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A novel metal ion sensor was fabricated through electrochemically immobilized Hg spheres on surface-unpassivated CdSe quantum dots modified paraffin wax impregnated graphite electrode. The size and surface morphology of the CdSe QDs and CdSe QDs - Hg modified electrode was characterized by transmission electron microscope and field emission scanning electron microscopy. The modified electrode was also characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The modified electrode was used for the determination of trace level lead ion which was preconcentrated onto the modified electrode by differential pulse anodic stripping voltammetry (DPASV). Numerous key variables affecting the current response of lead ion have been optimized. The proposed electrode has a linear concentration range of 5.2 ng/L–4.2 µg/L with a optimized deposition time of 180 s and the detection limit is found to be 1.7 ng/L (S/N = 3). The electroanalytical performance of the modified electrode was successfully tested in a real sample of tap water and sea water spiked with Pb(II) ion. The proposed electrode shows excellent selectivity and sensitivity over other heavy metals, such as copper, zinc, manganese and tin. Hg(II) immobilized CdSe QDs modified electrode has shown great potential application in detecting metal ions at very low concentrations.

Monolayer-scale pyridine-2-sulfonic acid (PySA) or pyridine-2-carboxylic acid (PyCA) modified glassy carbon electrode (GCE) was prepared for anodic stripping voltammetry (ASV) analysis of Cd2+ and Pb2+. PySA or PyCA was covalently modified on GCE by electroreduction of PySA or PyCA in 0.5 M aqueous H2SO4, yielding a PySA/GCE or PyCA/GCE. The electrodes were characterized by X-ray photoelectron spectroscopy and electrochemical techniques. In combination with the in-situ bismuth film method, both PySA/GCE and PyCA/GCE offered very high analytical performance for ASV analysis of Cd2+ and Pb2+, including the very low values of limit of detection (LOD, S/N = 3) and high stability. The PySA/GCE gave a LOD of 4 ppt for Cd2+ or of 7 ppt for Pb2+. The PyCA/GCE gave a LOD of 7 ppt for Cd2+ or of 11 ppt for Pb2+. The Cu2+ and Ni2+ interferences, which still appear as a challenge for ASV analysis of Cd2+ and Pb2+, were found to be well inhibited by the additions of K4Fe(CN)6 and Ga(III) into the detection solution. The modified electrode was used for Cd2+ and Pb2+ analysis in real water samples with satisfactory results.

Oxidation behavior of tretinoin (TRN) was evaluated using anodic stripping voltammetry (ASV), differential pulse voltammetry (DPV) and cyclic voltammetry (CV) techniques in Britton-Robinson (B-R) pH 7. The glassy carbon (GC) electrode was used to deposit the compound (TRN) into its surface to record a well-defined oxidation peak at 0.75 V in the presence of Ag/AgCl reference electrode and a Pt counter electrode. Some analytical parameters were studied to obtain the best oxidation signal, for example; buffer solution, pH, accumulation potential and time, amplitude, frequency, scan rate and convection rate. The high sensitivity anodic peak was obtained using B-R, pH 7, 40 s accumulation time, −0.6 V accumulation potential, 50 mV amplitude, 20 Hz frequency, 350 mV s−1 scan rate, and 1000 rpm. These parameters were chosen as optimum conditions for the continued experiments. The analytical performance of the used technique was evaluated using the study of repeatability, stability, recovery, calibration curve and detection limit. Repeatability and stability was monitored for 5 × 10−6 mol L−1 of TRN to give 0.24% relative standard deviation (RSD%) for eighth anodic measurements, while the stability was been very well for 80 min. The calibration curve was studied over the range of 1 × 10−6–1 × 10−5 mol L−1 (n = 6), yielded, a linear relationship between concentrations and anodic current for TRN. A detection limit (LOD) was calculated to be 7.5 × 10−9 mol L−1 (2.25 ppb), while a quantification limit (LOQ) was yielded 2.49 × 10−8 mol L−1 (7.47 ppb). Anodic stripping voltammetry method was developed and applied for the determination of TRN in the human urine and plasma samples.

The worm-like nitrogen-doped-carbon framework (WNCF) with abundant edge-plane-like defective sites (EDSs) was synthesized by using natural wax gourd (Benincasa hispida) as the main carbon precursor and milk yielded by Chinese Holstein cattle (Holstein Friesian) as the nitrogen precursor for the first time. The Nafion-dispersed WNCF (Nafion-WNCF) was employed to design a highly sensitive electrochemical sensor for the trace determination of toxic heavy metal lead (II) (Pb2+) by the differential pulse anodic stripping voltammetry (DPASV). Some key experimental factors including calcination temperature of WNCF, pH value of the buffer solution, deposition potential, deposition time and the concentration of bismuth (Bi3+) were optimized for the stripping analysis of Pb2+. Under the optimum experimental condition, Nafion-WNCF modified bismuth film glassy carbon electrode (Nafion-WNCF/BFGCE) exhibits a wide linear range from 0.5 μg L−1 to 100 μg L−1 and a low detection limit of 0.2 μg L−1 (S/N = 3) for detecting Pb2+. Especially, Nafion-WNCF/BFGCE was successfully applied to determine Pb2+ in tap water and lake water samples. All the results suggest that the WNCF can be considered as a green and low-cost nanomaterial for the precision detection of Pb2+ in real samples.

Cadmium (Cd) and lead (Pb) pollution is a significant environmental and human health concern, and methods to detect Cd and Pb on site are valuable. Stencil-printed carbon electrodes (SPCEs) are an attractive electrode material for point-of-care (POC) applications due to their low cost, ease of fabrication, disposability and portability. At present, SPCEs are exclusively formulated from graphitic carbon powder and conductive carbon ink. However, graphitic carbon SPCEs are not ideal for heavy metal sensing due to the heterogeneity of graphitic SPCE surfaces. Moreover, SPCEs typically require extensive modification to provide desirable detection limits and sensitivity at the POC, significantly increasing cost and complexity of analysis. While there are many examples of chemically modified SPCEs, the bulk SPCE composition has not been studied for heavy metal detection. Here, a glassy carbon microparticle stencil printed electrode (GC-SPE) was developed. The GC-SPEs were first characterized with SEM and cyclic voltammetry and then optimized for Cd and Pb detection with an in situ Bi-film plated. The GC-SPEs require no chemical modification or pretreatment significantly decreasing the cost and complexity of fabrication. The detection limits for Cd and Pb were estimated to be 0.46 μg L−1 and 0.55 μg L−1, respectively, which are below EPA limits for drinking water (5 μg L−1 Cd and 10 μg L−1 Pb) [1]. The reported GC-SPEs are advantageous with their low cost, ease of fabrication and use, and attractive performance. The GC-SPEs can be used for low-level metal detection at the POC as shown in the report herein.

