A Sensitive Electrochemical Approach for Melamine Detection Using a Disposable Screen Printed Carbon Electrode

We report here a simple and easy electrochemical approach for sensitive detection of non‐electroactive melamine using a disposable screen printed carbon electrode (SPCE) with uric acid as the recognition element. It is based on the competitive adsorptive behavior of melamine at the preanodized SPCE causing suppression in the oxidation current of uric acid. A linear range up to 126 ppb with a detection limit of 1.6 ppb (S/N=3) is achieved at the preanodized SPCE by differential pulse voltammetry. The electrochemical method is successfully applied to detect the melamine content in tainted milk powder and dog food.     

A Simple Electrochemical Approach Based on Inexpensive Wall‐Jet Screen‐Printed Ring Disk Electrode to Evaluate Oxygen Reduction Catalysts

A simple electrochemical approach to evaluate oxygen reduction catalysts using an inexpensive screen‐printed ring disk carbon electrode system, consisting of a ring electrode deposited with MnO₂ and a disk electrode modified with the catalysts for study, is developed in this study. The as‐prepared MnO₂ is selective and sensitive for H₂O₂ oxidation in the presence of O₂ and is crucial to the proposed approach. By coupling with a wall‐jet electrochemical cell, the product generated from the reduction reaction at the disk electrode can effectively be monitored at the MnO₂‐deposited ring electrode. Model catalysts of nano‐Au and nano‐Pd representing 2e^? reduction of O₂ to H₂O₂ and 4e^? reduction to H₂O, respectively, were evaluated as electrode materials in oxygen reduction reaction to demonstrate the applicability of the proposed method.     

Sensitive Electrochemical Detection of Horseradish Peroxidase at Disposable Screen‐Printed Carbon Electrode

A rapid, simple and sensitive electrochemical assay of horseradish peroxidase (HRP) performed on disposable screen‐printed carbon electrode was developed. HRP activities were monitored by square‐wave voltammetric (SWV) measuring the electroactive enzymatic product in the presence of o‐aminophenol and hydrogen peroxide substrate solution. SWV analysis demonstrated a greater sensitivity and shorter analysis time than the widely used amperometric and differential‐pulsed voltammetric methods. The voltammetric characteristics of substrate and enzymatic product as well as the parameters of SWV analysis were optimized. Under optimized conditions, a linear response for HRP from 0.003 to 0.1 U/mL and a detection limit of 0.002 U/mL (1.25×10^?15 mol in 25 μL) were obtained with a good precision (RSD=8%; n=6). This rapid and sensitive HRP assay with microliter‐assay volume could be readily integrated to portable devices and point‐of‐care (POC) diagnosis applications.     

Electrochemical Investigation of Gold Based Screen Printed Electrodes: An Application for a Seafood Toxin Detection

Although commercial screen-printed electrodes (SPEs) are used extensively for biosensor purposes nowadays, detailed studies on characterization are still limited. In this study, the surface of the gold-based screen-printed electrode (SPGE) was carefully modified with self-assembly-monolayer through an optimized immobilization procedure. The key physical and chemical properties with regeneration capacity of the developed biosensors were assessed by various characterization techniques. Then SPGE was used to determine its sensitivity, limit of detection (LOD) and limit of quantification (LOQ) for a toxin substance of domoic acid in seafood that has become more common and rising concern of marine wildlife and seawater pollution. LOD in phosphate buffered saline (PBS) and cell culture media were obtained as 2.93 ng mL⁻¹ and 4.28 ng mL⁻¹, respectively. The reduced sensitivity for antibody-based biosensors in the cell culture medium was probably due to interaction of nonspecific compounds with DA in the culture medium compared to the much less complex environment of PBS. In addition, the regeneration capacity has been found very limited due to inherent heterogeneity and low robustness. This study can be used for the main challenges with the design requirements of commercial SPE-based biosensors to provide a detailed perspective for further toxicity studies.     

As(III) Voltammetric Detection by Means of Disposable Screen‐Printed Gold Electrochemical Sensors

Abstract

In this paper a disposable gold screen‐printed working electrode was tested for arsenic detection in aqueous solutions using Square Wave Anodic Stripping Voltammetry (SWASV). The dynamic range of the sensor and its response were characterised in standard As(III) solutions; particular efforts were devoted to optimize electrode surface conditioning and electrolyte solution composition. The detection limit was 2.5 µg l^?1 using 60 s as deposition time. A portable battery‐operated device was used to demonstrate the possibility to use the sensor for on‐site analysis. Analysis of spiked samples was also performed.     

