Rhodamine urea derivatives as fluorescent chemosensors for Hg

New rhodamine derivatives bearing urea group have been synthesized for the detection of metal ions. Especially, the dimeric system 2 displayed a selective fluorescent enhancement and colorimetric change upon the addition of Hg²⁺, in which the spirolactam (nonfluorescent) to ring opened amide (fluorescent) process was utilized. The association constant of 2 with Hg²⁺ was calculated as 3.2 × 10⁵ M⁻¹.     

Selective Detection of Hg2+ Ions with Boron Dipyrromethene‐Based Fluorescent Probes Appended with a Bis(1,2,3‐triazole)amino Receptor

By using a copper‐promoted alkyne–azide cycloaddition reaction, two boron dipyrromethene (BODIPY) derivatives bearing a bis(1,2,3‐triazole)amino receptor at the meso position were prepared and characterized. For the analogue with two terminal triethylene glycol chains, the fluorescence emission at 509 nm responded selectively toward Hg²⁺ ions, which greatly increased the fluorescence quantum yield from 0.003 to 0.25 as a result of inhibition of the photoinduced electron transfer (PET) process. By introducing two additional rhodamine moieties at the termini, the resulting conjugate could also detect Hg²⁺ ions in a highly selective manner. Upon excitation at the BODIPY core, the fluorescence emission of rhodamine at 580 nm was observed and the intensity increased substantially upon addition of Hg²⁺ ions due to inhibition of the PET process followed by highly efficient fluorescence resonance energy transfer (FRET) from the BODIPY core to the rhodamine moieties. The Hg²⁺‐responsive fluorescence change of these two probes could be easily seen with the naked eye. The binding stoichiometry between the probes and Hg²⁺ ions in CH₃CN was determined to be 1:2 by Job′s plot analysis and ¹H NMR titration, and the binding constants were found to be (1.2±0.1)×10¹¹ m ^?2 and (1.3±0.3)×10¹⁰ m ^?2, respectively. The overall results suggest that these two BODIPY derivatives can serve as highly selective fluorescent probes for Hg²⁺ ions. The rhodamine derivative makes use of a combined PET‐FRET sensing mechanism which can greatly increase the sensitivity of detection.     

Rhodamine based derivative and its zinc complex: synthesis and recognition behavior toward Hg(II)

A simple fluorescent probe, which contains rhodamine and aminoquinoline moieties, was designed and prepared for selective detection of Hg²⁺ in acetonitrile. RbQ exhibited high selectivity and sensitivity toward Hg²⁺ over other common metal ions. The recognition of RbQ toward Hg²⁺ can be detected by fluorescence spectra, absorption spectra, and even by naked eyes. The binding ratio of the RbQ–Hg²⁺ complex was found to be 1:1 according to Job plot experiment, and the limit of detection was 1.05×10⁻⁷ M. Moreover, the prepared complex RbQ–Zn²⁺ (RbQZ) could detect Hg²⁺ in a ratiometric way and showed lower limit of detection (2.95×10⁻⁸ M) than RbQ in the same condition. Finally, we also demonstrated that the aminoquinoline–zinc complex could be served as a new and effective FRET donor for rhodamine derivatives.     

Rhodamine-based chemodosimeter for fluorescent determination of Hg in 100% aqueous solution and in living cells

A rhodamine spirolactam derivative (1) bearing a hydrophilic carboxylic acid group is developed as a fluorescent chemodosimeter for bivalent mercury ions (Hg²⁺) in 100% aqueous solution. It exhibits a highly sensitive “turn-on” fluorescent response toward Hg²⁺ with a 42-fold fluorescence intensity enhancement under 1 equiv. of Hg²⁺ added. The chemodosimeter can be applied to the quantification of Hg²⁺ with a linear range covering from 3.0 × 10⁻⁷ to 1.0 × 10⁻⁵ M and a detection limit of 9.7 × 10⁻⁸ M. Most importantly, the fluorescence changes of the chemodosimeter are remarkably specific for Hg²⁺ in the presence of other metal ions, which meet the selective requirements for practical application. Moreover, the experiment results show that the response behavior of 1 towards Hg²⁺ is pH independent in neutral condition (pH 5.0–8.0) and the response is fast (response time less than 3 min). Furthermore, the ring-opening mechanism of the rhodamine spirolactam induced by Hg²⁺ was supported by NMR, MS, and DFT theoretical calculations. In addition, the proposed chemodosimeter has been used to detect Hg²⁺ in water samples and image Hg²⁺ in living cells with satisfying results.     

