Linear Sweep Anodic Stripping Voltammetry Research Articles

Ionic liquid-modified multi-walled carbon nanotube paste electrode for cadmium and lead ion determinations

The detection of trace heavy metal ions is important in monitoring water quality, a vital freshwater source. This study presents the preparation of a multi-walled carbon nanotube (MWCNTs) paste electrode using a pasting mixture of 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid ([Bmim][PF6] IL) and paraffin oil for the determination of Cd2+ and Pb2+. Scanning electron microscopy, Fourier-transform infrared spectroscopy, and Raman spectroscopy were applied to characterize the paste composites. The electrochemical behavior of the fabricated electrodes was analyzed by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques. The [Bmim][PF6]-MWCNTs electrode showed enhanced sensitivity for Cd2+ and Pb2+ detections over linear sweep anodic stripping voltammetry (LSASV) performances. Experimental results showed that the MWCNTs-IL-1 electrode using a pasting mixture of 10 μL of [Bmim][PF6] and 190 μL of paraffin oil was the most suitable for Cd2+ and Pb2+ determinations. The LSASV conditions for Cd2+ and Pb2+ analysis at the MWCNTs-IL-1 electrode were optimized, including the deposition potential, deposition time, and pH of the working solution. The stripping peak currents were linearly correlated with the concentration ranges of Cd2+ (1–35 μg/L) and Pb2+ (1–90 μg/L) for both individual and simultaneous determinations. The MWCNTs-IL-1 electrode exhibited high repeatability, reproducibility, and stability over a 30-day storage period. The real applicability of the MWCNTs-IL-1 electrode was demonstrated by successful determinations of Cd2+ and Pb2+ concentrations in tap water and surface water samples, which agreed with the results obtained by inductively coupled plasma mass spectrometry.

Immunoassay based on peroxidase silver conjugate for the determination of human immunoglobulins against tick‐borne borreliosis (lyme disease) by voltammetry and spectrophotometry

AbstractIn this work two strategies for the synthesis of peroxidase silver conjugates for the qualitative and quantitative determination of immunoglobulins (IgG) to ixodid tick‐borne borreliosis (ITBB) (Lyme disease) in human serum were proposed. The first approach for Ab‐HRP@AgNP conjugate synthesis involved silver nanoparticles (Ag NPs) capped with a commercial peroxidase conjugate (Ab‐HRP) by passive adsorption. The second strategy was based on the initial coupling of Ag NPs with human anti‐species antibodies (Ab) by passive adsorption followed by the introduction of horseradish peroxidase (HRP) enzyme into the reaction mixture as a blocking reagent for Ab@AgNP@HRP conjugate synthesis. The formation of peroxidase silver conjugates was proved by UV/Vis spectroscopy and Transmission Electron Microscopy (TEM). The catalytic activity of Ab‐HRP@AgNP and Ab@AgNP@HRP conjugates was evaluated by Michaelis‐Menten kinetics. A commercially available 96‐well microtiter plate with recombinant antigens to ITBB was used as a platform for immobilization of analyzed IgG. The HRP in Ab‐HRP@AgNP conjugate was found to retain a sufficient level of activity for interaction with the H2O2 substrate to form an intensely colored reaction product. Therefore Ab‐HRP@AgNP conjugate can be used in enzyme‐linked immunosorbent assay (ELISA) with spectrophotometric detection of 3,3’,5,5’‐Tetramethylbenzidine (TMB Ox) for quantitative determination of IgG to ITBB in human serum in the concentration range 12.5–800 ng ml−1 with LOD 2 ng ml−1. Ab@AgNP@HRP conjugate is recommended for the electrochemical determination of IgG to ITBB in human serum at LOD 3 ng ml−1 with registration of silver oxidation by linear sweep anodic stripping voltammetry (LSASV). Ag NPs in Ab‐HRP@AgNP and Ab@AgNP@HRP conjugates do not change electrochemical activity during storage and can be used as an electrochemical label in LSASV method in case of HRP inactivation. The immunoassay based on peroxidase silver conjugates expands the analytical potential for the determination of IgG to ITBB especially during the period of increasing incidence.

