A Halloysite Nanotubes-based Probe for Efficient Fluorescence Detection and Adsorption Removal of Pb2+ in Water.

The detection and removal of Pb2+ is of utmost importance for environmental protection and human health due to its toxicity, persistent pollution, and bioaccumulation effects. To address the limitations associated with organic small molecule-based fluorescence probes such as poor water solubility and single functionality in detecting Pb2+, a fluorescence probe based on halloysite nanotubes was developed. This probe not only enables specific, rapid, and reliable detection of Pb2+ but also facilitates efficient removal of it from water. The development of this bifunctional fluorescent probe provides a valuable insight for designing more advanced probes targeting heavy metal ions.

Nanohybrid of antimonene@Ti3C2Tx-based electrochemical aptasensor for lead detection.

Lead ions (Pb2+), as one of many common heavy metallic environmental pollutants, can cause serious side-effects and result in chronic poisoning to people's health, so it is highly significant to monitor Pb2+ efficiently and sensitively. Here, we proposed an antimonene@Ti3C2Tx nanohybrid-based electrochemical aptamer sensor (aptasensor) for high sensitive Pb2+ determination. The sensing platform of nanohybrid was synthesized by ultrasonication, possessing the advantages of both antimonene and Ti3C2Tx, which not only can vastly enlarge the sensing signal of the proposed aptasensor, but also greatly simplified its manufacturing flow, because antimonene can strongly interact with aptamer through noncovalently bound. The surface morphology and microarchitecture of the nanohybrid were perused by several methods such as scanning electron microscope (SEM), energy-dispersive X-ray mapping spectroscopy (EDS), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and atomic force microscope (AFM). Under optimal empirical conditions, the proposed aptasensor exhibited a wide linear correlation of the current signals with the logarithm of CPb2+ (Log CPb2+) over the span from 1 × 10-12 to 1 × 10-7 M and provided a trace discernment limit of 3.3 × 10-13 M. Moreover, the constructed aptasensor displayed superior repeatability, great consistency, eminent selectivity, and beneficial reproducibility, implying its extreme potential application for water quality control and the environmental monitoring of Pb2+.

Detection Techniques for Lead Ions in Water: A Review.

Lead pollution has increasingly become the focus of environmental pollution, which is a great harm to the ecological environment and human health. Strict control of the emission of lead pollutants and accurate monitoring of lead are very important. The lead ion detection technologies are introduced here, including spectrophotometry, electrochemical method, atomic absorption spectrometry, and other detection methods, and the methods' applicability, the advantages, and disadvantages are discussed. The detection limits of voltammetry and atomic absorption spectrometry are as low as 0.1 µg/L, and those of atomic absorption spectrometry are as low as 2 µg/L. The detection limit of photometry is higher (0.01 mg/L), but this method can be achieved in most laboratories. The application of different extraction pretreatment technologies in lead ion detection is introduced. The new technologies develop at home and abroad, such as precious metal nanogold technology, paper microfluidic technology, fluorescence molecular probe technology, spectroscopy, and other emerging technologies in recent years, are reviewed, and the principle and application of various technologies are expounded.

Effective Removal of Metal ion and Organic Compounds by Non-Functionalized rGO.

Effective removal of heavy metals from water is critical for environmental safety and public health. This work presents a reduced graphene oxide (rGO) obtained simply by using gallic acid and sodium ascorbate, without any high thermal process or complex functionalization, for effective removal of heavy metals. FTIR and Raman analysis show the effective conversion of graphene oxide (GO) into rGO and a large presence of defects in rGO. Nitrogen adsorption isotherms show a specific surface area of 83.5 m2/g. We also measure the zeta-potential of the material showing a value of -52 mV, which is lower compared to the -32 mV of GO. We use our rGO to test adsorption of several ion metals (Ag (I), Cu (II), Fe (II), Mn (II), and Pb(II)), and two organic contaminants, methylene blue and hydroquinone. In general, our rGO shows strong adsorption capacity of metals and methylene blue, with adsorption capacity of qmax = 243.9 mg/g for Pb(II), which is higher than several previous reports on non-functionalized rGO. Our adsorption capacity is still lower compared to functionalized graphene oxide compounds, such as chitosan, but at the expense of more complex synthesis. To prove the effectiveness of our rGO, we show cleaning of waste water from a paper photography processing operation that contains large residual amounts of hydroquinone, sulfites, and AgBr. We achieve 100% contaminants removal for 20% contaminant concentration and 63% removal for 60% contaminant concentration. Our work shows that our simple synthesis of rGO can be a simple and low-cost route to clean residual waters, especially in disadvantaged communities with low economical resources and limited manufacturing infrastructure.

