Simultaneous determination of cholesterol, ascorbic acid and uric acid as three essential biological compounds at a carbon paste electrode modified with copper oxide decorated reduced graphene oxide nanocomposite and ionic liquid

Antioxidant Determination with the Use of Carbon-Based Electrodes

Antioxidants are compounds that prevent or delay the oxidation process, acting at a much smaller concentration, in comparison to that of the preserved substrate. Primary antioxidants act as scavenging or chain breaking antioxidants, delaying initiation or interrupting propagation step. Secondary antioxidants quench singlet oxygen, decompose peroxides in non-radical species, chelate prooxidative metal ions, inhibit oxidative enzymes. Based on antioxidants’ reactivity, four lines of defense have been described: Preventative antioxidants, radical scavengers, repair antioxidants, and antioxidants relying on adaptation mechanisms. Carbon-based electrodes are largely employed in electroanalysis given their special features, that encompass large surface area, high electroconductivity, chemical stability, nanostructuring possibilities, facility of manufacturing at low cost, and easiness of surface modification. Largely employed methods encompass voltammetry, amperometry, biamperometry and potentiometry. Determination of key endogenous and exogenous individual antioxidants, as well as of antioxidant activity and its main contributors relied on unmodified or modified carbon electrodes, whose analytical parameters are detailed. Recent advances based on modifications with carbon-nanotubes or the use of hybrid nanocomposite materials are described. Large effective surface area, increased mass transport, electrocatalytical effects, improved sensitivity, and low detection limits in the nanomolar range were reported, with applications validated in complex media such as foodstuffs and biological samples.

Development of a New Electrochemical Sensor Based on Mag-MIP Selective Toward Amoxicillin in Different Samples

This work describes an electrochemical sensor for the selective recognition and quantification of amoxicillin and a β-lactam antibiotic in real samples. This sensor consists of a carbon paste electrode (CPE) modified with mag-MIP (magnetic molecularly imprinted polymer), which was prepared by precipitation method via free radical using acrylamide (AAm) as functional monomer, N,N'-methylenebisacrylamide (MBAA) as a crosslinker, and potassium persulfate (KPS) as initiator, to functionalized magnetic nanoparticles. The magnetic non-imprinted polymers (mag-NIP) were prepared using the same experimental procedure without analyte and used for the preparation of a CPE for comparative studies. The morphological, structural, and electrochemical characteristics of the nanostructured material were evaluated using Field emission gun scanning electron microscopy (FEG-SEM), Transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), Vibrating sample magnetometry (VSM), X-ray diffraction (XRD), and voltammetric technique. Electrochemical experiments performed by square wave voltammetry show that the mag-MIP/CPE sensor had a better signal response compared to the non-imprinted polymer-modified electrode (mag-NIP/CPE). The sensor showed a linear range from 2.5 to 57 μmol L^-1 of amoxicillin (r ² = 0.9964), with a limit of detection and a limit of quantification of 0.75 and 2.48 μmol L^-1, respectively. No significant interference in the electrochemical signal of amoxicillin was observed during the testing experiments in real samples (skimmed milk and river water). The proposed mag-MIP/CPE sensor could be used as a good alternative method to confront other techniques to determine amoxicillin in different samples.

Large Optical Nonlinearity of the Activated Carbon Nanoparticles Prepared by Laser Ablation

Carbon nanoparticles (CNPs) with high porosity and great optical features can be used as a luminescent material. One year later, the same group investigated the NLO properties CNPs and boron-doped CNPs by 532 nm and 1064 nm laser excitations to uncover the underlying physical mechanisms in their NLO response. Hence, a facile approach, laser ablation technique, was employed for carbon nanoparticles (CNPs) synthesis from suspended activated carbon (AC). Morphological properties of the prepared CNPs were studied by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). UV-Vis and fluorescence (FL) spectra were used to optical properties investigation of CNPs. The size distribution of nanoparticles was evaluated using dynamic light scattering (DLS). The nonlinear optical (NLO) coefficients of the synthesized CNPs were determined by the Z-scan method. As a result, strong reverse saturable absorption and self-defocusing effects were observed at the excitation wavelength of 442 nm laser irradiation. These effects were ascribed to the presence of delocalized π-electrons in AC CNPs. To the best of our knowledge, this is the first study investigating the NLO properties of the AC CNPs.

