Colloidal metal or semiconductor nanospheres can be used to prepare nanocrystals, nanowires, and photonic crystals by assembling them into an ordered structure. In particular, nanosphere assemblies with proper surface modifications create good labels for biosensors because they can be detected by various analytical techniques, including optical response, fluorescence, Raman scattering, atomic and magnetic force, and electrical conductivity. However, only a limited number of studies have been reported for the fabrication of the nanosphere assembly in such a way that the ordered arrangement of the nanospheres endows the assembly with specific electrical, optical or other physicochemical properties. Some methods have been developed to prepare the self-assembled structure of building blocks such as colloidal crystallization in aqueous droplet or the use of surfactant as covalent linker to induce the ordered structure formation. However, these approaches have fatal drawback in controlling precisely the ordered arrangement of the building block particles. Consequently, more efficient and readily available technique, "DNA-assisted fabrication of nanoparticle assembly" is needed for the preparation of the functional assembly with controlled morphology.
DNA is the basic building block of life and composed of four bases; namely, adenine (A), guanine (G), thymine (T), and cytosine (C), on a backbone of alternating sugar molecules and phosphate ions. The double-stranded helical structure of the DNA is formed by the interaction of complementary sequences and the selective hydrogen bonding between the bases. The highly specific A-T and G-C hydrogen bonding endows DNA with the molecular recognition mechanism that could be used to organize complex and ordered structures. DNA-mediated assembly has potential applications in various areas including nanocrystalline quantum dots for nanobarcodes and display devices, photonic crystals for photonic bandgap materials, biosensors, and others.
In our group, we are developing various surface modification techniques for the adsorption of oligonucleotides on the surface of nanosphere building blocks. To bind DNA on building blocks covalently, several synthetic routes for monodisperse nanospheres with special surface functional groups are tried through emulsion polymerization or sol-gel method. The adsorption characteristics of the biomolecules are studied with the aids of various spectroscopic methods.