A diaminomaleonitrile-appended BODIPY chemosensor for the selective detection of Cu2+ via oxidative cyclization and imaging in SiHa cells and zebrafish

Small-Molecule Fluorescent Probes for Binding- and Activity-Based Sensing of Redox-Active Biological Metals

Although transition metals constitute less than 0.1% of the total mass within a human body, they have a substantial impact on fundamental biological processes across all kingdoms of life. Indeed, these nutrients play crucial roles in the physiological functions of enzymes, with the redox properties of many of these metals being essential to their activity. At the same time, imbalances in transition metal pools can be detrimental to health. Modern analytical techniques are helping to illuminate the workings of metal homeostasis at a molecular and atomic level, their spatial localization in real time, and the implications of metal dysregulation in disease pathogenesis. Fluorescence microscopy has proven to be one of the most promising non-invasive methods for studying metal pools in biological samples. The accuracy and sensitivity of bioimaging experiments are predominantly determined by the fluorescent metal-responsive sensor, highlighting the importance of rational probe design for such measurements. This review covers activity- and binding-based fluorescent metal sensors that have been applied to cellular studies. We focus on the essential redox-active metals: iron, copper, manganese, cobalt, chromium, and nickel. We aim to encourage further targeted efforts in developing innovative approaches to understanding the biological chemistry of redox-active metals.

A Sensitive Probe of Meso-Cyanophenyl Substituted BODIPY Derivative as Fluorescent Chemosensor for the Detection of Multiple Heavy Metal Ions

A fluorescent turn-on chemosensor (BA) was constructed by attaching bis(pyridin-2-ylmethyl)-amine (DPA) unit to the BODIPY scaffold. It can give a prominent green/yellow fluorescent response selectivity with each of Zn2+/Hg2+/Cd2+/Ca2+/Mn2+/Pb2+/Al3+. The 1:1 stoichiometry of BA and metal ions was drawn from the analysis of Job's plot. The limit detection of BA in recognition of Zn2+/Hg2+/Cd2+/Ca2+/Mn2+/Pb2+/Al3+ is ranged in 50.8-146.6 nM. There exists a linear relationship between the fluorescence intensity and concentration of metal ions (Zn2+: 4-15 µM). The mechanism of fluorescence signal "turn-on" is based on the photo induced transfer (PET) in the excited state of BA. The coordinated metal ions significantly weakened the electron-donating ability nitrogen atom in DPA, thus recovering the emission character of BODIPY. The substituted group at the phenyl ring in meso-position of BODIPY scaffold determines the recognizable list of metal ions.

Investigating the Properties of Triangle Terthiophene and Triphenylamine Configured Propeller-like Photochromic Dye with Ethyne Bridge

Synthesis-oriented design led us to the construction of a propeller-like dye, containing the triangle terthiophene and triphenylamine units. It reveals typical photochromic properties with alternated UV (390 nm) and visible light (˃ 440 nm) irradiation and the dye solution (in THF) color was also toggled between yellow-green and colorless. A new absorption band was observed in visible region (415-600 nm). Additionally, the photochromic dye was highly emissive with the absolute quantum yield being 0.27. After UV light irradiation, the emission was quenched significantly (Φ = 0.08) at photo-stationary state, and thus establishing a switchable emission "on-off" system by alternated UV/visible light irradiation cycle. Detailed structural analysis was carried out based on the optimized dye structure. Both the antiparallel conformation and the distance of reactive carbon atoms (< 4.2 Å) led to the smoothly photochromic behavior.

Configuration of super-fast Cu2+-responsive chemosensor by attaching diaminomaleonitrile to BODIPY scaffold for high-contrast fluorescence imaging of living cells

A highly fluorescent Cu2+-responsive sensor, 2-amino-3-(BODIPYmethyleneamino)maleonitrile (BD) was constructed by attaching diaminomaleonitrile to a BODIPY scaffold. Cu2+ can be selectively recognized on a 2-s time-scale by way of fluorescence emission. When Cu2+ and BD coexist in solution, typical BODIPY emission was observed and the emission intensity could be increased to 334 times that of the blank dye solution. The mechanism of fluorescence increase is based on the generation of highly fluorescent species by Cu2+-triggered oxidative cyclization of the attached diaminomaleonitrile. The absolute fluorescence quantum yield (AFQY) of the cyclization product is 98% determined by integrating sphere. The highly emissive character can be attributed to the imidazole ring and dicarbonitrile on the BODIPY scaffold. It surpasses the meso-phenyl substituted analogue in AFQY and detection limits (DL). The specific Cu2+ recognition behavior was also validated in Hela cells with high-contrast fluorescence images.