An electrochemical sensor for high sensitive determination of lysozyme based on the aptamer competition approach

Protein is a kind of basic substance that constitutes a life body. The determination of protein is very important for the research of biology, medicine, and other fields. Lysozyme is relatively small and simple in structure among all kinds of proteins, so it is often used as a standard target detector in the study of aptamer sensor for protein detection. In this paper, a lysozyme electrochemical sensor based on aptamer competition mechanism is proposed. We have successfully prepared a signal weakening electrochemical sensor based on the lysozyme aptamer competition mechanism. The carboxylated multi-walled carbon nanotubes (MWCNTs) were modified on the glassy carbon electrode, and the complementary aptamer DNA with amino group was connected to MWCNTs. Because of the complementary DNA of daunomycin into the electrode, the electrochemical signal is generated. When there is a target, the aptamer binds to lysozyme with higher binding power, and the original complementary chain breaks down, resulting in the loss of daunomycin inserted into the double chain and the weakening of electrochemical signal. Differential pulse voltammetry was used to determine lysozyme, the response range was 1–500 nM, the correlation coefficient was 0.9995, and the detection limit was 0.5 nM. In addition, the proposed sensor has good selectivity and anti-interference.

A novel non-enzymatic glucose sensor based on NiFe(NPs)-polyaniline hybrid materials

This article was focused on the elaboration of NiFe-Polyaniline glucose sensors via electrochemical technique. Firstly, the PANi (polyaniline) fibers were synthesized by oxidation of the monomer aniline on FTO (fluorine tin oxide) substrate. Secondly, the Nickel-Iron nanoparticles (NiFe (NPs)) were obtained by the Chronoamperometry method on the Polyaniline surface. The NiFe-PANi hybrid electrode was characterized by scanning electron microscopy (SEM), force atomic microscopy (AFM), Fourier-transformed infrared (FTIR), and X-ray diffraction (XRD). The electrochemical glucose sensing performance of the NiFe alloy nanoparticle was studied by cyclic voltammetry and amperometry. The fabricated glucose sensor Ni-Fe hybrid material exhibited many remarkable sensing performances, such as low-response time (4 s), sensitivity (1050 μA mM^-1 cm^-2), broad linear range (from 10 μM -1 mM), and low limit of detection (LOD) (0.5 μM, S/N = 3). The selectivity, reliability, and stability of the NiFe hybrid material for glucose oxidation were also investigated. All the results demonstrated that the NiFe-PANi/FTO hybrid electrode is very promising for application in electrochemical glucose sensing.

A novel electrochemical lung cancer biomarker cytokeratin 19 fragment antigen 21-1 immunosensor based on Si3N4/MoS2 incorporated MWCNTs and core-shell type magnetic nanoparticles

Lung cancer is one of deadliest and most life threatening cancer types. Cytokeratin 19 fragment antigen 21-1 (CYFRA 21-1) is a significant biomarker for the diagnosis of non-small cell lung cancer (NSCLC). Due to these reasons, a novel electrochemical immunosensor based on a silicon nitride (Si3N4)-molybdenum disulfide (MoS2) composite on multi-walled carbon nanotubes (Si3N4/MoS2-MWCNTs) as an electrochemical sensor platform and core-shell type magnetic mesoporous silica nanoparticles@gold nanoparticles (MMSNs@AuNPs) as a signal amplifier was presented for CYFRA21-1 detection in this study. Capture antibody (Ab1) immobilization on a Si3N4/MoS2-MWCNT modified glassy carbon electrode (Si3N4/MoS2-MWCNTs/GCE) was firstly successfully performed by stable electrostatic/ionic interactions between the -NH2 groups of the capture antibody and the polar groups of Si3N4/MoS2. Then, specific antibody-antigen interactions between the electrochemical sensor platform and the signal amplifier formed a novel voltammetric CYFRA21-1 immunosensor. The prepared composite materials and electrochemical sensor surfaces were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). A linearity range of 0.01-1.0 pg mL-1 and a low detection limit (LOD) of 2.00 fg mL-1 were also obtained for analytical applications. Thus, the proposed immunosensor based on Si3N4/MoS2-MWCNTs and MMSNs@AuNPs has great potential for medical diagnosis of lung cancer.

