The Brownian diffusion of sub-microrneter-sized particles (diameter 0.52 mu m) in the vicinity of a nanostructured surface was experimentally characterized. The surface consisted of a repeating pattern of rectagular grooves with depth 35 nm and pitch 400 nm. It was found that the one-dimensional particle diffusivity parallel to the nanogrooves was significantly higher than the diffusivity perpendicular to the grooves (1.5 18 +/- 0.274 (S.E.) mu m(2)/s compared to 0.704 +/-0.090 mu m(2)/s). No such anisotropy in the one-dimensional Brownian diffusivity was found for particles near a flat surface. (c) 2005 Elsevier Inc. All rights reserved.