Core -Shell Nanostructured Nanoparticle Films as Chemically Sensitive Interfaces Li Han, David R. Daniel, Mathew M. Maye, and Chuan-Jian Zhong* Department of Chemistry, State University of New York at Binghamton, Binghamton, New York 13902 This paper reports the results of an investigation of vapor molecule sorption at different types of nanostructured nanoparticle films. Core-shell nanoparticles of two dif- ferent core sizes, Au 2 -nm and Au 5 -nm , and molecular linkers of two different binding properties, 1 ,9 -nonanedi- thiol and 1 1 -mercaptoundecanoic acid, are utilized as building blocks for constructing chemically sensitive interfaces. The work couples measurements of two dif- ferent transducers, interdigitated microelectrodes and quartz crystal microbalance, to determine the correlation of the electronic resistance change and the mass loading with vapor sorption. The responses to vapor sorption at these nanostructured interfaces are demonstrated to be dependent on the core size of nanoparticles and the chemical nature of linking molecules. The difference of molecular interactions of vapor molecules at the nano- structured interface is shown to have a significant impact on the response profile and sensitivity. For the tested vapor molecules, while there are small differences for the sorption of nonpolar and hydrophobic vapor molecules, there are striking differences for the sorption of polar and hydrophilic vapor molecules at these nanostructured interfacial materials. The implication of the findings to the delineation of design parameters for constructing core- shell nanoparticle assemblies as chemically sensitive interfacial materials is also discussed. The study of nanostructured functional materials has attracted tremendous interest because of their potential utilities in micro- electronics, catalysis, molecular recognition, and chemical and biological sensors. 1-5 Recent advances involve organic monolayer- encapsulated inorganic nanoscrystal cores, 1-2,6-9 i.e., “core-shell” nanoparticles. The nanoscale functional properties of this type of nanoparticle are closely related to size, shape, and surface properties. A key challenge to the ultimate exploitation of this class of novel nanomaterials is the development of abilities to assemble the nanoparticles into nanostructured thin films with predictable structural properties. A number of approaches to constructing functionalized nanoparticle and assemblies have been emerging. 8-12 One important advance in the study of core-shell nanoparticle reactivities is the finding of place-exchange reactivity reported first by the Murray group. 9 The shell reactivity enables the engineering of the shell structure with a desired composition or functionality. In the area of exploring nanoparticles for chemical sensing and molecular recognition, several recent studies have demon- strated intriguing functional properties involving nanostructure/ liquid and nanostructure/ gas interfaces. 7-9,11,13-19 In a report by Wohltjen and Snow, 18 a chemiresistor sensor based on octanethi- * To whom correspondence should be addressed. Phone: 607-777-4605. E-mail: cjzhong@ binghamton.edu. (1) Templeton, A. C.; Wuelfing, W. P.; Murray, R. W. Acc. Chem. Res. 2000 , 33, 27 and references therein. (2) Whetten, R. L.; Shafigulin, M. N.; Khoury, J. T.; Schaff, T. G.; Vezmar, I.; Alvarez, M. 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