Colorimetric and Ratiometric Fluorescent Chemosensor Based on Diketopyrrolopyrrole for Selective Detection of Thiols: An Experimental and Theoretical Study

A sensitive zinc probe operating via enhancement of excited-state intramolecular charge transfer

Novel highly sensitive fluorescent probes for zinc cations based on the diketopyrrolopyrrole scaffold were designed and synthesized. Large bathochromic shifts (≈80 nm) of fluorescence are observed when the Zn²⁺-recognition unit (di-(2-picolyl)amine) is bridged with the fluorophore possessing an additional pyridine unit able to participate in the coordination process. This effect originates from the dipolar architecture and the increasing electron-withdrawing properties of the diketopyrrolopyrrole core upon addition of the cation. The new, greenish-yellow emitting probes, which operate via modulation of intramolecular charge transfer, are very sensitive to the presence of Zn²⁺. Introduction of a morpholine unit in the diketopyrrolopyrrole structure induces a selective six-fold increase of the emission intensity upon zinc coordination. Importantly, the presence of other divalent biologically relevant metal cations has negligible effects and typically even at a 100-fold higher concentration of Mg²⁺/Zn²⁺, the effect is comparable. Computational studies rationalize the strong bathochromic shift upon Zn²⁺-complexation. Decorating the probes with the triphenylphosphonium cation and morpholine unit enables selective localization in the mitochondria and the lysosome of cardiac H9C2 cells, respectively.

Synthesis of polysubstituted pyrroles via isocyanide-based multicomponent reactions as an efficient synthesis tool

The present review covers all synthetic methods based on isocyanide-based multicomponent reactions for the preparation of polysubstituted pyrroles as the parent cores of many essential drugs, biologically active compounds, and compounds with wide application in materials science.

Simply Structured Conjugated Compounds with Cyanoacrylate or Acrylonitrile Groups for Sensing of p-Toluenethiol

Simply structured conjugated compounds with cyanoacrylate (CA 1 - 4) and acrylonitrile (AN 1 - 4) terminal groups were synthesized by a Knoevenagel condensation reaction in one step and investigated for their recognition properties to p-toluenethiol by UV-vis, fluorescence spectra, and FT-IR measurements. When p-toluenethiol was added to CA 1, the FT-IR spectra revealed a cleavage of alkene caused by the addition reaction between p-toluenethiol and CA 1. An increase in p-toluenethiol concentration, a blue-shifted absorption band, and a decrease in the fluorescence intensity of CA 1 were observed because of the decrease in its effective conjugated length. Therefore, the most simply structured CA 1 was found to be the most effective and the most sensitive chemical sensor for p-toluenethiol.

A colorimetric and fluorescent chemosensor based on diarylethene for simultaneous detection and discrimination of biothiols

In this work, a novel probe D-HBT-NBD (1O) based on diarylethene to detect biothiols (including Cys, Hcy and GSH) was synthesized and the relative colorimetric and fluorescent properties were tested. The probe exhibited excellent photochromic properties and showed apparent colorimetric and fluorescent signals for Cys, Hcy and GSH. The probe can selectively detect Cys, Hcy and GSH by naked eyes for its open-ring isomer 1O and can discriminate Cys from Hcy/GSH by apparent color change from light orange to dark pink at the closed-ring state under the irradiation of UV light. At the excitation wavelength of 465 nm, the probe could be used to discriminate GSH from Cys/Hcy with no fluorescent emission at 570 nm. Taking advantage of the photochromic property of the diarylethene moiety and the different fluorescent properties of NBD derivatives of GSH and Cys/Hcy, 1O could be used as a novel probe to discriminate Cys, Hcy and GSH from each other simultaneously. Meanwhile, a logic gate was constructed based on the colorimetric and fluorescent properties of 1O.

