A highly pH sensitive water-soluble polyfluorene derivative (PFP-aa) has been designed and synthesized by Suzuki coupling reaction. The PFP-aa contains two amino and four carboxylic acid groups in each repeat unit (RU). The protonation and deprotonation of both the carboxylate and amine are controlled by medium pH values. The polymer charge is anticipated to control electrostatic repulsion between polymer chains and lead to different levels of aggregation behaviors. Different fluorescent responses of the PFP-aa are demonstrated as the environmental pH is changed from 3 to 12. Different sugars can bind to boronic acid to form boronic esters with different binding constants following proton release, thus generating diverse changes in pH. It is demonstrated that PFP-aa can be used as a pH sensor to detect D-fructose.