The Application of Microelectrodes for the Measurements of Trace Metals in Water

New Long-Term Use Solid Bismuth Microelectrode Arrays for Rapid and Sensitive Determination of Sunset Yellow in Isotonic Beverages and Water Samples by Adsorptive Stripping Voltammetry

This article reports on the long-term use, solid bismuth microelectrode arrays for the first time. The presented working microelectrode is characterized by particular advantages compared to bismuth film electrodes and solid single bismuth microelectrodes; these advantages include environmentally friendly properties and the amplification of recorded currents, which are subsequently more resistant to interference. The proposed solid bismuth microelectrode array was applied to develop an adsorptive stripping voltammetric procedure for Sunset Yellow determination. The main experimental parameters were optimized. The calibration graph was linear from 5 × 10-9 to 1 × 10-7 mol L-1 (time of accumulation, 60 s). The detection limit was equal to 1.7 × 10-9 mol L-1. The relative standard deviation for a concentration of Sunset Yellow of 2 × 10-8 mol L-1 was 4.1% (n = 7). Potential interference effects were examined. The presented analytical procedure was applied for the determination of Sunset Yellow in isotonic beverages and the results were confirmed by HPLC as a comparative method. The correctness of the presented procedure was also confirmed by satisfactory recovery values obtained during the analysis of spiked environmental water samples.

Adsorptive Stripping Voltammetric Quercetin Determination in Pharmaceuticals and Urine Samples Using a Long Service-Life Array of Carbon Composite Microelectrodes

This article presents for the first time a new working electrode with a long service life- the bismuth-plated array of carbon composite microelectrodes for the simple, fast and sensitive determination of quercetin by adsorptive stripping voltammetry. The main experimental conditions were selected. The calibration graph was linear from 1 × 10-9 to 2 × 10-8 mol L-1 with an accumulation time of 60 s. The detection limit was equal to 4.8 × 10-10 mol L-1. The relative standard deviation for 2 × 10-8 mol L-1 of quercetin was 4.4% (n = 7). Possible interference effects resulting from the presence of other organic and surface active compounds and interfering ions were studied. The developed procedure was successfully applied to determine quercetin in pharmaceutical preparations and the spiked urine samples.

Lithography-free interdigitated electrodes by trench-filling patterning on polymer substrate for Alzheimer's disease detection

Microelectrodes have played a crucial role in electrochemistry for the last few decades. However, the conventional lithographic processes, the key players in fabrication, are nonetheless technologically challenging, pricey, and lack reproducibility. In this work has developed a novel and low-cost patterned-replication fabrication technology for interdigitated electrode array (IDA) electrodes on the polymer substrate. Conventional UV-lithography has been utilized to fabricate the nickel IDA electrode pattern as a master mold on the stainless-steel substrate, which was replicated onto the polymer substrate by the hot-emboss technique. Then, gold was deposited on the replicated wafer by electron beam evaporation, and finally adhesive tape lift-off was used to obtain the gold IDA electrode. The fabricated IDA electrode was applied for electrochemical detection of various p-aminophenol (PAP) concentrations as a representative biomarker with a detection limit of 0.01 nM. Finally, different levels of amyloid beta 42 (Aß42) and amyloid beta aggregated (Aß Agg.), two Alzheimer's disease (AD) biomarkers, were measured using the developed IDA electrode via e-ELISA using enzyme by-products PAP. While quantified, the proposed IDA electrode successfully detects Aß42 and Aß Agg. with the lower detection limit (LOD) of 3.9 and 7.81 pg/ml, respectively.

On-field high-resolution quantification of the cobalt fraction available for bio-uptake in natural waters using antifouling gel-integrated microelectrode arrays

We report the optimization, characterization, and validation of Adsorptive Square Wave Cathodic Stripping Voltammetry on antifouling gel-integrated microelectrode arrays for autonomous, direct monitoring of cobalt(II) metal species. Detection is accomplished by complexation with an added nioxime ligand. The limit of detection established for a 90 s accumulation time was 0.29 ± 0.01 nM in freshwater and 0.27 ± 0.06 nM in seawater. The microelectrode array was integrated in a submersible probe to automatically dose the complexing agent nioxime and realize an integrated sensing system. For the first time ever, the potentially bioavailable Co(II) fraction was determined in La Leyre River-Arcachon Bay continuum, enabling to evaluate the potential ecotoxicological impact of freshwater-carried Co(II) in the Arcachon Bay. The measured potentially bioavailable Co(II) concentrations were hazardous for aquatic biota along the continuum. The electrochemical Co(II) data were compared to ICP-MS data in various fractions to determine spatial Co(II) speciation.

