A novel near infrared optical molecular probe (CyL) derived from heptamethine cyanine dye was developed for the selective detection of Hg2+ over other metal ions in aqueous solutions. The detection conditions for Hg2+ were optimized. A linear range from 1.0 × 10−7 M to 5.0 × 10−6 M and a detection limit of 1.93 × 10−8 M with a correlation coefficient of 0.9992 were achieved under the optimal conditions. In the recognition of Hg2+, CyL alone peaks at 760 nm and exhibits a shoulder at 690 nm. Hg2+ can modulate the aggregation state of CyL through coordination of thiosemicarbazide on CyL and Hg2+, and thus results in an obvious shift in the maximal absorption wavelength of CyL in the NIR region. The ESI mass spectra of CyL–Hg2+ solution have been used to prove the conversion of CyL from monomers to aggregates. Finally, the proposed method has been successfully applied to the determination of Hg2+ in cosmetic samples.

•A ratiometric fluorescent heptamethine cyanine-based probe for HClO was developed.•HClO was measured with the excitation and the dual-emission wavelengths at NIR Region.•The mechanism relies on HClO-promoted desulfurization to afford a guanidine group.•The probe showed high sensitivity and good selectivity towards HClO.An interesting ratiometric fluorescent probe with unique optical performance was reported in this work. By modifying on the bridge-head of heptamethine cyanine chromophore with an N-phenyl-N’-ethylene amine thiourea substituent as a chemodosimetric recognition unit, the probe exhibited ratiometric fluorescent response towards hypochlorous acid (HClO). Upon addition of HClO, the absorbance spectra showed a great red shift as large as 150 nm from 650 nm to 800 nm. Employing the isosbestic absorption point at 730 nm as an excitation wavelength, a ratiometric fluorescent sensing mode with two long emission wavelengths at 760 nm and 820 nm was acquired, and thus the probe displayed significant behavior with both the excitation wavelength and the dual-emission wavelengths located at NIR (650–900 nm) region exclusively. Also, the probe showed excellent performance in high sensitivity and good selectivity towards HClO over other reactive oxygen species and a wide variety of coexist species in biological pH condition and had been successfully used to detect hypochlorous acid in serum samples and tap water samples.Download high-res image (167KB)Download full-size image

A semicarbazide-based naphthalimide was designed and synthesized as a colorimetric fluorescent probe. Upon reaction with Cu2+ in a buffer solution of pH 7.4 (buffer water/acetonitrile = 80:20, v/v), the probe exhibits color changes from colorless to jade-green accompanying remarkable enhancement in its fluorescence, which could be mechanistically ascribed to the Cu2+-promoted hydrolysis of the semicarbazide moiety leading to the release of the green fluorescent 4-amino-1,8-naphthalimide fluorophore. The probe also displayed excellent performance in high sensitivity as well as good selectivity for Cu2+ over other metallic cations.

A near infrared probe for sensitive colorimetric and fluorimetric detection of nerve agent mimics, DCP and DCNP, was reported based on the activation of a carboxylic acid group by the mimics to conduct an intramolecular amidation reaction in the heptamethine chromophore, where its absorption or excitation maximum wavelength could be greatly red-shifted by attenuating the electron-donating ability of the amine group in the bridgehead site of heptamethine cyanine.

A highly selective and sensitive ratiometric fluorescent chemosensor for Ag+ in aqueous solution was developed, in a linear range of 0.6 × 10−7 to 50 × 10−7 mol L−1, based on a A–Ag+–A binding mode with a heptamethine cyanine motif containing one adenine moiety.

Based on a T–Hg2+–T binding mode, a sensitive ratiometric fluorescent chemosensor for aqueous Hg2+ was developed with a heptamethine cyanine chromophore containing a thymine moiety.