In Situ Deposition of Gold Nanoparticles and L-Cysteine on Screen-Printed Carbon Electrode for Rapid Electrochemical Determination of As(III) in Water and Tea.

In this study, a screen-printed carbon electrode (SPCE) based on in situ deposition modification was developed for the sensitive, rapid, easy and convenient determination of As(III) in water and tea by linear sweep anodic stripping voltammetry (LSASV). The screen-printed carbon electrodes were placed in a solution consisting of As(III) solution, chlorauric acid and L-cysteine. Under certain electrical potential, the chloroauric acid was reduced to gold nanoparticles (AuNPs) on the SPCE. L-cysteine was self-assembled onto AuNPs and promoted the enrichment of As(III), thus enhancing the determination specificity and sensitivity of As(III). The method achieved a limit of determination (LOD) of 0.91 ppb (µg L-1), a linear range of 1~200 µg L-1, an inter-assay coefficient of variation of 5.3% and good specificity. The developed method was successfully applied to the determination of As(III) in tap water and tea samples, with a recovery rate of 93.8%~105.4%, and further validated by inductively coupled plasma mass spectrometry (ICP-MS). The developed method is rapid, convenient and accurate, holding great promise in the on-site determination of As(III) in tap water and tea leaves, and it can be extended to the detection of other samples.

An Au(111)-dominant polycrystalline gold/gold nanoparticles/1,8-naphthyridine/glassy carbon electrode for anodic stripping voltammetry determination of As(III)

We report the fabrication of a 1,8-naphthyridine (Naph), gold nanoparticles and then Au(111)-dominant polycrystalline gold (Au(111)dpg) modified glassy carbon electrode (GCE) for linear sweep anodic stripping voltammetry (LSASV) determination of As(III). An ultrathin film of Naph was chemically bonded on a GCE by electroreduction of Naph in acidic solution. The bipyridine group of Naph on the Naph/GCE can capture gold nanoparticles (AuNPs) by coordination adsorption and can then direct an Au(111) oriented crystalline growth during gold staining in HAuCl4–NH2OH solution, due to the different affinities of Au(110), Au(100) and Au(111) facets to the pyridine unit in Naph. The prepared Au(111)dpg/AuNPs/Naph/GCE and the control electrodes were characterized by electrochemical methods, X-ray photoelectron spectroscopy, X-ray diffraction and scanning electron microcopy. LSASV determination of As(III) was performed on the Au(111)dpg/AuNPs/Naph/GCE with high performance. Sensitivity values of 11.6 µA ppb–1 (2.3∼75 ppb) and 3.1 µA ppb–1 (2.3∼75 ppb), as well as limit of detection values of 0.15 ppb and 0.52 ppb (S/N = 3) were obtained on the basis of the LSASV oxidation signals of As(0)→As(III) and As(III)→As(V), respectively. The Au(111)dpg/AuNPs/Naph/GCE was applied for As(III) determination in river water samples with satisfied results.

A compact N-nitrosodiphenylamine imprinted sensor based on a Pd nanoparticles-MIP microsphere modified screen-printed graphene electrode

