Detection Limit For Hg2 Research Articles

A smartphone-assisted down/up-conversion dual-mode ratiometric fluorescence sensor for visual detection of mercury ions and l-penicillamine

Establishment of a rapid, sensitive, visual, accurate and low-cost fluorescence detection system to detect multiple targets was of great significance in food safety evaluation, ecological environment monitoring and human health monitoring. In this work, a smartphone-assisted down/up-conversion dual-mode ratiometric fluorescence sensor was proposed based on metal-organic framework (NH2-MIL-101(Fe)) and CdTe quantum dots (CdTe QDs) for visual detection of mercury ions (Hg2+) and L-penicillamine (L-PA), in which NH2-MIL-101(Fe) was used as the reference signal and CdTe QDs was used as the response signal. The down-conversion fluorescence system at excitation wavelength of 300 nm (ex: 330 nm) was used to detect Hg2+ and L-PA, in which the detection limit of Hg2+ was 0.053 nM with the fluorescence color changed from green to blue, and the detection limit of L-PA was 1.10 nM with the fluorescence color changed from blue to green. Meanwhile, the up-conversion fluorescence system at excitation wavelength of 700 nm (ex: 700 nm) was used to detect Hg2+ and L-PA. The detection limits of Hg2+ and L-PA were 0.11 nM and 2.93 nM, respectively. The detection of Hg2+ and L-PA were also carried out based on the color extraction RGB values identified by the smartphone with a detection limit of 0.091 nM for Hg2+ and 8.97 nM for L-PA. In addition, the concentrations of Hg2+ and L-PA were evaluated by three-dimensional dynamic analysis in complex environments. The smartphone-assisted down/up-conversion dual-mode ratiometric fluorescence sensor system provides a new strategy for detection Hg2+ and L-PA in food safety evaluation, environmental monitoring and human health monitoring.

Colorimetric probe for sequential chemosensing of mercury(II) and cyanide ions in aqueous media, based on a benzoxadiazole-pyrazolin-5-one glycoconjugate with INHIBIT logic gate response

A new and efficient water-soluble probe L for the sequential detection of Hg2+ and CN− ions has been developed by the condensation of benzoxadiazole and glycoconjugated pyrazoline-5-one. The resulting probe has a water solubility of 45 g/L at room temperature and interacts selectively with Hg2+ ions in water over other cations by changing its color from yellow to red and forming the [L/Hg2+: 2:1] complex. On the other hand, the formed complex [L/Hg2+: 2:1] reacts selectively with CN− anions in an aqueous solution. This reaction is accompanied by a blue shift in wavelength from 545 nm to 472 nm with a color change from red to yellow visible to the naked eye. These reversible and repeatable colorimetric responses of probe L towards Hg2+ and CN− ions can be represented as a molecular logic gate 'IMPLICATION', where Hg2+ and CN− ions are considered as inputs and the absorbance at 472 nm as output. The detection limit for Hg2+ and CN− ions was found to be 2.31 ppb and 4.34 ppb, respectively. From a practical point of view, probe L was used to prepare a test strip based on filter paper treated with L. The resulting test strip selectively changes color after the sequential addition of Hg2+ and CN− ions in water at pH7. These high performances in terms of selectivity and sensitivity allow the probe L to be used for the sequential detection of Hg2+ and CN− ions in aqueous media.

Red-Emissive Sulfur-Doped Carbon Dots for Selective and Sensitive Detection of Mercury (II) Ion and Glutathione.

Carbon dots (CDs) show great potential in bioimaging and biosensing because of their good biocompatibility and excellent optical properties. However, CDs with intense red emissions for sensitive and selective detection are rarely reported. Herein, we prepared the red-emissive carbon dots (RCDs) through a facile hydrothermal method using tetra (4-carboxyphenyl) porphyrin (TCPP) and thiourea as starting materials. The obtained RCDs were characterized by TEM, XRD, and XPS. RCDs exhibited high water solubility and strong red emission (λem = 650 nm), with the fluorescence quantum yield as high as 26.7%, which was greatly higher than that of TCPP. Moreover, the as-prepared RCDs could be acted as a highly selective and sensitive probe for the detection of Hg2+ and glutathione (GSH) through the fluorometric titration method. The detection limits of Hg2+ and GSH were calculated to be 1.73 and 1.6 nM, respectively. The cellular experiments demonstrated the good biocompatibility of RCDs and their feasibility in bioimaging. Thus, this work provided a simple strategy to design and synthesize the highly red-emissive carbon dots, which showed promising application in biological and environmental assays.

