Salt Effect on the Heat-Induced Association Behavior of Gold Nanoparticles Coated with Poly(N-isopropylacrylamide) Prepared via Reversible Addition−Fragmentation Chain Transfer (RAFT) Radical Polymerization

Abstract

Poly(N-isopropylacrylamide) (PNIPAM) with a narrow molecular weight distribution was prepared by reversible addition-fragmentation chain transfer (RAFT) radical polymerization. A dithioester group at the chain end of PNIPAM thus prepared was cleaved by treating with 2-ethanolamine to provide thiol-terminated PNIPAM with which gold nanoparticles were coated via reactions of the terminal thiol with gold. The thermoresponsive nature of the maximum wavelength of the surface plasmon band and hydrodynamic radius (Rh) for the PNIPAM-coated gold nanoparticles were found to be sensitively affected by added salt. In pure water, Rh for the PNIPAM-coated gold nanoparticles at 40 degrees C (>lower critical solution temperature (LCST)) was smaller than that at 25 degrees C (<LCST) due to the shrinkage of the PNIPAM chains on the gold surface. The maximum wavelength of the plasmon band in pure water was almost independent of the temperature, the color of the solution remaining pink regardless of temperature. On the other hand, in the presence of 50 mM NaCl, the plasmon band at 40 degrees C was red shifted compared with that at 25 degrees C because of interparticle associations, the pink color at 25 degrees C changing to blue-purple at 40 degrees C. Furthermore, Rh for the PNIPAM-coated gold nanoparticles at 40 degrees C was significantly larger than that at 25 degrees C. Heat-induced association and dissociation for the PNIPAM-coated gold nanoparticles were completely reversible in 50 mM NaCl aqueous solutions, which is responsible for the reversible thermoresponsive color change.

Colorimetric detection of lead (II) based on silver nanoparticles capped with iminodiacetic acid

“…1b, it is clear that the absorption spectrum of IDA-Ag NPs underwent a little red-shift compared with that of bare Ag NPs, which also demonstrates that IDA modified onto the surface of Ag NPs. Similar spectral changes were found in Ag NPs modified with bipyridine [27][28][29]. It has been proved that the adsorption of organic compounds on the metal nanoparticles resulted in a red shift in the SPR band, mainly caused by the lessening of the plasma oscillation frequency or a change in the dielectric constant of the microenviroment around the nanoparticles.…”

Living Radical Polymerization by the RAFT Process - A Second Update

“…AA [251] BA [251,252] BA [253] MA [54,252] St [254,255] HPA [251] St [256] SMe [251] BP/NPMI [257] S S 93 [216] BA [216] (BA) [216] S S 94* [255] AEP [87] BA [62,216] (BA) [216] TFPA [93] MMBL [258] AcS [259] St [260] St [261] PFS [93] NIPAM [262,263] St/MMBL [258] MMA/BA [62] BP/NPMI [257] BP/NMMI [257] BP/NEMI [257] TFPA-b-tBA [93] PFS-b-tBA [93] …”

Preparation of thermo and pH-responsive polymer@Au/Fe3O4 core/shell nanoparticles as a carrier for delivery of anticancer agent

“…First, we studied the temperatureand pH-responsive behaviors of the polymer@Au-Fe 3 O 4 NPs in the distilled water. However, we knew that heating the polymer-coated Au/Fe 3 O 4 NPs solution (250 mg L -1 ) above the LCST of the copolymer did not result in any change in color or opaque of the polymer@Au/Fe 3 O 4 (Yusa et al 2007;Zhang et al 2013). When the smart polymer-coated Au/Fe 3 O 4 NPs were dispersed in PBS with ionic strength of 10 mM, rather than deionized water, the NPs did display temperature-responsive behavior.…”

“…MC Cormick et al reported that watersoluble polymers prepared by RAFT radical polymerization can stabilize gold NPs by reduction of dithioester end groups to thiol groups in the presence of HAuCl 4 (Lowe et al 2002). Recently, the temperature behaviors of bulk and surface-grafted PNIPAAms were probed, and it was found that surface-bound polymer exhibited more gradual responses over a wide range of temperature (Yusa et al 2007;Shi et al 2014). For example, Hamner et al reported that DNAmediated assembly and encoded nanocarrier drug release could be regulated by thermoresponsive PNIPAAm-b-PMAA-protected AuNP .…”