Fluorescent ion indicators for detecting heavy metals

Michael A. Kuhn; Brian Hoyland; Scott Carter; Cailan Zhang; Richard P. Haugland

doi:10.1117/12.208483

8 May 1995 Fluorescent ion indicators for detecting heavy metals

Michael A. Kuhn, Brian Hoyland, Scott Carter, Cailan Zhang, Richard P. Haugland

Author Affiliations +

Proceedings Volume 2388, Advances in Fluorescence Sensing Technology II; (1995) https://doi.org/10.1117/12.208483
Event: Photonics West '95, 1995, San Jose, CA, United States

Abstract

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 Hg²⁺, Cu²⁺, Ni²⁺ and Cd²⁺. The fluorescence response of these indicators to ion binding results from photoinduced electron transfer 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_d) near 1 (mu) M (approximately 1 ppm) and detection limits near 100 nM (approximately 100 ppb) at pH 7. However, several indicators exhibit very high affinity for their target ion; for example, Magnesium Green^TM binds Zn²⁺ with a K_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⁺, Na⁺, Ca²⁺ and Mg²⁺. 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.

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Michael A. Kuhn, Brian Hoyland, Scott Carter, Cailan Zhang, and Richard P. Haugland "Fluorescent ion indicators for detecting heavy metals", Proc. SPIE 2388, Advances in Fluorescence Sensing Technology II, (8 May 1995); https://doi.org/10.1117/12.208483

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