Synthesis of biocompatible chitosan functionalized Ag decorated biocomposite for effective antibacterial and anticancer activity

The transition-metal dichalcogenides (TMDCs) like MoS₂ and WS₂ are a new and interesting class of materials and show considerable promise for use in a wide variety of fields, including nanomedicine for cancer. The eco-friendly, biodegradability, toxicity, and antimicrobial activity remain an open issue. Herein, we focused on the current demands of two dimensional (2D) TMDCs and produced high-quality, few-layered MoS₂ nanosheets. Noble metal Ag incorporated into the 2D-CS/MoS₂ NC by the liquid exfoliated process. The manufactured CS/MoS₂/Ag hybrid NC showed excellent antibacterial activity against two microorganisms such as Gram-positive (21, 27, and 33 mm) and Gram-negative bacteria (23, 30, and 39 mm). The CS/MoS_2/Ag hybrid NC was designed to have significant antibacterial activity against E.coli bacteria than S.aureus. Furthermore, the hybrid NC has a 74.18% cell inhibition against MCF-7 cancer cells. According to the literature relevant, it is the first extensive experimental analysis on the nano-bio interaction of 2D TMDCs nanomaterials in MCF-7 breast cancer cells.

Hydrogen peroxide assisted synthesis of sulfur quantum dots for the detection of chromium (VI) and ascorbic acid

Sulfur quantum dots (SQDs), heavy-metal-free quantum dots, are regarded as the next generation promising green nanomaterials compared with traditional heavy-metal-based quantum dots. However, there have been few reports on the synthesis and application of SQDs for analytical detection. Herein, an H₂O₂-assisted top-down method is used to synthesize SQDs. The as-obtained SQDs have good water dispersion, stability, photoluminescence (PL) properties and achieving a quantum yield (QY) to 11%. After adding Cr (VI) in SQDs, the fluorescence intensity decreases base on inner filter effect (IFE). Moreover, Cr (VI) can be reduced to Cr(III) when ascorbic acid (AA) is introduced into the SQDs - Cr (VI) system, accompanying the recovery of the fluorescence intensity. The fluorescence sensor displays high sensitivity and quickly response toward Cr (VI) and AA in a range of 10-120 μmol L^-1 and 20-500 μmol L^-1 with a detection limit of 0.36 μmol L^-1 and 1.21 μmol L^-1, respectively. In addition, the fluorescence sensor has been applied for the determination of Cr (VI) and AA in real samples.

Vitamin C-Sources, Physiological Role, Kinetics, Deficiency, Use, Toxicity, and Determination

Vitamin C (L-ascorbic acid) has been known as an antioxidant for most people. However, its physiological role is much larger and encompasses very different processes ranging from facilitation of iron absorption through involvement in hormones and carnitine synthesis for important roles in epigenetic processes. Contrarily, high doses act as a pro-oxidant than an anti-oxidant. This may also be the reason why plasma levels are meticulously regulated on the level of absorption and excretion in the kidney. Interestingly, most cells contain vitamin C in millimolar concentrations, which is much higher than its plasma concentrations, and compared to other vitamins. The role of vitamin C is well demonstrated by miscellaneous symptoms of its absence-scurvy. The only clinically well-documented indication for vitamin C is scurvy. The effects of vitamin C administration on cancer, cardiovascular diseases, and infections are rather minor or even debatable in the general population. Vitamin C is relatively safe, but caution should be given to the administration of high doses, which can cause overt side effects in some susceptible patients (e.g., oxalate renal stones). Lastly, analytical methods for its determination with advantages and pitfalls are also discussed in this review.

