A new ditopic ratiometric receptor for detecting zinc and fluoride ions in living cells

Organoplatinum Complex Exhibiting Aggregation-Enhanced Emission (AEE) and Dual-Channel Ion-Sensing Properties by Terminating the Molecular Configuration Transformation (MCT) and Excited-State Intramolecular Proton Transfer (ESIPT)

Emitters produce weak emissions when they undergo structural changes such as molecular configuration transformation (MCT) or excited-state intramolecular proton transfer (ESIPT) but give out strong emissions after terminating these distortions. Herein, an organoplatinum complex, Pt-ppy-ABP, carrying a salicylaldehyde-based Schiff base unit is synthesized. It exhibits weak emission in dilute solutions but shows bright emission at the aggregated state or after interacting with F- and Zn2+. This suggests that it has an aggregation-enhanced emission (AEE) property and holds potential in ion detection. Supported by theoretical calculations and femtosecond transient absorption results, this complex suffers excited-state structural changes including MCT from a square-planar configuration to a tetrahedral one, as well as intramolecular rotation of a monodentate ligand and ESIPT, showing weak emission in its solutions. At the aggregated state, it releases strong yellow emissions because of the restraints of MCT and ligand rotation. Upon interacting with F- or Zn2+, it emits bright-red or -green emissions, achieving detection limits of 10-7 M. The sensing mechanism is concluded as deprotonation- and coordination-induced ESIPT terminations, respectively. Given its AEE property and ion-responsive emissions, its application in information encryption is also explored. Finally, these findings should provide valuable clues for the developments of chemosensors with dual-channel recognition abilities.

Study of a Fluorescent System Based on the Naphthalene Derivative Fluorescent Probe Bound to Al3

The naphthalene derivative fluorescent probe F6 was synthesized and a 1 × 10^-3 mol/L solution of Al³⁺ and other metals to be tested was prepared for the subsequent experiments. The Al³⁺ fluorescence system of the naphthalene derivative fluorescent probe F6 was successfully constructed as demonstrated by fluorescence emission spectroscopy. The optimal time, temperature and pH of the reaction were investigated. The selectivity and anti-interference ability of the probe F6 for Al³⁺ were investigated by fluorescence spectroscopy in a methanol solution. The experiments showed that the probe has high selectivity and anti-interference ability for Al³⁺. The binding ratio of F6 to Al³⁺ was 2:1, and the binding constant was calculated to be 1.598 × 10⁵ M^-1. The possible mechanism of the binding of the two was speculated. Different concentrations of Al³⁺ were added to Panax Quinquefolium and Paeoniae Radix Alba. The results showed that the recoveries of Al³⁺ were 99.75-100.56% and 98.67-99.67%, respectively. The detection limit was 8.73 × 10^-8 mol/L. The experiments demonstrated that the formed fluorescence system can be successfully adapted for the determination of Al³⁺ content in two Chinese herbal medicines, which has good practical application.

A Highly Selective Turn-On Fluorescent Probe for the Detection of Zinc

A novel turn-on fluorescence probe L has been designed that exhibits high selectivity and sensitivity with a detection limit of 9.53 × 10⁻⁸ mol/L for the quantification of Zn²⁺. ¹H-NMR spectroscopy and single crystal X-ray diffraction analysis revealed the unsymmetrical nature of the structure of the Schiff base probe L. An emission titration experiment in the presence of different molar fractions of Zn²⁺ was used to perform a Job’s plot analysis. The results showed that the stoichiometric ratio of the complex formed by L and Zn²⁺ was 1:1. Moreover, the molecular structure of the mononuclear Cu complex reveals one ligand L coordinates with one Cu atom in the asymmetric unit. On adding CuCl₂ to the ZnCl₂/L system, a Cu-Zn complex was formed and a strong quenching behavior was observed, which inferred that the Cu²⁺ displaced Zn²⁺ to coordinate with the imine nitrogen atoms and hydroxyl oxygen atoms of probe L.

