In Situ Detection of Particle Aggregation on Electrode Surfaces

Partially blocked electrodes (PBEs) are important; many applications use non‐conductive nanoparticles (NPs) to introduce new electrode functionalities. As aggregation is a problem in NP immobilization, developing an in situ method to detect aggregation is vital to characterise such modified electrodes. We present chronoamperometry as a method for detection of NP surface aggregation and semi‐quantitative sizing of the formed aggregates, based on the diffusion limited current measured at PBEs as compared with the values calculated numerically for different blocking feature sizes. In contrast to voltammetry, no approximations on electrode kinetics are needed, making chronoamperometry a more general and reliable method. Sizing is shown for two modification methods. Upon drop casting, significant aggregation is observed, while it is minimized in electrophoretic NP deposition. The aggregate sizes determined are in semi‐quantitative agreement with ex situ microscopic analysis of the PBEs.     

Ring‐disc Microelectrodes towards Glutathione Electrochemical Detection

An alternative approach for space‐resolved glutathione (GSH) detection using a ring‐disc microelectrode and an appropriate electroactive probe (acetaminophen) is reported. Acetaminophen is electrochemically oxidized at one of the electrodes and a fraction of the reaction product (N‐acetyl‐p‐quinoneimine) diffuses to the other, where it is detected. The collection efficiency value is dependent on the concentration of glutathione in solution, which consumes N‐acetyl‐p‐quinoneimine during its transit from the disc to the ring. Collection efficiency values close to 100 % were obtained by confining the electroactive species in a gap (<2 μm) that resembles a thin layer cell in a SECM configuration. The proposed indirect method was used to image the transport of GSH across an impermeable membrane in a SECM experiment. The method proved to be useful as a proof of concept for space‐resolved GSH electrochemical detection and a topography independent electrochemical image was acquired.     

Quantitation of Cu+‐catalyzed Decomposition of S‐Nitrosoglutathione Using Saville and Electrochemical Detection: a Pronounced Effect of Glutathione and Copper Concentrations

S‐nitrosothiols (RSNOs) are composed of nitric oxide (NO) bound to the sulfhydryl group of amino acids of peptides or proteins. There is a great interest for their quantitation in biological fluids as they have a crucial impact on physiological and pathophysiological events. Most analytical methodologies for quantitation of RSNOs are based on their decomposition followed by the detection of the released NO. In order to obtain the optimal sensitivity for each detection method, the total decomposition of RSNOs is highly desired. The decomposition of RSNOs can be obtained by using catalytically active metal ions, such as Cu⁺, obtained from CuSO₄ in presence of a reducing agent such as glutathione (GSH) that is naturally present in biological environment. In this work, we have re‐investigated the decomposition of S‐nitrosoglutathione (GSNO) which is the most abundant in vivo low molecular weight RSNO, with a special emphasis on the effect of CuSO₄, GSH, and GSNO concentrations and of their ratio. To this aim, GSNO decomposition optimization was performed by both indirect (Griess assay) and direct (real time electrochemical detection of NO at NO‐microsensor) quantitation methods. Our results show that the ratio between CuSO₄, GSH and GSNO should be adjusted to tune the highest decomposition rate of GSNO and the most efficient electrochemical detection of released NO; also it shows the deleterious effect of very high GSH concentration on the detection of GSNO.     

Impedimetric Biosensor for Bovine Herpesvirus Type 1‐Antigen Detection

The bovine herpesvirus type 1 (BHV‐1) is a pathogen of great economic impact for livestock, which is related multi‐systemic infections that leads to mortality or morbidity of cattles. Thus, the search for cheap and practical methodologies that allow the selective detection of BHV‐1 antigen (BHV‐1 AG) is of utmost relevance. Therefore, an impedimetric label‐free immunosensor was herein, developed and its performance evaluated in biological samples enriched with BHV‐1 AG. Briefly, the biosensor construction was based on the immobilization of BHV‐1 antibody (BHV‐1 AB) and casein on the activated glassy carbon electrode surface. The BHV‐1 AB was isolated from egg yolk of immunized chickens, which is a less stressful protocol. The bio sensing principle was based on Electrochemical Impedance Spectroscopy by using Fe(CN)₆^4?/3? probe, which were also used to check variation of charge transfer resistance (?R_ct), when the electrode surface was increasingly blocked by immune complex. A linear relationship between ?R_ct and BHV‐1 AG concentration was verified in the range from 10 to 50 TCID₅₀ mL^?1, with LOQ of 2.00 TCID₅₀ mL^?1 and LOD of 0.66 TCID₅₀ mL^?1. Besides the suitable sensitivity, the immunosensor displayed accuracy, stability, and specificity to detect BHV‐1 AG in biological samples of serum, nasal secretions, semen and urine. Moreover, to the best of our knowledge this is the first immunosensor applied to BHV‐1 diagnostic.     