Two 3D Ln(III)-MOFs Based on Phosphineoxide Ligand: Synthesis, Structure Luminescent and Photocatalytic Properties

Two new 3D metal-organic frameworks (MOFs) ZZUT1 and ZZUT2 were prepared through the reaction of tris-(4-carboxylphenyl) phosphineoxide (H3TPO) ligand with nitrate of neodymium and praseodymium by solvothermal method. The structure, fluorescence and photocatalytic properties of ZZUT1 and ZZUT2 were studied. The crystalline structure of two 3D Ln(III)-MOFs both exhibit triclinic system and P-1 space group. The results of fluorescence analysis showed that two 3D Ln(III)-MOFs could selectively recognize acetone molecule through the fluorescence quenching mechanism. Meanwhile, ZZUT1 and ZZUT2 showed good adsorption and degradation ability on organic dye methylene blue (MB) in photocatalytic condition, and the degradation efficiency can reach to more than 90%.

Photo-Induced Fluorochromism of a Star-Shaped Photochromic Dye with 2,4-Dimethylthiazole Attaching to Triangle Terthiophene

A photochrmic triangle terthiophene dye with 2,4-dimethylthiazole attached was synthesized and shows regular photochromic properties when irradiated with UV/Vis light alternately. It was found that the attaching of 2,4-dimethylthiazole has a significant effect on both the photochromism and fluorescence of triangle terthiophene. During the photocyclizatioin prcess, not only the color but also the fluorescence of the dye in THF can be toggled between ring-open and ring-closed forms of the dye. Additionally, the absolute quantum yields (AQY) of ring-open and ring-closed forms of the dye (0.32/0.58) were greatly larger than the literature report. Along with the 254 nm light irradiation, the fluorescence color changed from deep blue (428 nm) to sky blue (486 nm) in THF. A fluorochromism cycle could be established based on the UV/visible light irradiation cycle, which provides a strategy for the design of new type fluorescent diarylethene derivatives for biological application.

Investigating the Properties of Double Triangle Terthiophene Configured Dumbbell-Like Photochromic Dye with Ethyne and 1,3-Butadiene Bridge

Dumbbell-like photochromic dyes were constructed by incorporation of double triangle terthiophene with ethyne or 1,3-butadiene bridge. Regular photochromic behavior was investigated with alternated UV (365 nm) and Visible light (˃ 400 nm) irradiation. However, the different bridge group leads to distinct difference in their photochromic wavelength. For the ethyne bridged triangle terthiophene (DT1), the photochromic wavelength was observed around 500-700 nm (peak value: 605 nm) and the solution turned to red with 365 nm light irradiation. However, the photochromic wavelength was blue shift to 418-550 nm and the solution was turned to light yellow for 1,3-butadiene bridged dye (DT2). Both of the colored solution can be bleached via visible light irradiation. Additionally, the two dyes in THF were emissive with absolute quantum yield (QY) of 0.36/0.40. Along with the photo-induced photocyclization process, the emissive solution can be effectively quenched at photo-stationary sate (Φ = 0.05/0.04). And emission "on-off" cycle could be established based on the UV/visible light irradiation cycle.

Construction of a novel ESIPT and AIE-based fluorescent sensor for sequentially detecting Cu2+ and H2S in both living cells and zebrafish

The development of effective methods for tracking Cu²⁺ and H₂S in living organisms is urgently required due to their vital function in a variety of pathophysiological processes. In this work, a new fluorescent sensor BDF with excited-state intramolecular proton transfer (ESIPT) and aggregation-induced emission (AIE) features for the successive detection of Cu²⁺ and H₂S was constructed by introducing 3,5-bis(trifluoromethyl)phenylacetonitrile into the benzothiazole skeleton. BDF showed a fast, selective and sensitive fluorescence "turn off" response to Cu²⁺ in physiological media, and the situ-formed complex can serve as a fluorescence "turn on" sensor for highly selective detection of H₂S through the Cu²⁺ displacement approach. In addition, the detection limits of BDF for Cu²⁺ and H₂S were determined to be 0.05 and 1.95 μM, respectively. Encouraged by its favourable features, including strong red fluorescence from the AIE effect, large Stokes shift (285 nm), high anti-interference ability and good function at physiological pH as well as a low toxicity, BDF was successfully applied for the consequent imaging of Cu²⁺ and H₂S in both living cells and zebrafish, making it an ideal candidate for detecting and imaging of Cu²⁺ and H₂S in live systems.

