Design, synthesis and application of dual-channel fluorescent probes for ratiometric detection of HClO and H2S based on phenothiazine coumarins.

The ubiquity of diverse material entities in environmental matrices renders the deployment of unifunctional fluorescent indicators inadequate. Consequently, this study introduces a ratiometric dual-emission fluorescent sensor (Probe CP), synthesized by conjugating phenothiazine coumarin to hydroxycoumarin through a piperazine linker for concurrent detection of HClO and H2S. Upon interaction with HClO, the phenothiazine unit's sulfur atom undergoes oxidation to sulfoxide, facilitating a shift from red to green fluorescence in a ratiometric manner. Concurrently, at the opposite terminus of Probe CP, 2,4-dinitroanisole serves as the reactive moiety for H2S recognition; it restores the blue emission characteristic of 7-hydroxycoumarin while maintaining the red fluorescence emanating from phenothiazine coumarin as an internal standard for ratio-based assessment. Exhibiting elevated specificity and sensitivity coupled with minimal detection thresholds (0.0506 µM for HClO and 1.7292 µM for H2S) alongside rapid equilibration periods (3 min for HClO and half an hour for H2S), this sensor was efficaciously employed in cellular environments and within zebrafish models as well as imaging applications pertaining to alcohol-induced hepatic injury in murine subjects.

Development of a Ratiometric Fluorescent Probe with Zero Cross-Talk for the Detection of SO2 Derivatives in Foods and Live Cells.

Sulfur dioxide (SO2) derivatives are extensively utilized as both a preservative for foods and an active gaseous signal molecule in various physiological and pathological processes, but their excessive intake would bring harmful effects on human health; so, the determination of SO2 derivatives is of great importance. Herein, we developed a ratiometric fluorescent probe named 2-(2'-hydroxyphenyl)benzothiazole-3-ethyl-1,1,2-trimethyl-1H-benzo[e]indolium (HBT-EMBI) by introducing a hemicyanine unit of EMBI to an HBT group for the detection of SO2 derivatives via an excited-state intramolecular proton transfer (ESIPT) and intramolecular charge transfer (ICT) effects. The probe displays some advantages, such as a colorimetric change from purple to colorless, a ratiometric fluorescence with zero cross-talk, and a remarkably large emission shift (Δλ = 164 nm) under a single-wavelength excitation. Accordingly, the probe HBT-EMBI has been successfully employed for the colorimetric and ratiometric determination of SO2 derivatives in real food samples and the quantitative visualization of SO2 derivative variations in HepG2 cells.

A HBT-based bifunctional fluorescent probe for the ratiometric detection of fluoride and sulphite in real samples.

Based on a core of 2-(benzo[d]thiazol-2-yl)phenol (HBT), a bifunctional ratiometric fluorescent probe, HBT-FS, was constructed for the discriminative detection of fluoride (F-) and sulphite (SO32-) with high sensitivity and selectivity. HBT-FS itself displayed a green fluorescence with λEmmax = 498 nm. The treatment of HBT-FS with F- resulted in a red fluorescence (λEmmax = 634 nm) with a large Stokes shift and a 291-fold enhancement in the ratio of the fluorescence intensity (I634 nm/I498 nm). Upon the addition of SO32-, HBT-FS exhibited a blue fluorescence (λEmmax = 371 nm) and the ratiometric fluorescence enhancement was remarkable (9445 folds for I371 nm/I498 nm). HBT-FS was successfully used to qualitatively and quantitatively determine F- and SO32- in a ratiometric manner in real samples.

An instantaneous near-infrared trimethyl lock based fluorescent probe for biothiols with a large Stokes shift.

Using trimethyl lock as a useful mean, a selective and sensitive fluorescent probe was developed for the detection of biothiols with an emission in near infrared spectral region (694 nm) and a large Stokes shift (129 nm). The inserted trimethyl lock between the fluorophore and the sensing group, 2, 4-dinitrobenzensulfonate, highly improved the response rate of this probe toward GSH because the unfavorable steric interactions between three methyl groups resulted in an extremely rapid intramolecular lactonization reaction to form a hydrocoumarin. This probe displayed an instantaneous response (within seconds) to GSH at a very low concentration in aqueous medium and the detection limit was as low as 2.5 nM based on S/N = 3. The fluorescence intensity of the solution of probe 1 at 694 nm displayed a good linearity (R = 0.9917) with the concentration of GSH in a range of 0.0-5.0 µM. Importantly, this probe exhibited a good performance in detecting biothiols in serum samples, living cells and organism.

Fluorescence detection of glutathione and oxidized glutathione in blood with a NIR-excitable cyanine probe.

Cyanine has been widely utilized as a near infrared (NIR) fluorophore for detection of glutathione (GSH). However, the excitation of most of the reported cyanine-based probes was less than 800 nm, which inevitably induce biological background absorption and lower the sensitivity, limiting their use for detection of GSH in blood samples. To address this issue, here, a heptamethine cyanine probe (DNIR), with a NIR excitation wavelength at 804 nm and a NIR emission wavelength at 832 nm, is employed for the detection of GSH and its oxidized form (GSSG) in blood. The probe displays excellent selectivity for GSH over GSSG and other amino acids, and rapid response to GSH, in particular a good property for indirect detection of GSSG in the presence of enzyme glutathione reductase and the reducing agent nicotinamideadenine dinucleotide phosphate, without further separation prior to fluorescent measurement. To the best of our knowledge, this is the first attempt to explore NIR fluorescent approach for the simultaneous assay of GSH and GSSG in blood. As such, we expect that our fluorescence sensors with both NIR excitation and NIR emission make this strategy suitable for the application in complex physiological systems.

A red-emitting fluorescent probe for hydrogen sulfide in living cells with a large Stokes shift.

A red-emitting fluorescent probe was developed for the sensitive and selective detection of H2S. Upon treatment with H2S, this probe exhibited a remarkable fluorescence enhancement (10 fold) with a large Stokes shift (125 nm). The detection limit of this probe was as low as 5.7 nM based on S/N = 3. The application of this probe in the detection of intracellular H2S in living cells is successfully demonstrated.