In Vivo Monitoring of Mercury Ions Using a Rhodamine-Based Molecular Probe

3',6'-Bis(ethyl-amino)-2',7'-dimethyl-2-{[2-[(E)-3,4-methyl-enedioxy-benzyl-idene-amino]eth-yl}spiro-[isoindoline-1,9'-xanthen]-3-one

The title compound, C(36)H(36)N(4)O(4), was prepared as a spiro-lactam ring formation of the rhodamine dye for comparison with a ring-opened form. The xanthene ring system is approximately planar [r.m.s. deviations from planarity = 0.023 (9) Å for the xanthene ring]. The dihedral angles formed by the spiro-lactam and 1,3-benzodioxole rings with the xanthene ring system are 86.8 (1) and 74.3 (1)°, respectively.

Sensing mercury for biomedical and environmental monitoring

Mercury is a very toxic element that is widely spread in the atmosphere, lithosphere, and surface water. Concentrated mercury poses serious problems to human health, as bioaccumulation of mercury within the brain and kidneys ultimately leads to neurological diseases. To control mercury pollution and reduce mercury damage to human health, sensitive determination of mercury is important. This article summarizes some current sensors for the determination of both abiotic and biotic mercury. A wide array of sensors for monitoring mercury is described, including biosensors and chemical sensors, while piezoelectric and microcantilever sensors are also described. Additionally, newly developed nanomaterials offer great potential for fabricating novel mercury sensors. Some of the functional fluorescent nanosensors for the determination of mercury are covered. Afterwards, the in vivo determination of mercury and the characterization of different forms of mercury are discussed. Finally, the future direction for mercury detection is outlined, suggesting that nanomaterials may provide revolutionary tools in biomedical and environmental monitoring of mercury.

Convenient and highly effective fluorescence sensing for Hg2+ in aqueous solution and thin film

A quinolinocyclodextrin, that is, MQAS-beta-cyclodextrin (MQAS = N-(2-methyl-8-amino- quinolyl)-p-aminobenzene sulfonamide) was synthesized. Further experiments showed that it could form very stable stoichiometric 2:1 complex with Zn(2+) in water. Significantly, the resultant quinolinocyclodextrin/Zn(2+) complex showed the specific fluorescence response to Hg(2+) over other metal ions, which could be readily distinguished in either aqueous solution or the PVA-based thin film. This finding would enable Zn x 3(2) complex as a convenient and highly efficient fluorescence sensor for the detection of Hg(2+).

A bright water-compatible sugar-rhodamine fluorescence sensor for selective detection of Hg2+ in natural water and living cells

By combination of a sugar group and a rhodamine group into one molecule, a bright and specific fluorescent sensor for Hg(2+) in natural water and living cells was achieved. RG1 features the high quantum efficiency for a Hg(2+)-bound sensor in natural water and sensitivity to environmentally relevant mercury in complex natural samples. The limit of detection of Hg(2+) of 1 ppb level suggests that RG1 is capable of distinguishing between the safe and toxic levels of inorganic mercury in drinking water. RG1 also establishes excellent Hg(2+)-ion specificity over alkali-, alkaline-earth metals and the first-row transition metals as well as Pb(2+) and Ag(+). Investigation on the fluorescence imaging of Hg(2+) in living cells demonstrates that RG1 might be used for monitoring Hg(2+) within biological samples.

Detection of mercury in aquatic environments using EPRE reporter zebrafish

It has been proposed that transgenic zebrafish could be designed to detect low levels of chemical contaminants that cause oxidative stress in aquatic environments, such as heavy metals or pesticides. In this paper, we describe such a transgenic zebrafish that produces a luciferase-green fluorescent protein (LUC-GFP) fusion protein under conditions of oxidative stress. The reporter gene expression is under the regulation of the electrophile responsive element (EPRE), which activates gene expression in response to oxidative stressors. The GFP component of this fusion protein allows us to visually detect reporter gene activity in live animals to determine if activity is localized to a particular tissue. The luciferase component is capable of returning a quantitative assessment of reporter gene activity that allows us to determine if reporter gene activity is directly correlated to the concentration of the chemical inducer. We have tested this reporter construct in both transient and stable transgenic fish after exposure to a range of HgCl(2) concentrations. GFP expression from the EPRE-LUC-GFP construct was inducible in transient assays but was below the limit of detection in stable lines. In contrast, we observed inducible luciferase activity in both transient assays and stable lines treated with HgCl(2). We conclude that the EPRE is capable of driving reporter gene expression in a whole animal assay under conditions of oxidative stress. Furthermore, expression was induced at HgCl(2) concentrations that do not result in obvious morphological defects, making this approach useful for the detection of low levels of oxidative contaminants in aquatic environments.

