PREPARATION AND CHARACTERIZATION OF AU COLLOID MONOLAYERS

The design and initial characterization of two-dimensional arrays of colloidal Au particles are reported. These surfaces are prepared by self-assembly of 12 nn diameter colloidal Au particles onto immobilized polymers having pendant functional groups with high affinity for Au (i.e., CN, SH, and NH2). The polymers are formed by condensation of functionalized alkoxysilanes onto cleaned quartz, glass, and SiO2 surfaces. The assembly protocol is carried out completely in solution: cleaned substrates are immersed in methanolic solutions of organosilane, rinsed, and subsequently immersed in aqueous colloidal Au solutions. Two-dimensional arrays spontaneously form on the polymer surface, The resulting substrates have been characterized by UV-vis spectroscopy, transmission electron microscopy (TEM), and surface-enhanced Raman scattering (SERS). TEM data show that the particles are spatially separated but close enough to interact electromagnetically (small spacing compared to lambda). The UV-vis data show that collective particle surface plasmon modes are present in the 650-750 nm region, suggesting that these assemblies are SERS-active. This is indeed the case, with enhancement factors of roughly 10(4). Au colloid monolayers possess a set of features that make them very attractive for both basic and applied uses, including uniform roughness, high stability, and biocompatibility.