Composite Carbon Paste Biosensor for Phenolic Derivatives Based on in Situ Electrogenerated Polypyrrole Binder

Sensing Methods for Hazardous Phenolic Compounds Based on Graphene and Conducting Polymers-Based Materials

It has been known for years that the phenolic compounds are able to exert harmful effects toward living organisms including humans due to their high toxicity. Living organisms were exposed to these phenolic compounds as they were released into the environment as waste products from several fast-growing industries. In this regard, tremendous efforts have been made by researchers to develop sensing methods for the detection of these phenolic compounds. Graphene and conducting polymers-based materials have arisen as a high potential sensing layer to improve the performance of the developed sensors. Henceforth, this paper reviews the existing investigations on graphene and conducting polymer-based materials incorporated with various sensors that aimed to detect hazardous phenolic compounds, i.e., phenol, 2-chlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol, pentachlorophenol, 2-nitrophenol, 4-nitrophenol, 2,4-dinitrophenol, and 2,4-dimethylphenol. The whole picture and up-to-date information on the graphene and conducting polymers-based sensors are arranged in systematic chronological order to provide a clearer insight in this research area. The future perspectives of this study are also included, and the development of sensing methods for hazardous phenolic compounds using graphene and conducting polymers-based materials is expected to grow more in the future.

Hydrothermal Monodisperse Microspherulite Pyrite: Novel Synthesis Process and Electrochemical Study of Its Oxidation

A simple one-step hydrothermal method was developed to synthesize pyrite (FeS₂) sheet- and bulklike pyrite mineral. The Fe/S molar ratio determines the phase of FeS₂, including pyrite and marcasite. The reaction temperature and time are key factors to regulate the structure, morphology, and size of pyrite. Scanning electron and transmission electron microscopy showed the formation of monodisperse microspherulite within 1 h reaction time, and the particles aggregated to large irregular polyhedron particles with increasing reaction time up to 4 h. Electrochemical oxidation tests demonstrated that their electrochemical activity significantly decreased with increasing synthesis time. At an elevated temperature of 200 °C, bulk pyrite was obtained after a 24 h reaction time, which could have promising applications in hydrothermal pyrite ore oxidation research.

Biocompatibility study of three distinct carbon pastes for application as electrode material in neural stimulations and recordings

Neural interfaces hold great promise for research and treatment of a wide variety of neurological diseases. Medical electrodes are designed to interface with the nervous system and provide control signals for neural prostheses. We fabricated previously a hook-up neural electrode. Here we investigate the in vitro cytotoxicity of three commercial carbon pastes used for printing the conductor tracks of this electrode. At first, the carbon pastes were characterized with respect to their microstructure and chemical composition. SEM images showed a grainy texture that is associated to the carbon/graphite microparticles dispersed by the polymeric binder. All the three pastes contained in major proportions carbon and in different proportions other elements. The surface roughness analysis evidenced differences in the smoothness of the carbon paste surfaces. Sterilization procedures did not alter the microstructure or surface morphology of the pastes. Finally, cell viability based on -(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) test and fluorescence staining experiments proved non-cytotoxicity and suitability of the studied carbon pastes as electrode material for measuring neural activity during surgeries (up to a certain time period).

Modification of electrode surfaces: deposition of thin layers of polypyrrole--Au nanoparticle materials using a combination of interphase synthesis and dip-in method

Formation of thin layers of the composite material by a method based on interphase polymerization induced by a transport-controlled redox reaction is described. The obtained films were of 0.2-1 microm thickness, consisted of polypyrrole and gold nanoparticles (up to 13.5 at. %), strongly adhered to the substrate surface, and were uniform. Different carbon materials and glass wool were employed as the substrates. The first step in the synthesis was deposition of an organic layer on the substrate. This was followed by dipping the substrate in an aqueous solution containing an oxidizer and appropriate washing and drying the composite film.

Highly sensitive amperometric biosensors for phenols based on polyaniline-ionic liquid-carbon nanofiber composite

