Pencil Lead Electrode Modified with Gold Thin Layer for Voltammetric Detection of Chromium (VI)

Cr(VI) is a toxic, mutagenic, and carcinogenic metal. This heavy metal have effect harmful on organism and the environment. In this study, an electroanalytic approach was improved for detection of the Cr(VI) using a pencil lead electrode modified with gold thin layer by cyclic voltammetry. Gold thin layer was electrodeposited on the pencil lead electrode surface with potential-sweeping technique at scan of potential from 1.2 V to 0 V. Since the Cr(VI) species depends on the pH, effect of supporting electrolytes matrix at various pH were investigated. It was found that Cr(VI) gave a reduction peak with a peak potential of 0.35 V vs Ag/AgCl in cyclic voltammogram with 0.1M HClO4 as supporting electrolyte. The calibration curve for Cr(VI) at gold thin layer modified pencil lead electrode shows linearity in range of 5 µM to 100 µM with a detection limit of 2.3 µM achieved

Development of a Novel, Low-Cost, Disposable Wooden Pencil Graphite Electrode for Use in the Determination of Antioxidants and Other Biological Compounds

The development of portable sensors that can be used outside the lab is an active area of research in the electroanalytical field. A major focus of such research is the development of low-cost electrodes for use in these sensors. Current electrodes, such as glassy-carbon electrodes (GCEs), are costly and require time-consuming preparation. Alternatives have been proposed, including mechanical pencil-lead electrodes (MPEs). However, MPEs themselves possess numerous drawbacks, particularly structural fragility. In this paper, we present a novel pencil-graphite electrode (PGE) fabricated from a regular HB#2 pencil. This PGE is a simple, disposable, extremely low-cost alternative to GCEs ($0.30 per PGE, vs.$190 + per GCE), and possesses the structural stability that MPEs lack. PGEs were characterized by square-wave voltammetry of ferricyanide, gallic acid, uric acid, dopamine, and several foodstuffs. In all cases, PGEs demonstrated sensitivities comparable or superior to those of the GCE and MPE (LOD = 5.62 × 10−4 M PGE, 4.80 × 10−4 M GCE, 2.93 × 10−4 M MPE). Signal areas and peak heights were typically four to ten times larger for the PGE relative to the GCE

Estruturas dendríticas de ouro e sua aplicação no desenvolvimento de biossensor para determinação de bisfenol a (BPA)

Bisfenol A (BPA) é uma substância orgânica usado na produção de policarbonatos e resinas epóxi. A exposição humana ao BPA através de alimentos e água potável pode resultar em doenças cardiovasculares, diabetes, distúrbios neurológicos, câncer de mama e próstata. Este trabalho visa o desenvolvimento de um biossensor baseado na enzima tirosinase para detecção de BPA. Biossensores representam boas alternativas às técnicas convencionais; eles aproveitam a especificidade e a sensibilidade dos sistemas biológicos em dispositivos pequenos e de baixo custo. Na preparação do biossensor, optamos pelo uso de eletrodos impressos de carbono, que constituem células eletroquímicas descartáveis. O substrato à base de carbono consiste em uma mistura de grafite, solventes e ligantes poliméricos. Esta superfície, rica em grupos funcionais de oxigênio, funcionou perfeitamente para realizar a eletrodeposição de ouro a partir de uma solução de íons cloroáuricos utilizando as técnicas de voltametria cíclica e cronoamperometria independentemente. Diferentes morfologias foram observadas por microscopia eletrônica de varredura. Os eletrodos modificados foram utilizados como suporte para a imobilização da enzima tirosinase, permitindo a preparação de um biossensor altamente seletivo e sensível para a detecção do BPA. Além disso, o biossensor proposto mostrou estabilidade a longo prazo e foi aplicado para um teste de recuperação de BPA em água mineral e de torneira. Os eletrodos de grafite também provaram ser um material adequado como plataforma para o desenvolvimento de sensores eletroquímicos. Estruturas de ouro hiper-ramificadas resultaram da eletrodeposição realizada sob condições experimentais semelhantes aos eletrodos impressos de carbono. Além disso, estudos preliminares revelaram a potencial aplicabilidade do eletrodo modificado para a eletrooxidação de BPA em meio alcalino.Bisphenol A (BPA) is an organic substance used in the production of polycarbonates and epoxy resins. Human exposure to BPA through food and drinking water can result in cardiovascular disease, diabetes, neurological disorders, breast, and prostate cancer. This work aims the development of a biosensor based on the enzyme tyrosinase for BPA detection. Biosensors represent good alternatives to conventional techniques; they take advantage of the specificity and sensitivity of biological systems in small and low-cost devices. In the preparation of the biosensor, we opted for the use of carbon printed electrodes, which constitute disposable electrochemical cells. The carbon-based substrate consists of a mixture of graphite, solvents and polymeric binders. This surface, rich in functional groups of oxygen, worked perfectly to perform the electrodeposition of gold from a solution of chloroauric ions using the techniques of cyclic voltammetry and chronoamperometry independently. Different morphologies were observed by scanning electron microscopy. The modified electrodes were used as support for the immobilization of the enzyme tyrosinase, allowing the preparation of a highly selective and sensitive biosensor for the detection of BPA. Additionally, the proposed biosensor showed long-term stability and was applied for a recovery test of BPA in mineral and tap-water. Graphite pencil electrodes also proved to be a suitable material as a platform for the development of electrochemical sensors. Hyperbranched gold structures resulted from electrodeposition performed under similar experimental conditions to the carbon printed electrodes. Furthermore, preliminary studies revealed the potential applicability of the modified electrode for the electrooxidation of BPA in an alkaline medium

