Self-Assembly of Uniform Branched Gold Nanoparticles Induced by Using Thiol-Terminated Poly(ethylene glycol)

Branched gold nanoparticles with a sufficiently monodisperse distribution of size and shape were successfully synthesised using a tree-type multi-amine-head surfactant (C18N3) with a 100 % yield using a seed-mediated method. C18N3 coated branched gold nanoparticles possess a positive zeta potential of ~40 eV, which can keep branched gold nanoparticles stable in aqueous solution for several months without precipitation and transfiguration. However, C18N3 molecules were partially replaced by thiol-terminated poly(ethylene glycol) (mPEG-SH), due to the branched morphology of the as prepared gold nanoparticles, to make branched gold nanoparticles passivated by the adsorbing polymer with a positive zeta potential (17 eV). The mPEG-SH passivated branched gold nanoparticles behaved as quasi-hard particles to overcome the restrictions of the rotational and positional degrees of freedom in neighbouring nanoparticles at high volume fractions, which favours the hydrophilic thiol-terminated poly(ethylene glycol) polymer passivated branched gold nanoparticles to self-arrange into close-packed 2D ensembles. Thus, the as prepared branched gold nanoparticles and their ensembles possess significant potential in bio-labelling, imaging, biosensing, therapeutic applications, and surface-enhanced Raman scattering.