Reduction Peak Research Articles

Synthesis, spectroscopic, electrochemistry and antioxidant properties of benzofuroxan and 2H-benzimidazole 1,3-dioxide derivatives: Effects of conjugation with electron-acceptor 1,2,3-triazolyl-1,2,4-oxadiazole

A series of novel benzofuroxan and of 2,2-dimethyl-2H-benzimidazole 1,3-dioxide derivatives conjugated to the strong electron-withdrawing 1,2,4-oxadiazole ring and to the amide isostere 1,2,3-triazole were synthesized. NHeterocycle-N-oxide-bearing carboxylic acids and 1,2,3-triazole-4-carbamidoximes served as convenient reactants for the obtention of the 1,2,4-oxadiazoles. By employing O-(benzotriazol-1-yl)-N,N,N’,N’-tetramethyluronium tetrafluoroborate (TBTU) as coupling reagent and 1,8-diazabicyclo[5.4.0]undec‑7-ene (DBU) as base in acetonitrile, in a one-pot sequence, at room temperature, products were obtained in generally high yields (64 – 93 %) after two 30 min steps and a simple purification process. NMR spectroscopy, X-Ray diffraction and DFT calculations helped to access the preferential tautomeric structures of selected compounds. UV–Vis spectroscopy revealed characteristic absorption peaks for 1,2,3-triazolyl-1,2,4-oxadiazoles 11aa-be, noteworthy an intramolecular charge transfer (ICT) band around 500–650 nm for benzimidazole-1,3-dioxide derivatives 11ba-be, while low fluorescence quantum yields and Stokes shifts were observed for all compounds. Both oxidation and reduction peaks were observed in Cyclic Voltammetry experiments, including irreversible reduction peaks for all 11aa-be compounds. TD-DFT calculations enabled comprehension of the molecular orbitals participation in the UV–Vis transitions, which depend on the N-oxide, the heterocycles and the substituted phenyl ring. Also, some compounds with electron withdrawing groups (Cl and CF3) also displayed good antioxidant activity in DPPH assays.

Cathodic luminol electrochemiluminescence on TiO2 nanotube array

This study introduces a novel fabrication of screen-printed electrode of hierarchical thin layers of TiO2 nanotube arrays (TNA) and its preliminary investigation for cathodic electrochemiluminescence (ECL) of luminol. The TNA growth on titanium foil by anodization technique was studied under various anodization times and counter electrodes (Pt wire and stainless-steel plate). Characterization using FTIR, UV-VIS DRS, and XRD revealed the increase of TiO2 formation at longer anodization times. The TNA synthesized with a stainless-steel counter electrode (TNA-SS) for 2000 s exhibited better nanotube growth and a higher electrochemical active surface area compared to the one using Pt counter electrode (TNA-Pt). The SEM characterization verified the nanotube morphology of TNA-SS with an average pore diameter of 50.46 nm and a tube length of ∼1100 nm. Notably, when TNA applied as the working electrode for the ECL of luminol, a reduction peak at −0.8 V accompanied by a clear ECL signal were observed, reaching an optimum intensity at 15 μM luminol. A comparative analysis between TNA-SS and TNA-Pt revealed the same trend of ECL signals with a significantly higher ECL intensity of TNA-SS than that of TNA-Pt. The ECL intensity of TNA-SS 2000s was also higher than TNA-SS 300s, confirming the importance of TNA surface area to the ECL activity. Nevertheless, the synthesized SPE-TNA shows great prospect to be applied in electroanalytical and sensing fields, offering opportunities for the development of electrochemiluminescence technologies.

Graphene nanoplatelets-polyaniline composite for the detection of cortisol

In this study, a highly selective Graphene oxide (GO)-Polyaniline (PANI) modified glassy carbon electrode (GCE) was fabricated and its electrocatalytic behaviour towards the electro-reduction of cortisol in human saliva was investigated. The synthesized nanocomposites were characterized using different analytical approaches. The electrochemical study of the PANI-GO modified electrode was analyzed by employing a cyclic Voltammetry (CV) study. The outcomes demonstrated a substantial enhancement in the reduction and oxidation current peaks of the modified GCE as associated to bare GCE, GO/GCE and PANI/GCE. Along with enhanced electronic properties, the biosensor displays the good selectivity and sensitivity, good reproducibility (95 %, n = 8), high stability (maintaining more than 95 % response even after 11 weeks of storage at −20C, 50 cycles), a wide linear range (100μ-10 mM) and small detection limit (30 μM). The utilization of PANI-GO in the electrode modification process may be attributed to these positive outcomes, given some of the amazing characteristics of the composite, such as its larger surface area, outstanding electrical conductivity, and good electrocatalytic behavior. Furthermore, the PANI-GO modified GCE was successfully validated by detecting cortisol in real human saliva samples using cyclic voltammetry, highlighting the effectiveness of the PANI-GO composite for non-invasive electrochemical cortisol detection.

