Detection Limit For Hg2 Research Articles

A dual sensor selective for Hg2+ and cysteine detection

Abstract A new sensor for Hg2+ and cysteine detection has been synthesized and tested. The sensor based on cinamaldehyde and pyrimidine absorbs visible light when exposed to Hg2+ and becomes colored. The sensor only changes color due to Hg2+ and does not change when exposed to some other metal ions. Calculations show the change in color is due to lowering of the HOMO-LUMO transition. Titrations show the sensor-Hg2+ complex is composed of two sensor molecules per Hg2+. The limit of detection for Hg2+ is 0.39 μM. The sensor-Hg2+ complex selectively responds to cysteine (Cys), but does not show a color change due to other amino acids. The limit of detection of Cys by the sensor-Hg2+ complex is 0.10 μM.

Flow Injection Photochemical Vapor Generation Coupled with Miniaturized Solution-Cathode Glow Discharge Atomic Emission Spectrometry for Determination and Speciation Analysis of Mercury.

A novel, compact, and green method was developed for the determination and speciation analysis of mercury, based on flow injection photochemical vapor generation (PVG) coupled with miniaturized solution cathode glow discharge-atomic emission spectroscopy (SCGD-AES). The SCGD was generated between a miniature hollow titanium tube and a solution emerging from a glass capillary. Cold mercury vapor (Hg(0)) was generated by PVG and subsequently delivered to the SCGD for excitation, and finally the emission signals were recorded by a miniaturized spectrograph. The detection limits (DLs) of Hg(II) and methylmercury (MeHg) were both determined to be 0.2 μg L-1. Moreover, mercury speciation analysis could also be performed by using different wavelengths and powers from the UV lamp and irradiation times. Both Hg(II) and MeHg can be converted to Hg(0) for the determination of total mercury (T-Hg) with 8 W/254 nm UV lamp and 60 s irradiation time; while only Hg(II) can be reduced to Hg(0) and determined selectively with 4 W/365 nm UV lamp and 20 s irradiation time. Then, the concentration of MeHg can be calculated by subtracting the Hg(II) from the T-Hg. Because of its similar sensitivity and DL at 8 W/254 nm, the simpler and less toxic Hg(II) was used successfully as a primary standard for the quantification of T-Hg. The novel PVG-SCGD-AES system provides not only a 365-fold improvement in the DL for Hg(II) but also a nonchromatographic method for the speciation analysis of mercury. After validating its accuracy, this method was successfully used for mercury speciation analysis of water and biological samples.

Mercury speciation by differential photochemical vapor generation at UV-B vs. UV-C wavelength

Photochemical vapor generation (PVG) is an effective sample introduction scheme for volatile mercury (Hg). Speciation of Hg++ and MeHg+ was fulfilled for the first time by differential PVG under UV-B vs. UV-C wavelength and applied to fish oil supplements. After liquid-liquid extraction, the aqueous extract was mixed with 0.4% anthranilic acid (AA)-20% formic acid (FA) in a quartz coil, and exposed sequentially to 311nm or 254nm UV light. The resulting Hg0 vapor was detected by atomic fluorescence spectrometry (AFS). At each wavelength, the AFS intensity was a linear function of Hg++ and MeHg+ concentrations, which were solvable from a set of two equations. This method achieved ultrahigh sensitivity with 0.50 and 0.63ngmL−1 limits of detection for Hg++ and MeHg+, respectively, and 73% recovery for MeHg+ at 10ngmL−1. Validation was performed by ICP-MS on total Hg. Obviation of chemical or chromatographic separation rendered this method rapid, green, and cost-effective.

Design of metal-ion-triggered assembly of label-free split G-quadruplex/duplex DNA for turn-on detection of Hg2+ in fetal calf serum

A simple oligonucleotide-based label-free turn-on fluorescent Hg2+ sensor depending on the transformation of the random single-stranded DNA (ssDNA) into a G-quadruplex/double-stranded DNA (dsDNA) assemble has been developed. The proposed sensor combines the advantages of the huge enhancement of Thioflavin T binding to G-quadruplex/dsDNA assemble and high selectivity of the thymine (T)-T mismatched base pairs to Hg2+. In the presence of Hg2+, the two separated ssDNA prefer to form a metal-dsDNA complex, which results in the two G-rich segments connecting to each other and forming a split G-quadruplex complex. First, the reporter ThT bind to the G-quadruplex and then intercalate to dsDNA, resulting in remarkable fluorescence enhancement (∼16-fold). The sensor affords a high sensitivity for Hg2+, with a low limit of detection (LOD) of 10nM based on a calculation of 3σ/slope. The main features of the proposed sensor include: (1) Simple design and easy operation, (2) the proposed sensor displays high sensitivity and lower limit of detection for Hg2+. (3) Environmental friendly and being used for assessing Hg2+ levels in fetal calf serum (FCS) with satisfactory results.

