Indolium Group Research Articles

Evaluation of viscosity in inflammation and ferroptosis process based on a bithiophene-containing hemicyanine dye with diminished solvatochromic effect

To decrease solvatochromic effect and keep a strong selective fluorescence response to the change of viscosity, we have designed and synthesized a novel mitochondria-targetable hemicyanine fluorescence probe BT-In for viscosity detection during inflammation and ferroptosis process. By using high electron-rich bithiophene as a low polar electron donor, and the electron-withdrawing indolium group as electron acceptor as well as mitochondrial targeting group, BT-In shows high selectivity and rapid response for viscosity in vitro and high fluorescence-on signal enhancement at 614 nm with a large Stokes shift of 112 nm. Bioimaging experiments display that the probe has good mitochondrial-targeting ability (Pearson's correlation coefficient 0.99) and high-contrast imaging ability for detecting viscosity in living systems.

Aggregation-Induced Fluorogens in Bio-Detection, Tumor Imaging, and Therapy: A Review

Aggregation-Induced Fluorogens in Bio-Detection, Tumor Imaging, and Therapy: A Review

A ratiometric styryl bridging triphenylamine-indolinium based fluorescent dye for detection of cyanide with a large emission shift in human breast cancer cells and test strips

ABSTRACT A new type of styryl bridging triphenyl amine-indolium conjugated dye has been developed for the colorimetric and ratiometric detection of cyanide. The detection of cyanide is confirmed by means of the fast nucleophilic attack of cyanide by the indolium group of the probe that results a speedy sensing process for cyanide with clear color and fluorescence change of the ICT process. The ratiometric fluorescence changes illustrated a linear response in the range of 0-18 μM with a low LOD value (1.7×10-7 M-1). The as-reported sensor not only function as a colorimetric sensor for “in-the-field” measurement by virtue of a “dip-stick” approach but also interact with a human breast cancer cell (MDA-MB 231) which reveals the realistic value of this probe for tracking cyanide anions in biological systems.

A novel indolium salt as a rapid colorimetric probe for cyanide detection in aqueous solution

In this study, a new chemosensor IDTTH for rapid detection of cyanide (CN─) based on 6,6,12,12-Tetrakis(4-hexylphenyl)-6,12-dihydrodithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]di- thiophene-2,8-dicarboxaldehyde-hemicyanine conjugate has been developed. The 6,6,12,12-tetrakis(4-hexylphenyl)-6,12-dihydrodithi-eno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]dithiophene was served as a signal unit and hemicyanine as a recognition unit. This probe shows high selectivity towards CN─ ions among tested anions. Addition of CN─ ions to probe IDTTH in semi-aqueous solution (acetonitrile/H2O = 1/1, V/V) could lead to a 195 nm blue shift of absorption band, together with colour changes from blue to yellow. The sensing mechanism is attributed to the nucleophilic addition between CN─ and the C=N bond of indolium group, which could be clearly clarified through the 1H NMR titration and MS spectral. Moreover, probe IDTTH could be used as the test strips with low cost to detect CN─ ions conveniently by naked eyes.

Mitochondria-Targeted Polydopamine Nanocomposite with AIE Photosensitizer for Image-Guided Photodynamic and Photothermal Tumor Ablation.

Photodynamic therapy (PDT) and photothermal therapy (PTT) are two kinds of treatment for tumors. Herein, a new aggregation-induced emission (AIE)gen (MeO-TPE-indo, MTi) is synthesized with a D-π-A conjugated structure. MTi, which has an electron donor and an acceptor on a tetraphenylethene (TPE) conjugated skeleton, can induce the effective generation of reactive oxygen species (ROS) for PDT. With the guide of the indolium group, MTi can target and image mitochondrion selectively. In order to get good dispersion in water and long-time retention in tumors, MTi is modified on the surface of polydopamine nanoparticles (PDA NPs) to form the nanocomposite (PDA-MeO-TPE-indo, PMTi) by π-π and hydrogen interactions. PMTi is a nanoscale composite for imaging-guided PDT and PTT in tumor treatment, which is constructed with AIEgens and PDA for the first time. The organic functional molecules are combined with nanomaterials for building a multifunctional diagnosis and treatment platform by utilizing the advantages of both sides.

A novel near-infrared ratiometric fluorescent probe for cyanide and its bioimaging applications.

