Biosensors as early warning detection systems for waterborne Cryptosporidium.

Waterborne disease is a global health threat contributing to a high burden of diarrhoeal disease, and growing evidence indicates a prospective increase in incidence coinciding with the profound effects of climate change. A major causative agent of gastrointestinal disease is Cryptosporidium, a protozoan waterborne parasite identified in over 70 countries. Cryptosporidium is a cause of high disease morbidity in children and the immunocompromised with limited treatment options for patients at risk of severe illness. The hardy nature of the organism leads to its persistence in various water sources, with certain water treatment procedures proving inefficient for its complete removal. While diagnostic methods for Cryptosporidium are well-defined in the clinical sphere, detection of Cryptosporidium in water sources remains suboptimal due to low dispersion of organisms in large sample volumes, lengthy processing times and high costs of equipment and reagents. A need for improvement exists to identify the organism as an emerging threat in domestic water systems, and the technological advantages that biosensors offer over current analytical methods may provide a preventative approach to outbreaks of Cryptosporidium. Biosensors are innovative, versatile and adaptable analytical tools that could provide highly sensitive, rapid, on-site analysis needed for Cryptosporidium detection in low-resource settings.

Complexation-Based Detection of Nickel(II) at a Graphene-Chelate Probe in the Presence of Cobalt and Zinc by Adsorptive Stripping Voltammetry.

The adsorptive stripping voltammetric detection of nickel and cobalt in water samples at metal film electrodes has been extensively studied. In this work, a novel, environmentally friendly, metal-free electrochemical probe was constructed for the ultra-trace determination of Ni2+ in water samples by Adsorptive Cathodic Stripping Voltammetry (AdCSV). The electrochemical platform is based on the adsorptive accumulation of Ni2+ ions directly onto a glassy carbon electrode (GCE) modified with dimethylglyoxime (DMG) as chelating agent and a Nafion-graphene (NGr) nanocomposite to enhance electrode sensitivity. The nafion-graphene dimethylglyoxime modified glassy carbon electrode (NGr-DMG-GCE) shows superior detection capabilities as a result of the improved surface-area-to-volume ratio and enhanced electron transfer kinetics following the incorporation of single layer graphene, while limiting the toxic effects of the sensor by removal of the more common mercury, bismuth and lead films. Furthermore, for the first time the NGr-DMG-GCE, in the presence of common interfering metal ions of Co2+ and Zn2+ demonstrates good selectivity and preferential binding towards the detection of Ni2+ in water samples. Structural and morphological characterisation of the synthesised single layer graphene sheets was conducted by Raman spectrometry, HRTEM and HRSEM analysis. The instrumental parameters associated with the electrochemical response, including accumulation potential and accumulation time were investigated and optimised in addition to the influence of DMG and graphene concentrations. The NGr-DMG-GCE demonstrated well resolved, reproducible peaks, with RSD (%) below 5% and a detection limit of 1.5 µg L-1 for Ni2+ reduction at an accumulation time of 120 s., the prepared electrochemical sensor exhibited good detection and quantitation towards Ni2+ detection in tap water samples, well below 0.1 mg L-1 set by the WHO and EPA standards. This comparable to the South African drinking water guidelines of 0.15 mg L-1.

Electrochemical Aptatoxisensor Responses on Nanocomposites Containing Electro-Deposited Silver Nanoparticles on Poly(Propyleneimine) Dendrimer for the Detection of Microcystin-LR in Freshwater.

