A new anionic water-soluble polyfluorene-poly(9,9-bis(4 '-sulfonatobutyl)fluorene-co-alt-1,4-phenylene) sodium salt (PFS) was synthesized by Suzuki-coupling reaction. The anionic polyfluorene shows bright blue photoluminescence and it Was found the photoluminescence could be highly quenched by a bioactive dye (Lucifer yellow cadaverine biotin-X dipotassium salt). PFS photoluminescence quenching only occurs effectively upon addition of avidin. The photoluminescence quenching process is sensitive to even subnanomolar amount of avidin (10(-10) M). The avidin facilitated photoluminescence quenching opens up opportunities of new Ultra-high efficiency and rapid response biosensors based on the polyfluorene electrolyte. (c) 2005 Elsevier Ltd. All rights reserved.