The stable o‐phthalaldehyde‐ferrocene/6‐ferrocenyl‐1‐hexanethiol pre‐column derivatization high‐performance liquid chromatography of dimethylarginine by novel dual fluorescence and electrochemical detector

Monomethylarginine, asymmetric dimethylarginine and symmetric dimethylarginine were separated on a Wakopak Combi ODS with an acetonitrile–100 mm potassium phosphate buffer (pH 7.0; 1:1, v/v). Dimethylarginines were derived from o‐phthalaldehyde for the fluorescence detector and from 6‐ferrocenyl‐1‐hexanethiol for the electrochemical detector. The detection limits of the dimethylarginines in spiked plasma were 0.3–0.5 pmol by electrochemical detection and 1–2 pmol by fluorescence detection. The detection limits were improved over 30 times by electrochemical detection and 10 times by fluorescence detection compared with previous reports. In previous derivatization liquid chromatography, the reaction solutions, o‐phthalaldehyde, 2‐mercaptethanol and dimethylarginines were unstable and required quick derivatization at 4°C. By our proposed pre‐column methods, the dimethylarginines were derivatized at room temperature and the fluorescent products were stable for 6 h. The manipulation performance was greatly advanced compared with previous LC reports. This is the first report on stable and sensitive dimethylarginines by dual detection. The selectivity was also improved by dual detection. The proposed method was applied to preliminary monitoring of dimethylargines in plasma and urine. Copyright © 2012 John Wiley & Sons, Ltd.     

Catalytic Hairpin Assembly‐Programmed DNA Three‐Way Junction for Enzyme‐Free and Amplified Electrochemical Detection of Target DNA

DNA three‐way junctions (DNA 3WJ) have been widely used as important building blocks for the construction of DNA architectures and dynamic assemblies. Herein, we describe for the first time a catalytic hairpin assembly‐programmed DNA three‐way junction (CHA‐3WJ) strategy for the enzyme‐free and amplified electrochemical detection of target DNA. It takes full advantage of the target‐catalyzed hairpin assembly‐induced proximity effect of toehold and branch‐migration domains for the ingenious execution of the strand displacement reaction to form the DNA 3WJ on the electrode surface. A low detection limit of 0.5 pM with an excellent selectivity was achieved for target DNA detection. The developed CHA‐3WJ strategy also offers distinct advantages of simplicity in probe design and biosensor fabrication, as well as enzyme‐free operation. Thus, it opens a promising avenue for applications in bioanalysis, design of DNA‐responsive devices, and dynamic DNA assemblies.     

Microplastics and associated emerging contaminants in the environment: Analysis,sorption mechanisms and effects of co-exposure

Microplastics (MPs) and other emerging pollutants exist together in the environment and their co-exposure represents a source of increasing concern as MPs have been reported to act as carriers of pollutants due to their high sorption capacity. The ingestion of contaminated MPs by organisms can enhance the desorption of pollutants, increasing their bioavailability and toxicity. This review examines the role of MPs as vectors of environmental emerging contaminants. First, the main tools used to identify and characterise MPs and the analytical methods used for the determination of associated emerging contaminants are discussed. Insightful explanations of the sorption interaction between several groups of emerging pollutants and MPs are provided. MP type (polarity, crystallinity, size) and aging process together with the environmental conditions and pollutant properties (hydrophobicity and dissociated forms) are key factors influencing the sorption process. The literature review showed that polyethylene and polystyrene were the most commonly studied polymers. Antibiotics, perfluoroalkyl compounds and triclosan showed high sorption capacities onto MPs. Finally, the effect of co-exposure to MPs-emerging pollutants and bioaccumulation in aquatic and terrestrial organisms is discussed. The combined exposure may impact the toxic effects in different ways, through synergistic or antagonic interactions. Examples of different scenarios are provided, but in general the research conducted on terrestrial systems is scarce. The results revealed a lack of standardization in laboratory studies and in the testing conditions that reflect actual environmental exposure.     