A sensitive and reagentless electrochemical aptatoxisensor was developed on cobalt (II) salicylaldiimine metallodendrimer (SDD-Co(II)) doped with electro-synthesized silver nanoparticles (AgNPs) for microcystin-LR (L, l-leucine; R, l-arginine), or MC-LR, detection in the nanomolar range. The GCE|SDD-Co(II)|AgNPs aptatoxisensor was fabricated with 5' thiolated aptamer through self-assembly on the modified surface of the glassy carbon electrode (GCE) and the electronic response was measured using cyclic voltammetry (CV). Specific binding of MC-LR with the aptamer on GCE|SDD-Co(II)|AgNPs aptatoxisensor caused the formation of a complex that resulted in steric hindrance and electrostatic repulsion culminating in variation of the corresponding peak current of the electrochemical probe. The aptatoxisensor showed a linear response for MC-LR between 0.1 and 1.1 µg·L-1 and the calculated limit of detection (LOD) was 0.04 µg·L-1. In the detection of MC-LR in water samples, the aptatoxisensor proved to be highly sensitive and stable, performed well in the presence of interfering analog and was comparable to the conventional analytical techniques. The results demonstrate that the constructed MC-LR aptatoxisensor is a suitable device for routine quantification of MC-LR in freshwater and environmental samples.

Environmental remediation of heavy metal ions from aqueous solution through hydrogel adsorption: a critical review.

Heavy metal ions such as Cd(2+), Pb(2+), Cu(2+), Mg(2+), and Hg(2+) from industrial waste water constitute a major cause of pollution for ground water sources. These ions are toxic to man and aquatic life as well, and should be removed from wastewater before disposal. Various treatment technologies have been reported to remediate the potential toxic elements from aqueous media, such as adsorption, precipitation and coagulation. Most of these technologies are associated with some shortcomings, and challenges in terms of applicability, effectiveness and cost. However, adsorption techniques have the capability of effectively removing heavy metals at very low concentration (1-100 mg/L). Various adsorbents have been reported in the literature for this purpose, including, to a lesser extent, the use of hydrogel adsorbents for heavy metal removal in aqueous phase. Here, we provide an in-depth perspective on the design, application and efficiency of hydrogel systems as adsorbents.

Aptameric Recognition-Modulated Electroactivity of Poly(4-Styrenesolfonic Acid)-Doped Polyaniline Films for Single-Shot Detection of Tetrodotoxin.

The work being reported is the first electrochemical sensor for tetrodotoxin (TTX). It was developed on a glassy carbon electrodes (C) that was modified with poly(4-styrenesolfonic acid)-doped polyaniline film (PANI/PSSA). An amine-end functionalized TTX-binding aptamer, 5'-NH2-AAAAATTTCACACGGGTGCCTCGGCTGTCC-3' (NH2-Apt), was grafted via covalent glutaraldehyde (glu) cross-linking. The resulting aptasensor (C//PANI⁺/PSSA-glu-NH2-Apt) was interrogated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in sodium acetate buffer (NaOAc, pH 4.8) before and after 30 min incubation in standard TTX solutions. Both CV and EIS results confirmed that the binding of the analyte to the immobilized aptamer modulated the electrochemical properties of the sensor: particularly the charge transfer resistance (Rct) of the PANI⁺/PSSA film, which served as a signal reporter. Based on the Rct calibration curve of the TTX aptasensor, the values of the dynamic linear range (DLR), sensitivity and limit of detection (LOD) of the sensor were determined to be 0.23-1.07 ng·mL(-1) TTX, 134.88 ± 11.42 Ω·ng·mL(-1) and 0.199 ng·mL(-1), respectively. Further studies are being planned to improve the DLR as well as to evaluate selectivity and matrix effects in real samples.

A fumonisins immunosensor based on polyanilino-carbon nanotubes doped with palladium telluride quantum dots.

