A single-wavelength excited NIR fluorescence probe for distinguishing GSH/H2S and Cys/Hcy in living cells and zebrafish through separated dual-channels

Efficient turn-on fluorescent probe cooperated by cascade response for disclosing the fluctuation of cysteine in cells

BACKGROUND

The research on cysteine (Cys) determination is deemed as a hot topic, since it has been reported to be connected with various physiological processes and disease prediction. However, existing Cys-responding probes may expose some defects such as long reaction time, disappointing photostability, and suboptimal sensitivity. Under such a circumstance, our team has proposed an efficient fluorescent probe with novel sensing mechanism to perfectly cope with the above-mentioned drawbacks.

RESULTS

A novel cascade reaction-based probe 9-(2,2-dicyanovinyl)-2,3,6,7-tetrahydro-1H,5H-pyrido[3,2,1-ij]quinolin-8-yl acrylate (DPQA) has been synthesized for the first time. Undergoing addition-cleavage and cyclization-rearrangement processes, DPQA reacts with Cys to generate an iminocoumarin product with relucent green fluorescence, namely 11-imino-2,3,6,7-tetrahydro-1H,5H,11H-pyrano[2,3-f]pyrido[3,2,1-ij]quinoline-10-carbonitrile (IMC-J), and the relative fluorescence quantum yield (Φf) soars from 0.007 to 0.793. Utilizing such a mechanism, DPQA shows a superb turn-on signal (172-fold), low detection limit (4.1 nM), and wide detection range (5-6000 nM) toward Cys detection. Encouraged by the admirable sensing performance of DPQA, bioimaging of endogenous Cys has been attempted in HeLa cells with satisfactory results. Moreover, cell model of H2O2-induced oxidative stress has been established and the Cys fluctuation during this process has been inspected, elucidating how living cells confront with the eruption of reactive oxygen species (ROS) storm.

SIGNIFICANCE

The probe DPQA with such an intriguing cascade responding process for Cys detection has been endowed with many merits, such as fast reaction and superior sensitivity, conducive to improving responsiveness and rendering it more suitable for further applications. Thereby, we expect that the DPQA would be an efficient tool for detecting Cys fluctuation in living cells of different physiological processes.

A near-infrared fluorescent probe with thiadiazole unit as key skeleton for ICT and ESIPT mechanism and effective detection of Cu2

Fluorescent probe L-I was synthesized to demonstrate that 1,3,4-thiadiazole is an attractive moiety and could be utilized as positive hydrogen bond acceptor for excited state intramolecular proton transfer (ESIPT) processes, guider of electrons movement for intramolecular charge transfer (ICT) process and identify group for mental ions. Furthermore, dicyanoisophorone framework was employed to improve the fluorescence characteristics and near-infrared (NIR) fluorescent emission at 695 nm accompanied by a Stoke's shift as large as 260 nm was obtained. L-I could selectively detect Cu2+ over other analytes taking advantages of high sensitivity, fast response within 30 s and low detection limit (0.026 μM). More important, L-I exhibited good performance for detection of Cu2+ in actual water samples, food products, traditional Chinese medicine and for cell imaging which demonstrates practical significance in the fields of environmental monitor, food safety and biotechnology.

A novel fluorescent probe for cascade detection of hydrogen sulfide and hypochlorous acid and its application in bioimaging

Herein we developed a cascade detection mode for the detection of HS- and ClO- by the novel probe NM-Cl bearing a conjugating naphthalene-dicyanoisophorone unit. The probe displayed sensitive and remarkable fluorescent enhancement in response to HS-, but not to other analytes. The mixture of probe and HS- constructed a specific sensing system for ClO- by fluorescent quenching response. The mechanism studies indicated that the successive reacting of HS- substitution Cl atom in probe and then addition of ClO- facilitation a thiofuran ring-forming induced differentiated fluorescence emission. This study provides a novel mechanism for the detection of HS- and ClO-, the imaging of cell and living animal further indicating the good application prospects of the probe in biosensing and bioimaging.

New Rhodamine-based sensor for high-sensitivity fluorescence tracking of Cys and simultaneously colorimetric detection of H2S

Sulfhydryl-containing compounds including cysteine (Cys), homocysteine (Hcy), glutathione (GSH) and hydrogen sulfide (H2S) are involved in many physiological processes. The development of single-molecule optical sensor for the distinguish detection of these bio-thiols is a critical and challenging effort. In this work, we designed a one-step synthesis of the Rhodamine-based sensor FR for specific fluorescent response of Cys and simultaneously colorimetric detection of H2S, in which the aldehyde and fluorine groups act as response sites. Sensor FR displays significant fluorescence enhancement at 565 nm toward Cys with high selectivity and low detection limits (49 nM) due to the low background fluorescent signal of the spirocyclic closed-state in Rhodamine structure. Meantime, after treatment of H2S, the color of the sensor changes significantly from colorless to blue-purple, which can be used as a visual colorimetric method to detect H2S. These response mechanisms were systematically characterized by 1H NMR and Mass spectrometry. Finally, sensor FR could be used to monitor exogenous and endogenous of intracellular Cys changes.

