Amperometric Study of Au‐Colloid Function on Xanthine Biosensor Based on Xanthine Oxidase Immobilized in Polypyrrole Layer

Four kinds of xanthine oxidase (XOD) based amperometric biosensors were fabricated and their analytical performances were compared. Polypyrrole (PPY)/XOD biosensor was constructed by electrochemical oxidation of pyrrole in the solution containing xanthine oxidase and pyrrole in this paper. Colloidal Au was then immobilized on the biosensor. On the other hand, electron mediator, Prussian Blue (PB), was deposited on the electrode before the immobilization of PPY/XOD to enhance electron‐transfer rate and current response. The results showed that PPY/XOD, PPY/XOD/Au‐colloid, PB/PPY/XOD and PB/PPY/XOD/Au‐colloid biosensors exhibit good response to xanthine in 1×10^?6 M and 2×10^?5 M and Michaelis‐Menten constants (K_m) of these biosensors were 242.2, 113.4, 144.5, 43.2 μmol?L^?1, respectively. The dependence of current responses with applied voltages was discussed, and different mechanisms of these biosensors were discussed. It has been found that colloidal Au can enhance the current response at the same concentration of xanthine solution and decrease the energy‐barrier of electron‐transfer reaction on the electrode.     

Sensitive Determination of Clomipramine at Poly‐ABSA/Pt Nano‐Clusters Modified Glassy Carbon Electrode

Abstract

Clomipramine, an important tricylic antidepressant drug with low redox activity, was effectively electrocatalyzed on poly‐aminobenzene sulfonic acid/Pt nano‐clusters modified glassy carbon electrode (i.e., poly‐ABSA/Pt/GCE) and generated a sensitive anodic peak at about 0.80 V in pH 8.1 PBS. ABSA was electropolymerized on the surface of GCE modified with Pt nano‐clusters. Pt nanoparticles provide a 3 D and conductive structure for the polymer immobilization. The resulting sensor exhibited a considerable enhancement in voltammetric response characteristics: extending the linear range and lowering the detection limit. The anodic peak current of clomipramine was linear with its concentration over two concentration intervals, viz., 1.0×10^?7～4.0×10^?6 M and 4.0×10^?6～4.0×10^?5 M, with the detection limit of 1.0×10^?9 M (S/N=3). This method was successfully applied to the determination of clomipramine in drug tablets and proved to be reliable compared with UV.     

Electrogenerated Chemiluminescence Ethanol Biosensor Based on Carbon Nanotube‐Titania‐Nafion Composite Film

Mesoporous titania‐Nafion composite doped with carbon nanotube (CNT) has been used for the immobilization of tris(2,2′‐bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺) and alcohol dehydrogenase on an electrode surface to yield a highly sensitive and stable electrogenerated chemiluminescence (ECL) ethanol biosensor. The presence of CNT in the composite film increases not only the sensitivity of the ECL biosensor but also the long‐term stability of the biosensor. The present biosensor responds linearly to ethanol in the wide concentration ranges from 1.0×10^?5 M to 1.0×10^?1 M with a detection limit of 5.0×10^?6 M (S/N=3). The present ECL ethanol biosensor exhibited higher ECL response compared to that obtained with the ECL biosensor based on the corresponding composite without CNT. The present CNT‐based ECL biosensor showed good long‐term stability with 75% of its initial activity retained after 2 weeks of storage in 50 mM phosphate buffer at pH 7.0.     

