Thrombin-mediated ratiometric two-photon fluorescent probe for selective imaging of endogenous ultratrace glutathione in platelet

A Facile Probe for Fluorescence Turn-on and Simultaneous Naked-Eyes Discrimination of H2S and biothiols (Cys and GSH) and Its Application

Hydrogen sulfide and biothiol molecules such as Cys and GSH acted important roles in many physiological processes. To simultaneously detect and distinguish them was quite necessary by a suitable fluorescent probe. A novel chemosensor 4-(4-(benzo[d]thiazol-2-yl)-2-methoxyphenoxy)-7-nitrobenzo[c][1,2,5]oxadiazole (BMNO) was designed to detect H₂S/Cys/GSH using the combination of nitrobenzofurazan (NBD) and benzothiazole fluorophores linked by a facile ether bond. The probe BMNO was developed for simultaneous identification of H₂S, Cys and GSH. Noticeably, the color changes (from colorless to light purple, light orange and light yellow) of probe BMNO solutions for sensing H₂S, Cys and GSH could be observed by naked eyes, respectively. The probe BMNO exhibited high selectivity and sensitivity for H₂S, Cys and GSH showing distinct optical signal with detection limit as low as 0.15 μM, 0.03 μM and 0.14 μM, respectively. The sensing mechanism was clarified by spectrum analysis and some controlled experiments. In addition, these outstanding properties of probe BMNO enabled its practical applications in detection H₂S in beer, and in cell imaging for Cys and GSH as well.

Rational design of an ESIPT-based fluorescent probe for selectively monitoring glutathione in live cells and zebrafish

Glutathione (GSH), an extremely important antioxidant, is a major participant in maintaining redox homeostasis and tightly associated with various clinical diseases. Thus, accurate and rapid detection of intracellular GSH is imperative to elucidate its role in physiological and pathological processes. Herein, by modifying 2-(2'-hydroxyphenyl) benzothiazole (HBT) scaffold, we developed an excited-state intramolecular proton transfer (ESIPT)-based fluorescent probe BTFMD for tracking GSH, which exhibited good selectivity, excellent water solubility, a large Stokes shift (181 nm) and fast response rate (within 10 min). Furthermore, the probe was successfully applied for imaging of endogenous GSH in live cells and zebrafish, and probing into the role of GSH in the development of cancer and Parkinson's disease.

Activity-Based Sensing: A Synthetic Methods Approach for Selective Molecular Imaging and Beyond

Emerging from the origins of supramolecular chemistry and the development of selective chemical receptors that rely on lock-and-key binding, activity-based sensing (ABS)-which utilizes molecular reactivity rather than molecular recognition for analyte detection-has rapidly grown into a distinct field to investigate the production and regulation of chemical species that mediate biological signaling and stress pathways, particularly metal ions and small molecules. Chemical reactions exploit the diverse chemical reactivity of biological species to enable the development of selective and sensitive synthetic methods to decipher their contributions within complex living environments. The broad utility of this reaction-driven approach facilitates application to imaging platforms ranging from fluorescence, luminescence, photoacoustic, magnetic resonance, and positron emission tomography modalities. ABS methods are also being expanded to other fields, such as drug and materials discovery.

Quinolone-based fluorescent probes for distinguished detection of Cys and GSH through different fluorescence channels

Dual-channel discrimination of Cys and GSH using a red fluorescent probe.

Reactive group effects on the photophysical and biological properties of 2-phenyl-1H-phenanthro[9,10-d]imidazole derivatives as fluorescent markers

The presented research focuses on the theoretical design and procedures for preparing protein conjugates with markers. For this purpose a series of phenanthroimidazole (PhI) analogous compounds was designed and investigated by means of first principle methods. Through the judicious choice of cross-linking reagents and the selection of reactive groups, five target fluorescent probes were selected, one of which was previously described using in vitro tests. For the best cognitive purpose and understanding of the nature of the protein conjugation, the studies describe the impact of the reactive group on the solvatochromism, the polarity of the charge transfer of the excited states, the Stokes' shift, ECD spectra and two-photon cross sections. The research is also extended to an analysis of PhI-Concanavalin A biocomplexes and changes in photophysical properties after conjugation. In order to identify valuable alternatives to commercial probes designed for cellular labelling in biological and biomedical imaging, biological properties were described such as ecotoxicity, log P and log BCF, and dye-protein binding was quantified by means of AutoDock and molecular dynamics simulations. The study showed that for phenanthroimidazole derivatives the factor which limits the possibility of their use in medical imaging is the presence of a pyridyl disulfide group, while the introduction of an N-hydroxysuccinimide ester may be used to create stable and valuable fluorescent probes with a wide spectrum for applications in biomedical imaging.

