A reaction-based ratiometric fluorescent sensor for the detection of Hg(ii) ions in both cells and bacteria

Synthetic ratiometric fluorescent probes for detection of ions

Metal cations and anions are essential for versatile physiological processes. Dysregulation of specific ion levels in living organisms is known to have an adverse effect on normal biological events. Owing to the pathophysiological significance of ions, sensitive and selective methods to detect these species in biological systems are in high demand. Because they can be used in methods for precise and quantitative analysis of ions, organic dye-based ratiometric fluorescent probes have been extensively explored in recent years. In this review, recent advances (2015-2019) made in the development and biological applications of synthetic ratiometric fluorescent probes are described. Particular emphasis is given to organic dye-based ratiometric fluorescent probes that are designed to detect biologically important and relevant ions in cells and living organisms. Also, the fundamental principles associated with the design of ratiometric fluorescent probes and perspectives about how to expand their biological applications are discussed.

Thiadiazole containing N- and S-rich highly ordered periodic mesoporous organosilica for efficient removal of Hg(ii) from polluted water

We report a new N- and S-rich highly ordered periodic mesoporous organosilica material DMTZ-PMO bearing thiadiazole and thiol moieties inside the pore-wall for very efficient and fast removal of Hg²⁺ from polluted water (uptake = 2081 mg g⁻¹).

Molecular probe designviathe “covalent-assembly” principle

Fluorescent probes are useful molecular tools. We summarize the recent progress with the “covalent-assembly” design principle, which warrants high-performance fluorescence probes exhibiting a highly sensitive turn-on signal from the dark background.

Deeper insight into protease-sensitive "covalent-assembly" fluorescent probes for practical biosensing applications

We report a rational and systematic study devoted to the structural optimisation of a novel class of protease-sensitive fluorescent probes that we recently reported (S. Debieu and A. Romieu, Org. Biomol. Chem., 2017, 15, 2575-2584), based on the "covalent-assembly" strategy and using the targeted enzyme penicillin G acylase as a model protease to build a fluorescent pyronin dye by triggering a biocompatible domino cyclisation-aromatisation reaction. The aim is to identify ad hoc probe candidate(s) that might combine fast/reliable fluorogenic "turn-on" response, full stability in complex biological media and ability to release a second molecule of interest (drug or second fluorescent reporter), for applications in disease diagnosis and therapy. We base our strategy on screening a set of active methylene compounds (C-nucleophiles) to convert the parent probe to various pyronin caged precursors bearing Michael acceptor moieties of differing reactivities. In vitro stability and fluorescent enzymatic assays combined with HPLC-fluorescence analyses provide data useful for defining the most appropriate structural features for these fluorogenic scaffolds depending on the specifications inherent to biological application (from biosensing to theranostics) for which they will be used.

Combining Wittig Olefination with Photoassisted Domino Reaction To Distinguish 5-Formylcytosine from 5-Formyluracil

In view of the important epigenetic functions of 5-formylcytosine (5fC), the development of quantitative detection methods for 5fC is a long-standing issue. In this regard, how to distinguish 5fC from 5-formyluracil to achieve higher accuracy is particularly difficult because the latter one is more reactive. Herein, we reported a phosphorus ylide, YC-CN, and introduced a triple domino reaction to fluorescently switch on 5fC with excellent selectivity, which also enable us to quantify 5fC mutations induced by γ-irradiation. This Wittig-initiated covalent labeling strategy provide a novel strategy for qualitative and quantitative detection of 5fC.

Recent Advances and Perspectives of Molecularly Imprinted Polymer-Based Fluorescent Sensors in Food and Environment Analysis

Molecular imprinting technology (MIT), also known as molecular template technology, is a new technology involving material chemistry, polymer chemistry, biochemistry, and other multi-disciplinary approaches. This technology is used to realize the unique recognition ability of three-dimensional crosslinked polymers, called the molecularly imprinted polymers (MIPs). MIPs demonstrate a wide range of applicability, good plasticity, stability, and high selectivity, and their internal recognition sites can be selectively combined with template molecules to achieve selective recognition. A molecularly imprinted fluorescence sensor (MIFs) incorporates fluorescent materials (fluorescein or fluorescent nanoparticles) into a molecularly imprinted polymer synthesis system and transforms the binding sites between target molecules and molecularly imprinted materials into readable fluorescence signals. This sensor demonstrates the advantages of high sensitivity and selectivity of fluorescence detection. Molecularly imprinted materials demonstrate considerable research significance and broad application prospects. They are a research hotspot in the field of food and environment safety sensing analysis. In this study, the progress in the construction and application of MIFs was reviewed with emphasis on the preparation principle, detection methods, and molecular recognition mechanism. The applications of MIFs in food and environment safety detection in recent years were summarized, and the research trends and development prospects of MIFs were discussed.

