A Reversible and Highly Selective Fluorescent Sensor for Mercury(II) Using Poly(thiophene)s that Contain Thymine Moieties

Highly Selective Ratiometric Sensors for Pb2+ Based on Luminescent Zn(II)-Coordination Polymers with Thiophenedicarboxylate. Crystal Structures and Spectroscopic Studies

The development of luminescent coordination polymers for the selective sensing of Pb2+ in water constitutes an active area of research that impacts analytical, environmental, and inorganic chemistry. Herein, two novel water-stable 2D Zn-coordination polymers {[Zn2(H2O)2(tdc)2(bpy)]·(H2O)}n 1 and [Zn(tdc)(tmb)]n 2 (tdc = thiophenedicarboxylate; bpy = 4,4'-bipyridine and tmb = 4,4'-trimethylenebipyridine) were synthesized, structurally determined by single crystal X-ray diffraction, and studied in-depth as luminescent sensors for a series of cations (Ca2+, Mg2+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+ Cd2+, Hg2+ and Pb2+) in 20% aqueous ethanol. These Zn-polymers possess photostability in 20% aqueous ethanol with a strong emission at 410 upon excitation at 330 nm and quantum yields of around Φ = 0.09. Under these conditions, Pb+2 can be efficiently sensed with polymer 2 through a fluorescent ratiometric response with selectivity over common interfering metal ions such as Cu2+, Cd2+ and Hg2+ in the micromolar concentration range (detection limit = 1.78 ± 10 μM). Such selectivity/affinity of Pb2+ over Hg2+ for luminescent chemosensors is still rare. On the basis of spectroscopic tools (1H NMR, far ATR-IR, PXRD), the X-ray crystal structure of 2, and Scanning Electron Microscopy with Energy-Dispersive X-ray Spectroscopic analysis, the ratiometric fluorescent response is proposed via an efficient metal-ion exchange driven through interactions between thiophenedicarboxylate rings and Pb2+ ions. The use of flexible luminescent Zn-coordination polymers as sensors for selective and direct detection of Pb2+ in aqueous media has been unexplored until now.

Flourescence sensors for heavy metal detection: major contaminants in soil and water bodies

Due to the increasing consumption of heavy metals, there is a rising need for specific and useful methods that are employed for the detection of heavy metals. Fluorescence sensing is a highly selective, rapid and biosensing technique that is employed in the determination of some heavy metals in any sample of soil or water, any other living person, the food being consumed or any other substance which are being used daily. These fluorescent methods are a type of analytical technique and they are mainly based on detection. Many types of metal conjugated molecules have been used of the detection of these heavy metals with various mechanisms. We have taken into account some specific sensor molecules as they were more suitable and easily accessible. These techniques that were employed in the detection of various heavy metals such as copper, lead and mercury have been discussed in the following review article.

Novel thermo and ion-responsive copolymers based on metallo-base pair directed host-guest complexation for highly selective recognition of Hg2+ in aqueous solution

The development of materials with highly selective recognition towards Hg²⁺ is of great significance in environmental monitoring. Herein, a novel thermo-responsive copolymer with Hg²⁺ recognition property is prepared via thermally-initiated copolymerization of 5'-O-Acryloyl 5-methyl-uridine (APU) and N-isopropylacrylamide (NIPAM). The chemical structure and stimuli-sensitive properties of poly(N-isopropylacrylamide-co-5-methyl-uridine) (P(NIPAM-co-APU)) linear polymers and hydrogel are thoroughly investigated. At the supramolecular level, P(NIPAM-co-APU) linear polymers could respond to both temperature and Hg²⁺ stimuli with highly selective recognition towards Hg²⁺ over other 18 metal ion species (at least 5 fold difference) and common anions. Upon capturing Hg²⁺ by APU units as host metal receptors, the lower critical solution temperature (LCST) of P(NIPAM-co-APU, PNU-7 and PNU-11) linear polymers are significantly shifted more than 10 °C due to the formation of stable APU-Hg²⁺-APU directed host-guest complexes. Accordingly, at the macroscopic level, P(NIPAM-co-APU) hydrogel display selective and robust recognition of Hg²⁺ under optimum conditions, and its maximum Hg²⁺ uptake capacity was 33.1 mg g^-1. This work provides a new option for Hg²⁺ recognition with high selectivity, which could be facilely integrated with other smart systems to achieve satisfactory detection of environmental Hg²⁺.

