Oxide-modified Electrode Research Articles

Enhanced electrocatalytic activity of hafnium doped tungsten oxide (Hf-WO3) for ultrasensitive detection of nonsteroidal anti-inflammatory drug

Efficient hafnium-doped tungsten oxide nanoparticles (Hf-WO3) were developed by hydrothermal approach and characterization was carried out by X-ray diffraction pattern (XRD), transmission electron microscopy (TEM), high resolution-transmission electron microscopy (HR-TEM), scanning transmission electron microscopy (STEM), X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS) techniques. Cyclic voltammetry (CV) and square wave voltammetry (SWV) techniques were employed to assess the electrochemical response of the fabricated carbon paste electrodes (CPE) for the analysis of mefenamic acid (MA). The objective of this work is to develop and optimize parameters to enhance the selectivity and sensitivity of Hf-WO3 modified sensor for the trace-level detection of MA, addressing its critical importance in both pharmaceutical and environmental analysis. The Hf-WO3 predominantly showed a monoclinic phase with some hexagonal peaks, confirming its good crystallinity and 1-D structure, which enhances charge transport and catalytic sites. XPS analysis confirmed the formation of pure Hf-WO3 by showing distinct W and Hf peaks and verifying their valences: W in the +6 state and Hf in the +4 state. CV showed that the Hf-WO3/CPE greatly enhances the electrochemical oxidation of MA compared to unmodified and tungsten oxide-modified electrodes, with a six-fold increase in peak current and notable redox activity attributed to improved surface properties and charge transfer efficiency. Under optimum experimental conditions, the Hf-WO3/CPE exhibits a low limit of detection (LOD) of 3.94 nM with dynamic concentration linearity ranging from 0.01 to 100.0 μM with good sensitivity of 1.74 μAμM−1cm−2. Furthermore, the Hf-WO3/CPE was employed in real-time analysis of MA in spiked urine samples and pharmaceutical tablet samples, which showed satisfactory recovery results ⁓ 98 %. Moreover, the electrode showed good stability over multiple measurements, and these results demonstrate that Hf-WO3/CPE is a promising sensor for MA detection.

Reduced graphene oxide-modified electrodes via fused deposition modeling 3D printing for hydrogen peroxide sensor

Abstract 3D printed electrochemical electrode processes have garnered significant interest due to their promising applications. However, broader implementation remains constrained due to challenges in material selection, complex fabrication processes, and reproducibility issues. Fused Deposition Modeling (FDM) 3D Printing presents a simplified alternative, enabling swift and cost-effective production of electrochemical sensors. This paper introduces a novel manufacturing approach that uses a dual-printer setup for printing sensor electrodes and subsequent surface modification with reduced graphene oxide (rGO) casting. The electrode surfaces, both before and after rGO drop casting, are comprehensively characterized, including physical morphology, chemical composition, and electrochemical performance. As a result, the electrode, after surface modification with rGO, exhibits a sensitivity increase exceeding fortyfold compared to the pristine printed surface, as demonstrated through hydrogen peroxide (H2O2) amperometric measurements. This outcome opens up new avenues and prospects for the manufacturing of 3D printed electrochemical sensors.

An integrated smartphone-based electrochemical detection system for highly sensitive and on-site detection of chemical oxygen demand by copper-cobalt bimetallic oxide-modified electrode.

Aportable and integrated electrochemical detection system has been constructed for on-site and real-time detection of chemical oxygen demand (COD). The system mainly consists of four parts: (i) sensing electrode with a copper-cobalt bimetallic oxide (CuCoOx)-modified screen-printed electrode; (ii) an integrated electrochemical detector for the conversion, amplification, and transmission of weak signals; (iii) a smartphone installed with a self-developed Android application (APP) for issuing commands, receiving, and displaying detection results; and (iv) a 3D-printed microfluidic cell for the continuous input of water samples. Benefiting from the superior catalytic capability of CuCoOx, the developed system shows a high detection sensitivity with 0.335 μA/(mg/L) and a low detection limit of 5.957 mg/L for COD determination and possessing high anti-interference ability to chloride ions. Moreover, this system presents good consistency with the traditional dichromate method in COD detection of actual water samples. Due to the advantages of cost effectiveness, portability, and point-of-care testing, the system shows great potential for water quality monitoring, especially inresource-limited remote areas.