A new near-infrared ratiometric type fluorescent probe was prepared. 3-formyl BODIPY derivatives without substituent group in the 2, 6-position was obtained through DDQ oxidation reaction. Furthermore, it reacted with indole salt to produce probe. This probe bears indolium group as the recognition site and the 3-formyl-BODIPY as fluorophore. The specific detection of cyanide was conducted the nucleophilic attack of cyanide toward the indolium group of the probe, breaking the intramolecular charge transfer (ICT) effect and generating a ratio change in the fluorescence signal. The probe has high selectivity and sensitivity for cyanide. Moreover, cell experiments indicated this probe was benign to HepG-2 cells, and has the potential application in imaging CN- in living HepG-2 cells.

A red‐emitting indolium fluorescence probe for membranes ‐ flavonoids interactions

The red-emitting indolium derivative compound (E)-2-(4-(diphenylamino)styryl)-1,3,3-trimethyl-3H-indol-1-ium iodide (H3) was demonstrated as a sensitive membrane fluorescence probe. The probe located at the interface of liposomes when mixed showed much fluorescence enhancement by inhibiting the twisted intramolecular charge transfer state. After ultrasonic treatment, it penetrated into lipid bilayers with the emissions leveling off and a rather large encapsulation efficiency (71.4%) in liposomes. The ζ-potential and particle size measurement confirmed that the charged indolium group was embedded deeply into lipid bilayers. The probe was then used to monitor the affinities of antioxidant flavonoids for membranes. It was verified that quercetin easily interacted with liposomes and dissociated the probe from the internal lipid within 60s under the condition of simply mixing. The assessment of binding affinities of six flavonoids and the coincident results with their antioxidation activities indicated that it was a promising membrane probe for the study of drug bio-affinities.

A novel “turn-on” fluorescent probe based on triphenylimidazole-hemicyanine dyad for colorimetric detection of CN− in 100% aqueous solution

A new colorimetric fluorescent probe (MCy) for CN− is designed and synthesized based on triphenylimidazole-hemicyanine dyad. The probe shows high selectivity towards CN− in 100% aqueous solution even in the presence of other competitive anions such as F−, Cl−, AcO−, NO2−, H2PO4−, I−, SCN−, SO42−, NO3−, HCO3−, Br− and S2−. Upon nucleophilic addition of CN− to the indolium group, the probe displays large blue-shift in UV–vis spectrum and remarkable “turn-on” fluorescence owing to the disruption of intramolecular charge transfer. Meanwhile, the probe also undergoes a naked-eye discernible color change from orange to light pink in the sunlight as well as an obvious fluorescence color change from non-emissive to bright blue under a UV lamp. The detection limit of CN− in aqueous solution can be as low as 20.6nM, which is much lower than the permissible level of CN− in drinking water according to the WHO. In addition, the probe has been successfully used to determine CN− in real water samples as well as to fabricate test paper kit for CN− detection.

A novel turn-on fluorescent probe for cyanide detection in aqueous media based on a BODIPY-hemicyanine conjugate

Abstract A novel BODIPY-hemicyanine based fluorescent probe 1 for cyanide (CN − ) detection was designed and synthesized. Among the tested anions, the probe showed high selectivity towards CN − . Only addition of CN − to probe 1 in aqueous solution (V H2O /V EtOH = 1/1) could result in a remarkable blue shift of the absorption band from 385 nm to 265 nm and induce 20-fold fluorescence enhancement at 515 nm. The sensing mechanism was based on nucleophilic addition between CN − and indolium group, which was confirmed by 1 H NMR and mass spectrum analysis. Plot of fluorescence intensity as a function of CN − concentrations exhibited a good linear relationship in the range of 0–10 μM, with a detection limit to be 1.53 ppb. Moreover, the proposed sensing approach could work in a wide pH range from 5.0–9.0 and reach an equilibrium instantaneously. Finally, probe 1 was successfully applied in detection of CN − in natural water samples and on test paper strips with satisfactory results.

A novel indolium salt as a highly sensitive and selective fluorescent sensor for cyanide detection in water

A highly sensitive fluorescent turn-on cyanide probe is developed based on benzylidenes containing methylindolium group. Three benzylidene derivatives were synthesized from the condensations of three benzaldehyde derivatives and methyleneindoline. Only one of these three derivatives shows strong blue fluorescent response selectively to CN− which can be clearly observed in submicromolar range as the result of the cyanide addition to the indolium group. The detection of cyanide with this compound is optimized in aqueous media using non-ionic surfactant and sonication method to give very low limit of detection in subnanomolar range. The probe is also developed into a paper-based and gel-based sensing kits that can readily detect cyanide ion in micromolar range by naked eye under a common black light (360nm) illumination.

