New water-soluble hyperbranched polyfluorenes bearing carboxylate side chains have been synthesized by the simple "A2 + B2 + C3" protocol based on Suzuki coupling polymerization. The linear polyfluorene analogue LPFA was also synthesized for comparative investigation. The optical properties of the neutral precursory polymers in CHCl3 and final carboxylic-anionic conjugated polyelectrolytes in buffer solution were investigated. The obtained hyperbranched polyelectrolyte HPFA2 with lower content of branch unit (2%) showed excellent solubility and high fluorescence quantum yield (Phi(F) = 89%) in aqueous solution. Fluorescence quenching of HPFA2 by different metal ions was also investigated, the polyelectrolyte showed high selectivity for Hg2+ and Cu2+ ions relative to other various metal ions in buffer solution. The Stern-Volmer constant K-sv was determined to be 0.80 x 10(6) M-1 for Hg2+ and 3.11 x 10(6) M-1 for Cu2+, respectively, indicating the potential application of HPFA2 as a highly selective and sensitive chemosensor for Hg2+ and Cu2+ ions in aqueous solution. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3431-3439, 2010