Size selective sampling using mobile, 3D nanoporous membranes

We describe the fabrication of 3D membranes with precisely patterned surface nanoporosity and their utilization in size selective sampling. The membranes were self-assembled as porous cubes from lithographically fabricated 2D templates (Leong et al., Langmuir 23: 8747-8751, 2007) with face dimensions of 200 mu m, volumes of 8 nL, and monodisperse pores ranging in size from approximately 10 mu m to 100 nm. As opposed to conventional sampling and filtration schemes where fluid is moved across a static membrane, we demonstrate sampling by instead moving the 3D nanoporous membrane through the fluid. This new scheme allows for straightforward sampling in small volumes, with little to no loss. Membranes with five porous faces and one open face were moved through fluids to sample and retain nanoscale beads and cells based on pore size. Additionally, cells retained within the membranes were subsequently cultured and multiplied using standard cell culture protocols upon retrieval.