Novel voltammetric tumor necrosis factor-alpha (TNF-α) immunosensor based on gold nanoparticles involved in thiol-functionalized multi-walled carbon nanotubes and bimetallic Ni/Cu-MOFs

TNF-α, as a pro-inflammatory cytokine, regulates some physiological and pathological courses. TNF-α level increases in some important diseases such as cancer, arthritis, and diabetes. In addition, it displays an important function in Alzheimer's and cardiovascular diseases. Herein, a novel, sensitive, and selective voltammetric TNF-α immunosensor was prepared by using gold nanoparticles involved in thiol-functionalized multi-walled carbon nanotubes (AuNPs/S-MWCNTs) as sensor platform and bimetallic Ni/Cu-MOFs as sensor amplification. Firstly, the sensor platform was developed on glassy carbon electrode (GCE) surface by using mixture of thiol-functionalized MWCNTs (S-MWCNTs) and AuNPs. Then, capture TNF-α antibodies were conjugated to sensor platform by amino-gold affinity. After capture TNF-α antibodies' immobilization, a new-type voltammetric TNF-α immunosensor was developed by immune reaction between AuNPs/S-MWCNTs immobilized with primer TNF-α antibodies and bimetallic Ni/Cu-MOFs conjugated with seconder TNF-α antibodies. The prepared TNF-α immunosensor was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), x-ray diffraction (XRD) method, x-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), thermogravimetric analysis, Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). A linearity range of 0.01-1.0 pg mL^-1 and a low detection limit of 2.00 fg mL^-1 were also obtained for analytical applications.

Polyethylene Terephthalate-Based Materials for Lithium-Ion Battery Separator Applications: A Review Based on Knowledge Domain Analysis

As the key material of lithium battery, separator plays an important role in isolating electrons, preventing direct contact between anode and cathode, and allowing free passage of lithium ions in the electrolyte. Polyethylene terephthalate (PET) has excellent mechanical, thermodynamic, and electrical insulation properties. This review aims to identify the research progress and development trends of PET-based material for separator application. We retrieved published papers (2004–2019) from the Scientific Citation Index Expanded (SCIE) database of the WoS with a topic search related to PET-based material for separator application. The research progress and development trends were analyzed based on the CiteSpace software of text mining and visualization.

Chiral poly(amide-imide)/ZnS nanocomposite as a new adsorbent for simultaneous removal of cationic dyes from aqueous solution

A new adsorbent, poly(amide-imide)/zinc sulfide nanocomposite (PAI/ZnS NC), was fabricated and identified by Fourier-transform infrared spectroscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, field emission-scanning electron microscopy, and transmission electron microscopy. Then, the obtained NC was applied for the simultaneous removal of auramine O (AO) and rhodamine B (RB) dyes from aqueous solution via the interactions of hydrogen bonding, π– π stacking, and Lewis acid–base interaction. The effects of operational variables including pH, PAI/ZnS NC mass, AO and RB concentration, and sonication time on removal efficiency were examined and optimized values were found to be 8.0, 16 mg, 11 mg L−1, and 6 min, respectively. The adsorption capacities of PAI/ZnS NC for the removal of AO and RB dyes were found to be 70.92 and 91.74 mg g−1, respectively. Ultraviolet–visible spectrophotometer was used to determine the amount of residual dye in solution. Fitting the experimental equilibrium data to isotherm models such as Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich reveals the suitability of the Langmuir model with high correlation coefficients ( R2 = 0.998 for AO and R2 = 0.999 for RB). Pseudo-first-order, pseudo-second-order, intraparticle diffusion, and Elovich kinetic models applicability was tested and the pseudo-second-order equation controls the kinetics of the adsorption process. Furthermore, this study establishes that PAI/ZnS NC can be successfully applied as a low-cost adsorbent and conserve its high efficiency after nine cycles for the removal of AO and RB dyes.