• A novel NDPhA imprinted sensor was firstly fabricated for sensitive and selective, determination of NDPhA. • NDPhA recognition sites were successfully furnished on PdNPs’ surface via 3D-imprinting technique. • The sensor is ready-to-use, cost-effective, flexibility, stability, and suited to large-scale production. Herein, we report the fabrication of a compact voltammetric sensor for the sensitive and selective determination of N -nitrosodiphenylamine (NDPhA) based on a screen-printed graphene electrode modified with a molecularly imprinted polymer coating on a palladium nanoparticle core (PdNPs@MIP/SPGrE). In addition, a novel approach for 3D-imprinting of NDPhA on the PdNPs surface is presented. PdNPs were first synthesized by chemical reduction using sodium borohydride. Then, Core-shell polymerization was achieved by successively coating the surface of PdNPs with poly(vinylpyrrolidone) and terminating with an MIP consisting of poly( N -Isopropylacrylamide)-co-trimethylolpropane trimethacrylate. Morphological, structural, and electrochemical characterization reveals that the as-prepared micro-sized spherical PdNPs@MIP has a uniform, high electro-catalytic activity and a specific surface area with many NDPhA imprinted sites. We constructed the compact NDPhA imprinted sensor by coating the SPGrE surface with PdNPs@MIP. Quantitative analysis was performed by linear sweep anodic stripping voltammetry (LSASV) using a deposition potential of +0.02 V for 60 s. The linear working ranges for NDPhA measurements were 0.01–0.1 μM (r 2 = 0.996) and 0.1–100 μM (r 2 = 0.992) with corresponding sensitivities of 51.935 and 0.821 (μA s) µM −1 , respectively. The system provides a good precision of %RSD 1.67% with an estimated detection limit (3S b , n = 3) of 0.0013 μM. The intraday and inter-day accuracy (%bias) of the certified reference material (CRM) are −0.74% and −1.01%, respectively. We demonstrate the successful application of the fabricated compact sensor to determine NDPhA in beverage and synthetic samples. The compact NDPhA imprinted sensor can provide an alternative approach to food quality control.

Anodic Stripping Voltammetric Analysis of Trace Arsenic(III) on a Au-Stained Au Nanoparticles/Pyridine/Carboxylated Multiwalled Carbon Nanotubes/Glassy Carbon Electrode.

A Au-stained Au nanoparticle (Aus)/pyridine (Py)/carboxylated multiwalled carbon nanotubes (C-MWCNTs)/glassy carbon electrode (GCE) was prepared for the sensitive analysis of As(III) by cast-coating of C-MWCNTs on a GCE, electroreduction of 4-cyanopyridine (cPy) to Py, adsorption of gold nanoparticles (AuNPs), and gold staining. The Py/C-MWCNTs/GCE can provide abundant active surface sites for the stable loading of AuNPs and then the AuNPs-initiated Au staining in HAuCl4 + NH2OH solution, giving a large surface area of Au on the Aus/Py/C-MWCNTs/GCE for the linear sweep anodic stripping voltammetry (LSASV) analysis of As(III). At a high potential-sweep rate of 5 V s−1, sharp two-step oxidation peaks of As(0) to As(III) and As(III) to As(V) were obtained to realize the sensitive dual-signal detection of As(III). Under optimal conditions, the ASLSV peak currents for oxidation of As(0) to As(III) and of As(III) to As(V) are linear with a concentration of As(III) from 0.01 to 8 μM with a sensitivity of 0.741 mA μM−1 and a limit of detection (LOD) of 3.3 nM (0.25 ppb) (S/N = 3), and from 0.01 to 8.0 μM with a sensitivity of 0.175 mA μM−1 and an LOD of 16.7 nM (1.20 ppb) (S/N = 3), respectively. Determination of As(III) in real water samples yielded satisfactory results.

Square Wave Anodic Stripping Voltammetry for Localized Detection of Mn2+ in Li-Ion Battery Environments

Li-ion batteries that incorporate manganese present several advantages, including low cost and low toxicity. However, these batteries often suffer from dissolution of manganese into the electrolyte solution, severely impeding battery performance. This work describes the quantitative detection of Mn2+ ions in battery relevant environment i.e. non-aqueous electrolyte within an inert atmosphere. To this end, an electrochemical probe was fabricated using electrochemical deposition of a Hg cap onto a 25 μm Pt disk microelectrode. The Pt/Hg microelectrode was fully characterized by optical microscopy, cyclic voltammetry, scanning electrochemical microscopy. Using square wave anodic stripping voltammetry to overcome reproducibility issues with classical linear sweep anodic stripping voltammetry, Mn2+ was quantified in non-aqueous solution with a limit of detection of 14 μM. Finally, using this detection scheme, the trapping ability of aza-15-crown-5 ether and dilithium iminodiacetate was investigated.

Detection Efficiency of Ag Nanoparticle Labels for a Heart Failure Marker Using Linear and Square-Wave Anodic Stripping Voltammetry.