Voltammetric Determination of Adrenaline Using a Poly(1‐Methylpyrrole) Modified Glassy Carbon Electrode

A voltammetric method using a poly(1‐methylpyrrole) modified glassy carbon electrode was developed for the quantification of adrenaline. The modified electrode exhibited stable and sensitive current responses towards adrenaline. Compared with a bare GCE, the modified electrode exhibits a remarkable shift of the oxidation potentials of adrenaline in the cathodic direction and a drastic enhancement of the anodic current response. The separation between anodic and cathodic peak potentials (ΔEp) for adrenaline is 30 mV in 0.1 M phosphate buffer solution (PBS) at pH 4.0 at modified glassy carbon electrodes. The linear current response was obtained in the range of 7.5 × 10^?7 to 2.0 × 10^?4 M with a detection limit of 1.68 × 10^?7 M for adrenaline by square wave voltammetry. The poly(1‐methypyrrole)/GCE was also effective to simultaneously determine adrenaline, ascorbic acid and uric acid in a mixture and resolved the overlapping anodic peaks of these three species into three well‐defined voltammetric peaks in cyclic voltammetry. The modified electrode has been successfully applied for the determination of adrenaline in pharmaceuticals. The proposed method showed excellent stability and reproducibility.     

High Sensitivity and Reproducibility of a Bismuth/Poly(bromocresol purple) Film Modified Glassy Carbon Electrode for Determination of Trace Amount of Cadmium by Differential Pulse Anodic Stripping Voltammetry

This work described a novel type of bismuth/poly(bromocresol purple) film modified glassy carbon electrode (denoted as Bi/Poly(BCP)/GCE) for anodic stripping analysis of trace Cd²⁺. The Bi/Poly(BCP)/GCE was fabricated in situ by depositing simultaneously bismuth and cadmium by reduction at ?1.20 V on the poly(BCP) film using a differential pulse voltammetry. Under the optimum conditions, the anodic stripping peak current response increased linearly with the Cd²⁺ concentrations in a range of 2.0×10^?8–1.0×10^?7 M and 1.0×10^?7–6.0×10^?6 M in 0.1 M NaAc‐HAc buffer solution (pH 5.0) with the detection limit of 6.5×10^?9 M (S/N=3). The Bi/poly(BCP)/GCE performed good reproducibility and high sensitivity. Finally, this proposed method was successfully applied to determine the concentration of Cd²⁺ in water samples.     

A Biosensor for Genetic Modified Soybean DNA Determination via Adsorption of Anthraquinone‐2‐sulphonic Acid in Reduced Graphene Oxide

An electrochemical DNA biosensor for DNA determination of genetically modified (GM) soybean (CaMV 35S target genes) was developed utilizing a new detection concept based on the adsoption of anthraquinone‐2‐sulphonic acid (AQMS) on the reduced graphene oxide nano‐particles (rGO) during DNA hybridization events. The aminated DNA probe for CaMV 35S was immobilized onto poly(n‐butyl acrylate) film modified with succinimide functional groups [poly(nBA‐NAS)] via peptide covalent bond. Nanosheets of rGO were entrapped in the poly(nBA‐NAS) film to form a conducting [poly(nBA‐NAS)‐rGO] film of the DNA biosensor. Besides facilitating the electron transfer reactions, the rGO also functioned as an adsorbent for AQMS. The sensing mechanism of the proposed DNA biosensor involved measuring the oxidation current of the AQMS adsorbed on the electrode surface at −0.50 V using differential pulse voltammetry (DPV) before and after a DNA hybridization event. Under optimum conditions, the DNA biosensor demonstrated a linear proportionality between AQMS oxidation signal and logarithm cDNA concentration from 1.0×10⁻¹⁵ M to 1.0×10⁻⁸ M target DNA with a detection limit of 6.3×10⁻¹⁶ M. The electrochemical DNA biosensor possessed good selectivity and a shelf life of about 40 days with relative standard deviation of reproducibility obtained in the range of 3.7–4.6% (n=5). Evaluation of the DNA biosensor using GM soybean DNA extracts showed excellent recovery percentages of 97.2–104.0.     