Bi2O3/ZnO nanocomposite: Synthesis, characterizations and its application in electrochemical detection of balofloxacin as an anti-biotic drug

In the present work, a chemically modified electrode has been fabricated utilizing Bi2O3/ZnO nanocomposite. The nanocomposite was synthesized by simple sonochemical method and characterized for its structural and morphological properties by using XRD, FESEM, EDAX, HRTEM and XPS techniques. The results clearly indicated co-existence of Bi2O3 and ZnO in the nanocomposite with chemical interaction between them. Bi2O3/ZnO nanocomposite based glassy carbon electrode (GCE) was utilized for sensitive voltammetric detection of an anti-biotic drug (balofloxacin). The modification amplified the electroactive surface area of the sensor, thus providing more sites for oxidation of analyte. Cyclic and square wave voltammograms revealed that Bi2O3/ZnO modified electrode provides excellent electrocatalytic action towards balofloxacin oxidation. The current exhibited a wide linear response in concentration range of 150-1000 nM and detection limit of 40.5 nM was attained. The modified electrode offered advantages in terms of simplicity of preparation, fair stability (RSD 1.45%), appreciable reproducibility (RSD 2.03%) and selectivity. The proposed sensor was applied for determining balofloxacin in commercial pharmaceutical formulations and blood serum samples with the mean recoveries of 99.09% and 99.5%, respectively.

A highly-sensitive vascular endothelial growth factor-A(165) immunosensor, as a tool for early detection of cancer

Biomarkers can be ideal indicators for assessing the risk of the presence of a disease. In this study, a label-free electrochemical biosensor was designed to quantify the vascular endothelial growth factor A (165) (VEGF-A(165)) antigen, using reduced graphene oxide-gold nanoparticle for early detection of breast cancer. The conductivity of gold nanoparticle along with its biocompatibility provide an enhanced surface, suitable for anti-VEGF antibody immobilization. 11-mercaptoundecanoic acid was used to facilitate a single-step and convenient bonding of the antibodies to the surface, compared to previous studies. The dynamic range of the biosensor was between 20 to 120 pg/ml and its limit of detection of the biomarker VEGF-A(165) was obtained to be about 0.007 pg/ml, using different electric signal transduction modes. Hence, the biosensor is a beneficial immunosensor with high sensitivity and ideal dynamic range for early-stage diagnosis of breast cancer and other cancers diseases associated with expression of VEGF-A(165). The as-prepared immunosensor could be efficiently employed for designing a point-of-care diagnostic platform.

Determination of paracetamol using a sensor based on green synthesis of silver nanoparticles in plant extract

The biosynthesis of nanometals using a plant extract is simple, efficient, fast, cost-effective and eco-friendly. In this study, a pine nut extract (Araucaria angustifolia) was obtained and used as a reducing and stabilizing agent in the synthesis of silver nanoparticles. An electrochemical sensor based on the silver nanoparticles obtained and exfoliated graphite nanoplatelets applied to a glassy carbon electrode was developed for the determination of paracetamol. To optimize the synthesis of the silver nanoparticles, important factors such as temperature, extract:water ratio, silver nitrate concentration and extract stability time were studied. The factors influencing the performance of the sensor were studied in detail and the results demonstrated good repeatability and electrode-to-electrode repeatability (relative standard deviations of 1.8 and 4.0 %, respectively). Under optimized conditions, there was a linear response to paracetamol concentrations of 4.98 × 10^-6 to 3.38 × 10^-5 mol L^-1, with a detection limit of 8.50 × 10^-8 mol L^-1. No reports on the biosynthesis of AgNPs using Araucaria angustifolia could be found in the literature. The sensor developed showed good stability and was used successfully for the quantification of paracetamol in pharmaceutical products.

Synthesis and Shape-Selective Catalytic Application of Ordered Cubic Ia3̅d Supermicroporous Materials Templated by Rosin-Derived Quaternary Ammonium Salt with a Hydroxyl Radical in the Headgroup

