Biowaste-derived gold nanoparticles on reduced graphene oxide: An innovative nanoplatform for the label-free immunosensing of dengue NS1.

Mercury meniscus on solid silver amalgam electrode as a sensitive electrochemical sensor for tetrachlorvinphos

Characterization of an electrochemical mercury sensor using alternating current, cyclic, square wave and differential pulse voltammetry

This study explores the electrochemical detection of imidacloprid (IMD) using a nickel‐based metal–organic framework‐modified glassy carbon electrode (Ni‐MOF/GCE). Differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) were employed to assess the electrode's performance for electrochemical sensing of IMD. The synthesized Ni‐MOF was characterized using various analytical techniques such as x‐ray diffraction, Fourier‐transform infrared spectroscopy, field emission scanning electron microscope, and energy dispersive spectroscopy. The DPV analysis at pH 8 demonstrated a clear catalytic redox response with a limit of detection (LOD) of 67.7 nM. Repeatability tests confirmed the electrode's reliability, and stability tests indicated significant detection capability even after 1 month. The EIS (Bode plot) effectively distinguishes IMD concentrations, yielding a LOD of 19.5 nM. These results suggest that both DPV and EIS techniques offer practical solutions to detect IMD. The Ni‐MOF/GCE electrode exhibits excellent potential for sensitive and reliable IMD detection, highlighting its applicability in environmental monitoring and paving the way for further development of Ni‐MOF‐based biosensors.

A novel strategy for improving the sensitivity of molecular imprinted electrochemical sensor was proposed and dopamine (DA) was selected as the template molecular in this assay. The electroactive membrane of poly-bromophenol blue (BB) which was polymerized on the electrode surface acted as molecular imprinted membrane of DA. To prepare poly-BB-DA molecularly imprinted polymer (MIP), CV scans were performed for 30 cycles in the potential range between -1.0 and 1.8 V at 50 mV/s in an acetate buffer solution (pH=4.0) containing 1.0×10 -3 mol/L DA and 3.0×10 -3 mol/L BB at 25 ℃. The MIP electrode was washed by methanol (50% in volume) for 12 min to remove template molecules. Dif- ferential pulse voltammetry (DPV) was performed after the rebinding reaction of the DA and the MIP membrane in DA sam- ple solutions for 6 min. With the increasing of the DA concentration, the binding sites in the membrane taken by DA mole- cules also increased, so was the peak current in the DPV analysis. The sensitivity was improved significantly due to the signal amplifying effect produced by the catalytic effect of electro oxidation of dopamine on BB membrane. The experimental con- ditions were also optimized. Electrochemical measurements for the MIP membrane characterization were carried out in the supporting electrolyte of 0.01 mol/L K3(Fe(CN)6) solution containing 0.5 mol/L KCl. CV was performed from -0.2 to 0.6 V at a scan rate of 100 mV/s. DPV was performed in the supporting electrolyte of 0.1 mol/L PBS (pH 7.4) over a potential range of -0.1 to 0.6 V, with the pulse amplitude of 50 mV and the scan rate of 50 mV/s. All measurements were carried out at room temperature (25 ℃). DA was determined by DPV, and there was a linear relationship between oxidation currents and DA concentrations in the range of 0~1.2×10

This paper examines the electrochemical oxidation of terbinafine with the boron doped diamond and glassy carbon electrodes. The studies were performed by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and square-wave voltammetry (SWV). The supporting electrolytes, solution pH, the range of potentials, and the scan rates were optimized. Terbinafine was irreversibly oxidized in all electrolytes, yielding well-defined peaks in the positive potential range. The peak potential shifted towards less positive values as the solution pH increased. Voltammetric determination of terbinafine was performed under the optimized conditions. Using the boron doped diamond electrode, a linear relationship between current and concentration was obtained between 5.44 × 10−7 and 5.18 and 10−6 mol/L with SWV and between 7.75 · 10−7 and 8.55 · 10−6 mol/L by DPV. At the glassy carbon electrode, a linear relationship between 7.75 · 10−7 and 8.55 · 10−6 mol/L was obtained by SWV and between 7.75 · 10−7 and 1.05 · 10−5 mol/L by DPV. The sensitivity, precision, and selectivity of the procedures were evaluated. In order to check the practical application of the developed methods, the concentration of terbinafine was determined in pharmaceutical preparations.

