An optical sensor for mercury ion based on the fluorescence quenching of tetra(p-dimethylaminophenyl)porphyrin

Water-soluble anionic N-confused porphyrin for sensitive and selective detection of heavy metal pollutants in aqueous environment

Efficient detection and quantification of metal ions in real time and in a cost-effective manner is a critical step in combating the increasing danger of heavy metal contamination of our biosphere. The potential of water-soluble anionic derivative of N-confused tetraphenylporphyrin (WS-NCTPP) has been investigated for quantitative detection of heavy metal ions. The results show that the photophysical properties of WS-NCTPP differ significantly in the presence of four metal ions, namely Hg(II), Zn(II), Co(II) and Cu(II). The variation in the spectral behaviour is driven by the formation of 1:1 complexes with all the four cations with varied degree of complexation. The selectivity of the sensing is studied through interference studies, indicating maximum selectivity for Hg(II) cations. Computational studies of the structural features of the metal complexes with WS-NCTPP help in establishing the geometry and binding interactions between the metal ions and the porphyrin nucleus. The results demonstrate the promising potential of the NCTPP probe which should be utilized for detection of heavy metal ions, especially mercury, in the near future.

Recent Trends and Future Perspectives of Emergent Analytical Techniques for Mercury Sensing in Aquatic Environments

Environmental emissions of mercury from industrial waste and natural sources, even in trace amounts, are toxic to organisms and ecosystems. However, industrial-scale mercury detection is limited by the high cost, low sensitivity/specificity, and poor selectivity of the available analytical tools. This review summarizes the key sensors for mercury detection in aqueous environments: colorimetric-, electrochemical-, fluorescence-, and surface-enhanced Raman spectroscopy-based sensors reported between 2014-2021. It then compares the performances of these sensors in the determination of inorganic mercury (Hg²⁺ ) and methyl mercury (CH₃ Hg⁺ ) species in aqueous samples. Mercury sensors for aquatic applications still face serious challenges in terms of difficult deployment in remote areas and low robustness, reliability, and selectivity in harsh environments. We provide future perspectives on the selective detection of organomercury species, which are especially toxic and reactive in aquatic environments. This review is intended as a valuable resource for scientists in the field of mercury sensing.

An Improved Synthesis of Water-Soluble Dual Fluorescence Emission Carbon Dots from Holly Leaves for Accurate Detection of Mercury Ions in Living Cells

Background

Carbon dots (CDs) emitting near-infrared fluorescence were recently synthesized from green leaves. However, the Hg²⁺ detection of CDs was limited because of the insufficient water solubility, low fluorescence and poor stability.

Methods

Dual fluorescence emission water-soluble CD (Dual-CD) was prepared through a solvothermal method from holly leaves and low toxic PEI_1.8k. PEG was further grafted onto the surface to improve the water solubility and stability.

Results

The Dual-CD solution can emit 487 nm and 676 nm fluorescence under single excitation and exhibit high quantum yield of 16.8%. The fluorescence at 678 nm decreased remarkably while the emission at 470 nm was slightly affected by the addition of Hg²⁺. The ratiometric Hg²⁺ detection had a wide linear range of 0–100 μM and low detection limit of 14.0 nM. In A549 cells, there was a good linear relation between F₄₈₇/F₆₇₆ and the concentration of Hg²⁺ in the range of 0–60 μM; the detection limit was 477 nM. Furthermore, Dual-CD showed visual fluorescence change under Hg²⁺.

Conclusion

Dual-CD has ratiometric responsiveness to Hg²⁺ and can be applied for quantitative Hg²⁺ detection in living cells.

