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.     

Catalytic gold nanoparticles for fluorescent detection of mercury(II) and lead(II) ions

In this study, we developed a fluorescence assay for the highly sensitive and selective detection of Hg²⁺ and Pb²⁺ ions using a gold nanoparticle (Au NP)-based probe. The Hg–Au and Pb–Au alloys that formed on the Au NP surfaces allowed the Au NPs to exhibit peroxidase-mimicking catalytic activity in the H₂O₂-mediated oxidation of Amplex UltraRed (AUR). The fluorescence of the AUR oxidation product increased upon increasing the concentration of either Hg²⁺ or Pb²⁺ ions. By controlling the pH values of 5 mM tris–acetate buffers at 7.0 and 9.0, this H₂O₂–AUR–Au NP probe detected Hg²⁺ and Pb²⁺ ions, respectively, both with limits of detection (signal-to-noise ratio: 3) of 4.0 nM. The fluorescence intensity of the AUR oxidation product was proportional to the concentrations of Hg²⁺ and Pb²⁺ ions over ranges 0.05–1 μM (R² = 0.993) and 0.05–5 μM (R² = 0.996), respectively. The H₂O₂–AUR–Au NP probe was highly selective for Hg²⁺ (>100-fold) and Pb²⁺ (>300-fold) ions in the presence of other tested metal ions. We validated the practicality of this simple, selective, and sensitive H₂O₂–AUR–Au NP probe through determination of the concentrations of Hg²⁺ and Pb²⁺ ions in a lake water sample and of Pb²⁺ ions in a blood sample. To the best of our knowledge, this system is the first example of Au NPs being used as enzyme-mimics for the fluorescence detection of Hg²⁺ and Pb²⁺ ions.     

A novel turn-on fluorescent probe for Hg2+ detection based on rhodamine B spirolactam derivative

ABSTRACT

In this work, a new turn-on fluorescent probe 1 for Hg²⁺ ions detection based on rhodamine B spirolactam was reported. Among tested metal ions, probe 1 shows high selectivity towards Hg²⁺ in the the mixture solution of methanol and 0.02 M HEPES buffer (V/V = 9:1, pH = 7.2). No absorption and emission band of probe 1 was observed in the range from 450 to 700 nm. While only addition of Hg²⁺ to probe 1 could lead to appearance of a new absorption band centered at 553 nm and a fluorescence emission band around 577 nm upon excitation at 520 nm. Moreover, it exhibits excellent linear relationship (R² = 0.9993) between fluorescence intensity at 577 nm and the concentration of Hg²⁺ from 1.6 to 32 μM. The sensing mechanism was proven to be spirolactam ring open induced by Hg²⁺ through ¹H NMR, MS, absorption and fluorescence spectra. In addition, probe 1 could detect Hg²⁺ in real water samples and on filter paper, which demonstrates its application in environment science.     

Smart lanthanide coordination polymer fluorescence probe for mercury(II) determination

Lanthanide coordination polymers (LCPs) have recently emerged as attractive biosensor materials due to their flexible components, high tailorable properties and unique luminescence features. In this work, we designed a smart LCP probe of Tb-CIP/AMP {(CIP, ciprofloxacin) (AMP, adenosine monophosphate)} for Hg²⁺ detection by using lanthanide ions as metal nodes, CIP as ligand molecule, and AMP as bridging linker and recognition unit. Tb-CIP/AMP emits strong green luminescence due to the inclusion of AMP, which withdraws the coordinated water molecules and shields Tb³⁺ from the quenching effect of O–H vibration in water molecules. The subsequent addition of Hg²⁺ into Tb-CIP/AMP can strongly quench the fluorescence because of the specific coordination interaction between AMP and Hg²⁺. As a kind of Hg²⁺ nanosensor, the probe exhibited excellent selectivity for Hg²⁺ and high sensitivity with detection limit of 0.16 nM. In addition, the probe has long fluorescence lifetime up to millisecond and has been applied to detect Hg²⁺ in drinking water and human urine samples with satisfactory results. We envision that our strategy, in the future, could be extended to the designation of other LCP-based hypersensitive time-gated luminescence assays in biological media and biomedical imaging.     

