Differential Pulse Voltammetry Response Research Articles

Graphene nanoribbon derived from multi-walled carbon nanotube: An efficient viral gene hosting and biosensing molecular platform for the electroanalysis of HIV-1 gene

Graphene nanoribbon (GNR) is a carbon nanomaterial with strikingly distinct characteristics compared to graphene. GNRs possess high aspect ratio, variable band gap, high surface area and high density of reactive edge states which make it an emerging flat molecular platform alternative to graphene. GNR is not much explored in sensing applications compared to graphene. Here, for the first time, we are reporting the application of GNRs, derived from multiwalled carbon nanotube (MWCNT), as an efficient flat molecular platform for hosting and biosensing of Human immune deficiency virus-1 (HIV-1) gene. For the construction of HIV-1 sensor, GNRs were synthesized by unzipping of MWCNTs and deposited onto glassy carbon electrode (GCE) followed by the immobilization of HIV-1 probe (ssDNA) onto the resulting GCE/GNR platform to obtain GCE/GNR/ssDNA sensor. Subsequently, the sensor was employed in the analysis of target gene (cDNA) by measuring the voltammetric response generated from hybridization between ssDNA and cDNA. Differential pulse voltammetry (DPV) responses recorded at different target gene concentrations displayed perfect linear correlation (R2 = 0.991). The sensor exhibited low detection limit (2.3 aM), low quantification limit (7.67 aM) and high sensitivity (5.5 μA aM−1 cm−2) which is possibly due to synergic effects of GNRs. Sensor exhibited acceptable stability, repeatability and displayed good selectivity when tested with mismatched target DNA sequences. Further, sensor’s diagnostic applicability was verified by spiking target gene in human blood sample which showed high recovery (4 %) indicating its practical utility in the electroanalysis of HIV-1 gene in human blood samples.

Development and application of fluorine doped bismuth vanadate reduced graphene oxide Nafion composite electrode as an electrochemical sensor for 4-chlorophenol

This study describes the synthesis of fluorine-doped bismuth vanadate (F0.1BiVO4) and its composite with graphene oxide (GO) to improve charge transport properties. Based on the structural and morphological analysis such as X-Ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), and RAMAN the composite of F0.1BiVO4/r-GO/Nafion was successfully prepared with no filth. It was used to selectively detect the environmental contaminant 4-chlorophenol (4-CP) on a modified glassy carbon electrode (GCE). The electron channeling ability of reduced graphene oxide (r-GO) with F0.1BiVO4 yielded a great electrochemical response (ER) in cyclic voltammetry compared to pure GCE and other modified electrodes. The differential pulse voltammetry response of 4-CP was highly sensitive with the detection of limit (LOD) of 0.56 nM and a wide linear response of 0.77–45.0 nM. Fluorine doping, in particular, was able to affect the crystal growth of BiVO4, which was the primary cause of the aforementioned improvement. On the other hand, r-GO acts as an electron bridge to improve charge transfer between electrolytes and F-BiVO4 due to its high electron transport rate. These results demonstrate the effectiveness of F0.1BiVO4/r-GO/Nafion/GCE for the electrochemical detection of 4-CP.

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.

Simultaneous determination of dopamine and uric acid based on electrocatalytic oxidation of Cu2O-Au and polyaniline nanocomposites