Speciation of trace mercury impurities in fish oil supplements

Fish oil supplement is becoming increasingly popular worldwide because of beneficial long-chain omega-3 polyunsaturated fatty acids. However, mercury (Hg) impurity causes considerable concern because of its toxicity and bioaccumulation in the food chain. In this work, Hg impurities were extracted from fish oil by liquid-liquid partitioning. The sample solution was then mixed with a reductant (0.4% anthranilic acid-20% formic acid) and sequentially exposed to 311 and 254 nm UV radiation. The resulting Hg0 vapor was detected by atomic fluorescence spectrometry. Speciation was fulfilled by solving a set of two linear equations. Recovery of MeHg+ was 73%; total Hg was validated by ICP-MS. This method achieved 0.50 and 0.63 ng mL−1 limits of detection for Hg++ and MeHg+, respectively. Average Hg++ and MeHg+ contents in fish oil samples (n = 38), 0.67 ± 0.45 and 1.1 ± 1.3 ng mL−1, respectively, were 2-3 orders of magnitude lower than those in fish.

The influences of different substituents on spectral properties of rhodamine B based chemosensors for mercury ion and application in EC109 cells

Six rhodamine-based “turn-on” fluorescence chemosensors (L1–L6) with different substituents for mercury (Hg2+) were readily synthesized and investigated; they displayed high selectivity and chelation enhanced ratiometric fluorescence change and colorimetric change with Hg2+ among the metal ions examined. Based on UV and fluorescence spectral data, the effects of different substituents on spectral properties of the probes were presented and discussed. The detection limit of Hg2+ to probe L1 was as low as 50 nmol/L because of its electron-donating group. Theoretical calculation also supported the process of reaction. Confocal laser scanning microscopy experiments showed that probe could be used to detect Hg2+ in living cells.

Using silicon-coated gold nanoparticles to enhance the fluorescence of CdTe quantum dot and improve the sensing ability of mercury (II)

The effect of silicon-coated gold nanoparticles with different gold core diameter and silica shell thickness on the fluorescence emission of CdTe quantum dots (QDs) was investigated. For gold nanoparticles with a diameter of 15nm, silica coating can only results in fluorescence recover of the bare gold nanoparticle-induced quenching of QDs. However, when the size of gold nanoparticle is increased to 60nm, fluorescence enhancement of the QDs could be obtained by silica coating. Because of the isolation of the silica shell-reduced quenching effect and local electric field effect, the fluorescence of QDs gets intense firstly and then decreases. The maximum fluorescence enhancement takes place as the silica shell has a thickness of 30nm. This enhanced fluorescence from silicon-coated gold nanoparticles is demonstrated for sensing of Hg2+. Under optimal conditions, the enhanced fluorescence intensity decreases linearly with the concentration of Hg2+ ranging from 0 to 200ng/mL. The limit of detection for Hg2+ is 1.25ng/mL. Interference test and real samples detection indicate that the influence from other metal ions could be neglected, and the Hg2+ could be specifically detected.

Lower Rim-Modified Calix[4]arene–Bentonite Hybrid System as a Green, Reversible, and Selective Colorimetric Sensor for Hg2+ Recognition

A new quinaldine-functionalized calix[4]arene receptor (QHQC) was synthesized, characterized, and analyzed for its selective sensing properties toward Hg2+ ions, and the binding event with characteristic color change can be followed by the naked eye. The sensing process is reversible, and the detection limit for Hg2+ ions is 2.95 × 10–6 M. A colorimetric solid state Hg2+ sensor was fabricated by intercalating this receptor molecule into the bentonite galleries via the ion-exchange method. This organic–inorganic hybrid sensor shows properties analogous to the receptor molecule and effectively detects Hg2+ ions rapidly with visual color change. The solid state Hg2+ sensor is economically affordable, environmentally benign, portable, reversible, and reusable.

