A “Reactive” Ratiometric Fluorescent Probe for Mercury Species

Luminescent magnetic nanoparticles encapsulated in MOFs for highly selective and sensitive detection of ClO-/SCN- and anti-counterfeiting

It is well-known that ClO- and SCN- can cause adverse effects on the environment and organisms; therefore, development of new strategies for detecting ClO- and SCN-, especially in water, are highly desirable. Here, we present luminous Eu(iii) complex-functionalized Fe3O4 nanoparticles encapsulated into zeolitic imidazolate framework materials (nano-ZIF-8) and successfully employ this nano-MOF as a fluorescence probe for selective and sensitive detection of ClO- and SCN-. The introduction of ClO- into nano-ZIF-8 solution induced a significant decrease in the characteristic fluorescence emission of Eu3+ at 613 nm. However, strong fluorescence emission was again observed when SCN- was successively injected into the prepared nano-ZIF-8-ClO-. Thus, a novel fluorescence system for simultaneous detection of free ClO- and SCN- was established. On the basis of the superior adsorption performance of nano-MOF materials, free residual ClO- and SCN- in water was rapidly, sensitively and selectively detected with a detection limit of 0.133 nM and 0.204 nM, respectively. Moreover, nano-ZIF-8 was successfully used for monitoring the concentration levels of ClO- and SCN- in specimens of tap water and Yellow River water. Furthermore, the reversibility and regeneration of nano-ZIF-8 in sensing ClO- and SCN- is advantageous for applications of nano-ZIF-8 in solid-state sensing and anti-counterfeiting. As far as we know, this is the first time that nano-MOFs have been used as a selective fluorescence probe for ClO-/SCN- detection and anti-counterfeiting.

Excited-state intramolecular proton-transfer (ESIPT) based fluorescence sensors and imaging agents

We review recent advances in the design and application of excited-state intramolecular proton-transfer (ESIPT) based fluorescent probes. These sensors and imaging agents (probes) are important in biology, physiology, pharmacology, and environmental science.

A thiocoumarin-based colorimetric and ratiometric fluorescent probe for Hg2+ in aqueous solution and its application in live-cell imaging

A new intramolecular charge transfer (ICT) based colorimetric and ratiometric fluorescent chemodosimeter for the detection of Hg²⁺ has been rationally designed and developed.

A fluorescent cross-linked supramolecular network formed by orthogonal metal-coordination and host–guest interactions for multiple ratiometric sensing

A supramolecular network can be used for the ratiometric sensing of pH, cyclen and Cl⁻ due to the incorporation of two fluorophores and two non-covalent interactions.

A red-emitting fluorescent probe for the detection of Hg2+ in aqueous medium, living cells and organisms with a large Stokes shift

A vinethene-based fluorescent probe has been developed for the sensitive and selective detection of Hg²⁺ with a low detection limit, a red emission and a large Stokes shift. The probe has been successfully applied to detect Hg²⁺ in aqueous solutions, living cells and organisms.

Ir(iii) complex-based phosphorescence and electrochemiluminescence chemodosimetric probes for Hg(ii) ions with high selectivity and sensitivity

Acetylacetonato Ir(iii) complexes showed turn-on, turn-off, or ratiometric responses in both phosphorescence and electrochemiluminescence channels.

A novel ESIPT-based fluorescent chemodosimeter for Hg2+ detection and its application in live-cell imaging

A novel ESIPT-based fluorescent chemodosimeter for the detection of Hg²⁺ has been rationally designed and developed.

ESIPT-based ratiometric fluorescence probe for the intracellular imaging of peroxynitrite

In this work, we set out to develop an ER directed ESIPT-based ONOO⁻ ratiometric fluorescent probe (ABAH-LW).