In this article, we compare linear sweep anodic stripping voltammetry (LASV) and square-wave anodic stripping voltammetry (SWASV) for detection of a nano metalloimmunoassay. Two separate immunoassays were examined: a model assay, based on interactions between antibodies, and a sandwich assay for the heart failure marker NT-proBNP. In both cases, one antibody is linked to a magnetic microbead, and one is linked to a spherical Ag nanoparticle label. Electrochemical detection is carried out on a paper device. The three analytical figures of merit studied were the precision of the measurements, the calibration sensitivity, and the limit of detection (LOD). For the NT-proBNP assay, the results show that after optimization of the pulse amplitude and frequency of the potential input for SWASV, the detection efficiency is substantially higher compared to LASV. Specifically, the calibration sensitivity increased by up to ~40 fold, the average coefficient of variation decreased by ~40%, and the (LOD) decreased to 300.0 pM. Finally, for a model immunoassay, a ~10-fold decrease in the LOD was observed for SWASV compared to LASV.

Preparation of Electrode Material Based to Bismuth Oxide-Attached Multiwalled Carbon Nanotubes for Lead (II) Ion Determination

Bi2O3 was proven an attractive compound for electrode modification in heavy metal electrochemical analysis. A novel method for synthesizing Bi2O3-attached multiwalled carbon nanotubes (Bi2O3@CNTs) in solution is successfully developed in this study. Characteristics of the obtained Bi2O3@CNTs were proven by modern techniques such as X-ray diffraction, Raman spectroscopy, scanning electronic microscopy, transmission electron microscopy, cyclic voltammetry, electrochemical impedance spectroscopy, and anodic stripping voltammetry. Microscopy images and spectra results reveal that Bi2O3 particles are mainly attached at defect points on multiwalled carbon nanotubes (MWCNTs) walls. Paste electrodes based on the MWCNTs and synthesized Bi2O3@CNTs were applied for electrochemical measurements. The redox mechanism of Bi2O3 on the electrode surface was also made clear by the cyclic voltammetric tests. The recorded cyclic voltammograms and electrochemical impedance spectroscopy demonstrate that the Bi2O3@CNTs electrode was in lower charge transfer resistance than the CNTs one and in the controlled diffusion region. Investigation on the electrochemical behavior of Pb2+ at the Bi2O3@CNTs electrodes found a significant improvement of analytical response, resulting in 3.44 μg/L of the detection limit and 2.842 μA/(μg/L) of the sensitivity with linear sweep anodic stripping voltammetry technique at optimized conditions.

A copper nanoparticle-based electrochemical immunosensor for carbaryl detection

A hapten-protein conjugate with copper nanoparticles (Hap-Car-BSA@CuNPs) was first synthesized in the present work for the determination of carbaryl. The copper nanoparticles (CuNPs) of the conjugate were used as electrochemical labels in the direct solid-phase competitive determination of carbaryl residues in flour from different crops. The signal was read by linear sweep anodic stripping voltammetry (LSASV) of copper (through the electrochemical stripping of accumulated elemental copper) on a gold-graphite electrode (GGE). To form a recognition receptor layer of monoclonal antibodies against the carbaryl on the surface of the GGE, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) and 1-hydroxy-2,5-pyrrolidinedione (NHS) were used as the best covalent cross-linkers. The concentrations of the antibodies and the Hap-Car-BSA@CuNPs conjugate were optimized for carbaryl detection by the electrochemical immunosensor. The electrochemical immunosensor can be used for highly sensitive determination of carbaryl residues in flour samples in the concentration range 0.8–32.3 μg·kg−1, with a limit of detection 0.08 μg·kg−1. The present work paves the path for a novel method for monitoring carbaryl in other food products, drinks, and soil samples.