A pyridyl functionalized rhodamine chemodosimeter for selective fluorescent detection of mercury ions and cell imaging

Rhodamines gain sustained attention owing to their great potential for probe design applications. Herein, the facile preparation of a new pyridyl functionalized rhodamine dye PR is reported, which has stable fluorescence signal in water with maximum emission peak at 594 nm and Stokes shift of 81 nm. Based on dye PR, a new fluorescent probe PRHg has been developed by modifying the spirolactone of PR with hydrazine hydrate so as to produce spirolactam recognizing group for sensing of Hg2+. PRHg exhibits high selectivity and sensitivity towards Hg2+ in water/ethanol (v/v = 4/1, pH = 7.0) by a specific Hg2+-binding promoted spirolactam ring opening and hydrolyzing process. And, the detection limit for Hg2+ is evaluated to be 8.5 nM. Besides, the probe can respond to Hg2+ within 40 min and over a wide pH range from 4.0 to 10.0. Moreover, PRHg (40 µM) performs low cytotoxicity to HeLa cells (over 91.0 % cell survival rate), which allows the probe to be employed for tracing intracellular Hg2+ by fluorescence imaging.

Self-Powered Photoelectrochemical Assay for Hg2+ Detection Based on g-C3N4-CdS-CuO Composites and Redox Cycle Signal Amplification Strategy

A highly sensitive self-powered photoelectrochemical (spPEC) sensing platform was constructed for Hg2+ determination based on the g-C3N4-CdS-CuO co-sensitized photoelectrode and a visible light-induced redox cycle for signal amplification. Through successively coating the single-layer g-C3N4, CdS, and CuO onto the surface of an electrode, the modified electrode exhibited significantly enhanced PEC activity. The microstructure of the material was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). However, the boost in photocurrent could be noticeably suppressed due to the consumption of hole-scavenging agents (reduced glutathione) by the added Hg2+. Under optimal conditions, we discovered that the photocurrent was linearly related to the Hg2+ concentration in the range of 5 pM–100 nM. The detection limit for Hg2+ was 0.84 pM. Moreover, the spPEC sensor demonstrated good performance for the detection of mercury ions in human urine and artificial saliva.

Colorimetric determination of Hg(II) ions based on core/shell Au@MnO2 nanoparticles with oxidase-like activity

In this work, we present core/shell Au@MnO2 nanoparticles-based visual sensing strategy for mercury ion (Hg2+) detection. The MnO2 shell of Au@MnO2 nanoparticles catalyzes the oxidation reaction between tetramethylbenzidine (TMB) and oxygen in the air, generating blue derivative (oxTMB) with an absorption peak at 650 nm. Glutathione (GSH) inhibits the formation of oxTMB, reversing the reaction and turning it back into colorless TMB molecules. While in the existence of Hg2+, GSH binds to Hg2+ due to the strong affinity between the Hg2+ and the -SH, and in this situation, Au@MnO2 catalyzes the oxidation of TMB to make the solution become blue. Using the colorimetric sensor, the detection limit of Hg2+ reached as low as 0.473 nM by UV–vis spectroscopy and 1 nM under the naked eye observation, which is lower than toxicity level of Hg2+ (10 nM) formulated by the U.S. Environmental Protection Agency.

Asymmetric Nanochannel Network-Based Bipolar Ionic Diode for Enhanced Heavy Metal Ion Detection

A higher rectification degree in ionic diodes is required to achieve better performance in applications. Nonetheless, the active geometrical change that is critical for inducing electrical potential asymmetry is difficult to realize in typical ionic diodes because of the intrinsic limitation of the fabrication method. Here, we propose a nanochannel-network-based bipolar diode with a high rectification degree of ∼1600─the highest value realized until now, to the best of our knowledge. Such a high rectification is obtained based on the synergetic effect of the bipolar surface charge and the optimization of the microchannel through experimental studies and multiphysics numerical simulations. It induces ion concentrations at the heterogeneous junction based on the accumulation effect under the forward potential bias. In particular, this proposed molecular concentration occurs in the ohmic region without vortex and instability that is inevitable at the conventional nano-electrokinetic concentration. Combining this accumulation with the horizontally aligned configuration of the nanochannel network membrane (NCNM), a highly sensitive and quantitative mercury ion (Hg2+) sensor based on a fluorescent signal is fabricated that allows direct measurement using a general fluorescent microscope. The detection limit of Hg2+ is 10 pM, which is ∼10 times lower than the best detection limit realized so far (∼100 pM) in fluorescent dye-based detection. This demonstrates the potential of asymmetric NCNM for high-performance ion transport in applications such as energy conversion, based on its design and material flexibility.

