Variation Of Peak Currents Research Articles

Electrochemical Sensor Based on CuO Nanoparticles-Modified Graphite Electrode for the Detection of Malachite Green

In this study, the development of a graphite paste electrode (GPE) modified by copper oxide nanoparticles (CuO@GP) to be used as a practical and economical sensor for the electrochemical sensing of malachite green (MG) has been elucidated. The sol–gel technique was applied for the synthesis of CuO nanoparticles (NPS) from copper chloride (CuCl[Formula: see text], where the surfactant cetylpyridinium chloride (C[Formula: see text]H[Formula: see text]NCl) played the role of a capping agent. The synthesized CuO NPS were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). A bare GPE was modified using these CuO NPS and thus developed; the new electrode was used as a working electrode (WE) in a 3-electrode system for studying the cyclic voltammetry (CV) and differential pulse voltammetry (DPV) responses of MG. Phosphate buffered saline (PBS) with a pH value of 6 was used as the optimum buffer. Using DPV, a widely linear operational range of 1–1000 [Formula: see text]M was obtained with a detection limit of 0.18 [Formula: see text]M. This CuO@GP provided excellent repeatability, reproducibility and prolonged stability for the MG molecule. For the selectivity study, various common interfering agents were used to observe MG’s corresponding peak current variation. Moreover, this electrode demonstrated a successful application for detecting MG in pond water and fish flesh. This method is effective for similar other applications.

A self-calibration electrochemical sensor for ultrasensitive detection of glutathione based on metal–organic framework-derived Cu nanoparticles/nitrogen-doped porous carbon composites

Glutathione (GSH) is considered to be one of the main factors in maintaining redox homeostasis in living organisms, and alterations in GSH levels are closely associated with many diseases. In this paper, polyvinylpyrrolidone (PVP)-doped copper metal–organic backbone (N-Cu-MOF) was synthesized and N-Cu-MOF was pyrolyzed to produce nano-copper modified nitrogen porous carbon materials (CuNPs@NPC). The CuNPs@NPC modified electrode showed an increased oxidation current due to the presence of CuCl solid-state electrochemistry signal amplification strategy. With the addition of GSH, CuCl was gradually converted to Cu-GSH as a non-electrically active material, which triggered an “extrusion effect” and resulted in a decreased peak current. Meanwhile, the peak current of the internal reference ratio (acetaminophen, APAP), which was added to the electrolyte solution, was almost unchanged. Using the ratio of the peak current variation (ΔICu/IAPAP) as the output signal, the CuNPs@NPC modified electrode achieved an ultra-sensitive detection of GSH in the range of 0.1 nM–10 μM. The detection limit was as low as 0.067 nM. In the detection of human cervical cancer cell lysate, the sensor has high accuracy and selectivity for GSH, which can bring enlightenment for the early diagnosis of clinical diseases.

Chitosan/genipin modified electrode for voltammetric determination of interleukin-6 as a biomarker of sepsis

Ultrasensitive electroanalytical monitoring of interleukin-6 levels in serum samples has emerged as a valuable tool for the early diagnosis of inflammatory diseases. Despite its advantages, there is a lack of strategies for the label-free voltammetric determination of cytokines. Here, a novel chitosan/genipin modified fluorine tin oxide electrode was developed providing an in-situ hydrogel formation (FTO/CSG). This platform was applied for the detection of interleukin-6, a major pro-inflammatory cytokine. Transmission electron microscopy (TEM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) indicated genipin serves as an efficient green cross-linker to build the immunosensing platform (FTO/CSG/anti-IL-6). EIS showed an increase in charge transfer resistance from 326 to 1360 kΩ after the immobilization of anti-IL-6 antibodies. By square wave voltammetry, this method achieved a detection limit of 0.03 pg mL−1 with a wide linear range of 0.05–1000 pg mL−1. Additionally, it displayed a high selectivity index when tested in the presence of three inflammatory cytokines as interfering proteins: IL-12, IL-1β, and TNF-α. The sample matrix effect showed a peak current variation lower than 5 %. The novel method was applied for the quantification of IL-6 in serum samples of septic mice. No statistical differences were observed between the standard ELISA and the proposed method using a confidence level of 95 %.

