Simultaneous determination of phenolic compounds by using a dual enzyme electrodes system

Study on the application of reduced graphene oxide and multiwall carbon nanotubes hybrid materials for simultaneous determination of catechol, hydroquinone, p-cresol and nitrite

In this paper, the reduced graphene oxide and multiwall carbon nanotubes hybrid materials (RGO-MWNTs) were prepared and a strategy for detecting environmental contaminations was proposed on the basis of RGO-MWNTs modified electrode. The hybrid materials were characterized by the scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and N(2) sorption-desorption isotherms. Due to the excellent catalytic activity, enhanced electrical conductivity and high surface area of the RGO-MWNTs, the simultaneous measurement of hydroquinone (HQ), catechol (CC), p-cresol (PC) and nitrite (NO(2)(-)) with four well-separate peaks was achieved at the RGO-MWNTs modified electrode. The linear response ranges for HQ, CC, PC and NO(2)(-) were 8.0-391.0 μM, 5.5-540.0 μM, 5.0-430.0 μM and 75.0-6060.0 μM, correspondingly, and the detection limits (S/N=3) were 2.6 μM, 1.8 μM, 1.6 μM and 25.0 μM, respectively. The outstanding film forming ability of RGO-MWNTs hybrid materials endowed the modified electrode enhanced stability. Furthermore, the fabricated sensor was applied for the simultaneous determination of HQ, CC, PC and NO(2)(-) in the river water sample.

Amperometric biosensor based on tyrosinase immobilized onto multiwalled carbon nanotubes-cobalt phthalocyanine-silk fibroin film and its application to determine bisphenol A

An amperometric bisphenol A (BPA) biosensor was fabricated by immobilizing tyrosinase on multiwalled carbon nanotubes (MWNTs)-cobalt phthalocyanine (CoPc)-silk fibroin (SF) composite modified glassy carbon electrode (GCE). In MWNTs-CoPc-SF composite film, SF provided a biocompatible microenvironment for the tyrosinase to retain its bioactivity, MWNTs possessed excellent inherent conductivity to enhance the electron transfer rate and CoPc showed good electrocatalytic activity to electrooxidation of BPA. The cyclic voltammogram of BPA at this biosensor exhibited a well defined anodic peak at 0.625 V. Compared with bare GCE, the oxidation signal of BPA significantly increased; therefore, this oxidation signal was used to determine BPA. The effect factors were optimized and the electrochemical parameters were calculated. The possible oxidation mechanism was also discussed. Under optimum conditions, the oxidation current was proportional to BPA concentration in the range from 5.0 x 10(-8) to 3.0 x 10(-6) M with correlation coefficient of 0.9979 and detection limit of 3.0 x 10(-8) M (S/N=3). The proposed method was successfully applied to determine BPA in plastic products and the recovery was in the range from 95.36% to 104.39%.

Biosensors for phenolic compounds by immobilization of tyrosinase in photocurable methacrylic-acrylic membranes of varying hydrophilicities

Electrochemical biosensors for phenolic compound determination were developed by immobilization of tyrosinase enzyme in a series of methacrylic-acrylic based biosensor membranes deposited directly using a photocuring method. By modifying the hydrophilicity of the membranes using different proportions of 2-hydroxyethyl methacrylate (HEMA) and butyl acrylate (nBA), we developed biosensor membranes of different hydrophilic characters. The differences in hydrophilicity of these membranes led to changes in the sensitivity of the biosensors towards different phenolic compounds. In general biosensors constructed from the methacrylic-acrylic based membranes showed the poorest response to catechol relative to other phenolic compounds, which is in contrast to many other biosensors based on tyrosinase. The decrease in hydrophilicity of the membrane also allowed better selectivity towards chlorophenols. However, phenol biosensors constructed from the more hydrophilic membrane materials demonstrated better analytical performance towards phenol compared with those made from less hydrophilic ones. For the detection of phenols, these biosensors with different membranes gave detection limits of 0.13-0.25 microM and linear response range from 6.2-54.2 microM phenol. The phenol biosensors also showed good phenol recovery from landfill leachate samples (82-117%).

