Sulfite oxidase biosensors based on tetrathiafulvalene modified screen-printed carbon electrodes for sulfite determination in wine

Screen-printed carbon electrodes have been modified with tetrathiafulvalene and sulfite oxidase enzyme for the sensitive and selective detection of sulfite. Amperometric experimental conditions were optimized taking into account the importance of quantifying sulfite in wine samples and the inherent complexity of these samples, particularly red wine. The biosensor responds to sulfite giving a cathodic current (at +200 mV vs screen-printed Ag/AgCl electrode and pH 6) in a wide concentration range, with a capability of detection of 6 μM (α = β = 0.05) at 60 °C. The method has been applied to the determination of sulfite in white and red samples, with averages recoveries of 101.5% to 101.8%, respectively.     

Electrochemical determination of chromium(VI) using metallic nanoparticle-modified carbon screen-printed electrodes

Carbon screen-printed electrodes (CSPEs) modified with metal nanoparticles present an interesting alternative in the determination of chromium(VI) by differential pulse voltammetry (DPV).Metallic silver and gold nanoparticle deposits have been obtained by electrochemical deposition. Scanning electron microscopy measurements show that the electrochemically synthesized silver and gold nanoparticles are deposited in aggregated form.The detection limit for the analytical procedures developed in this work were 8.5 × 10⁻⁷ and 4.0 × 10⁻⁷ M for silver and gold nanoparticle-modifed CSPE, respectively.In terms of reproducibility, the precision of the above-mentioned method was calculated at 6.7% in %R.S.D. values for silver and 3.21% for gold nanoparticle CSPE.     

Amperometric biosensors based on nafion coated screen-printed electrodes for the determination of cholinesterase inhibitors

Screen-printed electrodes coated with the nafion layer have been investigated for cholinesterase biosensor design. The butyrylcholinesterase (ChE) from horse serum was immobilised onto the nafion layer by cross-linking with glutaraldehyde vapours. The biosensors obtained showed better long-term stability and lower working potential in comparison to those obtained with no nafion coating. The sensitivity of a biosensor toward organophosphate pesticides is not affected by the nafion coating. The detection limits were found to be 3.5x10(-7) M for trichlorfon and 1.5x10(-7) M for coumaphos.     

Development of an immunosensor for the determination of rabbit IgG using streptavidin modified screen-printed carbon electrodes

Voltammetric enzyme immunosensors based on the employment of streptavidin modified screen-printed carbon electrodes (SPCEs) for the detection of rabbit IgG, as a model analyte, were described. Alkaline phosphatase (AP) and 3-indoxyl phosphate (3-IP) were used as the enzymatic label and substrate, respectively. The adsorption of streptavidin was performed by deposition of a drop of a streptavidin solution overnight at 4 °C on the pre-oxidized surface of the SPCEs. The analytical characteristics of these sensors were evaluated using biotin conjugated to AP.The immunosensor devices were based on a specific reaction of rabbit IgG with its biotinylated antibodies, which were immobilised on the modified screen-printed carbon electrodes through the streptavidin:biotin reaction. The immunosensors were used for a direct determination of AP labelled rabbit IgG, and for free rabbit IgG detection using a sequential competitive immunoassay. A calibration curve in the range of 5 × 10⁻¹¹ to 1 × 10⁻⁹ M of rabbit IgG was obtained with a estimated detection limit of 5 × 10⁻¹¹ M (7.0 ng/ml). These immunosensors were stable for 5 months if they were stored at 4 °C.     

Amperometric determination of sulfite with sulfite oxidase immobilized at a platinum electrode surface

Sulfite oxidase is immobilized on collagen membrane at the surface of a platinum electrode and catalyzes the oxidation of sulfite to sulfate with stoichiometric production of hydrogen peroxide. The hydrogen peroxide is detected amperometically at the platinum electrode at an applied potential of 700 mV. The system responds linearly to sulfite in the range 1–150 μM, with a detection limit of 0.2 μM. The enzyme retains over 95% of its activity for three weeks if stored at ?20° C when the probe is not in use.     

Amperometric immunosensor for the detection of Vibrio cholerae O1 using disposable screen-printed electrodes.

A disposable amperometric immunosensor was studied for the rapid detection of Vibrio cholerae (V. cholerae), the causative agent of cholera, employing an indirect sandwich enzyme linked immunosorbent assay (ELISA) principle. Screen-printed electrodes (SPEs) were fabricated (by using commercial and homemade carbon inks), electrochemically characterized and the assay conditions were optimized for capturing antibodies and antigen. Whole cell lysate (WCL) of V. cholerae was used to raise antibodies in rabbits and mice. The antibodies raised against WCL of V. cholerae were found to be specific, and no cross reactivity was observed with other enteric bacteria. 1-Naphthyl phosphate was used as a substrate with the amperometric detection of its enzymatic hydrolysis product 1-naphthol at a potential of +400 mV vs. Ag/AgCl reference electrode. A comparison between the amperometric detection technique and the standard ELISA was made in terms of the total assay time, the amount of biological materials used and the sensitivity of detection. The minimum detection limit of the amperometric immunosensor for V. cholerae was found to be 10(5) cells/ml in 55 min, while ELISA detected 10(6) cells/ml in 4 h.     

