Hollow protein microparticles formed through cross-linking by an Au 3+ initiated redox reaction.

Hollow microparticles (MPs) are of great relevance in the materials industry for a wide range of applications, such as catalysis, coatings, and delivery of theranostics. Here, we report the formation of hollow MPs through the assembly of lipoproteins in CaCO 3 templates. Proteins interact in the pores of CaCO 3 templates through attractive hydrophobic forces and form dense edges of hollow MPs. To further cross-link the proteins, Au 3+ was added to initiate a redox reaction, where proteins were oxidized forming inter- and intramolecular covalent bonds, while Au 3+ was reduced and gold nanoparticles (AuNPs) were formed. The obtained protein-based hollow MPs have a diameter of 6 μm and the AuNPs are embedded on their surface. Through this research, we suggest a new route to design biobased Au-protein hollow MPs in simple steps, which can allow new possibilities for carrying functional molecules and bioimaging.