Cholesteric Liquid Crystal Photonic Hydrogel Films Immobilized with Urease Used for the Detection of Hg2+

Mercury ion is one of the most widespread heavy metal contaminants which can accumulate in the body through multiple channels, posing a detrimental impact on human health. We demonstrate a simple and low-cost method for the detection of Hg2+ assisted by a cholesteric liquid crystal photonic hydrogel (polyacrylic acid (PAA)) film with immobilized urease (CLC-PAAurease film). In the absence of Hg2+, a significant change in color and an obvious red shift in the reflected light wavelength of the prepared film were observed, since urease can hydrolyze urea to produce NH3, resulting in an increasing pH value of the microenvironment of CLC-PAAurease film. Hg2+ can inhibit the activity of urease so that the color change of the film is not obvious, corresponding to a relatively small variation of the reflected light wavelength. Therefore, Hg2+ can be quantitatively detected by measuring the displacement of the reflected light wavelength of the film. The detection limit of Hg2+ is about 10 nM. This approach has a good application prospect in the monitoring of heavy metal ions in environmental water resources.

Greatness in Simplicity: Efficient Red Room-Temperature Phosphorescence from Simple Halogenated Maleimides with a 2D Layered Structure.

Herein, two maleimide derivatives substituted by Br (DBM) and I (DIM) with a two-dimensional (2D) layered structure are found to have highly efficient red room-temperature phosphorescence (RTP) at 660 nm in solid state, which is independent of their morphology (crystal, powder, and film). The red RTP of DBM and DIM is closely related to the synergism of nπ-ct-π* transitions and the 2D halogen-bonded network. Interestingly, the red RTP can be excited by visible light of 500 nm, which should be ascribed to the forbidden absorption from the ground state to the triplet state activated in the layered halogen-bonded framework. Due to the rich intermolecular interactions in the rigid layered structure, the red RTP of DBM is very stable under water or external force stimulation. Notably, Hg(II) and Cd(II) ions in a pure aqueous solution result in an opposite change in the RTP intensity of the DBM film. The detection limit of Hg(II) ion is as low as 2.5 × 10-5 nM, lesser than all reported values. The above results not only provide a new idea for the design of simple and efficient red RTP materials but also make it possible to develop solid-state phosphorescent probes for toxic heavy metal ions in environmental sewage with high sensitivity and selectivity.

A probe with hydrazinecarbothioamide and 1,8-naphthalimide groups for “turn-on” fluorescence detection of Hg2+ and Ag+ ions and live-cell imaging studies

The probe (L) having hydrazinecarbothioamide and 1,8-naphthalimide moieties was synthesized and evaluated for its metal ion sensing ability. It exhibits a selective and sensitive colorimetric as well as fluorescent recognition of Hg2+ and Ag+ ions in CH3OH - HEPES buffer solution (5 mM, 7:3, v/v, pH = 7.4) in presence of other metal ions. Probe L is weakly fluorescent upon excitation with 410 nm light, but after gradual addition of HgCl2 and AgNO3 enhancement in fluorescent intensity was observed. Detection limits of Hg2+ and Ag+ using L have been found to be 20 nM (Hg2+) and 40 nM (Ag+) over the pH range of 6 – 10 that is suitable for practical application under physiological pH conditions. The reversibility of interaction of L with Hg2+ ion was monitored using Na2EDTA by emission titration. The “OFF-ON’’ fluorescence switching can be observed with naked eye, in which fluorescent “OFF’’ is due to operation of PET process in free L. Whereas upon complexation with these two metal ions, PET is restricted and CHEF process becomes operational. Mass spectral analysis and Job’s plot yielded a binding ratio of 1:1 for both metal ions. NMR titration studies are consistent with binding of Hg2+ or Ag+ to NH group (attached with naphthalimide moiety) and sulfur atom of hydrazinecarbothioamide group. From cytotoxicity assay, 5 μM solution of L was considered in cellular imaging study and the potentiality of the probe L was established by using human breast cancer cell line (MDA-MB-231) and primary human dermal fibroblasts (HDF), through fluorescence cell imaging experiments for tracking both Hg2+ and Ag+ in living cells.