Construction of DNA Biosensors for Mercury (II) Ion Detection Based on Enzyme-Driven Signal Amplification Strategy

Mercury ion (Hg²⁺) is a well-known toxic heavy metal ion. It is harmful for human health even at low concentrations in the environment. Therefore, it is very important to measure the level of Hg²⁺. Many methods, reviewed in several papers, have been established on DNA biosensors for detecting Hg²⁺. However, few reviews on the strategy of enzyme-driven signal amplification have been reported. In this paper, we reviewed this topic by dividing the enzymes into nucleases and DNAzymes according to their chemical nature. Initially, we introduce the nucleases including Exo III, Exo I, Nickase, DSN, and DNase I. In this section, the Exo III-driven signal amplification strategy was described in detail. Because Hg²⁺ can help ssDNA fold into dsDNA by T-Hg-T, and the substrate of Exo III is dsDNA, Exo III can be used to design Hg²⁺ biosensor very flexibly. Then, the DNAzyme-assisted signal amplification strategies were reviewed in three categories, including UO₂²⁺-specific DNAzymes, Cu²⁺-specific DNAzymes and Mg²⁺-specific DNAzymes. In this section, the Mg²⁺-specific DNAzyme was introduced in detail, because this DNAzyme has highly catalytic activity, and Mg²⁺ is very common ion which is not harmful to the environment. Finally, the challenges and future perspectives were discussed.

A polymer membrane tethered with a cycloruthenated complex for colorimetric detection of Hg2+ ions

A new cyclometallated ruthenium complex (Ru1) involving a 2-(2-thienyl)pyridine and a benzo[e]indolium block connected with a hexanoic acid was successfully synthesized and characterized, which exhibited the high sensitivity and selectivity to Hg²⁺ over other common metal ions with the detection limit of as low as 0.053 μM in aqueous system. Then, it was grafted onto a polymer membrane to afford a Hg²⁺-sensitive membrane (sensor 1), which was characterized by FT-IR, SEM and XPS spectra, respectively. When sensor 1 was dipped into the aqueous solution of Hg²⁺ ions, the color of the membrane changed from dark-red to yellow, which could be observed by naked eyes easily. It should be noted that the membrane can absorb Hg²⁺ ions well in aqueous solution and the adsorption capacity of this polymer membrane for Hg²⁺ ions was determined by atomic absorption spectroscopy, indicating that it also could be used as a potential material for removal of Hg²⁺ ions.

A porphyrin-based optical sensor membrane prepared by electrostatic self-assembled technique for online detection of cadmium(II)

An optical sensor membrane was prepared by electrostatic self-assembled technique for online detection of cadmium ion (II) (Cd(II)). The optical indicator 5,10,15,20-tetrakis(4-N-methylpyridyl) porphyrin p-toluenesulfonate (TMPyP) was adsorbed on a hydrolyzed polyacrylonitrile (PAN) membrane by electrostatic attraction and further immobilized through layer-by-layer deposition of poly(allylamine hydrochloride) (PAH) and poly(sodium 4-styrenesulfonate) (PSS) on the membrane surface. The electrostatic self-assembly of polyelectrolytes on the membrane is influenced by pH and salt concentration of polyelectrolytes. The optical sensor membrane shows distinct color and spectral response to Cd(II) under static and flow-through conditions based on the coordination of TMPyP with Cd(II). A faster detection of Cd(II) is achieved at higher feed concentration of Cd(II) or appropriate lower immobilization capacity of TMPyP on the membrane. The flow-through detection is also influenced by the flow rate; higher flow rate led to faster response to Cd(II) during filtration. Compared with the static process, the flow-through conditions are more conducive to faster analysis of ppb level concentration of Cd(II) (10^-3 mg L^-1) due to a promoted mass transfer and filtration enrichment. Hence, the development of the optical sensor membrane in this study demonstrated the prospect to make membranes multifunctional with advantages for online chromatic warning in addition to adsorption/rejection of heavy metal ions in the solutions that are treated.