Novel Diketopyrrolopyrrole-Based π-Conjugated Molecules Synthesized Via One-Pot Direct Arylation Reaction

Diketopyrrolopyrrole (DPP) is an important type of π-conjugated building block for high-performance organic electronic materials. DPP-based conjugated materials are usually synthesized via Suzuki, Stille, or Negishi cross-coupling reactions, which require organometallic precursors. In this paper, a series of novel phenyl-cored DPP molecules, including five meta-phenyl-cored molecules and four para-phenyl-cored molecules, have been synthesized in moderate to good yields, in a facile manner, through the Pd-catalyzed direct arylation of C–H bonds, and their optoelectrical properties have been investigated in detail. All new molecules have been fully characterized by NMR, MALDI-TOF MS, elemental analysis, UV–visible spectroscopy, and cyclic voltammetry. This synthetic strategy has evident advantages of atom- and step-economy and low cost, compared with traditional cross-coupling reactions.

A two-photon ratiometric fluorescent probe for highly selective sensing of mitochondrial cysteine in live cells

We report herein a two-photon ratiometric fluorescent probe (DNEPI) for mitochondrial cysteine (Cys) detection on the basis of a merocyanine (compound 1) as the two-photon fluorophore and a 2,4-dinitrobenzensulfonyl (DNBS) unit as the biothiol reaction site. Upon reaction with Cys in DMSO/PBS (1/1, v/v), DNEPI showed a distinct ratiometric fluorescence emission characteristic (F_{583 nm}/F_{485 nm}) linearly proportional to Cys concentrations over the range of 2-10 μM, which was attribute to the enhanced intramolecular charge transfer (ICT) effect by cleavage of the sulfonic acid ester bond of DNEPI to release compound 1. More importantly, the probe could detect Cys with a fast response time (within 2 min) and the detection limit was quantitatively calculated as 0.29 μM. Furthermore, DNEPI not only exhibited high selectivity toward Cys over other similar biothiols, including homocysteine (Hcy) and glutathione (GSH), but also displayed significant mitochondrial-targeting ability, which were favorable for mitochondrial Cys-selective imaging. Subsequently, application of DNEPI to Cys imaging in live cells was successfully achieved by two-photon fluorescence microscopy, suggesting that the probe proposed here could be used to monitor mitochondrial Cys concentration changes in live cells with negligible interference from other biological thiols.

Near Infrared Boron Dipyrromethene Nanoparticles for Optotheranostics

Boron dipyrromethene (BODIPY) is a class of important emerging fluorescent dyes. Due to their unique chemical and optical properties, near infrared (NIR)-emitting BODIPY dyes containing nanoparticles have recently been developed for a wide array of cutting-edge cancer optotheranostic applications. These nanoparticles not only have robust photostability and tunable photophysical properties, but they can also be flexibly tailored to a multitude of functional uses. Based on these outstanding characteristics, such nanoparticles have shown great promise in diagnosis as biological sensors, as well as in their utilization in advanced imaging and photomedicine for cancer treatment. In particular, here, this study first discusses their use as photoswitchable fluorescence probes toward in vitro single-molecule imaging. Second, this study takes a look at their opportunities for photoacoustic imaging utilization. Third, approaches are discussed to construct new NIR-absorbing BODIPY nanoparticles for photodynamic therapy (PDT). Fourth, this study delves into the new approach to use such nanoparticles as an emerging version of triplet-triplet annihilation upconversion (TTA-UC) and their biological uses, such as their photoactivation prodrug therapy (PAPT) for cancer. Finally, new biological sensors based on NIR BODIPY nanoparticles are introduced.

