A tetraphenylethene-based zinc complex as a sensitive DNA probe by coordination interaction

A series of DNA targeted Cu (II) complexes containing 1,8-naphthalimide ligands: Synthesis, characterization and in vitro anticancer activity

Copper(II) complexes are very promising candidates for platinum-based anticancer agents. Herein, three Cu (II) complexes (1-3) containing 1,8-naphthalimide ligands were synthesized and characterized by FT-IR, elemental analysis, ESI-MS and single crystal X-ray diffraction (complex 3). In addition, a control compound (complex 4) without 1,8-naphthalimide ligand was synthesized and characterized. The in vitro anticancer activity of the synthesized complexes against five cancer cell lines and one normal cell line was evaluated by MTS assay. The results displayed the antitumor activity of complexes 1-3 was controlled by the aliphatic chain length of ligands, their cytotoxicity was in the order 3 > 2 > 1, giving the IC50 values ranging from 2.874 ± 0.155 μM to 31.47 ± 0.29 μM against five cancer cell lines. Complex 4 showed less activity in comparison with complex 1-3. Notably, complexes 1-3 displayed much higher selectivity (SI = 2.65 to 10.16) compared to complex 4 (SI = 1.0), indicated that the introduction of 1,8-naphthalimide group not only increased the activity of this series of compounds but also enhanced their specific selectivity to cancer cells. Compound 3 induced apoptosis in cancer cells and blocked the S-phase and G2/M of cancer cells. The interaction with DNA of complexes 3 and 4 was studied by UV/Vis spectroscopic titrations, competitive DNA-binding experiment, viscometry and CD spectra. The results showed that complex 3 interacted with DNA in an intercalating mode, but the interaction mode of compound 4 with DNA was electrostatic interaction.

Surfactant-based supramolecular dye assembly: A highly selective and economically viable platform for quantification of heparin antidote

Herein, we have employed a supramolecular assembly of a cationic dye, LDS-698 and a common surfactant sodium dodecyl sulfate (SDS) as a turn-on fluorescent sensor for protamine (Pr) detection. Addition of cationic Pr to the solution of dye-surfactant complex brings negatively charged SDS molecules together through strong electrostatic interaction, assisting aggregation of SDS way before its critical micellar concentration (CMC). These aggregates encapsulate the dye molecules within their hydrophobic region, arresting non-radiative decay channels of the excited dye. Thus, the LDS-698•SDS assembly displays substantial enhancement in fluorescence intensity that follows a nice linear trend with Pr concentration, providing limit of detection (LOD) for Pr as low as 3.84(±0.11) nM in buffer, 124.4(±6.7) nM in 1% human serum and 28.3(±0.5) nM in 100% human urine. Furthermore, high selectivity, low background signal, large stokes shift, and emission in the biologically favorable deep-red region make the studied assembly a promising platform for Pr sensing. As of our knowledge it is the first ever Pr sensory platform, using a very common surfactant (SDS), which is economically affordable and very easily available in the market. This innovative approach can replace the expensive, exotic and specialized chemicals considered for the purpose and thus showcase its potential in practical applications.

Interactions of Amino Group Functionalized Tetraphenylvinyl and DNA: A Label-Free "On-Off-On" Fluorescent Aptamer Sensor toward Ampicillin

As a type of aggregation-induced emission (AIE) fluorescent probe, tetraphenylvinyl (TPE) or its derivatives are widely used in chemical imaging, biosensing and medical diagnosis. However, most studies have focused on molecular modification and functionalization of AIE to enhance the fluorescence emission intensity. There are few studies on the interaction between aggregation-induced emission luminogens (AIEgens) and nucleic acids, which was investigated in this paper. Experimental results showed the formation of a complex of AIE/DNA, leading to the quenching of the fluorescence of AIE molecules. Fluorescent test experiments with different temperatures proved that the quenching type was static quenching. The quenching constants, binding constants and thermodynamic parameters demonstrated that electrostatic and hydrophobic interactions promoted the binding process. Then, a label-free "on-off-on" fluorescent aptamer sensor for the detection of ampicillin (AMP) was constructed based on the interaction between the AIE probe and the aptamer of AMP. Linear range of the sensor is 0.2-10 nM with a limit of detection 0.06 nM. This fluorescent sensor was applied to detect AMP in real samples.

