Nanostructured materials made of metals and metal oxides possess unique photo-physical properties that can be tuned via size, shape and composition. For example, semiconductor nanocrystals (or quantum dots) exhibit tunable emission combined with large extinction coefficients, high quantum yield and great photo-chemical stability. Similarly, gold nanorods exhibit longitudinal surface plasmon resonance bands that depend on both rod length and aspect ratios. These materials have generated a great deal of interest for use in a variety of applications. Some of those applications center on their integration within biological systems as carrier probes, drug delivery vehicles and sensing platforms. Such uses require the ability to embed these materials in various platforms, with control over their surface properties and their interactions with the surrounding environment. This provides hybrid platforms that can advance our understanding of various biologically challenging problems. It, however, requires access to hydrophilic nanoparticles that are both colloidally stable and surface reactive. 

We have developed a set of multifunctional and multi-coordinating polymer ligands that are ideally adapted for surface functionalizing QDs, as well as gold nanospheres, nanorods and nanoshells. The ligand design relies on the introduction of several anchoring groups with tunable metal-coordination, hydrophilic moieties (either polyethylene glycol or zwitterion moieties) to enhance affinity to buffer media and reactive functionalities into a single polymer chain, all via one-step nucleophilic addition reaction. Additionally, this synthetic route allows the insertion of target biomolecules in-situ during ligand synthesis. We have found that surface functionalization with these polymers yields nanomaterials that exhibit long-term colloidal stability over a broad range of biological conditions. We have further probed the interactions of these nanostructures with various systems including fluorescent proteins, redox complexes and cell membranes. Such interactions are affected by spatial arrangements, separation distance from the nanostructure surface and by the nature of the targeting molecules used. We will discuss the ligand design and interactions of the nanomaterials with proteins and redox complexes. We will also discuss the use of these nanocrystal-protein assemblies as sensing platforms.