A catechol biosensor based on a gold nanoparticles encapsulated-dendrimer

Tyrosinase has been immobilized on a Au nanoparticles encapsulated-dendrimer bonded conducting polymer on a glassy carbon electrode for the estimation of catechol. The modified electrode was characterized by cyclic voltammetry and AFM techniques. The principle of catechol estimation was based on the reduction of biocatalytically liberated quinone species at +0.2 V versus Ag/AgCl (3 M KCl), with good stability, sensitivity, and featuring a low detection limit (about 0.002 μM) and wide linear range (0.005 μM-120 μM). The electrochemical redox peak of catechol on the GCE/PolyPATT/Den(AuNPs)/tyrosinase was also investigated. A response time of 7 s, reusability up to 5 cycles and a shelf life of more than 2 months under refrigerated conditions were reported. Various parameters influencing biosensor performance have been optimized including pH, temperature, and applied potential. The utility and application of this nanobiosensor was tested in a real water samples.     

Electrochemical oxidation of catechol at poly(indole-5-carboxylic acid) electrode

In this work we examined the electrochemical properties of poly(indole-5-carboxylic acid), PIn₅COOH. The polymer was produced by electrochemical polymerisation using cyclic voltammetry (CV). It was shown that PIn₅COOH is electroactive in aqueous solutions showing two redox processes in acidic solution and one redox process in solutions with pH > 4. The oxidation of catechol (CT) on Pt/In₅COOH modified electrodes was investigated by cyclic voltammetry (CV) and rotating disc electrode (RDE) voltammetry. It was established that CT was oxidised only after the oxidation of polymer film was initiated and that polymer significantly enhanced the oxidation and reduction peak currents in comparison with bare Pt electrode. The variation of peak currents (i _pa, i _pc) as a function of CT concentration was found to be linear up to 6 mM. Experiments with a rotating disk electrode show that the oxidation reaction of catechol occures not only at the polymer/electrolyte interface but also in the polymer film.     

In situ Raman spectroscopic studies on potential-induced structural changes in polyaniline thin films synthesized via surface-initiated electropolymerization on covalently modified gold surface

The work describes the in situ Raman spectroelectrochemical studies on polyaniline (PANi) thin films covalently bound to the modified gold surface. The PANi thin films were synthesized via surface-initiated electrochemical polymerization on gold substrates initially modified by the formation of self-assembled monolayer of 4-aminothiophenol, or comparatively by the electrografting of 4-nitrobenzenediazonium salt followed by the electrochemical reduction of aromatic nitro-groups to form aniline-containing monolayer. Due to the defined surface-chain bonding and the ordered polymer structure, the obtained thin PANi films exhibit a narrow peak separation of the polymer redox transitions and negatively shifted potential of its full oxidation, as revealed by the PANi Raman spectra recorded at controlled potentials and cyclic voltammetry measurements.     

Detection of zeptomolar concentrations of alkaline phosphatase based on a tyrosinase and horse-radish peroxidase bienzyme biosensor

A bienzyme biosensor based on tyrosinase and horse-radish peroxidase is described in a flow injection analysis and cyclic voltammetry for measurement of phenol. Tyrosinase and horse-radish peroxidase were immobilized on the surface of a glassy carbon electrode by bovine serum albumin and glutaric dialdehyde. Phenol was oxidized by tyrosinase and horse-radish peroxidase via catechol to o-quinone in the presence of oxygen and hydrogen peroxide. The o-quinone was reduced to produce catechol (the substrate recycling) on the electrode surface. The enhanced sensitivity of the bienzyme electrode to phenol was observed in the flow injection system comparing with tyrosinase and horse-radish peroxidase monoenzyme electrodes. The mechanisms for enhanced amperometric response to phenol of bienzyme electrode were discussed. The biosensor was used to detect alkaline phosphatase (ALP). A detection limit of 1.4×10⁻¹⁵ M ALP (140 zmol/100 μl) was obtained after 1 h incubation with phenyl phosphate.     