Self-Assembled Cage for In Situ Detecting Silver Cation in Water

Here, a capsule-shaped cage comprising three monocationic arms was efficiently self-assembled by condensing a triscationic trisaldehyde and a trisamino linkage in water. Multivalence endows the cage with thermodynamic stability in water. Despite its triscationic nature, the cage is able to use its trisimino residue to coordinate a silver cation. As a comparison, other cations lead to cage decomposition or no coordination. The cage and Ag⁺-coordinated complex were both characterized and confirmed by NMR spectroscopy, mass spectrometry, and theoretical calculations. The metal-ligand complex exhibits a pale-yellow color that can be detectable by the naked eye. The Ag⁺-coordinated complex undergoes decoordination upon the addition of NaCl, during which the cage containing imine bonds remains intact. Such stability implies that the cage might be potentially employed in silver detection and mining.

Red emitting fluorogenic dye as an efficient turn-on probe for milk allergen

Development of simple, fast and non-destructive technique such as fluorescence based method for the quantification of milk allergens in various dairy products is a highly rewarding task. In this contribution, a red emitting fluorogenic dye, quinaldine red (QR) is reported for the detection and quantification of a milk allergen, beta lactoglobulin (β-LG) in milk and whey matrices, utilizing its high selectivity and sensitivity towards β-LG. Detail spectroscopic investigation reveals that binding of QR to the hydrophobic calyx site of β-LG protein substantially reduces the torsional agility and propensity of TICT state formation of QR, rendering the dye highly fluorescent in nature. This enables estimation of β-LG with LOD 52.1(±0.9) nM in buffer solution and 0.21(±0.01) μM in 5 % bovine milk matrix respectively. Additionally, high selectivity and sensitivity, excellent repeatability, quick response, and emission in the biologically favorable red spectral region make QR based fluorometric quantification of β-LG a highly attractive choice. Finally, the estimated β-LG concentrations in milk and whey matrices from fluorometric titration and densitometry methods are found to match excellently with each other, suggesting potential of QR as an efficient turn-on fluorescent probe for the quantification of β-LG (milk allergen) in various dairy products.

Sign control of circularly polarized luminescence of chiral Schiff-base Zn(II) complexes through coordination geometry changes

The handedness of circularly polarized luminescence (CPL) of Zn(II) complexes with a chiral Schiff-base ligand can be controlled by coordination geometry changes in solution and in the solid state. The relationships between molecular structure and chiroptical properties were discussed with the results of X-ray diffraction analysis and DFT calculations.

A novel fluorescent probe for the localization of nucleoli developed via a chain reaction of endogenous cysteine in cells

Nucleolus imaging is important for the understanding of gene expression, proliferation, and growth of cells. Traditional nucleoli localization mainly relies on the use of RNA fluorescent probes which are required in large amounts. These probes also have low selectivity, thus causing the generated images to have high background noise and the localization of nucleoli to become vague. In the present paper, a novel probe for nucleoli localization, BEB-A, which can specifically bind to RNA via the chain reaction of endogenous cysteine (Cys), was designed and developed. In addition to its mitochondria-targeting ability, the BEB-A probe could be used in the imaging of Cys in the cytoplasm, and its product, BEB-OH, could quickly penetrate into the cell nucleus to combine with nucleolar RNA to generate strong red fluorescence signals. The luminescence property and RNA-binding capability of the probe were also investigated via theoretical calculations and molecular docking simulations. This work presents a tool that can be applied to analyze the variation of Cys in mitochondria and RNA in cells.

Diastereoselective Control of Tetraphenylethene Reactivity by Metal Template Self-Assembly

The reaction of 4,4',4'',4'''-(ethene-1,1,2,2-tetrayl)tetraaniline with 2-pyridinecarboxaldehyde and iron(II) chloride resulted, after aqueous workup, in the diastereoselective formation of an [Fe₂ L₃ ]⁴⁺ triple-stranded helicate structure, irrespective of the stoichiometry employed. The helicate structure was characterized in solution by multinuclear NMR spectroscopy, and in the solid state by single-crystal X-ray crystallography. The reaction of iron(II) tetrafluoroborate or iron(II) bistriflimide with the tetraaniline and 2-pyridinecarboxaldehyde allowed the formation of an [Fe₈ L₆ ]¹⁶⁺ cube when the appropriate stoichiometry was used, but these structures were unstable with respect to hydrolysis. The pendant amine groups on the helicate can be functionalized by reaction with acid chlorides or anhydrides, and the resulting functionalized tetraphenylethene (TPE) units were isolated by the reaction of the helicate with tris(2-aminoethyl)amine. The emission properties of the TPE units were studied in THF/water mixtures, and they were found by dynamic light scattering to self-assemble into large (av. diameter 250 nm) structures.

