Fully Reversible Quantitative Phase Transfer of Gold Nanoparticles Using Bifunctional PNIPAM Ligands

Abstract

Ligand exchange with end-functionalized polymers is often applied to render nanoparticles with enhanced colloidal stability, to change the solubility in various environments, and/or to introduce new functionalities. Here we show that exchange of citrate molecules with α-trithiocarbonate-ω-carboxyl-terminated poly(N-isopropylacrylamide) can successfully stabilize spherical gold particles of different diameters ranging from 15 to 53 nm. This is verified by transmission electron microscopy, dynamic light scattering, and extinction spectroscopy. We show that the polymer-decorated nanoparticles respond to temperature and pH allowing access to control interparticle interactions. In a range of pH slightly below the pK of the terminal carboxyl groups, phase transfer of the particles from water to chloroform can be mediated by increasing the dispersion temperature above the lower critical solution temperature of poly(N-isopropylacrylamide). Upon cooling, fully reversible phase transfer to the water phase is observed. Extinction spectroscopy reveals phase transfer efficiencies close to 100% for every system under investigation.

Translational and rotational diffusion coefficients of gold nanorods functionalized with a high molecular weight, thermoresponsive ligand: a depolarized dynamic light scattering study

“…The initial CTAB stabilizer on the surface of the as-prepared AuNR was exchanged by PNIPAM to render the particles with a thermoresponsive polymer shell. 13 For this purpose, 0.46 g of PNIPAM were mixed with 45.9 mL Milli-Q water. 18 mL of the PNIPAM solution was added to AuNR-PNIPAM-1 and 20 mL to AuNR-PNIPAM-2.…”

“…By ligand exchange it is also possible to provide nanoparticles with additional properties, for example if stimuli-responsive polymers are used as ligands. 13 These hybrid particles can yield new multifunctional materials that can exploit synergistic effects and/or feature new properties that neither of the individual components possess on their own. Along these lines gold nanoparticles have been combined with thermoresponsive polymers to allow for photothermal manipulation of the polymer via laser excitation of the plasmonic particles.…”

Polymer ligand binding to surface-immobilized gold nanoparticles: a fluorescence-based study on the adsorption kinetics

“…The concentration of the particle dispersion was estimated from the extinction at a wavelength of 400 nm in the UV/vis spectrum. 41 Synthesis of a,x-functionalized polystyrene ligands. PS ligands were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization in bulk (Scheme 1).…”

Polymer@gold Nanoparticles Prepared via RAFT Polymerization for Opto-Biodetection

“…Also using polymers based on NiPAM, the pH and temperature responsiveness were explored for PNiPAM/Au nanocomposites at pH below the p K a . In these conditions, by increasing the temperature above the LCST, the nanocomposites migrate to an organic phase (chloroform), due to the increase of hydrophobic interactions, and this behavior was shown to be reversible [153].…”

“…On the other hand, by using thermal sensitive polymers, the drug release can be promoted by local heating [154,155]. For example, Becer et al [153] polymerized methacrylic acid (MAA) via RAFT polymerization and after reducing the RAFT end group, the thiolated PMAA was grafted to the Au NPs surfaces ( d ~ 50 nm). Subsequently, doxorubicin (DOX), which was employed as a model anticancer drug, was linked using cysteine (Cys) and a crosslinker.…”