Mercury Ions In Water Research Articles

Armored Urease: Enzyme-Bioconjugated Poly(acrylamide) Hydrogel as a Storage and Sensing Platform.

Jack bean urease is an important enzyme not only because of its numerous uses in medical and other fields but also because of its historical significance-the first enzyme to be crystallized and also the first nickel metalloenzyme. This enzyme hydrolyzes urea into ammonia and carbon dioxide; however, the stability of this enzyme at ambient temperature is a bottleneck for its applicability. To improve urease stability, it was immobilized on different substrates, particularly on polymeric hydrogels. In this study, the enzyme was coupled covalently with poly(acrylamide) hydrogel with an yield of 18μmol/cm3. The hydrogel served as the nanoarmor and protected the enzyme against denaturation. The enzyme immobilized on the polymer hydrogel showed no loss in activity for more than 30 days at ambient temperature, whereas free enzyme lost its activity within a couple of hours. The Michaelis-Menten constant (Km) for free and immobilized urease were 0.0256 and 0.2589mM, respectively, on the first day of the study. The Km of the immobilized enzyme was approximately 10 times higher than that of the free enzyme. The hydrogel technique was also used to prepare light diffracting polymerized colloidal crystal array in which urease enzyme was covalently immobilized. This system was applied for the detection of mercury (Hg2+) with the lower limit as 1ppb, which is below the maximum contaminant limit (2ppb) for mercury ions in water. The experimental details of these studies are presented in this chapter.

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 (dTn). This mutually templated dynamic chiral coassembly system (BNAn-dTn) 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 BNAn-dTn 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.

Diffusion-Controlled Simultaneous Sensing and Scavenging of Heavy Metal Ions in Water Using Atomically Precise Cluster–Cellulose Nanocrystal Composites

Development of a system that can simultaneously sense and scavenge toxic heavy metal ions at low concentrations is an ideal solution for in situ monitoring and purification of contaminated water. In this paper, we report on the synthesis and application of a novel system, luminescent atomically precise cluster–cellulose nanocrystal composite, namely, bovine serum albumin-protected gold nanoclusters (Au@BSA NCs)-loaded cellulose nanocrystal–alginate hydrogel beads, that can simultaneously sense and scavenge heavy metal ions, specifically mercury ions in water. Characterization of the system performed using scanning electron microscopy coupled with energy dispersive spectroscopy and X-ray photoelectron spectroscopy elucidated the physical and chemical characteristics of the system. Additionally, we proposed a new method to visualize the diffusion phenomenon and calculate the effective diffusion coefficient of heavy metal ions in hydrogel beads by monitoring the fluorescence-quenching dynamics of Au@BSA NCs ...

A simple and selective colorimetric mercury (II) sensing system based on chitosan stabilized gold nanoparticles and 2,6-pyridinedicarboxylic acid

The development of simple and cost-effective methods for the detection and treatment of Hg2+ in the environment is an important area of research due to the serious health risk that Hg2+ poses to humans. Colorimetric sensing based on the induced aggregation of nanoparticles is of great interest since it offers a low cost, simple, and relatively rapid procedure, making it perfect for on-site analysis. Herein we report the development of a simple colorimetric sensor for the selective detection and estimation of mercury ions in water, based on chitosan stabilized gold nanoparticles (AuNPs) and 2,6-pyridinedicarboxylic acid (PDA). In the presence of Hg2+, PDA induces the aggregation of AuNPs, causing the solution to change colors varying from red to blue, depending on the concentration of Hg2+. The formation of aggregated AuNPs in the presence of Hg2+ was confirmed using transmission electron microscopy (TEM) and UV–Vis spectroscopy. The method exhibits linearity in the range of 300nM to 5μM and shows excellent selectivity towards Hg2+ among seventeen different metal ions and was successfully applied for the detection of Hg2+ in spiked river water samples. The developed technique is simple and superior to the existing techniques in that it allows detection of Hg2+ using the naked eye and simple and rapid colorimetric analysis, which eliminates the need for sophisticated instruments and sample preparation methods.