A feedback-controlling digital microfluidic fluorimetric sensor device for simple and rapid detection of mercury (II) in costal seawater

By combination of miniaturization potential of digital microfluidics (DMF) and sensitivity of fluorescence probe, an integrated sensor device has been initially constructed for mercury detection in coastal waters. The actuation feature of the detecting target, seawater droplet, which remains unclear, was basically explored. To overcome a potential risk of driven failure, induced by diversity ion ingredients in seawater, a feedback control loop was included into control system. Analyzing method for coastal waters was well established on DMF, which showed satisfied stability and selectivity in Hg sensing under high salinity condition, with the sensitivity of Hg²⁺ at the parts per billion level and total testing time less than 20s. With the advantages of being fast, amenable to automation and low cost, this device is promising for the formation of simple and rapid sensor device, especially for a routine monitoring and emergency detection of Hg/or other metals in coastal waters.

A Mass-Ratiometry-Based CD45 Barcoding Method for Mass Cytometry Detection

Mass cytometry (CyTOF) is a critical cell profiling tool in acquiring multiparameter proteome data at the single-cell level. A major challenge in CyTOF analysis is sample-to-sample variance arising from the pipetting process, staining variation, and instrument sensitivity. To reduce such variations, cell barcoding strategies that enable the combination of individual samples prior to antibody staining and data acquisition on CyTOF are often utilized. The most prevalent barcoding strategy is based on a binary scheme that cross-examines the existence or nonexistence of certain mass signals; however, it is limited by low barcoding efficiency and high cost, especially for large sample size. Herein, we present a novel barcoding method for CyTOF application based on mass ratiometry. Different mass tags with specific fixed ratios are used to label CD45 antibody to achieve sample barcoding. The presented method exponentially increases the number of possible barcoded samples with the same amount of mass tags compared with conventional methods. It also reduces the overall time for the labeling process to 40 min and avoids the need for expensive commercial barcoding buffer reagents. Moreover, unlike the conventional barcoding process, this strategy does not pre-permeabilize cells before the barcoding procedure, which offers additional benefits in preserving surface biomarker signals.

Dinuclear HgII tetracarbene complex-triggered aggregation-induced emission for rapid and selective sensing of Hg2+ and organomercury species

Mercury-mediated chelate ring formation and subsequent aggregation gives strong fluorescence for rapid and selective sensing of Hg²⁺ and organomercury.

Rapid, reliable and highly selective detection of mercury species, including Hg²⁺ ions and organomercury, is of significant importance for environmental protection and human health. Herein, a new fluorescent dye 1,1,2,2-tetrakis[4-(3-methyl-1H-benzimidazol-1-yl)phenyl ethylene tetraiodide (Tmbipe) with aggregation-induced emission (AIE) potential was prepared and characterized. The presence of four positively charged methylated benzimidazole groups endows Tmbipe with excellent water solubility and almost undetectable background fluorescence. However, it can coordinate with two Hg²⁺ ions or two organomercury molecules (e.g. methylmercury and phenylmercury) to form a planar dinuclear Hg^II tetracarbene complex, which can then self-aggregate to turn on AIE fluorescence. Such a fluorescence turn-on process can be completed in 3 min. In addition, synergic rigidification of the tetraphenylethylene-bridged Tmbipe molecule by mercury-mediated chelate ring formation and subsequent aggregation results in obviously higher fluorescence enhancement than that given by the single aggregation-induced one. Low background, high fluorescence enhancement and rapid response time make Tmbipe a good fluorescent probe for reliable, sensitive and highly selective quantitation of both inorganic and organic mercury species. This probe was also demonstrated to work well for identification of mercury species accumulation in living cells.

Synthesis, recognition and sensing properties of dipyrrolylmethane-based anion receptors

Two tweezer-like anion receptors 2,2'‑bis(2‑cyano‑2‑phenylvinyl)‑5,5'‑dimethyl dipyrromethane (1) and 2,2'‑bis[2‑cyano‑2‑(4‑nitrophenyl)vinyl]‑5,5'‑dimethyl dipyrromethane (2) were synthesized in good yields, via a facile condensation of diformyldipyrromethane and the appropriate phenylacetonitrile. Anion recognition properties of these receptors were studied in detail in DMSO solution, by means of UV-vis and ¹H NMR titration techniques. The obtained results indicated that receptor 2 containing a terminal nitro group exhibited the strong and selective binding to biologically important fluoride and dihydrogenphosphate ions over other anions. In addition, the binding strength of receptor 2 with fluoride was enhanced by a factor of 18, relative to receptor 1 lacking the nitro group. Remarkably, the presence or absence of nitro group within receptor compounds also had a great influence on the anion-binding selectivity. In particular, a distinct color change of DMSO solution of receptor 2 was observed only upon addition of fluoride, showing the potential of 2 acting as an effective colorimetric sensor for the detection of fluoride anion.

