Dose-dependent inorganic mercury absorption by isolated perfused intestine of rainbow trout, Oncorhynchus mykiss, involves both amiloride-sensitive and energy-dependent pathways

Anthracene benzene conjugate (ABC): An asymmetric Schiff base for the selective detection of Ag+ ion using fluorimetry and its applications

Anthracene based chemosensor ABC has been synthesized and characterized through ¹H, ¹³C NMR, mass spectral studies. UV absorption and emission studies performed to identify the sensing behavior of chemosensor ABC. The probe ABC, originally bright fluorescent, selectively sense Ag⁺ ion by the quenching the fluorescence intensity through a "Switch On-off" process and quench the fluorescence due to the heavy atom effect interaction with the free chemosensor. The binding constant of the probe ABC with Ag⁺ was calculated as 5.4 × 10⁴ M^-1 and the limit of detection upto 1.4 nM level. The practical utilization of the probe ABC was demonstrated by applying to the real water and soil sample analysis, latent finger print, and the sensor as a fluorescent ink.

Curcumin Is an Iconic Ligand for Detecting Environmental Pollutants

The rapid increase in industrial revolution and the consequent environmental contamination demands continuous monitoring and sensitive detection of the pollutants. Nanomaterial-based sensing system has proved to be proficient in sensing environmental pollutants. The development of novel ligands for enhancing the sensing efficiency of nanomaterials has always been a challenge. However, the amendment of nanostructure with molecular ligand increases the sensitivity, selectivity, and analytical performance of the resulting novel sensing platform. Organic ligands are capable of increasing the adsorption efficacy, optical properties, and electrochemical properties of nanomaterials by reducing or splitting of band gap. Curcumin (diferuloylmethane) is a natural organic ligand that exhibits inherent fluorescence and electrocatalytic property. Due to keto-enol tautomerism, it is capable of giving sensitive signals such as fluorescence, luminescence, ultraviolet absorption shifts, and electrochemical data. Curcumin probes were also reported to give enhanced meterological performances, such as low detection limit, repeatability, reproducibility, high selectivity, and high storage stability when used with nanosystem. Therefore, research on curcumin-modified nanomaterials in the detection of environmental pollution needs a special focus for prototype and product development to enable practical use. Hence, this article reviews the role of curcumin as a natural fluorophore in optical and electrochemical sensing of environmentally significant pollutants. This review clearly shows that curcumin is an ideal candidate for developing and validating nanomaterials-based sensors for the detection of environmental pollutants such as arsenic, lead, mercury, boron, cyanide, fluoride, nitrophenol, trinitrotoluene, and picric acid and toxic gases such as ammonia and hydrogen chloride. This review will afford references for future studies and enable researchers to translate the lab concepts into industrial products.

A novel and stable fluorescent probe for tracking Hg2+ with large Stokes shift and its application in cell imaging

Giving the fact that mercury ions (Hg²⁺) is highly toxic, migratory and bioaccumulative and even very small amounts of mercury can cause serious damage to health, resulting in many diseases, such as abdominal pain, renal failure, nervous system damage. The content of mercury in drinking water quality standard of our country has been strictly limited. Therefore, it is of good research interest to develop a stable fluorescent probe capable of detecting the presence of mercury in biological cells. In this study, a novel fluorescent probe based on isophoronitriles scaffold, DNC-Hg, was designed and synthesized for monitoring mercury ion in living HeLa cells. The good properties of the probe may be attributed to the unique strong electron-absorbing group in the structural design, the good conjugation effect, and the mature Hg²⁺ recognition site. The probe exhibited good selectivity and stability, large Stokes shift(174 nm) and low cytotoxicity. Furthermore, this stable probe DNC-Hg could be used for cellular imaging.

Simultaneously colorimetric detection and effective removal of mercury ion based on facile preparation of novel and green enzyme mimic

In this work, an environmentally-friendly and cost-effective enzyme mimic was obtained by facile one-pot preparation of chitosan/Cu/Fe (CS/Cu/Fe) composite. This composite exhibited significantly enhanced oxidase-mimicking activity during catalyzing the oxidation of 3, 3', 5, 5'-tetramethylbenzidine (TMB). The CS/Cu/Fe composite was comprehensively characterized and the possible catalytic mechanism was reasonably explored and discussed. Benefiting from the thermal stability and the compatibility with carbohydrate, the CS/Cu/Fe composite was further integrated with agarose hydrogel to fabricate a portable analytical tube containing oxidase mimic. Based on the inhibition of the catalytic oxidation of TMB in the presence of cysteine, as well as the recovery of oxidase-like activity of CS/Cu/Fe due to the specific complexation of cysteine and mercury ion (Hg²⁺), the rapid colorimetric detection of Hg²⁺ was successfully carried out in the analytical tube. This colorimetric method showed good linear response to Hg²⁺ over the range from 40 nM to 8.0 μM with a detection limit of 8.9 nM. The method also revealed high selectivity and satisfactory results in recovery experiments of Hg²⁺ detection in tap water and lake water. Furthermore, it was found that the effective removal of Hg²⁺ could be realized in the analytical tube based on efficient Hg²⁺ adsorption by CS/Cu/Fe composite and agarose hydrogel. This study not only prepared a robust and low-cost enzyme mimic, but also proposed a smart strategy to simultaneously monitor and remove toxic Hg²⁺ from contaminated water.

