9.2. Protein-Based Hg(II) Detectors 3467 9.3. Oligonucleotide-Based Hg(II) Detector 3467 9.4. DNAzyme-Based Hg(II) Detectors 3469 9.5. Antibody-Based Hg(II) Detector 3469 10. Mercury Detectors Based on Materials 3469 10.1. Soluble and Fluorescent Polymers 3469 10.2. Membranes, Films, and Fibers 3471 10.3. Micelles 3473 10.4. Nanoparticles 3473 11. Perspectives 3474 12. Addendum 3475 12.1. Small Molecules 3475 12.2. Biomolecules 3477 12.3. Materials 3477 13. List of Abbreviations 3477 14. Acknowledgments 3478 15. References 3478

Tools and tactics for the optical detection of mercuric ion.

Hypertension 66 (20.3%) 24 (24.2%) 30 (16.3%) NS Diabetes 20 (6.2%) 7 (7.1%) 10 (5.4%) NS Excess weight 78 (24%) 27 (27.3%) 44 (23.9%) NS Smokers 64 (19.7%) 17 (17.2%) 35 (19.0%) NS Age >50 years 137 (42.2%) 54 (54.5%) 67 (36.4%) <0.02 Kidney disease 7 (2.2%) 1 (1%) 5 (2.7%) NS Family history, DM 102 (31.4%) 28 (28.3%) 66 (35.9%) NS

Conflict of interest statement. None declared.

Microbial whole-cell sensing systems of environmental pollutants

Contamination of the environment with heavy metal ions has been an important worldwide concern for decades. Mercury, which can accumulate in vital organs and tissues, such as the liver, brain, and heart muscle, is highly toxic and can have lethal effects on living systems. Mercury originates mainly from coal-burning power plants, oceanic and volcanic emissions, gold mining, and waste combustion. Futhermore, microbial biomethylation of Hg ions yields methyl mercury, a potent neurotoxin that passes through the food chain to the tissues of fish and marine mammals. Therefore, it is highly desirable to develop a sensitive and selective mercury detection method that can provide simple, practical, and high-throughput routine determination of levels of Hg ions for both environmental and food samples. Much effort has been devoted towards the design of sensing systems for Hg ions, including sensors based on organic chromophores or fluorophores, conjugated polymers, DNAzymes, gold nanoparticles, semiconductor quantum dots, proteins, and genetically engineered bacteria. However, most of these methods have some limitations such as poor selectivity with interference from closely related metals, insufficient sensitivity (limit of detection (LOD)> 100 nm), and in certain cases are nonstable or nonfunctional in aqueous media (because of low water solubility). Another emerging approach for the detection of Hg ions involves the use of oligonucleotides. Hg ions can specifically interact with thymine bases to form strong and stable thymine–Hg–thymine complexes (T–Hg–T). Various Hg ion detection assays based on this property of T– Hg–T coordination chemistry have been developed in recent years. Ono and Togashi have described a simple method based on Hg-induced DNA folding, which yields an intramolecular fluorescence resonance energy transfer process and allows the detection of Hg ions with high selectivity and sensitivity (up to 40 nm). Mirkin and co-workers recently reported the colorimetric detection of Hg ions in aqueous media using DNA-functionalized gold nanoparticle (AuNP) probes with specifically designed T–T mismatches with a sensitivity of up to 100 nm. Furthermore, Liu and coworkers developed an one-step, room temperature, colorimetric assay of Hg ions using DNA–nanoparticle conjugates with a sensitivity of 1 mm. According to the US Environmental Protection Agency (EPA) standard, the MAL (maximum allowable level) of Hg ions in drinking water is 10 nm (2.0 parts per billion (ppb)). This concentration is much lower than the detection limit of most available assays. Thus, the development of a highly sensitive, facile, and practical assay for Hg ions remains a challenge. Herein, we present a novel highly sensitive and selective fluorescence polarization assay (FPA) method for the detection of Hg ions on the basis of the formation of T–Hg–T complexes. The detection sensitivity can be significantly improved to 0.2 ppb (1.0 nm) by using a “gold nanoparticle enhancement” approach. Gold nanoparticle (AuNP) enhancement functions have been employed to substantially improve the performance and sensitivity of various biosensing systems. The enhanced effects were implemented by the use of AuNPs as labels for amplified quartz crystal microbalance detection and electrochemical detection, by the application of AuNPs as electron relays for the facilitation of interfacial electron transfer on electrodes. Recently, AuNP-enhanced effects in a responsive polymer gel and in network field-effect transistors were also reported. The fluorescence polarization value P is sensitive to changes in the rotational motion of fluorescently labeled molecules. It can be calculated by the Perrin equation [Eq. (1)], where t is the fluorescence lifetime, h is the viscosity

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Highly sensitive detection of mercury(II) ions by fluorescence polarization enhanced by gold nanoparticles.

