Role of acidity on the electrochemistry of Prussian Blue at plain and Nation filmcoated electrodes

Prussian Blue (PB) coated on plain platinum (Pt) shows a redox wave at 0.44V vs SCE in addition to the two usual redox waves at 0.82 and 0.12 V vs SCE when the electrodes were dipped in acidic KC1 solution. PB incorporated into Nation film-coated on Pt electrode exhibited the same behaviour even in the presence of neutral KG solution. In acidic KC1, the additional redox wave observed for PB incorporated into Nation film shifted positively to 0.39V vs SCE and the peak separation was reduced to 30mV. The observed additional redox wave for PB coated on plain Pt electrode and incorporated into Nafion film-coated Pt electrodes was assigned to the partial reduction of PB occurring due to the insertion of protons into the film. The effect of various cations on the electrochemistry of PB incorporated into Nafion film-coated electrode was also studied.     

Screen-printed enzyme electrodes for the detection of marker analytes during winemaking

Biosensors for malic acid and glucose have been developed, using screen-printed electrodes and two different classes of enzymes: NAD(P)⁺-dependent dehydrogenases and oxidases. The active surface of the electrodes was modified using Meldola Blue (malic acid) and Prussian Blue (glucose) and in this way sensitive, low cost and reliable NAD(P)H and H₂O₂ probes were obtained. Fixed potential amperometry was used for the detection of substrates in small volumes of sample (50 μl). Immobilization of the enzymes in a polyethylenimine-glutaraldehyde cross-linking membrane allowed sensors to be obtained with sufficient operational stability. The detection limits were of 10⁻⁵ M for malic acid and 10⁻⁶ M for glucose. The sensors were applied in the analysis of different samples of wine.     

Electrochemical sensors and biosensors based on heterogeneous carbon materials

Abstract  An overview of the use of electrochemical sensors made from heterogeneous carbon materials (carbon paste electrodes, screen-printed carbon electrodes) in the field of food analysis is presented. Sensors for inorganic and organic analytes as well as biosensors are summarized. Graphical abstract        

Comparative study of different alcohol sensors based on Screen-Printed Carbon Electrodes

Different very simple single-use alcohol enzyme sensors were developed using alcohol oxidase (AOX) from three different yeast, Hansenula sp., Pichia pastoris and Candida boidinii, and employing three different commercial mediator-based Screen-Printed Carbon Electrodes as transducers. The mediators tested, Prussian Blue, Ferrocyanide and Co-phthalocyanine were included into the ink of the working electrode. The procedure to obtain these sensors consists of the immobilization of the enzyme on the electrode surface by adsorption. For the immobilization, an AOX solution is deposited on the working electrode and left until dried (1 h) at room temperature. The best results were obtained with the biosensor using Screen-Printed Co-phthalocyanine/Carbon Electrode and AOX from Hansenula sp. The reduced cobalt–phthalocyanine form is amperometrically detected at +0.4 V (vs. Ag pseudo reference electrode). This sensor shows good sensitivity (1211 nA mM⁻¹), high precision (2.1% RSD value for the slope value of the calibration plot) and wide linear response (0.05–1.00 mM) for ethanol determination. The sensor provides also accurate results for ethanol quantification in alcoholic drinks.     

Development and evaluation of electrochemical glucose enzyme biosensors based on carbon film electrodes

Electrochemical glucose enzyme biosensors have been prepared on carbon film electrodes made from carbon film electrical resistors. Evaluation and characterisation of these electrodes in phosphate buffer saline solution has been carried out with and without pretreatment by cycling in perchloric acid or at fixed applied potential. Both pretreatments led to a reduction in the carbon surface oxidation peak and enabled better detection of hydrogen peroxide in the pH range of 5-7. Glucose oxidase enzyme was immobilised on the carbon surface by mixing with glutaraldehyde, bovine serum albumin and with and without Nafion. The performance of these two types of electrode was similar, that containing Nafion being more physically robust. Linear ranges were up to around 1.5 mM, with detection limits 60 μM, and pretreatment of the carbon film electrode at a fixed potential of +0.9 V versus SCE for 5 min was found to be the most beneficial. Michaelis-Menten constants between 5 mM and 10 mM were found under the different experimental conditions. Coating the immobilised enzyme layer with a thin layer of Nafion was found to give similar results in the determination of glucose to mixing it but with benefits against interferences for the analysis of complex matrices, such as wine. Potentialities, for a short-term-use or disposable sensors, are indicated.     