Laccase Biosensors Based on Mercury Thin Film Electrode

A biosensor was developed by immobilizing laccase onto mercury thin film electrode (MTFE) by means of gelatin that is then crosslinked with glutaraldehyde. Mercury thin film (MTF) was deposited onto glassy carbon electrode (GCE) and the obtained biosensor was utilized for the determination of phenolic compounds. The measurement was based on the amperometric detection of oxygen consumption in relation to analyte oxidation. The optimum experimental conditions for the biosensor were investigated and the system was calibrated for both catechol and phenol. A linear relationship between sensor responses and analyte concentrations was obtained in concentration range between 0.5 x 10(-6)-5.0 x 10(-6)M for catechol and 2.5 x 10(-6)-2.0 x 10(-6)M for phenol, respectively. Mercury thin film was also formed onto the surface of screen printed graphite electrodes and applied for the catechol detection. The linearity was observed in concentration range between 2.5 x 10(-6)-3.0 x 10(-5)M.

Dual laccase-tyrosinase based Sonogel-Carbon biosensor for monitoring polyphenols in beers

A biosensor based on the bi-immobilization of laccase and tyrosinase phenoloxidase enzymes has been successfully developed. This biosensor employs as the electrochemical transducer the Sonogel-Carbon, a novel type of electrode developed by our group. The immobilization step was accomplished by doping the electrode surface with a mixture of the enzymes, glutaricdialdehyde, and Nafion-ion exchanger, as protective additive. The response of this biosensor, denoted the dual Trametes versicolor laccase (La) and Mushroom tyrosinase (Ty) based Sonogel-Carbon, was optimized directly in beer real samples and its analytical performance with respect to five individual polyphenols was evaluated. The Lac-Ty/Sonogel-Carbon electrode responds to nanomolar concentrations of flavan-3-ols, hydroxycinnamic acids, and hydroxybenzoic acids. The limit of detection, sensitivity, and linear range for caffeic acid, taken as an example, were 26 nM, 167.53 nA M (-1), and 0.01-2 microM, respectively. In addition, the stability and reproducibility of the biosensor were also evaluated in beer samples. The Lac-Ty/sonogel-carbon electrode was verified as very stable in this matrix, maintaining 80% of its stable response for at least three weeks, with a RSD of 3.6% ( n = 10). The biosensor was applied to estimate the total polyphenol index in ten beer samples, and a correlation of 0.99 was obtained when the results were compared with those obtained using the Folin-Ciocalteau reagent.

Reagentless biosensor for phenolic compounds based on tyrosinase entrapped within gelatine film

A simple and new reagentless phenolic compound biosensor was constructed with tyrosinase immobilized in the gelatine matrix cross-linked with formaldehyde. The morphologies of gelatine and gelatine/tryosinase were characterized by SEM. The tyrosinase retains its bioactivity when being immobilized by the gelatine film. Phenolic compounds were determined by the direct reduction of biocatalytically liberated quinone at -0.1 V vs SCE. The process parameters for the fabrication of the enzyme electrode were studied. Optimization of the experimental parameters has been performed with regard to pH, operating potential, temperature and storage stability. This biosensor exhibits a fast amperometric response to phenolic compounds. The linear range for catechol, phenol, and p-Cresol determination was from 5 x 10(-8) to 1.4 x 10(-4) M, 5 x 10(-8) to 7.1 x 10(-5)M, and 1 x 10(-7) to 3.6 x 10(-5)M, with a detection limit of 2.1 x 10(-8) M, 1.5 x 10(-8) M, and 7.1 x 10(-8 )M, respectively. The enzyme electrode retained ca.77% of its activity after 7 days of storage at 4 degrees C in a dry state. The proposed sensor presented good repeatability, evaluated in terms of relative standard deviation (R.S.D.=8.6%) for eight different biosensors and was applied for determination in water sample. The recovery for the sample was from 99.0% to 99.8%.

Recent advances in analytical chemistry--a material approach

Advancements of materials research have profound direct impacts on developments in analytical chemistry and may hold the key to improvement of existing or new techniques at present times and near future. Applications of materials in analytical chemistry are reviewed, with focus on sensors, separations and extraction techniques. This review aims to survey examples of interesting works carried out in the last five years over a broad spectrum of materials classified as hybrids, nanomaterials and biomolecular materials.