(396f) pH-Induced Dispersion of Nanoparticle Clusters

Nanoparticle clusters, also referred to as agglomerates, colloidal clusters, or colloidal crystals, are a class of assemblies at the micrometer or sub-micrometer scale consisting of closely-packed nanoparticles. These materials have been explored for applications as photonic crystals as well as emerging applications in biological assays, sensors, paints, and ceramics. Surface modification of constituent nanoparticles has lead to the development of sensors that agglomerate into clusters in the presence of metals, protein ligands, or specific DNA sequences. Surprisingly, only a few studies have reported nanoparticle clusters that disperse in response to such cues and have been limited to particle interactions mediated by nucleic acid binding. Here, we expand the scope of nanoparticle cluster applications by demonstrating cluster dispersion into a stable colloidal suspension at a rate dependant upon pH as determined by the hydrolysis of cross-linked poly(N-vinylformamide) (PNVF) utilized as an inter-particle barrier. A PNVF shell was formed on silica nanoparticles by cross-linking PNVF using a novel cross-linker, 2-bis[2, 2'-di(N-vinylformamido)ethoxy] propane (BDEP), containing an acid-labile ketal. PNVF has been utilized in our work because it is water-soluble and non-toxic and has potential for biomedical applications. Liberated particles possessed colloidal stability attributable to steric hindrance as the inter-particle barrier hydrolyzed and liberated a polymer brush barrier on the nanoparticle surface. This study provides a framework for the combination of nanoparticle cluster technology with environmentally responsive materials such as ?smart? polymers for potential application as biosensors or even drug delivery systems.