Non-conjugated polyelectrolytes were used to quench oppositely charged fluorescent dye-ligand conjugate (DLC) molecules by bringing them to the vicinity of the polyelectrolyte backbone to form aggregates and hence quench the dye fluorescence. As target protein molecules are added to the solution, the specific interaction between the DLC and the protein disrupts the aggregate structure, thus recovering the luminescence. The binding of DLC to oppositely charged polyelectrolyte and the disruption of the aggregates are investigated by fluorescence spectroscopy. The static-quenching mechanism is clearly manifested in the Stem-Volmer plots that show the decrease in slope with increasing temperature. This polyelectrolyte-based sensing platform has a sensitivity of <100 pM. We also show the selectivity of this platform by comparing the fluorescence recovery between two proteins (avidin and bovine serum albumin) with similar molecular weight. Our results suggest a highly sensitive approach for detecting biological analytes. (C) 2007 Published by Elsevier Ltd.