Pyrene-Based "Turn-On" Fluorescent Polymeric Probe with Thioacetal Units in the Main Chain for Mercury(II) Detection in Aqueous Solutions and Living Cells

A water-soluble polymeric pyrene-based polythioacetal (PTA-Py) with thioacetal units in the main chain is simply synthesized by direct polycondensation of 3, 6-dioxa-1, 8-octanedithiol, 1-pyrene formaldehyde, and mPEG2k-SH. The probe PTA-Py shows a good fluorescence response to Hg2+ ions due to the Hg2+-promoted deprotection reaction of thioacetal groups to regenerate the original 1-pyrene formaldehyde compound. After adding Hg2+ to the PTA-Py solution, the fluorescence intensity (FI) gradually increases with increasing concentrations of Hg2+. Compared with other metal ions, the probe exhibits high sensitivity, good selectivity, and rapid response to Hg2+. The low detection limits are 12.3 nm in ethanol-PBS buffer and 13.3 nm in water, respectively. The results imply that the simply synthesized water-soluble polymeric probe had potential applications in the rapid detection of Hg2+ ions in aqueous solutions. Moreover, the polymeric PTA-Py shows high sensitivity for CH3Hg+ with detection limits of 26.5 nm in ethanol/PBS buffer. In addition, PTA-Py can efficiently detect Hg2+ ions in HeLa cells. The results demonstrate that a valuable method is developed for biocompatible polymeric sensors for Hg2+ ions in biological and environmental samples.

Fluorogenic In Situ Thioacetalization: Expanding the Chemical Space of Fluorescent Probes, Including Unorthodox, Bifurcated, and Mechanosensitive Chalcogen Bonds

Progress with fluorescent flippers, small-molecule probes to image membrane tension in living systems, has been limited by the effort needed to synthesize the twisted push-pull mechanophore. Here, we move to a higher oxidation level to introduce a new design paradigm that allows the screening of flipper probes rapidly, at best in situ. Late-stage clicking of thioacetals and acetals allows simultaneous attachment of targeting units and interfacers and exploration of the critical chalcogen-bonding donor at the same time. Initial studies focus on plasma membrane targeting and develop the chemical space of acetals and thioacetals, from acyclic amino acids to cyclic 1,3-heterocycles covering dioxanes as well as dithiolanes, dithianes, and dithiepanes, derived also from classics in biology like cysteine, lipoic acid, asparagusic acid, DTT, and epidithiodiketopiperazines. From the functional point of view, the sensitivity of membrane tension imaging in living cells could be doubled, with lifetime differences in FLIM images increasing from 0.55 to 1.11 ns. From a theoretical point of view, the complexity of mechanically coupled chalcogen bonding is explored, revealing, among others, intriguing bifurcated chalcogen bonds.

Ir(III) Complexes with AIE Characteristics for Biological Applications

Both biological process detection and disease diagnosis on the basis of luminescence technology can provide comprehensive insights into the mechanisms of life and disease pathogenesis and also accurately guide therapeutics. As a family of prominent luminescent materials, Ir(III) complexes with aggregation-induced emission (AIE) tendency have been recently explored at a tremendous pace for biological applications, by virtue of their various distinct advantages, such as great stability in biological media, excellent fluorescence properties and distinctive photosensitizing features. Significant breakthroughs of AIE-active Ir(III) complexes have been achieved in the past few years and great progress has been witnessed in the construction of novel AIE-active Ir(III) complexes and their applications in organelle-specific targeting imaging, multiphoton imaging, biomarker-responsive bioimaging, as well as theranostics. This review systematically summarizes the basic concepts, seminal studies, recent trends and perspectives in this area.

Colorimetric detection of Hg2+ with an azulene-containing chemodosimeter via dithioacetal hydrolysis

Azulene is a bicyclic aromatic chromophore that absorbs in the visible region. Its absorption maximum undergoes a hypsochromic shift if a conjugated electron-withdrawing group is introduced at the C1 position. This fact can be exploited in the design of a colorimetric chemodosimeter that functions by the transformation of a dithioacetal to the corresponding aldehyde upon exposure to Hg2+ ions. This chemodosimeter exhibits good chemoselectivity over other metal cations, and responds with an unambiguous colour change clearly visible to the naked eye. Its synthesis is concise and its ease of use makes it appropriate in resource-constrained environments, for example in determing mercury content of drinking water sources in the developing world.

A Highly Selective Fluorescent Probe for Hg2+ Based on a 1,8-Naphthalimide Derivative

Hg2+ has a significant hazardous impact on the environment and ecosystem. There is a great demand for new methods with high selectivity and sensitivity to determine mercury in life systems and environments. In this paper, a novel turn-on Hg2+ fluorescent probe has been reported with a naphthalimide group. The Hg2+ fluorescent probe was designed by the inspiration of the well-known specific Hg2+-triggered thioacetal deprotection reaction. A 1,2-dithioalkyl group was chosen as the specific recognition site of Hg2+. The probe showed weak fluorescence without Hg2+, and the color of the solution was light yellow. In the presence of Hg2+, the probe reacted specifically with the mercury ion to produce an aldehyde and emitted strong fluorescence, and the color of the solution also turned light green, thus realizing the monitoring of the mercury ion. The Hg2+ fluorescent probe showed outstanding sensitivity and selectivity toward Hg2+. Furthermore, the Hg2+ fluorescent probe could work in a wide pH range. The linear relationship between the fluorescence intensity at 510 nm and the concentration of Hg2+ was obtained in a range of Hg2+ concentration from 2.5 × 10-7 to 1.0 × 10-5 M. The detection limit was found to be 4.0 × 10-8 M for Hg2+. Furthermore, with little cell toxicity, the probe was successfully applied to the confocal image of Hg2+ in PC-12 cells.