A new fluorescent turn-on chemodosimeter for mercury ions in solution and its application in cells and organisms

Using the Hg²⁺-induced desulfurization reaction of thiosemicarbazide derivative, we designed and synthesized a novel “turn on” coumarin-based fluorescent probe L with a simple structure for detecting mercury ion (II). Spectroscopy revealed that the probe responds selectively to mercury ions over other metal ions with marked fluorescence enhancement. Detection of Hg²⁺ was effective at pH 7.0–9.5, with high selectivity and significant effect in HeLa cells, human umbilical vein endothelial cells and Escherichia coli, but no cytotoxicity. This probe could be an ideal and practical Hg²⁺ probe with important biological significance.     

Development of [(2E,6E)-2,6-bis(4-(dimethylamino)benzylidene)cyclohexanone] as fluorescence-on probe for Hg2+ ion detection: Computational aided experimental studies

Selective metal ion detection is highly desired in fluorometric analysis. In the current study a curcumin-based fluorescence-on probe/[(2E,6E)-2,6-bis(4-(dimethylamino) benzylidene) cyclohexanone]/probe was designed for the removal of one of the most toxic heavy metal ion i.e. Hg²⁺. The structure of the probe was confirmed by FTIR and ¹H NMR spectroscopic analysis displaying distinctive peaks. The complex formation between probe and Hg²⁺ ion was also studied by density functional theory to support the experimental results. Chelation enhanced fluorescence was observed upon interaction with Hg²⁺ ion. Different parameters like pH, effect of mercury ion concentration, contact time, interference study and effect of probe concentration on the fluorescence enhancement were also investigated. A rapid response was detected for Hg²⁺ ion with limit of detection and quantification as 2.7 nM and 3 nM respectively with association constant of 1 × 10¹¹ M^?2. The probe displayed maximum fluorescence intensity at physiological pH. The results showed that the synthesized probe can be employed as an excellent probe for the detection and quantification of Hg²⁺ ions in aqueous samples with high selectivity and sensitivity due to its higher binding energy and larger charge transferring ability.     

Fluorescence turn-on chemodosimeter for rapid detection of mercury (II) ions in aqueous solution and blood from mice with toxicosis

The heavy metal mercury (Hg) is a threat to the health of people and wildlife in many environments. Among various chemical forms, Hg²⁺ salts are usually more toxic than their counterparts because of their greater solubility in water; thus, they are more readily absorbed from the gastrointestinal tract into circulation. Therefore, new chemical receptors for detecting Hg²⁺ ions in circulation are needed. In this study, we developed a rhodamine-based turn-on fluorescence probe to monitor Hg²⁺ in aqueous solution and in blood of mice with toxicosis. The chemodosimeter responds to Hg²⁺ ions stoichiometrically, rapidly, and irreversibly at room temperature as a result of a chemical reaction that produces strongly fluorescent oxadiazole. The new fluorescent probe shows good fluorescence response, with high sensitivity and selectivity, toward Hg²⁺ ions in aqueous solution and in blood from mice with toxicosis and facilitates the naked-eye detection of Hg²⁺ ions.     

2-(2′-Hydroxyphenyl)-4(3H)-quinazolinone derivatives based fluorescent probes for mercury(II) via an intramolecular proton transfer mechanism

2-(2′,5′-Dihydroxy-phenyl)-4(3H)-quinazolinone (DHPQ), a new fluorescent dye that exhibits excited state intramolecular proton transfer (ESIPT) reaction and possesses good photophysical properties, is synthesised and used as fluorescent probe for detection of Hg²⁺. Mercuric ions can be detected and quantitated by measuring the fluorescent intensity decrease of the probe. The decrease of fluorescence intensity of DHPQ upon the addition of Hg²⁺ was attributed to the blocking of ESIPT reactions of DHPQ and quenching its fluorescence. The analytical performance characteristics of the proposed Hg²⁺ probe were investigated. The probe can be applied to the quantification of Hg²⁺ with a concentration range covering from 8.0?×?10^?7 to 2.0?×?10^?4?mol?L^?1, with a working pH range of 5.5–6.5. It shows excellent selectivity for Hg²⁺ over other transition metal cations. The proposed method was testified for the Hg²⁺ assay in river water samples with satisfying recoveries.     

