Fig. 1.

Device configuration. (a) Exploded view of the device: an upper PDMS layer containing sample and buffer channels, a bottom layer containing a gradient forming microchamber, and a semipermeable membrane sandwiched in between. (b) A sealed final device. Marked in red are the control boundaries where the concentration in the gradient forming chamber is controlled to be constant by the running sample and buffer solutions in the respective overlaying channels. (c) Fluidic path and molecular diffusion path. The solid arrows denote fluidic path, and the dotted arrows denote diffusion path. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of the article.)