We present a microfluidic biosensor that integrates membrane-based preconcentration with fluorescence detection. The concentration membrane was fabricated in polyacrylamide by an in situ photopolymerization technique at the junction of glass microchannels. Liposomes entrapping sulforhodamine B dye molecules were used for signal amplification. The biotin–streptavidin binding system was a model system for evaluating device performance. Biotinylated liposomes were preconcentrated at the membrane by applying an electric field across the membrane. The electric field causes the liposomes to migrate toward the membrane where they are concentrated by a sieving effect. Two orders of magnitude concentration was achieved after applying the electric field for only 2 min. The concentrated bolus was then eluted toward the detection unit, where the biotinylated liposomes were captured by immobilized streptavidin. The integrated system with the preconcentration module shows a 14-fold improvement in signal as opposed to a system that does not include preconcentration.