Synthesis and characterisation of uniform CoPt nanoparticles using red blood cell ghosts conjugated with peptides on their inner surface

Abstract

Hybrids of metal nanoparticles (NPs) and lipid vesicles are attractive materials in a wide variety of fields including catalysis, sensing, and biomedical applications. Lipid vesicles can entrap metal NPs on their surfaces, in the lipid bilayer, or within their aqueous cores, resulting in the stabilisation of metal NPs in aqueous environments. Metal NP-lipid vesicle hybrids have been prepared using lipid film hydration in the presence of colloidal metal NPs and in situ synthesis of metal NPs within lipid vesicles. Although these methods are useful for preparing metal NP-lipid vesicle hybrids, they generally suffer from low yield, poor selectivity, and low purity. Moreover, it is still difficult to precisely control the formation process of metal NPs, and the nanospace of lipid vesicles is too small to deposit a large number of metal NPs. We described here the design of a red blood cell ghosts (RBCGs), micro-sized biological membranes, for the synthesis of bimetallic cobalt-platinum nanoparticles (CoPt NPs) with diverse functions such as excellent magnetic properties and catalytic activities. RBCGs are red blood cells from which cytoplasmic components are removed by hypotonic haemolysis. Notable structural features of RBCG include biconcave hollow vesicles with large volume and surface area and the presence of a cytoskeleton composed of proteins beneath the inner membrane. The cytoskeleton allows the immobilisation of various functional molecules on the internal surface by the chemical modification. To deposit uniform CoPt NPs on the inner surface of RBCG, we fabricated RBCG in which a CoPt-binding peptide was chemically attached to the RBCG cytoskeleton. In situ synthesis of CoPt NPs was performed using peptide-conjugated RBCGs or RBCGs under the various conditions. Metal quantification, TEM and magnetic measurement reveal that CoPt NPs prepared using peptide-conjugated RBCGs have larger and uniform NPs with higher Co content than those prepared using RBCGs, resulting in improved magnetic properties.