Impedimetric Enzyme‐Free Detection of Glucose via a Computation‐Designed Molecularly Imprinted Electrochemical Sensor Fabricated on Porous Ni Foam

Here we report a new molecularly imprinted electrochemical sensor (MIECS) for the impedimetric enzyme‐free analysis of glucose. A computational modeling strategy was first utilized to screen promising functional monomers for imprinting assembly, and simulation data suggested that methacrylic acid (MAA) exhibited a preferable capability to recognize the target molecule compared to other common monomers. Then the MIECS was prepared via introducing MAA‐based recognition sites onto a porous Ni foam with large surface. The fabricated sensor was subtly characterized by Raman spectroscopy, scanning electron microscopy, and cyclic voltammetry, and an impedimetric method was selected to detect the glucose target in a basic medium. Experimental results demonstrated that the proposed MIECS could selectively recognize glucose against coexisting species, with good linear responses of the charge transfer resistance upon the target concentration in the scope of 10∼55 mM. These results indicate its potential applications in the recognization and detection of glucose in complex matrices.     

Chronoamperometry Measurement for Rapid Cucumber Mosaic Virus Detection in Plants

Cucumber mosaic virus (CMV) causes major losses to agricultural and horticultural crops around the world. Hence, a rapid assay for the detection of CMV which can be employed in both laboratory and field is essential. A portable electrochemical immunosensor system for the detection of CMV, based on immobilized CMV specific antibodies conjugated with gold nanoparticle was developed for this purpose. The conjugated antibodies were added with polymer and deposited onto carbon screen printed working electrodes. Optimization of the modified surface immunosensor was performed using sandwich immunoassay format (ELISA). The initial ELISA result for the standard curve development showed a limit of detection down to 0.1mg/mL. Subsequently, the immunosensor was tested for cross reactivity with other plant pathogens. The performance of the electrochemical immunosensor revealed that it has a high selectivity in sample matrix with other organism. This immunosensor provides a promising technology for simple and sensitive detection system that is essential in rapid detection of plant pathogens.     

Centri‐Voltammetric Folic Acid Detection

The need for practical detection of folic acid (FA) has been increased day by day. For this reason in this work, a two steps electroanalytical technique, centri‐voltammetry was utilized for FA detection for the first time. In order to get rid of the slow electrode kinetics of FA oxidation, the working electrode was modified with graphene‐Pt hibrid nanomaterial. Also for increasing the sensitivity, 1‐Chloro‐2‐[2‐(2‐methoxyethoxy) ethoxy]ethane (TEG?Cl) and 1,2‐di{2‐[2‐(2‐methoxyethoxy)ethoxy] ethoxy}‐4‐nitrobenzene (4NC?NO₂) was used as a carrier material. After the characterization of graphene‐Pt hybrid nanomaterial, experimental parameters like, 4NC?NO₂ amount, adsorption time, centri‐voltammetric parameters like centrifuge time and speed were optimized. After that, analytical characteristics such as linear range, relative standard deviation (R.S.D), limit of detection (LOD) and limit of quantification (LOQ) values were found. In this manner, linear range was obtained for FA between 1.0 μM–1000 μM with the equations of (R²=0.9977). R.S.D value was calculated for 0.83 mM FA (n=3) as 1.86 % while LOD and LOQ values were found as 1.00 μM and 3.34 μM respectively. After the examination of interference effect of substances like ascorbic acid and uric acid, established centri‐voltammetric technique was enforced for FA detection in pharmateutical tablets. As a result, the recovery value was calculated as 96.4 %.     

