Gold nanorods exhibit optical properties that are tunable with their shape, leading to sensing, imaging, and biomedical therapeutic applications. Colloidal preparations of gold nanorods impart surfactants or other species on the nanorod surfaces; a popular preparation leads to a surfactant bilayer on the surface. The specific chemistry at three distinct interfaces has roles to play in the growth and subsequent usage of these nanomaterials; these interfaces are the gold−surfactant interface, the hydrophobic surfactant bilayer, and, finally, the surfactant interface with the aqueous bulk. Each one of these interfaces provides strategies for altering nanorod properties such as stability against aggregation, toxicity, and ease of assembly. It is the solvent-accessible interface that dictates nanorod interactions with other particles, macromolecules, and living cells.

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In this paper we demonstrate that self-assembled monolayers (SAMs) of alkanethiols on gold can be used as effective photoresists. UV photolysis of an alkanethiol SAM generates the corresponding sulfonate in the monolayer film. The sulfonate is easily rinsed off of the surface with water, exposing a clean gold substrate, which can then be modified with subsequent chemistry. We describe here experiments in which an alkanethiol SAM on a gold film on silicon is irradiated through a mask, followed by immersion of the sample in an aqueous acid etching solution (HC1:HNOS: HzO = 3:1:4). The gold is etched away from the areas which have been exposed to UV radiation leaving a pattern which reproduces the original mask. The spatial resolution in the present experiments is limited by the mask which is a 6-rm wire grid. Scanning electron microscopy images of patterned samples show sharp edges to the features suggesting that spatial patterning on the 1-pm scale should be attainable with this simple chemistry. 20772401 from Argonne National Laboratory. We thank J. M. Laux and J. Tang for XPS analysis of the samples and Professor R. Penner for assisting us with optical microscopy of the samples.

havior is believed to be general for this class of intermediates.Acknowledgment. We are grateful to Kevin Peters and Erin O'Driscoll (University of Colorado) for their help in obtaining the picosecond spectra, to the University of Arkansas for a sabbatical leave, and to T. J. Meyer (University of North Carolina) for the use of his nanosecond equipment. We thank E. M. Arnett (Duke University) and R. A. McClelland (Toronto) for their thoughtful comments and suggestions. We appreciate the com-ments of a referee who made a number of valuable suggestions concerning our picosecond data.