Electrochemical Current Signal Research Articles

Time–frequency methods for trend removal in electrochemical noise data

Electrochemical current and potential noise signals in many cases exhibit a DC drift that should be removed prior to further data analysis. The theoretical ability of wavelet analysis and empirical mode decomposition to effectively remove only the DC drift component is evaluated based on their mutual performance for the first time. The correlation coefficient between individual signals after both trend removal techniques proved to be superior compared to the correlation coefficients between these and the signals after moving average, polynomial and linear trend removal. The residual power of these signals was compared and again the two time-frequency methods acknowledged their theoretical ability of removing only a well-defined part of the data. © 2012 Elsevier Ltd. All rights reserved.

A host–guest-recognition-based electrochemical aptasensor for thrombin detection

A sensitive electrochemical aptasensor for thrombin detection is presented based on the host-guest recognition technique. In this sensing protocol, a 15 based thrombin aptamer (ab. TBA) was dually labeled with a thiol at its 3′ end and a 4-((4-(dimethylamino)phenyl)azo) benzoic acid (dabcyl) at its 5′ end, respectively, which was previously immobilized on one Au electrode surface by AuS bond and used as the thrombin probe during the protein sensing procedure. One special electrochemical marker was prepared by modifying CdS nanoparticle with β-cyclodextrins (ab. CdS-CDs), which employed as electrochemical signal provider and would conjunct with the thrombin probe modified electrode through the host–guest recognition of CDs to dabcyl. In the absence of thrombin, the probe adopted linear structure to conjunct with CdS-CDs. In present of thrombin, the TBA bond with thrombin and transformed into its special G-quarter structure, which forced CdS-CDs into the solution. Therefore, the target-TBA binding event can be sensitively transduced via detecting the electrochemical oxidation current signal of Cd of CdS nanoparticles in the solution. Using this method, as low as 4.6pM thrombin had been detected.

A new electrochemical biosensor for DNA detection based on molecular recognition and lead sulfide nanoparticles

In this paper, we constructed a new electrochemical biosensor for DNA detection based on a molecule recognition technique. In this sensing protocol, a novel dual-labeled DNA probe (DLP) in a stem–loop structure was employed, which was designed with dabcyl labeled at the 3′ end as a guest molecule, and with a Pb nanoparticle labeled at the 5′ end as electrochemical tag to indicate hybridization. One α-cyclodextrin-modified electrode (α-CD/MCNT/GCE) was used for capturing the DNA hybridization. Initially, the DLP was in the “closed” state in the absence of the target, which shielded dabcyl from the bulky α-CD/MCNT/GCE conjugate due to a steric effect. After hybridization, the loop sequence (16 bases) formed a rigid duplex with the target, breaking the relatively shorter stem duplex (6 bases). Consequently, dabcyl was forced away from the Pb nanoparticle and became accessible by the electrode. Therefore, the target hybridization event can be sensitively transduced via detecting the electrochemical reduction current signal of Pb. Using this method, as low as 7.1 × 10 −10 M DNA target had been detected with excellent differentiation ability for even a single mismatch.

Enzyme-amplified electrochemical biosensor for detection of PML–RARα fusion gene based on hairpin LNA probe

In this study, an enzyme-amplified electrochemical biosensor was developed for detection of the promyelocytic leukemia/retinoic acid receptor alpha (PML/RARα) fusion gene in acute promyelocytic leukemia (APL). This new sensor employs a hairpin locked nucleic acids (LNAs) probe dually labeled with biotin and carboxyfluorescein molecule (FAM). The probe is immobilized at a streptavidin-modified electrode surface via the biotin–streptavidin bridge, and FAM serves as an affinity tag for the peroxidase conjugate binding. Initially, the immobilized hairpin probe was in the “closed” state in the absence of the target, which shielded FAM from being approached by the bulky anti-FAM-HRP conjugate due to the steric effect. Target binding opens the hairpin structure of the probe, the probe undergoes a significant conformational change, forcing FAM away from the electrode. As a result, the FAM label becomes accessible by the anti-FAM-HRP, and the target hybridization event can be sensitively transduced via the enzymatically amplified electrochemical current signal. This new biosensor demonstrates its excellent specificity for single-base mismatch and able to detect as little as 83fM target DNA even in the presence of human serum. We also employed this sensor to directly detect PCR real sample with satisfactory results.