Voltammetric Determination of Lead and Copper in Wine by Modified Glassy Carbon Electrode

This paper describes the determination of Pb and Cu with a Nafion-modified glassy carbon electrode and MnCo2O4 nanoparticles as working electrode for anodic stripping voltammetry. Pb and Cu were accumulated in HCl/KCl (0.1 mol dm-3) at a potential of -1.4 V (vs. Ag/AgCl electrode) for 480 s, followed by a linear sweep anodic stripping voltammetry (ASV) scan from -1.0 to +0.5 V. Under optimum conditions, the calibration curves were linear in the range of 0.01 - 8 and 0.01 - 5 mg dm-3 for Pb and Cu, respectively. Effect of sample dilution, accumulation time and potential were optimized. A study of interfering substances was performed. A significant increase in current was obtained at the modified electrode in comparison with the bare glassy carbon electrode. The modified electrode was successfully applied for determination of Pb and Cu in wine samples after a simple preparation procedure. Pb and Cu content in wine was used for estimation of the target hazard quotient (THQ) values for minimal and maximal levels of the metals.

Electrochemical Detection of Arsenite Using a Silica Nanoparticles-Modified Screen-Printed Carbon Electrode.

Arsenic poisoning in the environment can cause severe effects on human health, hence detection is crucial. An electrochemical-based portable assessment of arsenic contamination is the ability to identify arsenite (As(III)). To achieve this, a low-cost electroanalytical assay for the detection of As(III) utilizing a silica nanoparticles (SiNPs)-modified screen-printed carbon electrode (SPCE) was developed. The morphological and elemental analysis of functionalized SiNPs and a SiNPs/SPCE-modified sensor was studied using field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), and Fourier transform infrared spectroscopy (FTIR). The electrochemical responses towards arsenic detection were measured using the cyclic voltammetry (CV) and linear sweep anodic stripping voltammetry (LSASV) techniques. Under optimized conditions, the anodic peak current was proportional to the As(III) concentration over a wide linear range of 5 to 30 µg/L, with a detection limit of 6.2 µg/L. The suggested approach was effectively valid for the testing of As(III) found within the real water samples with good reproducibility and stability.

Electrochemical immunoassay for the detection of antibodies to tick-borne encephalitis virus by using various types of bioconjugates based on silver nanoparticles

This work reports for the first time a significantly improved and simplified electrochemical immunoassay to detect antibodies to tick-borne encephalitis virus (TBEV) using a 96-well microtiter plate as a platform for immobilization and silver nanoparticles (AgNPs) as electrochemical labels. The electrochemical assay is performed by detecting the elemental silver oxidation signal where the electroactive signalling silver species are released from the bioconjugates (Ab@AgNP, AbS@AgNP, and ProteinA@AgNP). For this purpose, AgNPs were synthesized and further tagged with biomolecules (antibodies to TBEV, cleaved antibodies to TBEV, and protein A). Signal is read by linear sweep anodic stripping voltammetry (LSASV) of silver ions (through the electrochemical stripping of accumulated elemental silver) on a graphite electrode (GE). AbS@AgNP was chosen as the best option for the new electrochemical immunoassay. The results of electrochemical measurements demonstrated that voltammetric signal increased with the increasing concentration of target antibodies to TBEV within the range from 100 to 1600 IU mL−1, with a detection limit of 90 IU mL−1. To verify the practical application of the novel electrochemical immunosensor, the quantity of immunoglobulins against TBEV in human serum was checked. The results may contribute to the development of alternative methods for monitoring TBEV in biological fluids.

Development of Electrochemical Sensor Based on Silica/Gold Nanoparticles Modified Electrode for Detection of Arsenite

Arsenic is an extremely poison element in earth crust and its contamination in environment is a global hazard. In this study, an efficient electrochemical detection of arsenite [As(III)] has been developed using linear sweep anodic stripping voltammetry (LSASV), based on adsorption of arsenic on the surface of screen printed carbon electrode modified silica/gold nanoparticles (SiNPs/AuNPs/SPCE). The surface property of modified electrode was characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX) and fourier transform infrared spectroscopy (FTIR). The morphology studies using FESEM showed that the distribution of SiNPs/AuNPs composite is not homogenous therefore resulting in some areas with aggregation on the working electrode surface. Several optimum voltammetric parameters were established such as supporting electrolyte, 1 M HCl; deposition potential, −0.4 V and deposition time, 300 s. Under optimum condition, a linear correlation was obtained in the range of 10 – 100 ppb with limit of detection 5.6 ppb. A variety of common coexistence ions such as Pb2+, Ni2+, Zn2+, Hg2+ and Cu2+ in water samples showed no interferences in arsenite detection. The proposed method showed high sensitivity and good reproducibility with a relative standard deviation of 4.52 %, providing potential application of arsenite detection in environment.