BackgroundIn this label-free bioassay, an electrochemiluminescence (ECL) immunosensor was developed for the quantification of breast cancer using HER-2 protein as a metastatic biomarker.MethodFor this purpose, the ECL emitter, [Ru(bpy)3]2+, was embedded into biocompatible chitosan (CS) polymer. The prepared bio-composite offered high ECL reading due to the depletion of human epidermal growth factor receptor 2 (HER-2) protein. Reduced graphene oxide (rGO) was used as substrate to increase signal stability and achieve greater sensitivity. For this, rGO was initially placed electrochemically on the glassy carbon electrode (GCE) surface by cyclic voltammetry (CV) technique. Next, the prepared CS/[Ru(bpy)3]2+ biopolymer solution was coated on a drop of the modified electrode such that the amine groups of CS and the carboxylic groups of rGO could covalently interact. Using EDC/NHS chemistry, monoclonal antibodies (Abs) of HER-2 were linked to CS/[Ru(bpy)3]2+/rGO/GCE via amide bonds between the carboxylic groups of Ab molecules and amine groups of CS. The electrochemical behavior of the electrode was studied using different electrochemical techniques such as electrochemical impedance spectroscopy (EIS), differential pulse voltammetry (DPV) and square wave voltammetry (SWV) and also ECL tests.ResultsAfter passing all optimization steps, the lower limit of detection (LLOQ) and linear dynamic range (LDR) of HER-2 protein were practically obtained as 1 fM and 1 fM to 1 nM, individually. Importantly, the within and between laboratory precisions were performed and the suitable relative standard deviations (RSDs) were recorded as 3.1 and 3.5%, respectively.ConclusionsAs a proof of concept, the designed immunosensor was desirably applied for the quantification of HER-2 protein in breast cancer suffering patients. As a result, the designed ECL-based immunosensor has the capability of being used as a conventional test method in biomedical laboratories for early detection of HER-2 protein in biological fluids.Graphic

Quercetin (Qu) is one of the most abundant flavonoids in the human diet. High concentrations of Qu can easily cause adverse effects and induce inflammation, joint pain and stiffness. In this study, Heme was used as a sensitive element and deposited and formed nanorods on a glassy carbon electrode (GCE) for the detection of Qu. The Heme/GCE sensor was characterized using scanning electron microscopy (SEM), cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) techniques. Under optimized conditions, the developed sensor presented a linear concentration ranging from 0.1 to 700 μmol·L−1 according to the CV and DPV methods. The detection limit for the sensor was 0.134 μmol·L−1 and its sensitivity was 0.12 μA·μM−1·cm−2, which were obtained from CV analysis. Through DPV analysis we obtained a detection limit of 0.063 μmol·L−1 and a sensitivity of 0.09 μA·μM−1·cm−2. Finally, this sensor was used to detect the Qu concentration in loquat leaf powder extract, with recovery between 98.55–102.89% and total R.S.D. lower than 3.70%. The constructed electrochemical sensor showed good anti-interference, repeatability and stability, indicating that it is also usable for the rapid detection of Qu in actual samples.

A sensitive electroanalytical method for determination of azapropazone has been investigated on the basis of the enhancement electrochemical response at glassy carbon electrode during oxidation of azapropazone, Cyclic voltammetric undergo one irreversible anodic peak at Ep = 0.48 mV in Britton - Robinson (BR) (pH 4.0). Cyclic voltammetric study indicated that the oxidation process is irreversible and adsorption controlled. The number of exchanged electrons in the electro -oxidation process was obtained. Differential pulse voltammetry (DPV) and square wave voltammetry (SWV) were studied and a linear calibration obtained from: 0.0014– 0.026µg/ml, 0.014–0.134µg/ml using DPV and SWV respectively. The RSD for five measurements were found in the ranges: 0.854% and 0.911% for DPV and SWV, respectively. Precision and accuracy of the developed method was checked by recovery studies. The method was applied to determine azapropazone in pure form, pharmaceutical formulations, and compared with official methods.

Diazepam (DZP) is a muscle-relaxing, anxiety-relieving sedative drug; nonetheless, it is also an addictive drug that may be abused. This work reports on the development of a novel electrochemical nanosensor for diazepam using SiO2-encapsulated-3-mercaptopropionic acid-capped AuZnCeSeS quantum dots (QDs) overcoated with a molecularly imprinted polymer (MIP) on screen-printed carbon electrodes (SPCEs). Electrochemical, spectroscopic and electron microscopic characterization of the nanomaterial and modified electrode surface was carried out and is reported herein. Specifically, electrochemical characterization of the QDs/SPCE using cyclic voltammetry (CV) revealed that the QDs exhibit a higher electrode surface area whilst electrochemical impedance spectroscopy (EIS) characterization demonstrated a lower charge transfer resistance (Rct). To fabricate the electrochemical nanosensor, firstly, alloyed AuZnCeSeS QDs were synthesized in the organic phase and thereafter capped with 3-mercaptopropionic acid (MPA) via a ligand exchange reaction. The MPA-AuZnCeSeS QDs were encapsulated in a SiO2 layer to form a SiO2-MPA AuZnCeSeS QDs system. The QDs were drop-casted onto SPCEs to form a SiO2-MPA AuZnCeSeS QDs/SPCE transducer interface. Organic based acrylamide, used as a functional monomer, was electropolymerized via CV on the QDs/SPCE in the presence of the diazepam template with ethylene glycol dimethacrylate as a crosslinker and 2,2'-azobis(2-methylpropionitrile) as an initiator. Under optimum experimental conditions, DZP was detected using EIS and square wave voltammetry (SWV). Using a portable potentiostat and a hand-held smartphone-based potentiostat, DZP was quantitatively detected in saliva using the MIP@QDs/SPCE with a limit of detection (LOD) of 2.3μM and 2.7μM, respectively. The LOD for DZP from SWV analysis was 1.0μM.

