Aptasensing of chloramphenicol in the presence of its analogues: reaching the maximum residue limit

A novel, label-free folding induced aptamer-based electrochemical biosensor for the detection of chloramphenicol (CAP) in the presence of its analogues has been developed. CAP is a broad-spectrum antibiotic that has lost its favor due to its serious adverse toxic effects on human health. Aptamers are artificial nucleic acid ligands (ssDNA or RNA) able to specifically recognize a target such as CAP. In this article, the aptamers are fixed onto a gold electrode surface by a self-assembly approach. In the presence of CAP, the unfolded ssDNA on the electrode surface changes to a hairpin structure, bringing the target molecules close to the surface and triggering electron transfer. Detection limits were determined to be 1.6 × 10(-9) mol L(-1). In addition, thiamphenicol (TAP) and florfenicol (FF), antibiotics with a structure similar to CAP, did not influence the performance of the aptasensor, suggesting a good selectivity of the CAP-aptasensor. Its simplicity and low detection limit (because of the home-selected aptamers) suggest that the electrochemical aptasensor is suitable for practical use in the detection of CAP in milk samples.

Selection and characterization of PCB-binding DNA aptamers

Polychlorinated biphenyls (PCBs) are persistent organic pollutants (POPs) that resist natural degradation and bioaccumulate in nature. Combined with their toxicity, this leads them to cause cancer and other health hazards. Thus, there is a vital need for rapid and sensitive methods to detect PCB residues in food and in the environment. In this study, PCB-binding DNA aptamers were developed using PCB72 and PCB106 as targets for aptamer selection. Aptamers are synthetic DNA recognition elements which form unique conformations that enable them to bind specifically to their targets. Using in vitro selection techniques and fluorometry, an aptamer that binds with nanomolar affinity to both the PCBs has been developed. It displayed high selectivity to the original target congeners and limited affinity toward other PCB congeners (105, 118, 153, and 169), suggesting general specificity for the basic PCB skeleton with varying affinities for different congeners. This aptamer provides a basis for constructing an affordable, sensitive, and high-throughput assay for the detection of PCBs in food and environmental samples and offers a promising alternative to existing methods of PCB quantitation. This study therefore advances aptamer technology by targeting one of the highly sought-after POPs, for the first time ever recorded.

Carbon nanotubes based electrochemical aptasensing platform for the detection of hydroxylated polychlorinated biphenyl in human blood serum

A novel strategy to sense target molecules in human blood serum is achieved by immobilizing aptamers (APTs) on multi-walled carbon nanotubes (MWCNT) modified electrodes. In this work, the aminated aptamer selected for hydroxylated polychlorinated biphenyl (OH-PCB) was covalently immobilized on the surface of the MWCNT-COOH modified glassy carbon electrode through amide linkage. The aptamers function as recognition probes for OH-PCB by the binding induced folding of the aptamer. The developed aptasensing device was characterized by electrochemical impedance spectroscopy (EIS), atomic force microscopy (AFM) and Fourier transform infrared spectroscopy (FTIR). The aptasensor displayed excellent performance for OH-PCB detection with a linear range from 0.16 to 7.5 μM. The sensitivity of the developed aptasensing platform is improved (1×10(-8) M) compared to the published report (1×10(-6) M) for the determination of OH-PCB (Turner et al., 2007). The better performance of the sensor is due to the unique platform, i.e. the presence of APTs onto electrodes and the combination with nanomaterials. The aptamer density on the electrode surface was estimated by chronocoulometry and was found to be 1.4×10(13) molecules cm(-2). The validity of the method and applicability of the aptasensor was successfully evaluated by the detection of OH-PCB in a blood serum sample. The described approach for aptasensing opens up new perspectives in the field of biomonitoring providing a device with acceptable stability, high sensitivity, good accuracy and precision.

Hazard characterization and identification of a former ammunition site using microarrays, bioassays, and chemical analysis

More than 100,000 tons of 2,4,6-trinitrotoluene were produced at the former ammunition site Werk Tanne in Clausthal-Zellerfeld, Germany. The production of explosives and consequent detonation in approximately 1944 by the Allies caused great pollution in this area. Four soil samples and three water samples were taken from this site and characterized by applying chemical-analytical methods and several bioassays. Ecotoxicological test systems, such as the algal growth inhibition assay with Desmodesmus subspicatus, and genotoxicity tests, such as the umu and NM2009 tests, were performed. Also applied were the Ames test, according to International Organization for Standardization 16240, and an Ames fluctuation test. The toxic mode of action was examined using bacterial gene profiling assays with a battery of Escherichia coli strains and with the human liver cell line hepG2 using the PIQOR Toxicology cDNA microarray. Additionally, the molecular mechanism of 2,4,6-trinitrotoluene in hepG2 cells was analyzed. The present assessment indicates a danger of pollutant leaching for the soil-groundwater path. A possible impact for human health is discussed, because the groundwater in this area serves as drinking water.