Design of a sandwich-mode amperometric biosensor for detection of PML/RARα fusion gene using locked nucleic acids on gold electrode

In this study, a novel DNA electrochemical probe (locked nucleic acid, LNA) was designed and involved in constructing an electrochemical DNA biosensor for detection of promyelocytic leukemia/retinoic acid receptor alpha (PML/RARα) fusion gene in acute promyelocytic leukemia for the first time. This biosensor was based on a ‘sandwich’ sensing mode, which involved a pair of LNA probes (capture probe immobilized at electrode surface and biotinyl reporter probe as an affinity tag for streptavidin–horseradish peroxidase (streptavidin–HRP). Since biotin can be connected with streptavidin–HRP, this biosensor offered an enzymatically amplified electrochemical current signal for the detection of target DNA. In the simple hybridization system, DNA fragment with its complementary DNA fragment was evidenced by amperometric detection, with a detection limit of 74fM and a linear response range of 0.1–10pM for synthetic PML/RARα fusion gene in acute promyelocytic leukemia (APL). Otherwise, the biosensor showed an excellent specificity to distinguish the complementary sequence and different mismatch sequences. The new pattern also exhibited high sensitivity and selectivity in mixed hybridization system.

Ruido electroquímico de la erosión-corrosión en cobre: su relación con los parámetros hidrodinámicos

This work presents the electrochemical noise results obtained of the surface degradation on copper, due to erosion corrosion phenomena, which were a function of the hydrodynamic parameters of the system (fluid movement). A modified rotating cylinder (RC) comprising three ring electrodes under two rotating speeds (880 and 1750 rpm with a Reynolds numbers 1486 Re and 2972 Re, respectively) were used. Characteristic electrochemical noise spectra as a function of the hydrodynamic parameters were found, as well as surface attack intensities the noise signal. An increase and a more uniform attack due to particle impact was related to larger particle size and lesser erosion corrosion intensity, in the form of more localized attack over the surface, was obtained for smaller ones. Erosion corrosion attack presents characteristic electrochemical current and potential noise signals, according to the laminar or transitional turbulent regime and particle size added.

Application of the inverse wavelet transform on electrochemical current signals to demonstrate the essence of high‐frequency variations

PurposeOne way to analyze electrochemical signals is the wavelet transform, which transforms a signal into another representation whereby the signal information is presented in a multi‐scale manner. Using the inverse wavelet transform, it is also possible to split a signal into different components of different frequency intervals. The inverse wavelet transform is the concept underpinning this paper, the aim of which is to demonstrate that high‐frequency variations in current signals are as valuable as low‐frequency variations.Design/methodology/approachThe set‐up for the experiments carried out consisted of two identical carbon steel working electrodes exposed to simulated concrete pore solution, sparged simultaneously with SO2 and CO2. The corresponding electrochemical current signal was studied using wavelet transform.FindingsHigh‐frequency components of current signals are as informative as low‐frequency components. High‐frequency variations could show some electrochemical activities that are not obvious in the other parts.Originality/valueThis paper shows that high‐frequency variations can be taken into consideration along with low‐frequency variations, since both can provide complementary information about electrochemical activities.