Amperometric sensors based on tyrosinase-modified screen-printed arrays

This paper describes the design, development and characteristics of a tyrosinase (polyphenol oxidase) modified amperometric screen-printed biosensor array, with the enzyme cross-linked in a redox-hydrogel namely the PVI₁₃-dmeOs polymer. Two types of Au-screen-printed four-channel electrode arrays, differing in design and insulating layer, were compared and investigated. Au-, graphite-coated-Au- and Carbopack C-coated-Au-surfaces, serving as the basis for tyrosinase immobilisation, were investigated and the performances of the different arrays were evaluated and compared in terms of their electrocatalytic characteristics, as well as operational- and storage stability using catechol as model substrate. It was found that the Carbopack C-coated array was the best choice for tyrosinase immobilisation procedure mainly due to a higher mechanical stability of the deposited enzyme layer, combined with good sensitivity and stability for up to 6 months of use. In the batch mode the biosensors responded linearly to catechol up to 30 μM with limits of detection from 0.14 μM. Parameters from cyclic voltammograms indicated that the reversibility of the direct electrochemical reaction for catechol on the three types of electrode surfaces (no tyrosinase modification) was not the limiting factor for the construction and performance of tyrosinase biosensors.     

Fabrication of a Novel Polymeric Scaffold for Amperometric Laccase Biosensor

Present work displays the preparation of an electrochemical biosensor using a conjugated polymer and laccase enzyme for catechol quantification in samples. The biosensing system is based on an enzyme immobilization on polymer modified graphite transducer surface. For that purpose, a random conjugated polymer, thienothiophene‐benzoxadiazole‐alt‐benzodithiophene (BOTT), was coated onto a graphite electrode surface via drop casting method followed by immobilization of a biomolecule (laccase) for sensing experiments. Herein, for the first time, we proposed a BOTT polymer as an inexpensive and effective way to fabricate highly sensitive and fast response biosensors. The proposed sensing system possessed superior properties with 0.38 μM limit of detection and 110.81 μA mM^?1 sensitivity. Furthermore, cyclic voltammetry and scanning electron microscopy techniques were used to examine the surface modifications. The proposed system could be useful for many future studies for catechol quantification in environmental samples.© 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2333–2339     

Electrochemical Properties of Oxidized Carbon Nano‐Onions: DRIFTS‐FTIR and Raman Spectroscopic Analyses

The electrochemical reactions of carboxylic and lactone groups on carbon nano‐onions (CNOs) in aqueous solutions result in non‐Kolbe products: alcohols, ketones, ethers and epoxides. The anodic/cathodic conversion of ox‐CNOs was assessed by Boehm titrations and by Raman and DRIFTS‐FTIR (diffuse reflectance infrared Fourier transform spectroscopy). The electrochemical properties of oxidized carbon nano‐onions were investigated by cyclic voltammetry in aqueous solutions. The ox‐CNOs are electrochemically active as a result of the reduction of the oxygen‐containing groups.     

A Novel Sensitive Electrochemical Sensor for the Simultaneous Determination of Hydroquinone and Catechol using Tryptophan-Functionalized Graphene

A novel tryptophan-functionalized graphene nanocomposite was employed for the simultaneous determination of hydroquinone and catechol. The analyte electrochemical behavior on the surface of tryptophan-functionalized graphene was investigated by cyclic voltammetry and differential pulse voltammetry. Compared to conventional graphene, enhanced peak currents were obtained that were attributed to the large number of defects on tryptophan-functionalized graphene that accelerated electron transfer between the electrode and analytes. The peak potential difference between hydroquinone and catechol at the tryptophan-functionalized graphene modified glassy carbon electrode was 104 millivolt, which was sufficiently wide to simultaneously determine hydroquinone and catechol. This method was used for the analysis of tap water.     

Structural characteristics and cyclic voltammetric behaviour of Sonogel-Carbon tyrosinase biosensors. A detailed comparative study of three immobilization matrixes

Structural characteristics an cyclic voltammetry of three amperommetric biosensors based on immobilization of tyrosinase on a Sonogel-Carbon electrode for detection of phenols are described. Cyclic voltammetry was applied to study the electrochemical behaviour of the electrode and the electrochemical reaction on the electrode surface. Scanning electron microscopy, X-ray energy dispersive spectroscopy and atomic force microscopy were used for the structure characterization of the electrode surface, enzyme film and polymers coatings. The influence of additive-protective polymers, such as polyethylene glycol and perfluorinated-Nafion ion-exchanger on the surface of the biosensor were explored.     

