Stable blue emissive hyperbranched conjugated polymer nanoparticles with tunable particle sizes were synthesized by Suzuki polymerization in miniemulsion, which could be facile soluble in common organic solvents after complete removal of surfactants. As highly sensitive fluorescent probes for picric acid, they exhibit 25 times higher fluorescence quenching ability and 100 times wider linear detection region (from 1.0 nM to 4.0 μM) compared to their linear conjugated polymer nanoparticle analogue.