A novel polyaniline-ionic liquid-carbon nanofiber (PANI-IL-CNF) composite was greenly prepared by in situ one-step electropolymerization of aniline in the presence of IL and CNF for fabrication of amperometric biosensors. The scanning electron micrographs confirmed that the PANI uniformly grew along with the structure of CNF and the PANI-IL-CNF composite film showed a fibrillar morphology with the diameter of around 95 nm. A phenol biosensor was constructed by immobilizing tyrosinase on the surface of the composite modified glassy carbon electrode via the cross-linking step with glutaraldehyde. The biosensor exhibited a wide linear response to catechol ranging from 4.0 x 10(-10) to 2.1 x 10(-6)M with a high sensitivity of 296+/-4 AM(-1)cm(-2), a limit of detection down to 0.1 nM at the signal to noise ratio of 3 and applied potential of -0.05 V. According to the Arrhenius equation, the activation energy for enzymatic reaction was calculated to be 38.8 kJmol(-1) using catechol as the substrate. The apparent Michaelis-Menten constants of the enzyme electrode were estimated to be 1.44, 1.33, 1.16, 0.65 microM for catechol, p-cresol, phenol, m-cresol, respectively. The functionalization of CNF with PANI in IL provided good biocompatible platform for biosensing and biocatalysis.

Quaternary ammonium functionalized clay film electrodes modified with polyphenol oxidase for the sensitive detection of catechol

Naturally occurring Cameroonian smectite clay has been grafted with trimethylpropylammonium (TMPA) groups and the resulting organoclay has been deposited onto a glassy carbon electrode surface as a suitable immobilization matrix for polyphenol oxidase (PPO). High sensitivity of the electrochemical device to catechol biosensing can be achieved when the enzyme was impregnated within the organoclay film subsequent to its deposition due to favorable electrostatic interaction between PPO and the TMPA-clay layer. The bioelectrode preparation method was also compatible with the use of a mediator (i.e., ferrocene) and the best performance was obtained with a three-layer configuration made of glassy carbon coated with a first layer of ferrocene (Fc), which was then covered with the PPO-impregnated TMPA-clay layer, and finally overcoated with an enzyme-free TMPA-clay film acting as a protecting overlayer to avoid leaching of the biomolecule in solution. The electrochemical behavior of the modified film electrodes was first characterized by cyclic voltammetry and, then, they were evaluated for the amperometric biosensing of the model analyte catechol in batch conditions and in flow injection analysis. Various experimental parameters likely to influence the biosensor response have been investigated, including the electrode preparation mode (composition configuration, thickness), the usefulness of a mediator, the operating potential and pH of the medium, as well as the advantageous features of the TMPA-clay in comparison to related film electrodes based on non-functionalized clays. The organoclay was found to provide a favorable environment to enzyme activity and the multilayer configuration of the film electrode to provide a biosensor with good characteristics, such as an extended linear range for catechol detection (2 x 10(-8) to 1.2 x 10(-5)M) and a detection limit in the nanomolar range (9 x 10(-9)M).

The Sonogel–Carbon materials as basis for development of enzyme biosensors for phenols and polyphenols monitoring: A detailed comparative study of three immobilization matrixes

Three amperometric biosensors based on immobilization of tyrosinase on a new Sonogel-Carbon electrode for detection of phenols and polyphenols are described. The electrode was prepared using high energy ultrasounds (HEU) directly applied to the precursors. The first biosensor was obtained by simple adsorption of the enzyme on the Sonogel-Carbon electrode. The second and the third ones, presenting sandwich configurations, were initially prepared by adsorption of the enzyme and then modification by mean of polymeric membrane such as polyethylene glycol for the second one, and the ion-exchanger Nafion in the case of the third biosensor. The optimal enzyme loading and polymer concentration, in the second layer, were found to be 285 U and 0.5%, respectively. All biosensors showed optimal activity at the following conditions: pH 7, -200 mV, and 0.02 mol l(-1) phosphate buffer. The response of the biosensors toward five simple phenols derivatives and two polyphenols were investigated. It was found that the three developed tyrosinase Sonogel-Carbon based biosensors are in satisfactory competitiveness for phenolic compounds determination with other tyrosinase based biosensors reported in the literature. The detection limit, sensitivity, and the apparent Michaelis-Menten constant K(m)(app) for the Nafion modified biosensor were, respectively, 0.064, 0.096, and 0.03 micromol, 82.5, 63.4, and 194 nA micromol(-1)l(-1), and 67.1, 54.6, and 12.1 micromol l(-1) for catechol, phenol, and 4-chloro-3-methylphenol. Hill coefficient values (around 1 for all cases), demonstrated that the immobilization method does not affect the nature of the enzyme and confirms the biocompatibility of the Sonogel-Carbon with the bioprobe. An exploratory application to real samples such as beers, river waters and tannery wastewaters showed the ability of the developed Nafion/tyrosinase/Sonogel-Carbon biosensor to retain its stable and reproducible response.