Two novel CN[sbnd] turn on fluorescent imaging materials with twin binding groups

In this work two novel fluorescent imaging materials for CN with twin binding groups (1 and 2) have been synthesized and fully characterized by standard analytical tools and spectroscopic techniques. The selectivity of 1 and 2 has been explored in aqueous solution, and the resulting turn-on fluorescence response toward CN among different anions was studied. The cyanide ion adduct was characterized using NMR and mass spectroscopy and detection mechanism was further confirmed to be the nucleophilic attack of the indolium group of probe by CN, which induces a turn-on fluorescence change. NMR and mass spectra indicate nucleophilic addition of CN to indolium group is reversible in ionization process. For the practical application of the sensors, 1 could be used for fluorescence-microscopic imaging of CN in biological applications.

Dual-Modal Colorimetric/Fluorescence Molecular Probe for Ratiometric Sensing of pH and Its Application.

As traditional pH meters cannot work well for minute regions (such as subcellular organelles) and in harsh media, molecular pH-sensitive devices for monitoring pH changes in diverse local heterogeneous environments are urgently needed. Here, we report a new dual-modal colorimetric/fluorescence merocyanine-based molecular probe (CPH) for ratiometric sensing of pH. Compared with previously reported pH probes, CPH bearing the benzyl group at the nitrogen position of the indolium group and the phenol, which is used as the acceptor for proton, could respond to pH changes immediately through both the ratiometric fluorescence signal readout and naked-eye colorimetric observation. The sensing process was highly stable and reversible. Most importantly, the suitable pKa value (6.44) allows CPH to presumably accumulate in lysosomes and become a lysosome-target fluorescent probe. By using CPH, the intralysosomal pH fluctuation stimulated by antimalaria drug chloroquine was successfully tracked in live cells through the ratiometric fluorescence images. Additionally, CPH could be immobilized on test papers, which exhibited a rapid and reversible colorimetric response to acid/base vapor through the naked-eye colorimetric analysis. This proof-of-concept study presents the potential application of CPH as a molecular tool for monitoring intralysosomal pH fluctuation in live cells, as well as paves the way for developing the economic, reusable, and fast-response optical pH meters for colorimetric sensing acid/base vapor with direct naked-eye observation.

A ratiometric fluorescence probe for monitoring cyanide ion in live cells

A ratiometric emission fluorescent probe 1,1-dimethyl-3-ethyl-2-(2-(N-ethyl-carbazol-3-yl)-vinyl)-1H-benzo[e]indolium iodide (Probe) is facilely synthesized via the ethylene bridging of N-ethylcarbazole-3-formaldehyde and 1,1,2-trimethyl-3-ethyl-1H-benz[e]indolium iodide, which is a useful fluorescent probe for monitoring cyanide ion at extremely low concentrations, quantitatively. The detection of cyanide is performed via the nucleophilic attack of cyanide toward the benzo[e]indolium group of the probe, resulting in a prominent fluorescence ratiometric change and a color change. The titration experiments for CN− show that it exhibits a large Stokes shift (92nm), high selectivity, excellent sensitivity and good stability for CN− sensing in DMSO system. The detection limit of Probe for CN− is found to be 0.23μM. Furthermore, the probe has excellent cell membrane permeability and is applied successfully to rapidly detect CN− in living cells.

Theoretical study on fluorescent probes for cyanide based on the indolium functional group

A series of fluorescent probes were investigated to explore the mechanism of the detection for CN−, and all of the probes have an indolium group. The interaction between the functional group and the cyanide ion was simulated to examine the selectivity of these probes. The influences of some other anions were also tested in the cyanide detecting process. The different binding abilities between CN− and F− in aqueous solution were distinguished using the potential energy calculations in consideration of hydrogen bonding interactions. The large change of the emitting wavelengths of the fluorescent probes before and after the addition of CN− was explained through the analysis of the molecular orbital properties. The results indicate the large structural change results in a significant emission shift when each probe captures a cyanide ion. According to this conclusion, new fluorescent probes were designed.