Ultrasound assisted fabrication of a novel optode base on a triazine based Schiff base immobilized on TEOS for copper detection

This work introduces novel selective and sensitive optical sensor based on a nano sized triazine based Schiff base (H₂L) immbolized on a transparent glass substrate through the sol-gel process to detection of copper (II) ions in aqueous solutions. This sensor can determine the copper (II) in the range of 8.54 × 10^-8-1.0 × 10^-5 mol L^-1 with a low detection limit of 1.53 × 10^-8 mol L^-1. The optimized geometry of H₂L and its copper complex was obtained based on DFT/B3LYP levels of theory with B3LYP/6-311 + G(d,p) and LANL2DZ/6-311 + G(d,p) basis sets respectively. The calculated electronic properties of them including the molecular orbital, Mulliken population analysis, contour of electrostatic potential, and molecular electrostatic potential map confirmed the behavior of the sensor. Some advantage of the fabricated sensor such as high selectivity, sensitivity, short response time, easy production, fast regeneration, low cost, being portable and user friendly can make it a good choice to detection of Cu(II) ion in various application. The suggested sensor was revealed excellent sensitivity in the natural samples that confirmed by Inductively Coupled Plasma-Mass (ICP) spectrometry method.

Water-soluble mercury ion sensing based on the thymine-Hg2+-thymine base pair using retroreflective Janus particle as an optical signaling probe

Herein, we report an optical sensing platform for mercury ions (Hg²⁺) in water based on the integration of Hg²⁺-mediated thymine-thymine (T-T) stabilization, a biotinylated stem-loop DNA probe, and a streptavidin-modified retroreflective Janus particle (SA-RJP). Two oligonucleotide probes, including a stem-loop DNA probe and an assistant DNA probe, were utilized. In the absence of Hg²⁺, the assistant DNA probe does not hybridize with the stem-loop probe due to their T-T mismatch, so the surface-immobilized stem-loop DNA probe remains a closed hairpin structure. In the presence of Hg²⁺, the DNA forms a double-stranded structure with the loop region via Hg²⁺-mediated T-T stabilization. This DNA hybridization induces stretching of the stem-loop DNA probe, exposing biotin. To translate these Hg²⁺-mediated structural changes in DNA probe into measurable signal, SA-RJP, an optical signaling label, is applied to recognize the exposed biotin. The number of biospecifically bound SA-RJPs is proportional to the concentration of Hg²⁺, so that the concentration of Hg²⁺ can be quantitatively analyzed by counting the number of RJPs. Using the system, a highly selective and sensitive measurement of Hg²⁺ was accomplished with a limit of detection of 0.027nM. Considering the simplified optical instrumentation required for retroreflection-based RJP counting, RJP-assisted Hg²⁺ measurement can be accomplished in a much easier and inexpensive manner. Moreover, the detection of Hg²⁺ in real drinking water samples including tap and commercial bottled water was successfully carried out.

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

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

Metal-organic frameworks as biosensors for luminescence-based detection and imaging

Metal-organic frameworks (MOFs), formed by the self-assembly of metal centres or clusters and organic linkers, possess many key structural and chemical features that have enabled them to be used in sensing platforms for a variety of environmentally, chemically and biomedically relevant compounds. In particular, their high porosity, large surface area, tuneable chemical composition, high degree of crystallinity, and potential for post-synthetic modification for molecular recognition make MOFs promising candidates for biosensing applications. In this review, we separate our discussion of MOF biosensors into two categories: quantitative sensing, focusing specifically on luminescence-based sensors for the direct measurement of a specific analyte, and qualitative sensing, where we describe MOFs used for fluorescence microscopy and as magnetic resonance imaging contrast agents. We highlight several key publications in each of these areas, concluding that MOFs present an exciting, versatile new platform for biosensing applications and imaging, and we expect to see their usage grow as the field progresses.