A Novel Eco-Friendly and Highly Sensitive Solid Lead-Tin Microelectrode for Trace U(VI) Determination in Natural Water Samples

For the first time a solid state lead-tin microelectrode (diameter ϕ 25 µm) was utilized for U(VI) ion determination by adsorptive stripping voltammetry. The described sensor is characterized by high durability, reusability and eco-friendly features, as the need for using lead and tin ions for metal film preplating has been eliminated, and consequently, the amount of toxic waste has been limited. The advantages of the developed procedure resulted also from the utilization of a microelectrode as a working electrode, because a restricted amount of metals is needed for its construction. Moreover, field analysis is possible to perform thanks to the fact that measurements can be carried out from unmixed solutions. The analytical procedure was optimized. The proposed procedure is characterized by two orders of magnitude linear dynamic range of U(VI) determination from 1 × 10^-9 to 1 × 10^-7 mol L^-1 (120 s of accumulation). The detection limit was calculated to be 3.9 × 10^-10 mol L^-1 (accumulation time of 120 s). RSD% calculated from seven subsequent U(VI) determinations at a concentration of 2 × 10^-8 mol L^-1 was 3.5%. The correctness of the analytical procedure was confirmed by analyzing a natural certified reference material.

Screen-printed electrochemical sensors for environmental monitoring of heavy metal ion detection

Heavy metal ions (HMIs) are known to cause severe damages to the human body and ecological environment. And considering the current alarming situation, it is crucial to develop a rapid, sensitive, robust, economical and convenient method for their detection. Screen printed electrochemical technology contributes greatly to this task, and has achieved global attention. It enabled the mass transmission rate and demonstrated ability to control the chemical nature of the measure media. Besides, the technique offers advantages like linear output, quick response, high selectivity, sensitivity and stability along with low power requirement and high signal-to-noise ratio. Recently, the performance of SPEs has been improved employing the most effective and promising method of the incorporation of different nanomaterials into SPEs. Especially, in electrochemical sensors, the incorporation of nanomaterials has gained extensive attention for HMIs detection as it exhibits outstanding features like broad electrochemical window, large surface area, high conductivity, selectivity and stability. The present review focuses on the recent progress in the field of screen-printed electrochemical sensors for HMIs detection using nanomaterials. Different fabrication methods of SPEs and their utilization for real sample analysis of HMIs using various nanomaterials have been extensively discussed. Additionally, advancement made in this field is also discussed taking help of the recent literature.

All-in-Fiber Electrochemical Sensing

Electrochemical sensors have found a wide range of applications in analytical chemistry thanks to the advent of high-throughput printing technologies. However, these techniques are usually limited to two-dimensional (2D) geometry with relatively large minimal feature sizes. Here, we report on the scalable fabrication of monolithically integrated electrochemical devices with novel and customizable fiber-based architectures. The multimaterial thermal drawing technique is employed to co-process polymer composites and metallic glass into uniform electroactive and pseudoreference electrodes embedded in an insulating polymer cladding fiber. To demonstrate the versatility of the process, we tailor the fiber microstructure to two configurations: a small-footprint fiber tip sensor and a high-surface-area capillary cell. We demonstrate the performance of our devices using cyclic voltammetry and chronoamperometry for the direct detection and quantification of paracetamol, a common anesthetic drug. Finally, we showcase a fully portable pipet-based analyzer using low-power electronics and an "electrochemical pipet tip" for direct sampling and analysis of microliter-range volumes. Our approach paves the way toward novel materials and architectures for efficient electrochemical sensing to be deployed in existing and novel personal care and surgical configurations.

Ranolazine-Functionalized Copper Nanoparticles as a Colorimetric Sensor for Trace Level Detection of As3

This study involves environmentally friendly synthesis of copper nanoparticles in aqueous medium without inert gas protection, using ranolazine as a capping material. UV-Visible (UV-Vis) spectrometry showed that ranolazine-derived copper nanoparticles (Rano-Cu NPs) demonstrate a localized surface plasmon resonance (LSPR) band at 573 nm with brick-red color under optimized parameters, including pH, reaction time, and concentrations of copper salt, hydrazine hydrate, and ranolazine. The coating of ranolazine on the surface of Cu NPs was studied via Fourier transform infrared (FTIR) spectroscopy. Scanning electron microscopy (SEM) revealed that Rano-Cu NPs consist of spherical particles. X-ray diffraction (XRD) verified that Rano-Cu NPs are crystalline in nature. Atomic force microscopy (AFM) showed that the average size of Rano-Cu NPs was 40 ± 2 nm in the range of 22⁻95 nm. Rano-Cu NPs proved to be highly sensitive as a selective colorimetric sensor for As³⁺ via color change from brick red to dark green, in the linear range of 3.0 × 10^-7 to 8.3 × 10^-6 M, with an R² value of 0.9979. The developed sensor is simple, cost effective, highly sensitive, and extremely selective for As³⁺ detection, showing a low detection limit (LDL) of 1.6 × 10^-8 M. The developed sensor was effectively tested for detection of As³⁺ in some water samples.