Effective detection of dopamine (DA) and uric acid (UA) has significant diagnostic values, while the analytical methods with high convenience, distinguishability and sensitivity still need to be developed. A highly sensitive and selective electrochemical sensor based on a polyaniline (PANI) nanocomposite embedding Au and Cu2O hybrid (PANI/Cu2O-Aux) with adjustable proportions of Cu2O and Au was developed for simultaneous detection of dopamine (DA) and uric acid (UA) in the presence of high concentrations of ascorbic acid (AA) and other interferents. The Cu2O-Aux architecture improved the electrocatalytic activity by inducing a modifiable synergistic effect between Au and Cu2O. Differential pulse voltammetry (DPV) responses of DA and UA on modified electrodes of PANI/Cu2O-Aux showed remarkable enhancement compared to the single-component Au or Cu2O-decorated PANI. The optimal ratio of Cu2O: Au was 1:1, which gave the highest redox signals for DA and UA. The DPV response ranges of simultaneous detection were 0.01–200 μM for DA and 0.1–1000 μM for UA, with detection limits (S/N = 3) of 0.0076 μM and 0.035 μM, respectively. The sensor also exhibited excellent anti-interference and stability, and was successfully applied to measure DA and UA in human urine samples with high accuracy. This research demonstrates the tunability of catalytic properties in PANI/Cu2O-Aux nanocomposites by the integration of binary nanocatalysts, providing insights into both structural and practical aspects.

Intelligent laser-induced graphene sensor for multiplex probing catechol isomers

Herein, we unveil the intelligent detection of multiple catechol isomers in complex environments utilizing both laser-induced graphene (LIG) and artificial neural network (ANN). The large scale-up manufacturing of LIG-based sensors (LIGS) with three-electrode configuration on polyimide (PI) is achieved by direct laser-writing and screen-printing technologies. Our LIGS shows excellent electrochemical performance toward catechol isomers, i.e., hydroquinone (1,4-dihydroxybenzene, HQ), catechol (1,2-dihydroxybenzene, CT), and resorcinol (1,3-dihydroxybenzene, RC), with a low limit of detection (LOD) (CC, 0.079 µmol/L; HQ, 0.093 µmol/L; RC, 1.18 µmol/L). Moreover, the ANN model is developed for machine-intelligent to predict concentrations of catechol isomers under an interfering environment via a single LIGS. Using six unique parameters extracted from the differential pulse voltammetry (DPV) response, the machine learning-based regression provides a coefficient of correlation with 0.998 and is able to correctly predict the total and individual concentrations in complex river samples. Hence, this work provides a guide for the preparation and application of LIGS via facile and cost-efficient mass production and the development of an intelligent sensing platform based on the ANN model.

Paper-based microfluidic device for selective detection of peanut allergen Ara h1 applying black phosphorus-Au nanocomposites for signal amplification

This paper developed a portable microfluidic paper-based analysis device (μ-PAD) combined with the electrochemical technique for efficient and sensitive detection of peanut allergen Ara h1. The proposed μ-PAD works based on the variation of differential pulse voltammetry (DPV) response current induced by peanut allergen Ara h1. Black phosphorus (BP)–Au nanocomposites were introduced both to improve the electron transfer rate at the electrode interface for signal amplification, and to immobilize the specific Ara h1 aptamers through Au–S bonding to recognize the target in food matrices. This μ-PAD had good specificity and detection stability for Ara h1 allergen and could complete the entire analysis process within 20 min, achieving a wide linear response range (25–800 ng mL−1) and a low detection limit (LOD, 11.8 ng mL−1). In the Ara h1 allergen detection applied to real peanut products (cookies, milk, and bread), the constructed μ-PAD obtained acceptable recoveries (93.50%–101.86%) with relative standard deviations (RSDs) of 0.36–2.97% (n = 3), with a good correlation with the ELISA results (R2 = 0.9956). Therefore, the portable μ-PAD based on BP-Au nanocomposites was demonstrated to provide an effective strategy for rapid analysis and screening of Ara h1 allergen in food, which has broad application prospects.