Detection of Trace Phenol Based on Mesoporous Silica Derived Tyrosinase‐Peroxidase Biosensor

A novel electrochemical biosensor for phenol based on immobilization of tyrosinase‐peroxidase on mesoporous silica is described. The enhanced sensitivity of the tyrosinase‐horseradish peroxidase based biosensor to phenol was observed on comparing with tyrosinase or horseradish peroxidase monoenzyme modified electrodes. Two enzymes retained their enzymatic activities for phenol determination without any mediator. The preparation conditions of the biosensor are discussed. Optimization of the experimental parameters was performed with regard to pH and operating potential. The phenol sensor exhibited a fast response of less than 10 seconds. The sensitivity of the biosensor for phenol was 14 μA μM^?1 cm^?2 with a linear range from 2×10^?7 to 2.3×10^?4 M and a detection limit of 4.1×10^?9 M. The biosensor showed a good stability and reproducibility.     

Electro‐oxidized Monolayer CVD Graphene Film Transducer for Ultrasensitive Impedimetric DNA Biosensor

We report the effect of electrochemical anodization on the properties of monolayer graphene as the main aim of this research and consequently using the resulting label‐free impedimetric biosensor for DNA sequences detection. Monolayer graphene was grown by chemical vapor deposition (CVD) with methane as precursor on copper foil, transferred onto a glassy carbon electrode and electrochemically anodized. Raman spectroscopy and X‐Ray photo electron spectroscopy revealed enhancement of defect density, roughness and formation of C−O−C, C−O−H and C=O functional groups after anodization. Amine‐terminated poly T probe was linked covalently to the carboxylic groups of anodized graphene by the zero‐length linker to fabricate the impedance‐based DNA biosensor. The anodized graphene electrode demonstrated a superior performance for electrochemical impedance detection of DNA. The DNA biosensor showed a large linear dynamic range from 2.0×10⁻¹⁸ to 1.0×10⁻¹² M with a limit of detection of 1.0×10⁻¹⁸ M using electrochemical impedance spectroscopy (EIS) method. Equivalent circuit modeling shows that DNA hybridization is detected through a change in charge transfer resistance.     

Silver Doped Poly(L‐valine) Modified Glassy Carbon Electrode for the Simultaneous Determination of Uric Acid,Ascorbic Acid and Dopamine

In this paper, a silver doped poly(L ‐valine) (Ag‐PLV) modified glassy carbon electrode (GCE) was fabricated through electrochemical immobilization and was used to electrochemically detect uric acid (UA), dopamine (DA) and ascorbic acid (AA) by linear sweep voltammetry. In pH 4.0 PBS, at a scan rate of 100 mV/s, the modified electrode gave three separated oxidation peaks at 591 mV, 399 mV and 161 mV for UA, DA and AA, respectively. The peak potential differences were 238 mV and 192 mV. The electrochemical behaviors of them at the modified electrode were explored in detail with cyclic voltammetry. Under the optimum conditions, the linear ranges were 3.0×10^?7 to 1.0×10^?5 M for UA, 5.0×10^?7 to 1.0×10^?5 M for DA and 1.0×10^?5 to 1.0×10^?3 M for AA, respectively. The method was successfully applied for simultaneous determination of UA, DA and AA in human urine samples.     

Voltammetric Determination of Xanthine with a Single‐Walled Carbon Nanotube‐Ionic Liquid Paste Modified Glassy Carbon Electrode

Single‐walled carbon nanotube (SWNT) and room temperature ionic liquid (i.e., 1‐butyl‐3‐methylimidazolium hexaflourophosphate, BMIMPF₆) were used to fabricate paste modified glassy electrode (GCE). It was found that the electrode showed sensitive voltammetric response to xanthine (Xt). The detection limit was 2.0×10^?9 M and the linear range was 5.0×10^?9 to 5.0×10^?6 M. The electrode also displayed good selectivity and repeatability. In the presence of uric acid (UA) and hypoxanthine (Hx) the response of Xt kept almost unchanged. Thus this electrode could find application in the determination of Xt in some real samples. The analytical performance of the BMIMPF₆‐SWNT/GCE was demonstrated for the determination of Xt in human serum and urine samples.     