Fluorescent Protein-Based Turn-On Probe through a General Protection-Deprotection Design Strategy

We demonstrated a general protection-deprotection strategy for the design of fluorescent protein biosensors through the construction of a turn-on Hg²⁺ sensor. A combination of fluorescent protein engineering and unnatural amino acid mutagenesis was used. Unlike previously reported fluorescent protein-based Hg²⁺ sensors that relied on the binding of Hg²⁺ to the sulfhydryl group of cysteine residues, a well-established chemical reaction, oxymercuration, was transformed into biological format and incorporated into our sensor design. This novel Hg²⁺ sensor displayed good sensitivity and selectivity both in vitro and in live bacterial cells. Over 60-fold change in fluorescence signal output was observed in the presence of 10 μM Hg²⁺, while such a change was undetectable when nine other metal ions were tested. This new design strategy could expand the repertoire of fluorescent protein-based biosensors for the detection of small-molecule analytes.

Synthesis of precipitating chromogenic/fluorogenic β-glucosidase/β-galactosidase substrates by a new method and their application in the visual detection of foodborne pathogenic bacteria

We developed a new efficient method for the synthesis of important indoxyl glycoside substrates for β-glucosidase and β-galactosidase by using 1-acetylindol-3-ones as intermediates. This method was used to synthesise novel precipitating fluorogenic substrates for β-glucosidase based on 2-(benzothiazol-2'-yl)-phenols. We also assessed the application of these substrates in the detection of foodborne pathogenic bacteria.

A novel ratiometric fluorescent probe based on 1, 8-naphthalimide for the detection of Ho3+ and its bioimaging

A ratiometric fluorescent probe for the detection of Ho³⁺ in DMSO-aqueous medium was designed and synthesized based on 1, 8-naphthalimide. The probe displayed response to Ho³⁺ with a fluorescence decrease at 512nm and enhancement at 480nm, accompanying with a distinct fluorescence change from bright yellow-green to cyan. Besides, the probe exhibited a lower detection limit (6×10^-8M) and could be used in intracellular fluorescence imaging. To the best of the knowledge, it was the first ratiometric fluorescent probe for Ho³⁺ detection. This probe was expected to be a useful tool for further elucidating the roles of Ho³⁺ in materials, biology and environment.

A coumarin based Schiff base probe for selective fluorescence detection of Al3+ and its application in live cell imaging

A new coumarin based Schiff base compound, CSB-1 has been synthesized to detect metal ion based on the chelation enhanced fluorescence (CHEF). The cation binding properties of CSB-1 was thoroughly examined in UV-vis and fluorescence spectroscopy. In fluorescence spectroscopy the compound showed high selectivity toward Al³⁺ ion and the Al³⁺ can be quantified in mixed aqueous buffer solution (MeOH: 0.01M HEPES Buffer; 9:1; v/v) at pH7.4 as well as in BSA media. The fluorescence intensity of CSB-1 was enhanced by ~24 fold after addition of only five equivalents of Al³⁺. The fluorescence titration of CSB-1 with Al³⁺ in mixed aqueous buffer afforded a binding constant, K_a=(1.06±0.2)×10⁴M^-1. The colour change from light yellow to colourless and the appearance of blue fluorescence, which can be observed by the naked eye, provides a real-time method for Al³⁺ sensing. Further the live cell imaging study indicated that the detection of intracellular Al³⁺ ions are also readily possible in living cell.

Unified synthesis of mono/bis-arylated phenols via RhIII-catalyzed dehydrogenative coupling

2,6-Bis-arylated phenols are rarely reported and are synthetically challenging. Directed C-H functionalization reactions, using a directing group (DG), might provide a convenient solution to their synthesis. However, this strategy usually results in partial cleavage of the directing group, preventing further/second C-H activation cascades. Herein we report a general strategy that allows for the precise control of the oxidation pathways so that directing groups can be either preserved or cleaved. We found that N-phenoxyacetamides could undergo ortho-arylation reactions with or without an external oxidant, yielding products with different oxidation states, notably the rare bis-arylated phenols. Notably, a unique rhodacycle intermediate was isolated, characterized by X-ray crystallography, and confirmed to be an active catalyst. Switching between internal and external oxidation could be a general strategy in diverse directed C-H functionalization reactions to realize bis-functionalized products.