Multi-element determination of metals and metalloids in waters and wastewaters, at trace concentration level, using electroanalytical stripping methods with environmentally friendly mercury free-electrodes: A review

Nowadays, water is no longer regarded as an inexhaustible resource and the excessive release and proliferation of toxic metal(loid)s into aquatic environments has become a critical issue. Therefore, fast, accurate, simple, selective, sensitive and portable methodologies to detect multiple elements in natural waters is of paramount importance. Electrochemical stripping analysis is an efficient tool for trace metal(loid)s determinations and bring new prospects for answering the current environmental concerns. This review presents a survey of the advancements made between 2003 and 2016 on the development and application of non-toxic mercury free electrodes on the simultaneous analysis of metals and metalloids in waters and wastewaters by means of electroanalytical stripping techniques. The advantages, limitations, improvements and real applications of these "green" sensors are discussed from a critical point of view.

Nanoparticle electrochemistry

This perspective article provides a survey of recent advances in nanoscale electrochemistry, with a brief theoretical background and a detailed discussion of experimental results of nanoparticle based electrodes, including the rapidly expanding field of “impact electrochemistry”.

Toward the development of smart and low cost point-of-care biosensors based on screen printed electrodes

Screen printing technology provides a cheap and easy means to fabricate disposable electrochemical devices in bulk quantities which are used for rapid, low-cost, on-site, real-time and recurrent industrial, pharmaceutical or environmental analyses. Recent developments in micro-fabrication and nano-characterization made it possible to screen print reproducible feature on materials including plastics, ceramics and metals. The processed features forms screen-printed disposable biochip (SPDB) upon the application of suitable bio-chemical recognition receptors following appropriate methods. Adequacy of biological and non-biological materials is the key to successful biochip development. We can further improve recognition ability of SPDBs by adopting new screen printed electrode (SPE) configurations. This review covers screen-printing theory with special emphasis on the technical impacts of SPE architectures, surface treatments, operational stability and signal sensitivity. The application of SPE in different areas has also been summarized. The article aims to highlight the state-of-the-art of SPDB at the laboratory scale to enable us in envisaging the deployment of emerging SPDB technology on the commercial scale.

Novel electrochemical method of fast and reproducible fabrication of metallic nanoelectrodes

A novel electrochemical wire etching method of fabrication of ultrasharp nanoelectrodes is reported. Tungsten wires can be sharpened to less than 10 nm tip radius in a reproducible manner in less than 1 min by using controllable hydrodynamic electrolyte flow combined with optimized electrochemical etching parameters. The method relies on the variations of the electric field at the surface of a metal wire, while the electrolyte solution is in motion, rather than on the ionic gradient generated in a static solution.

Arrays of microelectrodes: technologies for environmental investigations

Within this work it is our intention to provide an overview of the use of arrays or microelectrodes in the characterisation of environmental samples. Electrochemical methods are often a relatively simple and inexpensive alternative to spectroscopic or chromatographic methods for the analysis of a wide range of analytes. Arrays of microelectrodes display a number of advantages over simple planar macroelectrodes and the reasons for this will be detailed within this work. We will also describe some of the most common methods for constructing microarrays. The application of these arrays for analysis of environmental samples such as soil and water for heavy metal contamination has been the major focus of research in this field and comprises much of this review. However other systems will also be detailed such as determination of various anions or other samples such as pesticides.

The voltammetric behaviour of lead at a microband screen-printed carbon electrode and its determination in acetate leachates from glazed ceramic plates

Microband screen-printed carbon electrodes (μBSPCEs) without further modification have been investigated as disposable sensors for the measurement of lead in acetate leachates from ceramic glazed plates. Cyclic voltammetry was employed to elucidate the electrochemical behaviour of Pb(2+) at these electrodes in a variety of supporting electrolytes. The anodic peaks obtained on the reverse scans, showed that Pb had been deposited as a thin layer on the surface of the μBSPCE. The anodic peak of greatest magnitude was obtained in 0.1M pH 4.1 acetate buffer containing 13 mM Cl(-). The effect of chromium, copper, phosphate, sulphate and tin was examined and under the conditions employed, no significant change in current was found. The μBSPCEs were evaluated by carrying out lead determinations for acetate leachates from glazed ceramic plates. A highly decorated ornamental plate was found to leach 400 μg Pb(2+) (%CV=1.91%). A second plate, designed for dinnerware was found not to leach any detectable levels of Pb(2+). However, once fortified with 2.10 μg of Pb (equivalent to 100 ng/ml in the leachate), a mean recovery of 82.08% (%CV=4.07%) was obtained. The performance characteristics indicate that reliable data has been obtained for this application which could identify potentially toxic sources of lead.