A “toolbox” for biological and chemical monitoring requirements for the European Union's Water Framework Directive

Reporter genes lucFF, luxCDABE, gfp, and dsred have different characteristics in whole-cell bacterial sensors

At the EILATox-Oregon Workshop, nine luminescent whole-cell bacterial sensors were used for the determination of bioavailable metals in blind samples (17 synthetic and 3 environmental) A non-inducible luminescent control strain was used to determine sample matrix effects and bacterial toxicity Whole-cell bacterial sensors capable of determining arsenic, inorganic mercury and its organic derivatives, cadmium, lead or copper were used in suspensions and a bacterial sensor for the detection of inorganic mercury was immobilized onto ﬁbre-optic tips using calcium alginate Bioavailable amounts of metals were estimated using calibration plots, that were constructed to determine the range of metals giving rise to a linear relationship between luminescence and the amount of metals present in the standard solutions EILATox-Oregon sample 5, which contained 74 mg l−1 of Hg, gave a signiﬁcant response with both formats of the mercury sensor The bioavailable amounts of mercury according to the measurement of bacterial sensor in suspension and immobilized onto a ﬁbre-optic tip were 76 and 93 mg l−1, respectively The bacterial sensor for arsenic and copper showed a response with sample 6 (58 mg l−1 of As) and sample 8 (400 mg l−1 of metham sodium), respectively This study showed that the bacterial sensors in suspension or immobilized onto optical ﬁbres are capable of quantifying bioavailable metals from unknown samples The measurement protocol of bacterial sensors is simple and possible to perform in the ﬁeld Moreover, the samples do not need any pretreatment before analysis Construction and characterization of the strain for the detection of bioavailable copper are described Copyright © 2004 John Wiley & Sons, Ltd

Detection of bioavailable heavy metals in EILATox-Oregon samples using whole-cell luminescent bacterial sensors in suspension or immobilized onto fibre-optic tips.

Mercury and its organic compounds, especially methylmercury, are hazardous compounds that concentrate in biota via biomagnification and cause severe neurological disorders in animals. In this paper, a recombinant whole-cell bacterial sensor for the detection of the organic compounds of mercury was constructed. The sensor carries firefly luciferase gene as a reporter under the control of the mercury-inducible regulatory part of broad spectrum mer operon from pDU1358. In addition, a gene-encoding organomercurial lyase (an enzyme necessary for cleavage of the mercury−carbon bond) was coexpressed in the sensor strain. The sensitivity of the sensor was evaluated on some environmentally important organomercurial compounds. The lowest detectable concentrations were 0.2 nM (50 ng/L), 1 nM (0.34 μg/L), and 10 μM (2.3 mg/L) for methylmercury chloride, phenylmercury acetate, and dimethylmercury, respectively. The sensor responded also to inorganic mercury and, therefore, using the sensor described here together with...

Detection of organomercurials with sensor bacteria.

Oxidative stress and photoinhibition can be separated in the cyanobacterium Synechocystis sp. PCC 6803.

Changing of principal σ factor in RNA polymerase holoenzyme to a group 2 σ factor redirects transcription when cyanobacteria acclimate to suboptimal environmental conditions. The group 2 sigma factor SigB was found to be important for the growth of the cyanobacterium Synechocystis sp. PCC 6803 in high-salt (0.7 m NaCl) stress but not in mild heat stress at 43°C although the expression of the sigB gene was similarly highly, but only transiently up-regulated at both conditions. The SigB factor was found to regulate many salt acclimation processes. The amount of glucosylglycerol-phosphate synthase, a key enzyme in the production of the compatible solute glucosylglycerol, was lower in the inactivation strain ΔsigB than in the control strain. Addition of the compatible solute trehalose almost completely restored the growth of the ΔsigB strain at 0.7 m NaCl. High-salt conditions lowered the chlorophyll and phycobilin contents of the cells while protective carotenoid pigments, especially zeaxanthin and myxoxanthophyll, were up-regulated in the control strain. These carotenoids were up-regulated in the ΔsigCDE strain (SigB is the only functional group 2 σ factor) and down-regulated in the ΔsigB strain under standard conditions. In addition, the HspA heat shock protein was less abundant and more abundant in the ΔsigB and ΔsigCDE strains, respectively, than in the control strain in high-salt conditions. Some cellular responses are common to heat and salt stresses, but pretreatment with mild heat did not protect cells against salt shock although protection against heat shock was evident.

Kaisa Hakkila

Papers

Reporter genes lucFF, luxCDABE, gfp, and dsred have different characteristics in whole-cell bacterial sensors

Detection of bioavailable heavy metals in EILATox-Oregon samples using whole-cell luminescent bacterial sensors in suspension or immobilized onto fibre-optic tips.

Detection of organomercurials with sensor bacteria.

Oxidative stress and photoinhibition can be separated in the cyanobacterium Synechocystis sp. PCC 6803.

The SigB σ Factor Regulates Multiple Salt Acclimation Responses of the Cyanobacterium Synechocystis sp. PCC 6803