Ti3C2Tx-Au hybrid composites-based electrochemical biosensors for calreticulin biomarker detection

A sensitive biosensor is critical for early breast cancer treatment and prognosis. Herein, a label-free electrochemical immunosensor is proposed for the sensitive detection of calreticulin (CALR), a new breast cancer biomarker. The biosensor relied upon an electroactive hybrid of ultra-thin Ti3C2Tx nanosheets preadsorbed with Au NPs and methylene blue (MB)(MB–Ti3C2Tx–Au), which served as redox-active centers and an electroactive probe to detect CALR biomarkers respectively. The detection mechanism followed a simple inhibition strategy, where the optimal differential pulse voltammetry (DPV) response of preadsorbed MB over the Ti3C2Tx–Au electrode decreased in proportion to the concentration of CALR biomarkers owing to the formation of the antibody-antigen immunocomplex. The biosensor could detect CALR-biomarker in the concentration range of 0.0015 to 0.94 ng mL−1 with a limit of detection (LOD) of 0.28 pg mL−1 and showed excellent antifouling properties against commonly encountered biomolecules such as hemoglobin (Ig), immunoglobulin G (IgG), neuron-specific enolase (NSE), and tumor necrosis factor-alpha (TNF). The proposed strategy provides an efficient method for utilizing MXene nanosheets to construct advanced biosensors with promising clinical applications.

Electrochemical Determination of Acetaminophen Using a Hydrophilic Single-Walled Carbon Nanohorn Modified Glassy Carbon Electrode

A simple and novel electrochemical sensor based on a hydrophilic single-walled carbon nanohorn (SWCNH) modified glassy carbon electrode (GCE) was designed for the determination of acetaminophen (APAP). The hydrophilic SWCNH/GCE was characterized using Transmission electron microscopy (TEM), Raman spectroscopy, X-ray diffractometer (XRD), and X-ray photoelectron spectroscopy (XPS). This proposed sensor exhibits remarkable performance for the electrocatalytic detection of APAP. The hydrophilic SWCNH/GCE shows a good differential pulse voltammetry (DPV) response at APAP concentration from 100 to 1000 μM with sensitivity and a detection limit of 2.63 μAμM−1cm−2 and 1 μM. Regarding the reaction mechanism, the hydrophilic SWCNH/GCE could easily electro-catalyze APAP oxidation to form N-acetyl-p-benzoquinone-imine (NAPQI). Then NAPQI is rapidly degraded to p-benzoquinone in solutions of 0.1 M Na2SO4 and 0.05 M H2SO4 at pH 1.

Electrochemical Detection of Cortisol by Silver Nanoparticle-Modified Molecularly Imprinted Polymer-Coated Pencil Graphite Electrodes.

The sensitive cortisol detection by an electrochemical sensor based on silver nanoparticle-doped molecularly imprinted polymer was successfully improved. This study describes the method development for cortisol detection in both aqueous solution and biological samples using molecularly imprinted poly(hydroxyethyl methacrylate-N-methacryloyl-(l)-histidine methyl ester)-coated pencil graphite electrodes modified with silver nanoparticles (AgNPs) by differential pulse voltammetry (DPV). The cortisol-imprinted pencil graphite electrode (PGE) has a large surface area because of doped AgNPs with enhanced electroactivity. The prepared molecularly imprinted polymer was characterized by scanning electron microscopy. The DPV response of the synthesized electrode with outstanding electrical conductivity was clarified. Cortisol-imprinted polymer-coated PGEs (MIP), cortisol-imprinted polymer-coated PGEs with AgNPs (MIP@AgNPs), and nonimprinted polymer-coated PGEs with AgNPs (NIP@AgNPs) were evaluated for sensitive and selective detection of cortisol in aqueous solution. Five different cortisol concentrations (0.395, 0.791, 1.32, 2.64, and 3.96 nM) were applied to the MIP@AgNPs, and signal responses were detected by the DPV with a regression coefficient (R2) value of 0.9951. The modified electrode showed good electrocatalytic activity toward cortisol for the linear concentration range from 0.395 to 3.96 nM, and a low limit of detection was recorded as 0.214 nM. The results indicate that the MIP@AgNPs sensor has great potential for sensitive and selective cortisol determination in biological samples.

NH2-MIL-125(Ti)/Reduced Graphene Oxide Enhanced Electrochemical Detection of Fenitrothion in Agricultural Products.