Electrochemical Detection Using an Engraved Microchip – Capillary Electrophoresis Platform

The present study describes a simple strategy to integrate electrochemical detection with an assembled microchip‐capillary electrophoresis platform. The electrochemical cell was integrated with a microfluidic device consisting of five plastic squares interconnected with fused silica capillaries, forming a four‐way injection cross between the separation channel and three side‐arms (each of 15 mm in length) acting as buffer/sample reservoirs. The performance of the system was evaluated using electrodes made with either carbon ink, carbon nanotubes, or gold and under different experimental conditions of pH, capillary length, and injection time. Using this system it was possible to separate the neurotransmitters dopamine and cathecol and to quantify phenol from a real sample using a linear calibration curve with a calculated LOD of 0.7 µM. A similar concept was applied to determine glucose, by including a pre‐reactor filled with beads modified with glucose oxidase (GOx). The latter system was used to determine glucose in a commercial sample, with a recovery of 95.2 %. Overall, the presented approach represents a simple, inexpensive, and versatile approach to integrate electrochemical detection with CE separations without requiring access to microfabrication facilities.     

BisPNA‐assisted Detection of Double‐stranded DNA via Electrochemical Impedance Spectroscopy

A highly effective strategy for quantification of plasmid which was a special dsDNA based on bisPNA by electrochemical impedance spectroscopy was presented in this work. Firstly, through Au?S bond, thiol‐terminated bisPNA probes were immobilized onto the gold electrode surface. Then bisPNA probes directly hybridized with target plasmid DNA pBR322 based on the PNA.DNA‐PNA invasion triplex without denaturation. In the presence of redox electroactive ions [Fe(CN)₆]^3?/4? as hybridization indicator, the charge transfer resistance (R_ct) was produced, and R_ct was measured via electrochemical impedance spectroscopy. Under optimal conditions, this strategy showed a good linear relationship between the ΔR_ct which was the difference of R_ct obtained before and after bisPNA hybridized with plasmid pBR322, and logarithm of the concentration of plasmid pBR322 within the range from 1 nM to 100 nM (R²=0.993), with a limit of detection (LOD) of 0.1 nM. Furthermore, this bisPNA‐assisted biosensor showed good stability and satisfactory analytical reliability. In addition, this novel bisPNA‐assisted biosensor also exhibited excellent analytical results in human serum.     

Determination of serum cholestanol by semi‐micro high‐performance liquid chromatography with electrochemical detection

A simple and sensitive method that dose not require derivatization for determining cholestanol has been developed using HPLC with electrochemical detection (HPLC‐ECD). The current peak height was linearly related to the amount of cholestanol injected, ranging from 1 to 200 μM (r = 0.999). The detection limit (S/N = 3) of cholestanol was 0.23 μM (1.2 pmol). Total cholestanol in control human and mouse serum was determined by the present method with a recovery rate of more than 90% and an RSD (n = 5) of less than 7.3%. Further, this method was successfully applied to monitor experimental hypercholestanolemia in mice fed a high‐cholestanol diet, an animal model of cerebrotendinous xanthomatosis (CTX). In conclusion, we found this method to be both simple and useful for the determination of cholestanol in serum, helping in the diagnosis of CTX. Copyright © 2009 John Wiley & Sons, Ltd.     

Flower‐like Ni(II)‐based Metal‐organic Framework‐decorated Ag Nanoparticles: Fabrication,Characterization and Electrochemical Detection of Glucose

Glucose concentration monitoring is important for the prevention, diagnosis and treatment of diabetes. In this work, a composite material of AgNPs/MOF‐74(Ni) was prepared for electrochemical determination of glucose. AgNPs/MOF‐74(Ni) was characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X‐ray photoelectron spectroscopy (XPS). The electrochemical properties of the glassy carbon electrodes modified with the AgNPs/MOF‐74(Ni) composites were characterized by cyclic voltammetry (CV) and current‐time curve (I‐t curve) with three electrode system. The determination of glucose with the electrode modified by AgNPs/MOF‐74(Ni) has a linear range of 0.01～4 mM with the correlation coefficient (R²) of 0.994. The detection limit is 4.7 μM (S/N=3) and the sensitivity is 1.29 mA ? mM^?1 ? cm^?2. In addition, this sensing system possesses reasonable reproducibility and stability. The good performance of electrochemical determination for glucose is attributed to the concerted effect of silver nanoparticles and MOF‐74(Ni) on the promotion of glucose oxidation     

An Electrochemical Sensor for the Detection of Cu2+ Based on Gold Nanoflowers‐modifed Electrode and DNAzyme Functionalized Au@MIL‐101 (Fe)