An impedimetric immunosensor for fumonisins was developed based on poly(2,5-dimethoxyaniline)-multi-wall carbon nanotubes doped with palladium telluride quantum dots onto a glassy carbon surface. The composite was assembled by a layer-by-layer method to form a multilayer film of quantum dots (QDs) and poly(2,5-dimethoxyaniline)-multi-wall carbon nanotubes (PDMA-MWCNT). Preparation of the electrochemical immunosensor for fumonisins involved drop-coating of fumonisins antibody onto the composite modified glassy carbon electrode. The electrochemical impedance spectroscopy response of the FB1 immunosensor (GCE/PT-PDMA-MWCNT/anti-Fms-BSA) gave a linear range of 7 to 49 ng L-1 and the corresponding sensitivity and detection limits were 0.0162 kΩ L ng-1 and 0.46 pg L-1, respectively, hence the limit of detection of the GCE/PT-PDMA-MWCNT immunosensor for fumonisins in corn certified material was calculated to be 0.014 and 0.011 ppm for FB1, and FB2 and FB3, respectively. These results are lower than those obtained by ELISA, a provisional maximum tolerable daily intake (PMTDI) for fumonisins (the sum of FB1, FB2, and FB3) established by the Joint FAO/WHO expert committee on food additives and contaminants of 2 µg kg-1 and the maximum level recommended by the U.S. Food and Drug Administration (FDA) for protection of human consumption (2-4 mg L-1).

Efficient Electrochemiluminescence Sensing in Microfluidic Biosensors: A Review.

Microfluidic devices are capable of handling 10-9 L to 10-18 L of fluids by incorporating tiny channels with dimensions of ten to hundreds of micrometers, and they can be fabricated using a wide range of materials including glass, silicon, polymers, paper, and cloth for tailored sensing applications. Microfluidic biosensors integrated with detection methods such as electrochemiluminescence (ECL) can be used for the diagnosis and prognosis of diseases. Coupled with ECL, these tandem devices are capable of sensing biomarkers at nanomolar to picomolar concentrations, reproducibly. Measurement at this low level of concentration makes microfluidic electrochemiluminescence (MF-ECL) devices ideal for biomarker detection in the context of early warning systems for diseases such as myocardial infarction, cancer, and others. However, the technology relies on the nature and inherent characteristics of an efficient luminophore. The luminophore typically undergoes a redox process to generate excited species which emit energy in the form of light upon relaxation to lower energy states. Therefore, in biosensor design the efficiency of the luminophore is critical. This review is focused on the integration of microfluidic devices with biosensors and using electrochemiluminescence as a detection method. We highlight the dual role of carbon quantum dots as a luminophore and co-reactant in electrochemiluminescence analysis, drawing on their unique properties that include large specific surface area, easy functionalization, and unique luminescent properties.

Conducting polyamic acid membranes for sensing and site-directed immobilization of proteins.

A biosensor platform based on polyamic acid (PAA) is reported for oriented immobilization of biomolecules. PAA, a functionalized conducting polymer substrate that provides electrochemical detection and control of biospecific binding, was used to covalently attach biomolecules, resulting in a significant improvement in the detection sensitivity. The biosensor sensing elements comprise a layer of PAA antibody (or antigen) composite self-assembled onto gold (Au) electrode via N-hydroxysuccinimide (NHS) and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) linking. The modified PAA was characterized by Fourier transform infrared (FTIR), (1)H nuclear magnetic resonance (NMR), and electrochemical techniques. Cyclic voltammetry and impedance spectroscopy experiments conducted on electrodeposited PAA on Au electrode using ferricyanide produced a measurable decrease in the diffusion coefficient compared with the bare electrode, indicating some retardation of electron transfer within the bulk material of the PAA. Thereafter, the modified PAA surface was used to immobilize antibodies and then to detect inducible nitric oxide synthase and mouse immunoglobulin G (IgG) using enzyme-linked immunosorbent assay (ELISA), surface plasmon resonance (SPR), and amperometric techniques. ELISA results indicated a significant amplified signal by the modified PAA, whereas the SPR and amperometric biosensors produced significant responses as the concentration of the antigen was increased. Detection limits of 3.1×10(-3)ng/ml and 2.7×10(-1)ng/ml were obtained for SPR and amperometric biosensors, respectively.

Humidity Sensing Applications of Lead-Free Halide Perovskite Nanomaterials.