Smartphone‐Assisted Quinoline‐Based Chromogenic Probe for the Selective Detection of Hg2+ in Protic Media

AbstractHigh selectivity and sensitivity detection of Hg2+ in aqueous environment by the naked‐eye has always been a challenge. In this paper, a simple ligand based on 2‐(hydroxymethyl)quinolin‐8‐ol (L) was synthesized and its structure was confirmed by NMR, IR and mass analysis. The probe L showed distinct colorimetric upon interaction with Hg2+ in CH3OH‐H2O (8 : 2, v/v) media. The ligand L exhibit unique absorbance band at 243 nm due to ligand‐to‐ligand charge transfer (LLCT). Upon interaction with Hg2+, the L formed new UV‐Vis bands at 269 and 316 nm due to ligand‐to‐metal charge transitions (LMCT). The UV‐Vis spectral studies indicate the formation of a 1 : 1 host‐guest complex between the L and Hg2+ with an association constant of 8.6×104 M−1. The ligand L can work in the pH range of 3–8 without interfering with other competing ions. The detection limit of Hg2+ can reach a concentration of as low as 0.13 μM (2.6 ppb) with high selectivity, even in a solution containing diverse metal ions. Besides, the selective colour change of L with Hg2+ was integrated with smartphone to monitor the change in RGB tool and test paper kit. The binding mechanism of L with Hg2+ was studied by using 1H NMR, SEM and TDDFT analysis. Overall, ligand L demonstrates a promising and potential for the detection of toxic contaminate in aqueous environment.

Label-free biosensing of mercury(II) in milk using an aptamer-gated graphene field-effect transistor

• A specific Hg(II) biosensor based on aptamer-modified SGGT is developed. • The sensitivity and selectivity were improved by aptamer and BSA modification. • The biosensor had a high recovery rate for Hg(II) evaluation in real milk samples. Due to the environmental pollution by the growing urban, agricultural and industrial disposals, dairy products are susceptible to heavy metal pollution in the production process. As one of the most toxic heavy metals, mercury cause serious damage to the environment and even public health. Effective monitoring of Hg(II) in large number of diary samples requires the development of rapid assaying methods. In this research work, we report the preparation of a label-free biosensor for Hg(II) using an aptamer-gated graphene field-effect transistor (Apt-SGGT) with the gate electrode modified by a structure-switching aptamer against Hg(II) and blocked with bovine serum albumin. The aptamer immobilized on the gate electrode acts as both a receptor and a reporter for Hg(II) by specifically recognizing Hg(II) through stable T-Hg 2+ -T coordination complex, triggering the folding of the single-stranded aptamer into a duplex structure. The conformational change results in the redistribution of the surface charge on the gate electrode, and produces a large channel current response by the inherent field-effect amplification. This sensing mechanism can effectively enhance the selectivity of the SGGT-based biosensor to mercury ions by significantly reducing the unspecific responses of other interfering cations. The detection limit of Hg(II) by Apt-SGGT sensor was as low as 5 nM, and the linear detection range was from 5 to 200 nM. The sensor can realize the detection of mercury ion residues in milk with a high recovery rate, and has a good application prospect in the detection and analysis of heavy metal residues in complex systems.

Membrane analytical test system for highly sensitive determination of Hg2+ ions in natural waters

Abstract. A membrane test system has been developed for sensitive and specific detection of Hg2+ ions in natural waters. The test system uses gold nanoparticles synthesized by citrate reduction and a nitrocellulose membrane with a band of the conjugate of mercaptosuccinic acid (MSA) and bovine serum albumin (BSA). In the presence of Hg2+ ions, they are reduced by citrate and adsorbed on the surface of gold nanoparticles. The resulting product moves along the membrane of the test strip under the action of capillary forces and specifically binds to the MSA-BSA conjugate with the formation of a visually detectable colored band. The analysis takes 20 minutes without requiring additional manipulations or instrumentation. Under optimized conditions, the detection limit for Hg2+ ions was 0.13 ng/mL. The efficiency of the proposed approach was confirmed by its approbation for the control of natural waters; Hg2+ recovery ranged from 70 to 120%.

