(256j) Self-Assembly of Semiconductor and Protein into Monodisperse Supraparticles

Authors: 
Nguyen, T. D., University of Michigan
Bahng, J. H., University of Michigan
Glotzer, S. C., University of Michigan
Kotov, N. A., University of Michigan
Terminal assemblies enable a simple means for fabricating complex bio-nano systems from a variety of components. They can also be called bionic assemblies because they combine the properties of inorganic and biological components. Self-assembly process that involves inorganic nanoparticles (NPs) and biological materials results in highly ordered terminal structures, which are potential analytical and drug delivery tools. The scientific value these systems are the possibility to integrate biological functions of proteins with properties of inorganic NPs in a way that leverages the attributes of both components. Such systems are fundamentally and technologically attractive due to their uniformity, versatility and simplicity of preparation. In this work we prepared various types of supraparticles (SPs), we combine ~5 nm protease protein with different NPs: ~3.4 nm FeS2NPs, ~15 nm ZnO nanopyramid NPs, ~18 nm ZnO nanoplate NPs and ~5 nm ZnO nanosphere. We observed spontaneous formation of spherical supraparticles with a narrow size distribution containing both components. Assembly was originated from the competition between electrostatic repulsion and non-covalent attractive interactions. Non-covalent interactions between protease and like-charged NPs lead to drastically different self-assembly behavior previously unseen for each component individually, and which mimics the cooperative assemblies of proteins. We also demonstrate remarkable that the catalytic curve profile has changed, but the catalytic activity is retained in a determinate temperature and pH.

The FeS2/protein and ZnO/protein SPs were examinated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). These results reveal the formation of uniformly sized, spherical SPs with a TEM diameter about 150 ± 13nm which matches the diameter determined from Dynamic light scattering (DLS). Image of individual NP inside a SP can be distinguished by its crystal lattice. Besides the SPs were investigated by tomography 3D and the overall attractive potential between the similarly charged FeS2 or ZnO NPs and Protease is investigated by theoretical calculations. Further were examined the effect of ionic strength and temperature of assembly on the diameter of the SPs. Various spectroscopy data were performed which shows the positions of all peaks in the UV-Visible / Circular Dichroism spectra remain unchanged, indicating that the electronic state and conformation of the protease molecules in the SPs are preserved.