Controllable Self-Assembly of Pills and Cages via Imine Condensation for Silver Cation Detection

By condensing a trisamino linker with one of the two analogous bisaldehyde ligands, pills and tetrahedrons could be self-assembled. The self-assembled preference could be controlled by tuning the reaction conditions, including the size of side chain, concentration, and temperature. Coordination of silver cation quenches the fluorescence of the fluorene moieties on the pill, opening up opportunities for Ag⁺ cation detection.

An AIE-based metallo-supramolecular assembly enabling an indicator displacement assay inside living cells

We report a novel metallo-supramolecular assembly (Z/E-TPE2CyZn-PV), which consists of a tetraphenylethene (TPE)-based dinuclear Zn2+-cyclen complex and pyrocatechol violet (PV). The assembly is developed for indicator-displacement assays (IDAs) inside living cells.

A novel pyridinium modified tetraphenylethene: AIE-activity, mechanochromism, DNA detection and mitochondrial imaging

A cationic AIE-gen demonstrates multiple functions including mechanoluminochromic and solvatochromic effects, fluorescence turn-on responses to DNA-binding and mitochondria-specific living cell imaging.

Hierarchical self-assembly of squaraine and silica nanoparticle functionalized with cationic coordination sites for near infrared detection of ATP

Optical activity of hierarchical supramolecular assemblies based on organic dyes would create multiple functional architectures. In this work, three kinds of silica nanoparticles with or without functional groups were synthesized. For the first time, silica nanoparticles can induce positively charged squaraine (SQ) to aggregate to form supramolecular assemblies. Adenosine-5'-triphosphate (ATP) as building blocks was absorbed on the surface of silica nanoparticles through metal-anion coordination and electrostatic interactions, in which the aggregates of SQ was transferred to monomer. The thickness being composed of ATP and SQ on the outside of nanoparticles is about 5 nm. These supramolecular assemblies showed selective turn-on fluorescence response to ATP in near infrared (NIR) region over other ions through metal-anion coordination and electrostatic interactions. These functional silica nanoparticles possessing many advantages provide proof-of-principle "seed crystals" for construction of supramolecular assemblies and platforms for sensing with facile performance.

Detecting the Formation and Transformation of Oligomers during Insulin Fibrillation by a Dendrimer Conjugated with Aggregation-Induced Emission Molecule

The fibrillation of protein is harmful and impedes the use of protein drugs. It also relates to various debilitating diseases such as Alzheimer's diseases. Thus, investigating the protein fibrillation process is necessary. In this study, poly(amido amine) dendrimers (PAMAM) of generation 3 (G3) and generation 4 (G4) were synthesized and conjugated with 4-aminobiphenyl, an aggregation-induced emission (AIE) moiety, at varied grafting ratios. Among them, one fluorescence probe named G3-biph-3 that was grafted average 3.25 4-aminobiphenyl to the G3, can detect the transformations both from native insulin to oligomers and from oligomers to fibrils. The size difference of native insulin, oligomers, and fibrils was proposed to be the main factor leading to the detection of the above transformations. Different molecular weights of sodium polyacrylate (PAAS) were also applied as a model to interact with G3-biph-3 to further reveal the mechanism. The results indicated that PAMAM with a certain generation and grafted with appropriate AIE groups can detect the oligomer formation and transformation during the insulin fibrillation process.

Enabling the Triplet of Tetraphenylethene to Sensitize the Excited State of Europium(III) for Protein Detection and Time-Resolved Luminescence Imaging

A tetraphenylethene (TPE) group that exhibits aggregation-induced emission is incorporated into the ligand of a Eu(III) complex (TPEEu) to sensitize the excited state of Eu(III). In steady-state measurements, TPEEu exhibits weak luminescence when dissolved in aqueous solutions even at a high concentration level, but emits strong fluorescence of TPE and phosphorescence of Eu(III) upon binding with bovine serum albumin. With a delay time of 0.05 ms and a gate time of 1.0 ms in time-resolved measurements, only phosphorescent emission of Eu(III) is observed with a high on/off ratio. Moreover, this probe is successfully used in time-resolved luminescence imaging to eliminate the background signal from biological autofluorescence without a washing process. This work provides a general strategy in designing Ln(III) complexes for detecting a broad range of biological molecules.