Validation of Arxula Yeast Estrogen Screen assay for detection of estrogenic activity in water samples: Results of an international interlaboratory study

Endocrine-active substances can adversely impact the aquatic ecosystems. A special emphasis is laid, among others, on the effects of estrogens and estrogen mimicking compounds. Effect-based screening methods like in vitro bioassays are suitable tools to detect and quantify endocrine activities of known and unknown mixtures. This study describes the validation of the Arxula-Yeast Estrogen Screen (A-YES®) assay, an effect-based method for the detection of the estrogenic potential of water and waste water. This reporter gene assay, provided in ready to use format, is based on the activation of the human estrogen receptor alpha. The user-friendly A-YES® enables inexperienced operators to rapidly become competent with the assay. Fourteen laboratories from four countries with different training levels analyzed 17β-estradiol equivalent concentrations (EEQ) in spiked and unspiked waste water effluent and surface water samples, in waste water influent and spiked salt water samples and in a mixture of three bisphenols. The limit of detection (LOD) for untreated samples was 1.8ng/L 17β-estradiol (E2). Relative repeatability and reproducibility standard deviation for samples with EEQ above the LOD (mean EEQ values between 6.3 and 20.4ng/L) ranged from 7.5 to 21.4% and 16.6 to 28.0%, respectively. Precision results are comparable to other frequently used analytical methods for estrogens. The A-YES® has been demonstrated to be an accurate, precise and robust bioassay. The results have been included in the ISO draft standard. The assay was shown to be applicable for testing of typical waste water influent, effluent and saline water. Other studies have shown that the assay can be used with enriched samples, which lower the LOD to the pg/L range. The validation of the A-YES® and the development of a corresponding international standard constitute a step further towards harmonized and reliable bioassays for the effect-based analysis of estrogens and estrogen-like compounds in water samples.

An improved electrochemical aptasensor for chloramphenicol detection based on aptamer incorporated gelatine

Because of the biocompatible properties of gelatine and the good affinity of aptamers for their targets, the combination of aptamer and gelatine type B is reported as promising for the development of biosensing devices. Here, an aptamer for chloramphenicol (CAP) is mixed with different types of gelatine and dropped on the surface of disposable gold screen printed electrodes. The signal of the CAP reduction is investigated using differential pulse voltammetry. The diagnostic performance of the sensor is described and a detection limit of 1.83 × 10⁻¹⁰ M is found. The selectivity and the stability of the aptasensor are studied and compared to those of other CAP sensors described in literature.

A novel active-passive sampling approach for measuring time-averaged concentrations of pollutants in water

Passive sampling with in situ devices offers several advantages over traditional sampling methods (i.e., discrete spot sampling), however, data interpretation from conventional passive samplers is hampered by difficulties in estimating the thickness of the diffusion layer at the sampler/medium interface (δ), often leading to inaccurate determinations of target analyte concentrations. In this study, the performance of a novel device combining active and passive sampling was investigated in the laboratory. The active-passive sampling (APS) device is comprised of a diffusion cell fitted with a pump and a flowmeter. Three receiving phases traditionally used in passive sampling devices (i.e., chelex resin, Oasis HLB, and silicone rubber), were incorporated in the diffusion cell and allowed the simultaneous accumulation of cationic metals, polar, and non-polar organic compounds, respectively. The flow within the diffusion cell was accurately controlled and monitored, and, combined with diffusion coefficients measurements, enabled the average δ to be estimated. Strong agreement between APS and time-averaged total concentrations measured in discrete water samples was found for most of the substances investigated. Accuracies for metals ranged between 87 and 116%, except Cu and Pb (∼50%), whilst accuracies between 64 and 101%, and 92 and 151% were achieved for polar and non-polar organic compounds, respectively. These results indicate that, via a well-defined in situ preconcentration step, the proposed APS approach shows promise for monitoring the concentration of a range of pollutants in water.

Prokaryotic gene profiling assays to detect sediment toxicity: evaluating the ecotoxicological relevance of a cell-based assay

Despite their complexity, ecotoxicological measurements using higher level responses remain a major tool in the assessment of ecosystem integrity. Nevertheless, the past decade saw an increasing number of cell based testing systems have found widespread application in ecotoxicology. One such test is bacterial bioreporters carrying a stress sensitive promoter fused to an easily detectable reporter gene. In the presence of a specific toxic stress,the expression cassette is switched on and the reporter gene is produced. This study evaluated the use of 14 different Escherichia coli bioreporter strains sensitive to different types of toxicity in the assessment of the ecological status of a small river basin in Flanders, Belgium. The river is fed at two geographically separate locations by two distinct and well-described effluents, one from a household sewage treatment facility and one from the discharge of the wastewater treatment facility of a large chemical plant. The results of the bacterial gene profiling assay were related to active biomonitoring results obtained through higher-level responses of caged Dreissena polymorpha, Chironomus riparius, and Cyprinus carpio deployed at the locations sampled for the bacterial assay. The results of the gene induction assay and the active biomonitoring data correlated well and corresponded to the flow dilution data, which is used here as a surrogate forthe chemical pollution gradient present in the river basin.