Facile Chip-Based Array Monolithic Microextraction System Online Coupled with ICPMS for Fast Analysis of Trace Heavy Metals in Biological Samples

Trace heavy metals have great impact on biological system; therefore, it is essential to develop suitable analytical methods for the determination of trace heavy metals in biological samples to elucidate their biochemical and physiological functions in organisms. Herein, we presented a chip-based array monolithic microextraction system and combined it with inductively coupled plasma mass spectrometry (ICPMS) for online analysis of trace Hg, Pb, and Bi in real-world biological samples. Six ethylenediamine modified poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) (poly(GMA-co-EDMA-NH2)) capillary monolithic columns were embedded parallelly in microchannels of a microfluidic chip for array monolithic microextraction. Various parameters affecting the chip-based array monolithic microextraction of target metals were investigated. The sample throughput of the proposed method was 16 h-1, with the limits of detection for Hg, Pb, and Bi of 23, 12, and 13 ng L-1, respectively. The developed method was validated by the determination of trace Hg, Pb, and Bi in HepG2 cells and human urine samples, and the recoveries for the spiked samples were in the range of 90.4-102%. This chip-based array monolithic microextraction system is easy to prepare, and the proposed online analytical system provides a new platform for trace elements analysis in biological samples with the merits of high sample throughput, high sensitivity, and low sample/reagents consumption.

Semiquantitative analysis of mercury in landfill leachates using double-pulse laser-induced breakdown spectroscopy.

Laser-induced breakdown spectroscopy (LIBS) is showing to be a promising, quick, accurate, and practical technique to detect and measure metal contaminants and nutrients in urban wastes and landfill leachates. Although conventional LIBS presents some limitations, such as low sensitivity, when used in the single pulse configuration if compared to other spectroscopic techniques, the use of the double-pulse (DP) configuration represents an adequate alternative. In this work DP LIBS has been applied to the qualitative and quantitative analysis of mercury (Hg) in landfill leachates. The correlation analysis performed between each intensified charge-coupled device pixel and the Hg concentration allowed us to choose the most appropriate Hg emission line to be used for its measure. The normalization process applied to LIBS spectra to correct physical matrix effects and small fluctuations increased from 0.82 to 0.98 the linear correlation of the calibration curve between LIBS and the reference data. The limit of detection for Hg estimated using DP LIBS was 76 mg Kg-1. The cross validation (leave-one-out) analysis yielded an absolute average error of about 21%. These values showed that the calibration models were close to the optimization limit and satisfactory for Hg quantification in landfill leachate.

Label-free detection of Hg2+ based on Hg2+-triggered toehold binding, Exonuclease III assisted target recycling and hybridization chain reaction

We constructed a fluorometric and sensitive analysis of mercury (II) based on toehold-mediated strand displacement reaction, exonuclease III (Exo III) assisted target recycling, hybridization chain reaction (HCR), fluorescence intercalator SYBR Green I (SG) and grapheme oxide (GO). Firstly, toehold-mediated strand displacement reaction was constructed by using thymine-Hg2+-thymine (T-Hg2+-T) recognition mechanism between the helper hairpin DNA and assisted DNA. And then, the Exo III disintegrated the double-stranded DNA (dsDNA) by catalyzing the gradual removal of mononucleotides from 3′-hydroxyl terminus of dsDNA with a blunt 3′ terminus. It resulted in the target and assisted DNA recycling and released a trigger strand DNA at the same time. Finally, the trigger strand DNA initiated the hybridization chain reaction (HCR), forming long double helices, which achieved a secondary amplification due to the continuous target recycling, trigger strand DNA release and HCR. The number of T-T mismatches, the concentration of SG, Exo III and GO, the incubation time of Exo III were all optimized. Under the optimized condition, the limit of detection for Hg2+ can be down to 7.37 pM with a linear range from 0 to 1.5nM. This sensor exhibits high selectivity against other metal ions, and it works well for real samples.

Sensitive determination of Hg together with Mn, Fe, Cu by combined photochemical vapor generation and pneumatic nebulization in the programmable temperature spray chamber and inductively coupled plasma optical emission spectrometry

Continuous photo-induced generation of mercury cold vapor has been successfully coupled with conventional pneumatic nebulization in programmable temperature spray chamber (PCVG–PN–PTSC) allowing fast, sensitive and easy multi-element analysis. The applied technique enabled simultaneous determination of non-volatile forming elements (Fe, Cu, Mn) and volatile Hg, while 15%v/v formic acid is present in the sample. PTSC elevated temperature (40°C) causes partial conversion of sample matrix into vapor form, thus improving plasma robustness. The efficiency of Hg vapor generation and its transport to the plasma is close to 100%. Moreover, spray chamber temperature stabilization improved the precision of the measurements (Hg signal RSD below 0.5%). The achieved limit of detection for Hg (90pgmL−1) at 194.23nm with no monochromator purge is better by almost two orders of magnitude than that obtained by conventional PN-ICP-OES. On the other hand, LODs for non-vapor forming elements are comparable to those obtained with pneumatic nebulization. The linear dynamic ranges for all examined elements are at least three orders of magnitude up to 1000ngmL−1. None mutual interference between examined analytes (Hg, Fe, Cu, Mn) has been observed. The method was validated by the analysis of two CRM materials of different matrix composition (waste water ERM CA713 and estuarine sediment ERM CC580) giving satisfactory results. As low as 2 ppb of Hg can he directly determined in waste water. The proposed procedure uses mild reagents and allows for fast multi-element analysis, and matches green chemistry requirements.