Dehydroabietylamine-decorated imino-phenols: supramolecular gelation and gel phase selective detection of Fe3+, Cu2+ and Hg2+ ions under different experimental conditions

Dehydroabietylamine-linked Schiff bases 1–3 have been synthesized, characterized and employed in metal ion sensing in a sol–gel medium. The compounds have a propensity for gel formation from aqueous organic solvents.

Fluorescein Hydrazide-Appended Metal-Organic Framework as a Chromogenic and Fluorogenic Chemosensor for Mercury Ions

In this work, we prepared a fluorescein hydrazide-appended Ni(MOF) (Metal-Organic Framework) [Ni3(BTC)2(H2O)3]·(DMF)3(H2O)3 composite, FH@Ni(MOF). This composite was well-characterized by PXRD (powder X-ray diffraction), FT-IR (Fourier transform infrared spectroscopy), N2 adsorption isotherm, TGA (thermogravimetric analysis), XPS (X-ray photoelectron spectroscopy), and FESEM (field emission scanning electron microscopy). This composite was then tested with different heavy metals and was found to act as a highly selective and sensitive optical sensor for the Hg2+ ion. It was found that the aqueous emulsion of this composite produces a new peak in absorption at 583 nm, with a chromogenic change to a pink color visible to the naked eye upon binding with Hg2+ ions. In emission, it enhances fluorescence with a fluorogenic change to green fluorescence upon complexation with the Hg2+ ion. The binding constant was found to be 9.4 × 105 M-1, with a detection limit of 0.02 μM or 5 ppb. This sensor was also found to be reversible and could be used for seven consecutive cycles. It was also tested for Hg2+ ion detection in practical water samples from ground water, tap water, and drinking water.

Ultrasensitive and turn-on homogeneous Hg2+ sensing based on a target-triggered isothermal cycling reaction and dsDNA-templated copper nanoparticles

In this work, an ultrasensitive and turn-on sensor for homogeneous Hg2+ detection has been constructed based on a target-triggered isothermal cycling reaction and rapid label-free signal output with dsDNA-templated copper nanoparticles (CuNPs). As the key component of the sensor, a hairpin DNA without any labels was designed to contain different functional sequence segments and to resist digestion by exonuclease due to the protruding 3'-terminus. In the presence of Hg2+, the formation of a T-Hg2+-T structure turned the protruding 3'-terminus of the hairpin DNA to a blunt end that could be efficiently digested by Exo III, accompanied by Hg2+ release, followed by another digestion cycle. Hence, the Hg2+-triggered isothermal cycling reaction accumulated numerous dsDNA templates that facilitated fluorescent CuNP generation and finally output an amplified signal used to identify the target. This protocol is capable of Hg2+ sensing in a concentration range of 5 orders of magnitude with a detection limit down to 3.9 pM. The as-constructed sensor also revealed high selectivity, as well as satisfactory results in recovery experiments of Hg2+ detection in real water samples.

Ratiometric Detection of Mercury (II) Ions in Living Cells Using Fluorescent Probe Based on Bis(styryl) Dye and Azadithia-15-Crown-5 Ether Receptor

Bis(styryl) dye 1 bearing N-phenylazadithia-15-crown-5 ether receptor has been evaluated as a ratiometric fluorescent chemosensor for mercury (II) ions in living cells. In aqueous solution, probe 1 selectively responds to the presence of Hg²⁺ via the changes in the emission intensity as well as in the emission band shape, which is a result of formation of the complex with 1:1 metal to ligand ratio (dissociation constant 0.56 ± 0.15 µM). The sensing mechanism is based on the interplay between the RET (resonance energy transfer) and ICT (intramolecular charge transfer) interactions occurring upon the UV/Vis (380 or 405 nm) photoexcitation of both styryl chromophores in probe 1. Bio-imaging studies revealed that the yellow (500-600 nm) to red (600-730 nm) fluorescence intensity ratio decreased from 4.4 ± 0.2 to 1.43 ± 0.10 when cells were exposed to increasing concentration of mercury (II) ions enabling ratiometric quantification of intracellular Hg²⁺ concentration in the 37 nM-1 μM range.

