Controlled dispersion of silver nanoparticles into the bulk of thermosensitive polymer microspheres: Tunable plasmonic coupling by temperature detected by surface enhanced raman scattering

By in situ reduction of Ag ⁺ ions pre-dispersed inside thermosensitive microspheres of poly[(N-isopropylacrylamide)-co-(methacrylic acid)] (P(NIPAM-co-MAA)), a 3D copolymer-supported network of silver nanoparticles is created and extensively characterized by surface-enhanced Raman scattering (SERS). The effective dispersion and the suitable density of the silver nanoparticles in the composite microspheres are demonstrated by the thermal-induced SERS signal and its high reproducibility during thermocycling. When the temperature of the system increases above 32 °C, spatial separation of the silver nanoparticles decreases and the numbers of Ag nanoparticles and P(NIPAM-co-MAA) microspheres under illumination spot increase as a result of the shrinkage of the P(NIPAM-co-MAA) chains, leading to the ramp of the SERS effect. By means of the high reversibility of the thermosensitive phase transition of the P(NIPAM-co-MAA) microspheres, SERS activity of the silver nanoparticle network embedded in the microsphere can be well controlled by thermal-induced variation of special separation. A 3D polymer-supported network ((P(NIPAM-co-MAA)) of silver nanoparticles is synthesized and SERS activity of the silver nanoparticle network embedded in the microsphere can be well controlled by thermal-induced variation of special separation. When the temperature is above 32°C, the spatial separation of the silver nanoparticles decreases and an increase in the numbers of Ag nanoparticles is measured as a result of the shrinkage of the P(NIPAM-co-MAA) chains.