Electrochemical detection of the p53 gene using exponential amplification reaction (EXPAR) and CRISPR/Cas12a reactions.

Animproved electrochemical sensor has been developed for sensitive detection of the p53 genebased on exponential amplification reaction (EXPAR) and CRISPR/Cas12a. Restriction endonuclease BstNI is introduced to specifically identify and cleave the p53 gene, generating primers to trigger the EXPAR cascade amplification. A large number of amplified products are then obtained to enable the lateral cleavage activity of CRISPR/Cas12a. For electrochemical detection, the amplified product activates Cas12a to digest the designed block probe, which allows the signal probe to be captured by the reduced graphene oxide-modified electrode (GCE/RGO), resulting in an enhanced electrochemical signal. Notably, the signal probe is labeled with large amounts of methylene blue (MB). Compared with traditional endpoint decoration, the special signal probe effectively amplifies the electrochemical signalsby a factor of about 15.Experimental results show that the electrochemical sensor exhibits wide ranges from 500 aM to 10pM and 10pM to 1nM, as well as a relatively low limit detection of 0.39 fM, which is aboutan order of magnitude lowerthan that of fluorescence detection. Moreover, the proposed sensor shows reliable application capability in real human serum, indicating that this work has great prospects for the construction of a CRISPR-based ultra-sensitive detection platform.

Metallic Nanomaterials with Biomedical Applications

Metallic nanomaterials have attracted extensive attention in various fields due to their photocatalytic, photosensitive, thermal conducting, electrical conducting and semiconducting properties. Among all these fields, metallic nanomaterials are of particular importance in biomedical sensing for the detection of different analytes, such as proteins, toxins, metal ions, nucleotides, anions and saccharides. However, many problems remain to be solved, such as the synthesis method and modification of target metallic nanoparticles, inadequate sensitivity and stability in biomedical sensing and the biological toxicity brought by metallic nanomaterials. Thus, this Special Issue aims to collect research or review articles focused on electrochemical biosensing, such as metallic nanomaterial-based electrochemical sensors and biosensors, metallic oxide-modified electrodes, biological sensing based on metallic nanomaterials, metallic nanomaterial-based biological sensing devices and chemometrics for metallic nanomaterial-based biological sensing. Meanwhile, studies related to the synthesis and characterization of metallic nanomaterials are also welcome, and both experimental and theoretical studies are welcome for contribution as well.

Non-enzymatic Electrochemical Sensing of 3-Hydroxybutyric Acid by Incorporating Manganese Oxide Modified Electrode and Nitroprusside Electrolyte

The development of 3-hydroxybutyric acid (3-HB) biosensors via electrochemical method is commonly based on the use of enzymes that usually display inherent instability. Here, a novel non-enzymatic 3-HB electrochemical sensor platform by incorporating manganese oxide nanoparticles (Mn2O3 NPs) modified screen printed carbon electrode (SPCE) and sodium nitroprusside (SNP) electrolyte was reported for the first time. The mechanism of this sensor based on the formation of electroactive SNP-HB species with assistance of Mn2O3 catalyst. By the enhanced electroactivity of the complex, 3-HB can be quantitatively measured based on the increased peak current and shifted peak potential in cyclic voltammograms of SNP reduction. SNP concentration and Mn2O3 loading were optimized for maximum current response. The sensitivity of as-prepared sensor system was examined under different pH values (6.4–7.4) in the range of 0–10 mM 3-HB. The highest sensitivity of 39.07 μA·mM−1·cm−2 and 5.84 mV·mM−1 with LOD of 0.5 mM was achieved at pH 7.4 of electrolyte solution. The proposed sensor provided favorable stability and selectivity against various interferents. In addition, the ability to quantitatively detect 3-HB in artificial urine was also demonstrated, suggesting that our sensor can be a promising candidate for practical applications.