Over the past decade, perovskite-based nanomaterials have gained notoriety within the scientific community and have been used for a variety of viable applications. The unique structural properties of these materials, namely good direct bandgap, low density of defects, large absorption coefficient, high sensitivity, long charge carrier lifetime, good selectivity, acceptable stability at room temperature, and good diffusion length have prompted researchers to explore their potential applications in photovoltaics, light-emitting devices, transistors, sensors, and other areas. Perovskite-based devices have shown very excellent sensing performances to numerous chemical and biological compounds in both solid and liquid mediums. When used in sensing devices, Perovskite nanomaterials are for the most part able to detect O2, NO2, CO2, H2O, and other smaller molecules. This review article looks at the use of lead-free halide perovskite materials for humidity sensing. A complete description of the underlying mechanisms and charge transport characteristics that are necessary for a thorough comprehension of the sensing performance will be provided. An overview of considerations and potential recommendations for the creation of new lead-free perovskite nanostructure-based sensors is presented.

Metallo-graphene nanocomposite electrocatalytic platform for the determination of toxic metal ions.

A Nafion-Graphene (Nafion-G) nanocomposite solution in combination with an in situ plated mercury film electrode was used as a highly sensitive electrochemical platform for the determination of Zn(2+), Cd(2+), Pb(2+) and Cu(2+) in 0.1 M acetate buffer (pH 4.6) by square-wave anodic stripping voltammetry (SWASV). Various operational parameters such as deposition potential, deposition time and electrode rotation speed were optimized. The Nafion-G nanocomposite sensing platform exhibited improved sensitivity for metal ion detection, in addition to well defined, reproducible and sharp stripping signals. The linear calibration curves ranged from 1 µg L(-1) to 7 µg L(-1) for individual analysis. The detection limits (3σ blank/slope) obtained were 0.07 µg L(-1) for Pb(2+), Zn(2+) and Cu(2+) and 0.08 µg L(-1) for Cd(2+) at a deposition time of 120 s. For practical applications recovery studies was done by spiking test samples with known concentrations and comparing the results with inductively coupled plasma mass spectrometry (ICP-MS) analyses. This was followed by real sample analysis.

Spectroscopy, Morphology, and Electrochemistry of Electrospun Polyamic Acid Nanofibers.

Polyamic acid (PAA) nanofibers produced by using the electrospinning method were fully characterized in terms of morphology and spectroscopy. A PAA nanofiber-modified screen-printed carbon electrode was applied to the detection of selected sulfonamides by following an electroanalytical protocol. The polyamic acid (PAA) nanofibers were characterized using Fourier transform infrared (FTIR) spectroscopy to study the integrity of polyamic acid functional groups as nanofibers by comparing them to chemically synthesized polyamic acid. A scanning electron microscope (SEM) was used to confirm the morphology of the produced nanofibers and 3D arrangement at the electrode interface. The Brunauer-Emmett-Teller (BET) method was used to determine the surface area of the nanofibers. Atomic force microscopy (AFM) was used to study the porosity and surface roughness of the nanofibers. Electrochemical evaluation based on diffusion-controlled kinetics was applied to determine the number of electrons transferred in the system, the surface concentration of the deposited PAA thin film (2.14 × 10-6 mol/cm2), and the diffusion coefficient (De) for the PAA nanofiber-modified screen-printed carbon electrode (9.43 × 10-7 cm-2/s). The reported LODs for sulfadiazine and sulfamethazine detection are consistent with requirements for trace-level monitoring by early warning diagnostic systems.

Electrochemical application of cobalt nanoparticles-polypyrrole composite modified electrode for the determination of phoxim.

In this study, cobalt nanoparticles (CoNPs) were synthesized and cobalt nanoparticles modified glassy carbon electrode (CoNPs/GCE) was prepared by drop coating the nanoparticles on glassy carbon electrode. After preparing polypyrrole modified glassy carbon electrode (PPy/GCE) using electropolymerization of pyrrole in LiClO4 solution, cobalt nanoparticles-polypyrrole composite modified glassy carbon electrode (CoNPs/PPy/GCE) was fabricated by drop coating the CoNPs on the PPy/GCE. Different characterization techniques such as scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, FTIR spectroscopy, electrochemical impedance spectroscopy and cyclic voltammetry were used to study the morphological structure and electrochemical behavior of the sensors. The results demonstrated that PPy chains interacted with CoNPs through donor-acceptor bonds. Among all the electrodes, CoNPs/PPy/GCE exhibited highest electroactive surface area and lowest electron transfer resistance towards phoxim. Under the optimal conditions, the sensor showed linear relationship between the reduction peak current and the concentration of phoxim in the range of 0.025 µM-12 µM with the detection limit as 4.5 nM. Besides, the composite electrode demonstrated excellent reproducibility, good stability and selectivity towards the possible interfering substances. All of these properties made CoNPs/PPy/GCE a suitable electrochemical sensor for the electrochemical determination of phoxim in water samples using square wave voltammetry.