A polymer membrane tethered with a cycloruthenated complex for colorimetric detection of Hg2+ ions

A new cyclometallated ruthenium complex (Ru1) involving a 2-(2-thienyl)pyridine and a benzo[e]indolium block connected with a hexanoic acid was successfully synthesized and characterized, which exhibited the high sensitivity and selectivity to Hg²⁺ over other common metal ions with the detection limit of as low as 0.053 μM in aqueous system. Then, it was grafted onto a polymer membrane to afford a Hg²⁺-sensitive membrane (sensor 1), which was characterized by FT-IR, SEM and XPS spectra, respectively. When sensor 1 was dipped into the aqueous solution of Hg²⁺ ions, the color of the membrane changed from dark-red to yellow, which could be observed by naked eyes easily. It should be noted that the membrane can absorb Hg²⁺ ions well in aqueous solution and the adsorption capacity of this polymer membrane for Hg²⁺ ions was determined by atomic absorption spectroscopy, indicating that it also could be used as a potential material for removal of Hg²⁺ ions.

A highly sensitive and selective colorimetric probe based on a cycloruthenated complex: an Hg2+-promoted switch of thiophene coordination

A cyclometalated ruthenium complex [Ru(pthb)(bpy)2]+ (1, bpy = 2,2'-bipyridine, Hpthb = 3,3-dimethyl-2-(5-pyridylthiophen-2-yl)vinyl-benzo[e]indolium-1-propylsulfonate) could be converted from a C-coordinated structure to non-metallated species with N,S-bonded Hpthb upon treatment with mercury(ii) ions in water. Strikingly, the switch in the coordination mode resulted in a great absorption change along with a change in the solution color of 1 from dark red to light yellow. Therefore, 1 can be used as a colorimetric probe to detect mercury(ii) ions by the naked eye. Although the emission was not observed for 1 in water, it still demonstrated an appreciably low detection limit of 21 nM by using UV-Vis absorption spectroscopy, which was comparable with those of some probes determined by ratiometric fluorescence spectroscopy.

A new 3-hydroxyphthalimide-based turn-on fluorescent probe for Hg2+ detection in aqueous solution

A new 3-hydroxyphthalimide-based turn-on fluorescent probe is designed and synthesized. This probe can be used to determine the presence of Hg2+ ions by fluorescence spectroscope with high selectivity over other metal ions in aqueous solution. The analytical detection limit for Hg2+ is as low as 6.5 × 10−7 M. The recognition mechanism is attributed to Hg2+-promoted carbonothioate group cleavage and a subsequent excited-state intramolecular proton transfer mechanisms.

A Eu3+-inspired fluorescent carbon nanodot probe for the sensitive visualization of anthrax biomarker by integrating EDTA chelation

The rapid and sensitive visualization of 2,6-dipicolinic acid (DPA, a unique anthrax biomarker) is essential to prevent anthrax disease or biological terrorist attack. In this study, a Eu³⁺-labeled ethylenediaminetetraacetic acid loaded hyperbranched polyethyleneimine carbon nanodot (hPEI-CD-EDTA-Eu³⁺) nanoprobe has been proposed for the ratiometric DPA detection. The sensing mechanism is based on the rapid DPA-Eu³⁺ chelation within 30 s and subsequent enhanced fluorescence emission through the antenna effect. With the introduction of EDTA chelating unit, the resulted fluorescence of Eu³⁺-complex is greatly enhanced, which endows sensitive DPA perception. By employing hPEI-CD as the internal reference, ratiometric DPA sensing is realized with a good linearity in the concentration range from 1.0 to 100 nM, with a limit of detection of 190 pM (S/N = 3). The specific chelation affinity between Eu³⁺ and DPA provides satisfying selectivity over other amino acids and ions. Using nanoprobe-loaded polyvinylidene fluoride paper as the analytical device, point-of-care DPA visualization is achieved. Furthermore, the practical application of designed paper device is validated by the visual detection of metabolic DPA-release from Bacillus subtilis spores.

The functionalized ruthenium(II) polypyridine complexes for the highly selective sensing of mercury ions

A series of new ruthenium(II) polypyridine complexes appending with thioether groups were designed, synthesized and characterized. The sensing ability of the complexes toward mercury ions were studied by electronic absorption and emission spectra, and the reaction of the complexes with mercury ions were also confirmed by ESI mass spectroscopy and ¹HNMR spectroscopy. The thioether groups would react with mercury ion fast to form aldehyde group leading to the significant change in the spectra. The color of the complex changed from yellow to orange after addition of mercury ions, and the color of the emission changed from red orange to dark red with a large red shift (~80 nm). Importantly, these kinds of ruthenium(II) complexes show a unique recognition of mercury ions over other metal ions. The complexes with more thioether groups also showed a better sensitivity toward mercury ions, this is good strategy for the further design of the new phosphorescent probes for sensing of mercury ions.