A copper-based metal-organic framework/reduced graphene oxide-modified electrode for electrochemical detection of paraquat.

An electrochemical device using copper-based metalorganic franmeworks (MOF) associated with reduced graphene oxide to improve the charge transfer, stability, and adherence of the structures on the surface of the electrodeswas developed. The syntheses of these materials were confirmed usingscanning electron microscopy, thermogravimetric analysis, X-ray diffraction, Fourier transform infrared and Raman spectroscopy. For the first time, this type of sensor was applied to a systematic study to understand the action mechanism of MOFs and reduced graphene oxide in the electrochemical detection of paraquat pesticide. Under optimized conditions, paraquat was detectedin standard solutions bydifferential pulse voltammetry (- 0.8 to - 0.3V vs Ag/AgCl), achieving a linear response range between 0.30 and 5.00μmol L-1. The limits of detection and quantification were 50.0nmol L-1 and 150.0nmol L-1, respectively. We assessed the accuracy of the proposed device to determine paraquat in water and human blood serum samples by recovery study, obtaining recovery values ranging from 98 to 104%. Furthermore, the selectivity of the proposed electrode for paraquat detection was evaluated against various interferences, demonstrating their promising application in environmental analysis.

Enhanced Electrocatalytic Detection of Choline Based on CNTs and Metal Oxide Nanomaterials

Choline is an officially established essential nutrient and precursor of the neurotransmitter acetylcholine. It is employed as a cholinergic activity marker in the early diagnosis of brain disorders such as Alzheimer’s and Parkinson’s disease. Low levels of choline in diets and biological fluids, such as blood plasma, urine, cerebrospinal and amniotic fluid, could be an indication of neurological disorder, fatty liver disease, neural tube defects and hemorrhagic kidney necrosis. Meanwhile, it is known that choline metabolism involves oxidation, which frees its methyl groups for entrance into single-C metabolism occurring in three phases: choline oxidase, betaine synthesis and transfer of methyl groups to homocysteine. Electrocatalytic detection of choline is of physiological and pathological significance because choline is involved in the physiological processes in the mammalian central and peripheral nervous systems and thus requires a more reliable assay for its determination in biological, food and pharmaceutical samples. Despite the use of several methods for choline determination, the superior sensitivity, high selectivity and fast analysis response time of bioanalytical-based sensors invariably have a comparative advantage over conventional analytical techniques. This review focuses on the electrocatalytic activity of nanomaterials, specifically carbon nanotubes (CNTs), CNT nanocomposites and metal/metal oxide-modified electrodes, towards choline detection using electrochemical sensors (enzyme and non-enzyme based), and various electrochemical techniques. From the survey, the electrochemical performance of the choline sensors investigated, in terms of sensitivity, selectivity and stability, is ascribed to the presence of these nanomaterials.

Universal and Programmable Rolling Circle Amplification-CRISPR/Cas12a-Mediated Immobilization-Free Electrochemical Biosensor.