A new rhodamine spiro scaffold with a six-membered reactive ring was developed by inserting a nitrogen atom in the known probe rhodamine B spiro thiohydrazide, which switched the recognition preference of the probe from Hg2+ to Cu2+. This probe is shown to be an efficient “turn-on” fluorescent chemodosimeter for Cu2+ in a neutral aqueous medium. Mechanism studies suggested that the probe opened its spiro-ring by a Cu2+-induced transformation of the cyclic thiosemicarbazide moiety to an isothiocyanate group.

A new “dual-mode” chromogenic and fluorescent turn-on probe (2) for the selective sensing of biological thiols is reported. In MeOH–H2O cosolvent at physiological pH 7.40 (MeOH–H2O = 3:7), biological thiols cleave the 2,4-dinitrobenzenesulfonyl group to release the chromo- and fluorophore merocyanine (3).

A novel rhodamine thiospirolactone chemosensor 1 was found to develop prominent absorbance and fluorescence enhancements in the presence of Hg2+ in aqueous solution and this was suggested to result from the thiospiro ring opening induced by Hg2+ binding.

A irreversible Hg2+ selective ratiometric fluorescence probe FR, a fluorescein fluorophore linked to a rhodamine B hydrazide by a thiourea spacer, was designed and synthesized. The developed probe FR exhibited great ratiometric fluorescence enhancement and remarkable yellow-magenta color change toward Hg2+ with excellent selectivity in aqueous acetone solution, and the ratiometric fluorescence response to Hg2+ was not interfered by other metal cations including Fe3+, Co2+, Ni2+, Cr3+, Zn2+, Pb2+, Cd2+, Ca2+, Mg2+, Ba2+ and Mn2+. The linear range and the detection limit of this supposed ratiometric fluorescence method for Hg2+ were 0.0–10.0 × 10−6 and 5 × 10−8 M, respectively.

A new highly sensitive and selective colorimetric method for fluoride determination in water is described. The novel reagent used is a hemicyanine dye (HC), which forms a stable complex with Zr–EDTA, the fluoride-binding site, through the hydroxyl groups. The hemicyanine-chelating Zr–EDTA complex (HC–Zr–EDTA) is ready to react with fluoride ion to release HC. This result in remarkable color change of the sensing solutions from red (λmax = 513 nm) to yellow (λmax = 427 nm) at pH 4.40. When applied to the colorimetric determination of fluoride ions, a linear range from 3.0 × 10−6 to 5.0 × 10−5 mol/L and a detection limit of 2.8 × 10−6 mol/L with a correlation coefficient of 0.9993 can be achieved under the optimized conditions. Because of the specific affinity of fluorides for the [Zr–EDTA], there is little interference by other ions. This method has been successfully applied to the determination of fluorides in toothpaste samples.

A highly selective and sensitive ratiometric fluorescent chemosensor for Ag+ in aqueous solution was developed, in a linear range of 0.6 × 10−7 to 50 × 10−7 mol L−1, based on a A–Ag+–A binding mode with a heptamethine cyanine motif containing one adenine moiety.

A new “dual-mode” chromogenic and fluorescent turn-on probe (2) for the selective sensing of biological thiols is reported. In MeOH–H2O cosolvent at physiological pH 7.40 (MeOH–H2O = 3:7), biological thiols cleave the 2,4-dinitrobenzenesulfonyl group to release the chromo- and fluorophore merocyanine (3).

A near infrared probe for sensitive colorimetric and fluorimetric detection of nerve agent mimics, DCP and DCNP, was reported based on the activation of a carboxylic acid group by the mimics to conduct an intramolecular amidation reaction in the heptamethine chromophore, where its absorption or excitation maximum wavelength could be greatly red-shifted by attenuating the electron-donating ability of the amine group in the bridgehead site of heptamethine cyanine.

A novel rhodamine thiospirolactone chemosensor 1 was found to develop prominent absorbance and fluorescence enhancements in the presence of Hg2+ in aqueous solution and this was suggested to result from the thiospiro ring opening induced by Hg2+ binding.