Investigation of the electro-oxidation and oxidation of catechol in the presence of sulfanilic acid

The electrochemical oxidation of catechol (1) in the presence of sulfanilic acid (2) was investigated. Some electrochemical (EC) techniques such as cyclic voltammetry and controlled-potential coulometry were used. The oxidation reaction of catechol (1) with periodate in the presence of sulfanilic acid (2) was also investigated spectrophotometrically. The results indicate that the o-quinone derived from catechol participate in Michael addition reaction with sulfanilic acid (2). In addition, according to the ECE mechanism, the observed homogeneous rate constant (k_obs) for the reaction of o-quinone derived from catechol (1) with sulfanilic acid (2) has been estimated by digital simulation of cyclic voltammograms.     

电化学组装法制备对-巯基苯胺/聚苯胺纳米有序导电聚合物膜

提出了制备二维纳米有序有机导电聚合物膜的新方法--电化学组装法,应用该方法在电位脉冲的作用下使苯胺聚合到对-巯基苯胺修饰的金电极上,获得了致密、有序的对-巯基苯胺/聚苯胺(p-aminothiolphenol/polyaniline,PATP/PANI)导电寡聚物薄膜.用STM研究了Au(111)/PATP、Au(111)/PATP/PANI膜表面的二维有序性,用SERS谱表征了Au(粗糙表面)/PATP、Au(粗糙表面)/PATP/PANI膜的结构和成分,并以[Fe(CN)₆]^3-/[Fe(CN)₆]^4-为探针研究了其电子传递性能.结果表明用电化学组装法制备的PATP/PANI膜在纳米尺度上是二维有序的,且具有良好的电子传递性能.     

Surface-enhanced Raman scattering studies of 1,10-phenanthroline adsorption and its surface complexes on a gold electrode

This paper reports on the interface processes of 1,10-phenanthroline (phen) at a roughened Au electrode by surface-enhanced Raman scattering (SERS) for the first time. Both the adsorption and coordination of phen on the roughened gold electrode have been studied. In comparison to the normal Raman spectrum of phen monohydrate, the frequency and relative intensity change significantly in the SERS spectra. As evidenced by cyclic voltammetry, the electrochemical behavior of the Au electrode is strongly modified by the adsorbed phen. It was found that a new pair of redox peaks appeared in the cyclic voltammogram only when both phen and X (X = Cl-, Br-) were present. Information on coordination bonds of Au-N and Au-X as well as on adsorbed bonds of Au-N(ad) and Au-X(ad), was obtained by the SERS spectra. In situ SERS investigations together with electrochemical measurements convincingly prove the formation of surface complexes 1,10-phenAu2X6 or [1,10-phenAuX2]AuX4 during the electro-oxidation process of Au while phen and X coadsorbed on the surface.     

Sensitive Voltammetric Determination of Captopril Using a Carbon Paste Electrode Modified with Nano-TiO2/Ferrocene Carboxylic Acid

A carbon paste electrode (CPE) modified with ferrocene carboxylic acid (FcCA) and TiO2 nanoparticles was constructed by incorporating TiO2 nanoparticles and ferrocene carboxylic acid into the carbon paste matrix.The electrochemical behavior of captopril (CAP) at the surface of the modified electrode was investigated using electroanalytical methods.The modified electrode showed excellent electrocatalytic activity for the oxidation of CAP in aqueous solutions at physiological pH values.Cyclic voltammetric curves showed that the oxidation of CAP at the surface of the modified electrode reduced its overpotential by more than 290 mV.The modified electrode was used for detecting captopril using cyclic voltammetry and square wave voltammetry techniques.A calibration curve in the range of 0.03 to 2400μmol/L was obtained that had a detection limit of 0.0096 μmol/L (3σ) under the optimized conditions.The modified electrode was successfully used for the determination of captopril in pharmaceutical and biological samples.     

