A “Reactive” Ratiometric Fluorescent Probe for Mercury Species

Visualization of sialidase activity in Mammalian tissues and cancer detection with a novel fluorescent sialidase substrate

Sialidase removes sialic acid from sialoglycoconjugates and plays crucial roles in many physiological and pathological processes. Various human cancers express an abnormally high level of the plasma membrane-associated sialidase isoform.Visualization of sialidase activity in living mammalian tissues would be useful not only for understanding sialidase functions but also for cancer diagnosis. However, since enzyme activity of mammalian sialidase is remarkably weak compared with that of bacterial and viral sialidases, it has been difficult to detect sialidase activity in mammalian tissues. We synthesized a novel benzothiazolylphenol-based sialic acid derivative (BTP-Neu5Ac) as a fluorescent sialidase substrate. BTP-Neu5Ac can visualize sialidase activities sensitively and selectively in acute rat brain slices. Cancer cells implanted orthotopically in mouse colons and human colon cancers (stages T3-T4) were also clearly detected with BTP-Neu5Ac. The results suggest that BTP-Neu5Ac is useful for histochemical imaging of sialidase activities.

An overview of the recent developments on Hg2+ recognition

Adverse influences of mercury on living organisms are well known. Despite efforts from various regulatory agencies, the build-up of Hg²⁺ concentration in the environment is of serious concern. This necessitates the search for new and efficient reagents for recognition and detection of Hg²⁺ in environmental samples.

Recent development of two-photon fluorescent probes for bioimaging

Fluorescent probes are essential tools for studying biological systems.

A water soluble FRET-based ratiometric chemosensor for Hg(ii) and S2−applicable in living cell staining

A new water soluble rhodamine-based ratiometric dual ‘off–on–off’ probe can selectively detect Hg²⁺ions in ppb level through time dependent FRET process with reversibility in presence of S²⁻anions.

A highly selective fluorescent chemosensor for iron ion based on 1H-imidazo [4,5-b] phenazine derivative

Two kinds of fluorescent sensors (S and S1) for Fe(3+) bearing 1H-Imidazo [4,5-b] phenazine derivatives have been designed and synthesized. Between the two sensors, S showed excellent fluorescent specific selectivity and high sensitivity for Fe(3+) in DMSO solution. The test strip based on S was fabricated, which could act as a convenient and efficient Fe(3+) test kit. The recognition mechanism of the sensor toward Fe(3+) was evaluated by MS, IR and XRD. The detection limit of the sensor S towards Fe(3+) is 4.8×10(-6)M. And other cations, including Hg(2+),Ag(+), Ca(2+), Cu(2+), Co(2+), Ni(2+), Cd(2+), Pb(2+), Zn(2+), Cr(3+), and Mg(2+) had no influence on the probing behavior.

A chemodosimeter for the ratiometric detection of hydrazine based on return of ESIPT and its application in live-cell imaging

A probe based on 2-(2'-hydroxyphenyl) benzothiazole (HBT) has been synthesized and used for the ratiometric detection of hydrazine. The probe is designed in such a way that the excited state intramolecular proton transfer (ESIPT) of the HBT moiety gets blocked. The chemodosimetric approach of hydrazine to the probe results in the recovery of the ESIPT by removal of a free HBT moiety through subsequent substitution, cyclization, and elimination processes. The probe is successfully demonstrated to enable the detection of hydrazine in live cells.

Synthesis of pyridine-based 1,3,4-oxadiazole derivative as fluorescence turn-on sensor for high selectivity of Ag+

An oxadiazole derivative(OXD) containing symmetrical pyridine-2-formamidophenyl-binded moiety was synthesised as fluorescence turn-on sensor OA1. Its ultraviolet-visible(UV-vis) and fluorescent spectra(FS) gave prominent fluorescence enhancement only for monovalent silver ion(Ag(+)) in HEPES buffer solution (10 mM, pH = 7.0, DMF-H2O, 9:1, v/v), which indicated the photo-induced electron transfer(PET) occurred from the donor of pyridine-2-formamidophenyl group to oxadiazole fluorophore. The present study demonstrated that OA1 was a viable candidate as fluorescent receptor for a new Ag(+) sensor. And the results of fluorescent spectral titration showed this sensor formed 1:1 complex with Ag(+).

2-(Benzothiazol-2-yl)-phenyl-β-d-galactopyranoside derivatives as fluorescent pigment dyeing substrates and their application for the assay of β-d-galactosidase activities

2-(Benzothiazol-2-yl)-phenyl-β-d-galactopyranoside derivatives were synthesized as novel artificial fluorescent pigment dyeing substrates for β-d-galactosidase. The substrates, which exhibited non-fluorescence or weak fluorescence in solution phase, were smoothly hydrolyzed by β-d-galactosidase from Aspergillus oryzae and yielded a water-insoluble strong fluorescent pigment. The difference of fluorescent intensity exhibited a linear relationship with the amount of enzyme.

