Fluorescent ion indicators for detecting heavy metals

摘要

A series of fluorescent ion indicators were tested for their spectral response to submicromolar levels of 13 divalent and trivalent metal ions in aqueous solution. Upon binding their target ions, these fluorescent. compounds exhibit changes in fluorescence emission intensity that are easily detectable, making them useful for direct the detection of soluble heavy metal ions including Hg{sup}(2+), Cu{sup}(2+), Ni{sup}(2+) and Cd{sup}(2+). The fluorescence response of these indicators to ion binding results from photoinduced electron transfer (PET) effects, fluorophore/quencher interactions, fluorescence quenching by heavy metal ions or a combination of these processes. The majority of the indicators we tested bind their target ions reversibly with dissociation constants (K{sub}d) near 1μM (～1 ppm) and detection limits near 100 nM (～100 ppb) at pH 7. However, several indicators exhibit very high affinity for their target ion; for example, Magnesium Green binds Zn{sup}(2+) with a k{sub}d near 20 nM. All the indicators synthesized and tested are based on water-soluble fluorophores that have high fluorescence quantum yields (from 0.3 to 0.7) and can be excited with an Ar laser, fluorometer or hand-held UV lamp. Furthermore, the excitation and emission spectra of these indicators are insensitive to pH changes over the range of 5 to 10, as well as to high concentrations of K{sup}+, Na{sup}+, Ca{sup}(2+) and Mg{sup}(2+). These properties make the indicators useful for the direct measurement of metal ions in solutions, such as biological fluids, sea water and waste streams, that contain high concentrations of salts. Supported by the Office of Naval Research (No.N00014-C-0270).