Single-fluorophore-based fluorescent probes enable dual-channel detection of Ag and Hg with high selectivity and sensitivity

A new type of fluorescent probe capable of detecting Ag⁺ and Hg²⁺ in two independent channels was developed in the present work. Specifically, in CH₃CN–MOPS mixed solvents with CH₃CN/MOPS ratio (v/v) of 15/85, this type of probe fluoresced weakly, and the addition of Ag⁺ remarkably induced fluorescence enhancement of the probe. In CH₃CN–MOPS mixed solvents with the percentage of CH₃CN increased up to 65%, the probe was highly fluorescent and addition of Hg²⁺ dramatically induced the fluorescence quenching. Thus, using such single-fluorophore-based probe and tuning the polarity of the mixed solvent, Ag⁺, and Hg²⁺ can be detected in independent channels with high selectivity and sensitivity. As a result, the mutual interference usually encountered in most cases of Ag⁺ and Hg²⁺ sensing owing to the similar fluorescence response that these two ions induced, can be effectively circumvented by using the probes developed herein.     

A fluorescent chemosensor for Hg based on naphthalimide derivative by fluorescence enhancement in aqueous solution

Naphthalimide derivative (compound 1) containing hydrophilic hexanoic acid group was synthesized and used to recognize Hg²⁺ in aqueous solution. The fluorescence enhancement of 1 is attributed to the formation of a complex between 1 and Hg²⁺ by 1:1 complex ratio (K = 2.08 × 10⁵), which has been utilized as the basis of fabrication of the Hg²⁺-sensitive fluorescent chemosensor. The comparison of this method with some other fluorescence methods for the determination of Hg²⁺ indicated that the method can be applied in aqueous solution rather than organic solution. The analytical performance characteristics of the proposed Hg²⁺-sensitive chemosensor were investigated. The chemosensor can be applied to the quantification of Hg²⁺ with a linear range covering from 2.57 × 10⁻⁷ to 9.27 × 10⁻⁵ M and a detection limit of 4.93 × 10⁻⁸ M. The experiment results show that the response behavior of 1 toward Hg²⁺ is pH independent in medium condition (pH 4.0–8.0). Most importantly, the fluorescence changes of the chemosensor are remarkably specific for Hg²⁺ in the presence of other metal ions, which meet the selective requirements for practical application. Moreover, the response of the chemosensor toward Hg²⁺ is fast (response time less than 1 min). In addition, the chemosensor has been used for determination of Hg²⁺ in hair samples with satisfactory results, which further demonstrates its value of practical applications.     

A Naphthalimide-Based Fluorescent Probe for the Detection and Imaging of Mercury Ions in Living Cells

The selective and efficient monitoring of mercury (Hg²⁺) contamination found in the environment and ecosystem has been carried out. Thus, a new 1,8-naphthalimide-based fluorescent probe NADP for the detection of Hg²⁺ based on a fluorescence enhancement strategy has been designed and synthesized. The NADP probe can detect Hg²⁺ with high selectivity and sensitivity and a low detection limit of 13 nm . The detection mechanism was based on a Hg²⁺-triggered deprotection reaction, resulting in a dramatic change in fluorescence from colorless to green at physiological pH. Most importantly, biological investigation has shown that the NADP probe can be successfully applied to the monitoring of Hg²⁺ in living cells and zebrafish with low cytotoxicity.     