Development of Ion Chemosensors Based on Porphyrin Analogues

Sensing of metal ions and anions is of great importance because of their widespread distribution in environmental systems and biological processes. Colorimetric and fluorescent chemosensors based on organic molecular species have been demonstrated to be effective for the detection of various ions and possess the significant advantages of low cost, high sensitivity, and convenient implementation. Of the available classes of organic molecules, porphyrin analogues possess inherently many advantageous features, making them suitable for the design of ion chemosensors, with the targeted sensing behavior achieved and easily modulated based on their following characteristics: (1) NH moieties properly disposed for binding of anions through cooperative hydrogen-bonding interactions; (2) multiple pyrrolic N atoms or other heteroatoms for selectively chelating metal ions; (3) variability of macrocycle size and peripheral substitution for modulation of ion selectivity and sensitivity; and (4) tunable near-infrared emission and good biocompatibility. In this Review, design strategies, sensing mechanisms, and sensing performance of ion chemosensors based on porphyrin analogues are described by use of extensive examples. Ion chemosensors based on normal porphyrins and linear oligopyrroles are also briefly described. This Review provides valuable information for researchers of related areas and thus may inspire the development of more practical and effective approaches for designing high-performance ion chemosensors based on porphyrin analogues and other relevant compounds.

A Lawsone–DAMN based colorimetric chemosensor for rapid naked-eye detection of mercury(ii)

A highly sensitive and selective chemosensorLexhibited well-defined naked-eye visible color changes from yellow to pink, which was used for Hg²⁺detection in acetonitrile. For the selective recognition of Hg²⁺ions, it forms a 1 : 1 stoichiometric complex involving naphthoquinone hydroxyl and diaminomaleonitrile nitrogen functionalities.

Porphyrinic MOFs for reversible fluorescent and colorimetric sensing of mercury(ii) ions in aqueous phase

A simple, rapid and visual assay for Hg²⁺ detection is designed based on assembling Zr–O clusters and porphyrin ligands.

Development of mercury (II) ion biosensors based on mercury-specific oligonucleotide probes

Mercury (II) ion (Hg(2+)) contamination can be accumulated along the food chain and cause serious threat to the public health. Plenty of research effort thus has been devoted to the development of fast, sensitive and selective biosensors for monitoring Hg(2+). Thymine was demonstrated to specifically combine with Hg(2+) and form a thymine-Hg(2+)-thymine (T-Hg(2+)-T) structure, with binding constant even higher than T-A Watson-Crick pair in DNA duplex. Recently, various novel Hg(2+) biosensors have been developed based on T-rich Mercury-Specific Oligonucleotide (MSO) probes, and exhibited advanced selectivity and excellent sensitivity for Hg(2+) detection. In this review, we explained recent development of MSO-based Hg(2+) biosensors mainly in 3 groups: fluorescent biosensors, colorimetric biosensors and electrochemical biosensors.

Highly selective and sensitive optical sensor for determination of Pb2+ and Hg2+ ions based on the covalent immobilization of dithizone on agarose membrane

A highly sensitive and selective optical membrane for determination of Hg(2+) and Pb(2+) was prepared by covalent immobilization of dithizone on agarose membrane. In addition to its high stability, reproducibility and relatively long lifetime, the proposed optical sensor revealed good selectivity for target ions over a large number of alkali, alkaline earth, transition, and heavy metal ions. The proposed optical membrane displays linear responses from 1.1×10(-8) to 2.0×10(-6) mol L(-1) and 1.2×10(-8) to 2.4×10(-6) mol L(-1) for Hg(2+) and Pb(2+), respectively. The limits of detection (LOD) were 2.0×10(-9) mol L(-1) and 4.0×10(-9) mol L(-1) for Hg(2+) and Pb(2), respectively. The prepared optical membrane was successfully applied to the determination of Hg(2+) and Pb(2+) in industrial wastes, spiked tap water and natural waters without any preconcentration step.

Phosphorescent chemosensor for Hg2+ based on an iridium(iii) complex coordinated with 4-phenylquinazoline and carbazole dithiocarbamate

A colorimetric phosphorescent chemosensor Ir(pqz)2(cdc) showed satisfactory selective, sensitive, naked eye detection and fluorescence change response to Hg²⁺ in MeCN.