Picomolar glutathione detection based on the dual-signal self-calibration electrochemical sensor of ferrocene-functionalized copper metal-organic framework via solid-state electrochemistry of cuprous chloride

Chemical biosensing techniques are essential for food analysis and disease diagnosis. Nanomaterials with redox activity show great potential in electrochemical analysis, acting as signal labels or signal amplification unit, which can reflect the targets concentration in foods and biological samples. Here, an ultra-sensitive dual-signal intrinsic self-calibration electrochemical platform for GSH was firstly fabricated based on the novel electroactive nanomaterial of ferrocene-functionalized copper metal–organic framework (Fc-Cu-MOF). Due to the solid-state electrochemical property of cuprous chloride (CuCl), a sharp characteristic peak with an increased signal appears with the coexistence of chloride ions in solution. The stronger specific affinity between Cu+ and GSH than that of Cu+ and Cl- triggers a “crowding effect” that causes the current signal of CuCl decrease greatly. Meanwhile, the peak current of ferrocene keeps unchanged as an internal reference. Based on the ratio of the peak current variation (ΔICu/ΔIFc) as the signal output, Fc-Cu-MOF modified electrode showed wider linear range in 0.1 nM −1 μM for GSH with the detection limit as low as 0.025 nM. And the sensor was successfully applied in the determination of GSH with excellent recoveries in various real samples such as food and serum samples, providing good prospect in application of bioanalysis and food screening.

Voltammetric determination of pethidine in biofluids at a carbon cloth electrode modified by carbon selenide nanofilm

Developing a sensitive portable sensor for the screening of illicit drugs is always challenging. Due to the importance of pethidine (PTD) tracking in addiction diagnosis, many demands have recently increased for a selective and real-time sensor. Herein, a simple electrochemical sensor has been developed based on conductive carbon cloth (CC) modified with carbon selenide nanofilms (CSe2NF) to provide a CSe2NF/CC electrode as a novel PTD sensing tool. Profiting from the ingenious design of doping strategy during the synthesis process, Se was doped in the carbonaceous skeleton of the CC. Thus, the active surface area of the CSe2NF (4.61 cm2) increased respect to the unmodified CC (0.094 cm2) to embed a suitable sensing interface in the fast PTD assay. By optimizing some effective experimental parameters such as pH, supporting electrolyte, Se powder amount, scan rate and accumulation time, the sensor catalyzed efficiently the oxidation reaction of PTD at 0.97 V. Based on peak current variations, the PTD was measured over a broad concentration range from 29 nM up to 181.8 μM with a limit of detection (LOD) as low as 19.3 nM compared to the other reported PTD sensors. The developed flexible sensor recognized the spiked PTD concentrations in some biofluids, including human blood, urine and saliva. The results of PTD analysis in the non-spiked and spiked blood, urine and saliva samples as the real samples by the developed sensor were validated by HPLC analysis as the reference method using t-test statistical method at confidence level of 5%. This sensing strategy based on the binder‐free electrode could be promising for designing some sizable wearable sensors at a low cost. The high sensitivity of the sensor, which is a bonus for the rapid and on-site measurement of PTD, may open up a route for noninvasive routine analysis in clinical samples.

Molybdenum Disulfide Supported on Metal-Organic Frameworks as an Ultrasensitive Layer for the Electrochemical Detection of the Ovarian Cancer Biomarker CA125.

Metal-organic frameworks (MOFs) are composed of metal ions/clusters and organic ligands, showing accessible functional sites, ultra-high porosity, and large specific surface area. Tricopper benzene-1,3,5-tricarboxylate (CuBTC), as a three-dimensional MOF architecture with an open and robust micro-/nanoconfiguration, possesses excellent catalytic performance and superior electric conductivity as compared to bulk MOF. In this study, CuBTC was used as a substrate on which molybdenum disulfide (MoS2) was in situ constructed by a hydrothermal reaction to enhance the electron- and ion-transfer capability. Then, gold nanoparticles (AuNPs) were electroreduced on a CuBTC@MoS2-modified electrode by linear sweep voltammetry for strengthening the connection between CA125 antibodies (CA125 Ab) and the substrate material. Due to the synergistic effect of CuBTC@MoS2 and AuNPs, our biosensor showed excellent electrochemical performance. Subsequently, CuBTC@MoS2-AuNPs/CA125 Ab-functionalized electrodes were used for the detection of the ovarian cancer biomarker CA125 from 0.5 mU/mL to 500 U/mL by differential pulse voltammetry. The results showed that the peak current decreased with the increase of concentration, and there was a logistic regression relationship between peak current variation and concentration. As interfering substances, carcinoembryonic antigen, human epididymis protein 4, and bovine serum albumin were applied for specific analysis. Our biosensor showed an obviously large response signal for CA125 detection than those observed for other interfering substances. Finally, serum samples collected from five patients were tested on our sensors with good consistency toward clinical standards, showing high practicability. This work demonstrated a tactic for simultaneously integrating the nanostructure, electroconductivity, and biocompatibility to construct advanced biosensors for cancer biomarkers.