A Highly Sensitive Electrochemiluminescence Choline Biosensor Based on Poly(aniline‐luminol‐hemin) Nanocomposites

Poly(aniline‐luminol‐hemin) nanocomposites are prepared on an electrode surface through electropolymerization, and a highly sensitive electrochemiluminescence (ECL) biosensor for choline is developed based on the poly(aniline‐luminol‐hemin) nanocomposites and an enzyme catalyzed reaction of choline oxidase (CHOD). The obtained nanocomposites are characterized by scanning electron microscopy (SEM), atomic absorption spectrometry (AAS) and ECL. The results indicate that hemin can be incorporated into the poly(aniline‐luminol) nanocomposites using the facile electropolymerization method, and the poly(aniline‐luminol‐hemin) nanocomposites are rod shaped porous nanostructure. Moreover, the poly(aniline‐luminol‐hemin) nanocomposites exhibit higher ECL intensity than poly(aniline‐luminol) nanocomposites in alkaline media due to the catalytic effect of hemin on the ECL of the polymerized luminol and the electron transfer ability of hemin in the nanocomposites. CHOD is immobilized on the surface of the poly(aniline‐luminol‐hemin) nanocomposites modified electrode with glutaraldehyde, and the ECL biosensor based on poly(aniline‐luminol‐hemin)/CHOD exhibits a wider linear range for the choline detection. The enhanced ECL signals are linear with the logarithm of concentration of choline over the range of 1.0×10^?11～1.0×10^?7 mol L^?1 with a low detection limit of 1.2×10^?12 mol L^?1. Moreover, the proposed biosensor is successfully applied to the detection of choline in milk.     

Trace Analysis of Al (III) Ions Based on the Redox Current of a Conducting Polymer

A conducting polymer was electrochemically prepared on a Pt electrode with newly synthesized 3′‐(4‐formyl‐3‐hydroxy‐1‐phenyl)‐5,2′ : 5′,2″‐terthiophene (FHPT) in a 0.1 M TBAP/CH₂Cl₂ solution. The polymer‐modified electrode exhibited a response to proton and metal ions, especially Al(III) ions. The poly[FHPT] was characterized with cyclic voltammetry, EQCM, and applied to the analysis of trace levels of Al(III) ions. Experimental parameters affecting the response of the poly[FHPT] were investigated and optimized. Other metal ions in low concentration did not interfere with the analysis of Al(III) ions in a buffer solution at pH 7.4. The response was linear over the concentration range of 5.0×10^?8–7.0×10^?10 M, and the detection limit was 5.0×10^?10 M using the linear sweep voltammetry (LSV). Employing the differential pulse voltammetry (DPV), the response was linear over the 1.0×10^?9–5.0×10^?11 M range and the detection limit was 3.0×10^?11 M. The relative standard deviation at 5.0×10^?11 M was 7.2% (n=5) in DPV. This analytical method was successfully verified for the analysis of trace amounts of Al(III) ions in a human urine sample.     

Determination of pesticides in vegetable samples using an acetylcholinesterase biosensor based on nanoparticles ZrO2/chitosan composite film

An amperometric pesticides inhibition biosensor has been developed and used for determination of pesticides in vegetable samples. To eliminate the interference of ascorbic acid, multilayer films of polyelectrolyte (chitosan/polystyrensulfonate) were coated on the glass carbon electrode. Then, acetylcholinesterase was immobilized on the electrode based on surface-treated nanoporous ZrO₂/chitosan composite film as immobilization matrix. As a modified substrate, acetylthiocholine was hydrolysed by acetylcholinesterase and produced thiocholine which can be oxidized at +700?mV vs. SCE. Pesticides inhibit the activity of enzyme with an effect of decreasing of oxidation current. The experimental conditions were optimized. The electrode has a linear response to acetylthiocholine within 9.90?×?10^?6 to 2.03?×?10^?3?M. The electrode provided a linear response over a concentration range of 6.6?×?10^?6 to 4.4?×?10^?4?M for phoxim with a detection limit of 1.3?×?10^?6?M, over a range of 1.0?×?10^?8 to 5.9?×?10^?7?M for malathion, and over a range of 8.6?×?10^?6 to 5.2?×?10^?4?M for dimethoate. This biosensor has been used to determine pesticides in a real vegetable sample.     