A Tunable Palette of Molecular Rotors Allows Multicolor, Ratiometric Fluorescence Imaging and Direct Mapping of Mitochondrial Heterogeneity

Environment-sensitive molecular probes offer the potential for a comprehensive mapping of the complex cellular milieu. We present here a radically new strategy of multiplexing highly sensitive, spectrally tuned fluorescent dyes for sensing cellular microenvironment. To achieve this multicolor, ratiometric cellular imaging, we first developed a series of highly sensitive, tunable molecular rotors for mitochondrial imaging, with emission wavelengths spanning the visible spectrum. These fluorogenic merocyanine dyes are all sensitive to solvent viscosity despite distinctive photophysical features. Our results show that merocyanine dyes can show a rotor-like behavior despite significant changes to the conventional donor-acceptor or push-pull scaffolds, thereby revealing conserved features of rotor dye chemistry. Developing closely related but spectrally separated dyes that have distinct response functions allows us to do ″two-color, two-dye″ imaging of the mitochondrial microenvironment. Our results with multidye, combinatorial imaging provide a direct visualization of the intrinsic heterogeneity of the mitochondrial microenvironment. The overall mitochondrial microenvironment (including contributions from local membrane order) as reported through two-color fluorescence ″ratio″ changes of multiplexed rotor dyes shows dynamic heterogeneity with distinct spatiotemporal signatures that evolve over time and respond to chemical perturbations. Our results offer a powerful illustration of how multiplexed dye imaging allows the quantitative imaging of mitochondrial membrane order and cellular microenvironment.

A novel aluminum-sensitive fluorescent chemosensor based on 4-aminoantipyrine: An experimental and theoretical study

A practical and an efficient Schiff base fluorescent chemosensor, salicylidene-4-aminoantipyrinyl-4-aminophenol (A2) has been synthesized through the condensation procedure of 1-phenyl-2,3-dimethyl-4-(N-2-hydroxybenzylidene)-3-pyrazoline-5-one and 4-aminophenol. Compound A2 has displayed a considerable fluorescence enhancement with high selectivity and sensitivity toward Al³⁺ ion and exhibited an emission band at 484 nm, which contained a low detection limit (LOD) of 1.06 × 10^-7 M. In accordance to the experimental study, DFT, TDDFT calculations, and the enhancement of fluorescence intensity might be attributed to the inhibition of Photoinduced Electron Transfer (PET) along with the Excited-State Intramolecular Proton Transfer (ESIPT). As it has been specified by Job's plot and DFT calculations, the binding stoichiometries of A2 with Al³⁺ are 1:1, while the association constant (Ka) of Al³⁺ has been calculated and observed to be 2.67 × × 10⁵ M^-1. Furthermore, the binding behavior and sensing mechanism of A2 with Al³⁺ have been confirmed through the experiments of ¹H NMR titration.

A unique benzimidazole-naphthalene hybrid molecule for independent detection of Zn2+ and N3- ions: Experimental and theoretical investigations

Single crystal X-ray structurally characterized benzimidazole-naphthalene hybrid (NABI) functions as a unique dual analyte sensor that can detect Zn²⁺ cation and N₃^- anion independently. The NABI forms chelate with Zn²⁺ to inhibit internal charge transfer (ICT) and CHN isomerisation resulting chelation enhanced fluorescence (CHEF). On the other hand, the sensing of N₃^- is based on formation of supramolecular H-bonded rigid assembly. The association constant of NABI for Zn²⁺ and N₃^- ions are 19 × 10⁴ M^-1 and 11 × 10² M^-1, respectively. Corresponding limit of detections (LOD) are 6.85 × 10^-8 and 1.82 × 10^-7 M, respectively. NABI efficiently detects intracellular Zn²⁺ and N₃^- ions with no cytotoxicity on J774A.1cells under fluorescence microscope. DFT studies unlock underlying spectroscopic properties of free NABI and Zn²⁺/N₃^- bound forms.

