Weakly emissive silicon nanoparticles with an average diameter of about 5 nm are prepared Via Pulsed laser ablation of silicon wafers in water. Electrostatic assembly of water-soluble conjugated polyelectrolytes on the Surface of the silicon nanoparticles steadily enhances the photoluminescence of these nanocomposites, indicating the possibility of energy transfer between the semiconductor nanoparticles and the conjugated polymer, or silicon nanoparticle-induced elimination of chain aggregates of the conjugated polyelectrolyte. Fluorescence emission of the hybrid silicon-conjugated polymer nanocomposites is steeply quenched by cytochrome c, and the minimum detection concentration for the redox-active protein is found to be 50 nM. The sensitization is realized by ultrafast photo-induced electron transfer between the electron-deficient protein and the conjugated polyelectrolyte binding on the silicon nanoparticle surfaces. The results offer guidelines to explore novel sensors for detecting nanoparticles, and also help develop high-efficiency sensory materials based on electrostatic complexes of conjugated polyelectrolytes and inorganic semiconductor nanoparticles. (C) 2010 Elsevier Ltd. All rights reserved.