Aminoquinoline based highly sensitive fluorescent sensor for lead(II) and aluminum(III) and its application in live cell imaging

We have synthesized a new probe 5-((anthracen-9-ylmethylene) amino)quinolin-10-ol (ANQ) based on anthracene platform. The probe was tested for its sensing behavior toward heavy metal ions Hg²⁺, Pb²⁺, light metal Al³⁺ ion, alkali, alkaline earth, and transition metal ions by UV–visible and fluorescent techniques in ACN/H₂O mixture buffered with HEPES (pH 7.4). It shows high selectivity toward sensing Pb²⁺/Al³⁺ metal ions. Importantly, 10-fold and 5- fold fluorescence enhancement at 429 nm was observed for probe upon complexation with Pb²⁺ and Al³⁺ ions, respectively. This fluorescence enhancement is attributable to the prevention of photoinduced electron transfer. The photonic studies indicate that the probe can be adopted as a sensitive fluorescent chemosensor for Pb²⁺ and Al³⁺ ions.     

A Schiff base‐grafted nanoporous silica material as a reversible optical probe for Hg2+ ion in water

A novel organic–inorganic silica‐based fluorescent probe was designed, synthesized and characterized by different techniques such as XRD, BET, TGA, and FT‐IR. The fluorescence properties of the probe were studied in the presence of a variety of metal‐ions in water. The results revealed that various metal‐ions negligibly vary the emission intensity of the probe except for Hg²⁺, which quenched the intensity dramatically. The selectivity of the probe toward Hg²⁺ ion was further investigated in the presence of common competing metal‐ions and the results demonstrated the high selectivity of the probe toward Hg²⁺ ion. The fluorescence emission of the probe was also studied as a function of the concentration of Hg²⁺ ion. A nanomolar limit of detection was estimated for Hg²⁺, indicating a high sensitivity. Furthermore, the probe showed INHIBIT‐type logic behavior with Hg²⁺ and H⁺ as inputs. Also, the optimum pH range was studied in addition to reversibility and real world applicability of the probe.     

A rhodamine hydrazide–4-nitroindole-3-carboxaldehyde based turn on Hg2+ chemosensor: cytoplasmic live cell imaging,logic gate and memory device applications and computational studies

A new, highly sensitive probe L² for the selective detection of Hg²⁺ in organo-aqueous (H₂O:CH₃CN, 1:1, v/v, HEPES buffer, pH 7.2) medium has been synthesized from rhodamine 6G-hydrazide and 4-nitroindole-3-carboxaldehyde. It was thoroughly characterized by physicochemical techniques including single crystal X-ray diffraction studies. The reaction of L² with Hg²⁺ gives a 1:1 stoichiometry resulting in a 146 fold fluorescence enhancement and a binding constant (K_f) of 3?×?10⁴ M^?1. The spirolactam form of the probe is non-fluorescent; however, it shows dual channel (absorbance and fluorescence) recognition of Hg²⁺ via CHEF effect through the opening of the spirolactam ring. The quantum yields of L² (0.00045) and L²-Hg²⁺ (0.29) show the higher stability of complex in the excited state over the free ligand. The 44.5?nM LOD value demonstrates the detection of Hg²⁺ at a very low concentration range. Cell imaging studies show the cytoplasmic recognition of Hg²⁺ by L². Experimental results are comparable with theoretical values obtained by DFT studies. The fluorescence emission of the complex was completely quenched by I^- and from the reversibility studies an advance level INHIBIT logic gate and memory device can be framed.     

FRET based selective and ratiometric ‘naked-eye’ detection of CN in aqueous solution on fluorescein–Zn–naphthalene ensemble platform

We have developed a FRET-based ratiometric fluorescent probe for the detection of CN⁻ using a fluorescein–Zn–naphthalene ensemble (NFH·Zn²⁺). The sensing mechanism was ascribed by displacement approach. The chemosensor exhibits high selectivity and sensibility for CN⁻. The speculation was supported by fluorescence emission spectra, UV–vis spectrum, ¹H NMR titration experiments, and mass spectra. The interconversion of probe NFH and NFH·Zn²⁺ via the complexation/decomplexation by the modulation of Zn²⁺/CN⁻ mimics INHIBIT gate. In addition, it also shows an excellent performance in ‘dip stick’ method.     

