High-performance fluorescence probe for fast and specific visualization of norepinephrine in vivo and depression-like mice.

Norepinephrine (NE), as an important neurotransmitter, is closely associated with the pathogenesis of anxiety and depressive disorders. Effective monitoring of NE fluctuation aids in the diagnosis of depression and the therapeutic assessment of the antidepressant intervention. The construction of novel fluorescent probes with high specificity towards NE for imaging in depression models is still in demand urgently. In this work, a novel resorufin-based red-emitting fluorescent probe for real-time tracking NE was developed. NE can significantly increase the fluorescence of probe LNE by triggering deprotection of carbonothioate ligand via nucleophilic substitution. The probe LNE demonstrated significant NE selectivity and sensitivity over other analytes in vitro. In addition, probe LNE showed a fast response time (<10 min), and the change in fluorescence signal was positively linked with NE concentration, which could be utilized to track the dysregulation of NE in vivo. More importantly, this powerful probe was successfully employed for real-time visual and imaging of NE in living cells and depression-like behavior animals.

A novel naphthalimide-based fluorescent probe for the colorimetric and ratiometric detection of SO2 derivatives in biological imaging.

SO2 is a well-known signal molecule and one of reactive sulfur species, which closely participates in many metabolic processes. While unbalanced metabolism of sulfur dioxide can lead to serious complications of various diseases. Therefore, a rapid and accurate monitoring of SO2 derivatives with high selectivity and sensitivity would be beneficial for their bio-analytic studies. Herein, a novel ratiometric fluorescent probe (NG-TCF) based on ICT mechanism for monitoring SO2 was developed. The probe underwent a nucleophilic addition of HSO3-/SO32- to give rise to a 120 nm blue-shift dual-emission signal changes in enhanced green channel and subdued red channel under a single wavelength excitation. The probe showed fast response rate (within 7 min), good sensitivity (the detection limit is 1.53 µM), and specific response toward HSO3-/SO32- over other bio-species, including H2S and ClO-. Moreover, the probe can be applied for visual ratio imaging of exogenous and endogenous SO2 derivatives in living cells.

TPE-based fluorescent probe for dual channel imaging of pH/viscosity and selective visualization of cancer cells and tissues.

The development of efficient fluorescence-based detection tools with high contrast and accuracy in cancer diagnosis has recently attracted extensive attention. Changes in the microenvironments between cancer and normal cells provide new biomarkers for precise and comprehensive cancer diagnosis. Herein, a dual-organelle-targeted probe with multiple-parameter response is developed to realize cancer detection. We designed a tetraphenylethylene (TPE)-based fluorescent probe TPE-PH-KD connected with quinolinium group for simultaneous detection of viscosity and pH. Due to the restriction on the double bond's rotation, the probe respond to viscosity changes in the green channel with extreme sensitivity. Interestingly, the probe exhibited strong emission of red channel in acidic environment, and the rearrangement of ortho-OH group occurred in the basic form with weak fluorescence when pH increased. Additionally, cell colocalization studies revealed that the probe was located in the mitochondria and lysosome of cancer cells. Following treatment with carbonyl cyanide m-chloro phenylhydrazone (CCCP), chloroquine, and nystatin, the pH or viscosity changes in the dual channels are also monitored in real-time. Furthermore, the probe TPE-PH-KD could effectively discriminate cancer from normal cells and organs with high-contrast fluorescence imaging, which sparked more research on an efficient tool for highly selectively visualizing tumors at the organ level.

A novel flavone-based ESIPT ratiometric fluorescent probe for selective sensing and imaging of hydrogen polysulfides.

Hydrogen polysulfides (H2Sn) as an important member of reactive sulfur species is closely relevant to many physiological functions in redox homeostasis and metabolism. Dual-channel monitor the changes of H2Sn level in vivo is highly desired. Herein we design a simple ratiometric fluorescent probe based on flavone skeleton for highly selective detection of H2Sn. The probe HF-NA-MC bearing 2-fluoro-5-nitrobenzoic acid group inhibited the intramolecular ESIPT process, which show the blue fluorescence of adjacent naphthalene unit. In the presence of H2Sn, the enol form of probe is converted to conjugated keto form, resulted in a 90 nm red-shift of fluorescence emission from 450 nm to 540 nm. The ratiometric intensity (I540/I450) of the probe exhibits a good linear relationship toward H2Sn in the range of 0-120 µM, and the detection limit is estimated to be 0.63 µM. The ratiometric fluorescent probe shows high specificity and anti-interference ability for H2Sn over other related reactive sulfur species. The probe HF-NA-MC shows promising outlook and could be applied to the confocal imaging of H2Sn by dual emission channels in Hela cells.

Sequential detection of hypochlorous acid and sulfur dioxide derivatives by a red-emitting fluorescent probe and bioimaging applications in vitro and in vivo.

Hypochlorous acid (HOCl) and sulfur dioxide derivatives (SO3 2-/HSO3 -) play critical roles in complex signal transduction and oxidation pathways. Therefore, it is meaningful and valuable to detect both HOCl and SO2 derivatives in biosystems by a fluorescence imaging assay. In this work, we developed a red-emitting fluorescent probe (DP) by the condensation of malononitrile and phenothiazine derivatives through a C[double bond, length as m-dash]C double bond. DP was designed with a donor-π-acceptor (D-π-A) structure, which enables absorption and emission in the long wavelength region. In the presence of HOCl, specific oxidation of the thioether of phenothiazine in DP to a sulfoxide derivative (DP[double bond, length as m-dash]O) occurs, resulting in a hypochromic shift (572 nm to 482 nm) of the absorption spectra and "OFF-ON" response of the maximum emission at 608 nm. After the activation of the C[double bond, length as m-dash]C double bond by oxidation, DP[double bond, length as m-dash]O reacts specifically with SO3 2-/HSO3 - via a 1,4-nucleophilic addition reaction leading to a decrease in the intensity of the absorption and emission spectra, which enabled the realization of sequential detection of HOCl and SO3 2-/HSO3 - by a single fluorescent probe. The detection limits of DP for HOCl and SO3 2-/HSO3 - were calculated to be 81.3 nM and 70.8 nM/65.1 nm, respectively. The results of fluorescence microscopic imaging indicated that DP shows potential for the detection of intracellular HOCl and SO3 2-/HSO3 -. Using adult zebrafish and nude mice as live animal models, DP was successfully used for the fluorescence imaging of HOCl and SO3 2-/HSO3 - in vivo.

A red-emission fluorescence probe based on 1,4-addition reaction mechanism for the detection of biothiols in vitro and in vivo.

In this work, a new fluorescence probe (DC) with a donor-π-acceptor (D-π-A) structure was designed and synthesized for the detection of three kinds of biothiols (Cys, Hcy and GSH) in live cells and organisms. DC displayed an intense red-emission centered at 625 nm. In the presence of biothiols, the nucleophilic addition reaction between the C=C double bond of DC and the sulfhydryl group (-SH) of biothiols occurred, resulting in obvious fluorescence quenching responses. DC exhibited high selectivity towards biothiols over other common bioactive species with low detection limits (0.26, 0.43, and 0.44 µM for Cys, Hcy and GSH, respectively). In addition, DC displayed a rapid response to biothiols within 4 min. The applications of DC in biothiols detection and imaging were then successfully demonstrated for the real-time monitoring of endogenous and exogenous biothiols in live cells and live animals.