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Screening Mercury Levels in Fish with a Selective

Fluorescent Chemosensor

Christopher J. Chang*

J. Am. Chem. Soc. 2005, 127, 16030-16031

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Mercury

The long atmospheric residence time of Hg0 vapor and its oxidation to soluble inorganic Hg2+ provides a pathway for contaminating vast amounts of water and soil.

The bacteria living in the sediments of aqueous environments transform inorganic Hg2+ into methylmercury, a potent neurotoxin that concentrates through the food chain in the tissues of fish and marine mammals.

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Current techniques for mercury screening: Atomic absorption/emission spectroscopy Inductively coupled plasma mass spectrometry

Fluorescent platforms for Hg2+ detection: Small molecules DNAzymes Protein Oligonucleotide

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Synthesis of Mercuryfluor-1 (MF1)

71%

75%

9%37%

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Fluorescence response of 1 μM MF1 to Hg2+ in aqueous solution. Spectra shown are for Hg2+ concentrations of 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.8, 1.0, 1.2, 1.6, and 2.0 μM. Spectra were acquired in 20 mM HEPES (pH 7) with excitation at 480 nm.

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Fluorescence responses of MF1 to various metal ions. Bars represent the final integrated fluorescence response (Ff) over the initial integrated emission (Fi). Initial spectra were acquired in 20 mM HEPES, pH 7. White bars represent the addition of an excess of the appropriate metal ion (1 mM for Li+, Na+, K+, Mg2+, and Ca2+, 67 μM for all other cations) to a 1 μM solution of MF1. Gray bars represent the addition of 6.7 μM Hg2+ to the solution. Excitation was provided at 495 nm, and the emission was integrated over 505-700 nm. 1. Hg2+; 2. Li+; 3. Na+; 4. K+; 5. Mg2+; 6. Ca2+; 7. Sr2+; 8. Mn2+; 9. Fe2+; 10. Co2+; 11. Ni2+; 12. Cu2+; 13. Zn2+; 14. Cd2+; 15. Pb2+.

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Ionic radii

Metal ion Li+ Na+ K+ Mg2+ Ca2+ Sr2+ Mn2+ Fe2+

Ionic radius

(pm)90 116 152 86 114 132 97 92

Metal ion Co2+ Ni2+ Cu2+ Zn2+ Cd2+ Pb2+ Hg2+ Ag+

Ionic radius

(pm)88.5 83 87 88 109 133 116 129

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Fluorometric analysis of mercury in fish using MF1. Fish were taken from California waters and digested with microwave irradiation, and emission responses were calibrated versus independent measurement of mercury content by atomic absorption spectroscopy: Lime Saddle Marina (bluegill, 0.1 ppm Hg), Calero Resevoir (bass, 1.0 ppm Hg), Lake Almaden (bass, 2.5 ppm Hg), Almaden Resevoir (bass, 5.5 ppm Hg), Guadelupe Resevoir (bass, 7.5 ppm Hg). Excitation was provided at 495 nm, and the emission was integrated over 505-700 nm.

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SHN O

HN

+ Hg2+H2O

HgS

low fluorescence high fluorescence

+

Figure. Fluorescence metal titrations. The Hg(II) reaction is 87% complete and the Ag(I) reaction 73% complete after 10 min under stoichiometric conditions and at room temperature.

J. Am. Chem. Soc. 1992, 114,9704-9705ref6

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Figure. Relative fluorescence intensities of 1 (2.74 10-5 M) and 2 (2.75 x10-5 M) in the presence of various metal cations (c = 2.8 x10-3 M, only for Cd2+ c = 4.5 x10-3 M), complete complexation.

1 2

J. Am. Chem. Soc. 1999, 121, 5073-5074ref7

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J. Am. Chem. Soc. 2000, 122, 968-969ref8

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fluorescence resonance energy transfer (FRET)

Angew. Chem. Int. Ed. 2004, 43, 4300–4302ref21

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以適當的霧化器 (Nebulizer)將待測樣品溶液先經霧化處理後，再配合載送氣流輸送，將所形成含待分析元素之氣膠 (Aerosol)輸送至電漿 (Plasma)中，樣品受熱後，經由一系列去溶劑、分解、原子化 /離子化等反應，將位於電漿中之待分析元素形成單價正離子，再透過真空界面傳輸進入質譜儀 (Mass spectrometer)，繼而配合質量分析器 (Mass-analyzer)將各特定質荷比 (Mass-to-charge ratios)之離子予以解析後，再以電子倍增器加以檢測，來進行多元素之定性及定量工作。