A non-immobilizing electrochemical DNA sensing strategy with homogenous hybridization based on the host–guest recognition technique

In this paper, we report a new strategy for electrochemical DNA detection in homogeneous solution based on the host–guest molecule recognition technique. In this sensing protocol, a novel dually labeled DNA probe (DLP) in a stem–loop structure was employed, which was designed with dabcyl labeled at one end as a guest molecule, and with Au nanoparticle labeled at the other end as electrochemical tag to indicate the hybridization occurrence. One α-CD/MCNTs/GCE was used for capturing the DNA hybridization and electrochemical signal transduction. Before the hybridization, the DLP remained in the stem–loop structure, which forced the dabcyl molecular to be closed to the Au nanoparticle. Due to the steric effect of the Au nanoparticle, the dabcyl was prevented from conjugating with the α-CD on the electrode and resulting in that the DLP could not be captured by the electrode. After hybridized with the target DNA, the target-binding DLP caused the DLP's loop–stem structure opened and then the dabcyl molecule was easily entering the cavity of the α-CD modified electrode and resulting in that the DLP could be captured by the α-CD modified electrode and the capture efficiency was proportion with the concentration of the target DNA. Therefore, the target hybridization event can be sensitively transduced via detecting the electrochemical reduction current signal of AuCl 4 − of Au nanoparticles labeled at the DLP. Using this strategy, as low as 2.6 × 10 −10 M DNA target had been detected with excellent differentiation ability for even single mismatch.

A Sandwich‐Type Electrochemical Biosensor for Detection of BCR/ABL Fusion Gene Using Locked Nucleic Acids on Gold Electrode

AbstractIn this study, a sandwich‐type electrochemical enzyme‐based LNA‐modified DNA biosensor was developed to detect relative gene in chronic Myelogenous Leukemia first. This biosensor is based on a ‘sandwich’ detection strategy, which involves a pair of probes (a capture probe immobilized at the electrode surface and a reporter probe labeled biotin as an affinity tag for avidin‐HRP) modified LNA. Since biotin can be connected with avidin‐HRP, this biosensor offers an enzymatically amplified electrochemical current signal for the detection of target DNA. This new pattern exhibits high sensitivity and selectivity, and this biosensor has been used for an assay of PCR real sample with satisfactory result.

Ultrasensitive detection of mercury (II) ions using electrochemical surface plasmon resonance with magnetohydrodynamic convection

A high-precision technique that can detect mercury (II) ions down to 1 fM concentration in aqueous solutions is introduced. The technique combines the conventional electrochemical method, surface plasmon resonance (SPR), and magnetohydrodynamic (MHD) convection. Mercury ions are electroplated onto a gold SPR sensing surface, and then detected quantitatively by applying a potential scan with cyclic voltammetry. Both the SPR angular shift and the electrochemical current signal are recorded for identification and quantification of the mercury ions. The detection sensitivity is further enhanced by applying an MHD convection in the presence of a magnetic field, which does not require any moving parts intruding into the aqueous solution. The technique thus has a great advantage for small detection volume. In the presence of supporting electrolytes, 1 mM nitric acid and 10 mM potassium nitrate, Hg 2+ ionic solutions with concentrations ranging from 1 fM to 1 μM are tested under different magnetic flux densities of B = 0 , 0.27, 0.53, and 0.71 T. The experimental results demonstrate that the stripping signals of the 1 fM to 1 μM Hg 2+ ions are enhanced by 10–60% with the flux density B = 0.71 T .

Analysis of the dynamics of Intergranular corrosion process of sensitised 304 stainless steel using recurrence plots

This study presents the assessment of the dynamics of intergranular corrosion of austenitic stainless steel with different degrees of sensitization through the analysis of electrochemical current noise signals. Samples of S30400 stainless steel were aged at 923 K for 50, 250 and 1,000 min before being quenched in water. The double Loop Electrochemical Potentiokinetic Reactivation test was applied to assess the degree of sensitization. The electrochemical noise data were analysed using a novel mathematical tool named Recurrence Plots (RP). This method allowed us to assess the dynamics of the intergranular corrosion process of the steel in a H2SO4 + KSCN solution at room temperature. The study was conducted using a recurrence quantification analysis (RQA) from which it was possible to determine the percent of recurrence (%R), the percent of determinism (%D) and the information Entropy of the corrosion process. It was found that these parameters increased with the sensitisation intensity, which indicates that sensitisation induced a more deterministic dynamics on the electrochemical process.

