Facile Preparation of Hierarchical Structures Using Crystallization-Kinetics Driven Self-Assembly

Hierarchical structures (HSs) constructed by nanoparticle-based building blocks possess not only the properties of the primary building blocks but also collective properties of the assemblies. Here we report the facile preparation of hierarchical Ag nanoparticles/polyhedral oligomeric silsequioxane molecule (POSS) hybrid branched structures within tens of seconds by using spin-coating and doctor-blade methods. An assembly mechanism mainly controlled by POSS-crystallization kinetics and space resistance of Ag nanoparticles toward the diffusion of POSS molecules was tentatively proposed. It was demonstrated as a universal method for the preparation of hierarchical hybrid branched structures on arbitrary substrates, as well as by using other different POSS and inorganic nanoparticles. As a demonstration, Ag hierarchical structures obtained by heat treatment exhibit excellent SERS performance with enhancement factors as high as on the order of 10⁷, making them promising sensors for the detection of trace amount of analyte adsorbed on the surface. Two-dimensional SERS mapping was also demonstrated by using a direct imaging system with high mapping speed and high resolution. Moreover, the substrates with Ag hierarchical structures were used as a SERS sensor for in situ detection due to the excellent SERS performance and stability of the structures.