Ultrasensitive SERS Substrate Integrated with Uniform Subnanometer Scale “Hot Spots” Created by a Graphene Spacer for the Detection of Mercury Ions

Mercuric ion (Hg2+) is one of the most toxic and serious environment polluting heavy metal ions, which can be accumulated in human body through food chains and drinking water, and causes serious damage to human organs. Therefore, development of the efficient and sensitive method for detection of Hg2+ is very necessary. In this study, the high surface sensitivity and fingerprint information about the chemical structures based on surface‐enhanced Raman scattering (SERS) for sensing applications are taken advantage of. Au triangular nanoarrays/n‐layer graphene/Au nanoparticles sandwich structure with large‐area uniform subnanometer gaps are fabricated and used to detect Hg2+ in water via thymine–Hg2+–thymine coordination; the detection limit of Hg2+ is as low as 8.3 × 10−9m. Moreover, this SERS substrate is used to detect the Hg2+‐contaminated sandy soil and shows excellent performance. This study indicates the sandwich structure has a great potential in detection of toxic metal ions and environmental pollutants.

Quencher-Free Fluorescence Method for the Detection of Mercury(II) Based on Polymerase-Aided Photoinduced Electron Transfer Strategy.

A new quencher-free Hg2+ ion assay method was developed based on polymerase-assisted photoinduced electron transfer (PIET). In this approach, a probe is designed with a mercury ion recognition sequence (MRS) that is composed of two T-rich functional areas separated by a spacer of random bases at the 3′-end, and a sequence of stacked cytosines at the 5′-end, to which a fluorescein (FAM) is attached. Upon addition of Hg2+ ions into this sensing system, the MRS folds into a hairpin structure at the 3′-end with Hg2+-mediated base pairs. In the presence of DNA polymerase, it will catalyze the extension reaction, resulting in the formation of stacked guanines, which will instantly quench the fluorescence of FAM through PIET. Under optimal conditions, the limit of detection for Hg2+ ions was estimated to be 5 nM which is higher than the US Environmental Protection Agency (EPA) standard limit. In addition, no labeling with a quencher was requiring, and the present method is fairly simple, fast and low cost. It is expected that this cost-effective fluorescence method might hold considerable potential in the detection of Hg2+ ions in real biological and environmental samples.

Facile preparation of fluorescent Au nanoclusters-based test papers for recyclable detection of Hg2+ and Pb2+

A simple, portable and recyclable method has been developed for on-site and real-time detection of Hg2+ and Pb2+ by naked eyes by using Au nanoclusters-based test paper as the fluorescent sensor. The high specificity of Hg2+ and Pb2+ to Au nanoclusters provided excellent selectivity over 15 kinds of other ions. Interestingly, an apparent fluorescent quenching of the test paper was shown when exposed to Hg2+, while a significant fluorescent enhancement was observed in the presence of Pb2+, which could be attributed to aggregation-induced fluorescence quenching and enhancement. The limit of detection for Hg2+ and Pb2+ by naked eyes was 5μM and 50μM, respectively. More importantly, the cyclic utilization of the test paper was achieved by immersing the test papers into ethylenediamine tetraacetic acid to recover the fluorescence of the test paper, which contributed to reducing resource consumption. Otherwise, the GSH-AuNCs test paper was competent for a practical application in environmental water samples with strong anti-interference ability.

A Selective Colorimetric and Turn-on Fluorescent Chemosensor for Hg2+ in Aqueous Solution.

A simple colorimetric and turn-on fluorescence receptor FT (thiophene appended fluorescein-hydrazone derivative) was prepared and its cation-sensing properties were investigated. Receptor FT displayed a selective colorimetric change (from colorless to orange color) upon binding to Hg2+ in DMSO/H2O (1:9, v/v) solution. The association constant of FT-Hg2+ complex was calculated to be 3.03×109M-1, and the detection limit for Hg2+ was found to be 0.24ppm.