Ultrasensitive sliver nanorods array SERS sensor for mercury ions

With years of outrageous mercury emissions, there is an urgent need to develop convenient and sensitive methods for detecting mercury ions in response to increasingly serious mercury pollution in water. In the present work, a portable, ultrasensitive SERS sensor is proposed and utilized for detecting trace mercury ions in water. The SERS sensor is prepared on an excellent sliver nanorods array SERS substrate by immobilizing T-component oligonucleotide probes labeled with dye on the 3′-end and –SH on the 5′-end. The SERS sensor responses to the specific chemical bonding between thymine and mercury ions, which causes the previous flexible single strand of oligonucleotide probe changing into rigid and upright double chain structure. Such change in the structure drives the dyes far away from the excellent SERS substrate and results in a SERS signal attenuation of the dye. Therefore, by monitoring the decay of SERS signal of the dye, mercury ions in water can be detected qualitatively and quantitatively. The experimental results indicate that the proposed optimal SERS sensor owns a linear response with wide detecting range from 1pM to 1μM, and a detection limit of 0.16pM is obtained. In addition, the SERS sensor demonstrates good specificity for Hg2+, which can accurately identify trace mercury ions from a mixture of ten kinds of other ions. The SERS sensor has been further executed to analyze the trace mercury ions in tap water and lake water respectively, and good recovery rates are obtained for sensing both kinds of water. With its high selectivity and good portability, the ultrasensitive SERS sensor is expected to be a promising candidate for discriminating mercury ions in the fields of environmental monitoring and food safety.

A FRET-based fluorescent probe for mercury ions in water and living cells

On the basis of fluorescence resonance energy transfer (FRET), a new rhodamine derivative (DRh) was synthesized as a ratiometric fluorescent probe for detecting Hg2+ in water and living cells samples. The recognition properties of the probe DRh with metal ions had been investigated in H2O/CH3CN (9:1, v/v; Tris-HCl 50mmolL−1; pH=7.0) solution by the UV–Vis spectrophotometry and the fluorescence spectrophotometry. The results showed that the probe DRh exhibited the selective recognition of Hg2+. Upon the addition of Hg2+, the spirolactam ring of probe DRh was opened. The 1:1 stoichiometric structure between DRh and Hg2+ were supported by Job's plot, MS and DFT theoretical calculations. The linearly fluorescence intensity ratio (I582/I538) is proportional to the concentration of Hg2+ in the range 0–30μmolL−1. The limit of detection (LOD) of Hg2+ is 0.008μmolL−1 (base on S/N=3). The present probe was applied to the determination of Hg2+ in neutral water samples and gave recoveries ranging from 104.5 to 107.9%. Furthermore, the fluorescent probe also can be applied as a bioimaging reagent for Hg2+ detection in HeLa cells.

Aggregation induced emission of a cyanostilbene amphiphile as a novel platform for FRET-based ratiometric sensing of mercury ions in water

A self-assembled FRET system on the basis of a cyanostilbene amphiphile has been constructed for ratiometric sensing of mercury ions in water.

Real-time detection of mercury ions in water using a reduced graphene oxide/DNA field-effect transistor with assistance of a passivation layer

Field-effect transistor (FET) sensors based on reduced graphene oxide (rGO) for detecting chemical species provide a number of distinct advantages, such as ultra-sensitivity, label-free, and real-time response. However, without a passivation layer, channel materials directly exposed to an ionic solution could generate multiple signals from ionic conduction through the solution droplet, doping effect, and gating effect. Therefore, a method that provides a passivation layer on the surface of rGO without degrading device performance will significantly improve device sensitivity, in which the conductivity changes solely with the gating effect. In this work, we report rGO FET sensor devices with Hg2+-dependent DNA as a probe and the use of an Al2O3 layer to separate analytes from conducting channel materials. The device shows good electronic stability, excellent lower detection limit (1nM), and high sensitivity for real-time detection of Hg2+ in an underwater environment. Our work shows that optimization of an rGO FET structure can provide significant performance enhancement and profound fundamental understanding for the sensor mechanism.

A Novel “Turn On” Glucose-Based Rhodamine B Fluorescent Chemosensor for Mercury Ions Recognition in Aqueous Solution

A novel “turn-on” fluorescent sensor based on glucose and rhodamine B for detection of mercury ions was designed and synthesized. The fluorescent sensor showed an extreme specificity for mercury ions than for other metal ions in aqueous solution. On adding mercury ions to the solution of glucose-based rhodamine B sensor, the absorption and fluorescence signals enhanced remarkably at 567 and 587 nm, respectively. Titration of sensor with mercury ions showed 1:1 stoichiometric reaction. The cyclic voltammetric measurement of an increasing amount of mercury ions in the solution of glucose-based rhodamine B sensor commendably showed the change in the fluorescence characteristics. Furthermore, the successful detection of trace amount of mercury ions in water indicated that glucose-based rhodamine B sensor can be used for the detection of the limited mercury ions in drinking water.