Employing Label‐free Electrochemical Biosensor Based on 3D‐Reduced Graphene Oxide and Polyaniline Nanofibers for Ultrasensitive Detection of Breast Cancer BRCA1 Biomarker

A label‐free DNA biosensor based on three‐dimensional reduced graphene oxide (3D‐rGO) and polyaniline (PANI) nanofibers modified glassy carbon electrode (GCE) was successfully developed for supersensitive detection of breast cancer BRCA1. The results demonstrated that 3D‐rGO and PANI nanofibers had synergic effects for reducing the charge transfer resistance (R_ct), meaning a huge enhancement in electrochemical activity of 3D‐rGO‐PANI/GCE. Probe DNA could be immobilized on 3D‐rGO‐PANI/GCE for special and sensitive recognition of target DNA (1.0×10^?15–1.0×10^?7 M) with a theoretical LOD of 3.01×10^?16 M (3S/m). Furthermore, this proposed nano‐biosensor could directly detect BRCA1 in real blood samples.     

A Novel Nitric Oxide Cellular Biosensor Based on Red Blood Cells Immobilized on Gold Nanoparticles

Abstract

We have developed a novel nitric oxide (NO) cellular biosensor based upon the immobilization of red blood cells (RBCs) onto nanometer‐size colloidal gold that is attached to an electrochemically pretreated glassy carbon electrode via the bridging of an ethylenediamine monolayer. The biosensor has been characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), and electrochemistry. The immobilized RBCs display an excellent electrocatalytic response to nitric oxide. The electrocatalytic currents are proportional to the NO concentration in the range from 1.0×10^–8 to 1.0×10^–6 M and the detection limit is as low as 5.0×10^–9 M (S/N=3). Furthermore, the biosensor is very stable and relatively free of potential interference.     

Xanthine Biosensor Based on Didodecyldimethylammonium Bromide Modified Pyrolytic Graphite Electrode

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Application of graphene oxide nanosheets as probe oligonucleotide immobilization platform for DNA sensing

In this work, a simple and novel electrochemical biosensor based on a glassy carbon electrode (GCE) modified with graphene oxide nanosheets (GO) was developed for detection of DNA sequences. The morphology of prepared nanoplatform was investigated by scanning electron microscopy, infrared (FTIR) and UV/Vis absorption spectra. The fabrication processes of electrochemical biosensor were characterized with cyclic voltammetry and electrochemical impedance spectroscopy (EIS) in an aqueous solution. The optimization of experimental conditions such as immobilization of the probe BRCA1 and its hybridization with the complementary DNA was performed. Due to unique properties of graphene oxide nanosheets such as large surface area and high conductivity, a wide liner range of 1.0 × 10^?17–1.0 × 10^?9 M and detection limit of 3.3 × 10^?18 M were obtained for detection of BRCA1 5382 mutation by EIS technique. Under the optimum conditions, the proposed biosensor (ssDNA/GO/GCE) revealed suitable selectivity for discriminating the complementary sequences from non-complementary sequences, so it can be applicable for detection of breast cancer.     

