Hybrid conjugated polymer-Ag@PNIPAM fluorescent nanoparticles with metal-enhanced fluorescence

Abstract

Hybrid nanoparticles with core–shell structures have shown brilliant potential application in many research fields. In this paper, a novel core–shell Ag@PNIPAM nanocomposite particle which combines the thermoresponsive property of poly(N-isopropylacrylamide) (PNIPAM) and the metal-enhanced fluorescence (MEF) effect of Ag colloids is demonstrated. The cationic conjugated polymer poly[9,9′-bis(6′′-(N,N,N-trimethylammonium)-hexyl)fluorene-2,7-ylenevinylene-co-alt-1,4-phenylene dibromide] (PFV) is then assembled onto the surface of these core–shell nanoparticles by the self-assembly technique. The fluorescence intensity of the prepared PFV/Ag@PNIPAM nanoparticles shows excellent thermostability in the temperature region from 20 °C to 50 °C, and the thermoquenching of PFV is greatly inhibited due to the MEF effects of Ag nanoparticles. Compared with the PFV solution without adding Ag@PNIPAM nanoparticles, a 1.6-fold and 3.1-fold enhancement can be observed when the temperature of the PFV/Ag@PNIPAM dispersion was 20 °C and 50 °C, respectively. In addition, the PFV/Ag@PNIPAM nanoparticles can exhibit excellent cytocompatibility, as well as strong and stable fluorescence when co-cultured with A549 lung cancer cells. These unique properties make these PFV/Ag@PNIPAM core–shell nanoparticles a desirable material especially in the field of efficient cellular imaging and biosensing.