Selective fluorescent sensor for mercury ions in aqueous media using a 1,4-dihydropyridine derivative

Novel 1,4-dihydropyridine (DHP) derivatives containing 3 carboxylic acid units are synthesized via cyclotrimerization of N-substituted β-aminoacrylates followed by basic hydrolysis of the triester. These DHP derivatives are readily soluble in aqueous media buffered at pH 8.0 and the solutions give blue fluorescent signals with quantum yields of 7–23%. One of these compounds, bearing a p-methoxyphenyl N-substituted group, shows specific fluorescent quenching with the mercuric ion (Hg²⁺). The fluorescent signal of the DHP derivative decays over a period of minutes to hours depending on the Hg²⁺ concentration, which implies that the sensing mechanism involves chemical reaction between the Hg²⁺ ion and the DHP compound. The ¹H NMR and MS data suggest that Hg²⁺ mediates the oxidation of the DHP ring into a pyridinium ring. The event is useful for fluorescent detection of Hg²⁺ at the micromolar level within 30 min, with a detection limit of 0.2 μM in aqueous medium.     

FRET‐based Fluorescent and Colorimetric Probe for Selective Detection of Hg(II) and Cu(II) with Dual‐mode

A dual‐function fluorescence resonance energy transfer (FRET)‐based fluorescent and colorimetric probe was rationally fabricated from an energy donor coumarin moiety and an energy acceptor rhodamine moiety linked by a thiohydrazide arm for selective detection of Hg²⁺ and Cu²⁺. Two distinct mechanisms were used for the selective detection. Results revealed that probe 1 showed high fluorescent selectivity towards Hg²⁺ and evident colorimetric selectivity for Cu²⁺, which was suitable for ‘naked‐eye’ detection.     

Rhodamine-Appended Bipyridine: XOR and OR Logic Operations Integrated in an Example of Controlled Metal Migration

A new bipyridyl derivative 1 bearing rhodamine B as visible fluorophore was designed, synthesized and characterized as a fluorescent and colorimetric sensor for metal ions. Interaction with Cu²⁺, Zn²⁺, Cd²⁺, Hg⁺, and Hg²⁺ ions was followed by UV/Vis and emission spectroscopy. Upon addition of these metal ions, different colorimetric and fluorescent responses were observed. “Off-on-off” (Cu²⁺, Zn²⁺, and Hg²⁺) and “off-on” (Hg⁺ and Cd²⁺) systems were obtained. Probe 1 was explored to mimic XOR and OR logic operations for the simultaneous detection of Hg⁺–Cu²⁺ and Hg⁺–Zn²⁺ pairs, respectively. DFT calculations were also performed to gain insight into the lowest-energy gas-phase conformation of free receptor 1 as well as the atomistic details of the coordination modes of the various metal ions.     

A highly selective chemodosimeter for the rapid detection of Hg2+ ions in aqueous media

A novel S,S′-diallyl carbohydrazonodithioate derivative 3 of rhodamine B hydrazone was developed as a chemodosimeter for selective detection of mercury ions based on Hg²⁺ promoted cyclization. The allyl groups of 3 play a key role in the binding and selection of Hg²⁺ ions. The probe responds selectively to Hg²⁺ over various other competitive cations with marked chromo- and fluorogenic changes. The formation of stable oxadiazole derivative 8 was a strong driving force for this high selectivity. Practically, this probe is more promising because of the remarkable high selectivity, faster response, low detection limit, and aqueous solubility of 3.     

Vanillin-coumarin hybrid molecule as an efficient fluorescent probe for trace level determination of Hg(II) and its application in cell imaging

An efficient Hg²⁺ selective fluorescent probe (vanillin azo coumarin, VAC) was synthesized by blending vanillin with coumarin. VAC and its Hg²⁺ complex were well characterized by different spectroscopic techniques like ¹H NMR, QTOF-MS ES⁺, FTIR and elemental analysis as well. VAC could detect up to 1.25 μM Hg²⁺ in aqueous methanol solution through fluorescence enhancement. The method was linear up to 16 μM of Hg²⁺. Negative interferences from Cu²⁺, Ni²⁺, Fe³⁺, and Zn²⁺ were eliminated using EDTA as a masking agent. VAC showed a strong binding to Hg²⁺ ion as evident from its binding constant value (2.2 × 10⁵), estimated using Benesi-Hildebrand equation. Mercuration assisted restricted rotation of the vanillin moiety and inhibited photoinduced electron transfer from the O, N-donor sites to the coumarin unit are responsible for the enhancement of fluorescence upon mercuration of VAC. VAC was used for imaging the accumulation of Hg²⁺ ions in Candida albicans cells.     