In this work, we report double-shelled yolk-shell Si@C structure as a high-performance electrochemical sensing material for heavy metal ions. A SiO2-assisted polybenzoxazine (PB) coating strategy is used to synthesize highly monodispersed Si@C microspheres. After thermal carbonization of PB layers and selective removal of the SiO2 layers, Si@C microspheres were prepared. The resultant Si@C microspheres exhibit uniform spherical morphology and clearly double-shelled yolk-shell structures. The obtained Si@C microspheres are employed to prepare the chemically modified electrode for the sensitive determination of Cd(II) and Pb(II). By the method of anodic stripping voltammetry, the Si@C-based electrode shows a very wide linear dynamic range for target ions (e.g., 0.5–400 μg L−1 for Cd(II) and Pb(II)) and low limit of detections (e.g., 0.068 μg L−1 for Cd(II) and for 0.105 μg L−1 Pb(II)). The remarkable results, such as excellent resistance to interference ions, good repeatability, and reproducibility were also obtained. Furthermore, compared with those Cd(II) and Pb(II) sensors known in the literature, the analytical performance of Si@C-based electrode is better. Finally, when further used to determine Cd(II) and Pb(II) in tap water and lake water, the results of fabricated electrode successfully achieve good consistency with the data obtained from inductively coupled plasma-mass spectrometry (ICP-MS).

The crucial point of this study was to verify the hypothesis that both thallium species are not affected by the procedure of photolysis when it is applied as a method of simplification of sample matrix containing surfactants, and that this method of sample pretreatment leads to reliable results of Tl speciation analysis. It is important especially because of high instability of Tl(III), which makes partial reduction of Tl(III)DTPA complex unavoidable. After conservation of Tl speciation by addition of DTPA the photolysis assisted with nanostructured hierarchically organized film was performed using “solar lamp” (Fe2O3/WO3/Fe2O3 film, pH 6, 380–800 nm). The results imply that under proposed photolysis conditions Tl(I) is not oxidized in the presence of water matrix, SDS nor DTPA. Also, even 100-fold excess of Fe(III) ions over Tl(I) ions does not accelerate the oxidation of Tl(I) to Tl(III), and already 2 h of heterogeneous photolysis allow to limit the interferences caused by SDS and obtain reliable results. The data obtained by anodic stripping voltammetry (ASV) were verified using an inter-method comparison with SEC ICP MS. Moreover, after 2 h irradiation the reduction rate of Tl(III)DTPA standard solution increased only slightly from 2-3% to 4–6%. The presence of river water matrix causes a slightly higher (9%) reduction of the trivalent form. These changes are irrelevant in the context of instability of Tl(III) compounds. This study indicates that “soft decomposition” can be applied in speciation analysis of thallium in water matrix.

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.

An ion imprinting polymer (IIP) electrochemical sensors based on chitosan-graphene oxide composites polymer modified glassy carbon electrode (CS/GO-IIP) was developed for the highly sensitive and selective detection of Cu (II) by the dip coating method. The Cu (II) ion-imprinted polymers were synthesized by chemically cross-linking with epichlorohydrin after the CS/GO/Cu (II) composite dropped on the glassy carbon electrode surface. The introduction of GO can improve the electrical conductivity of the electrode and amplify the electrochemical signal. The sensor was characterized by FT-IR, EDS, SEM, AFM, Raman spectroscopy and electrochemical measurements. Under the optimized conditions, a linear dependence was observed from 0.5 to 100 μmol/L with a detection limit of 0.15 μmol/L. The detection of Cu (II) was hardly interfered by the traditional metal cations. The CS/GO-IIP sensor showed excellent reproducibility via repetitive differential pulse anodic stripping voltammetry and the RSD was 3.3%. More importantly, the performance of CS/GO-IIP sensor was verified in tap and river water samples and has an acceptable recovery rates.

Heavy metals are ubiquitous in the environment, and their excessive discharge and bioaccumulation can cause cardio-vascular and urinary diseases in humans. Among them, lead ion (Pb2+) and cadmium ions (Cd2+) are designated as the most typical toxic metal ions in human blood and drinking water. Thus, high-performance monitoring of Pb2+and Cd2+ pollution is necessary. Nanomaterials have been extensively used in electrochemical sensing due to their excellent physicochemical properties. In this study, we prepared ordered mesoporous carbon doped hollow spherical bismuth oxide nanocomposites (hsBi2O3-OMC NCs), and constructed it into an electrochemical sensor for highly sensitive and specific detection of Pb2+ and Cd2+ in environmental media and human blood based on the differential pulse anodic stripping voltammetry (DPASV). The experimental results demonstrate that the detection range could be broadened to 200 nM with detection limits of 0.025 nM for Pb2+ and 0.045 nM for Cd2+. Compared with conventional detection techniques, this sensor exhibited simple operation, minimal background interference, multipath applicability and economic efficiency. Therefore, we believe that this work is significant for pollution monitoring, environmental restoration and emergency treatment.

In this paper, a novel & highly sensitive copper sensor based on a dopamine modified carbon ceramic electrode (CCE) is presented. By immersing the CCE in aqueous solution of dopamine (0.2 M), after a short period of time, a thin film of dopamine was rapidly formed on the surface of the electrode due to its strong adsorption properties. The prepared modified carbon ceramic electrode was characterized by scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR). Then, the effective parameters on sensor response were optimized and anodic stripping voltammetry (ASV) was used for quantitative determination of copper. The calibration plot was linear over the copper concentration range of 0.1–250 µg L−1. The limit of detection (LOD) was found 0.03 µg L−1 of Cu(II), and for seven successive determinations of 10 and 140 µg L−1 Cu(II), the relative standard deviations were obtained 1.5% and 1.1%, respectively. The dopamine modified carbon ceramic electrode (CCE/DOP), prepared in this study, showed high selectivity and sensitivity via formation of a Cu-dopamine complex and applied for the determination of Cu(II) in real samples with good results.

The sensitive monitoring of mercury (II) selenide nanoparticles (HgSe NPs) is of great potential relevance in environmental studies, since such NPs are believed to be the ultimate metabolic product of the lifesaving mechanism pathway of Hg detoxification in biological systems. In this context, we take advantage of using gold-nanostructured screen-printed carbon electrodes (SPCE-Au) for the rapid, simple and sensitive electrochemical quantification of engineered water-stable HgSe NPs, as an advantageous alternative to conventional elemental analysis techniques. HgSe NPs are first treated in an optimized oxidative/acidic medium for Hg2+ release, followed by sensitive electrochemical detection by anodic stripping voltammetry (ASV). To the best of our knowledge, this is the first time that water-stable HgSe NPs are quantified using electrochemical techniques. The low limit of detection achieved (3.86 × 107 HgSe NPs/mL) together with the excellent repeatability (RSD: 3%), reproducibility (RSD: 5%) and trueness (relative error: 10%), the good performance in real sea water samples (recoveries of the analytical signal higher than 90%) and the simplicity/low cost of analysis make our method an ideal candidate for HgSe NPs monitoring in future environmental studies.