We described the comprehensive synthesis, characterization, and catalytic performance of a novel type of the ordered cubic Ia3̅d supermicroporous silicas by using tetraethyl orthosilicate as a silicon source and a hydroxyl-functionalized quaternary ammonium salt as a template under alkali conditions. The effects of various reaction conditions on the pore structure and morphology of the silica materials were thoroughly investigated. Our results showed that under a wide range of reaction conditions, supermicroporous silicas with a highly ordered cubic Ia3̅d structure can be produced with a large BET specific surface area of 1741 m²/g, high pore volume of 0.91 cm³/g, concentrated pore size at 19.1 Å, and crystalline morphology. After Al doping, the obtained aluminosilicates preserved a highly ordered cubic supermicroporous structure. By using the H-form aluminosilicates as catalysts, we selectively dimerized β-pinene. The catalysts exhibited an excellent catalytic activity for β-pinene dimerization with a conversion yield up to 100%. Compared with conventional mesoporous H-form Al-MCM-48 catalysts, the prepared supermicroporous catalysts exhibited superior catalytic performance due to their excellent shape-selective properties, producing the β-pinene dimer in a yield up to 72.4% with dimer/oligomer ratios in the range of 7.5-10.1. This study featured a detailed preparation and characterization of supermicroporous silica with novel microstructures and showed its utility in catalytic dimerization.

Anchoring Metallic MoS2 Quantum Dots over MWCNTs for Highly Sensitive Detection of Postharvest Fungicide in Traditional Chinese Medicines

Carbendazim, a very common contamination to the traditional Chinese medicines (TCMs), has posed serious threat to the environment and human health. However, sensitive and selective detection of carbendazim (MBC) in the TCMs is a big challenge for their complex chemical constituents. In this work, a 0D/1D nanohybrid was developed by anchoring 1T-phased MoS₂ quantum dots (QDs) over multiwall carbon nanotubes (MWCNTs) via a facile assembly method. High-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis (TGA) together with EIS reveal that the 1T-phased QDs can anchor over MWCNTs via van der Waals forces, and the anchoring improves the nanohybrid surface area and conductivity. Therefore, the electrochemical sensor fabricated based on the MoS₂ QDs@MWCNT nanohybrid shows excellent catalytic activity to MBC oxidation. Under optimized conditions, the sensor presents a linear voltammetry response to MBC concentration from 0.04 to 1.00 μmol·L^-1, a low detection limit of 2.6 × 10^-8 mol·L^-1, as well as high selectivity, good reproducibility, and long-term stability. Moreover, the sensor has been successfully employed to determine MBC in two typical TCMs and the obtained recoveries are in good accordance with the results achieved by HPLC, showing that the constructed sensor plate holds great practical application in MBC analysis with complex matrix.

Electrochemical dual signal sensing platform for the simultaneous determination of dopamine, uric acid and glucose based on copper and cerium bimetallic carbon nanocomposites

A highly sensitive electrochemical sensor for the simultaneous dual signal determination of dopamine (DA), uric acid (UA) and glucose (Glu) has been obtained using nanocomposites based on the copper and cerium bimetallic nanoparticles and carbon nanomaterials of graphene and single-walled carbon nanotubes in the presence of Tween 20 (GR-SWCNT-Ce-Cu-Tween 20) modified glassy carbon electrode. The surface morphology of the nanocomposites was characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), and the electrochemical behavior of the sensor was investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) with potassium ferricyanide as probe. In the coexistence system of DA, UA and Glu, three clear and well-isolated voltammetric peaks were obtained by CV and differential pulse voltammetry (DPV), and oxidation peak currents of DA and UA are positively correlated with their concentrations respectively, while the peak current of Glu is negatively correlated with its concentration. Linearity was obtained in the ranges of 0.1-100 µM for dopamine, 0.08-100 µM for uric acid and 1-1000 µM for glucose with DPV, and the detection limits (S/N = 3) of 0.0072 µM, 0.0063 µM, and 0.095 µM for DA, UA and Glu, respectively. The method was successfully applied to the determination of DA, UA and Glu in blood serum samples, which provided a reference for further sensor research.

