Crystallization kinetics-induced self-assembly of inorganic element blocks and the surface-enhanced Raman scattering based on Ag hierarchical structures

In this chapter, on basis of the concept of element blocks which can be extended to inorganic element blocks consisting of inorganic nano-cores such as inorganic nanoclusters, nanoparticles, and nanocrystals. The self-assembly behaviors and strategies of inorganic element blocks, as well as novel properties of assembly structures applied in high-performance surface-enhanced Raman scattering (SERS) were first briefly introduced. Crystallization behaviors of symmetric and asymmetric polyhedral oligomeric silsesquioxane (POSS) molecules were applied to the formation of unique fractal hierarchical structures of POSS/Ag hybrid films by using a facile spin-coating method, where POSS molecules and Ag nanoparticles have comparable sizes. A mechanism of crystallization kinetics-induced self-assembly of inorganic element blocks was proposed and demonstrated to be a novel universal method for various kinds of POSS molecules, other inorganic nanoparticles, and arbitrary substrates to form a fractal hierarchical structure. Ag fractal hierarchical structures obtained by heat treatment of a POSS/Ag hybrid film showed excellent SERS activity and performed as an effective in situ SERS-active media due to their stable adhesion to the substrate. In addition, an ultra-stable in situ SERS sensor based on Ag hybrid nanoassembly and an in situ SERS detection using a smartphone were also demonstrated. It is expected that the mechanism of crystallization kinetics-induced self-assembly could be extended to other material systems, such as small organic molecules, polymers, salts, atomic clusters, biomolecules, as well as relatively large colloidal particles.