The abuse of organophosphate pesticides causes serious threats to human health, which threatens approximately 3 million people and leads to more than 2000 deaths each year. Therefore, it is necessary to determine the residue of fenitrothion (FT) in environmental and food samples. Herein, we developed a non-enzymatic electrochemical sensor with differential pulse voltammetry signal output to determine FT in model solutions and spiked samples. Delicately, the sensor was designed based on the fabrication of hydrothermally synthesized titanium-based metal-organic frameworks (MOFs) material (NH2-MIL-125(Ti))/reduced graphene oxide (RGO) (NH2-MIL-125(Ti)/RGO) nanocomposites for better target enrichment and electron transfer. The peak response of differential pulse voltammetry for FT under optimized conditions was linear in the range of 0.072-18 μM with the logarithm of concentrations, and the detection limit was 0.0338 μM. The fabricated sensor also demonstrated high stability and reproducibility. Moreover, it exhibited excellent sensing performances for FT in spiked agricultural products. The convenient fabrication method of NH2-MIL-125(Ti)/RGO opens up a new approach for the rational design of non-enzymatic detection methods for pesticides.

A novel 3D bio-printing “liver lobule” microtissue biosensor for the detection of AFB1

In this paper, a novel “liver lobule” microtissue biosensor based on 3D bio-printing is developed to rapidly determine aflatoxin B1 (AFB1). Methylacylated Hyaluronic acid (HAMA) hydrogel, HepG2 cells, and carbon nanotubes are used to construct “liver lobule” models. In addition, 3D bio-printing is used to perform high-throughput and standardized preparation in order to simulate the organ morphology and induce functional formation. Afterwards, based on the electrochemical rapid detection technology, a 3D bio-printed “liver lobule” microtissue is immobilized on the screen-printed electrode, and the mycotoxin is detected by differential pulse voltammetry (DPV). The DPV response increases with the concentration of AFB1 in the range of 0.1–3.5 μg/mL. The linear detection range is 0.1–1.5 μg/mL and the calculated lowest detection limit is 0.039 μg/mL. Thus, this study develops a new mycotoxin detection method based on the 3D printing technology, which has high stability and reproducibility. It has wide application prospects in the field of detection and evaluation of food hazards.

Facile preparation of a cost-effective platform based on ZnFe2O4 nanomaterials for electrochemical cell detection

Circulating tumor cells (CTCs) are important tumor markers that indicate early metastasis, tumor recurrence, and treatment efficacy. To identify and separate these cells from the blood, new nanomaterials need to be developed. The present study explored the potential application of ZnFe2O4 magnetic nanoparticles in capturing CTCs with cell surface markers. Folic acid was coupled to l-cysteine-capped ZnFe2O4 nanoparticles (ZC) to provide binding sites on ZnFe2O4 nanoparticles for the recognition of folate bioreceptors, which are highly expressed in MCF-7 breast cancer cells. The cytotoxicity of ZnFe2O4 nanoparticles and ZC against MCF-7 was analyzed with the MTT assay. After 24 h of incubation, there were IC50 values of 702.6 and 805.5 µg/mL for ZnFe2O4 and ZC, respectively. However, after 48 h of incubation, IC50 values of ZnFe2O4 and ZC were reduced to 267.3 and 389.7 µg/mL, respectively. The cell quantification was conducted with magnetically collected cells placed on a glassy carbon electrode, and the differential pulse voltammetry (DPV) responses were analyzed. This cost-effective ZnFe2O4-based biosensing platform allowed cancer cell detection with a limit of detection of 3 cells/mL, ranging from 25 to 104 cells/mL. In future, these functionalized zinc ferrites may be used in electrochemical cell detection and targeted cancer therapy.