A low-noise ratiometric fluorescence biosensor for detection of Pb2+ based on DNAzyme and exonuclease III-assisted cascade signal amplification.

As a common heavy metal ion with strong toxicity and wide distribution, lead ions (Pb2+) had great harm to the human body. In this work, a low-noise ratiometric fluorescence biosensor was developed based on Pb2+-dependent DNAzyme and exonuclease III (Exo III)-assisted cascade signal amplification. Firstly, the substrate chain of DNAzyme (S-DNA) was modified on the surface of magnetic beads (MBs) through the combination of biotin and streptavidin, and then the enzyme chain of DNAzyme (E-DNA) was connected to the MBs by forming a double-stranded DNA (dsDNA) with S-DNA. A hairpin DNA (HP) labelled with Cy3 and Cy5 respectively at both ends was used as a fluorescence probe. The emission peaks of Cy3 and Cy5 can appear at 562 nm and 665 nm respectively, and their fluorescence intensity ratio (F562/F665) was chosen as the acquisition signal. The ratiometric sensor can reduce the interference of detection environment and avoid false positive reactivity. Due to the cleavage of DNAzyme and the release of single-stranded DNA (ssDNA) in the presence of Pb2+, the hairpin structure of HP was opened and the FRET between two fluorophores disappeared, resulting in the strengthened signal of Cy3 and the weakened signal of Cy5. Furthermore, the ratio [Formula: see text] signal increased gradually with the increase of Pb2+ concentration. When the concentration of Pb2+ was in the range of 0.1-1000 nM, [Formula: see text] had a good linear relationship with [Formula: see text], the correlation coefficient (R2) was 0.997, and the limit of detection (LOD) was 77 pM. The presented ratiometric fluorescence biosensor had lower LOD and wider detection range via comparing with other methods. At the same time, the sensor also obtained the satisfactory results for detection of Pb2+ in tap water, tea, and rice flour samples. The provided ratiometric biosensor has great potential in the monitoring of various targets. A low-noise ratiometric fluorescence biosensor based on the FRET between two fluorophores was developed, and the DNAzyme and exonuclease III-assisted cascade signal amplification was used to improve the sensitivity of the method. The biosensor had a detection limit as low as 77 pM.

Signal-on fluorescent sensing strategy for Pb2+ detection based on 8-17 DNAzyme-mediated molecular beacon-type catalytic hairpin assembly circuit.

Based on a Pb2+-specific 8-17 DNAzyme-induced catalytic hairpin assembly (CHA), a simple signal-on fluorescence strategy for lead ion detection was established. 8-17 DNAzyme was used as the recognition element of Pb2+, which catalyzed the cleavage of the RNA base embedded in the DNA substrate strand, while releasing part of the substrate strand (S') as CHA initiator. And two hairpin probes (H1 and H2-FQ) were designed according to the sequence of S' for CHA, in which H2-FQ was labeled with the fluorophore FAM and quencher BHQ-1 as fluorescent "molecular switch" based on fluorescence resonance energy transfer (FRET). In the presence of Pb2+, the CHA reaction was triggered to form a large number of H1-H2 complexes, enabling enzyme-free isothermal amplification and a signal-on fluorescence strategy. In the concentration range of 0.5-1000 nM, the fluorescence signal increases with the increase of Pb2+ concentration. The quantitative detection limit of Pb2+ by this method is 0.5 nM, which has better detection performance compared with the FQ-labeled 8-17 DNAzyme method. The established biosensor exhibits good specificity and can be effectively used for the detection of Pb2+ in real samples of river water and grass carp. Through ingenious nucleic acid sequence design, DNAzyme and CHA reactions are integrated to realize the enzyme-free isothermal amplifications and sensitive detection of Pb2+, which holds potential versatility in food supervision and environmental monitoring.

Fully inkjet-printed paper-based Pb2+ optodes for water analysis without interference from the chloramine disinfectant.