A Penicillamine Biosensor Based on Tyrosinase Immobilized on Nano‐Au/ PAMAM Dendrimer Modified Gold Electrode

Gold electrodes were modified with submonolayers of 3‐mercaptopropionic acid and further reacted with poly(amidoamine) (PAMAM) dendrimers to obtain thin films. The high affinity of PAMAM dendrimer for nano‐Au with its amine groups was used to realize the role of nano‐Au as an intermediator to immobilize the enzyme of tyrosinase. The characterization of the modified electrode was investigated by cyclic voltammetry, electrochemical impedance spectroscopy and atomic force microscopy (AFM). Tyrosinase can catalyze the oxidation of catechol to o‐benzoquinone. When penicillamine was added to the solution, it reacted with o‐benzoquinone to form the corresponding thioquinone derivatives, which resulted in decrease of the reduction current of o‐benzoquinone. Based on this, a new electrochemical sensor for determination of penicillamine has been developed.     

Differential Pulse Voltammetric Determination of L-Cysteine After Cyclic Voltammetry in Presence of Catechol with Glassy Carbon Electrode

An electrochemical method of determination of cysteine has been developed in the solution containing catechol as the indicator. Nucleophilic addition of the thiol species to the electrogenerated o-quinone results in the formation of o-quinone-cysteine adducts that easily accumulate use at the surface of the electrode in the acidic solution. Therefore, the use of cyclic voltammetry leads to the amplification of the o-quinone-cysteine adduct's reductive current. As cyclic voltammetry was performed prior to differential pulse voltammetry, the peak of o-quinone-cysteine could be separated preferentially from o-quinone in the differential pulse voltammogram and the selectivity of the method has been assessed with no interference from ascorbic acid, glycine, L-tyrosine, or L-lysine. The magnitude of o-quinone-cysteine peak is proportional to the concentration of cysteine, and thus it can be exploited to determine cysteine within the injection. The results were consistent with those obtained by means of HPLC analysis.     

Electrochemical behavior of catechol and 3,4-dihydroxytoluene in acetonitrile at a platinum-disk electrode modified with a tyrosinase containing polyacrylamide film.

A modified platinum-disk electrode coated with a non-plasticized polyacrylamide (PAA) membrane was used to study electrochemically an enzymatic reaction between tyrosinase in the PAA membrane and catechol and 3,4-dihydroxytoluene in acetonitrile (AN). Tyrosinase, a hydrophilic biofunctional material, was immobilized in the thin PAA membrane, which adhered to the platinum-disk electrode and was stable in AN. The enzymatic activity of tyrosinase in the PAA membrane to the above substrates in AN was confirmed by cyclic voltammetry and amperometry. The apparent maximum velocities (Vmaxapp) and the apparent Michaelis constants (Kmapp) were determined from the amperometric results; the apparent turnover numbers were also determined. The reduction potentials of the substrates were reported vs. the cathodic peak potential of ferrocene in AN to improve the reliability of the potential data and to make possible a comparison of the potentials in different solvents. The electrochemical system discussed in this report can be used for tracing enzymatic reactions with substrates dissolving in aprotic dipolar solvents and for investigating solvent effects on enzymatic activities.     

Study on surface acid-base property of carboxylic acid-terminated self-assembled monolayers by cyclic voltammetry and electrochemical impedance spectroscopy

Cyclic voltammetry and electrochemical impedance spec-troscopy were used to study the surface acid-base property of carboxylic acid-terminated self-assembled monolayers(SAMs).A carboxylic acid-terminated thiol,such as thioctic acid(1,2-dithiolane-3-pentanoic acid),was self-assembled on gold electrodes.Electron transfer between the bulk solution and the SAM modified electrode was studied at different pH using Fe(CN)63-as a probe.The surface pka of thioctic acid was determined by cyclic voltammetry and electrochemical impedance spectroscopy to be 5.6 ±0.1 and 5.8±0.1,respectively.The method is compared with other methods of monolayer pKa measurement.     

