Supramolecular colloidal systems of gold nanoparticles/amphiphilic cyclodextrin: A FE-SEM and XPS investigation of nanostructures assembled onto solid surface

Properly functionalized amphiphilic cyclodextrins (CDs) can act as capping agents for gold colloids in solution (Mazzaglia, A.; et at. J. Phys. Chein. C 2008, 112, 6764). In the present work, we report a study on a hybrid gold nanoparticles/amphiphilic CD supramolecular system assembled onto a surface by both field emission scanning electron microscopy (FE-SEM) and X-ray photoelectron spectroscopy (XPS) techniques. Amphiphilic CDs bearing respectively thioalkyl chains with different length in the primary site (thiohexyl in SC6NH2 and thiohexadecyl in SC16NH2) and oligoethylene amino groups in the secondary ones were drop-cast onto glass and silicon surfaces. FE-SEM pointed Out On the mesoscopic scale the presence of CDs aggregates with sizes of about 100-300 nm, mostly displaying the known vesicular aspect. Both CDs can interact closely with Gold nanoparticles of 10-20 nm. The binding mode was investigated in detail by XPS pointing to the coordination of CD amino groups with the external thin shell of gold nanoparticles. In the present case, the anchorage of the CDs to the noble metal occurs via the amino groups, which are unexpectedly favored with respect to the less accessible thioether groups. This investigation can potentially open perspectives in the design and control of devices engineered onto surface for biosensing or drug delivery.