In this study, we developed an electrochemical sensor for sensitive detection of Cu²⁺ based on gold nanoflowers (AuNFs)‐modified electrode and DNAzyme functionalized Au@MIL‐101(Fe) (MIL: Materials of Institute Lavoisier). The AuNFs‐modified indium tin oxide modified conductive glass electrode(AuNFs/ITO) prepared via electrodeposition showed improved electronic transport properties and provided more active sites to adsorb large amounts of oligonucleotide substrate (DNA1) via thiol‐gold bonds. The stable Au@MIL‐101(Fe) could guarantee the sensitivity because of its intrinsic peroxidase mimic property, while the Cu²⁺‐dependent DNA‐cleaving DNAzyme linked to Au@MIL‐101(Fe) achieved the selectivity toward Cu²⁺. After the DNAzyme substrate strand (DNA2) was cleaved into two parts due to the presence of Cu²⁺, the oligonucleotide fragment linked to MIL‐101(Fe) was able to hybridize with DNA1 adsorbed onto the surface of AuNFs/ITO. Due to the peroxidase‐like catalytic activity of MIL‐101(Fe) and the affinity recognition property of DNAzyme toward Cu²⁺, the electrochemical biosensor showed a sensitive detection range from 0.001 to 100 μM, a detection limit of 0.457 nM and a high selectivity, demonstrating its potential for Cu²⁺ detection in real environmental samples.     

纳米材料电化学与生物传感器——有机微污染物检测新途径

本文介绍了近年来纳米材料电化学与生物传感器在有机微污染物检测中的研究现状,分析了这些传感器中纳米材料修饰电极的特点,重点阐述了纳米材料在有机微污染物检测中的重要作用,列举了一些纳米材料电化学与生物传感器在有机微污染物检测中的应用。最后对纳米材料电化学与生物传感器用于有机微污染物的检测研究进行了简要评述和展望。     

Folic‐Acid‐Modified Conducting Polymer: Electrochemical Detection of the Cell Attachment

Here, postfunctionalization and bioapplication of a π‐conjugated polymer named 4‐[4H‐dithieno(3,2‐b:2′,3′‐d)pyrrol‐4‐yl]aniline (DTP‐aryl‐NH₂) are reported, which is successfully synthesized via electropolymerization onto the glassy carbon electrode. Folic acid (FA) is used to modify the amino functional polymer via N‐(3‐dimethylaminopropyl)‐N′‐ethylcarbodiimide hydrochloride/N‐hydroxysuccinimide chemistry for the further steps. The selective adhesion of folate receptor positive cells on the surface is followed by the electrochemical methods. Cyclic voltammetry and electrochemical impedance spectroscopy have been used to characterize stepwise modification of the electroactive surface. After optimization studies such as scan rate during the polymer deposition, FA amount for the efficient surface targeting, incubation time with the cells etc., analytical characterization is carried out. The surface morphologies at each step are imaged by using fluorescence microscopy.

     

蛋白质磷酸化作用的电化学检测方法

蛋白质的磷酸化作用是一种可逆的翻译后修饰方式,几乎参与生物体内所有关键生命活动,在核内基因的特定表达、细胞的分裂分化以及各种生命活动的转导中发挥重要意义。基于磷酸化前后电化学信号的改变,利用电化学传感器的方法能快速简便地检测蛋白质的磷酸化作用,且具有较高的选择性和灵敏度。本文回顾了几种常用的电化学检测磷酸化作用的方法,基于电极材料的不同进行了分类与总结,汇总了每种方法中用到的修饰电极的纳米材料及生物分子,最后总结了电化学方法检测蛋白质磷酸化的优缺点,并对有效检测磷酸化作用进行了前景展望。     

In situ and operando electrochemistry of redox enzymes

Understanding the biocatalytic or the interfacial electron transfer processes of redox enzymes is decisive to develop high-performance biofuel cells, mimetic catalysts, bioelectrosynthesis reactors, biosensors, and bioelectronic devices. The state-of-art of redox enzyme electrochemistry lies in using in situ and operando instrumentation, in which protein electrochemistry is resourcefully coupled to or hyphenated with numerous analytical techniques. Nevertheless, there is still a lot to research about the manipulation of redox proteins in the unusual sample holding environments, and bioelectrodes engineering emerges as a key. Here, we discuss these challenges in detail, focusing on contemporary instrumentation setups.