New acridine derivatives bearing immobilized azacrown or azathiacrown ligand as fluorescent chemosensors for Hg and Cd

Two new acridine derivatives bearing azacrown or azathiacrown ligand were synthesized as fluorescent chemosensors for Hg²⁺ and Cd²⁺ in aqueous solution. Compounds 1 and 2 displayed selective CHEF (chelation enhanced fluorescence) effects with Hg²⁺ or Cd²⁺ among the metal ions examined. The practical use of these probes was demonstrated by their applications to the detection of Hg²⁺ and Cd²⁺ ions in mammalian cells.     

An Aurone‐derived Low‐molecular‐weight Fluorescence Probe for the Detection of Hg2+ in Aqueous Solution and Living Cells

A low‐molecular‐weight fluorescent probe 1 (M.W. = 238.24) based on aurone was synthesized, and its application in fluorescent detection of Hg²⁺ in aqueous solution and living cells was reported. It exhibited an “on–off” fluorescent response toward Hg²⁺ in aqueous solution. Both the color and fluorescence changes of the probe were remarkably specific for Hg²⁺ in the presence of other common metal ions, satisfying the selective requirements for biomedical and environmental monitoring application. The probe has been applied in direct measurement of Hg²⁺ content in river water samples and imaging of Hg²⁺ in living cells, which further indicates the potential application values in environmental and biological systems.     

A two-photon excited luminescence of water-soluble rhodamine-platinum(II) complex: fluorescent probe specific for Hg2+ detection in live cell

The first example of cyclometalated platinum(II)-containing rhodamine probe (1) with two-photon induced luminescent properties was synthesized and investigated for mercury detection. A highly selective color change of 1, from light yellow to pink, is observed only in the presence of Hg²⁺ due to the formation of 1,3,4-oxadiazole ring in 2. This selectivity of Hg²⁺ with color changes can be observed easily by the naked-eye. Meanwhile, a remarkable turn-on and selective 20-fold fluorescent enhancement of 1 upon binding with Hg²⁺ over the other tested metal ions was observed. The water-soluble probe 1 was successfully applied in the visualizing of the site of Hg²⁺ accumulation as well as estimating of trace amounts of mercury ions in live HeLa cells by two-photon microscopy.     

A bis(rhodamine 6G)-based fluorescent sensor for Hg2+: microwave-assisted synthesis,photophysical properties,and computational studies

A fluorescent and colorimetric sensor based on rhodamine 6 g (RD6g) was designed, synthesized, and characterized using microwave irradiation. The sensing behavior of this compound was studied by UV–visible and fluorescence spectroscopy. Sensor RD6g exhibits a high selectivity and an excellent sensitivity and is a dual-responsive colorimetric and fluorescent Hg²⁺-specific sensor in aqueous buffer solution. Mercury ions give rise to the development of a very fluorescent ring-open amide spirolactam system. The detection limit for Hg²⁺ was found to be 1.2?×?10^?8 M. The binding ratio of RD6g-Hg²⁺ complex was determined to be 1:1 according to the Job’s plot. The reversibility of RD6g?Hg²⁺ complex has been achieved with CN^? anions. The test strip based on RD6g was developed, which could be used as a suitable and methodical Hg²⁺ test kit.

     

A highly selective fluorescent probe for Hg based on a rhodamine-coumarin conjugate

A fluorescent probe 1 for Hg²⁺ based on a rhodamine-coumarin conjugate was designed and synthesized. Probe 1 exhibits high sensitivity and selectivity for sensing Hg²⁺, and about a 24-fold increase in fluorescence emission intensity is observed upon binding excess Hg²⁺ in 50% water/ethanol buffered at pH 7.24. The fluorescence response to Hg²⁺ is attributed to the 1:1 complex formation between probe 1 and Hg²⁺, which has been utilized as the basis for the selective detection of Hg²⁺. Besides, probe 1 was also found to show a reversible dual chromo- and fluorogenic response toward Hg²⁺ likely due to the chelation-induced ring opening of rhodamine spirolactam. The analytical performance characteristics of the proposed Hg²⁺-sensitive probe were investigated. The linear response range covers a concentration range of Hg²⁺ from 8.0 × 10⁻⁸ to 1.0 × 10⁻⁵ mol L⁻¹ and the detection limit is 4.0 × 10⁻⁸ mol L⁻¹. The determination of Hg²⁺ in both tap and river water samples displays satisfactory results.     