A new,improved sensor for ascorbate determination at copper hexacyanoferrate modified carbon film electrodes

A new, improved sensor for the electrocatalytic determination of ascorbate has been developed that has both a low applied operating potential and a low detection limit. The sensor was constructed by depositing copper hexacyanoferrate film either electrochemically or chemically onto carbon film electrode, and it was then characterised by cyclic voltammetry and electrochemical impedance spectroscopy. Chemically deposited films were shown to be the best for ascorbate determination and were used as an amperometric sensor at +0.05 V versus SCE to determine ascorbate in wines and juice. The linear range extended to 5 mM with a limit of detection of 2.1 M, the sensor was stable for more than four months, and it could be used continuously for at least 20 days.     

A glucose biosensor using methyl viologen redox mediator on carbon film electrodes

A new methyl viologen-mediated amperometric enzyme electrode sensitive to glucose has been developed using carbon film electrode substrates. Carbon film electrodes from resistors fabricated by pyrolytic deposition of carbon were modified by immobilization of glucose oxidase through cross-linking with glutaraldehyde in the presence of bovine serum albumin. The mediator, methyl viologen, was directly immobilised with the enzyme together with Nafion cation-exchange polymer. The electrochemistry of the glucose oxidase/methyl viologen modified electrode was investigated by cyclic voltammetry and by electrochemical impedance spectroscopy. The biosensor response to glucose was evaluated amperometrically; the detection limit was 20 μM, the linear range extended to 1.2 mM and the reproducibility of around 3%. When stored in phosphate buffer at 4 °C and used every day, the sensor showed good stability over more several weeks.     

Anodic stripping voltammetry at in situ bismuth-plated carbon and gold microdisc electrodes in variable electrolyte content unstirred solutions

Carbon and gold microdisc electrodes (30 and 10 μm, respectively) have been tested as substrates for in situ bismuth film plating from unstirred solutions of variable acetate buffer content and were subsequently used in the anodic stripping voltammetry determination of Pb(II) and Cd(II) ions. The effects of Bi(III) concentration, analyte accumulation time, stirring as well as supporting electrolyte content have been studied. Under optimal conditions good voltammetric responses were obtained by means of square wave anodic stripping voltammetry in unstirred analyte solutions of 5 × 10⁻⁸ to 10⁻⁶ M, even in the absence of added buffer. In an indicative application, Pb(II) ion levels were determined in tap water using bismuth-plated carbon microdisc electrodes.     

Electrohydrodynamic conduction pumps with cylindrical electrodes for pumping of dielectric liquid film in an open channel

In the present study, electrohydrodynamic conduction pumping of n-hexane and n-decane liquid films in an open channel has been investigated experimentally. These two dielectric liquids have nearly the same electrical properties but with their different viscosities. The effects of film thicknesses, the arrangement of electrodes and the gap between pumps on the flow rate of liquid films have been also studied. The pumps with cylindrical electrodes have been installed in the channel. The best performance of the conduction pumps, revealing with experimental results, has been achieved at 8 mm thickness of liquid film with the gap size of 55 mm for both dielectric liquids in the present layout of the pumps.     

An electropolymerized Nile Blue sensing film-based nitrite sensor and application in food analysis

This paper reports a poly-Nile Blue (PNB) sensing film based electrochemical sensor and the application in food analysis as a possible alternative for electrochemical detection of nitrite. The PNB-modified electrode in the sensor was prepared by in situ electropolymerization of Nile Blue at a prepolarized glassy carbon (GC) electrode and then characterized by cyclic voltammetry (CV) and pulse voltammetry in phosphate buffer (pH 7.1). Several key operational parameters affecting the electrochemical response of PNB sensing film were examined and optimized, such as polarization time, PNB film thickness and electrolyte pH values. As the electroactive PNB sensing film provides plenty of active sites for anodic oxidation of nitrite, the nitrite sensor exhibited high performance including high sensitivity, low detection limit, simple operation and good stability at the optimized conditions. The nitrite sensor revealed good linear behavior in the concentration range from 5.0 × 10⁻⁷ mol L⁻¹ to 1.0 × 10⁻⁴ mol L⁻¹ for the quantitative analysis of nitrite anion with a limit of detection of 1.0 × 10⁻⁷ mol L⁻¹. Finally, the application in food analysis using sausage as testing samples was investigated and the results were consistent with those obtained by standard spectrophotometric method.     