Two cluster-based metal–organic frameworks with selective detection of Hg2+ ion and magnetic properties

Two cluster-based metal–organic frameworks have been synthesized—one exhibits highly selective fluorescent detection of trace Hg2+ and the other shows antiferromagnetic interactions between Mn3+ ions.

Highly selective and sensitive tool for the detection of Hg(II) using 3-(Trimethoxysilyl) propyl methacrylate functionalized Ag-Ce nanocomposite from real water sample

Mercury and its derivates cause distinct toxicity and it is detrimental to the ecosystem where the excessive concentration contributes towards the environmental pollutants. The current study reported a colorimetric method for the detection of Hg(II) ion with high specificity and selectivity using Ag-Ce nanocomposite (NC) functionalized by 3-(Trimethoxysilyl) propyl methacrylate. The synthesized Ag-Ce NC was characterized by using double beam UV-visible spectrophotometer, zeta sizer, EDS, TEM, FT-IR, XRD and particle size analyzer. The synthesized particle possessed an average particle size of 27 ± 1 nm and zeta potential of -39.32 ± 3 mV. The brownish yellow colored Ag-Ce NC changed to colorless in presence of Hg(II) where the colorimetric detection was extremely specific and superior towards Hg(II) ion on comparing the tests with other metal ions. An excellent linear correlation was observed between absorbance (395 nm) and Hg(II) concentrations (1 nM-10 μM) (R² = 0.988) with LOD of 0.03 nM. A cotton swab based probe was prepared for selective, elegant and low cost colorimetric method to detect Hg(II). The parametric study was performed for optimizing the suitable condition. The colorimetric probe developed by this study for Hg(II) detection using Ag-Ce NC shows excellent practical applicability.

A dual thiourea-appended perylenebisimide "turn-on" fluorescent chemosensor with high selectivity and sensitivity for Hg2+ in living cells

Sensing heavy metal ions particularly for the most toxic Hg²⁺ is a long-term pursuit for chemists because of its obvious and extreme harmfulness to both the environment and human health. Herein, a novel 'turn-on' perylenebisimide-thiourea fluorescent probe PBI-BTB is achieved for rapid detection of Hg²⁺ in a DMSO/H₂O (5/1, v/v) solution through a typical Hg²⁺-promoting desulfurization reaction, which has been investigated through Job's plot titration, FT-IR, ¹H NMR and HRMS analysis. A remarkable fluorescence emission enhancement at 540 and 580 nm is observed in the presence of Hg²⁺, which is visible to the naked eye with high selectivity and sensitivity. Moreover, probe PBI-BTB combined strong anti-interference recognition with short response time (< 1 min). The rapid fluorescence response with low limit of detection (0.35 μM) in a wide pH range of 3.0-11.0 makes PBI-BTB a promising candidate for detection of Hg²⁺ without any buffer system. Furthermore, the practicability of probe PBI-BTB upon the Hg²⁺ recognition in human liver cancer cells (HepG-2) has been studied through fluorescent live cell imaging which reveals the probe's low toxicity to organism as well as the favorable cell permeability of PBI-BTB for detecting Hg²⁺ in biological systems.

Dietary bioaccumulation potential of silver nanomaterials compared to silver nitrate in wistar rats using an ex vivo gut sac technique

Chronic dietary bioaccumulation tests with rodents are required for new substances, including engineered nanomaterials (ENMs), in order to provide information on the potential hazards to human health. However, screening tools are needed to manage the diversity of ENMs and alternative methods are desirable with respect to animal welfare. Here, an ex vivo gut sac method was used to estimate the dietary bioaccumulation potential of silver nanomaterials. The entire gastrointestinal tract (except the caecum) was removed and filled with a gut saline containing 1 mg L^-1 of Ag as either AgNO₃, silver nanoparticles (Ag NPs) or silver sulphide nanoparticles (Ag₂S NPs), and compared to controls with no added Ag. The gut sacs were incubated for 4 h, rinsed to remove excess media, and the total Ag determined in the mucosa and muscularis. There was no detected Ag in the control treatments. Within the Ag treatments, 1.4-22% of the exposure dose was associated with the tissues and serosal saline. Within the mucosa of the AgNO₃ treatment, the highest Ag concentration was associated with the intestinal regions (3639-7087 ng g^-1) compared to the stomach (639 ± 128 ng g^-1). This pattern was also observed in the Ag NP and Ag₂S NP treatments, but there was no significant differences between any Ag treatments for the mucosa. However, differences between treatments were observed in the muscularis concentration. For example, both the Ag NP (907 ± 284 ng g ^-1) and Ag₂S NP (1482 ± 668 ng g^-1) treatments were significantly lower compared to the AgNO₃ treatment (2514 ± 267 ng g^-1). The duodenum demonstrated serosal accumulation in both the AgNO₃ (~10 ng mL^-1) and Ag NP (~3 ng mL^-1) treatments. The duodenum showed some of the highest Ag accumulation with 41, 61 and 57% of the total Ag in the mucosa compared to the muscularis for the AgNO₃, Ag NP and Ag₂S NP treatments, respectively. In conclusion, the ex vivo gut sac method demonstrates the uptake of Ag in all Ag treatments, with the duodenum the site of highest accumulation. Based on the serosal saline accumulation, the ranked order of accumulation is AgNO₃ > Ag NPs > Ag₂S NPs.

