Composite silica nanospheres covalently anchored with gold nanoparticles at the outer periphery of thermoresponsive polymer brushes

We report on the fabrication of water-dispersible composite silica nanospheres covalently anchored with gold nanoparticles (AuNPs) possessing thermo-tunable spatial distributions at the outer periphery of thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) brushes. Starting from initiator-functionalized silica nanoparticles, surface-initiated atom transfer radical polymerization (ATRP) of N-isopropylacrylamide (NIPAM) afforded hybrid silica nanoparticles coated with PNIPAM brushes. The substitution reaction of halogen terminal groups of grafted PNIPAM chains with sodium azide and subsequent click reaction with 1,2-dithiolane-3-pentanoic acid-N-propargylamide afforded hybrid silica nanoparticles coated with 1,2-dithiolane end-capped PNIPAM brushes. AuNPs were then covalently anchored to the outer periphery of hybrid silica nanoparticles by utilizing strong chemisorption of surface-attached dithiolane moieties to AuNPs. Dynamic laser light scattering (LLS) measurements revealed that thermosensitive PNIPAM brushes at the surface of hybrid silica nanoparticles exhibit reversible thermo-induced collapse/swelling transitions, leading to the facile thermo-modulation of spatial distributions of AuNPs covalently attached at the periphery of composite silica nanospheres and thermo-reversible surface plasmon absorption band shift. The reported strategy of covalent assembly of AuNPs into well-defined composite nanospheres possessing thermo-tunable characteristics might be further exploited for colorimetric temperature sensing and responsive SERS detection purposes.