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Investigation of Tethered Thermoresponsive N-Isopropylacrylamide Hydrogel Thin Films Via the Incorporation of Cadmium Selenide/Zinc Selenide Nanoparticles

Beinn V. O. Muir1, Yun Zong2, Cathrin Corten3, Dirk Kuckling3, Wolfgang Knoll4, and Curtis W. Frank1. (1) Department of Chemical Engineering, Stanford University, 381 North South Mall, Stanford, CA 94305-5025, (2) Institute of Materials Research and Engineering, 3 Research Link, Singapore, 117602, Singapore, (3) Fachrichtung für Chemie und Lebensmittelchemie, Dresden, D-01062, Germany, (4) Materials Science, Max Planck Institute for Polymer Research, Ackermannweg 10, Mainz, 55128, Germany

Semiconductor quantum dots (QDs) are highly luminescent nanocrystals that exhibit narrow emission wavelengths tunable by changing the nanoparticle diameter and elemental components. Incorporation of QDs into a cross-linked hydrophilic polymer matrix forms an optically active scaffold. The QDs can be incorporated into the polymer matrix through hydrogen bonding, covalent attachment to the preformed polymer matrix, and/or in-situ gelation using the QDs as a cross-linking agent. The polymer matrix can be selected such that it undergoes rapid volume changes to external stimuli gradients such as temperature or pH, due to a balance between polymer elastic energy and osmotic pressure. For surface-confined thin films, volume changes are known to occur in the millisecond regime, a timescale ideal for actuator and sensor applications. The importance of these hydrogel-nanoparticle hybrid materials is twofold, (i) utilization of the QD emission in biosensing configurations, and (ii) characterization of the polymer matrix and cross-link junction dynamics through the use of optical techniques such as surface plasmon resonance (SPR) and fluorescence correlation spectroscopy (FCS). Here we report the incorporation of CdSe/ZnSe semiconductor QDs into temperature sensitive N-isopropylacrylamide copolymer thin films, and the analysis of the materials optical properties as a function of polymer conformation for thin tethered films.