Electrostatic assembly of binary nanoparticle superlattices using protein cages

Abstract

Binary nanoparticle superlattices are periodic nanostructures with lattice constants much shorter than the wavelength of light and could be used to prepare multifunctional metamaterials. Such superlattices are typically made from synthetic nanoparticles, and although biohybrid structures have been developed, incorporating biological building blocks into binary nanoparticle superlattices remains challenging. Protein-based nanocages provide a complex yet monodisperse and geometrically well-defined hollow cage that can be used to encapsulate different materials. Such protein cages have been used to program the self-assembly of encapsulated materials to form free-standing crystals and superlattices at interfaces or in solution. Here, we show that electrostatically patchy protein cages--cowpea chlorotic mottle virus and ferritin cages--can be used to direct the self-assembly of three-dimensional binary superlattices. The negatively charged cages can encapsulate RNA or superparamagnetic iron oxide nanoparticles, and the superlattices are formed through tunable electrostatic interactions with positively charged gold nanoparticles. Gold nanoparticles and viruses form an AB(8)(fcc) crystal structure that is not isostructural with any known atomic or molecular crystal structure and has previously been observed only with large colloidal polymer particles. Gold nanoparticles and empty or nanoparticle-loaded ferritin cages form an interpenetrating simple cubic AB structure (isostructural with CsCl). We also show that these magnetic assemblies provide contrast enhancement in magnetic resonance imaging.

Intra- and interparticle magnetism of cobalt-doped iron-oxide nanoparticles encapsulated in a synthetic ferritin cage

“…Pyrococcus furiosus ferritin (PfFt), in particular, has several unique advantages, such as enabling a "gentle" reactive environment that can lead to the formation of materials that are difficult to obtain at the nanoscale using conventional free solution environments 1 , a high thermal stability 2 , and producing well crystallized samples 1 due to the relatively few internal nucleation sites for mineralization; qualities which lead to good tunability and a high quality nanoparticle that is ideal for the examination of nanoparticle magnetism. Importantly, ferritin-based nanoparticles are also particularly well suited as building blocks for macroscopic self-assembly that provides an avenue for the study of dipolar-driven magnetism 1, [3][4][5] .…”

DNA-mediated engineering of multicomponent enzyme crystals

“…However, the ability to engineer lattices composed of multiple proteins, or of proteins and inorganic nanomaterials, has been limited, and the choice of protein building blocks is often restricted by structural constraints, which limits the catalytic functionalities that can be incorporated into these structures. Currently, the primary methods for making protein lattices have relied on the use of natural protein-protein interactions (17), interactions between proteins and ligands on the surfaces of inorganic NPs (17,18), metal coordination chemistry (19), small molecule ligand-protein interactions (20)(21)(22)(23), genetically fusing protein complexes with specific symmetries (24,25), or DNA-mediated assembly of viruses (26,27). Here, we introduce a new method for effecting protein crystallization by trading protein-protein interactions for complementary oligonucleotide-oligonucleotide interactions.…”

Nanoscale device architectures derived from biological assemblies: The case of tobacco mosaic virus and (apo)ferritin

“…While it is difficult to realize this resolution by conventional top-down methods, biological self-assembly has helped to realize a preliminary binary NP structure. 181) However, self-assembly methods require improved tuning of the size and shape of the assembled structures so that they can be placed on electrical circuits. Therefore, new methods and possibly new strategies are needed.…”