Coupling of Anodic Stripping Voltammetry with Sampled-Current Voltammetry on an Electrode Array: Application to Lead Detection

Electrochemical detection systems are very promising for pollution monitoring owing to their easy miniaturization and low cost. For this purpose, we have recently developed a new concept of device based on Electrodes Array for Sampled-Current Voltammetry (EASCV), which is compatible with miniaturization and portability. In this work, to improve the sensitivity of the analytical method, we added a preconcentration step before EASCV analysis, combining sampled-current voltammetry with anodic stripping voltammetry. Lead was chosen as analyte for this probe of concept owing to its high toxicity. The conditions for electrodeposition of lead on gold were optimized by means of under potential deposition. Current intensities 300 times higher than with linear sweep anodic stripping voltammetry were obtained, showing the interest in the method. The value of the sampling time directly affected the sensitivity of the sensor given by the slope of the linear calibration curve. The sensor exhibited a limit of detection of 1.16 mg L−1, similar to those obtained with linear sweep anodic stripping voltammetry.

Gold nanoparticles decorated three-dimensional porous graphitic carbon nitrides for sensitive anodic stripping voltammetric analysis of trace arsenic(III)

A new material of three-dimensional porous graphitic carbon nitride (g-C3N4) decorated by gold nanoparticles (AuNPs) (AuNPs/g-C3N4) was designed using a mesoporous molecular sieve (SBA-15) as the sacrificial template. Cast-coating the as-prepared AuNPs/g-C3N4 on the glassy carbon electrode (GCE) can yield an AuNPs/g-C3N4/GCE for sensitive linear sweep anodic stripping voltammetry (LSASV) analysis of trace As(III). The as-prepared AuNPs/g-C3N4/GCE electrode demonstrates superiorities compared to that of a gold nanoparticles modified GCE (AuNPs/GCE) prepared by electrochemical deposition. These results show the specialties of g-C3N4 for increasing the activity and sensitivity of gold nanoparticles. Under an optimum conditions (400 s preconcentration at −0.45 V in 0.50 M aqueous H2SO4, 5 V s−1), the LSASV peak current for the As(0)-As(III) oxidation responded linearly to As(III) concentration from 0.005–1.00 μM (r2 = 0.992) with an extremely low limit of detection (LOD) of 2.9 nM (0.22 ppb, S/N = 3); meanwhile the peak current for the As(III)–As(V) oxidation was also linear with As(III) concentration from 0.05 to 1.0 μM (r2 = 0.990) with a LOD of 16 nM (1.2 ppb, S/N = 3). More importantly, the feasibility of AuNPs/g-C3N4/GCE for analyzing inorganic As(III) in real water further demonstrates the practicability for our designed electrode.

Multiwall carbon nanotube modified by antimony oxide (Sb2O3/MWCNTs) paste electrode for the simultaneous electrochemical detection of cadmium and lead ions