This work delineates a simple and sensitive mercury free electrode as an electrochemical sensor for simultaneous determination of Pb (II) and Cd (II) using multiwalled carbon nanotubes wrapped poly O-cresophthalein complexone film (MWCNTs-POCF) modified electrode by anodic stripping voltammetry. The surface morphology of MWCNTs-POCF modified electrode was characterized by scanning electron microscopy (SEM). MWCNTs-POCF electrode was also characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (ESI). Differential pulse anodic stripping voltammetry (DPASV) was employed for the determination of Pb (II) and Cd (II) ions. When compared with MWCNTs and POCF modified electrodes, MWCNTs-POCF modified electrode exhibited good analytical performance towards the determination of Pb (II) and Cd (II) ions in terms of sensitivity and simplicity. Certain electrochemical parameters to regulate and improve the performance of the sensor were examined. Under optimized experimental conditions the modified electrode exhibited a detection limit of 0.98 μg/L for Pb (II) and 1.9 μg/L for Cd (II). The analytical proficiency of the developed metal ion sensor was used for the determination of Pb (II) and Cd (II) in the real water sample and the results obtained were satisfactory with very good recovery.

The distribution of surface functional groups was tuned through the use of the trimethylsilane spacer units which kept statistically fixed intermolecular intervals between functional molecules. We propose a simple and efficient procedure that does not require any optimization: statistical horizontal distances between the functionalities can be defined a priori regardless of the conditions of the functionalization (assuming only the minimal reaction time). We studied three various distributions of propyl silver carbonate functional units obtained through a five steps synthesis route. We showed that the quantity of immobilized complexes is proportional to the spacer density. The efficiency of the method was tested by differential pulse anodic stripping voltammetry (DPASV), which confirmed the assumed number of immobilized metal complexes on the sample surface.

The thick-film modified graphite sensors (TMGE) as working electrodes are used for determination of heavy metals in bovine seminal plasma by anodic stripping voltammetry. The technique proposed is a very simple, express and no any sample preparation such as acid deproteinization or autoclave digestion is necessary. The sample of seminal plasma is just diluted with electrolyte solution in the analysis process. The aliquot of the sample is injected in the electrochemical cell and the analytical signal is measured. The analytical signal dependences on the accumulation potential, accumulation time and sweep rate have been studied. The standard addition method is used for calculating of heavy metal concentrations in the samples. The accuracy of the developed technique is proved by comparison with the results obtained by the independent method of ICP-AES (atomic emission spectrometry with inductively coupled plasma). The detection limits (3SDblank) are found to be 3.6 μg·L−1 for Pb and 40 μg·L−1 for Cu in bovine seminal plasma (taking into account sample dilution). The relative standard deviation (RSD) obtained by the proposed technique do not exceed 13%.

This work describes a planar sensor chip with three integrated electrodes for the determination of Hg(II) by anodic stripping voltammetry (ASV). The sensor features Au-film working and auxiliary electrodes and a Ag-film reference electrode; all three metal-film electrodes are deposited on a silicon substrate by sputtering. Definition of the geometrical pattern of the sensor chip involves appropriate application of simple plastic masks during deposition of the metal electrodes making this approach simpler, faster and less laborious than photolithography. The Au-film working electrode is characterized by optical techniques and cyclic voltammetry and the chemical and instrumental conditions for Hg(II) determination by ASV are studied in detail. The limit of detection of Hg(II) is 0.6 μg L−1, the within-sensor repeatability (expressed as the coefficient of variation of 20 measurements at the 20 μg L−1 Hg(II) level) is 3.7% and the between-sensor reproducibility (expressed as the coefficient of variation of 6 measurements at different sensors at the 20 μg L−1 Hg(II) level) is 11.8%. The sensor chip is successfully applied to the determination of Hg(II) in a fish oil sample. The proposed fabrication approach offers scope for the mass-production of robust integrated sensors at low cost which are applicable to on-site analysis.

In this paper, a functional nanoprobe based on graphene oxide (GO) composites was successfully prepared for detection of mercury ion (Hg(II)) with high sensitivity. GO as a substrate was modified and used for the growth of polymer chains to synthesize polyacrylonitrile-grafted GO (PAN-g-GO) by activator generated by electron transfer atom transfer radical polymerization (AGET ATRP). Under the condition of visible light shines, the PAN-g-GO was further modified to prepare [poly(acrylonitrile-co-vinyl(diphenyl pyridine))]-grafted GO (P(AN-co-PHPY)-g-GO) nanomaterial by one-step synthesis. Finally, P(AN-co-PHPY)-g-GO as a nanoprobe was dropped to the surface of the glassy carbon electrode and assembled to the electrochemical sensor. Moreover, it can effectively improve the enrichment capacity of mercury ions and increase the electron transfer rate on the electrode surface. Differential pulse anodic stripping voltammetry (DPASV) was used to evaluate the electrochemical performance. Under optimum conditions, the response of Hg(II) at this resulting sensor was linear in the range of 2.0 μM~0.1 nM with a detection limit of 0.06 nM. Additionally, this sensor showed excellent reproducibility, selectivity and stability.

A portable electrode with approachable, available and simple processing is of great significance for the effective detection on-site in the practical situation. This work reported a new type of disposable carbon cloth working electrode (CCE), which was fabricated in large scale only through simple pretreatment without complex modification, and used for on-site detection of heavy metal ions Cd2+ and Pb2+ by differential pulse anodic stripping voltammetry (DPASV). The portable electrodes showed a wide detection range and the low detection limits, as well as the successful application for the simultaneous detection of Cd2+ and Pb2+ in real samples without mutual interference or interference from other ions. Better yet, the novel disposable electrode exhibited unique advantages of convenience, portability, reliable, low-cost and potential of mass production compared to conventional glassy carbon electrode (GCE), which may be an alternative advantageous choice for practical on-site detection.

