pubs.acs.org/cm Published on Web 12/18/2009 r 2009 American Chemical Society 504 Chem. Mater. 2010, 22, 504–509 DOI:10.1021/cm9031336 Poly(N-isopropyl acrylamide)-Gold Nanoassemblies on Macroscopic Surfaces: Fabrication, Characterization, and Application Smrati Gupta,* ,† Mukesh Agrawal, Petra Uhlmann, Frank Simon, and Manfred Stamm* Leibniz-Institut f € ur Polymerforschung Dresden e.V., Hohe Strasse 6, 01069 Dresden, Germany. † Current address: Technische Universit € at Dresden, Makromolekulare Chemie, Zellescher Weg 19, 01069 Dresden, Germany. Received October 10, 2009. Revised Manuscript Received November 24, 2009 In this study, we report on the fabrication of the nanoassemblies consisting of the poly(N-isopropyl acrylamide) (PNIPAAm) brushes immobilized with gold nanoparticles (Au NPs). The employed process involves grafting of the carboxyl terminated PNIPAAm chains on an underlying substrate in a brush conformation followed by the immobilization of surface functionalized Au NPs by means of physical interaction (hydrogen bonding). Atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and UV-vis spectroscopy have been employed to characterize the prepared PNIPAAm-Au nanoassemblies. Polymer brushes have been found to suppress the nanoparticles’ aggregation and, hence, facilitate the complete surface coverage. Furthermore, we demonstrated the application of resulting PNIPAAm-Au nanoassemblies in the fabrication of the temperature nanosensors. The employed approach is simple and highly versatile for the modification of macroscopic surfaces with a wide range of NPs. Introduction Metal nanoparticles (NPs) represent a special class of the materials, which has recently attracted much atten- tion of the researchers because of their fascinating proper- ties and potential applications in a wide range of areas including in the fabrication of nanosensors, catalysts, electronics, and optical and magnetic devices. 1,2 Earlier studies reveal that the most prominent challenge in deal- ing with nanoscale particles is to prevent their aggrega- tion in the media. 2 Due to the high surface energy, they tend to aggregate, and aggregation limits their use in above-mentioned applications. A great deal of efforts has been devoted to the stabilization of NPs by exploi- ting a wide range of stabilizers such as self-assembled monolayers, 3 polymer brushes, 4 dendrimers, 5 latex particles, 6 microgels, 7 and so on. 8 Among these systems, polymer brushes have been found to offer an easy and effective way for the stabilization of NPs on macroscopic surfaces. Polymer brushes are the assemblies of macro- molecules that are tethered by one end to the underlined substrate in such a way that the distance between two grafted chains is lower than that of the radius of the gyration of a polymer chain. 9 Recently, a lot of research has been done on the stabilization of NPs by exploiting the planar and spherical polyelectrolyte brushes. 10 Earlier studies demonstrate that polymer brushes serve as a perfect template for the preparation, stabilization, and application of NPs on the account of their nanometer dimensions, well-defined structure, and ability to control assembly of NPs over multiple length scales, superior precision over template architecture, and the availability of a greater variety of functional groups. 11 Recently, a great deal of the research efforts have been devoted to the gold (Au) NPs owing to their unique optical properties. 12 In addition, many attempts have *To whom correspondence should be addressed. E-mail: smrati.gupta@ chemie.tu-dresden.de (S.G.); stamm@ipfdd.de (M.S.). (1) For recent reviews on nanoparticles, see: (a) Kotov, N. A. Layer- by-layer Assembly of Nanoparticles and Nanocolloids: Inter- molecular Interactions, Structure, and Material Perspectives. In Multilayer Thin Films; Decher, G., Schlenoff, J. B., Eds.; Wiley-VCH: Weinheim, 2003, pp 207-269. (b) Burda, C.; Chen, X.; Narayanan, R.; El-Sayed, M. A. Chem. Rev. 2005, 105(4), 1025. (2) Yonezawa, T.; Toshima, N. Polymer-stabilized Metal Nanoparti- cles. In Advanced Functional Molecules and Polymers; Nalwa, H. S., Ed.; Gordon and Breach: London, U.K., 2001, pp 65-86. (3) Ulman, A. Chem. Rev. 1996, 96, 1533. (4) (a) Gupta, S.; Agrawal, M.; Uhlmann, P.; Simon, F.; Oertel, U.; Stamm, M. Macromolecules 2008, 41, 8152. (b) Gupta, S.; Uhlmann, P.; Agrawal, M.; Lesnyak, V.; Gaponik, N.; Simon, F.; Stamm, M.; Eychm€ uller, A. J. Mater. Chem. 2008, 18, 214. (5) Scott, R. W. J.; Wilson, O. M.; Crooks, R. M. J. Phys. Chem. 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