Metal nanoparticles are of fundamental interest to many researchers because of their controllable grain diameter and their potential applications in emerging areas of nanotechnology due to their unique electronic and optical properties. Their distinguishing shapes and combinations, such as nanobarcodes, nanorods, and nanowires produce unique functions along with the rare functions of bulk metals. A building up of structures in a particle-by-particle fashion simultaneously organizes many particles into self-assembled materials with the requirement of easily controlling the chemical reactivity and interparticle connectivity on a single-particle level.
Creating a functionality on the surface of nanoparticles is desirable for the purpose of particle handling and the construction of functional architectures, however, it is intractable and unavailable due to the necessity of multistep-processing. Gold nanoparticles prepared by ligand exchanges, such as cationic thiols, can usually be formed by the following closely controlled two-step protocols: Gold nanoparticles (AuNPs) are synthesized at the aqueous/organic solution interface, and then covered with a thiol molecule in organic media (1st step). The passivation layer is exchanged or modified in a functional compound solution for time periods of over 10 hours (2nd step). The layer thus treated, however, has only provided a low-density coverage of functional molecules on the surface of the nanoparticles, so that the nanoparticle must be modified with alkylthiols before the first step.
To construct nano-superstructures, it is necessary to develop nanoparticles as a functional accessory, having not only the desired size, but also a specific reaction and interaction sites with a template molecule. We now present a simple preparation method of positively charged-AuNPs with a one step-processing without an extra controlled procedure, organic solvents, and ligand exchange. Moreover, AuNP has an interesting raspberry like-configuration as a buliding-block of the nanoarchitecture. A novel positively-charged AuNP was prepared using a reducer such as aniline. |