Preparation of Au/Ag Multilayers via Layer-by-Layer Self-assembly in Spherical Polyelectrolyte Brushes and Their Catalytic Activity

Spherical polyelectrolyte brushes （SPBs） consisting of polystyrene （PS） core and poly（2-aminoethyl methacrylate hydrochloride） （PAEMH） shell were prepared by photo-emulsion polymerization. Au nanoparticles （Au-NPs） with controlled size and size distribution were synthesized in situ using SPBs as nanoreactors. Via layer-by-layer deposition technique on the surface of SPBs, nano-composite particles with Au/Ag-NPs bilayer and Au/Ag/Au-NPs trilayer were prepared. The structures of the as-prepared Au/Ag multilayer SPBs were characterized by UV-Vis spectroscopy, TEM, ICP-AES and DLS. The charge reversal of the nano-composite particles observed by zeta potential confirmed the success of layer-by-layer assembly. The Au/Ag-NPs bilayer nano-composite particles showed high catalytic efficiency with an apparent activation energy of about 41.2 kJ/mol in the reduction reaction of 4-nitrophenol to 4-aminophenol in the existence of sodium borohydride monitored. The catalytic activity ofAu/Ag-NPs multilayer SPBs close to that of Au-NPs SPBs and much higher than that of Ag-NPs SPBs reveals its potential applications in cost-effective catalysts with high-performance.

Analysis of Spherical Polyelectrolyte Brushes by Small Angle X-ray Scattering

Spherical polyelectrolyte brushes （SPBs） with PS core and poly（acrylic acid） （PAA） brushes were prepared and analyzed by SAXS in this article. A radial electron density profile of SPB was brought up, which fits well with the SAXS result and shows a core-shell structure. The effect of pH on SPB form was represented by SAXS and it proves that the chains of SPB will stretch in response to increased pH owning to the increased electrostatic repulsion. SPBs immobilized with magnetic nanoparticles or bovine serum albumin （BSA） were prepared and analyzed by SAXS as well. SAXS could characterize the changes of electron density inside brushes of SPBs due to the immobilization of magnetic nanoparticles or BSA. This provides significant supports for further application of immobilized metal nanoparticles or proteins.

Heavy Metal Ions Removal by Nano-sized Spherical Polymer Brushes

Nano-sized spherical polymer brushes （SPBs） consisting of both a polystyrene （PS） core and a brush shell of poly（acrylic acid） （PAA）, poly（N-acrylcysteamine） （PSH）, or poly（N-acrylcysteamine-co-acrylic acid） （P（SH-co-AA））, were prepared by photo-emulsion polymerization. The core-shell structure was observed by dynamic light scattering and transmission electron microscopy. Due to the strengthened Donnan effect, the PAA brush can adsorb heavy metal ions. Effects of the contact time, thickness of PAA brush and pH value on the adsorption results were investigated. Due to the coordination between the mercapto groups and heavy metal ions as well as the electrostatic interactions, SPBs with mercapto groups are capable to remove heavy metal ions selectively from aqueous solutions. The order of adsorption capacity of the heavy metal ions by SPBs with mercapto groups is： Hg2＋ ≈ Au3＋ 〉 Pb2＋ 〉 CH2＋ 〉 Ni2＋. The adsorbed heavy metal ions can be eluted from SPB by aqueous HCI solution, and the SPBs can be recovered. After three regenerations the recovered SPBs still maintain their adsorption capacity.

Synthesis of Self-assemble pH-responsive Cyclodextrin Block Copolymer for Sustained Anticancer Drug Delivery

Well-defined pH-responsive poly（e-caprolactone）-graft-β-cyclodextrin-graft-poly（2-（dimethylamino）ethyl- methacrylate）-co-poly（ethylene glycol） methacrylate amphiphilic copolymers （PCL-g-β-CD-g-P（DMAEMA-co-PEGMA）） were synthesized using a combination of atom transfer radical polymerization （ATRP）, ring opening polymerization （ROP） and ＂click＂ chemistry. Successful synthesis of polymers was confirmed by Fourier transform infrared spectroscopy （FTIR）, proton nuclear magnetic resonance （^1H-NMR）, and gel permeation chromatography （GPC）. Then, the polymers could self- assemble into micelles in aqueous solution, which was demonstrated by dynamic light scattering （DLS） and transmission electron microscopy （TEM）. The pH-responsive self-assembly behavior of these copolymers in water was investigated at different pH values of 7.4 and 5.0 for controlled doxorubicin （DOX） release, and these results revealed that the release rate of DOX could be effectively controlled by altering the pH, and the release of drug loading efficiency （DLE） was up to 88% （W/W）. CCK-8 assays showed that the copolymers had low toxicity and possessed good biodegradability and biocompatibility, whereas the DOX-loaded micelles remained with high cytotoxicity for HeLa cells. Moreover, confocal laser scanning microscopy （CLSM） images revealed that polymeric micelles could actively target the tumor site and the efficient intracellular DOX release from polymeric micelles toward the tumor cells further confirmed the anti-tumor effect. The DOX-loaded micelles could easily enter the cells and produce the desired pharmacological action and minimize the side effect of free DOX. These results successfully indicated that pH-responsive polymeric micelles could be potential hydrophobic drug delivery carriers for cancer targeting therapy with sustained release.