Fluorescent, colourimetric, and ratiometric probes based on diverse fluorophore motifs for mercuric(II) ion (Hg2+) sensing: highlights from 2011 to 2019

Though it has not been shown to deliver any biological importance, mercuric(II) ion (Hg²⁺) is a deleterious cation which poses grievous effects to the human body and/or the ecosystem, hence, the need for its sensitive and selective monitoring in both environmental and biological systems. Over the years, there has been a great deal of work in the use of fluorescent, colourimetric, and/or ratiometric probes for Hg²⁺ recognition. Essentially, the purpose of this review article is to give an overview of the advances made in the constructions of such probes based on the works reported in the period from 2011 to 2019. Discussion in this review work has been tailored to the kinds of fluorophore scaffolds used for the constructions of the probes reported. Selected examples of probes under each fluorophore subcategory were discussed with mentions of the typically determined parameters in an analytical sensing operation, including modulation in fluorescence intensity, optimal pH, detection limit, and association constant. The environmental and biological application ends of the probes were also touched where necessary. Important generalisations and conclusions were given at the end of the review. This review article highlights 196 references.

Influence of Macrophyte and Gut Microbiota on Mercury Contamination in Fish: A Microcosms Study

The freshwater lakes of southwestern France are subject to the development of invasive macrophytes which are associated with mercury (Hg) contamination of the food web. The aim of this study was to determine the bioavailability of methylmercury (MeHg) produced by plant roots in aquatic ecosystems. A microcosm experiment was performed using isotopically enriched inorganic Hg at environmental concentrations (1 µg 199IHg·L−1). For all conditions, total Hg in fish as well as Hg species associated with different compartments (water, sediments, plant roots, fish) were analyzed by gas chromatography-inductively coupled plasma-mass spectrometry (GC-ICP-MS). In addition, sediment, plants, and fish gut microbiota were studied by MiSEQ sequencing. Some strains were isolated and tested for their ability to methylate Hg. The results revealed 199MeHg production in plant roots and the presence of this form in fish (tissues and gut), highlighting a MeHg trophic transfer. Moreover, methylator bacteria were identified from the gut contents of the fish when they were in the presence of plants. Some of them were related to bacteria found in the plant roots. On the basis of these results, the transfer of MeHg and bacteria from plants to fish is highlighted; in addition, Hg methylation is strongly suspected in the fish gut, potentially increasing the Hg bioaccumulation.

Copillar[5]arene-rhodamine conjugate as a selective sensor for Hg2+ ions

A new copillar[5]arene-coupled rhodamine probe 1 shows selective sensing of Hg²⁺ ions over a series of metal ions in CH₃CN by exhibiting color change of the solution as well as turn on fluorescence. It also shows interaction with Cu²⁺ by exhibiting different color and spectral change. Tetrabutylammonium iodide distinguishes between Hg²⁺ and Cu²⁺ ions.