Abnormal expression of microRNAs is closely related to human diseases. Ultrasensitive detection of microRNAs with wide linear dynamic range is necessary as the concentrations of microRNAs distributed in biological samples usually range from fM to nM. Here, we constructed an ultrasensitive electrochemical sensor for microRNA-21 based on the integration of a dual signal amplification strategy of hybridization chain reaction (HCR) and enzyme-induced metallization (EIM) with anodic stripping voltammetry (ASV). MicroRNA-21 was captured by capture probe H1 (CP H1) modified magnetic nanobeads (MBs) and amplified by HCR. Multiple alkaline phosphatases (ALP) were coupled based on the specific reaction of biotin and streptavidin. A dual amplification strategy of HCR and EIM enhanced electrochemical signal by approximately 120-fold from the perspectives of target amplification and detection signal amplification, which decreased the detection limit of microRNA-21 to 0.12 fM. Compared to the reports previously reported, a wider linear dynamic range of 2.5 fM to 25 nM spanning 7 orders of magnitude was obtained. The method provides high sensitivity, specificity and a wider linear dynamic range, which shows a great potential in the early diagnosis of diseases.

In this paper, single Hg nanoelectrodes were prepared by single nucleation/growth of mercury on the surface of single gold nanodisk electrodes, which were fabricated by improved laser-assisted pulling method. The nucleation/growth process was characterized by scanning electron microscopy (SEM), transition electron microscopy (TEM) and electrochemical method. Pb2+ and Cu2+ could be accumulated and melted with single Hg nanoelectrodes (amalgam formed) through preconcentration step, and then two typical anodic waves would be obtained through square-wave anodic stripping voltammetry (SWASV) method. The peak currents were corresponded to the concentration of Pb2+ and Cu2+, and thus the single Hg nanoelectrodes could be used as a kind of novel nanosensor for simultaneous detection of lead and copper with high sensitivity and selectivity.

The current study evaluates the effect of seawater physico-chemical characteristics on the relationship between the concentration of metals measured by Diffusive Gradients in Thin films (DGT) passive samplers (i.e., DGT-labile concentration) and the concentrations measured in discrete water samples. Accordingly, Inductively Coupled Plasma Mass Spectrometry (ICP-MS) was used to measure the total dissolved metal concentrations in the discrete water samples and the labile metal concentrations obtained by DGT samplers; additionally, lead and cadmium conditional labile fractions were determined by Anodic Stripping Voltammetry (ASV) and total dissolved nickel was measured by Cathodic Stripping Voltammetry (CSV). It can be concluded that, in general, the median ratios of DGT/ICP and DGT/ASV(CSV) were lower than 1, except for Ni (median ratio close to 1) and Zn (higher than 1). This indicates the importance of speciation and time-integrated concentrations measured using passive sampling techniques, which is in line with the WFD suggestions for improving the chemical assessment of waterbodies. It is the variability in metal content in waters rather than environmental conditions to which the variability of the ratios can be attributed. The ratios were not significantly affected by the temperature, salinity, pH, oxygen, DOC or SPM, giving a great confidence for all the techniques used. Within a regulatory context such as the EU Water Framework Directive this is a great advantage, since the simplicity of not needing to use corrections to minimize the effects of environmental variables could help in implementing DGTs within monitoring networks.

Mercury is a toxic heavy metal which pollutes air, land, and water posing a serious threat to the environment and human health. For a first-hand estimate, a qualitative method (colorimetric) for detection of mercury could suffice. However for precise measurement, below the threshold value, a quantitative method (electrochemical) is needed. The colorimetric strips were produced using mercapto-propionic acid derivatized rhodamine hydrazide (RS). RS developed a pink color when in contact with mercury (Hg2+) and the shade became darker with an increase in concentration. A new polymeric hydrogel was used to entrap RS to fabricate sensing strips for quasi-quantitative detection of Hg2+ through the naked eye. An electrochemical sensor was also developed for accurate quantification of Hg2+ at ppt level by modified glassy carbon electrode with the same RS and green reduced graphene oxide (RS-gRGO/GCE) via differential pulse anodic stripping voltammetry (DPASV). The dipstick exhibited high sensitivity, good selectivity and low detection limit (0.29 ppb) whereas metal free, label-free modified electrode performed very well with a high sensitivity (70.22 μA·ppb·cm−2), low detection limit (57 ppt), good selectivity, and reproducibility. These sensors will serve the purpose of common people for onsite estimation as well as scientific laboratories requiring precision measurements.

Traditional anodic stripping voltammetry (ASV) involves electrodeposition (reduction) of metal ions from solution over some time scale onto a working electrode followed by stripping (oxidation) of the deposited metal in a second step, where the stripping potential and quantity of charge passed provide information about the metal identity and solution concentration, respectively. ASV has recently been extended to the analysis of metal nanoparticles (NPs), which have grown popular because of their fascinating properties tunable by size, shape, and composition. There is a need for improved methods of NP analysis, and because metal NPs can be oxidized to metal ions, ASV is a logical choice. Early studies involved metal NPs as tags for the detection of biomolecules. More recently, anodic stripping has been used to directly analyze the physical, chemical, and structural properties of metal NPs. This review highlights the stripping analysis of NP assemblies on macroelectrodes, individual NPs in solution during collisions with a microelectrode, and a single NP attached to an electrode. A surprising amount of information can be learned from this very simple, low-cost technique.

Recently, graphitic carbon nitride (g-C3N4) has attracted great interest for photo(electro)chemical applications such as sensing, solar energy exploitation, photocatalysis, and hydrogen generation. This paper presents the potential application and benefits of g-C3N4 nanolayers as a green and highly efficient electrode modifier for the detection of trace lead ions in drinking water and urban dust samples. Carbon nitride nanosheets with a thickness of ∼6 A° and lateral of 100–150 nm were prepared through high-temperature polymerization of melamine followed by sonication-assisted liquid exfoliation. A glassy carbon electrode (GCE) was modified by a thin layer of g-C3N4 through drop casting and used for fast and sensitive (ppb range) detection of lead ions. It is shown that the g-C3N4 nanosheets have a total specific area of about 45 m2/g, causing an increase in the microscopic surface area of GCE by a factor of 20 in comparison to the bar electrode; hence, enhanced peak current intensity in voltammetric studies is attained. Differential pulse anodic stripping voltammetry indicates two linear anodic stripping responses of 2.4–7.5 ng mL−1 (R2 = 0.983) and 10.0–1000.0 ng mL−1 (R2 = 0.993). These ranges fulfill the requirements of the U.S. EPA and WHO standards for the quality control of drinking water. Measurements on urban dusts and drinking water also indicate the potential of the modified electrode for fast and ultrasensitive detection of lead ions in real samples. The advantages and figure of merit of the developed electrode for lead sensing are addressed.