Electrochemical Behaviour and Rapid Determination of L‐Dopa at Electrochemically Pretreated Screen Printed Carbon Electrode

A simple and rapid voltammetric method based on a disposable electrochemically pretreated screen‐printed carbon electrode is proposed for the determination of L ‐dopa. Under optimum differential pulse voltammetry conditions a limit of detection of 3.6×10^?7 M for L ‐dopa was obtained. The method was successfully applied to the determination of L ‐dopa in a commercial pharmaceutical formulation.     

Facile Fabrication of Zirconia Modified Screen‐Printed Carbon Electrodes for Electrochemical Sensing of Phosphate

We report here a facile method to immobilize zirconia nanoparticles on a disposable screen‐printed carbon electrode (designated as ZrO₂‐SPCE) for phosphate sensor application. Simply by ultrasonicating a bare SPCE in a ZrO₂ slurry, ZrO₂ nanoparticles can be immobilized effectively on the electrode surface as verified by surface characterization evidences. Using ferricyanide as a redox probe, an increase in the charge transfer resistance (R_ct) of ferricyanide upon adsorption of phosphate on ZrO₂ is used for the determination of phosphate. This ZrO₂‐SPCE phosphate sensor shows a wide linear range up to 1 mM and a detection limit of 1.69 µM (S/N=3). Practical applicability of the ZrO₂‐SPCE is demonstrated by detecting phosphate content in human blood samples.     

Electrochemical Aptasensors for Biological and Chemical Analyte Detection

Aptamers are short length, single-stranded DNA or RNA affinity molecules which interact with any desired targets such as biomarkers, cells, biological molecules, drugs or chemicals with high sensitivity. They have been extensively employed for medical applications due to having more advantages than the antibodies such as easier preparation and modification, higher stability, lower batch-to-batch variability and cost. Moreover, aptamers can be easily integrated efficiently with sensors, biosensors, actuators and other devices. In this review article, different applications of aptamers for biological and chemical molecules detection within the scope of electrochemical methods were presented with recent studies. In addition, the present status and future perspectives for highly-effective aptasensors for specific and selective analyte detection were discussed. As in stated throughout the review, combining of extraordinary properties of aptamers with the electrochemical-based biosensors could have improved the sensitivity of the assay and reduced limit of detection.     

Carbon Black‐Modified Electrodes as Sensitive Tools for the Electrochemical Detection of Nitrite and Nitrate

Both screen‐printed electrodes modified with a dispersion of carbon black (CB) and solid paste electrodes prepared using a nanostructured CB were developed and characterized. Indeed, increasing the peak currents and/or their shifting to negative potentials were observed, exhibiting efficient electrocatalytic activity towards nitrite oxidation with high sensitivity and low detection limit. Solid carbon paste electrodes (SCPEs) and solid carbon black paste electrodes (SCBPEs) were challenged in amperometric mode with nitrite since detection limit reached is 65 and 5 nM respectively. Nitrate was first reduced to nitrite in reductor column, then detected on SCBPEs. Nitrate and nitrite were determined in real samples.     

Chitosan/AuNPs Modified Graphene Electrochemical Sensor for Label‐Free Human Chorionic Gonadotropin Detection

A new immunosensor is presented for human chorionic gonadotropin (hCG), made by electrodepositing chitosan/gold‐nanoparticles over graphene screen‐printed electrode (SPE). The antibody was covalently bound to CS via its Fc‐terminal. The assembly was controlled by electrochemical Impedance Spectroscopy (EIS) and followed by Fourier Transformed Infrared (FTIR). The hCG‐immunosensor displayed linear response against the logarithm‐hCG concentration for 0.1–25 ng/mL with limit of detection of 0.016 ng/mL. High selectivity was observed in blank urine and successful detection of hCG was also achieved in spiked samples of real urine from pregnant woman. The immunosensor showed good detection capability, simplicity of fabrication, low‐cost, high sensitivity and selectivity.     