Role of PEPT1in the transport of cinnabar in Caco-2 cells

Cinnabar, a mercury-containing mineral medicine, has been used as an ingredient in Traditional Chinese Medicines for treatment of various diseases for thousands of years and is still widely used today. The toxicity of cinnabar is much less than other mercury-containing compounds. This study aimed to evaluate the possible role of oligopeptide transporter1 (PEPT1) in intestinal uptake of cinnabar. Thus, the Caco-2 cell model was employed to investigate the differential transport levels and the probable transporter involved in the transport of cinnabar, mercury sulfide (HgS) and mercury chloride (HgCl₂). Cells were incubated with the same molar concentration of cinnabar, HgS or HgCl₂ and then the inorganic mercury content of apical (AP), cellular and basolateral (BL) side of the cell was measured by ultra-high liquid chromatography-inductively coupled plasma mass spectrometry (UPLC-ICP/MS) after the treatment, respectively. Their transportation levels were also investigated when pH was changed to 5.5 in AP side to define the role of the H⁺ dependent transporter. Effects of cinnabar, HgS or HgCl₂ on transporter mRNA and protein expression levels were assayed by RT-PCR and Western-blot method, respectively. The possible transporter involved in the transport was examined by siRNA silencing and chemical inhibition. The results showed that the levels of inorganic mercury in the BL side for cinnabar and HgS were 49.39% and 30.41% of that in HgCl₂ group. The transport levels of cinnabar and HgCl₂ were significantly increased when the pH was changed to 5.5 on the AP side as compared with the control group (pH 7.4). Cinnabar significantly decreased the mRNA and protein expression of PEPT1. Transport levels of cinnabar were significantly decreased by PEPT1-siRNA and chemical inhibition of PEPT1. The present study demonstrates that PEPT1 may be an important transporter in the entry of cinnabar into the intestinal epithelium, and intestinal transport levels of cinnabar and HgS was lower than that of HgCl₂.

Practical aptamer-based assay of heavy metal mercury ion in contaminated environmental samples: convenience and sensitivity

Due to heavy metals' magnified pollution from their accumulation in the ecosystem, practical detection of ultra-low concentration of heavy metals in environmental sample is of great significance for environmental supervision and maintenance of people's health. Herein, a practical and sensitive assay of heavy metal mercury was developed by visually observing (or spectrum detecting) the change of cationic gold nanoparticles (AuNPs), which is directly caused by mercury ion induced hybridization between non-canonical base pairs. In this assay, signal probe's response was direct rather than the indirect salt induction, thus avoiding the defect of salt-induced indirect response. It makes the analysis more sensitive. The results showed that the response of 8.2 × 10^-8 M Hg²⁺ could be observed with naked eye and the detection limit of Hg²⁺ in spectrometric determination was 4.9 × 10^-11 M, which is more than one order of magnitude lower than that from indirect response pattern of signal probe. In addition, high specificity of the affinity chemistry for T-Hg-T renders the assay to be highly selective. Compared with the results of cold vapor atom adsorption spectroscopy (CVAAS), this analysis has good reliability for the detection of mercury. The results fully indicate that the developed assay is an ideal alternative for online detection of heavy metal mercury in environmental pollution samples.

A new thiosemicarbazone fluorescent probe based on 9,9'-bianthracene for Hg2+ and Ag. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2019;215:34-40. [PMID: 30825868 DOI: 10.1016/j.saa.2019.02.036]

A new 9,9'-bianthracene-based thiosemicarbazone (D1) has been successfully synthesized and utilized for chemosensors. The properties of D1 were systematically investigated by UV-Vis, fluorescence titration and theoretical calculations. As a result, D1 exhibits a characteristic fluorescence quenching phenomenon in the presence of Hg²⁺ or Ag⁺ compared to other metal cations (Na⁺, K⁺, Mg²⁺, Ba²⁺, Al³⁺, Zn²⁺, Fe²⁺, Pb²⁺, Cu²⁺, Co²⁺, Cd²⁺, Ni²⁺ and Mn²⁺). The detection limits of Hg²⁺ and Ag⁺ reach 6.62×10^-7M and 1.99×10^-5M, respectively. This is mainly attributed to the Hg²⁺ (or Ag⁺) forms a stable five-membered ring with the N atom in Schiff base CN and the S atom in thiourea. The results suggest that the probe D1 is a promising candidate for chemosensors in aqueous media due to its highly selectivity for Hg²⁺ and Ag⁺.

Ethical considerations in fish research

Fishes are used in a wide range of scientific studies, from conservation research with potential benefits to the species used to biomedical research with potential human benefits. Fish research can take place in both laboratories and field environments and methods used represent a continuum from non-invasive observations, handling, through to experimental manipulation. While some countries have legislation or guidance regarding the use of fish in research, many do not and there exists a diversity of scientific opinions on the sentience of fish and how we determine welfare. Nevertheless, there is a growing pressure on the scientific community to take more responsibility for the animals they work with through maximising the benefits of their research to humans or animals while minimising welfare or survival costs to their study animals. In this review, we focus primarily on the refinement of common methods used in fish research based on emerging knowledge with the aim of improving the welfare of fish used in scientific studies. We consider the use of anaesthetics and analgesics and how we mark individuals for identification purposes. We highlight the main ethical concerns facing researchers in both laboratory and field environments and identify areas that need urgent future research. We hope that this review will help inform those who wish to refine their ethical practices and stimulate thought among fish researchers for further avenues of refinement. Improved ethics and welfare of fishes will inevitably lead to increased scientific rigour and is in the best interests of both fishes and scientists.