A new hydroxynaphthyl benzothiazole derived fluorescent probe for highly selective and sensitive Cu(2+) detection

A new reactive probe, 1-(benzo[d]thiazol-2-yl)naphthalen-2-yl-picolinate (BTNP), was designed and synthesized. BTNP acts as a highly selective probe to Cu(2+) in DMSO/H2O (7/3, v/v, Tris-HCl 10mM, pH=7.4) solution based on Cu(2+) catalyzed hydrolysis of the picolinate ester moiety in BTNP, which leads to the formation of an ESIPT active product with dual wavelength emission enhancement. The probe also possesses the advantages of simple synthesis, rapid response and high sensitivity. The pseudo-first-order reaction rate constant was calculated to be 0.205min(-1). Moreover, application of BTNP to Cu(2+) detection in living cells and real water samples was also explored.

Accelerated hydration reaction of an unsymmetrical tolan evidenced by a Hg(ii)-trapped macrocycle and its application as a Hg(ii)-selective indicator

Hg(ii)-mediated hydration reactions of unsymmetrical quinoline type tolans were studied. The observed accelerated reactions of the tolans rely on the additional binding motifs of the tolan, as supported by the X-ray structure of the macrocycle (2b). The analyte-specific reaction allows us to detect Hg(ii) in buffered media.

Competitive excited-state single or double proton transfer mechanisms for bis-2,5-(2-benzoxazolyl)-hydroquinone and its derivatives

The excited state intramolecular proton transfer (ESIPT) mechanisms of 2-(2-hydroxyphenyl)benzoxazole (HBO), bis-2,5-(2-benzoxazolyl)-hydroquinone (BBHQ) and 2,5-bis(5'-tert-butyl-benzoxazol-2'-yl)hydroquinone (DHBO) have been investigated using time-dependent density functional theory (TDDFT). The calculated vertical excitation energies based on the TDDFT method reproduced the experimental absorption and emission spectra well. Three kinds of stable structures were found on the S1 state potential energy surface (PES). A new ESIPT mechanism that differs from the one proposed previously (Mordzinski et al., Chem. Phys. Lett., 1983, 101, 291. and Lim et al., J. Am. Chem. Soc., 2006, 128, 14542.) is proposed. The new mechanism includes the possibility of simultaneous double proton transfer, or successive single transfers, in addition to the accepted single proton transfer mechanism. Hydrogen bond strengthening in the excited state was based on primary bond lengths, angles, IR vibrational spectra and hydrogen bond energy. Intramolecular charge transfer based on the frontier molecular orbitals (MOs) also supports the proposed mechanism of the ESIPT reaction. To further elucidate the proposed mechanism, reduced dimensionality PESs of the S0 and S1 states were constructed by keeping the O-H distance fixed at a series of values. The potential barrier heights among the local minima on the S1 surface imply competitive single and double proton transfer branches in the mechanism. Based on the new ESIPT mechanism, the observed fluorescence quenching can be satisfactorily explained.

Molecular engineering of a dual emission near-infrared ratiometric fluorophore for the detection of pH at the organism level

A near-infrared ratiometric fluorophore (NIR-HBT) was rationally designed and constructed by expanding both the excitation and emission wavelength of the classical ratiometric fluorophore 2-(benzothiazol-2-yl)phenol (HBT) into the near-infrared region. The NIR-HBT was easily synthesized by incorporating the HBT module into the hemicyanine skeleton and showed evident NIR ratiometric fluorophore characteristics. Further application of the new fluorophore for pH detection demonstrated that NIR-HBT possesses superior overall analytical performance and NIR-HBT was successfully applied for detection of acidosis caused by inflammation in living animal tissue, which indicated the potential application value of NIR-HBT in biological imaging and sensing.

A novel 2-(2′-aminophenyl)benzothiazole derivative displays ESIPT and permits selective detection of Zn2+ ions: experimental and theoretical studies

Synthesis of a novel 2-(2′-aminophenyl)benzothiazole based probe (1) and demonstration of excited state intramolecular proton transfer (ESIPT) with a large Stokes shift (∼246 nm) are presented.

Synthesis, Crystal Structure and Fluorescent Properties of a Novel Benzothiazole-Derived Fluorescent Probe for Zn2+

A novel turn-on fluorescent probe containing a benzothiazole fluorophore has been synthesised and its structure confirmed by single crystal X-ray diffraction. The probe exhibited high selectivity to Zn2+ over other metal ions and demonstrated high sensitivity for Zn2+ with a 12-fold fluorescence enhancement. It also showed a fast response to Zn2+ and a complexation ratio towards Zn2+ of 1:1.