Synthesis and characterization of some novel polythiophene derivatives containing pyrazoline

Eight polythiophene derivatives containing pyrazoline side groups were synthesized by a chemical oxidative coupling polymerization using FeCl₃. The crystal structures of four monomers were determined which confirm the almost perpendicular orientation of the thiophene and pyrazoline rings, while the other substituents are more coplanar. Analyses of IR, ¹H-NMR, Raman and UV-Vis spectra demonstrated that the suggested polymerization was successful to generate the synthesized polythiophenes with the expected structures. The morphology of the synthesized polythiophenes was studied by SEM. The different substituents attached to the 1- and 3-positions of the pyrazoline side chain led to differences in optical properties, electrical conductivity, and thermal stability of the synthesized polythiophenes. By adding a pyrazoline side chain to polythiophenes, some polymers achieve good solubility, electrical conductivity of about 1.3 × 10^–6 S/cm, high fluorescence intensity (above 40,000 a.u.) at 505–550 nm and thermal stability up to 590°C in the air.

Hg (II)-mediated intramolecular cyclization of alkynyl hydrazones: Towards a new reaction-based sensing approach for Hg(II)

Drawing upon an intramolecular cyclization/annulation reaction sequence mediated by Hg 2+  ions, a BODIPY-based fluorescent probe decorated with an alkynyl hydrazone motif responds rapidly and selectively to Hg 2+  ions, with a detection limit of 29 nM and a fluorescence turn-on ratio of 15-fold. With the addition of Hg 2+  ions, the BODIPY-based alkynyl hydrazone transforms into a pyrazole ring to mediate a turn-on emission response clearly observable to the naked eye under visible light excitation.

A conjugated fluorescent polymer sensor with amidoxime and polyfluorene entities for effective detection of uranyl ion in real samples

It is an important challenge to develop a chemosensor for trace uranyl ion in an aqueous medium for sustainable development of nuclear energy and environmental conservation. A conjugated fluorescent polymer sensor P2 based on amidoxime groups and polyfluorene, which showed good hydrophilous resulting adequate contact with uranyl ions and selectivity and sensitivity even in the presence of other metal ions in DMA/H₂O (v/v = 20:80, pH = 6.0) solution, for uranyl ion was designed and prepared in this work. And it possesses good thermal stability and a larger Stokes shift (108 nm). Importantly, the fluorescence quenching occurred when P2 combining uranium. It had a good linear relationship with UO₂²⁺ concentration in the range of 10 to 200 nM with a fairly low LOD 7.4 × 10^-9 M. Interaction properties between the sensor P2 and UO₂²⁺ and the fluorescent mechanism were investigated by density functional theory (DFT). More importantly, the sensor can be successfully used for the detection of uranyl ion in environmental solutions. This work suggests that conjugated fluorescent polymer with amidoxime groups will be a prospective sensor of uranyl ion in the environmental sample.

Synthesis of a soluble adenine-functionalized polythiophene through direct arylation polymerization and its fluorescence responsive behavior

An adenine-functionalized polythiophene is synthesized via direct arylation polymerization using Boc-protection to overcome catalyst deactivation. The resulting copolymer is highly soluble and shows reversible fluorescence quenching.