Quinoline-derived fluorescent probes for the discrimination of Cys from Hcys/GSH and bioimaging in living cells

Development of thiol-specific fluorescent probes with selectivity in different thiol compounds is more practical and significant than those without that capacity. In this work, a new quinoline-derived fluorophore, hydroxyl-substituted quinoline-benzo[d]oxazole 6 with high fluorescence quantum yield is synthesized and esterified with acrylic acid to afford two fluorescent probes, BQA-1 and BQA-2 for selectively discriminating Cys from Hcys/GSH based on conjugate addition-cyclization mechanism. BQA-1 exhibits a large ratiometric fluorescence response toward Cys in aqueous pH 7.4 solution with big emission peak-shifting from 383 nm to 518 nm, over 130 nm. The detection limit is determined to be as low as 0.59 μM. In contrast to BQA-1, BQA-2 whose acrylic ester moiety is further modified with pyridine group, displays a turn-on fluorescence response to Cys with detection limit of 0.98 μM. Both BQA-1 and BQA-2 have relatively weak response to another two biothiols, Hcys and GSH and nearly no response to other nucleophiles. Furthermore, the potential application for the detection of biothiols in living cells has been demonstrated by cell imaging experiment.

Design and Characterization of Dicyanovinyl Reactive Dyes for the Colorimetric Detection of Thiols and Biogenic Amines

The synthesis of two new azobenzene dyes, namely CR-528 and CR-555, and their spectral properties in ethanol solution are described. The recognition of sulfur-containing analytes (2-mercaptoethanol (2-ME), sodium hydrosulfide (NaHS)), and biogenic amines (spermine, spermidine, ethanolamine) bestowed significant spectral changes with color changes from pink/purple to pale yellow/orange-yellow. The nitro acceptor group in the dicyanovinyl reactive dye contributes to higher sensitivity and lower detected analyte concentrations. The absorption maxima of both the dyes are at wavelengths compatible with low-cost light sources and detectors, making them excellent candidates for optical probes that are economic, simple to use, and do not require well-trained personnel.

Protein-induced fluorescence enhancement of two-photon excitable water-soluble diketopyrrolopyrroles

Fluorescent contrast agents are important tools in cell biology and medical imaging due to their high sensitivity and relative availability. Diketopyrrolopyrrole (DPP) derivatives have been recently studied for applications in bioimaging, but certain drawbacks due to their inherent structure have stifled progress towards their widespread implementation. Aggregation caused quenching (ACQ) associated with π-π stacking in relatively rigid extended conjugation systems as well as hydrophobicity of previously reported DPPs make most unsuitable for biological imaging applications. Addressing these deficiencies, we report the synthesis and photophysical characterization of two new water-soluble diketopyrrolopyrole (DPP) probes that exhibit pronounced protein-induced fluorescence enhancement (PIFE) upon binding serum albumin protein. In vitro studies were also performed showing low cytotoxicity for the new DPP probes. Two-photon fluorescence microscopy (2PFM) images were obtained via excitation at 810 nm and emission in the NIR window of biological transparency, illustrating the potential of these compounds as nonlinear optical bioimaging probes.

Fine Regulation of Porous Architectures of Core-Shell Silica Nanocomposites Offers Robust Nanoprobes with Accelerated Responsiveness

Probes bearing good aqueous solubility and biocompatibility as well as fast response can serve as ideal tools for evaluating the underlying molecular mechanism of endogenous production of H₂S caused by drugs; however, they are still lacking but highly desirable. Here, we demonstrate a novel strategy for constructing highly efficient H₂S nanoprobes through locking Förster resonance energy transfer borondipyrromethene (BODIPY) pairs in water-dispersible core-shell silica nanoparticles. Importantly, these nanocomposites can effectively confine complementary guests within the same cores due to the existence of a shield, thus guaranteeing efficient Förster resonance energy transfer. Interestingly, the interior microenvironment of such nanoparticles could be tuned by silylation agents. In this way, an ideal probe for rapid and ratiometric detection of H₂S within 15 s is established by optimizing the amount of silylation agent with a polar organic group. Obviously, the silylation agents are explored to serve as a platform not only for establishment of robust structures but also for optimizing the microenvironment of the interior to afford an ideal probe. These silica nanocomposites have also been successfully employed in disclosing the endogenous production of H₂S induced by estrogen in cardiomyocytes.