Ratiometric Detection of β-Amyloid and Discrimination from Lectins by a Supramolecular AIE Glyconanoparticle

While the development of AIE (aggregation-induced-emission) based fluorimetric probes for biological applications has been an active research area, probes with a ratiometric signal for biomolecular recognition have been rare. Here, a ratiometric AIE glyconanoparticle formed by the supramolecular assembly between a silole-based AIEgen and fluorescent glycoprobes for the detection of amyloid β (Aβ) peptides and fibrils, which are a signature of neurological disorders such as the Alzheimer's disease, is shown. Complexation of glycoprobes with the AIEgen produces an intensive fluorescence emission of the former because of a Förster resonance energy transfer between the two molecules. Subsequently, the presence of Aβ dissembles the particle, producing a fluorescence emission of the AIEgen. Interestingly, the addition of lectins that selectively recognize the glycoprobes results in a different ratiometric response of the particle, thereby enabling a discrimination from Aβ detection. This research offers insight into the simple construction of multifunctional ratiometric probes based on the supramolecular hybridization of a wide variety of AIEgens with fluorescent molecular probes.

A New Tetraphenylethylene-Derived Fluorescent Probe for Nitroreductase Detection and Hypoxic-Tumor-Cell Imaging

The fluorescence detection of nitroreductase (NTR) and evaluation of the hypoxia status of tumor cells are vital, not only for clinical diagnoses and therapy, but also for biomedical research. Herein, we report the synthesis and application of a new fluorometric "turn-on" probe for the detection of NTR (TPE-NO₂ ) that takes advantage of the aggregation-induced emission of tetraphenylethylene. TPE-NO₂ can detect NTR at concentrations as low as 5 ng mL^-1 in aqueous solution. The detection mechanism relied on the aggregation and deaggregation of tetraphenylethylene molecules. Moreover, this fluorescent probe can be used to monitor the hypoxia status of tumor cells through the detection of endogenous NTR.

[12]aneN3 Modified Tetraphenylethene Molecules as High-Performance Sensing, Condensing, and Delivering Agents toward DNAs

Four [12]aneN3 modified tetraphenylethene (TPE) compounds with different numbers of polyamine units and structure configurations, namely 1, 2, 3, and 4, were designed and synthesized. All compounds showed strong aggregation-induced emission (AIE) features. Compounds 2 and 4 showed significant emission enhancement after the addition of ssDNAs and dsDNAs of different lengths as well as calf thymus DNA (ctDNA). Compounds 1 and 3 showed very poor fluorescent responses toward DNAs. Gel electrophoresis demonstrated the abilities of 1-4 to condense DNA effectively. Complete retardation of plasmid DNA can be achieved at a concentration of 25 μM (1), 8 μM (for 2 and 3) and 4 μM (4). Experiments including fluorescent contrastive titrations, scanning electron microscopy, dynamic laser scattering, EB displacement, and gel electrophoresis demonstrated that the four compounds were able to integrate with DNA through electrostatic interactions and supramolecular stacking. A vicinal configuration around TPE (2) and more triazole-[12]aneN3 recognition sites (4) evidently enhanced the sensing capability toward oligonucleotides, and the TPE unit played an important role in the plasmid DNA condensation process because of its strong binding. With the advantages of low cytotoxicity, effective DNA sensing, and DNA condensing properties, compound 4 was successfully applied as a nonviral DNA vector and fluorescent tracer for label-free gene delivery, which is the first example of a nonviral gene vector with AIE activity.

New Insight of Tetraphenylethylene-based Raman Signatures for Targeted SERS Nanoprobe Construction Toward Prostate Cancer Cell Detection

We have designed and synthesized novel tetraphenylethylene (TPE) appended organic fluorogens and unfold their unique Raman fingerprinting reflected by surface-enhanced Raman scattering (SERS) upon adsorption on nanoroughened gold surface as a new insight in addition to their prevalent aggregation-induced emission (AIE) and aggregation-caused quenching (ACQ) phenomena. A series of five TPE analogues has been synthesized consisting of different electron donors such as (1) indoline with propyl (TPE-In), (2) indoline with lipoic acid (TPE-In-L), (3) indoline with Boc-protected propyl amine (TPE-In-Boc), (4) benzothaizole (TPE-B), and (5) quinaldine (TPE-Q). Interestingly, all five TPE analogues produced multiplexing Raman signal pattern, out of which TPE-In-Boc showed a significant increase in signal intensity in the fingerprint region. An efficient SERS nanoprobe has been constructed using gold nanoparticles as SERS substrate, and the TPE-In as the Raman reporter, which conjugated with a specific peptide substrate, Cys-Ser-Lys-Leu-Gln-OH, well-known for the recognition of prostate-specific antigen (PSA). The designated nanoprobe TPE-In-PSA@Au acted as SERS "ON/OFF" probe in peace with the vicinity of PSA protease, which distinctly recognizes PSA expression with a limit of detection of 0.5 ng in SERS platform. Furthermore, TPE-In-PSA@Au nanoprobe was efficiently recognized the overexpressed PSA in human LNCaP cells, which can be visualized through SERS spectral analysis and SERS mapping.