Highly selective and reversible colorimetric detection of mercury ions by a hydrophilic cycloruthenated complex in water

A new hydrophilic cyclometallated ruthenium complex Ru1-B with 4,4′-dicarboxylate-2,2′-bipyridine (abbreviated as dcbpy) and 2-(2-thienyl)pyridine (abbreviated as thpy) as ligands was successfully synthesized to selectively detect mercury ion in water. Only upon addition of mercury ions, the aqueous solution of the complex exhibits very remarkable color change from red to yellow with a dramatic blue-shift (120nm) of MLCT absorption bands. The detection limit of Hg2+ for this chemo-sensor in HEPES aqueous solution was 0.59μM. Interestingly, the complex can be recovered from complex-Hg2+ both in solution and silica gel plates by adding I−. Therefore, it can be used as a sensitive “naked-eye” indicator for Hg2+ in natural environment.

Detection of trace mercury ions in water by a novel Raman probe

The convenient chemical method for sensing mercury ion (Hg2+) has drawn significant attention in recent researches. Herein we report a simple, ultrasensitive and inexpensive protocol to detect trace mercury ions in water without complicatedly tagging, based on the facile synthesis of a nanocomposition, which is constructed with inositol hexaphosphate (IP6) stabilized gold nanoparticles (Au NPs) modified by crystal violet (CV) as Raman signal molecule and tri-sodium citrate (TC) as reducer, shortly named CV/TC/IP6/Au NPs. A possible mechanism for the Raman probe is the decreasing intensity of SERS band at 1173cm−1 of crystal violet (CV) with Hg2+ addition due to the reduction of Hg2+ by TC to Hg atom whose competition with CV molecules at the IP6/Au NPs surface, resulting in CV molecules detachment from the surface. The proposal Raman probe shows an unprecedented limit of detection (LOD) of 0.5pM for Hg2+. This SERS-based method of Hg2+ determination could be expected to have wide-range applications in many areas such as analysis of trace Hg2+ in river water.

Aggregation induced emission enhancement from Bathophenanthroline microstructures and its potential use as sensor of mercury ions in water

Bathophenanthroline (BA) microstructures of various morphologies have been synthesized using a reprecipitation method. The morphologies of the particles are characterized using optical and scanning electron microscopy (SEM) methods. An aqueous dispersion of BA microstructures shows aggregation induced emission enhancement (AIEE) compared to BA in a good solvent, THF. This luminescent property of aggregated BA hydrosol is used for the selective detection of trace amounts of mercury ion (Hg(2+)) in water. It is observed that Hg(2+) ions can quench the photoluminescence (PL) intensity of BA aggregates even at very low concentrations, compared to other heavy metal ions e.g. nickel (Ni(2+)), manganese (Mn(2+)), cadmium (Cd(2+)), cobalt (Co(2+)), copper (Cu(2+)), ferrous (Fe(2+)) and zinc (Zn(2+)). This strong fluorescence quenching of aggregated BA in the presence of Hg(2+) ions has been explained as a complex interplay between the ground state complexation between BA and Hg(2+) ions and external heavy atom induced perturbation by Hg(2+) ions on the excited states of the fluorophore BA.

Cyclometallated ruthenium complex-modified upconversion nanophosphors for selective detection of Hg2+ions in water

Upconversion detection nanocomposites were assembled for the selective luminescent detection of mercury ions in water. A hydrophobic cyclometallated ruthenium complex [Ru(II)(bpy)2(thpy)]PF6 (abbreviated as Ru1; bpy = 2,2'-bipyridine and thpy = 2-(2-thienyl)pyridine) is employed as a chemodosimeter to assemble on amphiphilic polymer-coating upconversion nanophosphors (UCNPs) based on the hydrophobic-hydrophobic interaction. Upon addition of Hg(2+), the nanocomposite not only exhibits a remarkable color change from deep-red to yellow, but also an enhanced upconversion luminescence (UCL) emission by hindering the luminescent resonance energy transfer (LRET) process from the upconversion emission of UCNPs to Ru1. Using the ratiometric UCL emission as a detection signal, the detection limit of Hg(2+) for this nanoprobe in aqueous solution is 8.2 ppb, which is much lower than that (329 ppb) determined by UV/Vis technology. Such an Hg(2+)-tunable LRET process provides a general strategy for fabricating a water-soluble upconversion-based nanoprobe for some special analyte.