A novel reaction-based colorimetric and ratiometric fluorescent sensor for cyanide anion with a large emission shift and high selectivity

A hybrid carbazole-hemicyanine dye (Cac) has been developed as a novel colorimetric and ratiometric fluorescent sensor for cyanide detection. Upon treatment with cyanide, Cac displayed a remarkable fluorescence ratiometric response, with the emission wavelength displaying a very large emission shift (214nm). The detection of cyanide was performed via the nucleophilic addition of cyanide anion to the indolium group of the sensor, which resulted in the blocking of the intramolecular charge transfer (ICT) process in the sensor, inducing a ratiometric fluorescence change and simultaneously an obvious color change. Furthermore, competitive anions did not showed any significant changes both in color and emission intensity ratio (I381/I595), indicating the high selectivity of the sensor to CN−.

Red turn-on fluorescent phenazine-cyanine chemodosimeters for cyanide anion in aqueous solution and its application for cell imaging

Two chemodosimeters PDMI and PMI for cyanide detection were designed and synthesized based on phenazine-cyanine dyes with N-methyl indolium group as receptor unit. According to the specific reactivity of indolium CN+ bond against cyanide anion, both of them featured high sensitivity with detection limit of 1.4μM and 200nM, respectively, and high selectivity against other anions. The quenching effect on phenazine-cyanine fluorophore by strong intramolecular charge transfer (ICT) from phenazine donor to indolium receptor made both PDMI and PMI non-emissive at the original state. After addition of cyanide, the ICT effect decreased and vanished leading to dramatic “off–on” fluorescence enhancement. PDMI which proceeded bilateral electrophilic reaction toward cyanide anion provided an emission signal at 580nm in HEPES buffer with naked-eye detectable color change. Probe PMI utilized an unreactive formyl group instead of one reactive N-methyl indolium group as the electron-withdrawing component. Due to the unilateral recognition process for cyanide the ICT orientation of PMI was redirected thus exhibited fluorescence enhancement with maximum emission at 630nm. Meanwhile, PMI was applied for monitoring intracellular cyanide in Hela cells and proved to achieve “off–on” fluorescent signal confirmed by confocal laser scanning microscopic imaging.

A new highly selective and turn-on fluorescence probe for detection of cyanide

A new compound was conveniently synthesized via the condensation of 2-hydroxy-1,3,5-benzenetricarbaldehyde (1) with 1-methyl-2,3,3-trimethyl-3H-indolium (2) in ethanol. Its recognition ability was firstly carried out in DMSO. After addition of all kinds of anions, only CN− can induce a turn on fluorescence accompanying a blue-green fluorescence color. The mechanism is based on nucleophilic addition reaction of cyanide anion with the polarized CN bond of the indolium group blocking the π-conjugation between indolium and 2-hydroxy-1,3,5-benzenetricarbaldehyde, which was proved by H NMR and ESI-MS. In addition, the detection was completed with 2min and the detection limit was found to be 45nmol/L.

A Fluorescent Turn-On Probe Based on Benzo [E] Indolium for Cyanide Ion in Water With High Selectivity

A highly selective fluorescent turn-on probe for CN(-) bearing a benzo [e] indolium group as a fluorophore and binding site was reported. The detection of CN(-) was performed via the nucleophilic attack of CN(-) toward the benzo [e] indolium group of the probe, resulting in a prominent fluorescence enhancement and an obvious color change. The probe shown a highly selectivity in water and could be performed in a range of pH value between 6 and 9. The detection limit was 4.6 × 10(-8) M, which could be detected CN(-) in drinking water. A simple paper test strip system for the rapid monitoring of CN(-) was developed.

A ratiometric fluorescent probe based on benzo [e] indolium for cyanide ion in water

A new ratiometric fluorescent cyanide probe bearing a benzo [e] indolium moiety as a fluorophore and binding site was developed. The detection of cyanide was performed via the nucleophilic attack of cyanide toward the benzo [e] indolium group of the probe, resulting in a prominent fluorescence ratiometric change and a color change. The probe was invested in water with high selectivity and sensitivity for cyanide. A simple paper test strip system for the rapid monitoring of cyanide was developed.

A highly selective fluorescence turn-on detection of cyanide based on the aggregation of tetraphenylethylene molecules induced by chemical reaction

A new selective and sensitive fluorescence turn-on detection of CN(-) is reported by taking advantage of aggregation induced-emission (AIE) behavior of tetraphenylethylene units and the nucleophilic attack of CN(-) on the indolium group in compound 1.