Chemical Sensors and Measurement

Chemical sensors have been widely used in the biomedical field. With the rapid development of microelectronics and microprocessing technology, chemical sensors have grown to be more and more miniaturized and integrated. Combined with new information processing technology, intelligent chemical sensor arrays such as e-Nose and e-Tongue have been developed. Meanwhile, microfluidic chips enable continuous monitoring of chemical substances in living organisms.

Metal supplementation to UASB bioreactors: from cell-metal interactions to full-scale application

Upflow anaerobic sludge bed (UASB) bioreactors are commonly used for anaerobic wastewater treatment. Trace metals need to be dosed to these bioreactors to maintain microbial metabolism and growth. The dosing needs to balance the supply of a minimum amount of micronutrients to support a desired microbial activity or growth rate with a maximum level of micronutrient supply above which the trace metals become inhibitory or toxic. In studies on granular sludge reactors, the required micronutrients are undefined and different metal formulations with differences in composition, concentration and species are used. Moreover, an appropriate quantification of the required nutrient dosing and suitable ranges during the entire operational period has been given little attention. This review summarizes the state-of-the-art knowledge of the interactions between trace metals and cells growing in anaerobic granules, which is the main type of biomass retention in anaerobic wastewater treatment reactors. The impact of trace metal limitation as well as overdosing (toxicity) on the biomass is overviewed and the consequences for reactor performance are detailed. Special attention is given to the influence of metal speciation in the liquid and solid phase on bioavailability. The currently used methods for trace metal dosing into wastewater treatment reactors are overviewed and ways of optimization are suggested.

Anodic stripping voltammetry at a new type of disposable bismuth-plated carbon paste mini-electrodes

A new type of disposable carbon paste mini-electrodes (CPmEs), with dimensions in the 50-300 microm range, have been fabricated by heat-shrinking the end-tip of plastic micropipette tips and filling them with carbon paste. The CPmEs have been characterized by microscopic and electrochemical means and tested as substrates for in situ plated Bi film electrodes (BiF-CPmEs), used in the determination of heavy metals by square wave anodic stripping voltammetry (SWASV). It was found that this new class of CPmEs combines the advantages of carbon paste electrodes (readily renewable surface and high surface area) with those of near-microelectrode behaviour (no stirring or electrolyte excess needed). During SWASV experiments in unstirred Pb(II) and Cd(II) solutions well-shaped stripping peaks were obtained whose height varied linearly with analyte concentration in the wide 1x10(-8) to 10(-6) M range, both in acetate buffer and unbuffered solutions. Under optimal conditions detection limits of 8x10(-10) and 1.3x10(-9) M were achieved for Pb(II) and Cd(II), respectively and in a trial application, these metal ions have been determined in a spiked tap water sample using a BiF-CPmE.

A solid paraffin-based carbon paste electrode modified with 2-aminothiazole organofunctionalized silica for differential pulse adsorptive stripping analysis of nickel in ethanol fuel

A solid paraffin-based carbon paste electrode modified with 2-aminothiazole organofunctionalized silica (SiAt-SPCPE) was applied to Ni(2+) determination in commercial ethanol fuel samples. The proposed method comprised four steps: (1) Ni(2+) preconcentration at open circuit potential directly in the ethanol fuel sample, (2) transference of the electrode to an electrochemical cell containing DMG, (3) differential pulse voltammogram registering and (4) surface regeneration by polishing the electrode. The proposed method combines the high Ni(2+) adsorption capacity presented by 2-aminothiazole organofunctionalized silica with the electrochemical properties of the Ni(DMG)(2) complex, whose electrochemical reduction provides the analytical signal. All experimental parameters involved in the proposed method were optimized. Using a preconcentration time of 20 min, it was obtained a linear range from 7.5 x 10(-9) to 1.0 x 10(-6) mol L(-1) with detection limit of 2.0 x 10(-9) mol L(-1). Recovery values between 96.5 and 102.4% were obtained for commercial samples spiked with 1.0 micromol L(-1) Ni(2+) and the developed electrode was totally stable in ethanolic solutions. The contents of Ni(2+) found in the commercial samples using the proposed method were compared to those obtained by graphite furnace atomic absorption spectroscopy by using the F- and t-test. Neither the F- nor t-values exceeded the critical values at 95% confidence level, confirming that there are not statistical differences between the results obtained by both methods. These results indicate that the developed electrode can be successfully employed to reliable Ni(2+) determination in commercial ethanol fuel samples without any sample pretreatment or dilution step.