Highly sensitive and selective fluorescent chemosensors for Hg(II) in an aqueous environment based on carbamodithioate

Two highly sensitive (detection limits ∼20 nM) and selective (selectivity >30) fluorescent chemosensors were developed for detecting Hg²⁺ in a fully aqueous environment by using the rarely-studied carbamodithioate to create an Hg²⁺ binding site.     

Characterization of a Hg2+-Selective Fluorescent Probe Based on Rhodamine B and Its Imaging in Living Cells

A small organic molecule P was synthesized and characterized as a fluorometric and colorimetric dual-modal probe for Hg²⁺. The sensing characteristics of the proposed probe for Hg²⁺ were studied in detail. A fluorescent enhancing property at 583 nm (>30 fold) accompanied with a visible colorimetric change, from colorless to pink, was observed with the addition of Hg²⁺ to P in an ethanol-water solution (8:2, v/v, 20 mM HEPES, pH 7.0), which would be helpful to fabricate Hg²⁺-selective probes with “naked-eye” and fluorescent detection. Meanwhile, cellular experimental results demonstrated its low cytotoxicity and good biocompatibility, and the application of P for imaging of Hg²⁺ in living cells was satisfactory.     

Fluorescent Gold Clusters as Logic Gates for the Detection of Different Metal Ions

Metal cations can be selectively detected by restoring and quenching the fluorescent intensity of an “ON–OFF” gold nanocluster (Au NC ) sensor. The fluorescent intensity of Au NCs with metal cations can be restored by chelating with ethylenediaminetetraacetic acid except for Hg²⁺ ions. A highly selective detection of Hg²⁺ ion is also achieved under the coexistence of Fe³⁺ or Cr³⁺ ions. This assay was applied successfully for detecting Hg²⁺ in a water sample. The dynamic range of the system was 1 ppm to 25 ppb, and the limit of detection was 25 ppb.     

Fluorescence turn-on chemosensor for Hg<Superscript>2+</Superscript> based on a rhodamine derivative and its application in bioimaging

A fluorescence turn-on chemosensor based on rhodamine B derivative (FD10) has been developed as a highly sensitive chemosensor for Hg²⁺. A prominent fluorescence enhancement was measured in the presence of Hg²⁺, which was in agreement with the changes in the absorption spectrum. Furthermore, by means of laser scanning fluorescence microscopy experiments, it was demonstrated that FD10 was cell-permeable and could be used as a fluorescent probe for monitoring Hg²⁺ in living cells. Supported by the National Natural Science Foundation of China (Grant No. 20801015) and Shanghai Leading Academic Discipline Project (Grant No. B108)     

A label-free and signal-on supersandwich fluorescent platform for Hg sensing

A label-free supersandwich fluorescent assay was demonstrated for the first time by taking Hg²⁺ as a detection candidate. The principle of the proposed supersandwich fluorescent platform is based on the formation of supersandwich structure by T-Hg²⁺-T coordination and the fluorescence enhancement of the intercalated Genefinder (GF) in double strand DNA (dsDNA). Such supersandwich fluorescent DNA sensor exhibits a linear range of 10–300 nM for the detection of Hg²⁺, with a detection limit of 2.5 nM on the basis of the 3σ/slope (σ represents the standard deviation of the blank samples), which is well below the permit of the U.S. Environmental Protection Agency (<10 nM). The detection can be fulfilled in less than 10 min. The proposed mix-and-detect fluorescent platform exhibits excellent sensitivity, selectivity, and convenient manipulation. The assay was successfully used to detect Hg²⁺ in the lake water samples, which suggested its potential in practical samples.     

A colorimetric and fluorescent chemosensor for detection of Hg2+ using counterion exchange of cationic polydiacetylene

In this study, a colorimetric and fluorescent chemosensor for mercury ions (Hg²⁺) was developed. Cationic polydiacetylene (PDA) vesicles with a quaternary ammonium cation and iodide as a counterion show a blue-to-red color transition; the color change is accompanied by a fluorescence enhancement in selective response to Hg²⁺ ions because of a perturbation of the ene–yne conjugated backbone induced by counterion exchange. It allows for selective detection of Hg²⁺ with the naked eye and the sensor is used to determine Hg²⁺ concentrations in tap water samples.