A lysosome-targeted fluorescent probe based on a BODIPY structure for Cys/Hcy detection

Cysteine (Cys) and homocysteine (Hcy) are important biothiols in living organisms. They play important roles in a variety of physiological and pathological processes. Therefore, it is very important to design an optical probe for the selective detection of Cys/Hcy. Herein, we report the design and synthesis of a fluorescent probe NBD-B-T based on a boron-dipyrromethene (BODIPY) structure, which showed an excellent lysosome targeting ability and an outstanding Cys/Hcy detection capacity. For NBD-B-T, the sensing group 7-nitro-2,1,3-benzoxadiazole (NBD) and the lysosomal targeting group morpholine were introduced. The results show that the NBD-B-T probe can detect Cys/Hcy with fluorescence emission turn-on performance. The low detection limits of this probe are about 76.0 nM for Hcy and 97.6 nM for Cys, respectively. The NBD-B-T probe has a low detection limit, high stability, and excellent selectivity and sensitivity. More importantly, the NBD-B-T can target lysosome, and simultaneously detect the Cys/Hcy in living cells.

High-selective two-site fluorescent probe for Cys/SO2 detection and cell imaging

A fluorescent probe has been designed using cyanine phenothiazine and 7-nitro-1,2,3-benzoxadiazole (NBD) for selective detection of Cys-SO2 components. The probe utilizes the NBD structure to achieve specificity towards Cys and employs a reaction mechanism between the double bond of cyanine and phenothiazine with SO32- to achieve selectivity towards SO2. Importantly, the NBPI phenothiazine structure incorporates a large C-O bond energy attached to NBD, effectively eliminating interference from Hcy and ensuring highly selective response to Cys. The optimized design of the probe enables excellent linearity and extremely low detection limits for Cys-SO2 components in vitro experiments. The probe NBPI allows separate detection of Cys-SO2 in the presence of both components. Furthermore, the probe NBPI demonstrated successful imaging of endogenous and exogenous Cys and SO2 in cell studies.

Meso-aryltellurium-BODIPY-based fluorescence turn-on probe for selective, sensitive and fast glutathione sensing in HepG2 cells

Glutathione (GSH) as one most abundant thiol, acts as important roles in regulating cellular redox activities, and various diseases are closely related with its abnormal levels. Thus, monitoring intracellular GSH levels is essential for understanding cellular metabolism of many related diseases. In this work, we firstly reported a new fluorescence turn-on sensor, which was capable of selectively, sensitively and rapid sensing GSH over other thiols, especially cysteine and homocysteine in solutions and living cells. A meso-aryltellurium boron dipyrromethene (BODIPY) was firstly designed and synthesized, which showed silenced emission due to an efficient photoinduced electron transfer (PET) process from electron-rich Te to BODIPY, and then upon exposure to GSH, the meso-Te-C bond could be rapidly cleaved by the thiol group of GSH, thus resulting in an obvious fluorescence "turn-on" phenomenon through inhibition of the PET effect. This probe exhibited excellent selectivity and sensitivity towards GSH with a short response time of 2 min, showing a remarkable fluorescence enhancement observed at 541 nm with a large fluorescence quantum yield increase from nearly 0 to 0.73 upon excitation at 500 nm in PBS/CH3CN (9/1, v/v). The detection limit towards GSH was further calculated to be 1.7 nM by the linear fluorescence change at 541 nm in the GSH-concentration ranging from 0 to 4 μM. Furthermore, its sensing mechanism was validated by using mass spectrometry, confirming the rapid cleavage of the Te-C bond by GSH. Finally, cell imaging experiments demonstrated that this probe could successfully detect GSH in living cells, highlighting its potential for rapid and sensitive detection of intracellular GSH level changes. Therefore, a new meso-aryltellurium-BODIPY fluorescence turn-on sensor was firstly developed, which could selectively, sensitively and fast detect cellular GSH over other thiols based on the rapid cleavage of the meso Te-C bond.