Amperometric biosensing of carbamate and organophosphate pesticides utilizing screen-printed tyrosinase-modified electrodes

A tyrosinase (Tyr) screen-printed biosensor based on the electroreduction of enzymatically generated quinoid products was electrochemically characterized and optimized for determination of carbamates and organophosphorus pesticides. A composite electrode prepared by screen-printing a cobalt (II) phthalocyanine (CoPc) modified cellulose-graphite composite on a polycarbonate support was employed as electrochemical transducer. The Tyr biosensor was prepared by immobilization of enzyme on the composite electrode surface by cross-linking with glutaraldehyde and bovine serum albumin. Parameters affecting the biosensor response such as response time, enzyme loading, concentration and pH of the buffer solution were optimized utilizing catechol as substrate. The maximum response for o-quinone enzymatically generated was obtained after 2 min of reaction. A good reproducibility and high operational stability were found for Tyr biosensor (60 units) at 50 mM phosphate buffer, pH 6.50. Under these conditions, the useful lifetime of biosensor was 10 days. After 15 days, the biosensor could be used with 20% of the initial value. Inhibition studies on the o-quinone steady-state current (at −0.20 V versus Ag/AgCl) were performed to investigate the inhibition kinetics of the pesticides in the enzymatic activity of mushroom tyrosinase. The results shown that the methyl parathion and carbofuran can lead to competitive inhibition process of the enzyme, while diazinon and carbaryl act as mixed inhibitors. Linear relationships were found for methyl parathion (6-100 ppb), diazinon (19-50 ppb), carbofuran (5-90 ppb) and carbaryl (10-50 ppb). Analysis of natural river water samples spiked with 30 ppb of each pesticide showed recoveries between 92.50% and 98.50% and relative standard deviations of 2%.     

Amperometric bienzyme screen-printed biosensor for the determination of leucine

Leucine plays an important role in protein synthesis, brain functions, building muscle mass, and helping the body when it undergoes stress. Here, we report a new amperometric bienzyme screen-printed biosensor for the determination of leucine, by coimmobilizing p-hydroxybenzoate hydroxylase (HBH) and leucine dehydrogenase (LDH) on a screen-printed electrode with NADP⁺ and p-hydroxybenzoate as the cofactors. The detection principle of the sensor is that LDH catalyzes the specific dehydrogenation of leucine by using NADP⁺ as a cofactor. The product, NADPH, triggers the hydroxylation of p-hydroxybenzoate by HBH in the presence of oxygen to produce 3,4-dihydroxybenzoate, which results in a change in electron concentration at the working carbon electrode, which is detected by the potentiostat. The sensor shows a linear detection range between 10 and 600 μM with a detection limit of 2 μM. The response is reproducible and has a fast measuring time of 5–10 s after the addition of a given concentration of leucine.     

Free sulphite determination in wine using screen-printed carbon electrodes with prior gas-diffusion microextraction

Gas-diffusion microextraction was employed in the extraction of sulphites in wines aiming their electrochemical determination, which was achieved by square-wave voltammetry using screen-printed carbon electrodes. Sulphites are additives commonly used in many produced goods, particularly food products. The developed methodology showed good limits of detection (0.4 mg L^− 1) and quantification (1.3 mg L^− 1). The proposed method was also compared with the reference methodology used by the wine industry (the Ripper method, an iodometry) showing no significant differences in the obtained results. Therefore, a simple, cheap and portable alternative for the determination of sulphites in wine is presented.     

Affinity biosensors based on disposable screen-printed electrodes modified with DNA

Simple and sensitive DNA sensors have been developed on a base on graphite screen-printed electrodes modified with DNA and enzymes. Cholinesterase and peroxidase immobilized by treatment with glutaraldehyde were used for the detection of human DNA antibodies of systemic lupus erythematosus and bronchial asthma patients. The amperometric signal was measured at +680 mV versus Ag/AgCl for DNA-cholinesterase sensor and −150 mV for DNA-peroxidase sensor 5 min after the injection of acethylthiocholine and hydroquinone, respectively. The addition of serum samples results in the sharp decrease of the signal due to the formation of DNA-antibody adducts followed by the suppression of the access of substrate to the enzyme active site. Sulfonamide medicines suppress the DNA-antibody interaction due to the competitive binding along DNA minor grooves. DNA sensor labeled with peroxidase showed the linear calibration range of 5×10⁻⁹ to 7×10⁻⁵ mol l⁻¹ of sulfamethoxazole and of 5×10⁻⁸ to 1×10⁻⁴ mol l⁻¹ of sulfathiazole.     