Graphene-modified pencil graphite mercury-film electrodes for the determination of trace metals by cathodic adsorptive stripping voltammetry

>Magister Scientiae - MScThis project focuses on the simple, fast and highly sensitive adsorptive stripping voltammetry detection of Nickel and Cobalt complexed with DMG and Nioxime respectively at a Reduced Graphene Oxide modified pencil graphite electrode in water samples. This research as well demonstrates a novel electrochemically reduced graphene oxide (ERGO)/mercury film (MF) nanocomposite modified PGE, prepared through successive electrochemical reduction of graphene oxide (GO) sheets and in-situ plated mercury film. The GO and graphene were characterized using FT-IR, HR-SEM, HR-TEM, XRD and Raman spectroscopy. The FT-IR results supported by Xray diffraction analysis confirmed the inclusion of oxygen moieties within the graphitic structure during the chemical oxidation step. Microscopic and spectroscopic analysis was used to confirm the stackings of graphene on the pencil electrode. The ERGO-PG-MFE, in combination with a complexing agents of [dimethylglyoxime (DMG) and Nioxime] and square-wave cathodic stripping voltammetry (SW-CSV), was evaluated towards the individual determination of Ni2+ and Co2+ respectively and simultaneous determination of both metals from the combination of DMG and Nioxime mixture. A single-step electrode pre-concentration approach was employed for the in-situ Hg-film electroplating, metal-chelate complex formation and its non-electrolytic adsorption at – 0.7 V for the individual analysis of Ni2+ and Co2+. The current response due to metal-ligand(s) complex reduction were studied as a function of experimental variables; deposition/accumulation potential, deposition/accumulation time, rotation speed, frequency and amplitude and carefully optimized for the individual determination of Ni2+and Co2+ and simultaneous determination of Ni2+ and Co2+ at low concentration levels (μg L-1) in 0.1 M NH3- NH4Cl buffer solution (pH 9.4) solution. The recorded limit of detection for the individual analysis of Ni2+and Co2+ was found to be 0.120 μg L-1 and 0.220 μg L-1 respectively, at an accumulation time of 120 s for both metals. The recorded limit of detection of the simultaneous analysis of Ni2+ and Co2+ was found to be 6.1 μg L-1 and 1.8 μg L-1 respectively. The ERGO-PG-MFE further demonstrated a highly selective stripping response toward all trace metal analysis. The testing of the applicability of graphene-based sensor and method in laboratory tap water samples was evaluated. This electrode was found to be sensitive enough to detect metal ions in the tap water samples at the 0.2 μg L-1 level for individual analysis and 0.001 μg L-1 for simultaneous, well below WHO standards

Electrochemical determination of gallic acid in food matrices using novel materials.