Voltammetric determination of trace copper(II), cadmium(II), and lead(II) using a Schiff base modified glassy carbon working electrode

A Schiff base ligand named bis(5-bromo-2-hydroxybenzaldehyde) 1,2-propanediimine has been used to fabricate a modified glassy carbon electrode for the selective voltammetric detection of the low-level of Cu(II). The electrochemical behavior of unmodified and modified electrodes was investigated using the cyclic voltammetry technique, while the optimization of the parameters affecting the electrode characteristics and its analytical performance were evaluated by employing the differential pulse anodic stripping voltammetry. Under the optimized conditions (pH 4, decomposition time 360 s, decomposition potential vs. SCE − 1.2 V), the peak current variation as a function of the copper(II) concentration in the range of 10–100 nM was linear, with a calculated detection limit of 4.2 nM. The evaluated selectivity, reproducibility, and repeatability of the developed modified electrode showed its satisfactory performance. The ability of the prepared electrode was evaluated by its application for the analysis of Cu(II) in a fish liver tissue sample. It was confirmed also that the proposed modifie delectrode can be successfuly used for the determination of Cd(II) and Pb(II).

Reduction of Humidity Effect in WO3 Thin Film‐Based NO2 Sensor Using Physiochemical Optimization

AbstractIn this work, the effect of humidity on WO3 thin films is studied. Two thin films of higher and lower oxidation states are characterized and studied for their interaction with water molecules on the metal oxide sensing surface. The film with higher oxidation is found to be more immune to humidity effect and hence, further used to reduce the same effect using absorbent filters and Nichrome deposited heater mesh. With the use of a Nichrome heater mesh, by increasing mesh temperature from 30 to 90 °C, there is a 63% reduction in absolute humidity at the sensor die. This in turn stabilizes the NO2 sensor response, by decreasing the humidity dependent (40% RH to 90% RH) peak current variation for 3 ppm NO2 exposure, from 65% to 26%. High‐temperature ageing at a temperature of 90 °C and 90% RH is found to be effective in significantly reducing humidity effect on sensor current output and only 8.4% change in peak current is observed for 3 ppm NO2 at variable humidity, which stabilizes the sensor current drift due to humidity variation.

Jet Mode Recognition of Electrohydrodynamic Direct-Writing Based on Micro/Nano Current.

The online recognition of jet mode is important for the accurate control and further application of electrohydrodynamic direct-writing (EDW) technology. An EDW system with a current detection module is built for jet mode recognition. The current of the EDW jet is measured to recognize the jet mode when printing patterned structures. Then, a data processing program with a digital Kaiser low-pass filter is developed in MATLAB, via which the noise of the current signal is reduced. The features of EDW current, including the current fluctuation and the peak current intervals, are studied to recognize different jet modes. The current characteristics of three jet modes are investigated: droplet ejection mode, Taylor cone ejection mode, and retractive ejection mode. The Taylor cone ejection mode has the smallest coefficient of variation of peak current. This work provides a good way of designing the optimized control algorithm and of realizing the closed-loop control system, which contributes to enhancing the jet stability and accelerating the application of EDW technology.