氯霉素在纳米钴修饰玻碳电极上的电化学行为及测定研究

研究了氯霉素在纳米钴修饰玻碳电极上的电化学行为及测定.实验结果表明,在0.3 mol/L NH3-NH4Cl(pH10.0)缓冲溶液中,氯霉素在裸玻碳电极或纳米钴修饰电极上均发生不可逆还原反应,但与裸玻碳电极相比,纳米钴修饰电极对氯霉素的还原具有明显的增敏作用,灵敏度增加约6倍.对支持电解质、修饰剂用量等各种实验条件进行了优化.测得峰电流Ip与氯霉素浓度在5.0×10(-6)～1.2×10(-4)mol/L范围内呈良好的线性关系,相关系数为0.997,检出限为3.0×10(-7)mol/L.利用优化后的条件对氯霉素滴眼液进行了测定,测量值与标示值符合,回收率在98.7%～102.2%.     

Flow-injection immuno-bioassay for interleukin-6 in humans based on gold nanoparticles modified screen-printed graphite electrodes

A flow-injection electrochemical immunoassay system based on a disposable immunosensor for the determination of interleukin-6 (IL-6) was proposed. The immunosensor was prepared by entrapping horseradish peroxidase (HRP)-labeled IL-6 antibody into gold nanoparticles-modified composite membrane at a screen-printed graphite electrode. With a non-competitive immunoassay format, the immunosensor was inserted in the flow system with an injection of sample, and the injected sample containing IL-6 antigen was produced transparent immunoaffinity reaction with the immobilized HRP-labeled IL-6 antibody. The formed antigen–antibody complex inhibited partly the active center of HRP, and decreased the immobilized HRP to H₂O₂ reduction. The performance and factors influencing the performance of the immunosensor were investigated. Under optimal conditions, the current change obtained from the labeled HRP relative to thionine–H₂O₂ system was proportional to the IL-6 concentration in the range of 5–100 ng L⁻¹ with a detection limit of 1.0 ng L⁻¹ (at 3δ). The flow-injection immunoassay system could automatically control the incubation, washing and measurement steps with acceptable reproducibility and good stability. Moreover, the proposed immunosensors were used to analyze IL-6 in human serum specimens. Analytical results of clinical samples show the developed immunoassay has a promising alternative approach for detecting IL-6 in the clinical diagnosis.     

Comparative immobilization of antibodies on modified screen-printed graphite electrodes

Immobilization of polyclonal antibodies was studied on native screen-printed graphite electrodes (SPEs) and variously modified electrodes. SPEs coated with didodecylammonium bromide (DDAB, a synthetic membranelike substance) films with gold nanoparticles gave the maximum electrochemical response. DDAB and gold nanoparticle films strongly changed the surface morphology, and the electrochemical signal became more intense and stable. This immobilization method increased the concentration of immobilized antibodies while their activity was retained. The detection limit of the enzymatic label (horseradish peroxidase) was 0.02 ng/L of sample.     

A novel modified screen-printed electrode with triazole surfactant assembled on silver nanoparticles for potentiometric determination of uranium

Journal of Radioanalytical and Nuclear Chemistry - Potentiometric modified screen-printed electrodes were developed for UO2(II) determination using a triazole-derivative alone (MSPE) or...     

Potentiometric determination of cetylpyridinium chloride using a new type of screen-printed ion selective electrodes

A new type of screen-printed ion-selective electrode for the determination of cetylpyridinium chloride (CPC) is presented. These new electrodes involve in situ, modified and unmodified screen-printed ion-selective electrodes for the determination of CPC. The screen-printed electrodes (SPEs) show a stable, near-Nernstian response for 1 × 10⁻² to 1 × 10⁻⁶ M CPC at 25 °C over the pH range 2-8 with cationic slope 60.66 ± 1.10. The lower detection limit is found to be 8 × 10⁻⁷ M and response time of about 3 s and exhibit adequate shelf-life (6 months). The fabricated electrodes can be also successfully used in the potentiometric titration of CPC with sodium tetraphenylborate (NaTPB). The analytical performances of the SPEs are compared with those for carbon paste electrode (CPE) and polyvinyl chloride (PVC) electrodes. The method is applied for pharmaceutical preparations with a percentage recovery of 99.60% and R.S.D. = 0.53. The frequently used CPC of analytical and technical grade as well as different water samples has been successfully titrated and the results obtained agreed with those obtained with commercial electrode and standard two-phase titration method. The sensitivity of the proposed method is comparable with the official method and ability of field measurements.     