Square wave voltammetry (SWV) and differential pulse voltammetry (DPV) are commonly used in electroanalysis, typically in aqueous solvents, as they are usually an order of magnitude more sensitive than linear sweep voltammetry (LSV)/cyclic voltammetry (CV), (e.g. detection limits as low as nanomolar are possible using SWV). These more sensitive techniques are often applied in the development of electrochemical sensors and biosensors over the last ten years due to the negligible capacitive current compared to faradaic current (in protic solvents).1,2 Over the last two decades there has been great attention focused on the improvement of electrochemical gas sensors to monitor toxic gases using amperometric gas sensors (AGSs), which typically employ water/sulphuric acid electrolytes as solvents. Room temperature ionic liquids (RTILs) have been attracting great attention3 as replacement electrolytes in AGSs due to their unique physical properties such as low volatility and negligible vapor pressure, wide electrochemical windows, high ionic conductivity, high chemical and thermal stability and their ability to dissolve a wide range of gases. To the best of our knowledge, there are limited studies on the sensitivity of SWV, DPV and LSV for the sensing of gaseous analytes in RTIL solvents. In this presentation, a comparison of three different electrochemical techniques (SWV, DPV and LSV) will be employed for two gases (ammonia and oxygen) in RTILs. As a control, oxygen gas will also be studied in acetonitrile and water solvents, and dissolved solid analytes are also studied (K3Fe(CN)6in water, ferrocene in acetonitrile and ferrocene in RTILs). For all dissolved solid analytes, SWV gave the highest current response compared to DPV and LSV, respectively. For dissolved gases, the behavior was different. For oxygen, LSV gave larger currents (although relatively comparable) to SWV, with DPV giving the lowest currents. For ammonia, LSV was far superior to both SWV and DPV and was consistent throughout eight different RTIL solvents. This suggests that the generally accepted methods for low concentration analyte detection may not apply for dissolved gases.

Recent Trends in Electrochemical Methods for Real-Time Detection of Heavy Metals in Water and Soil: A Review.

A new electrochemical sensor for 4-nitrophenol (4-NP) detection based on the reduced graphene oxide (RGO) and Au nanoparticle composite was developed. The RGO film was first electrodeposited onto a glassy carbon electrode (GCE). Then Au nanoparticles (AuNPs) were electrochemically deposited onto the RGO film. The morphology and electrochemical properties of the AuNP/RGO composite were investigated. The synergic effect of AuNPs and RGO nanosheets as co-modifiers greatly facilitates electron-transfer processes between the electrolyte and the GCE, and thus leads to a remarkably improved sensitivity for 4-NP detection. Two detection modes, differential pulse voltammetry (DPV) and square wave voltammetry (SWV), were applied. A wide linear range of values, 0.05–2.0 μM and 4.0–100 μM for DPV and 0.05–2.0 μM for SWV, were obtained. The limit of detection (LOD) of 4-NP was 0.01 μM and 0.02 μM for DPV and SWV, respectively. This sensor was successfully used in the detection of real water samples from Xiangjiang River.

Proton conductive 2D MXene-derived potassium titanate nanoribbons fabricated electrochemical platform for trace detection of enrofloxacin

An electrochemical sensor based on a cobalt oxide nanorod (Co3O4NR) modified glassy carbon electrode (GCE) (Co3O4NR-GCE) was prepared for simultaneous and selective determination of hydroquinone (HQ) and catechol (CT). Surface morphology and crystallinity of Co3O4NR were investigated employing field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) analysis. The structure (16 nm) of the Co3O4 nanorod was observed in the FESEM image. A sharp peak pattern in the XRD survey revealed the following crystal planes in Co3O4NR material: (111), (220), (311), (222), (400), (422), (511), and (440). Electrochemical characterization of modified Co3O4NR-GCE was carried out performing cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Selective and simultaneous detection of HQ and CT was carried out by performing CV and differential pulse voltammetry (DPV) analysis. In both studies, modified Co3O4NR-GCE showed well defined oxidation and reduction peaks for HQ and CT with enhanced peak current, and the oxidation peaks for HQ and CT were observed at 0.152 V and 0.254 V, respectively, in the CV analysis. Scan rate and pH variation analysis were performed to evaluate different kinetic parameters, including charge transfer coefficient (α = 0.56 for HQ and 0.66 for CT), heterogeneous charge transfer rate constant (ks = 56 for HQ and 72 for CT), and the number of electrons involved in HQ and CT oxidation. Quantitative analysis of HQ and CT was studied by observing the current response of DPV analysis with respect to concentration variation. Here, the detection limit was calculated as 0.2 µM for HQ with a linear concentration range of 5–200 µM, and 0.4 µM for CT with a linear concentration range of 5–150 µM. The practical applicability of the proposed sensor was investigated using sample solutions prepared in tap water. The reported sensor showed impressive selectivity towards HQ and CT in the presence of common interferents.

Design of an electrochemical hydrogel nanocomposite immunosensor for the detection of hemoglobin in blood