Electrochemical noise analysis of carbon steel in simulated concrete pore solution affected by CO2 and SO2 using wavelet transform

PurposeThe aim of this paper is to show that the use of energy distribution plot (EDP), usually employed by researchers to characterize the behavior of electrochemical signals in the framework of wavelet transform, could provide better understanding of the electrochemical behavior of a corroding surface if used along with the plot that is obtained from the standard deviation (SD) of partial signals (SDPS). A partial signal (PS) is obtained by limiting the inverse discrete wavelet transform to one crystal, and hence an SDPS is obtained by computing the SD of the corresponding PS.Design/methodology/approachThe electrochemical current signals, obtained from two identical working electrodes (carbon steel electrodes) exposed to simulated concrete pore solution, sparged simultaneously with SO2 and CO2 were studied using wavelet transforms.FindingsThe results show two steps of passive oxide layer formation: formation of defective passive oxide layer, and strengthening of the passive oxide layer. The passive oxide layer breakdown where CO2 as well as SO2 are involved occurred at a pH of approximately 11. Both the EDP and SDPS plots should be used, simultaneously, to characterize the processes occurring on the surfaces of the exposed electrodes.Practical implicationsThe results that were obtained can be regarded as the basis for better understanding and improvement of the noise analysis method.Originality/valueThis paper studies the corrosion behavior of carbon steel rebar before and after the simultaneous introduction of CO2 and SO2 gases in simulated pore solution, using EDP and SDPS plots obtained from the electrochemical current signals at different pH values.

An Enzyme-Based E-DNA Sensor for Sequence-Specific Detection of Femtomolar DNA Targets

In this work, we report an enzyme-based E-DNA sensor for the sequence-specific detection of nucleic acids. This DNA sensor employs a "stem-loop" DNA probe dually labeled with biotin and digoxigenin (DIG). The probe is immobilized at an avidin-modified electrode surface via the biotin-avidin bridge, and the DIG serves as an affinity tag for the enzyme binding. In the initial state of the sensor, the probe adopts the stem-loop structure, which shields DIG from being approached by a bulky horseradish peroxidase-linked-anti-DIG antibody (anti-DIG-HRP) due to the steric effect. After hybridization, the probe undergoes a significant conformational change, forcing DIG away from the electrode. As a result, the DIG label becomes accessible by the anti-DIG-HRP, and the target hybridization event can be sensitively transduced via the enzymatically amplified electrochemical current signal. By using this new strategy, we demonstrate that the prototype E-DNA sensor has been able to detect as low as femtomolar DNA targets with excellent differentiation ability for even single mismatches.

Label-Free Electrical Sensing of Small-Molecule Inhibition on Tyrosine Phosphorylation

Protein tyrosine kinases (PTKs) play a central role in human carcinogenesis and have emerged as the promising new targets. Small-molecule inhibitors of PTKs have shown impressive anticancer effects and are rapidly entering the clinic. PTK assays allow for high-throughput identification of small-molecule inhibitors. However, current methods of detecting kinase activity require the use of radioisotopes or expensive reagents; such as fluorescently labeled antibodies. We have developed a novel label-free approach for the quantitative detection of peptide tyrosine (Tyr) phosphorylation using the electrochemical oxidation current signal of Tyr. When the phosphorylation is achieved, the phosphorylated Tyr (Tyr-P) cannot be oxidized at approximately 0.65 V. However, when the phosphorylation is successfully inhibited using a small molecule, Tyr can be oxidized and result in a high current response on a multiwalled carbon nanotube-modified screen-printed carbon electrode. We determined the activity of cellular-sarcoma (c-Src) nonreceptor PTK, p60(c-Src), in combination with its highly specific substrate peptide, Raytide. Tyr kinase reactions were also performed in the presence of a well-defined small-molecule inhibitor, 4-amino-5-(4-chlorophenyl)-7- (tert-butyl)pyrazolo[3,4-d]pyrimidine (PP2). Based on the dependency of Tyr oxidation signal on inhibitor concentration, IC50 value, half-maximal inhibition of the inhibitor, was estimated as 5 nM for PP2. Our label-free electrochemical method is a promising candidate for pharmaceutical research and development in screening small-molecule inhibitors of PTKs.

