Colorimetric detection of Hg2+ with an azulene-containing chemodosimeter via dithioacetal hydrolysis

Azulene is a bicyclic aromatic chromophore that absorbs in the visible region. Its absorption maximum undergoes a hypsochromic shift if a conjugated electron-withdrawing group is introduced at the C1 position. This fact can be exploited in the design of a colorimetric chemodosimeter that functions by the transformation of a dithioacetal to the corresponding aldehyde upon exposure to Hg2+ ions. This chemodosimeter exhibits good chemoselectivity over other metal cations, and responds with an unambiguous colour change clearly visible to the naked eye. Its synthesis is concise and its ease of use makes it appropriate in resource-constrained environments, for example in determing mercury content of drinking water sources in the developing world.

A NIR fluorescent probe for the rapid detection of Hg2+ in living cells and in vivo mice imaging

A near-infrared fluorescent probe NIR-Hg, for the detection of Hg²⁺ ion, has been synthesized directly by condensing Changsha dye with 4-Phenyl-3-thiosemicarbazide and the structure has fully characterized by ¹HNMR, ¹³CNMR, and ESI-MS. The probe has been designed on the basis of the reaction that Hg²⁺ ion promotes thiosemicarbazide to oxazole in aqueous media and had been induced to produce turn-on fluorescence via an irreversible spirolactam ring-opening process. The probe NIR-Hg has exhibited fast response (1 min), high sensitivity with 44-fold fluorescence intensity enhancement under six equivalent amounts of Hg²⁺ added, high selectivity over other related metal ions and a low detection limit of 5.8 × 10^-8 M in the phosphate buffer. The linear response range covers the concentration of Hg²⁺ from 5 × 10^-7 to 5 × 10^-6 M. In addition, the probe has good cell-membrane permeability, which is suitable for fluorescence imaging for Hg²⁺ in living cells and in vivo mice.

Design of NIR Chromenylium-Cyanine Fluorophore Library for "Switch-ON" and Ratiometric Detection of Bio-Active Species In Vivo

The real-time monitoring of key biospecies in the living systems has received thrusting attention during the past decades. Specifically, fluorescent detection based on near-infrared (NIR) fluorescent probes is highly favorable for live cells, live tissues, and even animal imaging, owing to the substantial merits of the NIR window, such as minimal phototoxicity, deep penetration into tissues, and low autofluorescence background. Nevertheless, developing potent NIR fluorescent probes still poses serious challenges to the chemists because traditional NIR fluorophores are less tunable than visible-wavelength fluorophores. To address this issue, here we report a set of novel NIR hybrid fluorophores, namely, the hybrid chromenylium-cyanine fluorophore (CC-Fluor), in which both the fluorescence intensity and the emission wavelength can be easily adjusted by the conformational changes and substitution groups. Compared to known NIR fluorophores, the new CC-Fluors are substantially advantageous for NIR probe development: (1) CC-Fluors display tunable and moderate Stokes shifts and quantum yields; (2) the fluorophores are stable at physiological conditions after long-term incubation; (3) the absorption maxima of CC-Fluors coincide with the common laser spectral lines in mainstream in vivo imaging systems; (4) most importantly, CC-Fluors can be easily modified to prepare NIR probes targeting various biospecies. To fully demonstrate the practical utility of CC-Fluors, we report two innovative NIR probes, a ratiometric pH probe and a turn-on Hg(2+) probe, both are successfully employed in live animal imaging. Hence, the detailed studies allow us to confirm that CC-Fluors can work as an excellent platform for developing NIR probes for the detection of species in living systems.