Sensitive Water-Soluble Fluorescent Probe Based on Umpolung and Aggregation-Induced Emission Strategies for Selective Detection of Hg2+ in Living Cells and Zebrafish

Using Hg²⁺-induced umpolung reaction and aggregation induced emission (AIE), we have rationally developed a water-soluble fluorescent probe 2,2'-(((4-(4,5-bis(4-methoxyphenyl)-1-phenyl-1H-imidazol-2-yl)phenyl)methylene)bis(sulfanediyl))diethanol (MPIPBS) for Hg²⁺ detection. MPIPBS was found to have high selectivity and sensitivity toward Hg²⁺ detection. The mechanism of MPIPBS response to Hg²⁺ was verified by ¹H NMR titration, HPLC, and HRMS spectroscopy. The detection limit was examined to be 1.45 nM, which is lower than most reported probes for Hg²⁺. Taking advantage of excellent optical properties of AIEgen, a paper based sensor for Hg²⁺ detection was fabricated by immobilizing the MPIPBS on Waterman test paper. Meanwhile, MPIPBS showed satisfactory analytical performance in real water and urine samples. Further, thanks to the high water solubility, cell membrane permeability and low cytotoxicity, MPIPBS was further used to detect Hg²⁺ both in living cells and zebrafish. We anticipate that the prepared probe was available to detect Hg²⁺ in environment and biosamples.

Aggregation-induced emission enhancement (AIEE)-active tetraphenylethene (TPE)-based chemosensor for Hg2+ with solvatochromism and cell imaging characteristics

An aggregation-induced emission enhancement (AIEE)-active fluorescent sensor based on a tetraphenylethene (TPE) unit has been successfully designed and synthesized. Interestingly, the luminogen could detect Hg²⁺ with high selectivity in an acetonitrile solution without interference from other competitive metal ions, and the detection limit was 7.46 × 10⁻⁶ mol L⁻¹. Furthermore, the luminogen also showed interesting solvatochromic behavior and superior cell imaging performance.

A TPE-based AIEE-active fluorescent sensor for Hg²⁺ was synthesized. Furthermore, it showed solvatochromism and cell imaging characteristics.

Synthesis, photophysical properties, and self-dimerization studies of 2-λ5-phosphaquinolin-2-ones

Rationally designed phosphaquinolinone derivatives containing electron-donating and/or -withdrawing groups are reported, with dimerization constants up to 525 M⁻¹.

A highly selective and sensitive ESIPT-based coumarin–triazole polymer for the ratiometric detection of Hg2+

A reversible ESIPT based system for the detection of Hg²⁺ was developed. The system exhibited better properties compared to that of recently developed ratiometric fluorescent systems.

A paper-based chemosensor for highly specific, ultrasensitive, and instantaneous visual detection of toxic phosgene

A chemosensor containing an o-hydroxyaniline unit as the reaction site was developed for colorimetric and fluorimetric detection of phosgene, which showed fast response (15 s), high specificity, and an extremely low detection limit.

A carbonothioate-based far-red fluorescent probe for the specific detection of mercury ions in living cells and zebrafish

A simple far-red fluorescent probe was developed to monitor mercury ions in environmental water samples and in living systems.

Metal-coordination driven intramolecular twisting: a turn-on fluorescent-redox probe for Hg2+ ions through the interaction of ferrocene nonbonding orbitals and dibenzylidenehydrazine

A unique C2 symmetric azine bridged bi-ferrocenyl receptor has been designed and synthesized for the selective detection of Hg²⁺ ion with a low detection limit as 15 nM via turn on fluorescence with a blue shift.

An ultra-sensitive and ratiometric fluorescent probe based on the DTBET process for Hg2+ detection and imaging applications

In this article, we present an ultra-sensitive and ratiometric fluorescent probe (TR-Hg) for Hg²⁺ detection based on the mechanism of aggregation induced emission (AIE) and dark through-bond energy transfer (DTBET). The probe was constructed using tetraphenylethene as the dark donor and rhodamine B thiolactone as the acceptor. By exploiting the advantages of DTBET, which eliminates emission leakage from dark donors and provides nearly 100% energy transfer efficiency, TR-Hg exhibits more than a 30 000-fold fluorescence ratio enhancement after reacting with Hg²⁺. TR-Hg demostrates (i) a detection limit of 43 pM, which is the lowest among the reported ratiometric Hg²⁺ probes, (ii) excellent selectivity, fast response-time (<10 s) and a wide pH application range, (iii) strong applicability for paper-based colorimetric assay, where readout can be performed by the naked eye, and (iv) fluorescent imaging of Hg²⁺ in onion epidermal tissues, indicating its potential use in living organisms.

Tri-pillar[5]arene-based multi-stimuli-responsive supramolecular polymers for fluorescence detection and separation of Hg2+

A novel tri-pillar[5]arene based supramolecular polymer (JP5G) shows multiple stimuli-response properties and could detect and remove Hg²⁺ from aqueous solution.