Defect-enhanced electrochemical property of h-BN for Pb2+ detection

A new strategy has been developed for the determination of trace lead ions (Pb²⁺) based on hexagonal boron nitride (h-BN) laden with point defect. The defect-laden boron nitride (D-BN) was synthesized by a thermal polymerization route, in which melamine borate was used as a precursor. The defect microstructure was confirmed by photoluminescence (PL) and x-ray diffraction (XRD) techniques. As compared with h-BN, the D-BN-modified glassy carbon electrode (GCE) showed an enhanced electrochemical response towards Pb²⁺ peaking at - 0.551 V (vs. SCE), which was evidenced by linear sweep anodic stripping voltammetry (LSASV) results. The point defect plays a pivotal role in the electrocatalytic reaction process, which can mediate the electronic structure and surface properties of h-BN. Accordingly, the sensor presented a low detection limit of 0.15 μg/L towards Pb²⁺ and a wide linear response concentration range from 0.5 to 400 μg/L (correlation coefficient = 0.995). In view of its superior selectivity, stability, and reproducibility, the proposed method was applied for Pb²⁺ determination in real samples and exhibited satisfactory results. This work provides insight for the construction of electrochemical sensor with high-performance by engineering defects of modifying materials. Defect-loaden h-BN exhibited enhanced electrocatalytic redox reaction towards lead ions and thus a novel Pb²⁺ sensor with high performances was constructed.

Horseradish Peroxidase Labelled-Sandwich Electrochemical Sensor Based on Ionic Liquid-Gold Nanoparticles for Lactobacillus brevis

Lactobacillus brevis is the most common bacteria that causes beer spoilage. In this work, a novel electrochemical immunosensor was fabricated for ultra-sensitive determination of L. brevis. Gold nanoparticles (AuNPs) were firstly electro-deposited on the electrode surface for enhancing the electro-conductivity and specific surface area. Ionic liquid was used for improving the immobilization performance of the immunosensor. After optimization, a linear regression equation can be observed between the ∆current and concentration of L. brevis from 104 CFU/mL to 109 CFU/mL. The limit of detection can be estimated to be 103 CFU/mL.

A novel electrochemical aflatoxin B1 immunosensor based on gold nanoparticle-decorated porous graphene nanoribbon and Ag nanocube-incorporated MoS2 nanosheets

The accurate and precisive monitoring of aflatoxin B1 (AFB1), which is one of the most hazardous mycotoxins, especially in agricultural products, is significant for human and environmental health.

A simple and sensitive approach for the electrochemical determination of amaranth by a Pd/GO nanomaterial-modified screen-printed electrode

It is essential to develop easy-to-use sensors towards a better monitoring of food additives so that human health can be positively influenced. A type of critical food additive that is widely used in making soft drinks and diverse foodstuff is called amaranth. This study aimed at presenting a novel Pd/GO nanomaterial-modified screen-printed electrode (Pd/GO/SPE), which is responsible for providing a sensing interface during the process of specifying the electrochemical features of amaranth. The morphology and structure of the Pd/GO nanomaterial was investigated by Fourier-transform infrared spectroscopy, thermal gravimetric analysis, X-ray photoelectron spectroscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, scanning transmission electron microscopy, and high-resolution transmission electron microscopy. When the optimized conditions was adjusted, Pd/GO/SPE proved to be a capable sensor for conducting a very sensitive sensing towards the amaranth under a common working situation of 575 mV. In this regard, it was embarked on measuring some of the sensor features, including its sensitivity, linear dynamic range, and detection limit for amaranth with the values of 0.0948 μA μM-1, 0.08 μM-360.0 μM and 30.0 nM were obtained, respectively.

Preparation of Electrochemical Sensor Based on Zinc Oxide Nanoparticles for Simultaneous Determination of AA, DA, and UA

ZnO nanoparticles (NPs) were synthesized using a hydrothermal method. Scanning electron microscope (SEM) and X-ray diffraction have been used for characterizing the synthesized ZnO NPs. An electrochemical sensor was fabricated using ZnO NPs–modified glassy carbon electrode for simultaneous determination of ascorbic acid (AA), dopamine (DA), and uric acid (UA). The proposed electrochemical sensor exhibited excellent detection performance toward three analytes, demonstrating that it can potentially be applied in clinical applications. The results indicated the ZnO NPs–modified electrode can detect AA in the concentrations range between 50 and 1,000 μM. The ZnO NPs–modified electrode can detect DA in the concentrations range between 2 and 150 μM. The ZnO NPs–modified electrode can detect UA in the concentrations range between 0.2 and 150 μM. The limits of detections of AA, DA, and UA using ZnO NPs–modified electrode were calculated to be 18.4, 0.75, and 0.11 μM, respectively.