The development of a sensing platform with high sensitivity and specificity, especially programmability and universal applicability, for the detection of clinically relevant molecules is highly valuable for disease monitoring and confirmation but remains a challenge. Here, for the first time, we introduce the clustered regularly interspaced short palindromic repeats (CRISPR)/Cas system into an immobilization-free electrochemical biosensing platform for sensitively and specifically detecting the disease-related nucleic acids and small molecules. In this strategy, a modular rolling circle amplification (RCA) is designed to transform and amplify the target recognition event into the universal trigger DNA strand that is used as the trigger to activate the deoxyribonuclease activity of CRISPR/Cas12a for further signal amplification. The cleavage of the target-activated blocker probe allows the methylene blue-labeled reporter probes to be captured by the reduced graphene oxide-modified electrode, leading to an obviously increased electrochemical signal. We only need to simply tune the sequence for target recognition in RCA components, and this strategy can be flexibly applied to the highly sensitive and specific detection of microRNAs, Parvovirus B19 DNA, and adenosine-5'-triphosphate and the calculated limit of detection is 0.83 aM, 0.52 aM, and 0.46 pM, respectively. In addition, we construct DNA logic circuits (YES, NOT, OR, AND) of DNA inputs to experimentally demonstrate the modularity and programmability of the stimuli-responsive RCA-CRISPR/Cas12a system. This work broadens the application of the CRISPR/Cas12a system to the immobilization-free electrochemical biosensing platform and provides a new thinking for developing a robust tool for clinical diagnosis.

Highly sensitive electrochemical sensing of neurotransmitter dopamine from scalable UV irradiation-based nitrogen-doped reduced graphene oxide-modified electrode

Present study develops a facile, low-temperature and cost-effective route for the synthesis of nitrogen-doped reduced graphene oxide (N-rGO). The synthesized N-rGO was characterized using X-ray diffraction (XRD), micro-Raman and Fourier transform infrared (FTIR) spectroscopies. An electrochemical sensor using N-rGO-modified glassy carbon electrode (GCE) was fabricated for the determination of dopamine (DA), a neurotransmitter. Because the electrochemical determination and quantification of DA play a significant role in medical diagnosis, such as making soft material-based hydrogel for wound healing. Cyclic voltammetry (CV), amperometry, differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS)-based standard techniques were used to evaluate and establish the optimum electrochemical sensing performance, detection limit, steadiness and reliability of N-rGO/GCE sensing system to the DA detection. The DPV measurements resemble a wide linear range from 100 to 3000 $$\upmu \hbox {M}$$ and demonstrated a limit of detection (LOD) of 57 nM. It is evidently proved that N-rGO/GCE has great potential to be a preferable electrochemical sensing system for DA detection.

Electrochemical Behaviours of Guanine and Adenine and their Simultaneous Determination using a Three-Dimensional Porous Poly(dopamine)/Reduced Graphene Oxide-Modified Electrode

Electrochemical Behaviours of Guanine and Adenine and their Simultaneous Determination using a Three-Dimensional Porous Poly(dopamine)/Reduced Graphene Oxide-Modified Electrode

Fe3O4 Decorated Reduced Graphene Oxide Modified Electrode for Electrochemistry of Hemoglobin and Its Application as Trichloroacetic acid and Nitrite Sensor

Fe3O4 Decorated Reduced Graphene Oxide Modified Electrode for Electrochemistry of Hemoglobin and Its Application as Trichloroacetic acid and Nitrite Sensor

Squamous Cell Carcinoma Biomarker Sensing on a Strontium Oxide-Modified Interdigitated Electrode Surface for the Diagnosis of Cervical Cancer.

Cervical cancer is a life-threatening complication, appearing as the uncontrolled growth of abnormal cells in the lining of the cervix. Every year, increasing numbers of cervical cancer cases are reported worldwide. Different identification strategies were proposed to detect cervical cancer at the earlier stages using various biomarkers. Squamous cell carcinoma antigen (SCC-Ag) is one of the potential biomarkers for this diagnosis. Nanomaterial-based detection systems were shown to be efficient with different clinical biomarkers. In this study, we have demonstrated strontium oxide-modified interdigitated electrode (IDE) fabrication by the sol-gel method and characterized by scanning electron microscopy and high-power microscopy. Analysis of the bare devices indicated the reproducibility with the fabrication, and further pH scouting on the device revealed that the reliability of the working pH ranges from 3 to 9. The sensing surface was tested to detect SCC-Ag against its specific antibody; the detection limit was found to be 10 pM, and the sensitivity was in the range between 1 and 10 pM as calculated by 3σ. The specificity experiment was carried out using major proteins from human serum, such as albumin and globulin. SCC-Ag was shown to be selectively detected on the strontium oxide-modified IDE surface.