Determination of anthracene on Ag-Au alloy nanoparticles/overoxidized-polypyrrole composite modified glassy carbon electrodes.

A novel electrochemical sensor for the detection of anthracene was prepared by modifying a glassy carbon electrode (GCE) with over-oxidized polypyrrole (PPyox) and Ag-Au (1:3) bimetallic nanoparticles (Ag-AuNPs). The composite electrode (PPyox/Ag-AuNPs/GCE) was prepared by potentiodynamic polymerization of pyrrole on GCE followed by its overoxidation in 0.1 M NaOH. Ag-Au bimetallic nanoparticles were chemically prepared by the reduction of AgNO(3) and HAuCl(4) using C(6)H(5)O(7)Na(3) as the reducing agent as well as the capping agent and then immobilized on the surface of the PPyox/GCE. The nanoparticles were characterized by UV-visible spectroscopy technique which confirmed the homogeneous formation of the bimetallic alloy nanoparticles. Transmission electron microscopy showed that the synthesized bimetallic nanoparticles were in the range of 20-50 nm. The electrochemical behaviour of anthracene at the PPyox/Ag-AuNPs/GCE with Ag: Au atomic ratio 25:75 (1:3) exhibited a higher electrocatalytic effect compared to that observed when GCE was modified with each constituent of the composite (i.e., PPyox, Ag-AuNPs) and bare GCE. A linear relationship between anodic current and anthracene concentration was attained over the range of 3.0 × 10(-6) to 3.56 × 10(-4) M with a detection limit of 1.69 × 10(-7) M. The proposed method was simple, less time consuming and showed a high sensitivity.

Electrochemical aptasensor for endocrine disrupting 17ß-estradiol based on a poly(3,4-ethylenedioxylthiopene)-gold nanocomposite platform.

A simple and highly sensitive electrochemical DNA aptasensor with high affinity for endocrine disrupting 17ß-estradiol, was developed. Poly(3,4-ethylenedioxylthiophene) (PEDOT) doped with gold nanoparticles (AuNPs) was electrochemically synthesized and employed for the immobilization of biotinylated aptamer towards the detection of the target. The diffusion coefficient of the nanocomposite was 6.50 × 10(-7) cm(2) s(-1), which showed that the nanocomposite was highly conducting. Electrochemical impedance investigation also revealed the catalytic properties of the nanocomposite with an exchange current value of 2.16 × 10(-4) A, compared to 2.14 × 10(-5) A obtained for the bare electrode. Streptavidin was covalently attached to the platform using carbodiimide chemistry and the aptamer immobilized via streptavidin-biotin interaction. The electrochemical signal generated from the aptamer-target molecule interaction was monitored electrochemically using cyclic voltammetry and square wave voltammetry in the presence of [Fe(CN)(6)](-3/-4) as a redox probe. The signal observed shows a current decrease due to interference of the bound 17ß-estradiol. The current drop was proportional to the concentration of 17ß-estradiol. The PEDOT/AuNP platform exhibited high electroactivity, with increased peak current. The platform was found suitable for the immobilization of the DNAaptamer. The aptasensor was able to distinguish 17ß-estradiol from structurally similar endocrine disrupting chemicals denoting its specificity to 17ß-estradiol. The detectable concentration range of the 17ß-estradiol was 0.1 nM-100 nM, with a detection limit of 0.02 nM.