White emission magnetic nanoparticles as chemosensors for sensitive colorimetric and ratiometric detection, and degradation of ClO⁻ and SCN⁻ in aqueous solutions based on a logic gate approach

Fluorescent chemosensors for detecting single anions have been largely synthesized. However, the simultaneous detection and degradation of multiple anions remain a major challenge. Herein we report the synthesis of a white emission nanoprobe on the basis of a Coumarin-Rhodamine CR1-Eu complex coordinated to dipicolinic acid (dpa)-PEG-Fe3O4 nanoparticles for the selective detection of ClO(-) and SCN(-) ions on controlling by a logic gate. The obtained nanoprobe exhibits three individual primary colors (blue, green, and red) as well as white emission at different excitation energies. Interestingly, this nanoprobe shows a marked rose red to violet emission color change in response to ClO(-), a reversible violet to rose red emission color change in response to SCN(-), and high ClO(-) and SCN(-) selectivity and sensitivity with a detection limit of 0.037 and 0.250 nM, respectively. Furthermore, the SCN(-) and ClO(-) can degrade simultaneously through the redox reaction between ClO(-) and SCN(-).

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.

A ratiometric fluorescent probe for rapid, sensitive and selective detection of sulfur dioxide with large Stokes shifts by single wavelength excitation

A ratiometric fluorescent probe was developed for rapid, sensitive and selective detection of SO₃²⁻ with large Stokes shifts. Imaging intracellular SO₃²⁻ was successfully demonstrated in living HNE-2 cells.

A switch-on MRI contrast agent for noninvasive visualization of methylmercury

The first Gd(iii)-based T₁ MRI contrast agent, o-MeHgGad, is demonstrated for noninvasive visualization of CH₃Hg⁺.

A facile naphthalene-based fluorescent chemodosimeter for mercury ions in aqueous solution

A facile naphthalene-based fluorescence “turn-on” chemodosimeter for rapid, selective and sensitive detection of Hg²⁺ by mercury-promoted hydrolysis of the vinylether group has been reported.

Fluorescent and colorimetric sensors for environmental mercury detection

The development of fluorescent and colorimetric sensing strategies for environmental mercury is described.

Combining the PeT and ICT mechanisms into one chemosensor for the highly sensitive and selective detection of zinc

A novel fluorescent sensor (ZS1) based on the dual-mechanism of PeT/ICT for the highly sensitive and selective detection of Zn²⁺was designed and synthesized.

Synthesis and characterization of monometallic rhenium(i) complexes and their application as selective sensors for copper(ii) ions

Monometallic Re(i) complexes, selective and sensitive sensor of Cu(ii) ion, show substantial enhancement in the emission intensity, quantum yield, and lifetime due to the restriction of CN isomerization.

Producing a dual-fluorescent molecule by tuning the energetics of excited-state intramolecular proton transfer

We report herein the selective preparation of normal, tautomeric, and dual-fluorescent molecules with a common ESIPT core.

ESIPT and CHEF based highly sensitive and selective ratiometric sensor for Al3+ with imaging in human blood cells

We have synthesised a probe for the fluorescence ratiometric detection of Al³⁺. This probe can be used to image Al³⁺ in living cells.

An ESIPT-based fluorescent probe for highly selective and ratiometric detection of mercury(ii) in solution and in cells

A highly selective and sensitive ratiometric fluorescent probe for mercury(ii) has been developed. It has been demonstrated that the probe is able to detect Hg²⁺ level in water samples and living cell.

A highly sensitive hemicyanine-based fluorescent chemodosimeter for mercury ions in aqueous solution and living cells

A novel hemicyanine-based fluorescence turn-on chemodosimeter for Hg²⁺ by mercury triggered hydrolysis of vinyl ether group has been reported.

Palladium catalyzed Csp2–H activation for direct aryl hydroxylation: the unprecedented role of 1,4-dioxane as a source of hydroxyl radicals

Direct aryl hydroxylation has been achieved via palladium-catalysed C_sp2–H activation using versatile directing groups through unprecedented hydroxyl transfer from 1,4-dioxane.