Integration detection of mercury(ii) and GSH with a fluorescent "on-off-on" switch sensor based on nitrogen, sulfur co-doped carbon dots.

Using aurine and citric acid as precursors, we have synthesized stable blue-fluorescent nitrogen and sulfur co-doped carbon dots (NS-CDs), with a high quantum yield of up to 68.94% via a thermal lysis method. The fluorescent NS-CDs were employed as a sensitive sensor for the integration detection of Hg2+ and glutathione (GSH). This was attributed to Hg2+ effectively quenching the fluorescence of the NS-CDs by static quenching, and then GSH was able to recover the fluorescence owing to the stronger binding between Hg2+ and the sulfhydryl of GSH. Based on the “on-off-on” tactic, the detection limits of Hg2+ ions and GSH were 50 nM and 67 nM respectively. The fluorescence sensor was successfully applied to detect Hg2+ ions and GSH in actual samples (tap water and fetal bovine serum). Furthermore, we have proved that the sensor had good reversibility. Overall, our NS-CDs can serve as effective sensors for environmental and biological analysis in the future.

Ultrasensitive ratiometric fluorescent probes for Hg(II) and trypsin activity based on carbon dots and metalloporphyrin via a target recycling amplification strategy.

A convenient and ultrasensitive ratiometric fluorescent probe was innovatively developed for Hg(II) detection and trypsin activity evaluation based on carbon dots (CDs) and tetraphenylporphyrin tetrasulfonic acid (TPPS) using bovine serum albumin (BSA) as the substrate of trypsin. The ratiometric fluorescence signal arises from CDs (λem = 506 nm) and TPPS (λem = 645 nm) via an inner filter effect. Hg2+ can trigger the formation of TPPS-Mn2+ metalloporphyrin for target Hg2+ recycling amplification, while both TPPS-Hg2+ and TPPS-Mn2+ metalloporphyrins do not affect the fluorescence of CDs. Small amino acids and peptide fragments, which are the products of BSA under the digestion of trypsin, bind stronger with Hg2+ than with TPPS. The decomposition of both TPPS-Hg2+ and TPPS-Mn2+ metalloporphyrins leads to a variation in the ratiometric fluorescence signal. Under optimized conditions, this probe provided an inspiring detection limit of 0.086 nM for Hg2+ and 0.013 ng mL-1 for trypsin, which possessed acceptable sensitivity for Hg2+ detection and trypsin activity evaluation in authentic samples. This unprecedented CD-based ratiometric fluorescence proposal for ultrasensitive quantification of Hg2+ concentration and selective assessment of trypsin activity gives a new insight for designing metal ion assays or enzymatic activity bioassays under different enzymatic substrates in the near future.

The ultrathin palladium nanosheets for sensitive and visual Hg2+ detection in the food chain

The detection of mercury, one of the ten most dangerous chemicals, is significant to provide helpful information for assessing mercury toxicity and health risks. However, it is a challenge to explore simple, sensitive, accurate, and cheap Hg2+ detection methods. Noble metal nanomaterials are used for Hg2+ detection by the colorimetric method widely. Still, the pure noble metal materials’ detection limit of Hg2+ is high, and sensitivity enhancement usually requires further complex modification. Here, we use a facile one-step route to synthesize ultra-thin two-dimensional palladium nanosheets (PdNS), which have high selectivity and sensitivity for Hg2+ detection by colorimetric method with a low detection limit (0.55 ppb). The detection of Hg2+ by PdNS involves multiple mechanisms, including the formation of amalgam and PdO to improve the peroxidase-mimic activity of PdNS and PdNS motor function to increase its collision probability with the detection reactant. The PdNS can be used to detect Hg2+ in various actual samples. The detection results are highly consistent with the data obtained by the atomic fluorescence spectrometer (AFS). Then, we developed a Hg2+ detection kit, which can realize simple, sensitive, and accurate Hg2+ detection by naked eye or cellphone at a meager cost (0.3 dollars each sample).