Hybrid Material Based on Chitosan and Layered Double Hydroxides: Characterization and Application to the Design of Amperometric Phenol Biosensor

A new type of amperometric phenol biosensor based on chitosan/layered double hydroxides organic-inorganic composite film was described. This hybrid material combined the advantages of organic biopolymer, chitosan, and inorganic layered double hydroxides. Polyphenol oxidase (PPO) immobilized in the material maintained its activity well as the usage of glutaraldehyde was avoided. The composite films have been characterized by Fourier transform infrared. The results indicated that PPO retained the essential feature of its native structure in the composite film. The enzyme electrode provided a linear response to catechol over a concentration range of 3.6 x 10(-9) to 4 x 10(-5) M with a sensitivity of 2750 +/- 52 mA M(-1) cm(-2) and a detection limit of 0.36 nM based on S/N = 3. The apparent Michaelis-Menten constant K(app)(M) for the sensor was found to be 0.13 mM. The activation energy for enzymatic reaction was calculated to be 27.6 kJ mol(-1). Furthermore, the biosensor exhibited excellent long-term stability and satisfactory reproducibility.

Carbon-Nanotube-Enhanced Direct Electron-Transfer Reactivity of Hemoglobin Immobilized on Polyurethane Elastomer Film

In this study, we investigate the direct electron-transfer reactivity of immobilized hemoglobin (Hb) on a polyurethane elastomer (PUE) film for biosensor designs. The PUE film synthesized by an additional polymerization possesses good biocompatibility, uniformity, and conformability and is ready for protein immobilization. Electrochemical and spectroscopic measurements show that the presence of multiwalled carbon nanotubes (MWNTs) increased the protein-PUE interaction, varied polymer morphology, improved the permeability and the conductivity of the PUE film, and thus facilitated the direct electron transfer between the immobilized Hb and the conductivity surface through the conducting tunnels of MWNTs. The immobilized Hb maintains its bioactivities and displays an excellent electrochemical behavior with a formal potential of -(334 +/- 7) mV. The addition of NaNO2 leads to an increase of the electrocatalytic reduction current of nitrite at -0.7 V. This allows us to develop a nitrite sensor with a linear response range from 0.08 to 3.6 mM. The proposed method opens a way to develop biosensors by using nanostructured materials mixed with low electrical conductivity matrixes.

Organoclay-enzyme film electrodes

This paper aims at showing the interest of organoclays (clay minerals containing organic groups covalently attached to the inorganic particles) as suitable host matrices likely to immobilize enzymes onto electrode surfaces for biosensing applications. The organoclays used in this work were natural Cameroonian smectites grafted with either aminopropyl (AP) or trimethylpropylammonium (TMPA) groups. The first ones were exploited for their ability to anchor biomolecules by covalent bonding while the second category exhibited favorable electrostatic interactions with negatively charged enzymes due to ion exchange properties that were pointed out here by means of multisweep cyclic voltammetry. AP-clay materials were applied to the immobilization of glucose oxidase (GOD) and TMPA-clays for polyphenol oxidase (PPO) anchoring. When deposited onto the surface of platinum or glassy carbon electrodes as enzyme/organoclay films, these systems were evaluated as biosensing electrochemical devices for detection of glucose and catechol chosen as model analytes. The advantageous features of these organoclays were discussed by comparison to the performance of related film electrodes made of non-functionalized clays. It appeared that organoclays provide a favorable environment to enzymes activity, as highlighted from the biosensors characteristics and determination of Michaelis-Menten constants.

Bienzymatic amperometric biosensor for choline based on mediator thionine in situ electropolymerized within a carbon paste electrode

An amperometric enzyme biosensor for the determination of choline utilizing two enzymes, choline oxidase (CHOD) and horseradish peroxidase (HRP), is described. The biosensor consisted of CHOD cross-linked onto a HRP-immobilized carbon paste electrode. The biosensor was prepared by in situ electropolymerization of poly(thionine) within a carbon paste containing the enzyme HRP and thionine monomer and then CHOD was immobilized by using chitosan film through cross-linking with glutaraldehyde. The in situ electrogenerated poly(thionine) displays excellent electron transform efficiency between the enzyme HRP and the electrode surface, and the polymer enables improvement in enzyme immobilization within the paste. Several parameters such as the amount of thionine and enzyme, the applied potential, the pH, etc. have been studied. Amperometric detection of choline was realized at an applied potential of -0.2V vs saturated calomel electrode in 1/15M phosphate buffer solution (pH 7.4) with a linear response range between 5.0 x 10(-6) and 6.0 x 10(-4)M choline and a response time of 15s. When applied to the analysis of phosphatidylcholine in serum samples, a 0.997 correlation was obtained between the biosensor results and those obtained by a hospital method.