Electrochemical sensing of cytochrome c using Graphene Oxide nanoparticles as platform

An improved cytochrome c (Cyt c) biosensor based on immobilization of cytochrome c oxidase (COx) on the surface of graphene oxide nanoparticles (GONPs) electrodeposited onto pencil graphite (PG) electrode. Characterization of graphene oxide nanoparticle was done by Transmission electron microscopy (TEM), Fourier transform infra-red spectroscopy (FTIR) and X-ray diffraction study (XRD). The working electrode (COx/GONPs/PG) was characterized at its different stages of fabrication by scanning electron microscopy (SEM) and FTIR. Fabrication of Cyt c biosensor was done by connecting COx/GONPs/PG as working electrode, Ag/AgCl as reference electrode and Pt as auxiliary electrode to potentiostat. The mechanism of detection of present biosensor was based on oxidation of Cyt c (reduced) to Cyt c (oxidized) by COx resulting in flow of electrons through GONPs to the PG electrode, hence current generated is proportional to the concentration of Cyt c. Present biosensor exhibited optimum potential at 0.49 V with optimum pH 7.5 and optimum temperature 35°C. Biosensor showed linearity within 40-180 ng/ml having 40 ng/ml limit of detection. The precision i.e. within and between-batch coefficients of variation (CVs) were found <0.04% and <0.21% respectively. The enzyme electrode lost 50% of its initial activity when operated for more than 6 months on weekly basis. It was applied for detection of Cyt c level in in apparently healthy and diseased human sera. The present biosensing method was co-related with standard colorimetric method and co-relation coefficient was found 0.99.

Real time detection and monitoring of 2, 4-dinitrophenylhydrazine in industrial effluents and water bodies by electrochemical approach based on novel conductive polymeric composite

Much attention has been given to detection and monitoring of hydrazine-based compounds in recent time because of its significant negative impacts on human health and ecosystem (aquatic lives). This prompted the current study focusing on detection of 2, 4-dinitrophenylhydrazine (2, 4-dnphz) using electrochemically synthesized poly-para amino benzoic acid-manganese oxide (P-pABA-MnO₂) composite film. The synthesized P-pABA-MnO₂ composite film was characterized in terms of its structural and morphological properties by X-ray diffraction spectroscopy and field emission scanning electron microscopy respectively. In addition, functionalities and binding energy of p-PABA-MnO2 were confirmed using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy respectively. Finally, electrochemical properties were investigated using electrochemical impedance spectroscopy and cyclic voltammetry. The synthesized P-pABA-MnO₂ displayed good electrocatalytic reduction property towards 2, 4-dnphz with ultra-low limit of detection (0.08 μM; S/N = 3) and very high sensitivity (52 μAμ^-1Mcm^-2). The proposed sensor based on P-pABA-MnO₂ also demonstrated good stability in terms of repeatability, reproducibility and interferents effects. Lastly, the proposed sensor was satisfactorily used in detection of 2, 4-dnphz in environmental real samples.

Analytical performance of functional nanostructured biointerfaces for sensing phenolic compounds

Electrochemical biointerfaces are constructed with a wide range of nanomaterials and conducting polymers that strongly affect the analytical performance of biosensors. The analysis of progress toward electrochemical sensing platforms offers opportunities to provide devices for commercial use. The investigation of different methods for the synthesis of phenol biointerfaces leads to design challenges in the field of monitoring phenolic compounds. This paper review the innovative strategies and feature techniques in the construction of phenolic compound biosensors. The focus was made on the preparation methods of nanostructures and nanomaterials design for catalytic improvements of sensing interfaces. The paper also provides a comprehensive overview in the field of enzyme immobilization approaches at solid supports and technical formation of polymer nanocomposites, as well as applications of hybrid organic-inorganic nanocomposites in phenolic biosensors. This review also highlights the recent progress in the electrochemical detection of phenolic compounds and summarizes analytical performance parameters including sensitivity, storage stability, limit of detection, linear range, and Michaelis-Menten kinetic analysis. It also emphasizes advances from the past decade including technical challenges for the construction of suitable biointerfaces for monitoring phenolic compounds.