Gallic acid (GA), as an endogenous polyphenol, has shown many different important properties that have influenced its use in the food and pharmaceutical industry. These properties include its antioxidant, anti-cancer, anti-tumor, anti-HIV and anti-ulcerogenic activities. The most commonly used GA determination techniques have been the spectrophotometric and chromatographic techniques. However, these techniques have shown some drawbacks; they are expensive, labour intensive, time-consuming and are not suitable for in-situ measurements. Electrochemical methods using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) at inert glassy carbon electrode (GCE) or carbon paste electrodes (CPE) have also been used in the determination of GA. However, despite their easy application and fast result generation, their sensitivity and selectivity have been relatively inadequate for the analysis of GA found in beverages and pharmaceutical products. The aim of this study is therefore to investigate and develop novel nanomaterials-based electrochemical sensors for determination and analysis of GA that is fast, sensitive, cost-effective and selective. In this study, the detection of GA in red and white wines was achieved using CV, through the development of carbon-based working electrodes modified with graphene oxide nanoparticles and other metal oxide nanoparticles. The synthesised metal oxide nanoparticles were characterised using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy and Zetasizer (for particle size analysis). Meanwhile, characterisation of the developed electrodes was carried out using CV, DPV and electrochemical impedance spectroscopy. The electrochemical effects of the electrodes were analysed. This thesis presents the results of a novel graphene oxide nanocolloids-SiO2 nanoparticles combination used for the electrochemical determination of GA. The results show enhanced peak currents, with high sensitivity and selectivity. The anodic peak current was enhanced from 241 µA (for the bare GCE) to 411 µA (for the modified GCE) - with a limit of detection (LOD) of 2.09 x 10-6 mol L-1, within a concentration range of 6.25 x 10-6 to 1.0 x 10-3 mol L-1. The thesis also proposes that there is a synergistic effect between SiO2 nanoparticles and graphene oxide nanocolloids in the determination of GA. Synthesised amorphous zirconium oxide nanoparticles were used for the modification of a carbon paste electrode and used for the determination of GA. The electrode modification enhanced the electrochemical activity of GA, with increased sensitivity and selectivity. The modified electrode produced an enhanced anodic peak from 260 µA (for the bare electrode) to 451 µA (for the modified electrode) - with an LOD of 1.24 x 10-7 mol L-1, within a range of 1 x 10-6 to 1.0 x 1 x 10-3 mol L-1. The thesis additionally makes a novel proposal for the interaction and effect of the amorphous zirconia nanoparticles on the graphite in the CPE. Zinc oxide nanoparticles and cobalt oxide nanoparticles were also used individually for the modification of carbon paste electrodes. The modified electrodes showed an enhanced effect on GA oxidation. This enhanced effect was an increase in anodic peak current from 261 µA to 414 µA, when the CPE was modified. The LOD produced by the ZnO nanoparticles-modified CPE was 1.86 x 10-7 mol L-1, within a concentration range of 1 x 10-3 to 5 x 10-2 mmol L-1. Meanwhile, the effect of scan rate and the effect of pH show that the electrodes were more effective in acidic pH, and that the GA-electrode interaction was an adsorption-controlled process. Cobalt oxide nanoparticles were also synthesised, characterised and used for the modification of CPE. The modified electrode produced an enhanced anodic peak current from 302 µA (for the bare CPE) to 404 µA (for the modified electrode). The LOD of the modified electrode was studied and found to be 1.52 x 10-6 mol L-1, at a concentration range of 1 x 10-4 to 1 x 10-3 mol L-1. The modified electrodes were successfully used for the determination of GA in real samples of red and white wine. Based on the electrochemical activities of the different electrodes made, the Zirconium dioxide nanoparticles-modified carbon paste electrode seems to have produced the best results. The zirconium dioxide-modified CPE showed increased sensitivity and better limit of detection for GA

Microfluidic graphenised-paper electroanalytical devices (μGPED) for adsorptive cathodic stripping voltammetric detection of metal contaminants

Philosophiae Doctor - PhDThe need for clean, non-toxic drinking water supplies, free of pollutants and metal contamination is vital in impoverished areas and the developing world alike. With this in mind, the development of accurate, inexpensive, portable and simple devices for remote sensing applications is therefore pivotal for early detection and the prevention of illnesses. Over the last two decades, adsorptive stripping voltammetry (AdSV) has emerged as a superior detection method over common analytical techniques due to its low-cost instrumentation, unskilled labour and ability to detect a wide range of analytes