolecules such as proteins. Starting from recently reported Au@mSiO₂ seeds with a diameter of 45 nm, two strategies are presented to grow a mesoporous shell with large pores. The most interesting NPs (lp-Au@mSiO₂) were obtained with the biphasic stratification approach, yielding NPs with large conical pores (10-20 nm openings), characterized in depth by N₂-sorption and electron microscopies. Atomic force microscopy (AFM) with a sharp tip was used for the first time with these mesoporous materials to probe the accessibility of the pore openings. Biphasic stratification provides NPs with good colloidal and hydrolytic stabilities in aqueous saline medium (PBS) allowing the incubation of these NPs with two model proteins: horse radish peroxidase (HRP) and red fluorescent protein (RFP). lp-Au@mSiO₂ exhibit a significantly larger loading capacity with respect to NPs with similar diameter, either non-porous or with narrower pores, providing evidence that the proteins can indeed be encapsulated within the pores.