Detection of Heavy Metal Ions in Water by High-Resolution Surface Plasmon Resonance Spectroscopy Combined with Anodic Stripping Voltammetry

High-resolution differential surface plasmon resonance (SPR) with anodic stripping voltammetry (ASV) capability has been demonstrated for detecting heavy metal ions in water. Metal ions are electroplated onto the gold SPR sensing surface and are quantitatively detected by stripping voltammetry. Both the SPR angular shift and electrochemical current signal are recorded to identify the type and amount of the metal ions in water. The performance of the combined approach is further enhanced by a differential detection approach. The gold sensor surface is divided into a reference and a sensing area, and the difference in the SPR angles from the two areas is detected with a quadrant cell photodetector as a differential signal. Our system demonstrated quantitative detection of copper, lead, and mercury ions in water from part-per-million to sub-part-per-billion levels with good linearity.

Sequence-specific electrochemical detection of asymmetric PCR amplicons of traditional Chinese medicinal plant DNA.

In this study, an electrochemistry-based approach to detect nucleic acid amplification products of Chinese herbal genes is reported. Using asymmetric polymerase chain reaction and electrochemical techniques, single-stranded target amplicons are produced from trace amounts of DNA sample and sequence-specific electrochemical detection based on the direct hybridization of the crude amplicon mix and immobilized DNA probe can be achieved. Electrochemically active intercalator Hoechst 33258 is bound to the double-stranded duplex formed by the target amplicon hybridized with the 5'-thiol-derivated DNA probe (16-mer) on the gold electrode surface. The electrochemical current signal of the hybridization event is measured by linear sweep voltammetry, the response of which can be used to differentiate the sequence complementarities of the target amplicons. To improve the reproducibility and sensitivity of the current signal, issues such as electrode surface cleaning, probe immobilization, and target hybridization are addressed. Factors affecting hybridization efficiency including the length and binding region of the target amplicon are discussed. Using our approach, differentiation of Chinese herbal species Fritillaria (F. thunbergii and F. cirrhosa) based on the 16-mer unique sequences in the spacer region of the 5S-rRNA is demonstrated. The ability to detect PCR products using a nonoptical electrochemical detection technique is an important step toward the realization of portable biomicrodevices for on-spot bacterial and viral detections.

Estudio por impedancia y ruido electroquímico de la pasivación anódica del paladio en medio alcalino

Anodic passivation of palladium in alkaline medium is studied by. means of different electrochemical techniques like potentiodynamic polarization curves, electrochemical impedance spectroscopy and electrochemical noise. A chaotic analysis of electrochemical current noise signals (current oscillations) corresponding to different palladium oxides formed anodically seem to give information about the different potentials characteristics of palladium oxides formation.

Use of electrochemical current noise to detect initiation of pitting conditions on copper tubes

Many failures in copper pipes used for cold water transportation result from type 1 pitting. This occurs when tubes containing a deleterious film from the manufacturing process are exposed in an aggressive water. Present tests to detect the presence of deleterious films are unsatisfactory and a possible alternative rapid test method has been studied. The technique involves collection and analysis of the electrochemical current noise signals emitted by the copper tube during corrosion. Tubes with different amounts of carbon contamination, produced at BNF and deliberately engineered by industry, have been studied using an electrochemical current noise technique. After only 20 h on test, the standard deviation and coefficient of variation of electrochemical noise signals clearly distinguished between grit blasted tube and contaminated tube. A longer, 30 h, test was needed to separate those that were borderline but satisfactory from those that were bordeline/unsatisfactory.