Electrochemical oxidation of catecholamines and catechols at carbon nanotube electrodes

The differences in the electrochemical oxidation of two commonly known catecholamines, dopamine and norepinephrine, and one catechol, dihydroxyphenylacetic acid (DOPAC), at three different types of carbon based electrodes comprising conventionally polished glassy carbon (GC), nitrogen-doped carbon nanotubes (N-CNTs), and non-doped CNTs were assessed. Raman microscopy and X-ray photoelectron spectroscopy (XPS) were employed to evaluate structural and compositional properties. Raman measurements indicate that N-CNT electrodes have ca. 2.4 times more edge plane sites over non-doped CNTs. XPS data show no evidence of oxygen functionalities at the surface of either CNT type. N-CNTs possess 4.0 at. % nitrogen as pyridinic, pyrrolic, and quaternary nitrogen functionalities that result in positively charged carbon surfaces in neutral and acidic solutions. The electrochemical behavior of the various carbon electrodes were investigated by cyclic voltammetry conducted in pH 5.8 acetate buffer. Semiintegral analysis of the voltammograms reveals a significant adsorptive character of dopamine and norepinephrine oxidation at N-CNT electrodes. Larger peak splittings, DeltaE(p), for the cyclic voltammograms of both catecholamines and a smaller DeltaE(p) for the cyclic voltammogram for DOPAC at N-CNT electrodes suggest that electrostatic interactions hinder oxidation of cationic dopamine and norepinephrine, but facilitate anionic DOPAC oxidation. These observations were supported by titrimetry of solid suspensions to determine the pH of point of zero charge (pH(pzc)) and estimate the number of basic sites for both CNT varieties. This study demonstrates that carbon purity, the presence of exposed edge plane sites, surface charge, and basicity of CNTs are important factors for influencing adsorption and enhancing the electrochemical oxidation of catecholamines and catechols.     

Electrocatalytic Investigations of Cu(II) and Fe(III) Complexes of Salophen Derivative Schiff Bases on the Pencil Graphite Electrode

This present study describes a pencil graphite electrode surface covered with Cu(II) and Fe(III) complexes based on Salophen derivative Schiff bases in acetonitrile solution containing LiClO₄ as a supporting electrolyte. Cyclic voltammetry method was used for the surface modification procedure with 25 cycle at a sweep rate of 50 mV s^?1. Some characterization methods were used to identify of the prepared modified surfaces including cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), Ultraviolet‐visible Spectroscopy (UV‐Vis), and Scanning Electron Microscopy/Energy Dispersive X‐ray Spectroscopy (SEM/SEM‐EDX). The catalytic activity of these modified surfaces on the electrochemical oxidation of catechol (CC) was investigated and they compared with each other. The results demonstrated that these modified electrodes showed perfect electrocatalytic activity on the catechol determination, however the modified electrode prepared with the Cu(II) complex has higher catalytic activity than this prepared with the Fe(III) complex thanks to its the lower detection limit.     

Electrosynthesis of Molecularly Imprinted Poly‐o‐phenylenediamine on MWCNT Modified Electrode for Selective Determination of Meldonium

In this study, a molecularly imprinted polymer (MIP) was synthesized by electrochemical polymerization and used to construct an electrochemical sensor for determination of meldonium (MEL) selectively for the first time. The polymer film was generated by using o‐phenylenediamine (o‐PD) as a monomer on the surface of carboxylic acid functionalized multiwalled carbon nanotube (MWCNT) modified pencil rod electrode in the presence of MEL as a template. MEL imprinted (MEL‐imp) and non‐imprinted (N‐imp) polymer films and coated electrodes were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), profilometry, electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Voltammetric measurements were carried out in a ferrocyanide/ferricyanide redox probe solution for MEL‐imp and N‐imp electrodes in the presence and absence of template molecule. The decrease in peak current of redox probe was linear with the concentration of MEL in the range of 0.1–5 μg/mL and the limit of detection (3 s/b) was found to be 0.066 μg/mL under optimized experimental conditions. The proposed sensor was successfully applied for selective determination of MEL in human urine sample with long term stability and good reproducibility.