Fluorescent and colorimetric sensors for environmental mercury detection

The development of fluorescent and colorimetric sensing strategies for environmental mercury is described.

Porphyrin-based electrostatically self-assembled multilayers as fluorescent probes for mercury(ii) ions: a study of the adsorption kinetics of metal ions on ultrathin films for sensing applications

ESAM as fluorescent probes for Hg(ii) ions were developed. The adsorption process involved in analyte-solid probe interaction was studied by monitoring fluorescence quenching.

Aminoquinoline based highly sensitive fluorescent sensor for lead(II) and aluminum(III) and its application in live cell imaging

We have synthesized a new probe 5-((anthracen-9-ylmethylene) amino)quinolin-10-ol (ANQ) based on anthracene platform. The probe was tested for its sensing behavior toward heavy metal ions Hg(2+), Pb(2+), light metal Al(3+) ion, alkali, alkaline earth, and transition metal ions by UV-visible and fluorescent techniques in ACN/H2O mixture buffered with HEPES (pH 7.4). It shows high selectivity toward sensing Pb(2+)/Al(3+) metal ions. Importantly, 10-fold and 5- fold fluorescence enhancement at 429 nm was observed for probe upon complexation with Pb(2+) and Al(3+) ions, respectively. This fluorescence enhancement is attributable to the prevention of photoinduced electron transfer. The photonic studies indicate that the probe can be adopted as a sensitive fluorescent chemosensor for Pb(2+) and Al(3+) ions.

Mercury ion responsive wettability and oil/water separation

A novel Hg(2+) responsive oil/water separation mesh with poly(acrylic acid) hydrogel coating is reported. The mesh can separate oil and water because of the superhydrophilicity of the poly(acrylic acid) hydrogel coating on the mesh, and switch the wettability based on the chelation between Hg(2+) and poly(acrylic acid) . The reversible change in oil contact angle of as-prepared mesh is about 149° after immersion in Hg(2+) solution. This mesh is an ideal candidate for oil-polluted water purification, especially for water that contains Hg(2+) contaminant.

A new 3,5-bisporphyrinylpyridine derivative as a fluorescent ratiometric probe for zinc ions

A new 3,5-disubstituted pyridine with two porphyrin moieties was prepared through an efficient synthetic approach involving 2-formyl-5,10,15,20-tetraphenylporphyrin (1), piperidine, and catalytic amounts of [La(OTf)3]. 3,5-Bis(5,10,15,20-tetraphenylporphyrin-2-ylmethyl)pyridine (2) was fully characterized and its sensing ability towards Zn(2+), Cu(2+), Hg(2+), Cd(2+), and Ag(+) was evaluated in solution by absorption and fluorescence spectroscopy and in gas phase by using matrix-assisted laser desorption/ionization (MALDI)-TOF mass spectrometry. Strong changes in the ground and excited state were detected in the case of the soft metal ions Zn(2+), Cd(2+), Hg(2+), and Cu(2+). A three-metal-per-ligand molar ratio was obtained in all cases and a significant ratiometric behavior was observed in the presence of Zn(2+) with the appearance of a new band at 608 nm, which can be assigned to a metal-to-ligand charge transfer. The system was able to quantify 79 ppb of Zn(2+) and the theoretical calculations are in accordance with the stoichiometry observed in solution. The gas-phase sensorial ability of compound 2 towards all metal ions was confirmed by using MALDI-TOF MS and in solid state by using polymeric films of polymethylmethacrylate (PMMA) doped with ligand 2. The results showed that compound 2 can be analytically used to develop new colorimetric molecular devices that are able to discriminate between Hg(2+) and Zn(2+) in solid phase. The crystal structure of Zn(II) complex of 3,5-bisporphyrinylpyridine was unequivocally elucidated by using single-crystal X-ray diffraction studies.