Carbon quantum dots prepared with polyethyleneimine as both reducing agent and stabilizer for synthesis of Ag/CQDs composite for Hg2+ ions detection

A stable silver nanoparticles/carbon quantum dots (Ag/CQDs) composite was prepared by using CQDs as reducing and stabilizing agent. The CQDs synthesized with polyethyleneimine (PEI) showed an extraordinary reducibility. When Hg2+ was presented in the Ag/CQDs composite solution, a color change from yellow to colorless was observed, accompanied by a shift of surface plasmon resonance (SPR) band and decrease in absorbance of the Ag/CQDs composite. On the basis of the further studies on TEM, XPS and XRD analysis, the possible mechanism is attributed to the formation of a silver-mercury amalgam. Hence, a two dimensional sensing platform for Hg2+ detection was constructed upon the Ag/CQDs composite. Based on the change of absorbance, a good linear relationship was obtained from 0.5 to 50μM for Hg2+. And the limit of detection for Hg2+ was as low as 85nM, representing high sensitivity to Hg2+. More importantly, the proposed method also exhibits a good selectivity toward Hg2+ over other metal ions. Besides, this strategy demonstrates practicability for the detection of Hg2+ in real water samples with satisfactory results.

Synthesis and characterization of M(II) (M = Cd, Hg and Pb) complexes with naphthodiaza-crown macrocyclic ligand and study of metal ion recognition by fluorescence, 1H NMR spectroscopy, and DFT calculation

To find metal ion recognition by L (L = O2N2-donor naphthodiaza-crown macrocyclic ligand), the complexes [ML]2+ (M = Cd, Hg and Pb) were synthesized and characterized by IR, 1H, 13C NMR, and mass spectrometry, as well as elemental microanalysis. Hg(II) showed perceptible enhancement of the fluorescence of L in which ultra-low limit of detection for Hg(II) by L was determined as 1 nM in ethanol and DMSO. L reserved selectivity of Hg(II) in its binary mixtures with metal cations in solution. A 1 : 1 stoichiometry was found for the interaction of Hg(II) with L while Benesi–Hildebrand method was applied to calculate its complexation binding constant (KBH) employing fluorescence spectrophotometry. The monitoring of the chemical shifts in 1H NMR spectra of these complexes demonstrated that the central macrocycle of L was tailored for the size of Hg(II). Density functional theory calculations using B3LYP/6–31G* basis set demonstrated that the macrocycle cavity of L was properly fitted for complex formation with Hg(II) cation, while both Cd(II) and Pb(II) cations did not form strong bonds with L from inadequate cation size. The present study shows detection method of Hg(II) and also possible application of naphthodiaza as an appropriate fluorophore macrocyclic ligand for detecting other metal ions.

Improving sensitivity for microchip electrophoresis interfaced with inductively coupled plasma mass spectrometry using parallel multichannel separation

We reported sensitivity enhancement using multichannel parallel separation for microchip electrophoresis hyphenated with inductively coupled plasma mass spectrometry (MCE-ICP-MS) in this study. By using 2-20 array lanes for parallel separation, the sensitivity of the MCE-ICP-MS system was proportionally improved by 2-20 folds. No significantly adverse effect of parallel separation on column efficiency and resolution was observed. Rapid separation of Hg2+ and methylmercuric (MeHg) ion within 36s under an electric field of 800Vcm−1 was achieved in the 2-cm twenty-channels with a background electrolyte of 5mmolL−1 borate buffer (pH 9.2). Detection limits of Hg2+ and MeHg by the proposed system were decreased to 6.8–7.1ngL−1. Good agreement between determined values and certified values of a certified reference fish was obtained with recoveries ranged between 94–98%. All results prove its advantages including high sensitivity, high efficiency and low operation cost, which are beneficial to routine analysis of metal speciation in environmental, biological and food fields.

A simple AIE-based chemosensor for highly sensitive and selective detection of Hg2+ and CN−

A novel red-emitting chemosensor BCTT has been developed for the detection of Hg2+ and CN− in DMF-water solution with high sensitivity and selectivity. It exhibited a ‘turn-on’ fluorescence upon binding with Hg2+ based on its AIE properties and a ‘turn-off’ response to CN− due to the nucleophilic addition of CN− to the dicyanovinyl group with visible color changing from yellow to colorless. Remarkably, the detection limits for Hg2+ and CN− were 6.6 nM and 0.11 μM, respectively, which are much lower than the regulated limits in drinking water, promoting BCTT as a promising candidate in practical applications.