Development and Detailed Performance Study of a Carbon Paste Electrode for the Electrochemical Detection of Malachite Green

The present investigation aims to lighten a quick electrochemical detection technique of malachite green (MG) content using an easy and affordable carbon paste electrode (CPE). MG finds a wide area of application for controlling external fungi plus parasites on the fish egg for its antifungal and antiparasitic features. However, MG is noticed to be dreadfully poisonous and unsafe. Hence, the determination of MG in aquaculture is very much necessary. In this current report, the electrochemical behavior of CPE has been studied using a three-electrode system containing a silver-silver chloride (Ag/AgCl) reference electrode and a platinum counter electrode to record the corresponding cyclic voltammetry (CV) and differential pulse voltammetry (DPV) responses. CV plots in the applied potential range from 0.3 V to 1.5 V described a strong indication of MG existence, while DPV results successfully illustrated the quantification of several MG concentrations. The linear range of operation was from 10[Formula: see text][Formula: see text]M to 1000[Formula: see text][Formula: see text]M with the lowest limit of detection (LOD) as 0.78 [Formula: see text]M. Various concentrations like 50, 300, 600, 800, and 1000[Formula: see text][Formula: see text]M were assessed via principal component analysis (PCA) with effective data clustering (separability index (SI) found as 131.08). The prediction estimations of MG content using PLSR (partial least square regression) along with PCR (principal component regression) algorithms were also carried out, resulting in 95.39% and 93.02% prediction accuracies, respectively. Moreover, applying this CPE over natural aqueous sample extracts exhibited a reasonable recovery rate of 94.85–97.3%.

Molecularly Imprinted Polymer-Based Electrode for Tannic Acid Detection in Black Tea

The present study aims at developing a low-cost and reliable electrode based on the molecularly imprinted polymer (MIP) technology for the detection and quantification of tannic acid (TAN) in black tea samples. The material was synthesized using a copolymer of acrylic acid (AA) and ethylene glycol dimethacrylate (EGDMA), a cross-linker, on a graphite bed. The developed electrode material was characterized by ultraviolet–visible (UV–Vis) spectroscopy and scanning electron microscope (SEM). The performance of the electrode was evaluated by a three-electrode configuration using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The devised electrode (MIP_TAN) has shown a wide linear range of performance from 0.1 to 500 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{M}$ </tex-math></inline-formula> with a limit of detection (LOD) of 37 nM and evinced high repeatability, reproducibility, stability, and good selectivity. To predict the content of TAN, a partial least square regression (PLSR) model was developed utilizing DPV responses of the electrode and high-performance liquid chromatography (HPLC) as reference data. The prediction accuracy of PLSR was obtained as 96.315%. The electrode was examined on real samples of black tea, which produced satisfactory results.

Enhanced electrochemical properties of graphene-based screen-printed carbon electrode by PPy modification: Experimental and DFT investigations

Here, a novel method to enhance the electrochemical properties of graphene-modified screen-printed carbon electrode (G/SPCE) with polypyrrole (PPy) nanosheets is proposed. The mechanism of improving the electrochemical sensitivity of G/SPCE was investigated at the molecular level. G/SPCE was modified with PPy nanosheets synthesized by oxidative polymerization to improve its electrochemical properties. The cyclic voltammetry (CV) and differential pulse voltammetry (DPV) response of PPy-modified G/SPCE (PPy/G/SPCE) to K3[Fe(CN)6] (PF) were tested experimentally. The results show that the oxidation current sensitivity of G/SPCE to PF after PPy nanosheets modification increased from 11.12 μA·mM−1 to 12.91 μA·mM−1 in CV response, and from 8.44 μA·mM−1 to 10.72 μA·mM−1 in DPV response. The effective reaction area of PPy/G/SPCE was found to be increased by scanning electron microscopy. And the functional group CO/CO in PPy/G/SPCE, acting as a catalyst for the redox reaction of PF, was also found to be improved by X-ray photoelectron spectroscopy. Furthermore, the adsorption energy, electron transfer and density of states changes of PF molecule on pure and PPy-modified graphene were analyzed based on density functional theory calculation. The calculation results show that the adsorption energy and electron transfer of PPy-modified graphene to PF molecule are significantly increased. The response sensitivity of graphene to PF molecule is greatly enhanced by the synergistic effect generated of PPy and graphene.