In this study, a sensitive and reliable anodic stripping voltammetry (ASV) using a series of multiwall carbon nanotube modified by antimony oxide (Sb2O3/MWCNTs) paste electrodes was successfully introduced for the simultaneous electrochemical detection of Cd2+ and Pb2+ ions. Firstly, a composite of multiwall carbon nanotubes (MWCNTs) was successfully used to preparing a paste electrode. Then, the MWCNTs bulk electrode was further modified with various concentrations of Sb2O3 (1, 3, and 4 wt.%, respectively) for improving the cadmium ions (Cd2+) and lead ions (Pb2+) detection ability. Among the Sb2O3/MWCNTs electrodes, the modified electrode by 3 wt.% Sb2O3 exhibits remarkable analytical detection for Cd2+ and Pb2+ by linear sweep anodic stripping voltammetry (LSASV) technique. The proper linear curves of current response versus the concentration of Cd2+ (80–150 ppb) and Pb2+ (5–35 ppb) could be observed. Interestingly, the analytical sensitivity of the mixture Cd2+ and Pb2+ were 1.932 and 2.694 μA⋅L⋅μg–1, respectively, which were higher than 1.5 and 1.3 folds of the individual ions. It expects that the Sb2O3/MWCNTs paste electrode could provide a significant improvement to the electrode for the simultaneous electrochemical detection of Cd2+ and Pb2+ ions.

Arsenic(III) detection in water by flow-through carbon nanotube membrane decorated by gold nanoparticles

A carbon nanotube flow-through membrane electrode decorated by gold nanoparticles (GCME) was utilized for the detection of As(III) in water. The carbon nanotube membrane was prepared by vacuum filtration of multiwalled carbon nanotubes dispersion in 1-methyl-2-pyrrolidone providing a sheet resistance of 108 ± 6 Ω/sq with an areal mass of 60 μg cm−2. Gold nanoparticles were electrodeposited on the surface of GCME by applying a constant potential of −1.0 V for 15 s while a 1.0 mM HAuCl4 solution in 0.1 M NaCl was flowed through the GCME. The analytical response of As(III) by linear sweep anodic stripping voltammetry (LSASV) was monitored as a function of time showing that the nonconductive nature of As0 prevents the electrodeposition of a thick layer of arsenic on the electrode surface. Thus, accumulation of a large amount of arsenic can only be achieved with a large surface area of gold nanoparticles. The calibration curve was calculated by normalization of LSASV peak charge by the volume of analyte solution flowed through the GCME since different deposition time ranging from 10 to 120 s were required to detect the different concentration used for calibration. The analytical method provided a linear range from 0.75 to 750 ppb As(III) which is suitable for environmental monitoring of this pollutant.

Design of Enzyme-Based Biosensors for Monitoring Pollutants in Gold Mining Environments