Pd–Ag/Graphene Electrochemical Sensor for Chlorophenol Contaminant Determination

A graphene-supported Pd–Ag bimetallic alloy catalyst for rapid detection of low concentrations of chlorophenols (CPs) in environmental monitoring was prepared by wet chemical reduction. The catalyst was used to construct an electrochemical CP sensor. Catalyst-modified glassy carbon electrodes were evaluated for the determination of aqueous CP contaminants, i.e., 4-chlorophenol (4-CP), 3-chlorophenol (3-CP), 2-chlorophenol (2-CP), and 2,4-dichlorophenol (2,4-DCP), at low concentrations. Synergies between the Pd–Ag bimetallic alloy component and the graphene component of the electrochemical catalyst significantly affected the electrochemical reactions of the CPs, by enhancing the electron transfer rate and the electrochemical oxidation–reduction reaction efficiency. The optimal experimental conditions for a Pd0.5Ag0.5/reduced graphene oxide-modified electrode sensor were 0.1 mol/L phosphate-buffered saline, a scan rate of 100 mV/s, and pH 7. The detection ranges for the monochlorophenols (4-CP, 3-CP, and 2-CP) were wide, namely 0.1–80, 0.1–100, and 0.1–80 μmol/L, respectively. The dichlorophenol (2,4-DCP) detection range was broader, i.e., 0.002–100 μmol/L. The detection limits were low, namely 0.0075, 0.0077, 0.0047, and 0.00036 μmol/L (S/N = 3), respectively. These electrode sensors give good accuracy and reproducibility, and high recovery rates (almost 100%). They have anti-interference properties and long-term stability. The results indicate that such sensors could be used for detection of low concentrations of CPs in wastewater, and have good potential for use in practical applications.

Disposable amperometric immunosensor for Saccharomyces cerevisiae based on carboxylated graphene oxide-modified electrodes.

A sensitive and disposable amperometric immunosensor for Saccharomyces cerevisiae was constructed by using carbon screen-printed electrodes modified with propionic acid-functionalized graphene oxide as transduction element. The affinity-based biosensing interface was assembled by covalent immobilization of a specific polyclonal antibody on the carboxylate-enriched electrode surface via a water-soluble carbodiimide/N-hydroxysuccinimide coupling approach. A concanavalin A-peroxidase conjugate was further used as signaling element. The immunosensor allowed the amperometric detection of the yeast in buffer solution and white wine samples in the range of 10-107CFU/mL. This electroanalytical device also exhibited low detection limit and high selectivity, reproducibility, and storage stability. The immunosensor was successfully validated in spiked white wine samples.

Detection of Neurotransmitter (Levodopa) in Vegetables Using Nitrogen-Doped Graphene Oxide Incorporated Nickel Oxide Modified Electrode

Detection of Neurotransmitter (Levodopa) in Vegetables Using Nitrogen-Doped Graphene Oxide Incorporated Nickel Oxide Modified Electrode

A Selective Joint Determination of Salicylic Acid in Actinidia chinensis Combining a Molecularly Imprinted Monolithic Column and a Graphene Oxide Modified Electrode.