A Fluorescent Turn-On Sensor Toward Multiple Heavy Metal Ions Based on Meso-anisole Modified BODIPY Scaffold

A fluorescent turn-on sensor (BOPA) was configured by anchoring bis(pyridin-2-ylmethyl)-amine (DPA) unit to the BODIPY scaffold. It exhibits highly sensitivity and selectivity towards Pb²⁺, Ba²⁺, Cr³⁺, Cd²⁺, Hg²⁺, Zn²⁺ against the competent metal ions. Job's plot analysis supports the 1:1 stoichiometry of BOPA and metal ions. And linear relationship between fluorescence intensity and concentration of Zn²⁺ (representative metal ion) was observed over the range 0 ~ 20 μM Zn²⁺. The limit detection of BOPA in recognition of Pb²⁺, Ba²⁺, Cr³⁺, Cd²⁺, Hg²⁺, Zn²⁺ was ranged from 15.99 to 43.57 nM. Photo induced transfer (PET) in the excited state of BOPA determines the emission "off/on". Coordination of metal ions by DPA significantly weakened the electron-donating ability of nitrogen atom and inhibits the PET, recovering emission of BODIPY. In addition, the attachment of anisole at meso-position of BODIPY finely modulated the recognition of metal ions category.

Crystal structure of (Z)-2-(tert-butyl)-5-((5-(tert- butyl)-2H-pyrrol-2-ylidene)(mesityl)methyl)-1H-pyrrole, C26H34N2

C26H34N2, orthorhombic, Pbca (no. 61), a = 14.8062(2) Å, b = 15.8918(2) Å, c = 20.0121(3) Å, V = 4708.79(11) Å3, Z = 8, Rgt (F) = 0.0548, wRref (F 2) = 0.1701, T = 296.2 K.

A highly selective A-π-A “turn-on” fluorescent probe for hypochlorite in tap water

A highly selective fluorescence probe (BON) for hypochlorite (ClO-) was designed and synthesized. The probe was based on boron-dipyrromethene (BODIPY) dye as the fluorophore and diaminomaleonitrile (DAMN) as the recognition...

N-alkylation briefly constructs tunable multifunctional sensor materials: Multianalyte detection and reversible adsorption

A series of N-alkyl-substituted polybenzimidazoles (SPBIs), synthesized by simple condensation and N-alkylation, act as functional materials with tunable microstructures and sensing performance. For their controllable morphologies, the formation of nano-/microspheres is observed at the n(RBr)/n(PBI) feed ratio of 5:1. Products with different degrees of alkylation can recognize metal ions and nitroaromatic compounds (NACs). For example, SPBI-c, obtained at the feed ratio of 1:1, can selectively detect Cu2+, Fe3+, and NACs. By contrast, SPBI-a, obtained at the feed ratio of 0.1:1, can exclusively detect Cu2+ with high sensitivity. Their sensing mechanisms have been studied by FT-IR spectroscopy, SEM, XPS, and DFT calculations. Interestingly, the SPBIs can adsorb Cu2+ in solution and show good recyclability. These results demonstrate that polymeric materials with both sensing and adsorption applications can be realized by regulating the alkylation extent of the main chain, thus providing a new approach for the facile synthesis of multifunctional materials.

Double 3-Ethyl-2,4-dimethylpyrrole Configured Fluorescent Dye with Fluorine-Boron as the Bridge

Dipyrrolydiketones BF₂ complex was synthesized and characterized by NMR, HRMS, and single crystal diffraction. In non-polar environment, this BF₂ containing dye emitted bright blue-green fluorescence. No significant spectra shift was observed both in absorption and emission spectra, which indicates the insensitivity of absorption/emission toward environment. The alkyl substituted pyrrole rings lead to its highly emission character in solid state by enhancing the distance between dye molecules. Absolute quantum yields were determined to be 0.51-0.78/0.36 in selected organic medium and solid state, respectively. The emission dynamics was investigated by fluorescence lifetime and both monoexponential and bi-exponential decay was observed.