Orthogonal paper biosensor for mercury(II) combining bioluminescence and colorimetric smartphone detection

Mercury contamination in the environment has reached alarming levels. Due to its persistence and bioaccumulation, mercury is one of the most widespread toxic heavy metals found in air, water and food. Thus, it is mandatory to monitor mercury and its compounds, and the availability of sensitive and rapid biosensors is highly valuable.We developed a low-cost biosensor for orthogonal detection of mercury(II) integrating three different biorecognition principles on a three-leaf paper: i) a mercury-specific bioluminescent Escherichia coli bioreporter strain expressing NanoLuc luciferase as reporter protein, ii) a purified β-galactosidase (β-gal) enzyme which is irreversibly inhibited by mercury and other metal ions, and iii) an Aliivibrio fischeri bioluminescent strain which is used to quantitatively assess sample toxicity and correct the analytical signal accordingly.Both sensory elements and substrates, Furimazine for the bioluminescent reporter strain and chlorophenol red-β-D-galactopyranoside for colorimetric detection of β-gal, were integrated in the paper sensor to provide a stable all-in-one disposable cartridge which can be easily snapped into a smartphone with a clover-shaped 3D printed housing. This is the first integration of bioluminescence and colorimetric detection on a smartphone-paper sensor, providing a readout within 15 and 60 min for the colorimetric and bioluminescent detection respectively. The biosensor was applied to water samples spiked with different concentrations of mercury, interferents and toxic chemicals providing a limit of detection for Hg(II) at the ppb levels.

An anthraquinone-based “turn-on” fluorescence probe for Hg2+ detection and its application in cell imaging

A new highly sensitive fluorescence “turn-on” probe (HgP1) based on anthraquinone derivatives for the detection of Hg2+ has been designed and developed. Based on desulfurization effect, probe HgP1 shows high selectivity towards Hg2+ in CH3OH/HEPES (10 mM, pH = 7.4, 1/1, v/v) solution over other analytes. The detection limit for Hg2+ is 8.2 nM. In addition, the probe shows good biocompatibility and has been successfully used in living cell imaging.

A dual-channel colorimetric and ratiometric fluorescence chemosensor for detection of Hg2+ ion and its bioimaging applications

A new colorimetric and ratiometric fluorescence chemosensor 4-((3-(octadecylthio)-1,4-dioxo-1,4-dihydronaphthalen-2-yl)amino)benzenesulfonamide (4DBS) was synthesized and investigated for the selective detection of Hg2+ in DMSO-H2O (9:1, v/v) solution. The chemosensor was efficiently synthesized in two steps via Michael-like addition and nucleophilic substitution reactions. The ratiometric fluorescence turn-on response was obtained towards Hg2+, and its fluorescence emission peak was red-shifted by 140 nm with an associated color change from light maroon to pale yellow due to the intramolecular charge transfer effect. The formed coordination metal complex was further evaluated by FT-IR, 1H NMR, and quantum chemical analyses to confirm the binding mechanism. The detection process was sensitive/reversible, and the calculated limit of detection for Hg2+ was 0.451 µM. Furthermore, 4DBS was effectively utilized as a bioimaging agent for detection of Hg2+ in live cells and zebrafish larvae. Additionally, 4DBS showed distinguishing detection of Hg2+ in cancer cells in comparison with normal cells. Thus, 4DBS could be employed as an efficient bioimaging probe for discriminative identification of human cancer cells.

Highly selective fluorescence probe with peptide backbone for imaging mercury ions in living cells based on aggregation-induced emission effect

Mercury is an anthropogenic toxic heavy metal found in the environment. It is highly desirable to develop a fluorescence probe that can selectively and sensitively detect mercury ions using a turn-on response. This paper reports the successful development of a peptide fluorescence probe, TP-2 (TPE-Trp-Pro-Gln-His-Glu-NH2), which uses aggregation-induced emission effects and high selectivity to detect Hg2+. After fluorescence was activated, Hg2+ was efficiently detected using the change in fluorescence intensity. The detection limit for Hg2+ in the buffer solution was 41 nM (R2 = 0.9952). Owing to its high sensitivity, high cell permeability, and low biotoxicity, the probe could perform live cell imaging under biological conditions. This study demonstrated that TP-2 can detect Hg2+ in complex biological environments.