We report on the straightforward preparation of gold nanoparticles (AuNPs) through a direct metal-to-substrate electric discharge at ambient conditions at 1.2 kV between the source metal (gold) and low-cost graphite screen-printed electrodes (SPEs). Considering that sparked nanoparticles are generated on the basis of an evaporation-condensation process, comparative experiments by using Au and a eutectic Au/Si (97/3 wt%) alloy were conducted. The so-modified sparked AuNP-SPE and eAuNP-SPE, respectively, were characterized by scanning electron microscopy, cyclic voltammetry, and electrochemical impedance spectroscopy (EIS). Data revealed a 2.4-fold electro active surface of AuNPs in the case of eAuNP-SPE. Compared with the unmodified SPEs, sparked electrodes exhibited two distinct electrode-electrolyte interfaces, characterized by different time-constants. EIS data were successfully modeled to an equivalent electric circuit that considers sparked-induced morphological features of the sensing surface and concomitant alterations of the diffusion process. Both types of sparked electrodes endowed sensitivity to otherwise inactive plain SPEs to the anodic stripping voltammetric detection of arsenic. Compared with AuNP-SPE, eAuNP-SPE exhibited ca. 5-fold sensitivity and offered fast (30 s preconcentration time) measurements, linear response over the concentration range from 0.5 to 12 ppb and a limit of detection (3σ/m criterion) of 0.22 ppb. Moreover, eAuNP-SPEs were successfully applied to the determination of arsenic in drinking water. Results demonstrated a new type of AuNP-modified low cost electrodes lend themselves to extremely simple preparation while offering enhanced detection capabilities and a wide-scope of applicability.

Potentiometric microelectrodes are regarded as promising probes for ion sensing when only limited sample volumes are available. In this work, an all-solid-state ion-selective microelectrode (ISμE) has been developed by coating ionophore-based ion-selective membrane on a poly(3,4-ethylenedioxythiophene)-poly(sodium 4-styrenesulfonate) modified gold wire with a diameter of 14 μm for detection of copper. Under the optimized conditions, the proposed all-solid-state Cu2+-ISμE shows a Nernst response toward Cu2+ in 0.5 M NaCl in the range from 2.5 × 10−7 to 2.5 × 10−4 M with a detection limit of 4.0 × 10−8 M. Additionally, the Cu2+-ISμE has been used for monitoring the vertical distribution profile of Cu2+ in coastal sediment pore water with a small volume (e.g., 300 μL). The results agree well with those obtained by anodic stripping voltammetry, which indicates that the proposed potentiometric technique based on the all-solid-state ISμE is promising for detection of Cu2+ in coastal sediment pore water. The method for the preparation of the ISμE can be extended to detect other heavy metal ions in sediments by using different ion-selective membranes.

A sensitive and selective differential pulse-adsorptive anodic stripping voltammetry (DP ASV) method has been developed for trace determination of timolol maleate drug in complex matrices. The established method is first of its kind for timolol maleate (TM) determination with a wide linear dynamic range (1.0 × 10−9–2.0 × 10−5 mol L−1) coupled with limits of detection and quantification of 7.1 × 10−10 mol L−1 (0.31 μg L−1) and 2.4 × 10−9 mol L−1 (1.04 μg L−1), respectively. A relative standard deviation (±0.565%, n = 5) at 2.0 × 10−6 mol L−1 concentration of the drug was obtained. The method was validated by comparison with standard HPLC method. Statistical treatment of data using Student t and F tests at P = 0.05 revealed no significant differences between experimental and tabulated t and F values. Due to high selectivity towards TM and minimum interference from common organic and inorganic compounds the developed probe was successfully applied for trace analysis of TM in an eye drop, urine and water samples. The established method has a unique advantage to be quantitatively applied to a variety of samples due to rapid response, short analytical time and high sensitivity, and excellent selectivity with good reproducibility. The figures of merits were compared successfully with some reported electrochemical, chromatographic and spectrochemical methods. The interfacial properties of the modified Nafion/c-MWCNTs/GCE were explored by electrochemical impedance spectroscopy (EIS).

A novel gold-label silver-stain electrochemical immunosensor was developed based on polythionine-gold nanoparticles (PTh-Au) modified glassy carbon electrode (GCE) as a platform and secondary antibody labeled Au NPs (Ab2-Au) as immumoprobe for carcinoembryonic antigen (CEA) detection. The sandwich-type biosensor adopted anodic stripping voltammetry to detect silver stripping signal when the Ab2-Au of the formed immunocomplexes were stained with silver. The optimized detection conditions were investigated. The effect of different electrochemical responses at various concentrations of CEA was checked by anodic stripping voltammetry. This immunosensor showed a low detection limit of 0.055 ng/mL and a wide linear calibration of 0.1–120 ng/mL (R2 = 0.99856). Moreover, this immunoassay also existed the advantages of good reproducibility, stability and selectivity. Thus, this immunosensing protocol may provide a potential application for effective clinical detection of CEA.

Nano sized zinc ferrite (ZnFe2O4) particles have been synthesized by a simple solution combustion method and its electrochemical sensing application has been reported after modifying the glassy carbon electrode with thin film of zinc ferrite. The nanoparticles have been characterized by FTIR, XRD, BET, FESEM and TEM techniques to ascertain the particle size and its surface morphology. It has been used as an electrochemical sensing tool in the simultaneous measurement of lead and cadmium ions at trace level by differential pulse anodic stripping voltammetry (DPASV). All the experimental variables have been optimized and it has been utilized in real sample analysis. The sensor exhibited wide linearity in the concentration range 10–130 ppb with detection limits of 1.12 and 2.52 ppb for lead and cadmium metal ions, respectively.

In the present paper, for the first time, the integrated three-electrode screen-printed sensor with in situ plated bismuth film carbon working electrode was applied for the ultratrace determination of thallium(I) (Tl(I)). Under optimized conditions extremely low limits of detection were reached, 8.47 × 10−10 and 6.71 × 10−12 mol L−1 for the deposition times of 60 s and 300 s, respectively. The influences of foreign metal ions and surfactants on the voltammetric signal of thallium in natural samples were minimized using 1 × 10−5 mol L−1 EDTA and Amberlite XAD-7 resin added to the buffer solution (CH3COONH4, CH3COOH and NH4Cl) of pH = 4.6 ± 0.1. The developed voltammetric method with integrated three-electrode screen-printed sensor was validated with use of certified reference materials (surface, rain and natural water) and can be in future applied to field analyses of Tl(I).