Chromofluorescent indicator for intracellular Zn2+/Hg2+ dynamic exchange

The fluorescence of NABQ increases remarkably in the presence of Zn(2+) and is quenched by Hg(2+). As shown by confocal imaging, NABQ-Zn(2+) can penetrate cells, where the bound Zn(2+) is exchanged for Hg(2+). This results in the concomitant export of Hg(2+) from the cells, showing that NABQ can act as a Zn(2+) carrier and as a Hg(2+) extracting agent in living cells.

Localizing organomercury uptake and accumulation in zebrafish larvae at the tissue and cellular level

Using synchrotron x-ray fluorescence mapping, we have examined the uptake and localization of organic mercury in zebrafish larvae. Strikingly, the greatest accumulation of methyl and ethyl mercury compounds was highly localized in the rapidly dividing lens epithelium, with lower levels going to brain, optic nerve, and various other organs. The data suggest that the reported impairment of visual processes by mercury may arise not only from previously reported neurological effects, but also from direct effects on the ocular tissue. This novel approach is a powerful tool for directly investigating the molecular toxicology of heavy metals, and should be equally applicable to the study of a wide range of elements in developing embryos.

Turn-on fluorescence sensing of nucleoside polyphosphates using a xanthene-based Zn(II) complex chemosensor

Fluorescence sensing with small molecular chemosensors is a versatile technique for elucidation of function of various biological substances. We now report a new fluorescent chemosensor for nucleoside polyphosphates such as ATP using metal-anion coordination chemistry. The chemosensor 1-2Zn(II) is comprised of the two sites of 2,2'-dipicolylamine (Dpa)-Zn(II) as the binding motifs and xanthene as a fluorescent sensing unit for nucleoside polyphosphates. The chemosensor 1-2Zn(II) selectively senses nucleoside polyphosphates with a large fluorescence enhancement (F/F(o) > 15) and strong binding affinity (K(app) approximately = 1 x 10(6) M(-1)), whereas no detectable fluorescence change was induced by monophosphate species and various other anions. The 'turn-on,' fluorescence of 1-2Zn(II) is based on a new mechanism, which involves the binding-induced recovery of the conjugated form of the xanthene ring from its nonfluorescent deconjugated state which was formed by an unprecedented nucleophilic attack of zinc-bound water. The selective and highly sensitive ability of 1-2Zn(II) to detect nucleoside polyphosphates enables its bioanalytical applications in fluorescence visualization of ATP particulate stores in living cells, demonstrating the potential utility of 1-2Zn(II).

3',6'-Bis(ethyl-amino)-2-[(2-hydroxy-ethyl)-amino]-2',7'-dimethylspiro-[isoindoline-1,9'-xanthen]-3-one

In the title compound, C(28)H(32)N(4)O(3), the dihedral angle between the planes of the xanthene ring system and the spiro-lactam ring is 85.99 (3)°. Mol-ecules are linked by inter-molecular O-H⋯O and N-H⋯O hydrogen-bonding inter-actions.

A sensitive and selective near-infrared fluorescent probe for mercuric ions and its biological imaging applications

A new mercury(II) near-infrared region fluorescent probe 3,9-dithia-6-monoazaundecane-tricarbocyanine has been designed and synthesized. It consists of two functional moieties: the tricarbocyanine performs as the near-infrared region fluorophore, and the 3,9-dithia-6-monoazaundecane acts as the selected binding site for metal ions. The near-IR excitation and emission profiles of the probe can minimize cell and tissue damage and avoid native fluorescence from natural cellular species. It exhibits fluorescence increase upon the binding of the Hg(2+) based on the inhibition of the photoinduced electron transfer quenching mechanism. Excellent sensitivity and selectivity for mercuric ions are observed with this probe. The value of the system is demonstrated by its use in monitoring the real-time uptake of Hg(2+) within HepG2 cells and five day old zebrafish. The synthesis and remarkable properties of it help to extend the development of metal ions fluorescent probes for biological applications.

Organometallic activation of a fluorogen for templated nucleic acid detection

A nucleic acid detection scheme that employs DNA-mediated delivery of an organomercury activator to unmask a fluorophore is described. The approach relies on adjacent hybridization of two oligonucleotide conjugates containing organomercury and caged rhodamine functionalities. Postsynthetic conjugation of amino-modified DNAs enabled efficient preparation of these probes. Complementary DNA templates yielded fluorescence signals arising from metal-assisted rhodamine uncaging.