Nicking enzyme-assisted signal-amplifiable Hg2+ detection using upconversion nanoparticles

A highly specific and sensitive isothermal method for mercury detection using DNA-conjugated upconversion nanoparticles is reported. A single-stranded DNA containing thymine bases, used as the Hg²⁺-capturing element through the formation of thymine-Hg²⁺-thymine complex, is covalently attached to the NaYF₄: Yb^3+, Tm³⁺ nanoparticles. Luminescence resonance energy transfer takes place between the NaYF₄: Yb^3+, Tm³⁺ nanoparticles as donor and DNA-intercalating SYBR Green I as the acceptor upon excitation of 980 nm. The sensitivity and selectivity toward Hg²⁺ are enhanced using the nicking enzyme, Nt. Alwl, which leads to signal amplification. By monitoring the ratio of acceptor emission to a reference peak, the presence of Hg²⁺ ions are quantitatively determined with a lower detection limit of 0.14 nM, which is much lower than the US Environmental Protection Agency (EPA) limit of Hg²⁺ in drinking water.

"ON-OFF-ON" fluorescent probes based on nitrogen-doped carbon dots for hypochlorite and bisulfite detection in living cells

Although hypochlorite (ClO-) and bisulfite (HSO3-) play important roles in the biological immune system and the aging process of living organisms, they are also classified as a third type of carcinogens. Hence, a convenient and efficient method to monitor ClO- and HSO3- in ecological environments is highly desired. In this article, an "ON-OFF-ON" fluorescent probe based on nitrogen-doped carbon dots (N-CDs) for the detection of ClO- and HSO3- has been demonstrated successfully. Because of the destruction of the surface passivation layer, the fluorescence of the N-CDs was quenched by ClO-. Furthermore, the quenched fluorescence of the N-CDs was restored efficiently through the increase in conjugation from the attached sulfo groups, indicating the feasibility of ClO- and HSO3- detection. This fluorescent probe exhibited excellent sensitivity and selectivity to ClO- and HSO3- detection with the limits of detection (LODs) of 3.4 μM and 0.27 μM in aqueous solution, respectively. In addition, the as-prepared N-CDs were successfully applied to detect both ClO- and HSO3- in living cells due to their low toxicity and fast response speed.

Green silver-nanoparticle-based dual sensor for toxic Hg(II) ions

The present study focuses on the utilization of green silver nanoparticles, as they are preferred for sensing applications due to their environmentally friendly nature. We have examined the optical and electrochemical sensing behavior of silver nanoparticles from Agaricus bisporus (AgNP-AB) towards Hg(II) ions. The AgNP-AB was prepared by microwave reactor. The synthesized AgNP was used for the sensing of Hg(II) ions without the use of modifiers or further sophisticated instrumentation. The synthesized nanoparticles were successfully characterized by different techniques. AgNP-AB leads to aggregation with the addition of Hg(II) ions in aqueous medium, and develops a color change from brown to black which leads to the formation of AgNP-AB-Hg(II) complex. Moreover, the metal sensing ability of AgNP has been explored using electrochemical studies. AgNP-AB modified platinum electrode (AgNP-AB/PE) was developed for the fast sensing of toxic Hg(II) ions. The sensor exhibits a good limit of detection at 2.1 × 10^-6 M. The sensitivity of AgNP-AB/PE towards Hg(II) ions was analyzed with various metal ions. The sensing skill of the developed system was successfully checked with real water samples from Vembanade Lake, Kumarakom, Kerala. AgNP from A. bisporus is highly versatile and promising for different environmental applications.

Influence of Hofmeister I- on Tuning Optoelectronic Properties of Ampholytic Polythiophene by Varying pH and Conjugating with RNA

A significant tuning of optoelectronic properties of polythiophene (PT) chains due to Hofmeister iodide (I^-) ion is demonstrated in ampholytic polythiophene [polythiophene-g-poly{(N,N,N-trimethylamino iodide)ethyl methacrylate-co-methacrylic acid}, APT] at different pHs. In acidic medium, the absorption and emission signals of PT chromophore exhibit appreciable blue shift in the presence of I^- as counteranion only. The cooperative effect of undissociated -COOH and quaternary ammonium groups immobilize I^- near the apolar PT chain causing threading of grafted chains and hence twisting of the backbone attributing to the blue shift. As medium pH is increased, dethreading of the PT backbone occurs due to ionization of -COOH group, releasing quencher iodide ions from the vicinity of the PT chains resulting in a red shift in absorption and a sharp hike in fluorescence intensity (390 times) for an increase of excitons lifetime. With an increase of pH, morphology changes from a multivesicular aggregate with vacuoles to smaller size vesicles and finally to nanofibrillar network structure. Dethreading is also found when APT interacts with RNA showing a significant hike of fluorescence (22 times) for displacing iodide ions forming a nanofibrillar network morphology. Threading and dethreading also affect the resistance, capacitance, and Warburg impedance values of APT. Molecular dynamics simulation of a model APT chain in a water box supports the threading at lower pH where the iodide ions pose nearer to the PT chain than that at higher pH causing dethreading. So the influence of Hofmeister I^- ion is established for tuning the optoelectronic properties of a novel PT based polyampholyte by changing pH or by conjugating with RNA.