An activated biochar coming from pyrolysis of dead Posidonia oceanica residues has been tested as adsorbent material for Cd2+, Pb2+ and Cu2+ ions. The biomass, the activated and the non activated biochars were previously characterized by using several instrumental techniques. The pH of metal ion solution in kinetic and thermodynamic adsorption experiments was fixed at 5 whilst, the dependence on ionic medium, ionic strength and temperature have been evaluated carrying out batch experiments at different experimental conditions. Differential Pulse Anodic Stripping Voltammetry and Inductively Coupled Plasma Optical Emission Spectroscopy have been used to measure the metal ion concentration in the solutions. Several kinetic and isotherm equations were used to fit experimental data. The thermodynamic parameters ΔG, ΔH and ΔS of Pb2+ adsorption process were calculated by using Gibbs and van't Hoff equations. A speciation study of the Pb2+ ion was also done in order to evaluate the influence of ionic medium and ionic strength on the adsorption process. Information about adsorption mechanism was obtained from the analysis of thermodynamic parameters of adsorption and of the results of metal ions speciation and biochar characterization.

This work presents a simple and sensitive method to measure in situ free Cu(II) ions in biodiesel using organic-resistant screen-printed gold electrodes (SPGEs) and demonstrates the direct correlation of the content of Cu(II) ions with oxidation stability of biodiesel. Biodiesels contaminated with copper due to corrosion, spiking with standard solutions, and naturally occurring from the oil source, were analyzed after simple dilution in 90% (v/v) ethanol and 10% (v/v) water containing 0.1 mol L−1 HCl as electrolyte (final concentration). Square-wave anodic stripping voltammetry under hydroethanolic media enabled the determination of Cu(II) ions in biodiesel, while the total Cu content was determined by atomic absorption spectrometry. The Rancimat method measured the oxidation stability of biodiesels based on induction period (IP) values, and the results indicate a decrease in IP values due to the catalytic effect of copper in biodiesel, which present direct correlation with the free content of Cu(II) rather than the total copper content. Hence, we recommend the measurement of free metal ions in biodiesel to predict its lower oxidation stability using disposable SPGEs for in-loco analysis. This voltammetric sensor responds to Cu(II) ions in hydroethanolic media for 80 consecutive measurements before its replacement and it is considered highly-repetitive (RSD

This study aimed to investigate the effect of dissolved humic acid (dHA) on Zn bioavailability and the subsequent influence on the Zn-induced thyroid toxicity. Zn toxicity was assessed using a yeast bioassay in the presence and absence of dHA. With increasing concentration of dHA, the toxic effects decreased, and the free Zn concentrations detected by the anodic stripping voltammetry (ASV) method also decreased. The high correlation (R = 0.92, p 0.001) between toxic effects and free Zn concentrations indicated that Zn thyroid toxicity largely comes from the free Zn fraction. Water samples from the Qing River in Beijing were also assayed for thyroid toxicity. The results revealed that the metals might contribute to the toxicity. The known thyroid hormone-disrupting metals, namely, Zn, Cd and Hg, were analyzed. The cause-effect relationship between the observed thyroid toxicity and free Zn concentrations as well as their dose-effect relationships were examined. Our results showed that Zn might be the major contributor to the observed thyroid toxicity caused by metals. These results suggest that the ASV method and the identified major contributor (Zn) may be used in lieu of conventional environmental analyses to follow the progression of a risk assessment or remediation strategy.

Zinc Oxide (ZnO) nanorods were synthesized by using zinc acetate as a precursor via thermal decomposition method and then used to prepare ZnO@G nanocomposite by facile room-temperature approach using a colloidal coagulation effect. The as prepared ZnO@G nanocomposite was applied to modify the working electrode surface in an electrochemical sensor of Cd2+ and Pb2+for the first time. The morphologies of ZnO and ZnO@G nanocomposite were characterized by transmission electron microscopy, that exhibits the nanorod shape with an average diameter of 89 ± 18 nm, uniformly dispersed and intercalated between each G layer. Furthermore, the important factors affecting on the sensor sensitivity, including ZnO@G ratio, ZnO@G concentration, Bi3+ concentration and electrochemical parameters were systematically investigated using square-wave anodic stripping voltammetry. Under the optimal conditions, a linear range was found to be 10–200 μg L−1 and the detection limits were 0.6 and 0.8 μg L-1 for Cd2+ and Pb2+, respectively. Eventually, it was successfully used for the simultaneous detection of Cd2+ and Pb2+ in real wastewater samples and the results corresponded well with a standard inductively coupled plasma-optical emission spectroscopy.

Here, a needle-shaped electrode based on commercial acupuncture needle was fabricated and functionalized with dendritic gold nanostructures (AuNDs) and ion-exchange polymer (Nafion) for voltammetric speciation analysis of copper (Cu) in seawater. To achieve the enhanced performance for voltammetric determination of Cu in seawater, the acupuncture needle electrode (ANE) was functionalized with AuNDs via electrochemical deposition and covered with Nafion. AuNDs facilitate the electrochemical responses of Cu due to their excellent catalytic and electroconductive properties, whereas Nafion can stabilize the AuNDs deposited on the surface of the needle tip and enhance the voltammetric responses through its specific cation-exchange ability with Cu2+. The so-designed AuNDs/Nafion/ANE showed excellent performance for the determination of Cu in complex matrix like seawater. Under the optimal conditions, the response of Cu at this functional needle-shaped electrode was linear in the concentration range from 0.05 to 1 nmol L−1 with an ultralow detection limit of 15.4 pmol L−1. Additionally, the functional needle-shaped electrode has been successfully used for the direct determination of different Cu species in seawater via anodic stripping voltammetry.

A sensitive and selective TAPB-DMTP-COF (TAPB, 1,3,5-tris(4-aminophenyl)benzene; DMTP, 2,5-dimethoxyterephaldehyde; COF, covalent organic framework) modified carbon paste electrode was evaluated as a novel electrochemical sensor for the determination of lead in an aqueous medium. Lead was accumulated on the TAPB-DMTP-COF surface by the complexation with the amine groups, and detected by differential pulse anodic stripping voltammetry. Due to the distinct structure features of COF, the resulting sensor revealed a fast electron transfer rate and outstanding adsorption capacity for lead. The influence of various experimental parameters (the content of COF, pH of the electrolyte solution, accumulation potential, and accumulation time) on the peak current were investigated in the overall analysis procedure. Under optimum conditions, the method showed an excellent linearity to the concentration of lead in the range of 0.0050 to 2.0 μmol/L with a detection limit of 1.9 nmol/L, and the relative standard deviation was 3.1% for 0.50 μmol/L of lead (n = 11). This method not only displays the feasibility of COF based sensor for trace levels of metal ions detection but also broadens the scope of applications of COF based hybrid materials in electroanalytical chemistry.

