Design of organic ligands for controlled assembly and triggered aggregation of gold nanoparticles for chemical detection

Abstract

The plasmonic properties of gold nanoparticles (AuNPs) hold great potential in various applications. Their plasmonic properties are closely related to their shapes and aggregation states. A way to obtain nanostructures with altered plasmonic properties is by assembling AuNPs into higher-ordered structures. In this thesis, firstly, we developed a method to prepare AuNPs asymmetrically modified by two ligands (Janus AuNPs). A small patch of AuNP surface was selectively modified with amino groups while the rest of surface was passivated by polyethylene glycol. Such asymmetrically modified AuNPs could be used to fabricate plasmonic nanoclusters with altered plasmonic properties. Secondly, we discovered a phenomenon that AuNPs could spontaneously aggregate to form spherical colloidal superparticles when thiol molecules with a middle tetraethylene glycol segment and a hydrocarbon terminal (HS-TEG-hydrocarbon) were used as ligands in the synthesis. We found that a byproduct generated from the chemical reaction also played a key role in the formation of AuNPs. Finally, we designed a novel ligand to modified AuNPs and made them responsive to hydrogen peroxide. The ligand contains a phenylboronate moiety that can react with hydrogen peroxide and subsequently cause fragmentation of the molecule, leading to aggregation of AuNPs accompanied with a color change from red to blue. This AuNPs-based platform can be used for colorimetric detection of hydrogen peroxide and disease biomarkers after coupling to ELISA technique.