Abstract: A device is provided for the controlled sampling of fluid into a well formed within an upper surface, in which the well may be filled under dynamic wetting conditions by contacting a droplet on the upper surface with the top of the well. Wetting is supported by the increased hydrophilicity of the upper surface relative to that of the well side wall. The relative difference in hydrophilicity may be achieved by providing an upper surface with greater roughness than the side wall, effectively amplifying the hydrophilicity of the upper surface relative to that of the side wall. Wells are preferably formed in an unpolished surface of a siliconwafer, and can achieve a stable film with micron depth and an aspect ratio in excess of 100.