Oligo(p-phenylene ethynylene) with Cyanoacrylate Terminal Groups and Graphene Composite as Fluorescent Chemical Sensor for Cysteine

A chemical sensor for cysteine (Cys) was fabricated based on a fluorescent oligo(p-phenylene ethynylene)s (OPEs) and OPE-graphene oxide (GO) composite. OPE with cyanoacrylate terminal groups were synthesized by a Pd-catalyzed Sonogashira coupling reaction and Knoevenagel condensation for use as a chemical sensor for Cys. The optical properties and Cys sensing capability of the cyanoacrylate modified OPE and OPE-GO composite were investigated. In addition of Cys, the fluorescence of OPE was blue-shifted and decreased (fluorescence turn-off), while the fluorescence of the OPE-GO composite was enhanced (fluorescence turn-on). Thus, OPE with cyanoacrylate terminal groups and OPE-GO composite acts a highly sensitive fluorescent chemical sensor for Cys.

An excited state intramolecular proton transfer dye based fluorescence turn-on probe for fast detection of thiols and its applications in bioimaging

In this study, a new fluorescent probe 2-(2'-hydroxy-5'-N-maleimide phenyl)-benzothiazole (probe 1), was designed and synthesized by linking the excited state intramolecular proton transfer (ESIPT) fluorophore to the maleimide group for selective detection of thiols in aqueous solution. The fluorescence of probe 1 is strongly quenched by maleimide group through the photo-induced electron transfer (PET) mechanism, but after reaction with thiol, the fluorescence of ESIPT fluorophore is restored, affording a large Stokes shifts. Upon addition of cysteine (Cys), probe 1 exhibited a fast response time (complete within 30s) and a high signal-to-noise ratio (up to 23-fold). It showed a high selectivity and excellent sensitivity to thiols over other relevant biological species, with a detection limit of 3.78×10^-8M (S/N=3). Moreover, the probe was successfully applied to the imaging of thiols in living cells.

A new fluorescence turn-on probe for biothiols based on photoinduced electron transfer and its application in living cells

A new biothiol-selective fluorescent probe 1 based on photoinduced electron transfer (PET) mechanism was designed and synthesized. The UV-Vis absorption and fluorescent emission properties of probe 1 towards various analytes were studied in detail. The probe exhibited a large stokes shift (~200nm) after reacted with biothiols and could selectively detect cysteine (Cys) in dimethyl sulfoxide (DMSO)/H2O solution (9:1, v/v, 10mM phosphate buffer saline, pH3.5) over glutathione (GSH), homocysteine (Hcy) and other analytes with a detection limit of 0.117μM. In addition, probe 1 responded well to GSH, Hcy and Cys in the same above solution with pH5.5 and got the detection limits of 0.151μM, 0.128μM and 0.037μM, respectively. Probe 1 was of very low cytotoxicity and successfully applied for imaging of thiols in living cells.

An ultrafast turn-on thiol probe for protein labeling and bioimaging

A novel ultrafast turn-on thiol probe was developed that can be successfully applied to label protein thiols and imaging them in living cells.

Facile rhodamine-based colorimetric sensors for sequential detections of Cu(ii) ions and pyrophosphate (P2O74−) anions

Two rhodamine hydrazine derivatives Rh1 and Rh2 with catechol and ether functionalities have been synthesized and utilized towards sequential colorimetric detections of Cu(ii) and pyrophosphate (PPi) ions in a semi-aqueous medium.

Coupling a DNA–ligand ensemble with Ag cluster formation for the label-free and ratiometric detection of intracellular biothiols

A smart nanoprobe was constructed by coupling a DNA–ligand ensemble with Ag cluster formation for the ratiometric detection of intracellular biothiols.

Tetraphenylethene-functionalized diketopyrrolopyrrole solid state emissive molecules: enhanced emission in the solid state and as a fluorescent probe for cyanide detection

Tetraphenylethene-functionalized diketopyrrolopyrrole solid state red-emissive molecules (DPP1andDPP2) with enhanced emission in the solid state have been developed.

