Polymer-coated gold nanoparticles (PNIPAM-AuNPs) with temperature sensitive and intelligent fluorescent properties were prepared by ligand exchange between dimethylaminochalcone-terminated poly(N-isopropylacrylamide) (PNIPAM-DMAC) and 4-dimethylaminopyridine-stabilized gold nanoparticles (DMAP-AuNPs) precursor

and the morphology and structure of the as-prepared AuNPs were analyzed by UV-Vis

TEM

1H-NMR

FTIR and TGA.The as-synthesized PNIPAM-AuNPs can be well dispersed not only in water but also in ethanol

acetone

chloroform and tetrahydrofuran

and the corresponding characteristic peak of the surface plasmon resonance (SPR) absorption of the PNIPAM-AuNPs is observed at 537 nm

527.6 nm

527.4 nm

532.2 nm and 530.4 nm respectively.The surface grafting density of PNIPAM-DMAC is 1-2 polymer chains/nm2.The results of thermosensitive properties show that PNIPAM-AuNPs have a lower critical solution temperature (LCST) 2.5 K lower than that of PNIPAM-DMAC

and the SPR absorption peak of PNIPAM-AuNPs blueshifts to 525 nm from 537 nm after the phase transition.With the increase of the solvent polarity

the fluorescence characteristic wavelength of PNIPAM-AuNPs redshifts

and the fluorescence intensity first increases then decreases

which indicates solvent polarity sensitive fluorescence properties of PNIPAM-AuNPs.There are no fluorescent emitting properties of PNIPAM-AuNPs aqueous solution at 25 ℃

while at 45 ℃ the fluorescence intensity of PNIPAM-AuNPs enhances obviously

which endows PNIPAM-AuNPs with temperature on/off fluorescent properties.