We developed a paper-based colorimetric sensor for facile and cost-effective detection of Pb2+ in drinking and environmental water samples. The Pb2+ ion-selective optodes are fabricated by inkjet printing of ionophore, chromoionophore, and ion exchanger on cellulose paper. Pb2+ in water samples induces deprotonation of the pH chromoionophore and changes the optode color, which is acquired and analyzed by a smartphone. The paper-based optode without any plasticizer or polymer has a dynamic range and selectivity comparable to those of traditional optodes using PVC polymer and/or plasticizer. Furthermore, the response time of the plasticizer/polymer-free paper-based optode is much shorter than those of plasticized PVC-based optodes on paper and glass (5 min vs. 15 and 50 min). Moreover, the plasticizer/polymer-free optode preserves the water-wicking capability of porous cellulose paper, allowing for the design of pump-free microfluidic devices. Chloramine, a widely used disinfectant in drinking water, was found to be a strong and generic interference species for heavy metal ion detection via ion-selective optodes. A fully inkjet-printed lateral-flow paper-based device consisting of a sodium thiosulfate-based chloramine elimination zone and a plasticizer/polymer-free sensing zone was designed for Pb2+ detection in tap water disinfected by chloramine. The dynamic range of the Pb2+ sensor may be shifted from the current 10-6 to 10-5 M to lower concentrations by using stronger ionophores, but this work lays a foundation for the design of paper-based heavy metal ion sensors without detrimental interference from disinfectants.

Optimization of the Hydrothermal Activation Treatment with Sodium Hydroxide Solution for the Conversion of Coal Fly Ash to Zeolite and Its Adsorption Capability of Lead (II) Ions from the Liquid Phase.

Coal fly ash (FA) was treated by hydrothermal activation with sodium hydroxide solution at different concentrations to optimize the conversion method. Zeolite of the sodium type is prepared from coal FA by 1, 1.5, and 3 mol/L sodium hydroxide solutions (ZE1, ZE1.5, and ZE3). These adsorbents' morphology, crystal structure, scanning electron microscopy, Fourier transform (FT)-IR spectra, cation exchange capacity (CEC), specific surface area and pore volumes, and pHpzc were determined. An adsorption experiment was performed to evaluate the effects of contact time, pH, temperature, and coexistence. From the results, the values of CEC and specific surface area of prepared samples was in the order ZE3 < ZE1.5 < ZE1. The similar trends were observed in lead ions adsorption. In addition, our obtained data elucidate that the ion exchange with sodium ions in the interlayer ZE1 is one of the adsorption mechanisms of Pb2+ from water layer. Finally, lead ions adsorbed on ZE1 could be desorbed using a hydrochloric acid solution, showing that ZE1 could be reused as a water purification agent.

Dual-target electrochemical DNA sensor for detection of Pb2+ and Hg2+ simultaneously by exonuclease I-assisted recycling signal amplification.

With the development of exonuclease, the exonuclease has been used to construct a variety of aptasensor and to realize the signal amplification. Among them, based on silver nanoparticles (Ag NPs) and exonuclease I (Exo I)-assisted cycle signal amplification strategy, we designed a novel high-sensitivity dual-target electrochemical biosensor to detect Pb2+ or Hg2+ in water. In the presence of Hg2+, the Hg2+ was fixed to the aptamer chain by thymine-Hg2+-thymine (T-Hg2+-T), resulting in the decrease of signal. When Pb2+ was present, DNA single strand S2 dissociated and was bound to Pb2+, which automatically triggered Exo I to selectively cut the single chain from the recognition site to achieve the cyclic amplification of the electrochemical signal. The interaction between aptamer and Exo I was investigated by gel electrophoresis. Under the optimum conditions in the scan range -0.20 to 0.60 V, the biosensor had high sensitivity with a linear range of 100 pg/L to 10.0 mg/L, Pb2+ or Hg2+, and the detection limits were 17.0 pg/L (R2 = 0.993) and 12.0 pg/L (R2 = 0.993), respectively. The relative standard deviation (RSD) of the sensor was 0.5-2.6%, and the recovery of spiked standard solutions was between 98.3 and 110%. The cycle amplification strategy supported by this enzyme has promising applications in detection of the two metal ions in various fields.

Proinflammatory response caused by lead nanoparticles triggered by engulfed nanoparticles.