Remarkable role of positional isomers in the design of sensors for the ratiometric detection of copper and mercury ions in water

Cation sensing properties of the three positional isomers of rhodamine based sensors (1–3) are studied in water. The sensors differ only in the position of pyridine's nitrogen. The chemosensor 1, with pyridine nitrogen at ortho-position, showed a selective colorimetric detection of Cu(II) ions in water, at physiological pH 7.4 and also in medium containing BSA (bovine serum albumin) and blood serum. Notably the compound 2 and 3, with pyridine end located at meta- and para-positions did not show any color change with Cu(II) ions, although both the compounds showed turn-on change both in color and fluorescence with Hg(II) ions specifically. All the probes showed ratiometric changes with the specific metal ions. The changing position of nitrogen also changed the complexation pattern of the sensors with the metal ions. Probe 1 showed 2:1 complexation with Cu(II), whereas 2 and 3 showed 1:1 complexation with Hg(II) ions. The mechanism investigation showed that the change in color upon addition of metal ions is due to the ring-opening of the spirolactam ring of the probes. Cu(II) interacted with ligand 1 through a three-point interaction mode comprising carbonyl oxygen, amido nitrogen and pyridine nitrogen end. But in case of 2 and 3, Hg2+ only interacted through pyridine nitrogen ends. Quantitative estimation of Cu2+ and Hg2+ in complex biological media such as bovine albumin protein (BSA) and human blood serum were performed using these sensors. Rapid on-site detection as well as discrimination of these toxic ions was demonstrated using easily prepared portable test-strips.

Gold nanoparticles for designing of smart colorimetric logic gates operations and scavengers for mercury ions in water

A smart colorimetric AND logic gate based on citrate stabilized gold nanoparticles using DM and H2PO4− as inputs, which operates in aqueous media with low concentration, is reported. A mechanistic study revealed that the catechol groups of DM interact with the surface of the gold nanoparticles and the amino group of DM cross-linked to H2PO4− through hydrogen bonds leading to the aggregation of AuNPs showing a distinct colour change, which is supported by UV-vis study and TEM images. The purple coloured aggregated gold nanoparticles with DM and H2PO4− exhibit sharp colour change in the presence of Hg2+. On the basis of this observation, a nonimplication logic gate system is demonstrated with Hg2+ and (DM + H2PO4−) as the inputs. In this system, the Hg2+ ion is reduced to form Au–Hg amalgam with the aid of citrate anions as the reducing agent and exhibited a colour change from purple to reddish-brown, which is supported by XRD data, TEM images and UV-visible study. An AND logic gate thus developed was used for the quantitative analysis of Hg2+ in lake water at low concentration as a test sample, satisfactory results were obtained.

Facile ultrasensitive monitoring of mercury ions in water by fluorescent ratiometric detection

Abstract Prospects for analytical application of 2,5-diphenyloxazole-substituted 3-hydroxychromone for detection of mercury ions are presented. Sensitivity and selectivity for a number of metal ions both in methanol solution and in the plasticized polymer are outlined. Ultrasensitive and highly selective fluorescent ratiometric response of the polymer film containing the title compound for mercury ions in water media is revealed. Reversibility of ratiometric response to mercury ions and influence of plasticizer’s content in the polymer film on the optical feedback are also discussed.

NaYF4:Yb3+/Er3+ nanoparticle-based upconversion luminescence resonance energy transfer sensor for mercury(ii) quantification