Determination of Imidacloprid Based on the Development of a Glassy Carbon Electrode Modified with Reduced Graphene Oxide and Manganese (II) Phthalocyanine

AbstractAn electrochemical sensor of glassy carbon electrode modified with reduced graphene oxide and manganese (II) phthalocyanine (GCE/rGO/MnPc) was developed as an effective alternative in the determination of imidacloprid in honey samples. The peak current variation obtained with the proposed sensor, in the presence of imidacloprid, was higher compared to the bare GCE. The followed experimental conditions were optimized: reduced graphene oxide concentration (2.0 mg mL−1), manganese (II) phthalocyanine concentration (1.5 mg mL−1), electrolyte pH (6.5) and electrolyte concentration (1,50 mol L−1). The study also showed that the process of reduction of imidacloprid is irreversible and diffusion‐controlled, with a single reduction peak of approximately −0.9 V corresponding to the reduction of the nitro group (−NO2) present in the structure, generating a derived from hydroxylamine, in a process involving about four electrons. The determination of imidacloprid in honey samples exhibited recovery values within the EPA range (between 90.5 and 101.9 %). The proposed sensor GCE/rGO/MnPc can be used as an effective alternative in the determination of imidacloprid in honey samples.

A new sensing strategy based on thymine bases–Hg2+–methylene blue coordination on the electrospun PES–QDs platform for detection of Hg2+ in fruit juice samples

A novel label-free and highly sensitive electrochemical aptasensor for highly sensitive mercury ion detection has been successfully fabricated in fruit juice samples using of electrospun nanofibers polyethersulfone and quantum dots (NFs–QDs) at the surface of carbon paste electrode (CPE). In addition to the T bases used in the designed aptasensor which can be strong and specific binding to the Hg2+, the methylene blue (MB) also can interact specifically with the Hg2+ (T–Hg2+–MB), as well as interact with the guanine bases in the DNA aptamer as an receiver site for interaction. According to this, the proposed sensor has more receiver sites for interaction with the Hg2+. Here, the electrochemical signal of MB was employed for Hg2+ measurements which this signal was amplified by NFs–QDs nanocomposites. The Apt–MB binding event easily investigated by the peak current variations in Apt–MB1–Hg2+–MB2/NFs–QDs/CPE through cyclic voltammetry, differential pulse voltammetry (DPV) measurement. Also, this study was evaluated with electrochemical impedance spectroscopy. Under optimized conditions, the constructed aptasensor illustrated a wide linear range using the DPVs, from 0.1 to 150 nM and an excellent low detection limit of 0.02 nM. The quality of carefully choosing, an excellent stability and specificity sensitivity of the designed aptasensor were accredited by spiked juice samples as real sample. Moreover, the aptasensor exhibits the good reproducibility as well as has high selectivity to other cations. The recoveries of the Hg2+ assay of the fruit juice samples were obtained satisfactorily which can use for measurement of Hg2+ in the laboratory.

Effect of Different Load Impedances on ESD Generators and ESD Generator SPICE Models

The electrostatic discharge (ESD) generator calibration described in IEC 61000-4-2 (2008) only specifies contact mode discharge waveforms for the discharge-into-ground scenario. However, the actual device under test input impedance often differs from a short. To study the effect of different load impedances, a test method for ESD generator discharge under different load impedances is proposed. The method only slightly modifies the present calibration setup. The data show that the peak current variation between different brands of ESD generators for nonshorted load impedances is within the tolerance range given by the standard for the peak current. On the other hand, when performing system-efficient ESD design simulations, the load impedance seen by the ESD generator models is also different than a short. Therefore, the discharge current of a variety of ESD generator models is simulated with different load impedances and compared with ESD generator measurement results, which allows the selection of a suitable ESD generator model.

Optimization of an Electrochemical Sensor for Determination of Imidacloprid Based on β‐cyclodextrin Electropolymerization on Glassy Carbon Electrode

AbstractAn electrochemical sensor based on electropolymerization of β‐cyclodextrin (β‐CD) on a glassy carbon electrode (GCE) was developed for the determination of imidacloprid (IMP). That insecticide is the most commonly used insecticides globally and has been related to the death of bee colonies around the world are imperative. So the development of a simple, cheap and sensitive method for IMP determination is essential. This work aims the modification of a GCE by β‐CD film. The analytical response obtained with GCCE/β‐CD in the presence of the IMP showed an increase in the peak current variation of 947 % in relation to the bare GCE, indicating that the analyte was encapsulated in the β‐CD increasing the detection sensitivity. The followed experimental conditions were optimized: potential range (−1.3 to 0.9 V), presence or absence of dissolved oxygen (presence) and stirring during the electropolymerization (with agitation), number of cycles (5 scans), electrolyte pH (pH=5.0), scan rate (100 mV s−1) and concentration of β‐CD (6 mol L−1). The optimization promoted a peak current variation increase of 57 %, developing a more sensitivity methodology.

