Regulation of interparticle interactions enables the formation of functional nanoparticle assemblies

Abstract

Self-assembly is undoubtedly one of the most efficient ways to create complex materials with distinct functions. The ability to control the interparticle interactions between the building blocks is the key to achieving the desired outcomes from a self-assembly process. This requires the smart choice of building blocks that respond to stimuli in a precise fashion. Nanoparticles (NPs) are a unique class of building blocks, as they offer both their surface and core to install the desired interactions and functions. In the proposed thesis work, the surface of plasmonic NPs has been appropriately functionalized with the ligand of choice to regulate their interaction with biomolecules, leading to the formation of functional bio-nano hybrids. Further, the impact of such finely tuned interactions in NP self-assembly processes under equilibrium as well as non-equilibrium domains was studied. First, we have prepared a multifunctional bioplasmonic network via a long-range electrostatically directed self-assembly process between positively charged NPs and negatively charged ATP molecules in the presence of CaCl2. The screening of charges by Ca2+ ions and the coordination between ATP- Ca2+ helped in regulating the strength of electrostatic attraction between oppositely charged ATP molecules and AuNPs. This turned out to be decisive in transforming an uncontrolled aggregation (instant precipitation) into a kinetically controlled self-assembly process (bioplasmonic network). ATP and AuNP retained their inherent properties in the bioplasmonic network, thereby enabling their use for various catalytic, photocatalytic, and SERS-based applications. In another study, we observed that the dead ATP-AuNP precipitated state slowly transformed into the live bioplasmonic network. Detailed microscopic and spectroscopic studies revealed mechanistic insight into the role of the self-association property of ATP molecules in transforming the kinetically trapped precipitate into an active bioplasmonic network.