G-C3N4/MWCNT nanocomposite based electrochemical sensor for hydrogen peroxide detection

Hydrogen peroxide (H2O2) is an important chemical used in various industries like pharmaceutical, food, textile, material science, and cosmetics for various applications such as synthesis, medicine, disinfectant, bleaching, etc. The limited use is beneficial; however, the high level of H2O2 can create serious health issues for humans. Hence, precise and early detection is necessary. The present work reports electrochemical sensing of H2O2 by using graphitic carbon nitride multi-walled carbon nanotubes (g-C3N4/MWCNT) nanocomposite modified electrode. The formation of nanocomposite has been confirmed by X-ray diffraction (XRD) technique, scanning electron microscopy (SEM), and energy dispersive X-ray analysis (EDAX). The H2O2 sensing is done by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV). The results of all the techniques used have shown that g-C3N4/MWCNT nanocomposite does better H2O2 sensing (more sensitive) than g-C3N4 and MWCNT. To analyze the sensing kinetics, the DPV response is plotted against H2O2 concentration. The linear graph is acknowledged, which shows its potential for fabricating the sensor.

Dual-template imprinted polymer electrochemical sensor for simultaneous determination of malathion and carbendazim using graphene quantum dots.

Malathion (MAL) and carbendazim (CBZ) are organophosphate pesticides and fungicides, respectively. They are often used simultaneously in agriculture, and both have been shown to have harmful effects on humans and animals. Therefore, it is important to be able to measure both of these toxins simultaneously in order to assess their potential risks. This study aims to design a dual template electrochemical sensor using a cost-effective graphite-epoxy composite electrode (GECE) modified with molecularly imprinted polymers (MIPs) coated on graphene quantum dots (GQDs) for simultaneous detection of MAL and CBZ in real samples. GQDs were synthesized initially, and their surface was coated with MIPs that were formed using MAL and CBZ as the template molecules, ethylene glycol dimethyl acrylate as the cross-linker, and methacrylic acid as the functional monomer. The GQDs@MIP were characterized using Fourier transform infrared spectroscopy, field-emission scanning electron microscopy, and X-ray scattering spectroscopy. Parameters affecting the sensor response, such as the percentage of GQDs@MIP in the fabricated electrode, the pH of the rebinding solution and analysis solution, and the incubation time, were optimized. The optimum pH values of the rebinding solution were verified using density functional theory (DFT) calculations. Under the optimized conditions, differential pulse voltammetry (DPV) response calibration curves of MAL and CBZ were generated, and the results showed that the sensor had a linear response to MAL in the range of 0.02-55.00 μM with a limit of detection (LOD) of 2 nM (S/N = 3) and to CBZ in the range of 0.02-45.00 μM with a low LOD of 1 nM (S/N = 3). The results also demonstrated the proposed sensor's long-term stability and anti-interference capability. The practical applicability of the fabricated electrode was evaluated for real sample analysis, and good recovery values were obtained.

One-step synthesis of calcium-doped copper oxide nanoparticles as an efficient bifunctional electrocatalyst for sensor and supercapacitor applications

In this work, a facile and cost-effective coprecipitation method was used to synthesize calcium-doped copper oxide (Ca@CuO) nanoparticles for electrochemical detection of antipsychotic drug perphenazine (PPZ) and symmetric supercapacitor (SSC) applications. Various spectroscopic techniques were employed to analyze the structural and morphological properties of Ca@CuO. The electrochemical behavior of PPZ at Ca@CuO modified screen-printed carbon electrode (SPCE) was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods. The modified Ca@CuO/SPCE under optimized DPV response showed good linearity to PPZ concentrations in the range of 0.025–996.85 μM with a low limit of detection (LOD) of 0.0074 μM. Moreover, the developed sensor demonstrated good selectivity, stability, repeatability, and reproducibility. The real sample analysis of PPZ using the sensor was examined in biological samples with applicable recoveries. More interestingly, the pseudocapacitive type Ca@CuO/NF delivered an excellent specific capacitance of 314.4 F g−1 at 0.2 A g−1 and good stability with 92.7 % retention for 5000 cycles. In addition, the fabricated Ca@CuO//Ca@CuO SSC device displayed an energy density of 11.33 Wh kg−1 at a power density of 399.8 W kg−1. According to these results, Ca-doped metal oxide can be used as an efficient electrocatalyst for sensor and supercapacitor applications.

