Using light to covalently immobilize and pattern nanoparticles onto surfaces

There is considerable current interest in developing methods to integrate nanoparticles into optical, electronic, and biological systems due to their unique size-dependent properties and controllable shape. We report herein a versatile new approach for covalent immobilization of nanoparticles onto substrates modified with photoactive, phthalimide-functional, self-assembled monolayers. Upon illumination with UV radiation, the phthalimide group abstracts a hydrogen atom from a neighboring organic molecule, leading to radical-based photografting reactions. The approach is potentially "universal" since virtually any polymeric or organic-inorganic hybrid nanoparticle can be covalently immobilized in this fashion. Because grafting is confined to illuminated regions that undergo photoexcitation, masking provides a simple and direct method for nanoparticle patterning. To illustrate the technique, nanoparticles formed from diblock copolymers of poly(styrene-b-polyethylene oxide) and laden with Hostasol Red dye are photografted and patterned onto glass and silicon substrates modified with photoactive phthalimide-silane self-assembled monolayers. Atomic force microscopy and X-ray photoelectron spectroscopy are applied to characterize the grafted nanoparticle films while confocal fluorescence microscopy is used to image patterned nanoparticle deposition.