Crystal structure of 2-phenylethynyl-1,3,6,8-tetramethylBOPHY (BOPHY = bis(difluoroboron)-1,2-bis((1H-pyrrol-2-yl)methylene)hydrazine), C22H20B2F4N4

C22H20B2F4N4, orthorhombic, Pbca (no. 61), a = 9.2506(2) Å, b = 36.1677(13) Å, c = 12.9475(3) Å, V = 4331.9 Å3, Z = 8, R gt (F) = 0.0729, wR ref (F 2) = 0.1992, T = 294.4 K.

Crystal structure of 2-bromo-1,3,6,8-tetramethylBOPHY (BOPHY = bis(difluoroboron)-1,2-bis((1H-pyrrol-2-yl)methylene)hydrazine), C14H15B2BrF4N4

C14H15B2BrF4N4, orthorhombic, Pbca (no. 61), a = 11.970(1) Å, b = 10.049(1) Å, c = 27.847(1) Å, V = 3349.6 Å3, Z = 8, R gt(F) = 0.0697, wR ref(F 2) = 0.1585, T = 296 K.

CCDC no.: 2080820

Europium(III) complex fluorescent sensor for dual channel recognition of Sn2+ and Cu2+ ions in water

A new europium(III) complex Eu(tta)₃L₁ (1a) (L₁ = (2-(3,5-dimethoxyphenyl)-1H-imidazo[4,5-f][1,10]phenanthroline), tta = 2-thenoyltrifluoroacetone) has been prepared and synthesized. The structure of complex was completely determined by several different analytical techniques including single-crystal X-ray diffraction, ¹H and ¹³C NMR. The crystal structure of the complex 1a belonged to monoclinic system with the space group P2₁/n. Its fluorescent properties were systematically studied in details by adding different metal ions in deionized water. Upon addition of Sn²⁺, its fluorescence intensity was strengthened and centered at 460 nm. And when Cu²⁺ was added, its fluorescence emission intensity was quenched quickly. The LODs for Sn²⁺ and Cu²⁺ were calculated to be 4.52 × 10^-7 mol L^-1 and 1.11 × 10^-7 mol L^-1, respectively. Furthermore, this sensor was successfully employed to monitor Sn²⁺ and Cu²⁺ in practical samples.

A novel fluorescent BODIPY-based probe for detection of Cu2+ and H2S based on displacement approach

A new BODIPY-based fluorescent probe (BC-DPA) was prepared by a simple method for Cu²⁺ detection in aqueous media and living cells. BC-DPA displayed excellent selectivity toward Cu²⁺via fluorescence "turn-off" mode when a mononuclear Cu(Ⅱ) complex is formed. The corresponding BC-DPA-Cu(Ⅱ) complex, whose structure was characterized by X-ray crystallography, has Cu(Ⅱ) in a distorted octahedral geometry. On the basis of the displacement approach, the fluorescence of BC-DPA-Cu²⁺ was recovered in the presence of S^2-, which allowed the system to act as a sensitive "turn-on" sensor for hydrogen sulfide. Furthermore, BC-DPA exhibited noticeable permeability and low cytotoxicity, making it a useful tool to detect Cu²⁺ in biosystems.

The Effects of Copper Constituent of Coin Currency on Embryonic Zebrafish Development

Copper has demonstrated utility in multiple industrial applications for its high conductivity and antibacterial/antiviral properties. However, numerous findings have suggested potential hazards regarding pathogenesis. This study was conducted to demonstrate the application of zebrafish (Danio rerio) as a cost-effective biological assay to detect environmental pollution, i.e., heavy metal of coins. We demonstrated that zebrafish larvae exposed to copper-plated coins or copper (II) ion solution elicited a consistent phenotype of early mortality without signs of morphological defects in surviving individuals. Copper ion solution served as a standard to (1) corroborate copper exposure from coins and (2) demonstrate proportional increase in early mortality phenotype according to concentration. We found that 5 μM CuSO₄·5H₂O was the minimal concentration to elicit the observed phenotypes from copper toxicity. This study aimed to demonstrate how a simple protocol involving wild-type zebrafish larvae could provide an economical solution to water monitoring in areas of rapid technological advancement and increasing environmental concerns, especially in communities without access to expensive analytical methods.

A coumarin-based reversible fluorescent probe for Cu2+ and S2− and its applicability in vivo and for organism imaging

A highly selective fluorescent probe was designed to detect Cu²⁺ and S²⁻ in HeLa cells, zebrafish, and soybean root tissue.