Gold is a transition metal which has great economic value, however does not exist alone in the earth crust; but in combination with other metals and non-metals to form compounds. These other elements which could be heavy metals such as lead, cadmium and copper may be highly toxic depending on their concentrations in the gold ore. Mining in itself has many associated risk which could be related to health or environmental degradation. These risks are heightened when mining is done by artisanal miners who have little or no knowledge about safe practices. Artisanal mining is however predominant in the gold rich communities of developing countries such as Nigeria, Ghana, Mali, Senegal etc. Youths engage in illegal mining of gold ore without possible care for the dangers associated with it [1]. Consequences associated with such practices includes environmental pollution, degradation and health hazards such as poisoning outbreaks. A typical example of associated health risk was reported in our previous works [2][3] in which lead (Pb) poisoning outbreaks took the lives of hundreds of children below age five in Zamfara and Kebbi states, Nigeria in 2010 and 2016 respectively [4]. Pb was found to be very high in the mining environments and places where processing of gold ore was carried out. Environmental samples such as water, soil and vegetation on analysis using voltammetry and ICP-OES, gave values of Pb higher than 6000μg/L in water and 13000mg/Kg in soil. This concentration exceeded the WHO permissible limit of 10μg/L in water [5] and 400mg/kg for lead in residential soil [6]. These incidents are very worrisome as they could have been avoided or controlled with the right environmental practices and monitoring. Given the high levels of Pb in the blood of victims which was reported to have caused the deaths, [4] the need for investigation of the environmental matrices became imperative. This is in order to ascertain the actual levels of heavy metals and consequently design a biosensor which could be used onsite to continually monitor the environment. Lead and copper were detected in samples. Pb was the metal with very high concentration in most samples while copper was within acceptable limit. Enzymatic activity is known to be inhibited by the presence of heavy metals such as lead. Hence, they can be employed in the design of a biosensor for environmental monitoring. Glucose oxidase (enzyme) was immobilized in L-cysteine and coupled to gold electrode with Carbodiimide and this modified electrode (biosensor) was used in the catalysis of different concentrations of glucose standard (0.1mM – 20mM). The linear range was observed to be between 0.1mM – 10mM. To 2.5mM glucose standard solution, Pb standard solutions were successively added while stirring and measurement taken after 10 min of each successive addition. A sharp inhibition due to the presence of Pb was noticed between 5ppb – 20ppb while between 50 ppb – 500 ppb, an onward gradual inhibition continued but at a much slower rate giving almost a plateau. The glucose oxidase inhibition biosensor was optimized for pH, scan rate, temperature and reaction time and characterized using cyclic voltammetry, SEM and FT-IR. The sensitivity to very low concentration of Pb (5 ppb – 20ppb) in the pH range of most samples (6.5 – 7.5) collected from gold mining sites in Niger state, Nigeria makes it promising in its use for analysis of real life samples obtained from this region and in the final development of a portable onsite sensor. References. [1] Ogunlesi, M., Okiei, W., Adio-Adepoju, A. and M. Oluboyo, (2017). Electrochemical determination of the levels of cadmium, copper and lead in polluted soil and plant samples from mining areas in Zamfara [2] Okiei, W., Ogunlesi, M., Adio-Adepoju, A. and M. Oluboyo, (2016). Determination of Copper and Lead in Water Samples from Zamfara State, Nigeria by Linear Sweep Anodic Stripping Voltammetry. Int. J. Electrochem. Sci. 11: 8280-8294, doi 10.20964/2016.10.06 [3] Adio-Adepoju, A.A., Okiei, W.O., Ogunlesi, M.1., Ojobe, B.L., Ibrahim, G.O. and O.S. Sobowale, (2018). Analysis of Surface and Ground Water Samples in the Environs of Gold Mines Linked to Lead Poisoning Incident in Niger State, Nigeria. In T.M. Tundisi, & J.G. Tundisi (Eds.), Water Resources Management (pp. 30-44) São Carlos, SP: editorascienza. ISBN 978-85-5953-031- [4] MSF MedecinsSansFrontieres. MSF Briefing Paper, (2012). http://www.msf.org/en/article/lead-poisoning-crisis-zamfara-state-nworthern-nigeria [5] WHO World Health Organization, (2011). Guidelines for drinking water quality, 4th Edition, Incorporating 1st Addendum. WHO publication, Geneva ISBN: 9789241548151 [6] US EPA United States Environmental Protection Agency, (2001). 40 CFR Part 745. Lead; identification of dangerous Levels of Lead; Final Rule. https://www.gpo.gov/fdsys/pkg/FR-2001-01-05/pdf/01-84.pdf Figure 1

Synthesis of MnCo2O4 nanoparticles as modifiers for simultaneous determination of Pb(II) and Cd(II)

The porous spinel oxide nanoparticles, MnCo2O4, were synthesized by citrate gel combustion technique. Morphology, crystallinity and Co/Mn content of modified electrode was characterized and determined by Fourier transform infra-red spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray diffraction pattern analysis (XRD), simultaneous thermogravimetry and differential thermal analysis (TG/DTA). Nanoparticles were used for modification of glassy carbon electrode (GCE) and new sensor was applied for simultaneous determination of Pb(II) and Cd(II) ions in water samples with the linear sweep anodic stripping voltammetry (LSASV).The factors such as pH, deposition potential and deposition time are optimized. Under optimal conditions the wide linear concentration range from 0.05 to 40 μmol/dm3was obtained for Pb(II), with limit of detection (LOD) of 8.06 nmol/dm3 and two linear concentration ranges were obtained for Cd(II), from 0.05 to 1.6 μmol/dm3 and from 1.6 to 40 μmol/dm3, with calculated LOD of 7.02 nmol/dm3. The selectivity of the new sensor was investigated in the presence of interfering ions. The sensor is stable and it gave reproducible results. The new sensor was succesfully applied on determination of heavy metals in natural waters.