Upconversion luminescence is an anti-Stokes' emission process by converting long wavelength near-infrared (NIR, 980 nm) irradiation into shorter wavelength visible light emission, which demonstrates many advantages including no autofluorescence, low damage to samples, no photobleaching, and high sensitivity. Based on the Rhodamine B thiolactone (RBT) functionalized NaYF(4):15%Yb(3+),5%Er(3+) (UCNPs@RBT) nanocomposites, an ultrasensitive, selective, and rapid upconversion luminescence resonance energy transfer (UC-LRET) sensor has been developed for the detection of mercury ions (Hg(2+)) in water. Upconverting luminescence resonance energy transfer from the UCNPs to the RBT derivates occurs after the addition of Hg(2+) ions into the UCNPs@RBT colloidal solution. This UC-LRET recognition of Hg(2+) can be finished within 1 min and other cations have no influence on the detection of mercury ions. This newly developed sensor demonstrates high selectivity toward the mercury ions and enables ultrasensitive and rapid detection of mercury ions in water in the range of 5 nM to 10 μM with a 3σ limit of detection of 3.7 nM. This sensor can be used for a naked-eye detection of Hg(2+) ions via its green upconverting luminescence response under the infrared excitation (980 nm) with the merit of no autofluorescence interference and good photostability. In addition, by dipping the hydrogel of UCNPs@RBT nanocomposites onto the filter paper, a highly selective and convenient luminescent paper sensor for Hg(2+) ions was also developed.

Chemosensory rhodamine-immobilized mesoporous silica material for extracting mercury ion in water with improved sensitivity

Mesoporous silica material, SBA-15, is an excellent support for constructing fluorescent surface sensor. In this paper, we reported a three-step surface reaction involved strategy to construct efficient fluorescent surface sensor for mercury ion by clicking rhodamine fluoroionophores onto APES-functionalized SBA-15, which is fully characterized by IR spectra, TGA analysis, elemental analysis, nitrogen adsorption experiment and TEM. Our experimental results indicated that such a strategy exhibits an obviously higher loading efficiency within SBA-15 than a previously reported strategy. The Hg2+ extracting efficiency for SBAIR was found to be enhanced (ca. 89%). In addition to the high selectivity, the current chemosensor shows improved sensitivity and can respond to Hg2+ as low as ppb level (1.0 × 10−8 M, 2 ppb) in water.

A nanoparticle-supported fluorescence resonance energy transfer system formed via layer-by-layer approach as a ratiometric sensor for mercury ions in water

This article describes the design and preparation of a novel fluorescence resonance energy transfer (FRET)-based ratiometric sensor with the polymer nanoparticle as scaffold for detecting Hg2+ in aqueous media. In this study, a fluorescent dye fluorescein isothiocyanate (FITC, served as the donor) and a spirolactam rhodamine derivative (SRHB, served as mercury ion probe) were covalently attached onto polyethylenimine (PEI) and polyacrylic acid (PAA) respectively; and a ratiometric sensing system was then formed through the deposition of the donor- and probe-containing polyelectrolytes onto the negatively charged polymer particles via the layer-by-layer approach. The ratiometric fluorescent signal change of the system is based on the intra-particle fluorescence resonance energy transfer (FRET) process modulated by mercury ions. Under optimized structural and experimental conditions, the particle-based detection system exhibits stable response for Hg2+ in aqueous media. More importantly, in this newly developed particle-based detection system formed by LBL approach, varied numbers of the PAA/PEI layers which served as the spacer could be placed between the donor-containing layer and the probe-containing layer, hence the donor–acceptor distance and energy transfer efficiency could be effectively tuned (from ca. 25% to 76%), this approach has well solved the problem for many particle-based FRET systems that the donor–acceptor distance cannot be precisely controlled. Also, it is found that the ratiometric sensor is applicable in a pH range of 4.6–7.3 in water with the detection limit of 200nM. This approach may provide a new strategy for ratiometric detection of analytes in some environmental and biological applications.

Ratiometric Fluorescence Detection of Mercury Ions in Water by Conjugated Polymer Nanoparticles

We present dye-doped polymer nanoparticles that are able to detect mercury in aqueous solution at parts per billion levels via fluorescence resonance energy transfer (FRET). The nanoparticles are prepared by reprecipitation of highly fluorescent conjugated polymers in water and are stable in aqueous suspension. They are doped with rhodamine spirolactam dyes that are nonfluorescent until they encounter mercury ions, which promote an irreversible reaction that converts the dyes to fluorescent rhodamines. The rhodamine dyes act as FRET acceptors for the fluorescent nanoparticles, and the ratio of nanoparticle-to-rhodamine fluorescence intensities functions as a ratiometric fluorescence chemodosimeter for mercury. The light harvesting capability of the conjugated polymer nanoparticles enhances the fluorescence intensity of the rhodamine dyes by a factor of 10, enabling sensitive detection of mercury ions in water at levels as low as 0.7 parts per billion.