Inter-species differences of total mercury and methylmercury in farmed fish in Southern China: Does feed matter?

China is now the largest producer of marine farmed fish and there is a considerable concern of seafood safety due to potential mercury contamination. We analyzed both the total mercury (THg) and methylmercury (MeHg) concentrations in nine species of commercial fish from two marine-cage farms in Southern China. ¹³C and ¹⁵N stable isotopes were concurrently analyzed to identify the artificial feed sources and the trophic levels of farmed fish. Mercury concentrations of all species were much lower than the human health screening values and safety limits established by different countries. Mercury levels in artificial pellets were the main determinants of Hg accumulation in fish between two sites, while somatic growth dilution and size also played an important role. Among the different fish tissues, muscle was a major reservoir for Hg and contained the highest ratio of MeHg/THg, and liver was the second important organ for Hg accumulation in most fish species. Intestine was a critical organ for Hg biotransformation with its %MeHg differing greatly among different fish species. δ¹⁵N analysis could not be used to determine the trophic levels in culturing systems where artificial practices were involved. Based on the δ¹³C signatures, five species of fish were identified to solely feed on the artificial pellets, yet the Hg bioaccumulation differed significantly among these species. We therefore concluded that Hg bioaccumulation in different fish species may be dependent on their internal Hg biotransformation as well as their biokinetics.

4-Hydroxybenzaldehyde derived Schiff base gelators: case of the sustainability or rupturing of imine bonds towards the selective sensing of Ag+and Hg2+ionsviasol–gel methodology

The cholesterol appended hydroxybenzaldehyde derived Schiff bases1–4have been designed and synthesized. They are suitable for the naked-eye detection of metal ions such as Hg²⁺and Ag⁺using sol–gel methodology involving either rupturing or maintaining the imine bonds.

MoS2 nanosheet mediated ZnO–g-C3N4 nanocomposite as a peroxidase mimic: catalytic activity and application in the colorimetric determination of Hg(ii)

A novel colorimetric sensing platform using the peroxidase mimicking activity of ternary MoS₂-loaded ZnO–g-C₃N₄ nanocomposites (ZnO–g-C₃N₄/MoS₂) has been developed for the determination of Hg(ii) ions over co-existing metal ions. The nanocomposite was prepared using an exfoliation process, and the product was further characterized using SEM, TEM, XRD and FTIR analysis. The ZnO–g-C₃N₄/MoS₂ possesses excellent intrinsic catalytic activity to induce the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) in aqueous solution in the presence of H₂O₂ to generate deep blue coloured cation radicals (TMB⁺) which can be viewed with the naked eye and produce absorbance at a wavelength of 652 nm. The addition of a well known bioradical scavenger, glutathione (GSH), to the solution hinders the generation of cation radicals and turns the solution colourless. The introduction of Hg(ii) to this solution brings the blue colour back into it, due to the strong affinity of the thiol in the GSH. Based on this mechanism, we have developed a simple and rapid colorimetric sensor for the highly sensitive and selective detection of Hg(ii) ions in aqueous solution with a low detection limit of 1.9 nM. Furthermore, the prepared colorimetric sensor was effectively applied for the quantification analysis of real water samples.

A novel colorimetric sensing platform using the peroxidase mimicking activity of ternary MoS₂-loaded ZnO–g-C₃N₄ nanocomposites (ZnO–g-C₃N₄/MoS₂) has been developed for the determination of Hg(ii) ions over co-existing metal ions.

Cholesterol linked benzothiazole: a versatile gelator for detection of picric acid and metal ions such as Ag+, Hg2+, Fe3+ and Al3+ under different conditions

The interaction of compound 1 with nitrophenols and metal ions has been studied in sol–gel medium. The nitrobenzene gel selectively recognizes picric acid, Ag⁺ and Hg²⁺ ions. In CH₃CN, compound 1 further shows affinity towards Fe³⁺, Al³⁺ and Hg²⁺.