In this study, the cellular effects of lead (Pb) nanoparticles with a primary particle size of 80 nm were evaluated in two types of cell lines: human lung carcinoma A549 and macrophage-differentiated THP-1 cells (dTHP-1). The cellular responses induced by the Pb nanoparticles varied among the cell types. Exposure to Pb nanoparticles for 24 h at a concentration of 100 µg/ml induced interleukin-8 (IL-8) expression in dTHP-1 cells. Induction of IL-8 expression in A549 was lower than dTHP-1 cells. Pb nanoparticles also induced the gene expression of heme oxygenase-1 in dTHP-1 cells but not in A549 cells. Though cellular uptake of Pb nanoparticles was observed in both the cell types, the amount of internalized Pb particles was lower in A549 cells than that in dTHP-1 cells. Gene expression of metallothionein 2A was remarkably enhanced by Pb nanoparticle exposure in dTHP-1 cells. Compared with Pb nanoparticles, induction of cytokines caused by lead nitrate (Pb[NO3 ]2 ), a water-soluble Pb compound, was smaller. In conclusion, the present study revealed that Pb nanoparticles induced a stronger cellular response than Pb(NO3 )2 , primarily by eliciting cytokine production, in a cell type-dependent manner.

A sensitive fluorescent probe based on dithizone-capped ZnS quantum dots for quercetin determination in biological samples.

A simple turn on/off fluorescence approach based on dithizone-capped ZnS quantum dots (ZnS@DZ QDs) with the help of lead ions as a fluorescent probe for the quantitative determination of quercetin is reported. The interaction of lead ions with dithizone led to the formation of a rigid structure on the surface of ZnS@DZ QDs and turned on the fluorescence intensity of the QDs. After addition of quercetin to this probe and interaction with lead ions, the fluorescence emission turned off. Concerning the quenching fluorescence intensity of ZnS@DZ QDs/Pb2+ QDs probe induced by the target, under the optimum conditions, the probe enabled detection of quercetin in the concentration range from 0.54 µM to 21.7 µM with a correlation coefficient of 0.993 and detection limit of 0.25 µM. The present probe was applied successfully to the determine quercetin as a nutritional biomarker in human serum and 24-h urine samples.

Highly active G-quadruplex/hemin DNAzyme for sensitive colorimetric determination of lead(II).

A UV-vis, CD, and differential pulse voltammetric study was performed on the deactivation of the activity of parallel G-quadruplex/hemin DNAzymes (G4 DNAzymes) by Pb(II). The G4 DNAzyme carries a d[TC] sequence at its 3' end and is stabilized by potassium(I). On addition of Pb(II), the K(I) ions in the parallel G4 are replaced by Pb(II) to keep the parallel topology. Intruded Pb(II) decrease the affinity between the topology and hemin, this leads to a decrease of DNAzyme activity for catalyzing the oxidation of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) by hydrogen peroxide to form a green dye with an absorption maximum at 420 nm. The assay does not use any amplification, and has a linear response in the 0.01 to 10 µM Pb(II) concentration range and a 7.1 nM limit of detection. The method was successfully applied to the analysis of spiked water samples. Graphical abstractSchematic diagram of the colorimetric lead(II) assay based on the competition between K+ and Pb2+ stabilized G-quadruplex/hemin DNAzymes (G4 DNAzymes).

Photoelectrochemical aptasensor for lead(II) by exploiting the CdS nanoparticle-assisted photoactivity of TiO2 nanoparticles and by using the quercetin-copper(II) complex as the DNA intercalator.

A photoelectrochemical (PEC) aptasensor for Pb(II) detection is described. A nanocomposite consisting of CdS (2.5 µm) and TiO2 nanoparticles (10 nm) was used as a photoactive material, and gold nanochains (Au NCs) as the support for immobilization of the Pb(II)-binding aptamer. The quercetin-copper(II) complex was further employed as the intercalator for the improvement of the photoactivity by embedding it into dsDNA. In the presence of Pb(II), a Pb(II)-stabilized G-quadruplex was formed between Pb(II) and DNA S1. This is accompanied by unwinding of the dsDNA and the release of the quercetin-copper(II) complex from the surface of the sensor. This results in a decrease of the photocurrent that drops linearly from 5.0 × 10-12 to 1.0 × 10-8 mol·L-1 Pb(II) concentration range with a detection limit of 1.6 × 10-12 mol·L-1. The method was applied to the determination of Pb(II) in various samples and gave satisfactory results. Graphical abstractA photoelectrochemical aptasensor was fabricated for the detection of Pb(II) based on CdS-TiO2 nanocomposite modified indium tin oxide (ITO) electrode. Gold nanochains (AuNCs) were used as anchor to immobilize the aptamers S1 and S2 that form a double helix structure by DNA hybridization. After embedding of quercetin-copper(II) complex as intercalator and electron donor, the concentrations of Pb(II) were determined by the changes of photocurrents.

