Transformation of thiolated chitosan-templated gold nanoparticles to huge microcubes

• Mercapto groups were grafted to chitosan molecule by a reactive amine reduction.
• Functional polymer with well-defined monomer units controls AuNPs assembly.
• Assembled morphologies depend on the ratio of AuNPs to thiolate groups.
• Microcubes with side length of ∼20 μm was synthesized through a dialysis step.
• A edge-to-middle growth mechanism of gold microcubes was observed.

The l-cysteine molecules were successfully grafted to the 2-amino group of chitosan by a reactive amine reduction, and the as-synthesized thiolated chitosan (TC) molecules were used as the templates to direct the self-assembly of gold nanoparticles and induce the transformation of these assemblies to gold microcubes through a deep-going dialysis. We found that the ratio of gold nanoparticles to TC molecules could greatly affect the shape of the assembled clusters. Different stages of these clusters and microstructures during the dialysis process were characterized by scanning electron microscope (SEM), and the microcubes with average side length of about 20 μm were successfully synthesized. According to the morphology evolution of the assembly, it could be concluded that the microcubes were formed from external to internal. The SERS area mapping images of microcubes and some clusters were also collected to study the formation mechanism of gold microcubes. Our work demonstrates a simple and highly effective way to assemble gold nanoparticles into microcubes with unique properties.

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