An electrochemical sensor based on the use of CeO2 nanoparticles modified glassy carbon electrode (CeO2/GCE) was prepared and applied for determination of Cu(II) and Hg(II) individually and simultaneously. The differential pulse anodic stripping voltammetry (DPASV) results indicates that the CeO2 NPs based sensor exhibits good electroanalytical performance with two well-resolved voltammetric stripping peaks for Cu(II) and Hg(II). The proposed CeO2 NPs based sensor shows a wide linear range from 10 to 350 µg/L and a lower detection limit (3σ) 2.9 for Cu(II) and 3.3 µg/L for Hg(II) under optimized conditions. The developed sensor was successfully applied for the quantification of Cu(II) and Hg(II) in real sample matrices, and satisfactory results were obtained.

Graphite furnace atomic absorption spectrometry (GFAAS) is rarely used for direct trace analysis of whole blood because of strong interferences caused by the organic matrix. Especially it concerns bovine blood samples, containing more proteinaceous and lipid components in comparison with human blood. In our work, the novel two-stage probe atomization (TPA) technique for Cd and Pb determination by GFAAS in whole bovine blood with minimum sample pre-treatment has been developed. Making use of TPA and chemical modifier has eliminated matrix suppression and decreased the non-selective absorption level by several times. It allowed us to dispense with brief sample pre-treatment by a mixture of nitric acid and hydrogen peroxide (1:1) without autoclave digestion. The pyrolysis temperatures were 650 °C for Cd and 900 °C for Pb in the presence of Pd modifier. The analytical signal dependence on the number of concentrating cycles has been studied. The maximal number of capturing cycles was found (15 and 10 for Cd and Pb). Applying of multiple probe concentrating has additionally decreased the limits of detection (LODs) comparing with single TPA. The achievable LODs in optimized conditions were found to be 0.01 and 0.2 μg/L for Cd and Pb, respectively (3 s test). The accuracy of the proposed technique was confirmed by anodic stripping voltammetry (ASV). The relative standard deviation for 5.1 μg/L Cd and 26 μg/L Pb concentrations was 6.4% and 7.5%, respectively.

This work presents the development of a sensitive and friendly environment electrochemical methodology with high analytical performance for quinolone detection. The method is based on square-wave anodic stripping voltammetry which is simple and reliable for determination of quinolone family on the bismuth film electrode (BiFE). The deposition potential, deposition time, buffer solution pH, voltammetry detection technique and bismuth concentration at fixed quinolone concentration (1 μg L−1) were evaluated by fractionated factorial and central composite designs. The high cross-reactivity obtained in the evaluation of different quinolones showed that this methodology could be applied to quinolone family with limits of detection (LOD) close to 0.5 ng L−1. Since is widely known that quinolones can reach aquatic ecosystems, the developed electroanalytical method was applied in the monitoring of moxifloxacin (MOXI) concentrations in ecotoxicity studies by means of acute toxicity test using two cladoceran species as biological models: Daphnia magna and Ceriodaphnia dubia. As a result of ecotoxicity, both species showed comparable sensitivities at MOXI. Toxicity studies of quinolones on aquatic organisms are very limited so the effects of MOXI to cladoceran species are highlighted. The interaction of both disciplines –Chemistry and Ecology- would allow knowing of global behavior of quinolones in natural environments, from an integrative perspective. Fil: Kergaravat, Silvina Vanesa. Universidad Nacional del Litoral; Argentina Fil: Gagneten, Ana María. Universidad Nacional del Litoral; Argentina Fil: Hernández, Silvia Raquel. Universidad Nacional del Litoral; Argentina

This work describes a sensitive and selective method for the determination of aqueous Hg(II) by anodic stripping voltammetry at 2,4,6-Trimercaptotriazine (TMT)/gold nanoparticles (GNPs) modified electrode. The TMT/GNPs modified electrode was prepared by sequential coating of gold nanoparticles and TMT. The TMT/GNPs modified electrode was characterized by surface morphological studies, UV-Visible spectroscopy, and Electrochemical Impedance spectroscopy (EIS). Various operational parameters which influence the determination of Hg(II) such as electrolyte, pH, deposition time, and preconcentration time have been studied. TMT/GNPs modified electrode was highly sensitive towards the determination of Hg(II) and showed a linear range of 16 nM–2000 nM with a detection limit of 5.3 nM (S/N = 3). The electrode surface was regenerated on each stripping response, which was renewed by dipping the electrode in 0.2 M HNO3 for 3 min. Interference of other metal ions was also investigated and result confirms that the presence of other cations and anions did not show any interfernce. The newly developed TMT/GNPs modified electrode was successfully applied for the determination of Hg(II) in lake water samples with good recovery.

The application of a novel fully 3-D printed carbon nanofiber–graphite–polystyrene electrode has been investigated for the trace determination of Zn2+ by differential pulse anodic stripping voltammetry. The possibility of utilising a carbon pseudo-reference electrode was found to be successful. The effect of accumulation potential and time were investigated and optimised. Using an accumulation potential of −2.9 V (vs. C) and an accumulation time of 75 s a single sharp anodic stripping peak was recorded exhibiting a linear response from 12.7 μg/L to 450 μg/L. The theoretical detection limit (3σ) was calculated as 8.6 μg/L. Using the optimised conditions a mean recovery of 97.8%, (%CV = 2.0%, n = 5) for a tap water sample fortified at 0.990 μg/mL was obtained indicating the method holds promise for the determination of Zn2+ in such samples.

Double layered one-by-one imprinted hollow core-shells@ pencil graphite electrode was fabricated for sequential sensing of anti-HIV drugs. For this, two eccentric layers were developed on the surface of vinylated silica nanospheres to obtain double layered one-by-one imprinted solid core-shells. This yielded hollow core-shells on treatment with hydrofluoric acid. The modified hollow core-shells (single layered dual imprinted) evolved competitive diffusion of probe/analyte molecules. However, the corresponding double layered one-by-one imprinted hollow core-shells (outer layer imprinted with Zidovudine, and inner layer with Lamivudine) were found relatively better owing to their bilateral diffusions into molecular cavities, without any competition. The entire work is based on differential pulse anodic stripping voltammetry at double layered one-by-one imprinted hollow core-shells. This resulted in indirect detection of electro inactive targets with limits of detection as low as 0.91 and 0.12 (aqueous sample), 0.94 and 0.13 (blood serum), and 0.99 and 0.20 ng mL-1 (pharmaceutics) for lamivudine and zidovudine, respectively in anti-HIV drug combination.