A dicyanoisophorone-based long-wavelength fluorescent probe for detection of cysteine in vitro and in vivo

In this research, an "off-on" long-wavelength fluorescent probe (DCMN-Cl) based on (E)-2-(3-(2-(6-hydroxynaphthalen-2-yl)vinyl)-5,5-dimethylcyclohex-2-en-1-ylidene) malononitrile (DCMN) is designed and synthesized for cysteine (Cys) detection. DCMN-Cl exhibits a large Stokes shift (211 nm) and shows rapid response and high specificity to Cys. The fluorescence initensity at 635 nm reveals a good linear relationship with Cys concentration in the 0 to 50 μM range, and the detection limit is as low as 159 nM. The probe is also used for fluorescence imaging of Cys in cells and mice. Moreover, the probe provided visual evidence of Cu2+ and curcumin-induced intracellular Cys fluctuations.

Bioimaging and Sensing Thiols In Vivo and in Tumor Tissues Based on a Near-Infrared Fluorescent Probe with Large Stokes Shift

The well-known small-molecule biothiols have been used to maintain the normal metabolism of peroxy radicals, forming protein structures, resisting cell apoptosis, regulating metabolism, and protecting the homeostasis of cells in the organism. A large amount of research has found that abnormal levels of the above biothiols can cause some adverse diseases, such as changes in hair pigmentation, a slower growth rate, delayed response, excessive sleep and skin diseases. In order to further investigate the exact intracellular molecular mechanism of biothiols, it is imperative to explore effective strategies for real-time biothiol detection in living systems. In this work, a new near-infrared (NIR) emission fluorescence probe (probe 1) for sensitive and selective detection of biothiols was devised by combining dicyanoisophorone derivatives with the dinitrobenzenesulfonyl (DNBS) group. As expected, probe 1 could specifically detect biothiols (Cys, Hcy and GSH) through the dinitrobenzenesulfonyl group to form dye 2, which works as a signaling molecule for sensing biothiols in real samples. Surprisingly, probe 1 showed superior sensing characteristics and low-limit detection towards biothiols (36.0 nM for Cys, 39.0 nM for Hcy and 48.0 nM for GSH) with a large Stokes shift (134 nm). Additionally, the function of probe 1 as a platform for detecting biothiols was confirmed by confocal fluorescence imaging of biothiols in MCF-7 cells and zebrafish. More importantly, the capability of probe 1 in vivo has been further evaluated by imaging the overexpressed biothiols in tumor tissue. It is reasonable to believe that probe 1 can provide a valuable method to explore the relationship between biothiols and the genesis of tumor.

A novel "turn on" fluorescence probe based on a caffeic acid skeleton for detecting Al3+ and bioimaging application

The specificity detection of Al³⁺ is important for monitoring life health and environmental pollution. A fluorescence enhancement probe based on caffeic acid HAM was synthesized for detecting Al³⁺ with high sensitivity and good selectivity. When Al³⁺ was added in the aqueous solution of HAM, the formation of HAM-Al³⁺ complexes inhibited the PET process, which led to great enhancement of fluorescence. The addition of other metal ions cannot induce the change of fluorescence intensity. The sensing mechanism was proved by ¹H NMR titration, MS, and Job's plot. Moreover, probe HAM exhibited excellent properties, such as high sensitivity (LOD = 0.168 μM), fast response time (30 s), wide pH range (3-11), and good interference ability. Based on the above results, probe HAM was used to explore its bioimaging application in biological samples.

A selective fluorescent probe for hydrogen sulfide from a series of flavone derivatives and intracellular imaging

In this work, through the orthogonal design of two fluorophores and two recognition groups, a series of fluorescent probes were developed from the flavone derivatives for hydrogen sulfide (H₂S). The probe FlaN-DN stood out from the primarily screening on the selectivity and response intensities. It could respond to H₂S with both the chromogenic and fluorescent signals. Among the recent reported probes for the H₂S detection, FlaN-DN indicated the most highlighted advantages including the rapid response (within 200 s) and the high response multiplication (over 100 folds). FlaN-DN was sensitive to the pH condition, thus could be applied to distinguish the cancer micro-environment. Moreover, FlaN-DN suggested practical capabilities including a wide linear range (0-400 μM), a relatively high sensitivity (limit of detection 0.13 μM), and high selectivity towards H₂S. As a low cytotoxic probe, FlaN-DN achieved the imaging in living HeLa cells. FlaN-DN could detect the endogenous generation H₂S and visualize the dose-dependent responses to the exogenous H₂S level. This work provided a typical case of natural-sourced derivatives as functional implements, which might inspire the future investigations.