Development of a near-infrared ratiometric fluorescent probe for glutathione using an intramolecular charge transfer signaling mechanism and its bioimaging application in living cells

A novel near-infrared (NIR) ratiometric fluorescent probe HBT-GSH derived from conjugated benzothiazole was developed for the selective detection of glutathione (GSH) over cysteine (Cys) and homocysteine (Hcy). The probe was sophisticatedly designed based on the GSH selectively induced enhancement of intramolecular charge transfer (ICT) fluorescence. It was synthesized by masking the active phenol group of 2,6-bis(2-vinylbenzothiazolyl)-4-fluorophenol through an acetyl group that acts both as a trigger of the ICT fluorescence and as a recognition moiety for GSH. On its own, the probe HBT-GSH exhibited strong blue fluorescence emission at 426 nm and weak NIR fluorescence emission at 665 nm in aqueous solution, whereas the NIR fluorescence was significantly enhanced and the short emission decreased upon the addition of GSH. Thus an NIR ratiometric fluorescent probe for GSH was developed based on the GSH-selective removal of the acetyl group, therefore switching on the ICT in HBT-GSH. The fluorescence intensity ratio (I_665 nm/I_426 nm) showed a linear relationship with a GSH concentration of 0-100 μM with a detection limit of 0.35 μM. Moreover, the fluorescent probe was successfully used for the ratiometric fluorescence bioimaging of GSH in living cells.

A novel turn-on fluorescent probe for selective sensing and imaging of glutathione in live cells and organisms

A novel 1-oxo-1H-phenalene-2,3-dicarbonitrile (OPD)-based fluorescent probe was developed to sense and image GSH in HeLa cells, different imatinib-resistant K562 cells, D. magna and zebrafish embryos.

Dual-channel fluorescence detection of mercuric (II) and glutathione by down- and up-conversion fluorescence carbon dots

The fluorescent carbon dots (CDs) with high fluorescent quantum yield (φ_f = 62%) and down- and up-conversion fluorescence properties were synthesized by one-pot hydrothermal treatment of citric acid and tris(hydroxymethyl)methyl aminomethane. The CDs displayed the capability to absorb excitation wavelength at 660 nm and 330 nm with fluorescence emission wavelength at 398 nm and 399 nm, respectively. The CDs showed high selectivity towards Hg²⁺ against various metal ions. Around 70% fluorescence was quenched by 40 μM Hg²⁺ through dynamic and static quenching mechanisms. Because of stronger affinity between the thiol and Hg²⁺, over 90% fluorescence was recovered by adding 40 μM glutathione to CDs-Hg²⁺ system. The calibration curves exhibited wide linear region for Hg²⁺ (0-4 μM) and glutathione (0-30 μM). The limits of detection with down- and up-conversion for Hg²⁺ were calculated to be 0.23 μM and 0.25 μM, and for glutathione were 0.28 μM and 0.29 μM, respectively. Inspired by the sensing results, logic gates with Hg²⁺ and glutathione as inputs were also established. Most importantly, this method was applied to detect Hg²⁺ and glutathione in tap water and lake water, and the recovery values were obtained to be 96.2%-110.4% and 93.4%-96.9%.

A Ratiometric Two-Photon Fluorescent Cysteine Probe with Well-Resolved Dual Emissions Based on Intramolecular Charge Transfer-Mediated Two-Photon-FRET Integration Mechanism

The development of an efficient ratiometric two-photon fluorescence imaging probe is crucial for in situ monitoring of biothiol cysteine (Cys) in biosystems, but the current reported intramolecular charge transfer (ICT)-based one suffers from serious overlap between the shifted emission bands. To address this issue, we herein for the first time constructed an ICT-mediated two-photon excited fluorescence resonance energy transfer (TP-FRET) system consisting of a two-photon fluorogen benzo[ h]chromene and a Cys-responsive benzoxadiazole-analogue dye. Different from a previous mechanism that utilized single two-photon fluorogen to acquire a ratiometric signal, ICT was used to switch on the TP-FRET process of the energy transfer dyad by eliciting an absorption shift of benzoxadiazole with Cys to modulate the spectral overlap level between benzo[ h]chromene emission and benzoxadiazole absorption, resulting in two well-separated emission signal changes with large emission wavelength shift (120 nm), fixed two-photon excitation maximum (750 nm), and significant variation in fluorescence ratio (over 36-fold). Therefore, it can be successfully employed to ratiometrically visualize Cys in HeLa cells and liver tissues. Importantly, this new ICT-mediated TP-FRET integration mechanism would be convenient for designing ratiometric two-photon fluorescent probes with two well-resolved emission spectra suitable for high resolution two-photon fluorescence bioimaging.