Highly selective colorimetric and fluorescent BODIPY dyes for sensing of cysteine and/or homocysteine

Selective “naked eye” and fluorescent sensing of biothiols by visible-light excitable α- and β-formyl BODIPYs1and3was developed.

A cyanide-selective colorimetric “naked-eye” and fluorescent chemosensor based on a diketopyrrolopyrrole–hydrazone conjugate and its use for the design of a molecular-scale logic device

A novel diketopyrrolopyrrole (DPP)–hydrazone based receptor was designed and synthesized as a selective fluorescent and colorimetric chemosensor for cyanide in aqueous media via deprotonation between the hydrazide moiety of the probe and cyanide.

Preparation of a conjugation-ready thiol responsive molecular switch

In this work we synthesize molecular switches that are responsive to cysteine, homocysteine, and glutathione; three redox systems that make up the majority of the body's antioxidant defenses. Synthesized spiropyran isomers with conjugation-ready linkages showed good selectivity of response to these major antioxidant thiols over nucleophilic amino acids; however the position of the linking group can affect selectivity and reversibility of the switching response. An isomer with selectivity for cysteine against GSH and Hcy was identified.

Selective Fluorescence Detection of Cysteine over Homocysteine and Glutathione Based on a Cysteine-Triggered Dual Michael Addition/Retro-aza-aldol Cascade Reaction

In this work, a cysteine (Cys)-triggered dual Michael addition/retro-aza-aldol cascade reaction has been exploited and utilized to construct a fluorescent probe for Cys for the first time. The resulting fluorescent probe 8-alkynylBodipy 1 contains an activated alkynyl unit as Michael receptor and a Bodipy dye as fluorescence reporter and can highly selectively detect Cys over homocysteine (Hcy)/glutathione (GSH) as well as other amino acids with a significant fluorescence off-on response (∼4500-fold) and an ultralow detection limit (0.38 nM). The high selectivity of 1 for Cys could be attributed to a kinetically favored five-membered cyclic intermediate produced by the dual Michael addition of Cys with the activated alkynyl unit of 1. The big fluorescence off-on response is due to the subsequent retro-aza-aldol reaction of the five-membered cyclic intermediate that results in the release of a highly fluorescent 8-methylBodipy dye 2. The probe has been successfully used to detect and image Cys in serum and cells, respectively.

A Comparative Analysis of Acyl-Homoserine Lactone Synthase Assays

Quorum sensing is cell-to-cell communication that allows bacteria to coordinate attacks on their hosts by inducing virulent gene expression, biofilm production, and other cellular functions, including antibiotic resistance. AHL synthase enzymes synthesize N-acyl-l-homoserine lactones, commonly referred to as autoinducers, to facilitate quorum sensing in Gram-negative bacteria. Studying the synthases, however, has proven to be a difficult road. Two assays, including a radiolabeled assay and a colorimetric (DCPIP) assay are well-documented in literature to study AHL synthases. In this paper, we describe additional methods that include an HPLC-based, C-S bond cleavage and coupled assays to investigate this class of enzymes. In addition, we compare and contrast each assay for both acyl-CoA- and acyl-ACP-utilizing synthases. The expanded toolkit described in this study should facilitate mechanistic studies on quorum sensing signal synthases and expedite discovery of antivirulent compounds.

A new diketopyrrolopyrrole-based probe for sensitive and selective detection of sulfite in aqueous solution

A new probe was synthesized by incorporating an α,β-unsaturated ketone to a diketopyrrolopyrrole fluorophore. The probe had exhibited a selective and sensitive response to the sulfite against other thirteen anions and biothiols (Cys, Hcy and GSH), through the nucleophilic addition of sulfite to the alkene of probe with the detection limit of 0.1 μM in HEPES (10 mM, pH 7.4) THF/H2O (1:1, v/v). Meanwhile, it could be easily observed that the probe for sulfite changed from pink to colorless by the naked eye, and from pink to blue under UV lamp after the sulfite was added for 20 min. The NMR and Mass spectral analysis demonstrated the expected addition of sulfite to the C=C bonds.