An Electrochemical Sensor Based on Electropolymerization of ß‐Cyclodextrin and Reduced Graphene Oxide on a Glassy Carbon Electrode for Determination of Neonicotinoids

AbstractAn electrochemical sensor of glassy carbon electrode modified with reduced graphene oxide and β‐cyclodextrin (GCE/rGO/β‐CD) was developed as an effective alternative in the determination of neonicotinoid insecticides, imidacloprid, clothianidin and thiamethoxam, in honey samples. The peak current variation obtained with the proposed sensor was higher compared to the bare GCE in all the analytes. In the determination of imidacloprid the response increased by 1300 %, clothianidin by 670 % and thiametoxam by 630 %. In addition, the optimization of the experimental conditions provided the construction of a sensor with greater sensitivity. The study of interferers showed that inorganic ions (Ca2+, Mg2+, Fe2+, K+, Na+, e NH4+) and other insecticides (acetamiprid and dinotefuran) did not influence the reduction of imidacloprid, clothianidin and thiamethoxam. The determination of imidacloprid, clothianidin and thiamethoxam in honey samples exhibited recovery values within the EPA range (between 107.75 and 116 %). In conclusion, the developed sensor GCE/rGO/β‐CD proved to be an effective alternative in the determination of neonicotinoid insecticides in honey samples.

Sandwich-type electrochemical immunosensor for sensitive determination of IgG based on the enhanced effects of poly-L-lysine functionalized reduced graphene oxide nanosheets and gold nanoparticles

Poly-L-lysine functionalized reduced graphene oxide nanosheets (PLL-rGO) were prepared and thoroughly characterized with transmission electron microscopy, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, UV/Vis, and FTIR spectra. PLL-rGO nanosheets were homogeneously mixed with IgG primary antibodies and were coated onto a glassy carbon electrode (GCE) surface. After being treated with glutaraldehyde vapor and subsequently blocked with bovine serum albumin, IgG antibodies were immobilized onto the PLL-rGO/GCE interface to fabricate an electrochemical immunosensing system. The as-fabricated immunosensor was characterized with voltammetry and electrochemical impedance spectroscopy. After specific binding with IgG, the immunosensor was incubated in a horseradish peroxidase labeled IgG secondary antibody solution. Based on the reduction current of the catalytic reaction towards H2O2, the experimental conditions for IgG determination were optimized. Under optimal conditions, the peak current variation was linearly related to IgG concentration in the range of 0.15 ~ 160.0 ng mL−1 with a detection limit of 0.087 ng mL−1 (S/N = 3). The practical applications of the immunosensor have also been demonstrated by determining IgG in clinical serum samples. The accuracy of the immunosensor was demonstrated by ELISA method and a recovery test.

Sensitive immunosensing of squamous cell carcinoma antigen based on a nanocomposite of poly{3-amine-N-[3-(N-pyrrole)propyl]imidazole bromide} ionic liquid and gold nanoroots

Squamous cell carcinoma antigen (SCCA) is a good specific antigen for cancer diagnosis specifically for squamous cell carcinomas. In this study, 3-amine-N-[3-(N-pyrrole)propyl]imidazole bromide (APPIBr) ionic liquid was successfully synthesized and characterized by 1H NMR, HPLC-MS and FTIR. APPIBr ionic liquid is a unique functional material with a pyrrole moiety which can be polymerized by using electrochemical technique and an amine group for immobilizing biomolecules; thus, it is ideal for the fabrication of biosensors. Using chloroauric acid as precursor and N-dodecyl imidazole as functional monomer, gold nanoroots (AuNRs) were fabricated and characterized with TEM, SEM and XRD. An immunosensor was built on a glassy carbon electrode (GCE), through the steps of forming the poly(APPIBr)/AuNRs/GCE interface by electrodeposition of APPIBr, anti-SCCA immobilization, and several optimization steps to achieve a sensitive, accurate, precise, and selective anti-SCCA/poly(APPIBr)/AuNRs/GCE for the electrochemical immunosensing SCCA. It was found that poly(APPIBr)/AuNRs nanointerface can improve the sensing performance of the immunosensor. Under the optimized experimental conditions, there existed two linear regimes relating the peak current variation to the concentration of squamous cell carcinoma antigen in the range of 0.001–0.1ngmL−1 and 0.1–5.0ngmL−1. The detection limit was calculated to be 0.3pgmL−1. The developed sensor was demonstrated its capability in quantitative analysis of squamous cell carcinoma antigen in human serum with recoveries of 97.3%, 102.4% and 107.4%.