Fast and Selective Two-Stage Ratiometric Fluorescent Probes for Imaging of Glutathione in Living Cells

Two fluorescent, m-nitrophenol-substituted difluoroboron dipyrromethene dyes have been designed by nucleophilic substitution reaction of 3,5-dichloro-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY). Nonsymmetric and symmetric probes, that is. BODIPY 1 (with one nitrophenol group at the position 3) and BODIPY 2 (with two nitrophenol groups at the positions 3 and 5) were applied to ratiometric fluorescent glutathione detection. The detection is based on the two-step nucleophilic aromatic substitution of the nitrophenol groups of the probes by glutathione in buffer solution containing CTAB. In the first stage, probe 1 showed ratiometric fluorescent color change from green (λ_em = 530 nm) to yellow (λ_em = 561 nm) because of monosubstitution with glutathione (I_561nm/I_530nm). Addition of excess glutathione caused the second stage of ratiometric fluorescent color change from yellow to reddish orange (λ_em = 596 nm, I_596nm/I_561nm) due to disubstitution with glutathione. Therefore, different concentration ranges of glutathione (from less to excess) could be rapidly detected by the two-stage ratiometric fluorescent probe 1 in 5 min. While, probe 2 shows single-stage ratiometric fluorescent detection to GSH (from green to reddish orange, I_596nm/I_535nm). Probes 1 and 2 exhibit excellent properties with sensitive, specific colorimetric response and ratiometric fluorescent response to glutathione over other sulfur nucleophiles. Application to cellular ratiometric fluorescence imaging indicated that the probes were highly responsive to intracellular glutathione.

Live cell monitoring of glycine betaine by FRET-based genetically encoded nanosensor

Glycine betaine (GB) is one of the key compatible solutes that accumulate in the cell at exceedingly high level under the conditions of high salinity. It plays a crucial role in the maintenance of osmolarity of the cell without affecting the physiological processes. Analysis of stress-induced physiological conditions in living cells, therefore, requires real-time monitoring of cellular GB level. Glycine Betaine Optical Sensor (GBOS), a genetically-encoded FRET-based nanosensor developed in this study, allows the real-time monitoring of GB levels inside living cells. This nanosensor has been developed by sandwiching GB binding protein (ProX) between the Förster resonance energy transfer (FRET) pair, the cyan fluorescent protein (CFP) and yellow fluorescent protein (YFP). Conformational change in ProX, which was used as sensory domain, reported the change in the level of this compatible solute in in vitro and in vivo conditions. Binding of the GB to the sensory domain fetches close to both the fluorescent moieties that result in the form of increased FRET ratio. So, any change in the concentration of GB is correlated with change in FRET ratio. This sensor also reported the GB cellular dynamics in real-time in Escherichia coli cells after the addition of its precursor, choline. The GBOS was also expressed in yeast and mammalian cells to monitor the intracellular GB. Therefore, the GBOS represents a unique FRET-based nanosensor which allows the non-invasive ratiometric analysis of the GB in living cells.

Ultrasensitive fluorescent ratio imaging probe for the detection of glutathione ultratrace change in mitochondria of cancer cells

Glutathione (GSH) ultratrace change in mitochondria of cancer cells can mildly and effectively induce cancer cells apoptosis in early stage. Thus, if GSH ultratrace change in mitochondria of cancer cells could be recognized and imaged, it will be beneficial for fundamental research of cancer therapy. There have reported a lot of fluorescent probes for GSH, but the fluorescent probe with ultrasensitivity and high selectivity for the ratio imaging of GSH ultratrace changes in mitochondria of cancer cells is scarce. Herein, based on different reaction mechanism of sulfonamide under different pH, a sulfonamide-based reactive ratiometric fluorescent probe (IQDC-M) was reported for the recognizing and imaging of GSH ultratrace change in mitochondria of cancer cells. The detection limit of IQDC-M for GSH ultratrace change is low to 2.02nM, which is far less than 1.0‰ of endogenic GSH in living cells. And during the recognition process, IQDC-M can emit different fluorescent signals at 520nm and 592nm, which results in it recognizing GSH ultratrace change on ratio mode. More importantly, IQDC-M recognizing GSH ultratrace change specifically occurs in mitochondria of cancer cells because of appropriate water/oil amphipathy (log P) of IQDC-M. So, these make IQDC-M possible to image and monitor GSH ultratrace change in mitochondria during cancer cells apoptosis for the first time.