A triply amplified electrochemical lead(II) sensor by using a DNAzyme and via formation of a DNA-gold nanoparticle network induced by a catalytic hairpin assembly.

An amplified electrochemical biosensing scheme is described for lead(II) ions. It is making use of DNAzyme-assisted target recycling and catalytic hairpin assembly (CHA). The hairpin strand (substrate probe for the Pb2+-based DNAzyme; referred to as SP) is composed of trigger probe (TP) and a capture probe 1 attached to gold nanoparticles (AuNP). In the presence of the enzyme probe that partially hybridizes with SP, the introduction of Pb2+ triggers target recycling and drives the highly amplified translation of target Pb(II) to TP. The CHA reaction is further initiated by TP. The modified AuNP act as the connecting unit, and this leads to the formation of a 3D DNA-AuNP network on the electrode (which is the third amplification step). It can bind the positively charged redox mediator RuHex via electrostatic interaction for electrochemical detection. This biosensor has a low detection limit (95 pM) and any analytical range that covers the 100 pM to 5 µM Pb(II) concentration range. It is selective over other divalent metal ions. It was applied to the determination of Pb2+ in spiked real-world samples. Graphical abstract Schematic presentation of the electrochemical biosensor. The triply amplified electrochemical assay is based on the use of DNAzyme-assisted target recycling with catalytic hairpin assembly (CHA) reaction for sensitive and selective determination of lead ion (Pb2+). AuNP: gold nanoparticles; SP: substrate probe; EP: enzyme probe.

Synthesis of poly(1,5-diaminonaphthalene) microparticles with abundant amino and imino groups as strong adsorbers for heavy metal ions.

Poly(1,5-diaminonaphthalene) microparticles with abundant reactive amino and imino groups on their surface were synthesized by one-step oxidative polymerization of 1,5-diaminonaphthalene using ammonium persulfate as the oxidant. The molecular, supramolecular, and morphological structures of the microparticles were systematically characterized by IR and UV-vis spectroscopies, elementary analysis, wide-angle X-ray diffractometry, and transmission electron microscopy. The microparticles demonstrate electrical semiconductivity and high resistance to strong acid and alkali, and strong adsorption capability for lead(II), mercury(II), and silver(I) ions. The experimental conditions for adsorption of Pb(II) were optimized by varying the persulfate/monomer ratio, adsorption time, sorbent concentration, and pH value of the Pb(II) solution. The maximum adsorption capacity is 241 mg·g-1 for particles after a 24 h-exposure to a solution at an initial Pb(II) concentration of 29 mM. The adsorption data fit a Langmuir isotherm and follow a pseudo-second-order reaction kinetics. This indicates a chemical adsorption that is typical for a chelation interaction between Pb(II) and amino/imino groups on the sorbent. Graphical abstract Poly(1,5-diaminonaphthalene) microparticles with abundant functional amino and imino groups have been synthesized by one-step direct polymerization of non-volatile 1,5-diaminonaphthalene in aqueous medium for sustainable preparation of high-performance adsorbents to strongly adsorb lead(II), mercury(II), and silver(I) ions.

An integrated measurement of six response performance indicators for lead ion-selective electrodes and application.

A heavy metal ion-selective electrode (ISE) with highly multiple response performances, rather than a high single response performance, is needed urgently for in situ, real-time environmental monitoring. In this study, we present an integrated measurement of six response performance variables such as the response slope, selectivity, dynamical range, detection limit, response time, and lifetime. They are selected and used as the indicators of the quality assessment for Pb2+-ISEs. The measurement, named as electrode comprehensive quality index (IECQ), is a single number for a given ISE. The comprehensive qualities of 114 Pb2+-ISEs reported in the literature were evaluated through the index method. Twenty-one Pb2+-ISEs-based polymer membrane with top 3 IECQ values for seven different properties have been recommended by evaluating and screening of the electrodes. Five Pb2+-ISEs-based polymer membrane with the best single response performance were also provided. The recommended Pb2+-ISEs, along with the corresponding Pb2+-ISEs with the miniaturized configurations, will provide helpful guideline for the application of Pb2+-ISE with highly multiple response performances in real-time environmental monitoring.

Effect of erbium ion concentration on structural and luminescence properties of lead borosilicate glasses for fiber amplifiers.