Mode of action clustering of chemicals and environmental samples on the bases of bacterial stress gene inductions

Over the years, environment and the human population have seen an increasing exposure to both existing and newly developed chemicals. It is generally accepted that at least some of those are toxic, albeit as pure compound or in combination with others. In response to a growing public awareness and scientific data, the new European chemicals legislation (Registration, Evaluation and Authorization of Chemicals) is under implementation at the moment. As a consequence, during the coming years about 30,000 chemicals have to be assessed on their potential hazard for man and biota. Part of this assessment will be done using existing and new in vitro tests offering insight into the toxicity of chemicals and into their toxicological mode of action. This study presents data on a battery of 14 bacterial reporter gene assay allowing mode of action determination and statistical grouping of chemicals based on their induction profile. Gene induction results are used to group reference chemicals in a statistical cascade employing hierarchical tree and k-means clustering for initial grouping. Both complementary, yet mathematically different, algorithms are consequently confirmed by principal component analysis (PCA). The gene induction profiles of an environmental extract with documented in vivo effects and a chemical with limited toxicological are data available and projected in the PCA vector space. The projection allows correct mode of action grouping and indicates that effect predictions based on the known toxicological effects of the reference compounds can be made.

The impact of metal pollution on soil faunal and microbial activity in two grassland ecosystems

In this study the influence of metal pollution on soil functional activity was evaluated by means of Bait lamina and BIOLOG(®) EcoPlates™ assays. The in situ bait lamina assay investigates the feeding activity of macrofauna, mesofauna and microarthropods while the BIOLOG(®) EcoPlate™ assay measures the metabolic fingerprint of a selectively extracted microbial community. Both assays proved sensitive enough to reveal changes in the soil community between the plots nearest to and further away from a metal pollution source. Feeding activity (FA) at the less polluted plots reached percentages of 90% while plots nearer to the source of pollution reached percentages as low as 10%. After 2 and 6 days of incubation average well color development (AWCD) and functional richness (R') were significantly lower at the plots closest to the source of pollution. While the Shannon Wiener diversity index (H') decreased significantly at sites nearer to the source of pollution after 2 days but not after 6 days of incubation. Arsenic, Cu and Pb correlated significantly and negatively with feeding activity and functional indices while the role of changing environmental factors such as moisture percentage could not be ruled out completely. Compared to the Bait lamina method that is used in situ and which is therefore more affected by site specific variation, the BIOLOG assay, which excludes confounding factors such as low moisture percentage, may be a more reliable assay to measure soil functional activity.

Dose-response relationships and statistical performance of a battery of bacterial gene profiling assays

Because of increasing awareness and legislative demands, there is a demand for the development and use of biological assays for the assessment of the toxicity of chemicals, environmental samples. Recently, a growing number of bacterial reporter assays have been developed and implemented. Nevertheless, little data is published on the performance of these assays in terms of analytical parameters. We present results on a battery of 14 transgenic Escherichia coli strains carrying different promoter::reporter fusions. Growth characteristics and basal expression levels were modeled and fitted, data show that growth curves should be taken into account during test development. Our study shows that the induction profiles reflect the mode of action, e.g., paraquat clearly induces the soxRS operon. The sensitivity of the assay compares well to that of whole organism tests, e.g., fish and Daphnia for polar organics. Metal toxicity is detected less efficiently, e.g., cadmium is detected near the LC50 of carp, considered a relatively insensitive species towards cadmium. The assay variability ranges from 10 to 40% depending on the strain, comparable to that of other bioassays. The variability was shown to be determined by the intrinsic traits of the promoter-strain combination, not by operating conditions.

Mixture toxicity and gene inductions: can we predict the outcome?