A native-chemical-ligation-mechanism-based ratiometric fluorescent probe for aminothiols

Thiol-containing amino acids (aminothiols) such as cysteine (Cys) and homocysteine (Hcy) play a key role in various biological processes including maintaining the homeostasis of biological thiols. However, abnormal levels of aminothiols are associated with a variety of diseases. The native chemical ligation (NCL) reaction has attracted great attention in the fields of chemistry and biology. NCL of peptide segments involves cascade reactions between a peptide-α-thioester and an N-terminal cysteine peptide. In this work, we employed the NCL reaction mechanism to formulate a Förster resonance energy transfer (FRET) strategy for the design of ratiometric fluorescent probes that were selective toward aminothiols. On the basis of this new strategy, the ratiometric fluorescent probe 1 for aminothiols was judiciously designed. The new probe is highly selective toward aminothiols over other thiols and exhibits a very large variation (up to 160-fold) in its fluorescence ratio (I(458)/I(603)). The new fluorescent probe is capable of ratiometric detection of aminothiols in newborn calf and human serum samples and is also suitable for ratiometric fluorescent imaging of aminothiols in living cells.

Zn(2+) binding-enabled excited state intramolecular proton transfer: a step toward new near-infrared fluorescent probes for imaging applications

In order to facilitate the in vivo study of zinc-related biology, it is essential to develop a zinc-selective sensor that exhibits both near-infrared (NIR) emission and larger Stokes shift. A fluorescent sensor, Zinhbo-5, has been constructed by using bis(benzoxazole) ligand with 2, 2'-dipicolylamine (DPA) as metal ion receptor. In aqueous solution, Zinhbo-5 exhibits high sensitivity (K(d) = 2.58 nM(2) ) and selectivity for Zn(2+) cation, revealing about 14-fold fluorescence enhancement upon zinc binding to give green emission. Remarkably, Zn(2+) binding to Zinhbo-5 switches on the excited state intramolecular proton transfer (ESIPT), producing the desirable near-infrared region (over 710 nm) with large Stokes shift (ca. 240 nm). The new probe is demonstrated to be useful for in vivo imaging of the intracellular Zn(2+) ion. The Zinhbo-5 is also useful for detecting zinc ion distribution during the development of living zebrafish embryos.

A highly selective colorimetric sensor for Hg²⁺ based on nitrophenyl-aminothiourea

A simple and highly selective colorimetric sensor (L1) bearing thiosemicarbazide moiety as binding site and nitrophenyl moiety as signal group were synthesized. Sensor L1 showed great colorimetric single selectivity and high sensitivity for mercury cation in DMSO and DMSO/H(2)O binary solutions. When Hg(2+) was added to the DMSO solution of L1, dramatic color change from brown to colorless was observed. While the cations Ca(2+), Mg(2+), Cd(2+), Fe(3+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Pb(2+), Ag(+) and Cr(3+) could not cause any distinct interferer toward the recognition process for Hg(2+). The detection limit is allowable to 5.0 × 10(-6) and 1.0 × 10(-7)M level of Hg(2+) according to visual color change and UV-vis change, respectively. The recognition mechanism of the sensor toward mercury cation was evaluated in DMSO solutions by UV-vis and (1)H NMR. The sensor selectively sense Hg(2+)via the formation of a stable 1:1 complex through CS and CO group with Hg(2+). When these complex bonds formed, the sensor carried out an ICT transition induced color change.

A "turn-on" fluorescent Hg2+ chemosensor based on Ferrier carbocyclization

A "turn-on" fluorescent chemosensor with excellent selectivity and satisfactory sensitivity on Hg(2+) detection in 100% water media has been established employing a carbohydrate based Ferrier carbocyclization reaction. The probe has also presented satisfactory results for the imaging of Hg(2+) ions in cells and organisms.

Recognition of Hg2+ and Cr3+ in physiological conditions by a rhodamine derivative and its application as a reagent for cell-imaging studies

A new rhodamine-based receptor, derivatized with an additional fluorophore (quinoline), was synthesized for selective recognition of Hg(2+) and Cr(3+) in an acetonitrile/HEPES buffer medium of pH 7.3. This reagent could be used as a dual probe and allowed detection of these two ions by monitoring changes in absorption and the fluorescence spectral pattern. In both instances, the extent of the changes was significant enough to allow visual detection. More importantly, the receptor molecule could be used as an imaging reagent for detection of Hg(2+) and Cr(3+) uptake in live human cancer cells (MCF7) using laser confocal microscopic studies. Unlike Hg(ClO(4))(2) or Hg(NO(3))(2) salts, HgCl(2) or HgI(2) failed to induce any visually detectable change in color or fluorescence upon interaction with L(1) under identical experimental conditions. Presumably, the higher covalent nature of Hg(II) in HgCl(2) or HgI(2) accounts for its lower acidity and its inability to open up the spirolactam ring of the reagent L(1). The issue has been addressed on the basis of the single-crystal X-ray structures of L(1)·HgX(2) (X(-) = Cl(-) or I(-)) and results from other spectral studies.