A new combination between selective polymer monolith microextraction (PMME) and sensitive differential pulse voltammetry (DPV) was developed for the determination of the phytohormone salicylic acid (SA) in Actinidia chinensis. A molecularly imprinted monolithic column (MIMC) thermally in-situ polymerized in a micropipette tip by using SA as a template, 4-vinyl pyridine (4-VP) as a functional monomer and ethylene glycol dimethacrylate (EGDMA) as a cross-linker in the mixed porogen of toluene and dodecanol, was employed for the microextraction of SA. The prepared MIMC was characterized by a Fourier transform infrared spectrometer (FI-TR), scanning electron microscope (SEM) and thermo gravimetric analysis (TGA). The results confirmed the binary continuous structure of the porous network. The extracted SA was determined by DPV on a graphene oxide (GO) modified electrode. The joint conditions between MIMC and DPV were investigated practically. Under the optimum conditions, SA could be determined selectively and sensitively in a linear range from 0.1 to 60.0 μg g-1. The limit of detection was 0.03 μg g-1 and the recoveries were between 86.2 and 105.2%. The proposed joint method was successfully used to determine SA in Actinidia chinensis.

Facile fabrication of ascorbic acid reduced graphene oxide-modified electrodes toward electroanalytical determination of sulfamethoxazole in aqueous environments

In the present work, a novel reduced graphene oxide (rGO)-based electrochemical sensor has been developed for the detection of sulfamethoxazole (SMZ) using differential pulse voltammetry. Ascorbic acid (AA) under acid conditions has proven to be an efficient yet environmentally benign reductant to recover the outstanding electrochemical activity of graphene. Additionally, the ascorbic-acid-reduced graphene oxide exhibits a high total removal rate of epoxide and hydroxyl functional groups, with a rich presence of carbonyl and carboxyl functional groups, allowing an excellent solution processing ability for realizing further functionalization and applications, unlike reduced graphene oxide produced by conventional harmful reductants (e.g., hydrazine). Moreover, excellence in the determination of SMZ is likely due to selective reduction of oxygen functional groups on the graphene basal planes by ascorbic acid, which enhances π–π interactions with SMZ, which is present in anionic forms in natural aqueous systems. The AArGO-modified electrodes achieved a linear range of 0.5–50 μM with a limit of detection of 0.04 μM and satisfied recoveries in different water samples. Additionally, the cationic surfactant (e.g., cetyltrimethylammonium bromide, CTAB) showed a promoting effect toward SMZ determination. Collectively, the AArGO modified electrodes showed great improvement in the anodic oxidation reactivity of SMZ with high selectivity and stability, allowing promising and feasible applications in on-site environmental monitoring.

Electrochemical Behavior and Determination of Rutin at the Copper Nanoparticles-Doped Zeolite A/Graphene Oxide-Modified Electrode

In this work, a novel Cu‒zeolite A/graphene modified glassy carbon electrode was applied for the determination of rutin. The Cu‒zeolite A/graphene composites were prepared using copper doped zeolite A and graphene oxide as the precursor, subsequently reduced by chemical agents. Based on the Cu‒zeolite A/graphene modified electrode, the overpotential of the rutin oxidation was lowered by ~300 mV. Also the proposed Cu‒zeolite A/graphene modified electrode showed higher electrocatalytic performance than zeolite A/graphene electrode or graphene modified electrode. The electrochemical behavior of copper incorporated in the zeolite A modified electrode illustrated the adsorption-controlled reaction at the modified electrode. The behavior of electrocatalytic oxidation of rutin at the modified electrode was investigated. The diffusion coefficient of rutin was equal to 4.2 × 10–7 cm2/s. A linear calibration graph was obtained for rutin over the concentration range of 2.3 × 10–7–2.5 × 10–3 M. The detection limit for rutin was 1.2 × 10–7 M. The RSDs of 10 replicate measurements performed on a single electrode at rutin concentrations between 2.3 × 10–7–2.5 × 10–3 M were between 1.1 and 2.1%. Study of the influence of potentially interfering substances on the peak current of rutin showed that the method was highly selective. The proposed electrode was used for the determination of rutin in real samples with satisfactory results.

Highly sensitive biosensing of phenol based on the adsorption of the phenol enzymatic oxidation product on the surface of an electrochemically reduced graphene oxide-modified electrode

An electrochemically reduced graphene oxide and horseradish peroxidase enzyme modified electrode has been used for phenol determination.