As a consequence of the nature of most real-life exposure scenarios, the last decade of ecotoxicological research has seen increasing interest in the assessment of mixture ecotoxicology. Often, mixtures are considered to follow one of two models, concentration addition (CA) or response addition (RA), both of which have been described in the literature. Nevertheless, mixtures that deviate from either or both models exist; they typically exhibit phenomena like synergism, ratio or concentration dependency, or inhibition. Moreover, both CA and RA have been challenged and evaluated mainly for acute responses at relatively high levels of biological organization (e.g., whole-organism mortality), and applicability to genetic responses has not received much attention. Genetic responses are considered to be the primary reaction in case of toxicant exposure and carry valuable mechanistic information. Effects at the gene-expression level are at the heart of the mode of action by toxicants and mixtures. The ability to predict mixture responses at this primary response level is an important asset in predicting and understanding mixture effects at different levels of biological organization. The present study evaluated the applicability of mixture models to stress gene inductions in Escherichia coli employing model toxicants with known modes of action in binary combinations. The results showed that even if the maximum of the dose-response curve is not known, making a classical ECx (concentration causing x% effect) approach impossible, mixture models can predict responses to the binary mixtures based on the single-toxicant response curves. In most cases, the mode of action of the toxicants does not determine the optimal choice of model (i.e., CA, RA, or a deviation thereof).

Field application of a novel active-passive sampling technique for the simultaneous measurement of a wide range of contaminants in water

A first test of the field capabilities of a novel in situ sampling technique combining active and passive sampling (APS) was conducted in the sea. The proof-of-concept device uses a pump to draw water into a diffusion cell where dissolved target substances are accumulated onto sorbents which are selective for different classes of contaminants (i.e., metal cations, polar and non-polar organic compounds), simultaneously. A controlled laminar flow established in the diffusion cell enables measurements of contaminant concentrations that are fully independent from the hydrodynamic conditions in the bulk solution. APS measurements were consistent with those obtained using conventional passive sampling techniques such as organic diffusive gradients in thin films (o-DGT) and silicone rubber (SR) samplers (generally < 40% difference), taking into account the prevailing hydrodynamic conditions. The use of performance reference compounds (PRC) for hydrophobic contaminants provided additional information. Field measurements of metal ions in seawater showed large variability due to issues related to the device configuration. An improved field set-up deployed in supplementary freshwater mesocosm experiments provided metal speciation data that was consistent with passive sampling measurements (DGT), taking into account the hydrodynamic conditions. Overall, the results indicate that the APS technique provides a promising approach for the determination of a wide range of contaminants simultaneously, and independently from the hydrodynamic conditions in the bulk solution.

Mitigation of zinc leaching from waste ground tire rubbers through polymer encapsulation

The increasing disposal of waste tires is a growing environmental challenge requiring innovative recycling and reuse approaches. Crumb rubber, derived from end-of-life tires, has potential for various applications where resilience and elasticity are required. However, as highlighted by the upcoming ban on using crumb rubber granulate as infill for artificial turf in the EU, one of the most prominent issues, zinc leaching, urgently requires an effective solution. We studied a range of commercial polymer coatings as a zinc leaching barrier through batch and column leaching tests. This study demonstrates that coatings can reduce the leaching down to 1 % of that of uncoated rubber, reducing environmental risks while improving the prospects for continued use of crumb rubber in various applications. The physico-chemical relation between the coating structure and zinc leaching is elucidated for the most promising coatings by comparing the leaching results with FTIR, GPC and 1H NMR analyses. The use of certain additives shows a cumulative effect to further reduce zinc leaching, while improving UV- and moisture stability. Thermal stability is controlled by the stability of the polymer base. These findings allow us to tailor the mechanical properties to various applications requiring specific elasticity and durability, while retaining the versatility and adaptability of crumb rubber in a range of scenarios. Additionally, the use of additives, typically cheaper than the polymer matrix, enhances the economic viability. By effectively controlling zinc leaching and tailoring mechanical properties through coatings, this study offers a way to extend the life and utility of waste rubbers.

Characterization of the accumulation of metals and organic contaminants on a novel active-passive sampling device under controlled water flow conditions

Recently, a new sampling device combining active and passive sampling (APS) was developed for the measurement of time-averaged concentrations of metal species and both polar and non-polar organic contaminants in water. By coupling a diffusion cell (loaded with a set of sorbents selective for different substances) with a small pump and a flow meter, the APS device is able to perform in situ measurements that are independent of the hydrodynamic conditions in the exposure medium. In the present study, the diffusion layer thickness (δ) at the sorbent/solution interface within the diffusion cell was characterised under controlled flow conditions. Laboratory tests indicated that, in the range of flow rates investigated, the average diffusion layer thickness (δ¯) varied from ∼60 to ∼110 μm, depending on the type of substance measured and the position of the sorbent with respect to the flow direction. Due to its ability to maintain an approximately constant δ¯, good to excellent agreement was found between measurements performed with the APS device in non-complexing media and concentrations measured in discrete water samples for all the substances investigated. These results suggest that the APS device could overcome issues affecting the quantitative interpretation of measurements by conventional passive sampling devices and serve as a useful tool for simultaneously monitoring a wide range of contaminants in water.