Supramolecular aggregates as sensory ensembles

Recent research progress in sensing based on induced supramolecular aggregation or disaggregation.

Intriguingly tuning the fluorescence of AIEgen using responsive polyelectrolyte microspheres

We successfully synthesized counterion-sensitive TPE–METAC polyelectrolyte microspheres and tuned its fluorescence and size by ClO₄⁻, PF₆⁻ and TFSI⁻.

Zinc complexes as fluorescent chemosensors for nucleic acids: new perspectives for a "boring" element

Zinc(II) complexes are effective and selective nucleic acid-binders and strongly fluorescent molecules in the low energy range, from the visible to the near infrared. These two properties have often been exploited to quantitatively detect nucleic acids in biological samples, in both in vitro and in vivo models. In particular, the fluorescent emission of several zinc(II) complexes is drastically enhanced or quenched by the binding to nucleic acids and/or upon visible light exposure, in a different fashion in bulk solution and when bound to DNA. The twofold objective of this perspective is (1) to review recent utilisations of zinc(II) complexes as selective fluorescent probes for nucleic acids and (2) to highlight their novel potential applications as diagnostic tools based on their photophysical properties.

A cell apoptosis probe based on fluorogen with aggregation induced emission characteristics

A fluorogen-based aggregation-induced emission zinc-dipicolylamine (AIE-ZnDPA) probe with aggregation-induced emission characteristics has been designed and synthesized to detect cell apoptosis. AIE-ZnDPA does not respond to healthy cells but selectively stains and lights up fluorescence in the membranes of early stage apoptotic cells as well as the nuclei of late stage apoptotic cells. Without zinc coordination, the precursor lipophilic AIE dipicolylamine (AIE-DPA) probe stains healthy cells and shows high affinity for lipid droplets (LDs).

Supramolecular architecture and photophysical and biological properties of ruthenium(ii) polypyridyl complexes

A two-dimensional cyclic hybrid water–chloride anionic network has been structurally characterized in a metal–organic matrix. DNA interactions and the cytotoxicity of ruthenium(ii) complexes have been studied.

The phenanthroimidazole-based dizinc(ii) complex as a fluorescent probe for the pyrophosphate ion as generated in polymerase chain reactions and pyrosequencing

The phenanthroimidazole-based dizinc(II) complex is an efficient fluorescent probe for the pyrophosphate ion (PPi) in water with a very low detection limit, and also used to detect PPi released from DNA polymerization chain reaction.

Red fluorescent luminogen from pyrrole derivatives with aggregation-enhanced emission for cell membrane imaging

A dye emitted red fluorescence with aggregation-enhanced emission properties was reported here. It can be utilized to specifically recognize the cell membrane of MCF-7 and 293T cell lines during bio-imaging.

Amino-modified tetraphenylethene derivatives as nucleic acid stain: relationship between the structure and sensitivity

A series of new amino-functionalized tetraphenylethene (TPE) derivatives were designed and synthesized to study the effect of molecular structures on the detection of nucleic acid. Contrastive studies revealed that the number of binding groups, the length of hydrophobic linking arm and the configuration of TPE molecule all play important roles on the sensitivity of the probes in nucleic acid detection. Z-TPE3 with two binding amino groups, long linking arms, and cis configuration was found to be the most sensitive dye in both solution and gel matrix. Z-TPE3 is able to stain dsDNA with the lowest amount of 1 ng and exclusively stain 40 ng of short oligonucleotide with only 10 nt. This work is of important significance for the further design of TPE probes as biosensors with higher sensitivity.

A highly sensitive nucleic acid stain based on amino-modified tetraphenylethene: the influence of configuration

We designed and synthesized a new amino-functionalized tetraphenylethene (TPE) derivative as a highly sensitive dye for the detection of dsDNA and oligonucleotide in both solution and a gel matrix. We further revealed that the cis configuration dye showed a much higher sensitivity than its trans isomer for the first time.