Characterization of Carbon Film Electrodes for Electroanalysis by Electrochemical Impedance

The interfacial behavior of electrodes fabricated from carbon film resistors of 2 and 20 Ω in supporting electrolyte solutions of varying pH used in electroanalytical experiments has been characterized by electrochemical impedance spectroscopy with complementary cyclic voltammetric experiments. Equivalent circuits are proposed to fit the experimental data and the influence of electrode pretreatment has also been investigated.     

Electroanalytical sensors for nonconducting media based on electrodes supported on perfluorinated ion-exchange membranes

Electroanalytical sensors, suitable for the analysis and monitoring of electroactive analytes present in gaseous phase or low-conductive liquid media, and based on electrodes in close contact with perfluorinated ion-exchange polymers are reviewed. The basic operative mechanism of these sensors, in which ion-exchange polymers act as solid polymer electrolytes (SPE's), is thoroughly discussed, while stressing the fundamental reasons why their behavior differs from that of conventional membrane electrodes. The procedures for preparing composite working electrodes by coating one side of ion-exchange membranes with stable porous films of conductive materials are described, along with the most common strategies followed to assemble this type of sensors. Useful examples of measurements in electrolyte-free media of inorganic and organic electroactive species of interest mainly for environmental analysis are given. Future prospects for the development of these sensors are also discussed.     

正交设计和均匀设计用于硒-金膜修饰电极制备条件的选择

硒代胱氨酸在硒 金(Se Au)膜修饰玻碳电极上产生两个灵敏的氧化还原峰:峰II(-500mV左右)和峰III(-327mV左右),以峰II的峰电流作为评价指标,采用正交设计与均匀设计相结合的方法对Se Au膜修饰电极的制备条件进行优化得到最佳优化条件:底液0.1mol LKCl;沉积电位为-850mV;沉积时间为60s;SeO2浓度为8.3×10-3mol L;AuCl3浓度为8.9×10-4mol L。均匀设计的数据应用Matlab计算机软件处理。依此制备的Se Au膜修饰电极性能稳定,用于硒代胱氨酸伏安特性研究有良好的重现性。     

Molecularly imprinted polymers-based sensors for bisphenol-A: Recent developments and applications in environmental,food and biomedical analysis

Bisphenol A (BPA) is a well-known endocrine-disrupting industrial compound that is found throughout many aspects of our daily life; from the water we drink and the food we eat to the babies’ bottles and children’s plastic toys. Chronic exposure to BPA may result in some severe medical issues which account for the great importance of its monitoring and removal from everyday products. The use of molecularly imprinted polymers (MIPs) for that purpose has acquired a lot of traction in recent decades. MIPs are artificial antibodies with selective recognition cavities for specifically targeted substances. They are created using a variety of synthetic methods and employed in numerous types of sensors to be used in a wide range of applications. In this review, we focus on the different production methods of MIPs and the varied types of electrochemical and optical sensors that employed MIPs to detect and analyze BPA. Finally, the broad variety of applications of MIPs in environmental, foodstuff, and biological samples are thoroughly examined. Future expected trends and prospective developments are also assessed.     

Characterization of cobalt- and copper hexacyanoferrate-modified carbon film electrodes for redox-mediated biosensors

Cobalt and copper hexacyanoferrate films (CoHCF and CuHCF) were formed at carbon film electrodes by three different one-step processes: cycling the applied potential, application of a constant current, and chemically. All hexacyanoferrate films obtained were characterized electrochemically by cyclic voltammetry and electrochemical impedance spectroscopy. To evaluate their possible use as redox mediators for biosensors, they were applied to the determination of hydrogen peroxide in neutral phosphate buffer saline electrolyte. Chemically deposited CuHCF was found to be generally the most suitable as a mediator, although CoHCF made by potential cycling is the most useful when a very low detection limit is necessary.Dedicated to Professor George Horanyi on the occasion of his 70th birthday, in recognition of his outstanding contributions to electrochemistry.     

