Towards an Efficient Microsystem for the Real‐Time Detection and Quantification of Mercury in Water Based on a Specifically Designed Fluorogenic Binary Task‐Specific Ionic Liquid

Advances in ionic liquids as fluorescent sensors

Ionic liquids (ILs) are a class of liquid salts with characteristics such as a low melting point, an ionic nature, non-volatility, and tunable properties. Because of their adaptability, they have a significant influence in the field of fluorescence. This paper reviews the primary literature on the use of ILs in fluorescence sensing technologies. The kind of target material is utilized to classify the fluorescence sensors made with the use of ILs. They include using ILs as probes for metals, nitro explosives, small organic compounds, anions, and gases. The efficacy of an IL-based fluorescence sensor depends on the precise design to guarantee specificity, sensitivity, and a consistent reaction to the desired analyte. The precise method can differ depending on the chemical properties of the IL, the choice of fluorophore, and the interactions with the analyte. Overall, the viability of the aforementioned materials for chemical analysis is evaluated, and prospective possibilities for further development are identified.

Simplified Mercury Extraction from Coal Fly Ash for Quantification of Total Mercury by ELISA-based Immunoassay

A simplified two-step mercury extraction procedure enabled the selective and reproducible mercury recovery from actual coal fly ash (CFA). The optimized extraction procedure involving conventional enzyme-linked immunosorbent assay (ELISA)-based immunoassay allowed the ultra-sensitive quantification of total mercury content in CFA. The total mercury content of 41 CFA samples were successfully determined using the above-mentioned method, and the results were in agreement with those obtained by standard instrumental analysis (thermal decomposition atomic absorption spectrometry) within a 15% coefficient of variation. Our method for total mercury quantification is not only simple but suitable for management of the mercury content at coal-fired electric power plants and landfill sites, which deal with large amounts of waste CFA.

Nanoarchitectonics of Small Molecule and DNA for Ultrasensitive Detection of Mercury

Reliable and ultrasensitive detection of mercury ions is of paramount importance for toxicology assessment, environmental protection, and human health. Herein, we present a novel optoelectronic approach based on nanoarchitectonics of small-molecule templated DNA system that consists of an adenine (A)-conjugated small organic semiconductor (BNA) and deoxyribo-oligothymidine (dT_n). This mutually templated dynamic chiral coassembly system (BNAn-dT_n) with tunable chiroptical, morphological, and electrical properties is tapped in to enable ultrasensitive and selective detection of inorganic and organometallic mercury in water. We observe a rapid transformation of the BNA_n-dT_n coassembly into a metallo-DNA duplex [dT-Hg-dT]_n in the presence of mercury, which is utilized for a chiro-optical and conductivity-based rapid and subnanomolar sensitivity (≥0.1 nM, 0.02 ppb) to mercury ions in water (∼100 times lower than United States Environmental Protection Agency tolerance limit). This ultrasensitive detection of inorganic and organometallic mercury is driven by a novel chemical design principle that allows strong mercury thymine interaction. This study is anticipated to inspire the development of future templated DNA nanotechnology-based optoelectronic devices for the rapid and ultrasensitive detection of numerous other toxic analytes.

Selective and Sensitive Detection of Heavy Metal Ions in 100% Aqueous Solution and Cells with a Fluorescence Chemosensor Based on Peptide Using Aggregation-Induced Emission

A fluorescent peptidyl chemosensor for the detection of heavy metal ions in aqueous solution as well as in cells was synthesized on the basis of the peptide receptor for the metal ions using an aggregation-induced emission fluorophore. The peptidyl chemosensor (1) bearing tetraphenylethylene fluorophore showed an exclusively selective turn-on response to Hg(2+) among 16 metal ions in aqueous buffered solution containing NaCl. The peptidyl chemosensor complexed Hg(2+) ions and then aggregated in aqueous buffered solution, resulting in the significant enhancement (OFF-On) of emissions at around 470 nm. The fluorescent sensor showed a highly sensitive response to Hg(2+), and about 1.0 equiv of Hg(2+) was enough for the saturation of the emission intensity change. The detection limit (5.3 nM, R(2) = 0.99) of 1 for Hg(2+) ions was lower than the maximum allowable level of Hg(2+) in drinking water by EPA. Moreover, the peptidyl chemosensor penetrated live cells and detected intracellular Hg(2+) ions by the turn-on response.

An elegant and handy selective sensor for ppt level determination of mercury ions

Competitive adsorption of Hg²⁺ on graphene in the presence of fluorescein leads to mercury sensing ability for the graphene dye unit.

A colorimetric and fluorometric investigation of Cu(ii) ion in aqueous medium with a fluorescein-based chemosensor

A colorimetric and fluorometric chemosensor, 1,4-bis(1-fluorescein)-2,3-diaza-1,3-butadiene (L, 3) as Schiff base is developed for naked-eye detection of Cu²⁺ ion in aqueous medium due to the formation of a 1 : 1 copper–ligand complex.

Ultra-sensitive and selective Hg2+ chemosensors derived from substituted 8-hydroxyquinoline analogues

A mercury concentration of 15 ppt can be selectively detected, in aqueous medium, thanks to a thiophosphinatylated 8-hydroxyquinoline sensor.

A novel CMPO-functionalized task specific ionic liquid: synthesis, extraction and spectroscopic investigations of actinide and lanthanide complexes

A novel CMPO (carbamoylmethylphosphine oxide) based task specific ionic liquid (TSIL) with an NTf(2)(-) counter anion was synthesized and evaluated for actinide/lanthanide extraction from acidic feed solutions using several room temperature ionic liquids (RTILs). The extraction data were compared with those obtained with CMPO in the same set of RTILs and also in the molecular diluent, n-dodecane. The extracted species were analyzed by the conventional slope analysis method and the extraction followed an ion-exchange mechanism. The nature of bonding in the extracted complexes was investigated by various spectroscopic techniques such as FT-IR and UV-visible spectroscopy.

