Progress in Self-assembly of Polymer-coated Au Nanoparticles

Gold nanostructures with unique optical, electrical and catalytic properties have found widespread use in diverse fields ranging from optics and sensing to nanomedicine and catalysis. There is growing interest in self-assembly of gold nanostructures because their localized surface plasmon resonance undergoes strongly interparticle coupling in close proximity, leading to collective properties that are distinctively different from that of individual building blocks. Considerable progress has been made in tailored synthesis of gold nanostructures and surface-engineering approaches to introduce functional coatings on the nanostructures, giving rise to nanoscale building blocks with defined structural parameters and properties, which make them excellent model systems to study the self-assembly of nanoparticles driven by functiona coatings. Polymers, especially amphiphilic block copolymers, exhibit intrinsic self-assembly in solution and bulk phase. Accumulated evidence has demonstrated that both molecular structures of the polymers and self-assembly conditions have a key impact on the structures formed by self-assembly, producing a wide spectrum of structures such as spherical micelles, cylindrical micelles, lamellae, and vesicles. As such, polymer coatings, which are commonly explored to impart colloidal stability of nanostructures, have emerged as an intriguing class of functional coatings to direct their self-assembly. The ability to tailor the structural details of the polymer coatings such as molecular weight, graft density and amphiphilicity is key to achieve controlled morphology and functionality of the resultant plasmonic assemblies. In this review, we summarize current strategies for constructing well-defined Au nanoparticle building blocks including "one-pot synthesis", "grafting to", and "grafting from" strategies. Based on these methods, assemblies of polymer-decorated nanoparticles were designed and formed across multiple dimensions, which brings about potential applications resulting from emerging optical, electronic, and catalytic properties. A protypical example is surface-enhanced Raman scattering (SERS) which is greatly amplified in the interstitial space of the assemblies because of interparticle plasmonic coupling, providing a transduction mechanism for ultrasensitve detection. The ability of dissipating the energy of light irradiate through the combination of photothermal conversion and Mie-scattering makes it possible for the assemblies of Au nanoparticles to serve as imaging probes and therapeutic agents. Representative assemblies of Au nanoparticles, that have shown potentials for sensing and biomedicine, are highlighted in this review. We also emphasize the fundamental and technical challenges for precise control over polymer-guided self-assembly of gold nanoparticles. The combination of simulation and experiment open the avenue to a systematic understanding on the self- assembly of nanoparticles.