Our interest is to use tailored responsive polymer brushes for direct and controlled immobilization of metal/semiconductor nanoparticles on macroscopic surfaces as a very interesting tool to produce functional thin films with e.g. sensing and catalytic properties (Fig. 1)..
The employed approach offers the possibility of the organization of a variety of inorganic nanoparticles by irreversible bonding and homogenous distribution on an underlying substrate. The immobilization process was realized by chemical grafting of a variety of polymer brushes on a suitable substrate followed by the attachment of pre-/in-situ formed nanoparticles exploiting chemical/physical interactions between surface functionalities of nanoparticles and polymer chain segments. A number of polymer brushes including poly (acrylic acid), polystyrene, poly (2-vinyl pyridine) and poly (N-isopropyl acrylamide) brushes have been used and prepared on silicon substrate by the "grafting to" approach. A variety of inorganic nanoparticles such as quantum dots (CdTe) or noble metals (gold,silver, platinum, palladium) were immobilized on macroscopic surfaces to impart them photo luminescent, plasmonic or catalytic properties. In addition, responsiveness of grafted polymer brushes in terms of variation in thickness (due to changes in chain conformation) as a function of external stimuli such as solvent and pH allowed to use the resulting polymer brush-particle nanoassemblies in the fabrication of nanosensors and nanocatalytic sytems. The design of fabricated nanosensors is based on the modulation in the interparticle distance of immobilized nanoparticles due to swelling/deswelling of underlined polymer brushes in response to external triggers as pH, solvent or temperature.
Nanoassemblies composed of Au and bimetallic core-shell Au@Ag nanorods immobilized onto pH-responsive poly(2-vinylpyridine) (P2VP) brushes showed a significant displacement of 32 nm in the longitudinal plasmon band between the swollen and the collapsed state of the pH-sensitive polymer brushes, proving the potential application of these nanostructures for the fabrication of pH nanosensors capable of detect changes in the pH of aqueous media. The surface enhanced Raman spectroscopy (SERS) activity of these nanoassemblies was demonstrated using a dye molecule, rhodamine 6G (R6G), as model analyte. The remarkable SERS intensity of silver compared to gold was confirmed.