Highly Sensitive Fluorescence Detection of Hg2+ Based on a Water-soluble Conjugated Polymer with Carboxylate Groups

A label-free, highly selective, and highly sensitive fluorescent sensor to detect Hg²⁺ was developed using a water-soluble conjugated polymer with carboxylate groups (poly(2,5-bis(sodium 4-oxybutyrate)-1,4-phenylethynylene-alt-1,4-phenyleneethynylene, PPE-OBS) in this work. The fluorescence of PPE-OBS would be quenched because of the effect among the unique coordination-induced aggregation and electron transfers of PPE-OBS toward Hg²⁺. The linear relationship between the fluorescence intensity and concentration of Hg²⁺ was observed within the range from 6 × 10^-8 to 8 × 10^-5 mol L^-1 (R² = 0.9985), and the limit of detection was 2.10 × 10^-9 mol L^-1. The proposed method was applied to detect Hg²⁺ in environmental water samples, and satisfactory results were obtained.

Ce (III) - Porphyrin Sandwich Complex Ce2(TPP)3: A Rod-Like Nanoparticle as a Fluorescence Turn-Off Probe for Detection of Hg (II) and Cu (II)

In this study the researcher reports a novel, one step synthesized rod-like nanoparticles of cerium (III)-tetraphenylporphyrin sandwich complex as a spectrofluorometric sensor to measure trace amount of Hg (II) and Cu (II) metal ions. Moreover, the synthesized fluorescent probe was able to detect higher amounts (>10(-4) M) of Hg (II) in aqueous media by changing the color which can also be used as a selective mercury naked-eye sensor. The selectivity and sensitivity of the sensor based on its fluorescence quenching in the presence of Hg (II) and Cu (II) were studied according to the Stern-Volmer equation. The detection limit of the sensor was 16 nM for Hg (II) and about 2.34 μM for Cu (II) ions. Graphical Abstract Ce2(TPP)3 sandwich complex application as a fluorescent probe for measuring trace amounts of mercury and copper in real samples.

Synthesis and Characterization of Novel Polythiophenes Containing Pyrene Chromophores: Thermal, Optical and Electrochemical Properties

A novel series of pyrene containing thiophene monomers TPM1-5 were synthesized and fully characterized by FTIR, MS, ¹H- and (13)C-NMR spectroscopy; their thermal properties were determined by TGA and DSC. These monomers were chemically polymerized using FeCl3 as oxidizing agent to give the corresponding oligomers TPO1-5) and they were electrochemically polymerized to obtain the corresponding polymer films deposited onto ITO. All oligomers exhibited good thermal stability, with T10 values between 255 and 299 °C, and Tg values varying from 36 to 39 °C. The monomers showed an absorption band at 345 nm due to the S0 → S2 transition of the pyrene group, whereas the fluorescence spectra showed a broad emission band arising from the "monomer" emission at 375-420 nm. The obtained polymers exhibited two absorption bands at 244 and 354 nm, due to the polythiophene and the pyrene moieties, respectively. The fluorescence spectra of polymers showed a broad "monomer" emission at 380-420 nm followed by an intense excimer emission band at 570 nm, due to the presence of intramolecular pyrene-pyrene interactions in these compounds.

Synthesis and sensing applications of a new fluorescent derivative of cholesterol

The Hg²⁺ quenched emission of a specially designed fluorophore could be fully turned on upon the introduction of organophosphorus pesticides.

