We theoretically discuss and analyze the design of a microfluidic device which has recently been demonstrated experimentally to exhibit the phenomenon of absolute negative mobility ({ITALIC i.e.} net motion into the direction opposite to a net acting force) for non-interacting Brownian particles. Based on a model for the motion of a colloidal particle in a structured microfluidic system, that includes electroosmotic and electrophoretic effects as well as thermal fluctuations, we derive an analytic approximation for the average particle velocity, comparing very well with data of numerical simulations and experimental measurements.

PACS numbers: 85.85.+j, 05.40.--a, 05.60.--k, 82.70.Dd