Electrochemical Study of the Copolymer Formation Between o-Chlorophenol and o-Hydroxyphenol

Electrochemical copolymerization of o-chlorophenol (oCP) with o-hydroxyphenol (oHP) was carried out in aqueous <TEX>$H_2SO_4$</TEX> by using cyclic voltammetry (CV) technique. In addition, CV was used to evaluate the differences in electrochemical characteristics of the copolymer in comparison with the corresponding homopolymers, poly(o-chlorophenol) (PoCP) and poly(o-hydroxyphenol) (PoHP). The variation of peak currents with respect to sweep rates was compared between copolymer and homopolymers, PoCP and PoHP, films. Further support for copolymer characterization was obtained by recording UV-visible, IR spectra and elemental analysis. The mechanism of the electrochemical polymerization has been discussed. The monomer reactivity ratios (<TEX>$r_1$</TEX> and <TEX>$r_2$</TEX>) were calculated using Fineman-R<TEX>$\ddot{o}$</TEX>ss method and was found to be 0.4 and 1.3 repetitivelly and the copolymer structure is a block structure and more rich in oHP units.

Simulation studies on laser pulse stability for Dalian coherent light source

Dalian Coherent Light Source will use a 300 MeV LINAC to produce fully coherent photon pulses in the wavelength range between 150–50 nm by high gain harmonic generation free electron laser (FEL) scheme. To generate stable FEL pulses, a stringent tolerance budget is required for the LINAC output parameters, such as the mean beam energy stability, electron bunch arrival time jitter, peak current variation and the transverse beam position offset. In order to provide guidance for the design of the Dalian Coherent Light Source, in this paper, the sensitivity of FEL pulse energy fluctuation to various error sources of the electron bunch was performed using intensive start-to-end FEL simulations.

褶皱管束流能量稳定器

Stringent tolerance budget is restricted on the linear accelerator (linac) parameters, such as the mean beam energy stability, peak current variation, electron bunch arrival time jitter, and the transverse beam position offset, in order to generate stable output pulses in modern linac driven free electron laser facility. In this paper, a corrugated pipe is used as a beam energy stabilizer. Analytical and numerical methods for designing such kind of stabilizer are described, and the simulation results show that the beam energy jitter can be reduced more than 10% after this structure is adopted for the case of Dalian Coherent Light Source (DCLS) linac.

Fabrication of molecular imprinted polymer sensor for chlortetracycline based on controlled electrochemical reduction of graphene oxide

A molecular imprinted polymer (MIP) sensor was fabricated by directly eletropolymerizing monomer o-phenylenediamine in the presence of template chlortetracycline (CTC), based on controlled electrochemical reduction of graphene oxide (GO) at cathodic potentials. In comparison with GO, the reduced GO (RGO) increased the cyclic voltammetric peak currents of [Fe(CN)6]3−/[Fe(CN)6]4− redox pair by a factor of about 300%, which was influenced by the amount of used GO and the reduction time. Integrating the excellent response amplification of RGO and the special recognition of MIP, the new MIP sensor was used to detect CTC indirectly by using [Fe(CN)6]3−/[Fe(CN)6]4− redox pair as an electrochemical probe. The electrochemical performances of the sensor were evaluated with cyclic voltammetry and differential pulse voltammetry (DPV). The MIP sensor exhibited a wide-range linear correlation between the peak current variation (ΔI) of the DPV cathodic peak and the concentration of CTC in the range of 10.0–500.0μM. The use of the RGO-based MIP sensor gave satisfactory results in the analysis of tap water and laboratory wastewater samples.