Selective detection of Al3+and citric acid with a fluorescent amphiphile

The assembly and disassembly of a fluorescent amphiphile by Al³⁺and citrate, respectively, can be used to sense these analytes by fluorescence spectroscopy.

Palladium-catalyzed direct C–H arylations of dioxythiophenes bearing reactive functional groups: a step-economical approach for functional π-conjugated oligoarenes

A phosphine-free C–H arylation of dioxythiophenes bearing unprotected functional groups affords oligoarenes with good yields.

Fluorescent thiophene-based materials and their outlook for emissive applications

An overview of fluorescent thiophene-based materials and their applications, highlighting in particular the various methods employed to achieve highly emissive materials.

Carbamodithioate-based dual functional fluorescent probe for Hg(2+) and S(2-)

Carbamodithioate-based compound T1 was designed and synthesized as a dual-functional probe for Hg(2+) ions and S(2-) anions. The underlying signaling mechanism was intramolecular charge transfer (ICT). It could serve as a direct probe towards Hg(2+) ions through "on-off" fluorescence changes and an indirect probe towards S(2-) anions through "on-off-on" fluorescence changes.

Ca2+-controlled assembly for visualized detection of conformation changes of calmodulin

A new strategy has been designed for visualized detection of the conformation changes of calmodulin bound to target peptide (CaM-M13) based on the conformation sensitive property of a water-soluble conjugated polythiophene derivative (PMNT) and the electrostatic interactions of PMNT/CaM-M13. Interestingly, the direct visualized PMNT color changes under UV irradiation and the turbidity changes of samples in aqueous medium can be applied to detect the conformation changes as well as the controllable assembly of PMNT/CaM-M13 with Ca(2+) in aqueous medium. Because of the specific binding of Ca(2+), the assembly of PMNT/CaM-M13 can be applied to sense calcium as well.

Nucleobase-functionalized conjugated polymer for detection of copper(II)

In recent years, supramolecular organization of thiophene derivatives, oligo- and polythiophene, have been developed with various designs to achieve complex functions. Here, we describe the synthesis and characterization of a conjugated polymer with thymidine side chain bases and polythiophene backbones (PTT) instead of phosphate bonds in DNA, and the PTT exhibits exceptional fluorescence quenching efficiency upon binding of Cu(2+) ions in aqueous medium, which is suggested to be electron transfer from the π* orbit at the excited state of PTT to the 3d orbit of Cu(2+) ions and subsequent Cu(2+)-mediated interpolymer π-stacking aggregation. Furthermore, Cu(2+) ions can be selectively and easily monitored by the fluorescence quenching of PTT, which can be used for detection of Cu(2+) ions with good selectivity and high sensitivity in aqueous medium. Both experimental and theoretical methods have been devoted to demonstrate the strong affinity and steric interaction of PTT toward Cu(2+). These findings will illustrate new directions for the design of nucleobase-functionalized materials with transition metals responsive activity.

Citrate-induced aggregation of conjugated polyelectrolytes for Al(3+)-ion-sensing assays

This work shows the sodium citrate induced efficient interpolymer π-stacking aggregation of the planar cationic conjugated polyelectrolyte poly[{9,9-bis[6'-(N,N-trimethylamino)hexyl]-2,7-fluorenyleneethynylene}-alt-co-(1,4-phenylene)] dibromide (PFE) in aqueous solution, which results in the self-quenching of fluorescence. Using the citrate-induced aggregation properties of PFE and the strong chelation ability of citrate with aluminum ions (Al(3+)), a sensitive and selective Al(3+)-ion detection assay in aqueous solution was developed through monitoring of the fluorescence recovery of PFE. The fluorescence intensity recovery of PFE depends on the concentration of Al(3+) ions, and linear fluorescence recovery was observed in the range of 0.5-9 μM. The limit of detection of this assay is 0.37 μM. Its simplicity and rapidity mean this assay shows promise for the real-time detection of Al(3+).