Hg(2+) mediated quinazoline ensemble for highly selective recognition of Cysteine

A fluorimetric sensor for Hg(2+) ion and Cysteine based on quinazoline platform was designed and synthesized by one step reaction and characterized by using common spectroscopic methods. Time Dependent Density Functional Theory calculations shows that probe behaves as "ON-OFF" fluorescent quenching sensor via electron transfer/heavy atom effect. Receptor was found to exhibit selective fluorescence quenching behavior over the other competitive metal ions, and also the receptor-Hg(2+) ensemble act as an efficient "OFF-ON" sensor for Cysteine. Moreover this sensor has also been successfully applied to detection of Hg(2+) in natural water samples with good recovery.

Highly sensitive and selective spectroscopic detection of mercury(II) in water by using pyridylporphyrin-DNA conjugates

Single-labeled pyridylporphyrin-DNA conjugates are reported as highly sensitive and selective spectroscopic sensors for mercury(II) ions in water. The effects of chemical structure (thymine versus adenine), number of nucleotides (monomer versus octamer), and porphyrin metalation (Zn versus free base) on the sensitivity and selectivity of mercury(II) detection are explored. The results indicated that pyridylporphyrin rather than the nucleobase plays a crucial role in mercury(II) sensing, because porphyrin conjugates with both adenosine and thymidine exhibited excellent mercury(II) detection. Mercury(II) recognition was shown in emission quenching, as well as in a redshift of the porphyrin Soret band absorption. The limit of detection (LOD, 3σ/slope) of zinc(II) pyridylporphyrin-5'-oligodeoxythymidine (ZnPorT8) obtained by fluorescence quenching was calculated to be 21.14 nM. Other metal cations (Zn(2+), Cd(2+), Pb(2+), Mn(2+), Ca(2+), Ni(2+), Mg(2+), Fe(2+), Cu(2+), and Na(+)) did not interfere with the emission and absorption sensing of mercury(II). Free-base porphyrin-oligothymine conjugate 2HPorT8 displayed similar sensitivity to ZnPorT8 but different selectivity. The results also implied that the sensing properties of porphyrin-deoxythymidine conjugates could potentially be tuned by porphyrin metalation.

A manganese porphyrin-based sensor for flow-injection potentiometric determination of thiocyanate

Metalloporphyrin-based ion-selective electrodes for flow-injection potentiometric determination of thiocyanate are described. The detection system is based on a coated glassy carbon electrode membrane sensor incorporating 5,10,15,20-tetraphenyl-21H,23H-porphine manganese(III) chloride as the active ingredient. The influences of the membrane composition, pH, and the effects of flow-injection parameters on the response of the system were investigated. At the optimized flow-injection potentiometric conditions, the sensor exhibited a Nernstian slope of -58.0 mV per decade of thiocyanate activity over the range 4.2 × 10-7–7.6 × 10-2M , where 50 μL of each sample solution was injected into the carrier solution. The detection limit of thiocyanate in the FIP mode was 4.2 × 10-7M . The selectivity of the flow-injection potentiometric system with respect to several common inorganic and organic anions was superior to that of the batch mode using the same sensor and similar operating conditions. The sensor was applied to the determination of thiocyanate in urine samples.

A new Schiff's base ligand immobilized agarose membrane optical sensor for selective monitoring of mercury ion