Rationally designed upconversion nanoprobe for simultaneous highly sensitive ratiometric detection of fluoride ions and fluorosis theranostics

For many years, fluorosis has been known as a worldwide disease which seriously diminishes quality of life through skeletal embrittlement and hepatic damage. Aiming to develop novel drugs for simultaneous fluorosis diagnosis and therapy, in this work we explore the feasibility of a novel pyrogallic acid-titanium(iv) complex-modified upconversion nanoprobe (UCNP-PA-Ti) for F- capture and real-time quantification. Utilizing the strong interaction between Ti4+ and F-, the modified PA-Ti decomposes in F--containing solution, which not only weakens the FRET but results in upconversion luminescence (UCL) recovery. Both in vitro and in vivo experiments demonstrate a highly sensitive F- UCL response and therapeutic efficiency, which was promising for successful UCL image monitoring and the therapeutic process. Long blood circulation time and low toxicity ensured their safe application for fluorosis theranostics. Our work provides a new possibility for F- concentration detection within fluorosis therapeutic periods and encourages the development of novel drugs for fluorosis theranostics.

A new fluorene-based Schiff-base as fluorescent chemosensor for selective detection of Cr3+ and Al3

2-((9H-fluoren-2-ylimino) methyl)phenol (F3) was synthesized by condensation reaction of 9H-fluoren-2-amine and 2-hydroxybenzaldehyde in EtOH and characterized by its melting point, ¹H-,¹³C NMR and molecular mass. F3 exhibits a high selectivity for detection of Cr³⁺ and Al³⁺ ions as a fluorescent chemosensor and showed a single emission band at 536nm upon excitation at 333nm according to fluorescence emission studies. The addition of Cr³⁺ and Al³⁺ make a significant increase in fluorescent intensity at 536nm in CH₃CN, while other metal ions have almost no influence on the fluorescence. The fluorescence enhancement was attributed to the inhibited CN isomerization and the obstructed excited state intra-molecular proton transfer (ESIPT) of compound F3. Job's plot and DFT calculations data showed that the binding stoichiometries of F3 with Cr³⁺ and Al³⁺ are 2:1. The association constants (K_a) for Cr³⁺ and Al³⁺ were calculated and found to be 8.33×10⁴M^-1 and 5.44×10⁴M^-1, respectively. The detection limits were also calculated for Cr³⁺ and Al³⁺ and found to be 2.5×10^-7mol/L and 3.1×10^-7mol/L, respectively.

Indigo Carmine-Cu complex probe exhibiting dual colorimetric/fluorimetric sensing for selective determination of mono hydrogen phosphate ion and its logic behavior

A new selective probe based on copper complex of Indigo Carmine (IC-Cu₂) for colorimetric, naked-eye, and fluorimetric recognition of mono hydrogen phosphate (MHP) ion in H₂O/DMSO (4:1v/v, 1.0mmolL^-1 HEPES buffer solution pH7.5) was developed. Detection limit of HPO₄^2- determination, achieved by fluorimetric and ₃lorimetric method, are 0.071 and 1.46μmolL^-1, respectively. Potential, therefore is clearly available in IC-Cu₂ complex to detect HPO₄^2- in micromolar range via dual visible color change and fluorescence response. Present method shows high selectivity toward HPO₄^2- over other phosphate species and other anions and was successfully utilized for analysis of P₂O₅ content of a fertilizer sample. The results obtained by proposed chemosensor presented good agreement with those obtained the colorimetric reference method. INHIBIT and IMPLICATION logic gates operating at molecular level have been achieved using Cu²⁺and HPO₄^2- as chemical inputs and UV-Vis absorbance signal as output.

A functional applied material on recognition of metal ion zinc based on the double azine compound

A colorimetric and fluorescent probe L has been designed and synthesized, which bearing the double azine moiety and showing a detection limit of 2.725 × 10⁻⁷ M towards Zn²⁺. Based on the basic recognition mechanism of ESIPT and CHEF effect, the L has high selectivity and sensitivity to only Zn²⁺ (not Fe³⁺, Hg²⁺, Ag⁺, Ca²⁺, Co²⁺, Ni²⁺, Cd²⁺, Pb²⁺, Cr³⁺, and Mg²⁺) within the physiological pH range (pH = 7.0–8.4) and showed a fluorescence switch. Moreover, this detection progress occured in the DMSO/H₂O ∼ HEPES buffer (80/20, v/v; pH 7.23) solution which can conveniently used on test strip.