Impedimetric and electrochemical evaluation of a new redox active steroid derivative for hormone immunosensing.

Preparation and electrochemical interrogation of a novel redox active progesterone derivative progesterone thiosemicarbazone (PATC) is presented here together with an investigation into its suitability as conjugate in progesterone hormone immunosensing. PATC synthesis involved a condensation reaction between progesterone acetate and thiosemicarbazone hydrochloride. Voltammetric and pulse techniques confirmed the redox behaviour of the new compound with concentration and scan rate dependant irreversible behaviour evident at glassy carbon and gold transducers - ko (standard heterogeneous rate constant) was 2.56 × 10-3 cm2/s (ν = 100 mV/s in non-aqeuous media). Bioaffinity studies towards anti-progesterone antibodies involved a competitive ELISA format (optical) which confirmed recognition of the new progesterone derivative. Electrochemical impedance spectroscopy was employed as an interrogation technique in order to establish optimum binding and surface conditions for progesterone antigen-antibody interaction with the assistance of a redox probe (potassium hexacyanoferrate).

Polyester sulphonic Acid interstitial nanocomposite platform for peroxide biosensor.

A novel enzyme immobilization platform was prepared on a platinum disk working electrode by polymerizing aniline inside the interstitial pores of polyester sulphonic acid sodium salt (PESA). Scanning electron microscopy study showed the formation of homogeneous sulphonated polyaniline (PANI) nanotubes (∼90 nm) and thermogravimetric analysis (TGA) confirmed that the nanotubes were stable up to 230 °C. The PANI:PESA nanocomposite showed a quasi-reversible redox behaviour in phosphate buffer saline. Horseradish peroxidase (HRP) was immobilized on to this modified electrode for hydrogen peroxide detection. The biosensor gave a sensitivity of 1.33 µA (µM)(-1) and a detection limit of 0.185 µM for H(2)O(2). Stability experiments showed that the biosensor retained more than 64% of its initial sensitivity over four days of storage at 4 °C.

An Electrochemical DNA Biosensor Developed on a Nanocomposite Platform of Gold and Poly(propyleneimine) Dendrimer.

An electrochemical DNA nanobiosensor was prepared by immobilization of a 20mer thiolated probe DNA on electro-deposited generation 4 (G4) poly(propyleneimine) dendrimer (PPI) doped with gold nanoparticles (AuNP) as platform, on a glassy carbon electrode (GCE). Field emission scanning electron microscopy results confirmed the codeposition of PPI (which was linked to the carbon electrode surface by C-N covalent bonds) and AuNP ca 60 nm. Voltammetric interrogations showed that the platform (GCE/PPI-AuNP) was conducting and exhibited reversible electrochemistry (E°' = 235 mV) in pH 7.2 phosphate buffer saline solution (PBS) due to the PPI component. The redox chemistry of PPI was pH dependent and involves a two electron, one proton process, as interpreted from a 28 mV/pH value obtained from pH studies. The charge transfer resistance (Rct) from the electrochemical impedance spectroscopy (EIS) profiles of GCE/PPI-AuNP monitored with ferro/ferricyanide (Fe(CN)63-/4-) redox probe, decreased by 81% compared to bare GCE. The conductivity (in PBS) and reduced Rct (in Fe(CN)63-/4-) values confirmed PPI-AuNP as a suitable electron transfer mediator platform for voltammetric and impedimetric DNA biosensor. The DNA probe was effectively wired onto the GCE/PPI-AuNP via Au-S linkage and electrostatic interactions. The nanobiosensor responses to target DNA which gave a dynamic linear range of 0.01 - 5 nM in PBS was based on the changes in Rct values using Fe(CN)63-/4- redox probe.

Electrochemical Immunosensor Based on Polythionine/Gold Nanoparticles for the Determination of Aflatoxin B1.

