The effects of different metal cations on the fluorescence of water-soluble conjugated polymer (CP) and their quenching mechanism have been explored. Most transition metal cations, especially noble metal cations, such as Pd2+, Ru3+, and Pt2+ possessed higher quenching efficiency to CP fluorescence than that of the main group metal cations and other transition metal cations, which have filled or half-full outmost electron layer configurations. Base on this, rapid, sensitive detection of noble metal cations can be realized and a novel quencher-tether-ligand (QTL) probe was developed to detect avidin and streptavidin.