Lactobacillus brevis 23017 Relieves Mercury Toxicity in the Colon by Modulation of Oxidative Stress and Inflammation Through the Interplay of MAPK and NF-κB Signaling Cascades

Aims: Lactobacillus strains have protective effects against heavy metals while relieving oxidative stress and modulating the immune response. Mechanisms that ameliorate heavy metal toxicity and the relationship between probiotics and gut barrier protection in the process of heavy metal pathogenesis was poorly understood. Methods and Results: In this study, Lactobacillus brevis 23017 (LAB, L. brevis 23017), a selected probiotics strain with strong mercury binding capacities, was applied to evaluate the efficiency against mercury toxicity in a mouse model. Histopathological results along with HE stains show that L. brevis 23017 protects the integrity of the small intestinal villus, which slows weight loss in response to Hg exposure. The qRT-PCR results demonstrate that L. brevis 23017 maintains a normal mucosal barrier via modulation of tight junction proteins. Importantly, the present study demonstrates that L. brevis 23017 effectively ameliorates injury of the small intestine by reducing intestinal inflammation and alleviating oxidative stress in animal models. Moreover, L. brevis 23017 blocks oxidative stress and inflammation through MAPK and NF-κB pathways, as shown by western blot. Conclusions: Together, these results reveal that L. brevis 23017 may have applications in the prevention and treatment of oral Hg exposure with fermented functional foods by protecting gut health in daily life.

Mercury fractionation in marine macrofauna using thermodesorption technique: Method and its application

Mercury (Hg) is one of the most dangerous elements, and its toxicity and ability to accumulate in organisms depend on its chemical form. There are numerous methods of Hg speciation analysis, out of which the least expensive and the least time-consuming one is thermodesorption. The method has been successfully used for the analysis of abiotic samples - soils and sediments. The aim of this study was to verify whether the simplified thermodesorption method can be used in the analysis of the tissues of animal organisms from different trophic levels. Hg fractionation analyses were performed on a DMA-80 analyser (Milestone, Italy). The results presented in this paper are the first published data on Hg fractionation by thermodesorption method in animal tissues. The study showed that the 5-step thermodesorption method can be applied to various types of environmental matrices, which makes it universal. This method is of great importance in terms of estimating the Hg uptake and transfer in the trophic chain, and also enables the assessment of global Hg circulation in the environment. The presented method does not require previous digestion of samples or the use of expensive reagents. It can also be used for the preliminary selection of samples for MeHg analysis. The results obtained by this 5-step fractionation could be comparable with different research, conducted using other Hg analysers.

Label-free electrochemiluminescence assay for aqueous Hg2+ through oligonucleotide mediated assembly of gold nanoparticles

Development of ultrasensitive method for Hg²⁺ analysis is important for human health protection and environment monitoring. In this work, we present a highly sensitive and selective electrochemiluminescence (ECL) assay in a "turn-on" mode for the detection of Hg²⁺ through selective assembly of gold nanoparticles (AuNPs) on the surface of indium tin oxide (ITO) electrode. In the absence of Hg²⁺, the nonthiolated ssDNA could protected AuNPs against its assembly on ITO surface, producing rather low ECL emission for Ru(bpy)₃²⁺/TPA system. Conversely, binding of Hg²⁺ with the Hg²⁺-specific oligonucleotide through thymine-Hg²⁺-thymine coordination formed the double-stranded structure, which could not effectively adsorb to AuNPs in solution. The assembly of free-state AuNPs is achieved, which well preserves electronical conductivity. The presence of AuNPs can catalyze the electro-oxidation of TPA, producing significantly enhanced ECL signal. Through detecting the ECL signal mediated by assembly of AuNPs, the proposed method was able to ensure substantial signal amplification and a low background. It was demonstrated that the ECL intensity was correlated with the ssDNA-based recognition reaction, enabling quantitative analysis of Hg²⁺ over the range of 8pM to 2nM, with a detection limit of 2pM. ECL intensity of the system were extremely specific for Hg²⁺ even in the presence of 1000-fold higher concentrations of other metal ions. Analytical results of Hg²⁺ spiked into water samples by the proposed ECL method were in good agreement with that obtained by atomic fluorescent spectrometry or mass spectrometry data.

Black Phosphorus Quantum Dots as the Ratiometric Fluorescence Probe for Trace Mercury Ion Detection Based on Inner Filter Effect

In this work, a novel ratiometric fluorescence sensor has been constructed for the selective and sensitive detection of Hg²⁺, which is based on the inner filter effect (IFE) of tetraphenylporphyrin tetrasulfonic acid (TPPS) toward black phosphorus quantum dots (BP QDs). Highly fluorescent BP QDs were successfully synthesized from bulk BP by sonication-assisted solvothermal method via a top-down route. In the presence of Hg²⁺, the IFE originating from spectral overlap between the excitation of BP QDs and the absorption of TPPS is inhibited and the fluorescence of BP QDs is restored. At the same time, the red fluorescence of TPPS is quenched due to its coordination with Mn²⁺. These phenomena result from the rapid coordination between Mn²⁺ and TPPS in the presence of Hg²⁺, which leads to the dramatic decrease of the absorption of TPPS. On the basis of these findings, we design a ratiometric fluorescence sensor for the detection of Hg²⁺. The as-constructed sensor reveals a good linear response to Hg²⁺ ranging from 1 to 60 nM with a detection limit of 0.39 nM. Furthermore, the sensing assay is applicable to detecting Hg²⁺ in real samples.

