Ultrastructural characterization of colloidal metal films for bioanalytical applications by scanning force microscopy

Colloidal metal films (CMFs) are prepared by the attachment of silver, gold, or platinum (or other metal) particles to a glass slide modified by silanization with 3-mercaptopropyl silane. The covalent attachment of the metal particles occurs through the metal-sulfur bond. In these samples the local electromagnetic field is enhanced near the surface of the CMF due to excitation of plasmon resonances. This phenomenon can be used for a variety of analytical applications. Because the optical properties are strongly dependent on the morphology of the him, its structural characterization becomes of great importance. To further characterize CMFs we have used scanning force microscopy (SFM). Initial studies revealed lateral dimensions of the particles as well as the particle density. Height measurements were made using the three-dimensional topographic image of the surface yielded by SFM, and were used to evaluate the selective deposition of a silica spacer layer onto the metal particles. Comparative FM measurements in water and air using different imaging modes were performed to investigate the mechanical stability of CMFs against the forces exerted by the scanning tip. (C) 1996 American Vacuum Society.