Recognition of Hg2+ and Cr3+ in physiological conditions by a rhodamine derivative and its application as a reagent for cell-imaging studies

A new rhodamine-based receptor, derivatized with an additional fluorophore (quinoline), was synthesized for selective recognition of Hg(2+) and Cr(3+) in an acetonitrile/HEPES buffer medium of pH 7.3. This reagent could be used as a dual probe and allowed detection of these two ions by monitoring changes in absorption and the fluorescence spectral pattern. In both instances, the extent of the changes was significant enough to allow visual detection. More importantly, the receptor molecule could be used as an imaging reagent for detection of Hg(2+) and Cr(3+) uptake in live human cancer cells (MCF7) using laser confocal microscopic studies. Unlike Hg(ClO(4))(2) or Hg(NO(3))(2) salts, HgCl(2) or HgI(2) failed to induce any visually detectable change in color or fluorescence upon interaction with L(1) under identical experimental conditions. Presumably, the higher covalent nature of Hg(II) in HgCl(2) or HgI(2) accounts for its lower acidity and its inability to open up the spirolactam ring of the reagent L(1). The issue has been addressed on the basis of the single-crystal X-ray structures of L(1)·HgX(2) (X(-) = Cl(-) or I(-)) and results from other spectral studies.

Multimode selective detection of mercury by chiroptical fluorescent sensors based on methionine/cysteine

Two multimode Hg(II) sensors, L-MethBQA and L-CysBQA, were obtained by fusing methionine or S-methyl cysteine, into a bis-quinolyl amine-based chiral podand scaffold. Quinolyl groups serve as the fluorophore and possess nitrogen lone pairs capable of chelating metal ions. On exposure to Hg(2+) or Zn(2+), these sensors show signal enhancement in fluorescence. However, Cu(2+) quenches their fluorescence in 30:70 acetontrile/water. L-CysBQA complexes with Hg(2+), producing an exciton-coupled circular dichroism spectrum with the opposite sign to the one that is produced by Cu(2+) or Zn(2+) complexation. L-CysBQA binds Hg(2+) more strongly than Zn(2+) and is shown to differentiate Hg(2+) from other metal ions, such as Zn(2+), Cu(2+), Ni(2+), and Pb(2+), exceptionally well. The synergistic use of relatively soft sulfur, quinoline-based chiral ligands and chiroptically enhanced fluorescence detection results in high sensitivity and selectivity for Hg(2+).

Oligonucleotide-based label-free Hg2+ assay with a monomer-excimer fluorescence switch

A novel fluorescent Hg(2+) sensor was developed based on the T-Hg(2+)-T structure and a thioflavine T monomer-excimer fluorescent switch. Under optimum conditions, the selectivity is remarkably high, and Hg(2+) can be quantified over the dynamic range of 0.1 to 1.2 μM, with a limit of detection (LOD) of ~20 nM and a linear correlation coefficient of 0.995.

A universal sensor for mercury (Hg, Hg(I), Hg(II)) based on silver nanoparticle-embedded polymer thin film

Detection of mercury at concentration levels down to parts-per-billion is a problem of fundamental and practical interest due to the high toxicity of the metal and its role in environmental pollution. The extensive research in this area has been focused primarily on specific sensing of mercuric (Hg(2+)) ion. As mercury exists in the oxidation states, +2, +1 and 0 all of which are highly toxic, a universal sensor covering all the three while ensuring high sensitivity, selectivity, and linearity of response, and facilitating in situ as well as ex situ deployment, would be very valuable. Silver nanoparticle-embedded poly(vinyl alcohol) (Ag-PVA) thin film fabricated through a facile protocol is shown to be a fast, efficient and selective sensor for Hg(2+), Hg(2)(2+) and Hg in aqueous medium with a detection limit of 1 ppb. The sensor response is linear in the 10 ppb to 1 ppm concentration regime. A unique characteristic of the thin film based sensor is the blue shift occurring concomitantly with the decrease in the surface plasmon resonance absorption upon interaction with mercury, making the sensing highly selective. Unlike the majority of known sensors that work only in situ, the thin film sensor can be used ex situ as well. Examination of the thin film using microscopy and spectroscopy through the sensing process provides detailed insight into the sensing event.

Development and applications of fluorogenic probes for mercury(II) based on vinyl ether oxymercuration

Mercury is a major threat to the environment and to human health. It is highly desirable to develop a user-friendly kit for on-site mercury detection. Such a method must be able to detect mercury below the threshold levels for drinking water, 1-2 ppb. We developed a fluorescence method based on the oxymercuration of vinyl ethers to detect mercury in dental and environmental samples. Chloride ions interfered with the oxymercuration reaction, but the addition of AgNO(3) solved this problem. Fine electronic and structural tuning led to the development of a more responsive probe that was less sensitive to chloride ion interference. This second-generation probe could detect 1 ppb mercury ions in water.

A ferrocene-quinoxaline derivative as a highly selective probe for colorimetric and redox sensing of toxic mercury(II) cations

A new chemosensor molecule 3 based on a ferrocene-quinoxaline dyad recognizes mercury (II) cations in acetonitrile solution. Upon recognition, an anodic shift of the ferrocene/ferrocenium oxidation peaks and a progressive red-shift (Δλ = 140 nm) of the low-energy band, are observed in its absorption spectrum. This change in the absorption spectrum is accompanied by a colour change from orange to deep green, which can be used for a “naked-eye” detection of this metal cation.