A Review of Mercury Bioavailability in Humans and Fish

To estimate human exposure to methylmercury (MeHg), risk assessors often assume 95%–100% bioavailability in their models. However, recent research suggests that assuming all, or most, of the ingested mercury (Hg) is absorbed into systemic circulation may be erroneous. The objective of this paper is to review and discuss the available state of knowledge concerning the assimilation or bioavailability of Hg in fish and humans. In fish, this meant reviewing studies on assimilation efficiency, that is the difference between ingested and excreted Hg over a given period of time. In humans, this meant reviewing studies that mostly investigated bioaccessibility (digestive processes) rather than bioavailability (cumulative digestive + absorptive processes), although studies incorporating absorption for a fuller picture of bioavailability were also included where possible. The outcome of this review shows that in a variety of organisms and experimental models that Hg bioavailability and assimilation is less than 100%. Specifically, 25 studies on fish were reviewed, and assimilation efficiencies ranged from 10% to 100% for MeHg and from 2% to 51% for Hg(II). For humans, 20 studies were reviewed with bioaccessibility estimates ranging from 2% to 100% for MeHg and 0.2% to 94% for Hg(II). The overall absorption estimates ranged from 12% to 79% for MeHg and 49% to 69% for Hg(II), and were consistently less than 100%. For both fish and humans, a number of cases are discussed in which factors (e.g., Hg source, cooking methods, nutrients) are shown to affect Hg bioavailability. The summaries presented here challenge a widely-held assumption in the Hg risk assessment field, and the paper discusses possible ways forward for the field.

Plasmonic detection of mercury via amalgam formation on surface-immobilized single Au nanorods

Au nanorods were used as plasmonic transducers for investigation of mercury detection through a mechanism of amalgam formation at the nanorod surfaces. Marked scattering color transitions and associated blue shifts of the surface plasmon resonance peak wavelengths (λ_max) were measured in individual nanorods by darkfield microscopy upon chemical reduction of Hg(II). Such changes were related to compositional changes occurring as a result of Hg-Au amalgam formation as well as morphological changes in the nanorods' aspect ratios. The plot of λ_max shifts vs. Hg(II) concentration showed a linear response in the 10-100 nM concentration range. The sensitivity of the system was ascribed to the narrow width of single nanorod scattering spectra, which allowed accurate determination of peak shifts. The system displayed good selectivity as the optical response obtained for mercury was one order of magnitude higher than the response obtained with competitor ions. Analysis of mercury content in river and tap water were also performed and highlighted both the potential and limitation of the developed method for real sensing applications.

Mechanisms involved in the transport of mercuric ions in target tissues

Mercury exists in the environment in various forms, all of which pose a risk to human health. Despite guidelines regulating the industrial release of mercury into the environment, humans continue to be exposed regularly to various forms of this metal via inhalation or ingestion. Following exposure, mercuric ions are taken up by and accumulate in numerous organs, including brain, intestine, kidney, liver, and placenta. In order to understand the toxicological effects of exposure to mercury, a thorough understanding of the mechanisms that facilitate entry of mercuric ions into target cells must first be obtained. A number of mechanisms for the transport of mercuric ions into target cells and organs have been proposed in recent years. However, the ability of these mechanisms to transport mercuric ions and the regulatory features of these carriers have not been characterized completely. The purpose of this review is to summarize the current findings related to the mechanisms that may be involved in the transport of inorganic and organic forms of mercury in target tissues and organs. This review will describe mechanisms known to be involved in the transport of mercury and will also propose additional mechanisms that may potentially be involved in the transport of mercuric ions into target cells.

Application of a novel electrochemical sensor based on modified siliceous mesocellular foam for electrochemical detection of ultra-trace amounts of mercury ions

S-MCF particles were functionalized with dithizone groups, and applied as a new class of mesoporous electrode material for preconcentration and electrochemical detection of trace mercury ions in environmental samples.

Electrochemiluminescent molecular logic gates based on MCNTs for the multiplexed analysis of mercury(ii) and silver(i) ions

In this paper, logic gates with electrochemiluminescence (ECL) signal as outputs were constructed based on the use of the thymine (T)-rich (S₁) or cytosine (C)-rich (S₂) oligonucleotides for the selective analysis of mercury ions (Hg²⁺) or silver ions (Ag⁺).