Ion-Pair Complexation with Dibenzo[21]Crown-7 and Dibenzo[24]Crown-8 bis-Urea Receptors

Synthesis and ion-pair complexation properties of novel ditopic bis-urea receptors based on dibenzo[21]crown-7 (R(1) ) and dibenzo[24]crown-8 (R(2) ) scaffolds have been studied in the solid state, solution, and gas phase. In a 4:1 CDCl3 /[D6 ]DMSO solution, both receptors clearly show positive heterotropic cooperativity toward halide anions when complexed with Rb(+) or Cs(+) , with the halide affinity increasing in order I(-) <Br(-) <Cl(-) . In solution, the rubidium complexes of both receptors have higher halide affinities compared to the caesium complexes. However, Rb(+) and Cs(+) complexes of R(2) show stronger affinities toward all the studied anions compared to the corresponding cationic complexes of R(1) . Similar selectivity of the receptors toward the studied ion pairs was also observed also in the gas phase by competition experiments with mass spectrometry. A total of eight crystal structures with different rubidium and caesium halides and oxyanions were obtained in addition to the crystal structure of R(2) ⋅BaCl2 . The selectivity observed in solution and in the gas phase is explainable by the conformational differences observed in the crystal structures of ion-pair complexes with R(1) and R(2) . In the solid state, R(1) has an open conformation due to the asymmetric crown-ether scaffold, whereas R(2) has a compact, folded conformation. Computational studies of the ion-pair complexes of R(2) show that the interaction energies of the complexes increase in the order CsI<CsBr<CsCl<RbCl, supporting the selectivity observed in solution and the gas-phase.

Thiophene-based pyridine derivatives: synthesis, crystal structures, two-photon absorption properties and bio-imaging applications in the near-IR region

Two novel D–π–A structural chromophores showing large 2PA active cross-sections, low cytotoxicity and high stability in near-IR bio-imaging.

Highly selective detection of Hg2+ and MeHgI by di-pyridin-2-yl-[4-(2-pyridin-4-yl-vinyl)-phenyl]-amine and its zinc coordination polymer

Di-pyridin-2-yl-[4-(2-pyridin-4-yl-vinyl)-phenyl]-amine and its zinc coordination polymer are used to detect Hg²⁺ and MeHgI with high selectivity.

High-performance fluorescence sensing of lanthanum ions (La3+) by a polydentate pyridyl-based quinoxaline derivative

A polydentate pyridyl ligand, 2,3,6,7,10,11-hexa(2-pyridyl)-dipyrazino[2,3-f:2′,3′-h] quinoxaline (HPDQ), was found to have excellent light-emitting selectivity to La³⁺ over many other lanthanide metal ions (Ce³⁺, Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺, Tb³⁺, Dy³⁺, Ho³⁺, Er³⁺, Tm³⁺, Yb³⁺, and Lu³⁺).

A dual functional probe for "turn-on" fluorescence response of Pb(2+) and colorimetric detection of Cu(2+) based on a rhodamine derivative in aqueous media

A dual functional probe L based on rhodamine was devised and synthesized. Probe L can sense Pb(2+) and Cu(2+) in aqueous solution through two approaches: a significant fluorescence enhancement caused by Pb(2+) and a visible color change from colorless to orchid induced by Cu(2+). Competitive experiments showed that probe L had high fluorescence sensitivity for Pb(2+) and excellent colorimetric selectivity for Cu(2+) over many environmentally relevant ions. The mechanisms of L for sensing Pb(2+) and Cu(2+) have been well demonstrated by ESI-MS, (1)H NMR titration, IR, the crystal structure of L-Pb(2+) and density functional theory calculation of L-Cu(2+). In addition, fluorescence image detection of Pb(2+) in living cells displayed an enhanced fluorescence effect.

Solvent-dependent "turn-on" fluorescence chemosensor for Mg(2+) based on combination of C=N isomerization and inhibition of ESIPT mechanisms

A fluorescent chemosensor (L) for Mg(2+) has been synthesized and characterized, which exhibits turn-on fluorescence response for Mg(2+) only in alcohol solvent (methanol or ethanol) with high sensitivity and selectivity. But in both nonpolar and polar solvents (cyclohexane, DCM, DMSO or MeCN), L showed negligible fluorescent response for Mg(2+). In order to discover the unique phenomenon, optical measurements, liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) and a high performance liquid chromatography with a fluorescence detector (HPLC-FLD) of L and L with Mg(2+) ions in solvents were studied. In alcohol solvent, [L+alcohol molecule] was formed and the mechanism aspect of L concerning the remarkable fluorescence response for Mg(2+) has been discussed.