Fabrication of DNA‐based Biosensors Driven by Electrostatic Attractions on Electrodes Modified with Reduced Graphene Oxide and Multi‐walled Carbon Nanotubes

AbstractThe use of reduced graphene oxide (rGO) and multi‐walled carbon nanotubes (MWCNTs) has attracted considerable interest for fabrication of chemical sensors and biosensors in recent years. In this study, we report on two ultrasensitive DNA biosensors based on a sensing mechanism driven by the electrostatic attraction of [Ru(NH3)6]3+ cations on electrode surfaces modified with Au‐MWCNTs and Au‐rGO. A one‐step pot synthesis was used to prepare these nanocomposites for the development of the DNA‐based biosensors. The detection of DNA with the biosensors was based on the electrostatic attraction of [Ru(NH3)6]3+ cations by the anionic phosphate backbone of DNA. The interfacial changes on the electrode surface upon hybridisation were detected by differential pulse voltammetry (DPV). The high conductivity and high surface to volume ratio properties of the carbon materials enabled significant enhancement of the response for the target DNA detection. The DPV response gave linear concentration ranges (LCRs) of 0.1–10,000 pM and 1–100 pM with the Au‐MWCNT and Au‐rGO‐based biosensors, respectively. Thus, indicating that the MWCNT‐based biosensor was more sensitive for DNA detection and achieved a wider LCR. Nevertheless, both MWCNT and rGO‐based biosensors exhibited very good discrimination against mismatch sequences.

Voltammetric analysis of epinephrine using glassy carbon electrode modified with nanocomposite prepared from Co-Nd bimetallic nanoparticles, alumina nanoparticles and functionalized multiwalled carbon nanotubes.

Herein, we investigated the electrochemical behaviour of fMWCNTs decorated with Co-Nd bimetallic nanoparticles and alumina nanoparticles (Co-Nd/Al2O3@fMWCNTs). The nanocomposites were synthesised using simple mechanical mixing and characterised by FT-IR, XRD, UV–visible studies, SEM, TEM and EDAX. Moreover, the crystalline size of the synthesised nanoparticles was also calculated using XRD data (Debye–Scherer formula) and was found in the nm range. The electrochemical behaviour of epinephrine (EP) was examined in the presence of Co-Nd/Al2O3@fMWCNTs nanocomposite modified glassy carbon electrode (GCE) using various electrochemical techniques such as cyclic voltammetry (CV), differential pulse voltammetry (DPV), electrochemical impedance spectroscopy (EIS), and chronocoulometry. Among all the above-mentioned techniques, the DPV response of the modified Co-Nd/Al2O3@fMWCNTs/GCE under optimal circumstances revealed a dual linear range (0.2 to 4000 µM and 4000 to 14,000 µM) and LOD of 0.015 µM (S/N = 3). The sensitivities were determined to be 0.00323 µAµM−1 and 0.0004 µAµM−1 in 0.2 to 4000 µM and 4000 to 14,000 µM concentration ranges. Using chronocoulometry, the surface coverage of Co-Nd/Al2O3@fMWCNTs/GCE was calculated to be 1.37 × 10−8 mol cm−2. The fabricated Co-Nd/Al2O3@fMWCNTs/GCE demonstrated remarkable repeatability, with an RSD of 0.09%, and storage stability of 3 weeks, with 89.6% current retention. Lastly, it was found that Co-Nd/Al2O3@fMWCNTs/GCE worked well for EP analysis in a variety of biological fluids.Graphical abstract