Preparation,Characterization and Electrochemical Application of Graphene‐metallic Nanocomposites

Three different Graphene‐Metallic (Graphene‐Me) nanocomposites – Graphene‐Silver (Graphene‐Ag), Graphene‐Gold (Graphene‐Au) and Graphene‐Platinum (Graphene‐Pt) nanocomposites – were prepared and characterized. The electrochemical performances of these nanocomposites were tested by incorporating them with glassy carbon paste electrode (GCPE) and used them in biofuel cells (BFC) and as amperometric xanthine biosensor transducers. Present work contains the first application of Graphene‐Au and Graphene‐Ag nanocomposite in BFCs and also first application of these Graphene‐Me nanocomposites in xanthine biosensors. Considering BFC, power and current densities were calculated as 2.03 µW cm^?2 and 167.46 µA cm^?2 for the plain BFC, 3.39 µW cm^?2 and 182.53 µA cm^?2 for Graphene‐Ag, 4.43 µW cm^?2 and 230.15 µA cm^?2 for Grapehene‐Au and 6.23 µW cm^?2 and 295.23 µA cm^?2 for Graphene‐Pt nanocomposite included BFCs respectively. For the amperometric xanthine biosensor linear ranges were obtained in the concentration range between 5 µM and 50 µM with the RSD (n=3 for 30 µM xanthine) value of 4.28 % for plain xanthine biosensor, 3 µM and 50 µM with the RSD (n=3 for 30 µM xanthine) value of 9.37 % for Graphene‐Ag, 5 µM to 20 µM with the RSD (n=3 for 5 µM xanthine) value of 9.00 % and 30 µM to 70 µM with the RSD (n=3 for 30 µM xanthine) value of 8.80 % for Grapehene‐Au and 1 µM and 70 with the the RSD (n=3 for 30 µM xanthine) value of 2.59 % for Grapehene‐Pt based xanthine biosensors respectively.     

Supramolecular Assembly of β‐Cyclodextrin‐Capped Gold Nanoparticles on Ferrocene‐Functionalized ITO Surface for Enhanced Voltammetric Analysis of Ascorbic Acid

A supramolecular recognition functionalized electrode (βCD‐nanoAu/Fc‐ITO) which exhibits redox‐activity was prepared through supramolecular assembly of β‐cyclodextrin (βCD) capped gold nanoparticles (βCD‐nanoAu) on the ITO previously coated with a monolayer of ferrocene residues (Fc‐ITO). The immobilization of βCD‐nanoAu on Fc‐ITO was confirmed by atomic force microscopy (AFM), and the supramolecular nature of the immobilization approach was also confirmed by cyclic voltammetry. On the other hand, the electrocatalytic activity of βCD‐nanoAu/Fc‐ITO electrode was also studied. The electrocatalytic activity toward ascorbic acid (AA) was enhanced compared with that at the Fc‐ITO electrode, and a linear relationship existed between the anodic peak and the concentration of AA in the range of 5.3×10^?5 to 3.0×10^?3 M with a detection limit (S/N=3) of 4.1×10^?6 M.     

Development of an Amperometric Enzymatic Biosensor Based on Gold Modified Magnetic Nanoporous Microparticles

Gold modified nanoporous silica based magnetic microparticles have been prepared as support for the immobilization of the enzyme horseradish peroxidase (HRP). The enzyme modified gold microparticles were retained onto the surface of a solid carbon paste electrode with the help of a permanent magnet. The analytical performances of the resulting biosensor were characterized by studying hydroquinone (HQ) and hydrogen peroxide. The former was monitored by the direct electroreduction of the biocatalytically generated quinone. Several experimental parameters influencing the biosensor response were investigated. A linear response to HQ was obtained in the concentration range comprised between 5×10^?7 and 4.5×10^?6 M with a detection limit of 4×10^?7 M. The enzyme electrode provided a linear response to hydrogen peroxide over a concentration range comprised between 5×10^?7?1.3×10^?4 M with a detection limit of 4×10^?7 M. The inhibition of the biosensor response in the presence of thiols e.g. cysteine, captopril, glutathione and Nacystelyn (NAL) has been pointed out.