Cu(II) detection by a fluorometric probe based on thiazoline-amidoquinoline derivative and its application to water and food samples.

Two novel fluorescent probes for Cu2+ detection have been developed based on thiazoline-quinoline conjugates bearing a 4-ethynyl-N,N-dimethylaniline unit (QT1 and QT2). QT2 exhibits instantaneous fluorescence quenching of Cu2+ with an emissive change from bright orange to arctic blue under UV light irradiation (365 nm). The plots of I0/I against Cu2+ concentrations show a good linear relationship that ranges from 0 to 50 µM with a coefficient of determination (R2) = 0.9906 and a limit of detection (LOD) of 76 nM, which is considered low (4.84 ppb). A 1:1 complexation between QT2 and Cu2+ was confirmed by UV-Vis titration, ESI-MS, and SC-XRD. The QT2·Cu2+ complex was dissociated by the addition of EDTA. The fluorescence quenching mechanism involves the ligand-to-metal charge transfer (LMCT) of a paramagnetic Cu2+ complex. The QT2 probe on a paper-based strip was used to determine the amount of Cu2+ in water and food samples (shiitake mushrooms and oysters).

A novel "turn-on" fluorescent probe based on thiocarbamoyl-DHP for Hg2+ detection in water samples and living cells.

In this study, two fluorescent sensing probes, dihydropyridine (DHP) derivatives (DHP-CT1 and DHP-CT2) bearing phenoxy thiocarbonyl group, have been developed for Hg2+ detection. The tandem trimerization-cyclization of methylpropiolate with ammonium acetate gave 1.4-DHP and 1,2-DHP derivatives, which were reacted with O-phenylcarbonochloridothioate to produce DHP-CT1 and DHP-CT2, respectively. DHP-CT1 exhibits superior sensitivity and selectivity of fluorescence enhancement towards Hg2+ in aqueous media. The fluorescence intensity shows a good linear relationship with the concentration of Hg2+ in the range of 0-10 µM providing the extremely low LOD of 346 nM (69.4 ppb). The fluorescence enhancement is caused by the Hg2+ promoted hydrolysis of the thioamide bond releasing the fluorescent 1,4-DHP that was confirmed by NMR and HRMS. The quantitative analysis of Hg2+ in water samples using DHP-CT1 probe was demonstrated in aqueous solution and paper-based sensing strips. Furthermore, DHP-CT1 was also applied for monitoring intracellular Hg2+ in living RAW264.7 macrophages through fluorescence cell imaging.

A Dihydropyridine Derivative as a Highly Selective Fluorometric Probe for Quantification of Au3+ Residue in Gold Nanoparticle Solution.

Novel dihydroquinoline derivatives (DHP and DHP-OH) were synthesized in one pot via a tandem trimerization-cyclization of methylpropiolate. DHP and DHP-OH possess strong blue fluorescence with high quantum efficiencies over 0.70 in aqueous media. DHP-OH displays a remarkable fluorescence quenching selectively to the presence of Au3+ through the oxidation of dihydropyridine to pyridinium ion as confirmed by NMR and HRMS. DHP-OH was used to demonstrate the quantitative analysis of Au3+ in water samples with the limit of detection of 33 ppb and excellent recovery (>95%). This fluorescent probe was also applied for the determination of Au3+ residue in the gold nanoparticle solution and a paper-based sensing strip for the on-site detection of Au3+.

Glucopyranosyl-1,4-dihydropyridine as a new fluorescent chemosensor for selective detection of 2,4,6-trinitrophenol.

Glucopyranosyl-1,4-dihydropyridine (Glc-DHP) was synthesized as a new fluorescent chemosensor via cyclotrimerization of the ß-amino acrylate in the presence of TiCl4. This DHP derivative is soluble in aqueous medium and the solution gives a blue fluorescence signal with a quantum yield of 29%. The fluorescence signal of Glc-DHP was selectively quenched by 2,4,6-trinitrophenol (TNP) with a quenching coefficient (Ksv) of 4.47 × 10(4) and at one of the best reported detection limits of 0.94 µM. The quenching mechanism was confirmed to be of the static type at the low concentration region (less than 50 µM) with the significant quenching effect of competitive absorption starting from the concentration of 50 µM. Even in the real sample (seawater and industrial water), the quenching efficiencies of TNP on the fluorescence emission of Glc-DHP were proven to be at the same level with that of the test in pure water, demonstrating the practicability of the detection. Furthermore, a fluorescent paper sensor could be prepared by immersing the paper into the Glc-DHP solution. The fluorescence of the paper sensor disappeared either by writing with TNP solution or by exposure to TNP vapor. This detection could be observed by the naked eye under black light. The pH effect was proven to be a substantial factor in the quenching mechanism, providing an accurate determination of TNP, 2,4-dinitrophenol (DNP) and 4-nitrophenol (4NP) in real mixed-samples.