Covalent immobilization of quantum dots on macroscopic surfaces using poly(acrylic acid) brushes

We report on a generic approach for immobilizing quantum dots (CdTe nanoparticles) on thin, fluid films consisting of poly(acrylic acid) (PAA) polymer chains tethered by one end to an underlying substrate in a polymer brush configuration. The protocol involves covalent bonding (amide linkage) between amino groups present on the surface of CdTe nanoparticles and carboxylic groups of PAA polymer chains. The thickness of the PAA polymer brush employed (similar to 4.5 nm) is comparable to the nanoparticle size. Exploitation of such a thin polymer brush was found to suppress nanoparticle aggregation and facilitates complete surface coverage. Atomic force microscopy (AFM) was used to study the film morphology. Covalent linkage between nanoparticles and polymer brushes was proven by X-ray photoelectron spectroscopy (XPS). The change in the optical properties of the quantum dots after immobilization was studied by photoluminescence spectroscopy and fluorescence microscopy. The results suggest a simple, effective and highly versatile method for modification of various surfaces with different nanoscopic particles.