Quantitative Detection for Porphyromonas gingivalis in Tooth Pocket and Saliva by Portable Electrochemical DNA Sensor Linked with PCR

Here, a quantitative electrochemical analysis of periodontal bacteria in gingival crevicular fluid (GCF) and saliva by direct polymerase chain reaction (PCR) is presented. The electrochemical measurement was performed by mixing with PCR products and electrochemical indicator (bisbenzimidazole trihydrochloride). The peak current of indicator is reduced due to slower diffusion when the dye intercalates into the amplified DNA, and the degree of reduction in the peak current is correlates with the quantity of amplified DNA. Therefore, a quantitative analysis is possible by using our electrochemical method at the end point of PCR. In the GCF testing, The number of Porphyromonas gingivalis (Pg) detected by our electrochemical method at the end point of PCR were almost same compared with that were calculated by the conventional method of quantitative real? time PCR. In the saliva testing, the relationship between number of Pg in saliva and average pocket depth, and age‐dependence were also clearly observed. Since the saliva sample is obtained in a non‐invasive manner, this method is useful for the primary screening of periodontal disease. Moreover, our detection method is simple and uses a hand‐held potentiostat making it suitable for development of an on‐site periodontal diagnosis system.     

基于丝网印刷电极的阻抗型免疫传感器用于检测烯效唑

采用循环伏安法在丝网印刷碳电极表面电聚合聚苯胺/壳聚糖复合膜,利用静电吸附作用固定烯效唑抗体,制备了检测烯效唑的阻抗型免疫传感器.采用循环伏安法和电化学阻抗谱对电极修饰过程进行了表征,并考察了缓冲溶液pH值、温育温度及时间对免疫反应的影响.在优化的条件下研究了免疫传感器的性能.此免疫传感器具有灵敏度高、特异性强、重现性和稳定性好的特点,对烯效唑的线性检测范围为0.01 ～100 mg/L,相关系数为0.999,检出限为8μg/L(3σ).白菜样品中添加0.05,0.10和1.0 mg/kg烯效唑,平均回收率为98.5％ ～ 104.6％,相对标准偏差为3.3％ ～4.3％,检测结果与气相色谱法的检测结果相符.     

Incorporation of Disposable Screen‐Printed Electrodes for Use in Capillary Electrophoresis End‐Column Amperometric Detection System

The development and performance of an end‐column amperometric detection system integrated with disposable screen‐printed electrodes for capillary electrophoresis is presented. In this system, the electrode and capillary can be easily replaced and the capillary/electrode alignment procedure is straightforward. The use of easily replaceable screen‐printed electrodes offers a tremendous benefit for capillary electrophoresis applications requiring frequent replacement of the working electrode due to fouling. This simple and convenient system is very attractive for routine analyses by capillary electrophoresis with electrochemical detection. The separation and determination of uric acid in human urine is presented.     

Electroanalytical Device for Cadmium Speciation in Waters. Part 1: Development and Characterization of a Reliable Screen‐Printed Sensor

A reliable screen‐printed sensor for cadmium speciation analysis is presented here. Its development has been focused on the achievement of a reproducible and repeatable sensor. The electrode construction and its surface coating are discussed in detail. The optimized procedure has permitted to obtain very accurate sensors with detection limit of 0.2 μg (Cd) L^?1 using SWASV for only 60 s of deposition time. The electrochemically accessible, i.e. potentially bioavailable, fraction of the cadmium present in an untreated river water sample has been successfully quantified without degassing. These results give a glimpse of the potential of this membrane‐free sensor in real matrices.     

Graphene-based Disposable Electrochemical Sensor for Chlorhexidine Determination

In this work, simple, reliable, eco-friendly, and quantitative electrochemical sensors were developed to detect chlorhexidine Digluconate (CHX) in a variety of dosage forms, including mouthwashes and intimate douches, as well as chlorhexidine in spiked human saliva. Without any sample pre-treatment or extraction processes, CHX was measured in colored aqueous formulations. Based on carbon screen-printed electrodes, two potentiometric sensors (sensors I and II), utilizing graphene nanocomposites (Gr-NC), were designed (SPEs). An ionophore, 2-hydroxypropyl-β-cyclodextrin, was doped into the Poly Vinyl Chloride (PVC) polymeric membrane to improve sensor selectivity.     