Cyclometalated iridium-BODIPY ratiometric O2 sensors

Here we introduce a new class of ratiometric O2 sensors for hypoxic environments. Two-component structures composed of phosphorescent cyclometalated Ir(iii) complexes and the well-known organic fluorophore BODIPY have been prepared by the 1 : 1 reaction of bis-cyclometalated iridium synthons with pyridyl-substituted BODIPY compounds. Two different cyclometalating ligands are used, which determine the relative energies of the iridium-centered and BODIPY-centered excited states, and the nature of the linker between iridium and BODIPY also has a small influence on the photoluminescence. Some of the conjugates exhibit dual emission, with significant phosphorescence from the iridium site and fluorescence from the BODIPY, and thus function as ratiometric oxygen sensors. Oxygen quenching experiments demonstrate that as O2 is added the phosphorescence is quenched while the fluorescence is unaffected, with dynamic ranges that are well suited for hypoxic sensing (pO2 < 160 mmHg).

A highly selective colorimetric and ratiometric fluorescent probe for instantaneous sensing of Hg2+ in water, soil and seafood and its application on test strips

A new simple and efficient oligothiophene-based colorimetric and ratiometric fluorescent probe has been developed for highly sensitive and fast detection of Hg2+ in water, soil and seafood. The probe 5-(1,3-dithiolan-2-yl)-2,2':5',2″-terthiophene 3 TS can selectively detect Hg2+ via the Hg2+-promoted deprotection reaction of thioacetals, which caused a remarkable color change from colorless to yellow and a strong fluorescence enhancement with emission color varying from blue to yellow, enabling naked-eye detection of Hg2+. The probe shows high sensitivity with the detection limit down to 1.03 × 10-8 M. Visual color changes of 3 TS were observed on filter paper and TLC testing strips when they were impregnated on testing strips and immersed in Hg2+ solution. Moreover, the probe 3 TS has been successfully used to rapidly detect trace amounts of hazardous Hg2+ ions in tap, distilled, river and lake water, cropland soil, fish, shrimp and kelp samples with acceptable results and good recoveries.

A two-photon ratiometric ESIPT probe for fast detection and bioimaging of palladium species

A two-photon ratiometric ESIPT probe for fast detection of palladium species, which can be used for bioimaging has been designed.

A two-photon ratiometric ESIPT probe for the discrimination of different palladium species and its application in bioimaging

A two-photon ratiometric ESIPT probe for the discrimination of different palladium species which could be used for bioimaging.

Single excited state intramolecular proton transfer (ESIPT) chemodosimeter based on rhodol for both Hg2+ and OCl−: ratiometric detection with live-cell imaging

We have synthesised a ratiometric fluorescence chemodosimeter, STBR, for the detection of Hg²⁺ and OCl⁻ in one platform over other cations, anions and oxidants in aqueous solution.

A highly selective and sensitive turn-on chemodosimeter for hypochlorous acid based on an iridium(III) complex and its application to bioimaging

A novel and easily accessible luminescent iridium(iii) complex [Ir(tpy)2(N^N)]PF6 (, tpy = 2-(p-tolyl)pyridine, N^N = 4-[(4-amino-3-nitrophenoxy)-methylene]-4'-methyl-2,2'-bipyridine) for the sensing of HOCl has been designed and synthesized. The detection strategy is based on the HOCl-promoted cleavage of the PET quenching 4-amino-3-nitrophenyloxy moiety of the weakly emissive complex , which gives rise to a highly luminescent complex [Ir(tpy)2(N^N')]PF6 (, N^N' = 4-hydroxymethyl-4'-methyl-2,2'-bipyridine). Comparisons of the absorption, emission and mass spectra of in the absence and presence of HOCl have all confirmed the transformation of to . Titration and competition experiments have revealed high sensitivity and high selectivity of for HOCl, respectively. Significantly, the feasibility of the sensor under physiological conditions enables the successful luminescent imaging of HOCl in HeLa cells.

A reusable ratiometric two-photon chemodosimeter for Hg2+ detection based on ESIPT and its application in bioimaging

A novel reaction-based recyclable two-photon chemodosimeter for Hg²⁺ detection in nearly aqueous solution was developed, which could be used for bioimaging.

A highly selective ratiometric bifunctional fluorescence probe for Hg2+and F−ions

A dithioacetal-containing triarylborane behaves as a promising ratiometric bifunctional fluorescence probe to detect Hg²⁺and F⁻simultaneously.

New ‘aggregation induced emission (AIE)’ active cyclometalated iridium(iii) based phosphorescent sensors: high sensitivity for mercury(ii) ions

Strategic design and syntheses of an AIE active bis-cyclometalatediridium(iii) complex were carried out for highly selective and sensitive detection of mercuric ions.