This investigation reports, the effect of the concentration of erbium and lead ions on the physical, structural and optical properties of lead borosilicate glasses. These glasses were synthesized by the melt quench method. In the synthesis, the concentration of the erbium (Er3+ ) ion was varied in the order of 0.0, 0.1, 0.5, 1.0 and 2.0 mol% and lead (Pb2+ ) ion was varied in the order of 30, 29.9, 29.5, 29 and 28 mol%. The glasses were analyzed using X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and UV-vis-NIR spectroscopy. From XRD, the amorphous nature of lead borosilicate glasses was confirmed. The functional groups which were present in the glasses have been identified by analyzing the FT-IR spectrum. From the absorption spectra, the oscillator strengths as well as the Judd-Ofelt (JO) intensity parameters were determined and compared with other hosts. The JO intensity parameters were further used to calculate certain radiative properties for the excited luminescent levels of Er3+ ion. From emission spectra, full width at half maxima (FWHM), stimulated emission cross-sections (σe ) and certain lasing parameters were evaluated and compared with reference host glasses. The lifetimes of 4 I13/2 excited level of Er3+ ion have also been recorded and analyzed. The calculated and experimental lifetimes were compared in terms of quantum efficiencies. From the photoluminescence analysis, the erbium doped lead borosilicate glasses well suited for optical fiber amplifiers are discussed.

Reusable resistive aptasensor for Pb(II) based on the Pb(II)-induced despiralization of a DNA duplex and formation of a G-quadruplex.

The article describes a reusable biosensor for Pb(II) ions. A duplex DNA with a terminal amino group and containing a G-quadruplex (G4) aptamer was covalently conjugated to single walled carbon nanotubes on a field effect transistor (FET). The detection scheme is based on the despiralization of the DNA duplex because Pb(II) can induce the G4 aptamer to form a stabilizing G4/Pb(II) complex. This structural change affects the electrical conductivity of SWNTs which serves as the analytical signal. The biosensor was characterized via scanning electron microscopy, Raman, UV-vis, and voltage-current profiles. Under optimized conditions, the relative resistance at 0.02 V increases linearly with the logarithm of the Pb(II) concentration in the range from 1 ng·L-1 to 100 µg·L-1, and the limit of detection is 0.39 ng·L-1. Compared to other sensors, this oner demonstrates superior simplicity, sensitivity, and selectivity even in mixtures of heavy metal ions. It was applied to the determination of Pb(II) in (spiked) water and soil samples and gave good results. Graphical abstract Schematic of the fabrication a biosensor for Pb(II). It is making use of an SWNT-based FET, G4-DNA and complementary DNA with an amino group. Pb(II) can despiralize the DNA duplex to form a G-quadruplex which affects the electrical conductivity of SWNTs. After each detection, the single complementary strand DNA can rebind the G4-DNA, which makes the biosensor reusable.

Colorimetric Determination of Pb2+ in Perfect Aqueous Solution Using Carminic Acid as a Selective Chemosensor.

The commercially available natural organic dye, carminic acid (CA), an anthraquinone derivative bearing hydroxyl and carboxyl groups as recognition sites was found to be a colorimetric probe for Pb2+ in perfect aqueous solution under neutral conditions with specific selectivity and high sensitivity. Upon addition of Pb2+, the absorption maximum of CA showed a large red shift, and the resulted color change from red to purple could be easily identified even by the naked eye. The chemical stoichiometric ratio between CA and Pb2+ was determined to be 1:2 through Job plot, Pb2+ titration, and kinetic experiments. Moreover, other environmental relevant metal ions induced no or minimal spectral and color changes. The reversibility of Pb2+ to CA with EDTA even through several cycles was established for practical applications. The results indicated that CA can be a good candidate for simple, convenient and reversible colorimetric detection of Pb2+ in aqueous solution even though it was hard to be applied to determine Pb2+ on the water testing by US EPA.

A Rhodamine-Based Fluorescent Chemosensor for the Detection of Pb2+, Hg2+ and Cd2.

A new rhodamine-based fluorescent chemosensor (1) has been designed and synthesized by linking rhodamine 6G hydrazide with N-methylisatin via an imine linkage. The receptor can selectively recognize and sense Pb2+, Hg2+ and Cd2+ by showing different fluorescence characteristics. In ethanol/HEPES buffer medium, the addition of Cd2+ caused a yellowish-green fluorescence, while the presence of Pb2+ or Hg2+ gave rise to an orange fluorescence. Additionally, the sensor shows an irreversible fluorescence response to Pb2+ and reversible fluorescence responses to Hg2+ and Cd2+.