Amperometric enzyme electrodes for the determination of l-glutamate

Electrodes for amperometric measurement of l-glutamate were prepared by immobilization of l-glutamate oxidase on an Immobilon-AV Affinity membrane and attachment to an oxygen/hydrogen peroxide sensor. The response of the hydrogen peroxide sensor was linear over the concentration range 5.0 x 10(-8)-5.0 x 10(-4)Ml-glutamate, with a limit of detection of 35nM. Attachment of a size-exclusion membrane (cut-off for molecular weight > 100) or of a hydrophobic oxygen membrane eliminated electro-oxidizable interferences, but the response was attenuated by a factor of 2-3. The response may be amplified 10-fold by co-immobilizing l-glutamate dehydrogenase with the l-glutamate oxidase. The electrode initially lost 25% of its activity but was then stable for more than 320 days and at least 200 assays. The electrode was successfully used to assay glutamate in a protein tablet and in several food products. A flow-injection system was assembled for the continuous assay of l-glutamate.     

Electrochemical behavior of colchicine using graphite-based screen-printed electrodes

Miniaturized electrochemical graphite based sensor for the analysis of colchicine, along with its detailed construction was described. The electrochemical behavior of colchicine, both by cyclic and differential pulse voltammetry was investigated, showing an irreversible reduction and oxidation mechanism. The effect of several different electrochemical mediators was studied in order to decrease the oxidation potential of colchicine, but none of them showed a favorable electron transfer between the alkaloid and the electrode's surface. The influences of different biomolecules (calf thymus DNA, bovine serum albumin and beta-tubulin) over colchicine's electrochemical behavior were also presented. For quantitative determinations the anodic differential pulse voltammetric method in H(3)PO(4)/HClO(4) 0.01 M (pH 2.05) was selected, evaluating one of the oxidation peaks of colchicine at +970 mV versus Ag pseudo-reference. The electrochemical scanning parameters were optimized by an experimental design using response surface modelling. The method was validated according to ICH guidelines in the concentration range 85-1200 ng mL(-1) (R(2)=0.9966, n=7) colchicine in terms of linearity, accuracy, limits of detection (LOD) (41 ng mL(-1)), limits of quantification (LOQ) and fidelity and it was successfully applied to the determination of colchicine in tablets, without the interference of the excipients. The studied method showed the same sensitivity as the more complex HPLC procedure and micellar electrokinetic chromatography with spectrophotometric detection.     

Electrochemical determination of melamine using oligonucleotides modified gold electrodes

A novel and simple electrochemical method for determination of melamine is developed based on oligonucleotides film modified gold electrodes. The electrochemical probe of ferricyanide was used to investigate the interactions between oligonucleotides and melamine. Results of cyclic voltammetries, differential pulse stripping voltammetries, electrochemical impedance spectrometry and atomic force microscope, proved that melamine might interact with oligonucleotides mainly through electrostatic and hydrogen-bonding interactions. The interactions between oligonucleotides and melamine lead to the increase in the peak currents of ferricyanide, which could be used for electrochemical sensing of melamine. The redox peak currents of ferricyanide were linear with the concentration of melamine in the range from 3.9 × 10⁻⁸ to 3.3 × 10⁻⁶ M with a linear coefficiency of 0.990. The detection limit was 9.6 × 10⁻⁹ M. The proposed electrochemical biosensor is rapid, convenient and low-cost for effective sensing of melamine. Particularly, the proposed method was applied successfully to the determination of melamine in milk products, and the recovery was 95%.     

Glassy carbon electrodes modified with gold nanoparticles for the simultaneous determination of three food antioxidants

Electrochemical behavior of three antioxidants: butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and butylated hydroquinone (TBHQ), was investigated at a glassy carbon electrode modified with gold nanoparticles (AuNPs/GCE). This electrode was characterized by scanning electron microscopy (SEM). The experimental results indicated that the modified electrode was strongly electroactive during the redox reactions of BHA, BHT and TBHQ, and this was confirmed by the observed increased redox peak currents and shifted potentials; in addition, the oxidation products of BHA and TBHQ were found to be the same. The experimental conditions were optimized and the oxidation peaks of BHA and BHT were clearly separated. Based on this, an electrochemical method was researched and developed for the simultaneous determination of BHA, BHT and TBHQ in mixtures with the use of first derivative voltammetry; the linear concentration ranges were 0.10–1.50 μg mL⁻¹, 0.20–2.20 μg mL⁻¹ and 0.20–2.80 μg mL⁻¹, and detection limits were 0.039, 0.080 and 0.079 μg mL⁻¹, for BHA, BHT and TBHQ, respectively. The proposed method was successfully applied for the analysis of the three analytes in edible oil samples.