β-Hydroxy-α-naphthaldehyde [2-(quinolin-8'-yloxy) acetyl] hydrazone as an efficient fluorescent chemosensor for Mg2+

An efficient fluorescent sensor based on β-hydroxy-α-naphthaldehyde [2-(quinolin-8'-yloxy) acetyl] hydrazone (HL) for Mg2+ has been designed and synthesized. The receptor showed "off-on" fluorescent responses toward Mg2+ in acetonitrile. The reasons for this phenomenon is that the addition of Mg2+ to the solution of HL induce the formation of a 1:1 ligand-metal complex which inhibit excited-state intramolecular proton transfer (ESIPT).

Fluorescent sensing of fluoride in cellular system

Fluoride ions have the important roles in a lot of physiological activities related with biological and medical system, such as water fluoridation, caries treatment, and bone disease treatment. Great efforts have been made to develop new methods and strategies for F(-) detection in the past decades. Traditional methods for the detection of F(-) including ion chromatography, ion-selective electrodes, and spectroscopic techniques have the limitations in the biomedicine research. The fluorescent probes for F(-) are very promising that overcome some drawbacks of traditional fluoride detection methods. These probes exhibit high selectivity, high sensitivity as well as quick response to the detection of fluoride anions. The review commences with a brief description of photophysical mechanisms for fluorescent probes for fluoride, including photo induced electron transfer (PET), intramolecular charge transfer (ICT), fluorescence resonance energy transfer (FRET), and excited-state intramolecular proton transfer (ESIPT). Followed by a discussion about common dyes for fluorescent fluoride probes, such as anthracene, naphalimide, pyrene, BODIPY, fluorescein, rhodamine, resorufin, coumarin, cyanine, and near-infrared (NIR) dyes. We divide the fluorescent probes for fluoride in cellular application systems into nine groups, for example, type of hydrogen bonds, type of cleavage of Si-O bonds, type of Si-O bond cleavage and cylization reactions, etc. We also review the recent reported carriers in the delivery of fluorescent fluoride probes. Seventy-four typical fluorescent fluoride probes are listed and compared in detail, including quantum yield, reaction medium, excitation and emission wavelengths, linear detection range, selectivity for F(-), mechanism, and analytical applications. Finally, we discuss the future challenges of the application of fluorescent fluoride probes in cellular system and in vivo. We wish that more and more excellent fluorescent fluoride probes will be developed and applied in the biomedicine field in the future.

A reversible fluorescent-colorimetric imino-pyridyl bis-Schiff base sensor for expeditious detection of Al3+ and HSO3− in aqueous media

A reversible fluorescent-colorimetric imino-pyridyl bis-Schiff base receptor (N¹E,N⁴E)-N¹,N⁴-bis(pyridine-4-ylmethylene)benzene-1,4-diamine (L) for easy, convenient, rapid and sensitive detection of both Al³⁺ and HSO₃⁻ in aqueous medium has been developed.

A simple pincer-type chemosensor for reversible fluorescence turn-on detection of zinc ion at physiological pH range

A dihydrazone based pincer-type chemosensor (Y) which could detect zinc at physiological pH range with reversible fluorescence “Off–On–Off”.

A highly selective CHEF-type chemosensor for monitoring Zn2+ in aqueous solution and living cells

A new quinolone-based chemosensor was synthesized and successfully applied to quantify and image Zn²⁺ in water samples and living cells.

A single chemosensor for multiple analytes: fluorogenic detection of Zn2+ and OAc− ions in aqueous solution, and an application to bioimaging

A single fluorescent chemosensor 1 for multiple analytes (Zn²⁺ and OAc⁻) has been developed and it can monitor Zn²⁺ ions in living cells.

A new multifunctional Schiff base as a fluorescence sensor for Al3+ and a colorimetric sensor for CN− in aqueous media: an application to bioimaging

A new multifunctional Schiff-base receptor 1 which exhibits an excellent cell-permeable fluorescence for Al³⁺ and a color change for CN⁻ in aqueous media has been prepared.