Colorimetric detection of mercury ions based on plasmonic nanoparticles

The development of rapid, specific, cost-effective, and robust tools in monitoring Hg(2+) levels in both environmental and biological samples is of utmost importance due to the severe mercury toxicity to humans. A number of techniques exist, but the colorimetric assay, which is reviewed herein, is shown to be a possible tool in monitoring the level of mercury. These assays allow transforming target sensing events into color changes, which have applicable potential for in-the-field application through naked-eye detection. Specifically, plasmonic nanoparticle-based colorimetric assay exhibits a much better propensity for identifying various targets in terms of sensitivity, solubility, and stability compared to commonly used organic chromophores. In this review, recent progress in the development of gold nanoparticle-based colorimetric assays for Hg(2+) is summarized, with a particular emphasis on examples of functionalized gold nanoparticle systems with oligonucleotides, oligopeptides, and functional molecules. Besides highlighting the current design principle for plasmonic nanoparticle-based colorimetric probes, the discussions on challenges and the prospect of next-generation probes for in-the-field applications are also presented.

Regenerable multifunctional mesoporous silica nanocomposites for simultaneous detection and removal of mercury(II)

Mercury (Hg(2+)) is a highly toxic and widespread environmental pollutant. Herein, a regenerable and highly selective core-shell structured magnetic mesoporous silica nanocomposite with functionalization of thymine (T) and T-rich DNA (denoted as Fe3O4@nSiO2@mSiO2-T-TRDNA nanocomposite) has been developed for simultaneous detection and removal of Hg(2+). In this work, the thymine and T-rich DNA were immobilized onto the interior and exterior surface of outermost mesoporous silica, respectively. The detection mechanism is based on Hg(2+)-mediated hairpin structure formed by T-rich DNA functionalized on the exterior surface of the nanocomposites, where, upon addition of SYBR Green I dye, strong fluorescence is observed. In the absence of Hg(2+), however, addition of the dye results in low fluorescence. The limit of detection for Hg(2+) in a buffer is 2 nM by fluorescence spectroscopy. Simultaneously, the Fe3O4@nSiO2@mSiO2-T-TRDNA nanocomposite features a selective binding with Hg(2+) between two thymines immobilized at the interior surface of the mesopores and exhibits efficient and convenient Hg(2+) removal by a magnet. Kinetic study reveals that the Hg(2+) removal is a rapid process with over 80% of Hg(2+) removed within approximately 1 h. The applicability of the developed nanocomposites is demonstrated to detect and remove Hg(2+) from samples of Xiangjiang river water spiked with Hg(2+). In addition, distinguishing aspects of the Fe3O4@nSiO2@mSiO2-T-TRDNA nanocomposites for Hg(2+) detection and removal also include the regeneration using a simple acid treatment and resistance to nuclease digestion. Similar process can be used to functionalize the Fe3O4@nSiO2@mSiO2 nanocomposites with other nucleic acids and small molecules for environmental and biomedical applications.

Fluorescent organic nanoparticles based on branched small molecule: preparation and ion detection in lithium-ion battery

Fluorescent organic nanoparticles (FONs) as a new class of nanomaterials can provide more advantages than molecule based probes. However, their applications in specific metal ion detection have rarely been exploited. We design and synthesize a branched small-molecule compound with triazole as a core and benzothiadiazole derivative as branches. By a facile reprecipitation method, nanoparticles (NPs) of this compound can be prepared in aqueous solutions, which can show high selectivity and sensitivity to Fe(III) ions based on fluorescence quenching. In addition, the fluorescence intensity of these NPs is resistant to pH changes in solutions. Such characters of this kind of NPs can be utilized in Fe(3+) impurity detection in a promising cathode material (LiFePO4) for lithium ion batteries. When exposed to Fe(3+), both the triazole and benzothiadiazole groups contribute to the fluorescence quenching of NPs, but the former one plays a more important role in Fe(3+) impurity detection. The sensing mechanism has also been investigated which indicates that a Fe-organic complex formation may be responsible for such sensing behavior. Our findings demonstrate that specific metal ion detection can be realized by FONs and have extended the application field of FONs for chemical sensing in aqueous solutions.