Noncovalent Bio-Functionalizations Of Graphene As New Self-Assembly Platforms For Hybrid Nanostructures

Owing to its unusual mechanical, electronic and quantum properties, graphene is receiving more and more attention in recent years in nanotechnology and materials science, and it is a rapidly rising star of carbon nanomaterial after the discoveries of C60 and carbon nanotubes. Graphene based nanohybrid materials are associated with a wide range of applications in various aspects. However, the applications of graphene have been greatly hindered by its poor solubilities, due to its strong tendency to form aggregates because of the strongπ-πstacking interactions between graphene nanosheets. Chemical decorations of graphene thus become important in order to improve its stability and introduce special surface functionalities. The content of this dissertation focuses on functionalizing graphene oxide (GO) and reduced graphene oxide (RGO) with important biomolecules and making further efforts to fabricate graphene based hybrid heteronanostructures by self-assembly, which are detailed as follows:Highly dispersed GO and RGO solutions were prepared by non-covalent decorating DNA on the basal planes of GO and RGO nanosheets. The resulting DNA-carbon bioconjugates (DNA-GO or DNA-RGO) were stable over a wide range of pHs at high salt concentrations, which are especially suitable as self-assembly building blocks in further studies. We developed three strategies toward non-covalent modifications DNA on RGO to achieve minimized DNA damages (DNA hydrazinolysis), which are critically important for DNA hybridization-based applications. DNA-GO and DNA-RGO were then employed to scaffold the two-dimensional assembly of gold nanoparticles (AuNPs) into metal-carbon hybrid nanostructures (namely AuNP-DNA-GO or AuNP-DNA-RGO) driven by gold-thiol bonding. The resulting heteronanostructures incorporating metal nanoparticles obtained by self-assembly were highly stable and water-soluble, and could be easily isolated by gel electrophoresis to guarantee high purity. We then relied on atomic force microscopy (AFM) to check the assembled structures. This convenient self-assembly based method for constructing heterostructured nanomaterials is excellent at overcoming any incompatibilities between nanoparticle syntheses and the formation of hybrid structures. The assembled nanohybrids may find important applications in areas including electronics, optics, catalysis and biodetections. The adsorption of proteins at solid surfaces is a common phenomenon, making it important to study the interactions between graphene and proteins. Proteins such as bovine serum albumin (BSA) are good reductants due to their 21 Tyr residues. This property allowed us to use BSA as both a reductant and a stabilizer to prepare BSA-conjugated graphene oxide (BSA-GO) and reduced graphene oxide (BSA-RGO). BSA-GO was obtained when BSA mainly served as a decorating agent at room temperature and a less basic pH. Differently, BSA-RGO was obtained through a protein-based and environment-friendly one-step reduction and decoration strategy at a basic pH and elevated temperature. We further demonstrated that the decoration of protein as a "universal glue" molecule on the basal surfaces of GO and RGO resulted in general platforms toward the assembly of Au, Ag, Pt and Pd nanoparticles and Latex nanosphere, independent of their varying sizes, shapes, compositions and surface properties. The as-formed hybrid nanostructures were checked by AFM, transmission electron microscopy (TEM) and scanning electron microscope (SEM), and the results demonstrated that it was a highly efficient and controllable method for the fabrications of graphene-based hybrid nanomaterials. Because of the inertness of the graphene surface, it is usually considered a challenge to prepare highly dispersed graphene-based nanohybrid structures co-decorated with different nanomaterials. Our success paves a way to systematically investigate the structure-function relationships of hybrid nanomaterials and to realize combinatorial assemblies of nanomaterials aiming at special applications.