An aflatoxin B1 (AFB1) electrochemical immunosensor was developed by the immobilisation of aflatoxin B1-bovine serum albumin (AFB1-BSA) conjugate on a polythionine (PTH)/gold nanoparticles (AuNP)-modified glassy carbon electrode (GCE). The surface of the AFB1-BSA conjugate was covered with horseradish peroxidase (HRP), in order to prevent non-specific binding of the immunosensors with ions in the test solution. The AFB1 immunosensor exhibited a quasi-reversible electrochemistry as indicated by a cyclic voltammetric (CV) peak separation (ΔEp) value of 62 mV. The experimental procedure for the detection of AFB1 involved the setting up of a competition between free AFB1 and the immobilised AFB1-BSA conjugate for the binding sites of free anti-aflatoxin B1 (anti-AFB1) antibody. The immunosensor's differential pulse voltammetry (DPV) responses (peak currents) decreased as the concentration of free AFB1 increased within a dynamic linear range (DLR) of 0.6 - 2.4 ng/mL AFB1 and a limit of detection (LOD) of 0.07 ng/mL AFB1. This immunosensing procedure eliminates the need for enzyme-labeled secondary antibodies normally used in conventional ELISA-based immunosensors.

Bioaccumulation of total mercury in the earthworm Eisenia andrei.

Earthworms are a major part of the total biomass of soil fauna and play a vital role in soil maintenance. They process large amounts of plant and soil material and can accumulate many pollutants that may be present in the soil. Earthworms have been explored as bioaccumulators for many heavy metal species such as Pb, Cu and Zn but limited information is available for mercury uptake and bioaccumulation in earthworms and very few report on the factors that influence the kinetics of Hg uptake by earthworms. It is known however that the uptake of Hg is strongly influenced by the presence of organic matter, hence the influence of ligands are a major factor contributing to the kinetics of mercury uptake in biosystems. In this work we have focused on the uptake of mercury by earthworms (Eisenia andrei) in the presence of humic acid (HA) under varying physical conditions of pH and temperature, done to assess the role of humic acid in the bioaccumulation of mercury by earthworms from soils. The study was conducted over a 5-day uptake period and all earthworm samples were analysed by direct mercury analysis. Mercury distribution profiles as a function of time, bioaccumulation factors (BAFs), first order rate constants and body burden constants for mercury uptake under selected conditions of temperature, pH as well as via the dermal and gut route were evaluated in one comprehensive approach. The results showed that the uptake of Hg was influenced by pH, temperature and the presence of HA. Uptake of Hg(2+) was improved at low pH and temperature when the earthworms in soil were in contact with a saturating aqueous phase. The total amount of Hg(2+) uptake decreased from 75 to 48 % as a function of pH. For earthworms in dry soil, the uptake was strongly influenced by the presence of the ligand. Calculated BAF values ranged from 0.1 to 0.8. Mercury uptake typically followed first order kinetics with rate constants determined as 0.2 to 1 h(-1).

Label Free Poly(2,5-dimethoxyaniline)-Multi-Walled Carbon Nanotubes Impedimetric Immunosensor for Fumonisin B1 Detection.

An impedimetric immunosensor for fumonisin B1 (FB1) was developed from a poly(2,5-dimethoxyaniline)-multi-walled carbon nanotube (PDMA-MWCNT) composite on the surface of glassy carbon electrode (GCE). The composite was prepared electrochemically and characterized using cyclic voltammetry. The preparation of the FB1 immunosensor involved the drop-coating of a bovine serum albumin mixture of the anti-fumonisin antibody (anti-Fms) onto the composite polymer-modified GCE. The electrochemical impedance spectroscopy (EIS) responses of the FB1 immunosensor (GCE/PDMA-MWCNT/anti-Fms) have a linear range of 7 to 49 ng·L-1, and the corresponding sensitivity and detection limits are 0.272 kΩ L·ng-1 and 3.8 pg·L-1, respectively. The limit of detection of the immunosensor for certified corn sample (i.e., certified reference material) is 0.014 ppm FB1, which is in excellent agreement with the value published by the vendors and significantly more accurate than that obtained with enzyme-linked immunosorbent assay (ELISA).