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.     

Functionalization of Single‐Walled Carbon Nanotubes with Cubic Prussian Blue and Its Application for Amperometric Sensing

In this work, we synthesized electroactive cubic Prussian blue (PB) modified single‐walled carbon nanotubes (SWNTs) nanocomposites using the mixture solution of ferric‐(III) chloride and potassium ferricyanide under ambient conditions. The successful fabrication of the PB‐SWNTs nanocomposites was confirmed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV‐vis absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and cyclic voltammetry (CV). PB nanocrystallites are observed to be finely attached on the SWNTs sidewalls in which the SWNTs not only act as a carrier of PB nanocrystallites but also as Fe(III)‐reducer. The electrochemical properties of PB‐SWNTs nanocomposites were also investigated. Using the electrodeposition technique, a thin film of PB‐SWNTs/chitosan nanocomposites was prepared onto glassy carbon electrode (GCE) for the construction of a H₂O₂ sensor. PB‐SWNTs/chitosan nanocomposites film shows enhanced electrocatalytic activity towards the reduction of H₂O₂ and the amperometric responses show a linear dependence on the concentration of H₂O₂ in a range of 0.5–27.5 mM and a low detection limit of 10 nM at the signal‐to‐noise ratio of 3. The time required to reach the 95% steady state response was less than 2 s. CV studies demonstrate that the modified electrode has outstanding stability. In addition, a glucose biosensor is further developed through the simple one‐step electrodeposition method. The observed wide concentration range, high stability and high reproducibility of the PB‐SWNTs/chitosan nanocomposites film make them promising for the reliable and durable detection of H₂O₂ and glucose.     

Recent Advances in Anodic Stripping Voltammetry with Bismuth‐Modified Carbon Paste Electrodes

In this article, the results of some recent investigations on two types of bismuth‐modified carbon paste electrodes are presented. In the first study, the bismuth‐film carbon paste electrode (BiF‐CPE) operated in situ and employed in anodic stripping voltammetry of Cd(II) and Pb(II) at the low μg L^?1 level was of interest in view of choosing the proper Bi(III)‐to‐Me(II) concentration ratios (where Me: Pb or Cd). Such optimization has resulted in significant improvement of detection limits down to 1.0 μg L^?1 Cd and 0.8 μg L^?1 for Pb, which allowed us to apply the BiF‐CPE for analysis of selected real samples of tap and sea water. The BiF‐CPE was also further investigated for its application in highly alkaline media. In this case, attention was focused on the complex‐forming capabilities of the OH ^– ions and their effect on the anodic stripping characteristics of some heavy metals (i.e. Cd, Pb, Tl) as well as upon the formation of the bismuth film itself. The last example deals with the continuing characterization of the recently introduced carbon paste electrodes modified with bismuth powder (Bi‐CPEs) which combine the advantageous properties of carbon paste material with the favorable electrochemical properties of bismuth. Three series of electrodes, differing either in the content of metallic bismuth (from 8 to 50% w/w) or in the type of the carbon powder used (two spectroscopic types of graphite and powdered glassy carbon), were compared and the respective relations to the optimal carbon paste composition evaluated. Attractive electroanalytical performance of the Bi‐CPE in anodic stripping voltammetry is demonstrated for selected model mixtures of heavy metals (Mn, Zn, Cd, Pb, Tl, and In).     

Electrochemical biosensors for food analysis

Abstract  Food analysis has become a very important and interesting area of research because of the rapid expansion of food trade and highly increased mobility of today’s populations. Food quality control is essential both for consumer protection and also for the food industry. Application of the electrochemical biosensors in the field of food analysis is promising. This review covers the recent developments and issues in electrochemical biosensors for food analysis, such as ease of preparation, robustness, sensitivity, and realization of mass production of the detection strategies. This review also emphasizes the current development of electrochemical biosensors combined with nanotechnology. Graphical abstract