A highly selective optical sensor was developed for the Hg(2+) determination by chemical immobilization of 2-[(2-sulfanylphenyl)ethanimidoyl]phenol (L), on an agarose membrane. Spectrophotometric studies of complex formation between the Schiff's base ligand L and Hg(2+), Sr(2+), Mn(2+), Cu(2+), Al(3+), Cd(2+), Zn(2+), Co(2+) and Ag(+) metal ions in methanol solution indicated a substantially larger stability constant for the mercury ion complex. Consequently, the Schiff's base L was used as an appropriate ionophore for the preparation of a selective Hg(2+) optical sensor, by its immobilization on a transparent agarose film. A distinct color change, from yellow to green-blue, was observed by contacting the sensing membrane with Hg(2+) ions at pH 4.5. The effects of pH, ionophore concentration, ionic strength and reaction time on the immobilization of L were studied. A linear relationship was observed between the membrane absorbance at 650 nm and Hg(2+) concentrations in a range from 1×10(-2) to 1×10(-5) mol L(-1) with a detection limit (3σ) of 1×10(-6) mol L(-1). No significant interference from 100 times concentrations of a number of potentially interfering ions was detected for the mercury ion determination. The optical sensor was successfully applied to the determination of mercury in amalgam alloy and spiked water samples.

A disulfide-linked naphthalimide dimer for Hg(II) detection in aqueous solution

A disulfide linked naphthalimide dimer probe was designed for mercury ion (Hg(2+)) recognition in this work. The recognition was based on the strong affinity of mercury for sulfur. The experimental results revealed that the probe exhibited high selectivity and sensitivity toward Hg(2+) in comparison to other metal ions via a turn-on and reversible response to Hg(2+) in neutral buffer solution. More importantly, the probe demonstrated a linear response for Hg(2+) over a concentration range from 0 to 150 μM with a detection limit of 0.38 μM, which is just the limit of the safe concentration for humans. Upon addition of 150 μM Hg(2+), the enhancement of fluorescence reached a maximum (∼7-fold). The performances of the probe indicated that it could meet the selectivity requirements for biomedical and environmental application and also was sensitive enough to detect Hg(2+) in environmental and biological samples.

A selective fluorescence probe for mercury ion based on the fluorescence quenching of terbium(III)-doped cadmium sulfide composite nanoparticles

A fluorescent probe for mercury(II) ions, based on the quenching of fluorescence of terbium(III) ions doped in CdS nanoparticles, has been developed. The terbium(III)-doped cadmium sulfide composite nanoparticles were successfully synthesized through a straightforward one-pot process, with the biomolecule glutathione (GSH) as a capping ligand. In addition, the terbium(III) ions were observed an enhancement of emission intensity, owing to fluorescence energy transfer from the excited CdS particles to the emitting terbium(III). Because of a specific interaction, the fluorescence intensity of terbium(III)-doped CdS particles is obviously reduced in the presence of mercury(II) ions. The fluorescence quenching phenomenon of terbium(III) can be attributed to the fact that the energy transfer system was destroyed by combining with mercury(II). Under the optimal conditions, the fluorescent intensity of terbium(III) ions at 491nm decreased linearly with the concentration of mercury(II) ions ranging from 4.5nmolL(-1) to 550nmolL(-1). The limit of detection for mercury(II) was 0.1nmolL(-1). This method is simple, practical, relatively free of interference from coexisting substances and can be successfully applied to the determination of mercury(II) ions in real water samples. In addition, the probable mechanism of reaction between terbium(III)-doped CdS composite nanoparticles and mercury(II) was also discussed.

Recent trends in monitoring of European water framework directive priority substances using micro-sensors: a 2007-2009 review

This review discusses from a critical perspective the development of new sensors for the measurement of priority pollutants targeted in the E.U. Water Framework Directive. Significant advances are reported in the paper and their advantages and limitations are also discussed. Future perspectives in this area are also pointed out in the conclusions. This review covers publications appeared since December 2006 (the publication date of the Swift report). Among priority substances, sensors for monitoring the four WFD metals represent 81% of published papers. None of analyzed publications present a micro-sensor totally validated in laboratory, ready for tests under real conditions in the field. The researches are mainly focused on the sensing part of the micro-sensors. Nevertheless, the main factor limiting micro-sensor applications in the environment is the ruggedness of the receptor towards environmental conditions. This point constitutes the first technological obstacle to be overcome for any long-term field tests.