Electrochemical Characterization of Screen‐Printed Carbon Electrodes by Modification with Chitosan Oligomers

The kinetics on the current amplification of the disposable screen‐printed carbon electrodes (SPCEs) by modification with chitosan oligomers (COs), coupled with the Fe(CN) redox system, were characterized with the variation of electron‐transfer rate constant (k°) and the electroactive area (A_ea) at electrode surface. The nonlinear response characteristics of peak currents with increase in Fe(CN) bulk concentrations complicated the estimation of A_ea in cyclic voltammetric analysis. Upon the modification with COs, the rate constant of SPCEs was not much influenced and the current amplification was characterized with the increase of a better estimated A_ea, obtained from electrochemical impedance measurements and verified with the reciprocal of electron‐transfer resistances linearly proportional to the Fe(CN) bulk concentrations. It is hereby provided for an evaluation of the carbon based electrodes with modification.     

Label‐Free Electrochemical Aptasensor for Determination of Chloramphenicol Based on Gold Nanocubes‐Modified Screen‐Printed Gold Electrode

An ultrasensitive label‐free electrochemical aptasensor was developed for selective detection of chloramphenicol (CAP). The aptasensor was made using screen‐printed gold electrode modified with synthesized gold nanocube/cysteine. The interactions of CAP with aptamer were studied by cyclic voltammetry, square wave voltammetry (SWV) and electrochemical impedance spectroscopy. Under optimized conditions, two linear calibration curves were obtained for CAP determination using SWV technique, from 0.03 to 0.10 µM and 0.25–6.0 µM with a detection limit of 4.0 nM. The aptasensor has the advantages of good selectivity and stability and applied to the determination of CAP in human blood serum sample.     

A Capillary Electrophoresis End‐Column Amperometric Detection System Incorporating Disposable Copper‐Plated Screen‐Printed Carbon Electrodes

We report here the development of copper‐plated screen‐printed carbon electrodes (designated as Cu‐SPE) to employ as electrochemical detectors for the determination of sugars by capillary electrophoresis (CE). A simple end‐column amperometric detection system with easily exchangeable (or even disposable) electrode and capillary in CE is described in this study. A complex alignment procedure was not required in this system based on the end‐column electrode arrangement using an 85 cm length and 20 μm (i.d.) capillary. The optimized separation voltage and applied potential were 9 KV and 0.4 V (vs. Ag/AgCl), respectively, for the detection of sugars using the Cu‐SPE. Good resolution was obtained by this proposed system with migration times of 28.8, 29.5, 29.9, 30.7, 31.2, and 32.0 min for galactose, glucose, arabinose, fructose, xylose, and ribose, respectively.     

Detection of α‐Methylacyl‐CoA Racemase in Serum and Urine Using a Highly Sensitive Electrochemical Immunodetector

The detection of α‐methylacyl‐CoA racemase (AMACR), a novel biomarker for prostate cancer, is demonstrated in serum and urine using a novel immuno‐detection method. The detection system consists of a three‐electrode conventional electrochemical cell modified with a gating electrode for applying a gating voltage V_G to the immune complex immobilized on the working electrode to provide signal amplification. The detection system is realized by integrating gating electrodes with screen‐printed electrodes. This detection method does not require involved sample preparation procedures. The detection was demonstrated in serum and urine samples on the nanogram/mL level with V_G equal to 0.6 V. Detection in serum was also performed on the picogram/mL level with a limit of 100 picogram/mL with V_G=0.6 V being a necessary condition.     

A Microbial Sensor Based on Direct Electron Transfer at Shewanella Sp. Drop‐Coated Screen‐Printed Carbon Electrodes

Aerobically grown Shewanella sp. bacterial suspension drop‐coated on a disposable screen‐printed carbon electrode was found to possess electroactivity without the aid of redox mediator. Cyclic voltammetric studies revealed the characteristics of a mixed diffusion adsorption‐controlled electrochemical process for direct electron transfer at the bacteria‐modified electrode. Both FE‐SEM and ATR FT‐IR experiments were carried out to investigate the surface characteristics. The electroanalytical applicability was further demonstrated for electrocatalytic reduction of arsenite, hydrogen peroxide and nitrite. Low cost and very simple manufacturing procedure allow for the proposed bacterial sensor to be applied as disposable devices.