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.     

一种近红外发射荧光探针的合成及其荧光增强识别Hg2+

汞离子(Hg~(2+))由于高毒性以及容易对环境和人体造成损害,其检测越来越受到人们的重视。本文基于4-(二乙氨基)水杨醛设计合成了一种近红外发射荧光探针L,该探针可在MeCN/HEPES(体积比2/8,pH=7.4)缓冲溶液中高选择性地荧光增强识别Hg~(2+),其具有合成简便、抗干扰能力强、适用pH范围宽等特点。进一步研究表明,探针L可用于真实水样中Hg~(2+)的检测。     

Determination of Thiourea by On–Off Fluorescence Using Nitrogen-Doped Graphene Quantum Dots

A thiourea-detecting fluorescence sensor with Hg²⁺ as a switch was developed using nitrogen-doped graphene quantum dots (N-GQDs). The surface of N-GQDs had many organic functional groups on which Hg²⁺ was effectively bound and turned off the fluorescence of the N-GQDs. The fluorescence of N-GQDs was turned on by the thiol functional group of thiourea that bound strongly with Hg²⁺ and formed Hg²⁺/thiourea complexes. After constructing the sensor, the experimental conditions and parameters, such as the pH and Hg²⁺ concentration, were investigated and optimized. Under the optimum conditions, the constructed fluorescence sensor showed high sensitivity to thiourea at concentrations from 0.5 to 14?µM with a low detection limit of 41.7?nM. The sensor also exhibited high specificity, excellent stability, and good reproducibility so that the determination of thiourea in various samples had acceptable values with good recoveries from 99% to 106%. The relative standard deviation was less than 4.1% (n?=?3).     

A highly selective and sensitive fluorescein-based chemodosimeter for Hg2+ ions in aqueous media

A new fluorescein-based chemodosimeter (II) for Hg²⁺ ion was designed and synthesized, and it displayed excellent selective and sensitive toward Hg²⁺ ion over other commonly metal ions in aqueous media. II was a colorless, non-fluorescent compound. Upon addition of Hg²⁺ to the solution of II, the thiosemicarbazide moiety of II would undergo an irreversible desulfurization reaction to form its corresponding oxadiazole (IV), a colorful and fluorescent product. During this process, the spirocyclic ring of II was opened, causing instantaneous development of visible color and strong fluorescence emission in the range of 500-600 nm. Based on the above mechanism, a fluorogenic Hg²⁺-selective chemodosimeter was developed. The fluorescence increase is linearly with Hg²⁺ concentration up to 1.0 μmol L⁻¹ with a detection limit of 8.5 × 10⁻¹⁰ mol L⁻¹ (3σ). Compared with the rhodamine-type chemodosimeter, II is more stable in aqueous media and exhibits higher sensitivity toward Hg²⁺. The findings suggest that II will serve as a practical chemodosimeter for rapid detection of Hg²⁺ concentrations in realistic media.     

Detection of Hg2+ ion using highly selective fluorescent chemosensor in real water sample and in-vitro cell study upon breast adenocarcinoma (MCF-7)

A novel rhodamine-based chemosensor (R) was designed and synthesised for selective recognition of Hg²⁺ ion in real water samples collected from different places. The chemosensor was prepared in green condition with high yield. The selectivity of R was examined with various metal ions, among which only Hg²⁺ was identified selectively with off–on mechanism along with enhancement of fluorescence. Metal ions recognition has been carried out using UV–vis and fluorescence studies taking µM concentration of chemosensor R in HEPES buffer. The detection limit of R was calculated and found to be 4.4 × 10^–9 M. Quantum chemical (DFT) calculation was carried out in order to acquire knowledge about the stability of R in presence of Hg²⁺ ions. Cell viability and fluorescence microscopic experiments showed R as cytocompatible and can be used as a fluorescent probe for detecting Hg²⁺ in living cells.