We report an ultrasensitive electrochemical sensor for Hg2+ detection, on the basis of two Hg2+-specific oligonucleotide probes (a thiolated capture probe and a biotinated signal probe), "terminal" signal amplification of alkaline phosphatase catalyzed deposition of silver and in situ microliter-droplet anodic stripping voltammetry (ASV). The thiolated capture probe is immobilized on an Au-plated glassy carbon electrode, and the biotinated signal probe is then attached to the electrode surface through the thymine-Hg2+-thymine interaction in the presence of Hg2+. A streptavidin-alkaline phosphatase (ALP) composite is then immobilized on the electrode surface via biotin-streptavidin interaction. The immobilized ALP can catalyze the hydrolyzation of ascorbic acid 2-phosphate trisodium salt to generate ascorbic acid, which can reduce AgNO3 to form silver deposit on the modified electrode. Quantitative analysis of Hg2+ is conducted through microliter-droplet ASV of silver after its simultaneous chemical dissolution and cathodic preconcentration on the modified electrode. The sensor can linearly respond to the common logarithm of Hg2+ concentration from 0.1nM to 250μM with a limit of detection of 0.01nM (2 ppt, S/N = 3) and a sensitivity as high as 227μAdec-1.

This work describes a microfabricated electrochemical paper-based analytical device (ePAD) for the simultaneous voltammetric determination of Cd(II) and Zn(II) at trace levels. The ePAD integrates a wax-printed microfluidic channel and, on the reverse side of the paper, sputtered thin films of Sn, Pt and Ag serving as the working, counter and reference electrodes, respectively. The microfluidic channel ensures electrolytic contact between the electrodes with only 10 μL of working solution. The determination of Cd(II) and Zn(II) is performed at the 400 nm-thick sputtered Sn-film working electrode, in a pump-free and unstirred mode, by anodic stripping voltammetry. Under the selected conditions, the limits of detection were 0.9 μg L−1 Cd(II) and 1.1 μg L−1 Zn(II) and the between-sensor reproducibility was 5.7% for Cd(II) and 7.5% for Zn(II) at the 30 μg L−1 level (n = 5). The ePAD costs only 0.11$ and presents favorable fabrication and operational features, that make it suitable for simple, fast and on-site analysis.

A systematic electrochemical impedance spectroscopy (EIS) analysis at different potentials of an in situ-prepared bismuth-film glassy carbon electrode (BiFE) in 0.1 M acetate buffer solution is reported. This electrode is employed in the square-wave anodic stripping voltammetry (SWASV) technique for the determination of trace amounts of the heavy metals Zn, Cd, and Pb. The method was first validated for detection limit, linear range, sensitivity, precision and accuracy to clearly prove the superior action of BiFE compared with the bare glassy carbon electrode (GCE). Next, in order to investigate the characteristics of this sensor, EIS measurements were carried out at slightly more negative potentials than the potentials at which each individual stripping signal is detected, after the deposition step at different deposition potentials. For comparison, EIS measurements were also performed at open circuit potential. The studied trace metal concentration range (5–20 ppb) did not significantly influence the capacitive and resistive behaviour of the BiFE which explains why the performance of this sensor is superior compared with the bare GCE. The higher sensitivity of the SWASV method for BiFE compared with the bare GCE was explained by the lower polarisation resistance values of the former. Moreover, the potential of zero charge was also determined, and an explanation whether the system is under kinetic- and/or diffusion-controlled process is given.

As a novel and highly sensitive sensor, three-dimensional gold nanoelectrode ensembles (3D GNE) prepared by gold deposition inside the parallel pores of a porous template have been successfully applied in electrochemical determination experiments. In this study, we report on the fabrication of 3D gold nanotubes (GNT) and their application in determination of Hg (II) in water. The morphology and crystal structure of the 3D GNT were characterized by field emission scanning electron microscope (FE-SEM) and X-ray diffraction (XRD), respectively. The sensitivity of the fabricated electrode towards Hg (II) was examined using anodic stripping voltammetry (ASV) as a powerful technique in determination experiments. Under the optimized conditions, a linear response was achieved over a wide range (0.1–50 nM) for Hg (II) with a sensitivity of 0.247 µA/nM. The 3D GNT electrode exhibited good repeatability and reproducibility and a detection limit of 0.06 nM (S/N = 3) was achieved which is much lower than the limit set by the Environmental Protection Agency (EPA) for Hg (II) in drinkable water.

This paper describes the electrochemical behavior of poly-bithiophene (PBTh), poly-ethylene-3,4-dioxythiophene (PEDOT), and poly-3,4-ortho-xylendioxythiophene (PXDOT) in an EtOH/H2O (1:1) mixture using 0.1 M LiClO4 as supporting electrolyte and AcOH/AcONa to buffer pH. PBTh suffers fast degradation, whereas PEDOT and PXDOT show reasonable stability in the EtOH/H2O mixture. A strong interaction between the 3,4-alkoxythiophene polymers and the EtOH/H2O mixture was evidenced by a charge/discharge process limited by ionic movement and slow electron transfer (as signaled by a large ΔEp). Both of these processes were faster in ACN. The stability of the prepared films was studied through 100 charge/discharge cycles in ACN and in the EtOH/H2O mixture. Considerable electroactivity loss for PEDOT and PXDOT was observed in ACN, which may be caused by charge trapping phenomena and oligomer release. This loss diminished substantially in the EtOH/H2O mixture showing a current higher than 75% of the initial value and an electrochemical reversibility (i.e., the Qc/Qa ratio) higher than 90%. Due to the stability of the PEDOT and PXDOT films in the EtOH/H2O mixture, it was possible to use them in modified electrodes for Cu (II) detection using anodic stripping voltammetry, where concentration-dependent current signals were observed.

Nafion/Bismuth-Tin nanocomposites stabilized with polyoxyethylene 23 lauryl ether (brij) were produced in a mixture of nafion and brij dissolved in N-N dimethylformamide. Metal salts were reduced in the presence of sodium borohydride assisted by ultrasound. The average hydrodynamic diameter of polymer-metal particles was measured via dynamic light scattering (DLS) and related to the composition of the reactive mixture; growth kinetics were compared with the Liftshitz-Sloyozov-Wagner model, and we found that the polymer-tin system of nanoparticles was time stable and that the size of the nanoparticles, close to 100 nm, is not dependent on brij concentration. The selected nanocomposites with a total metal concentration of 13% w/w were structurally characterized by means of infrared (IR) and X-ray photoelectron spectroscopy (XPS). Furthermore, the morphology and phase-metal distribution was studied via electron microscopy (SEM and TEM). The nanocomposites were used as electrodes for cadmium detection through square-wave anodic stripping voltammetry (SWASV) in a sodium acetate buffer solution. The materials with higher bismuth content allowed obtaining better results in terms of the peak current; however, the addition of tin up to 50% allows producing material with greater resistance to oxidation.