A colorimetric probe based on diketopyrrolopyrrole and tert-butyl cyanoacetate for cyanide detection

A new colorimetric probe 1 comprising a diketopyrrolopyrrole-based Michael receptor, which recognized cyanide anions with high selectivity, was designed and synthesized.

Constructing a FRET-based molecular chemodosimeter for cysteine over homocysteine and glutathione by naphthalimide and phenazine derivatives

A chemodosimeter PHSN achieved turn-on fluorescence enhancement at 540 nm and discrimination of cysteine from homocysteine and glutathione in Hela cells.

Colorimetric and fluorogenic signalling of fluoride ions by diketopyrrolopyrrole-based chemosensor

A new colorimetric and on–off fluorescence sensor based on diketopyrrolopyrrole (DPP) was synthesized for detection of fluoride anion.

Diketopyrrolopyrrole: brilliant red pigment dye-based fluorescent probes and their applications

The review summarizes the recent development of various DPP-based fluorescent probes for tracing biologically and environmentally important species.

A solution processable fluorene-fluorenone oligomer with aggregation induced emission enhancement

Herein, we report a novel solution processable fluorenone based small molecule with an Aggregation Induced Emission Enhancement (AIEE) property. In contrast to previous reports, the presence of the fluorenone moiety in FF triggers the AIEE property.

Pyrene and diketopyrrolopyrrole-based oligomers synthesized via direct arylation for OSC applications

In this report, an atom efficient and facile synthetic strategy for accessing multi-diketopyrrolopyrrole (DPP)-based oligomers used in solution-processed organic field effect transistors (OFETs) and organic solar cells (OSCs) has been developed. The DPP units were successfully installed onto benzene and pyrene cores via palladium-catalyzed dehydrohalogenative coupling of mono-capped DPPs with multi-bromo-benzene or -pyrene (direct arylation), affording four oligomer small molecules (SMs 1-4) containing bis-, tri-, tri-, and tetra-DPP, respectively, in high yields of 78-96%. All the designed linear or branched DPP-based oligomers exhibit broad light absorptions, narrow band-gaps (1.60-1.73 eV), deep highest occupied molecular orbital (HOMO) levels (-5.26∼-5.18 eV), and good thermal stability (Td=390-401 °C). OFETs based on SMs 1-4 showed hole mobilities of 0.0033, 0.0056, 0.0005, and 0.0026 cm2 V(-1) s(-1), respectively. OSCs based on SMs 1-4 under one sun achieved power conversion efficiencies of 3.00%, 3.71%, 2.47%, and 1.86% accordingly, along with high open-circuit voltages of 0.86-0.94 V. For OSC devices of SM 1, SM 3, and SM 4, the solvent CHCl3 was solely employed to the formation of active layers; neither high boiling point additives nor annealing post-treatment was needed. Such a simple process benefits the large-scale production of OSCs via roll to roll technology.

Sensitive and regenerable organochalcogen probes for the colorimetric detection of thiols

Isothiazolone and isoselenazolone based colorimetric probes for the detection of thiols have been reported. A regenerable probe for the detection of organothiols is developed from isoselenazolone. Both of these probes possess higher selectivity for aromatic thiols, cysteine and glutathione.

Supramolecular analyte recognition: experiment and theory interplay

Synergy of experimental and theoretical tools has made significant impact in the assessment of supramolecular recognition of analytes of relevance to biology and the environment.

A colorimetric and ratiometric fluorescent probe for distinguishing cysteine from biothiols in water and living cells

A highly selective merocyanine-based fluorescent probe was developed, which can significantly distinguish Cys from Hcy and GSH by their kinetic profiles in water and respond to the intracellular Cys.