The beneficial effect of lauric acid addition in nucleation stage on the soot catalytic combustion performance of cerium-manganese catalyst

For cerium-manganese catalyst system, increasing the threshold of the amount of Mnx+ entering into the CeO2 lattice can generate more oxygen vacancies and adsorb more active oxygen species, thus promoting its soot catalytic combustion. However, this is difficult to achieve under the premise of fixed cerium-manganese ratio of the catalyst. Fortunately, the results of this study show that the addition of lauric acid at the nucleation stage of the cerium-manganese catalyst can effectively improve its activity and high temperature aging resistance. Combined with a series of characterization results, the addition of lauric acid can increase the threshold of Mnx+ content in CeO2 lattice, improve the structural performance of the catalyst, increase the specific surface area and pore volume of the catalyst, inhibit the secondary aggregation of catalyst particles, increase the content of surface Ce3+, increase the low temperature reduction performance and the content of surface chemical desorbed oxygen of the catalyst. In addition, it can also prevent the phase separation of cerium-manganese solid solution, the growth of grains, the increase of reduction peak temperature and the decrease of H2 consumption during high temperature aging. Moreover, the addition of lauric acid also greatly improves the release performance of active oxygen in cerium-manganese catalyst. Therefore, this study plays a positive role in promoting the commercial application of highly active cerium-manganese catalyst.

S Development of an electrochemical immunosensor using gold nanoparticles (AuNPs) for the detection of Apolipoprotein A1 (ApoA1) in chicken blood plasma

The research aims to develop an electrochemical immunosensing assay using gold nanoparticles (AuNPs) on screen printed carbon electrode (SPCE) for the specific detection of Apolipoprotein A1 (ApoA1) proteins in chicken blood plasma (CBP). The biotin anti-ApoAI antibody was first immobilized on magnetic beads (MBs), while antibody ApoA1 was then conjugated with AuNPs. After a series of sandwich-type immunoreaction complexes was performed on the screen-printed carbon electrode, AuNPs were quantified by subjecting the immunocomplex to a peroxidation process of high potential at 1.2 V for 330 s and immediately reduced and scanned by differential pulse voltammetry (DPASV). This study obtained a linear relationship between reduction peak current signals and ApoA1 concentration from 0 to 100% (correlation coefficient of 0.996 with a detection limit of 5% of chicken blood plasma (CBP). The efficacy of our immunosensor is predicated on the seamless integration of antibodies with MBs to the target analyte, which provide ample surface area, biocompatibility, and user-friendliness. This breakthrough improves preliminary food fraud detection's sensitivity, reliability, and usability. It could improve diagnostic food safety, leading to a worldwide health breakthrough.

Highly Active and Stable Pd/MgAl2O4 Catalysts for Methane Catalytic Combustion

Mesoporous MgAl2O4 is synthesized via a novel sol–gel combustion method and the concentration of oxygen defects on the surface is modulated through varying the calcination temperature (850, 900, 1000, and 1100 °C). Notably, the 1Pd/MgAl2O4‐1000 catalyst exhibits superior catalytic activity and stability. The turnover frequency (TOF) for 1Pd/MgAl2O4‐1000 is 0.079 and 0.058 s−1 under dry conditions (300 °C) and wet conditions (380 °C), respectively. The results of H2 temperature‐programmed reduction and X‐Ray photoelectron spectroscopy reveal that the principal active species within the Pd/MgAl2O4‐y catalyst is PdO. Specifically, the Pd–MgAl2O4‐1000 catalyst exhibits the lowest temperature reduction peak (120 °C) and the highest redox capability. Additionally, O2 temperature‐programmed oxidation further elucidates that PdOx species in the Pd/MgAl2O4‐1000 catalyst is prone to decomposition and the resultant palladium metal is readily reoxidized. Consequently, the rapidity of the redox cycle between PdO and Pd0 emerges as a pivotal factor in CH4 catalytic combustion. Furthermore, a correlation analysis among catalyst particle size, oxygen defect concentration, and TOF is conducted. The findings illustrate a distinct volcano‐shaped curve in the relationship between oxygen defect concentration and TOF for the 1Pd/MgAl2O4−y catalysts. A comparable trend is also evident in the correlation between Pd particle size and TOF.

Optimizing energy storage: Carbon implantation in NiO matrix unveils C–NiO's hybrid capacitive and battery-like behavior with enhanced electrochemical performance

Doping is a common strategy employed to enhance material properties. Numerous researchers have introduced carbon into the nickel oxide (NiO) matrix through various methods to improve the electrochemical performance for energy storage applications. This study investigates the impact of carbon implantation into the NiO matrix using a particle accelerator. Cyclic voltammetry profiles of carbon-implanted NiO (C–NiO) reveal distinct oxidation–reduction peaks, and one side of the CV curves exhibits a rectangular shape, confirming the hybrid capacitive and battery-like behavior of C–NiO. The reduced separation between oxidation–reduction peaks and the increased specific capacitance at higher scan rates validate the capacitive nature of C–NiO. Enhanced electrochemical performance was further explored through GCD, EIS, and BET techniques. C–NiO demonstrates impressive capacitance retention of 93.8 % after 5000 cycles. The Nyquist plot indicates that the improved performance of C–NiO is attributed to its heightened electrode activity, resulting from lower charge-transfer resistance. BET analysis confirms that C-doping leads to a larger surface area. In the NiO matrix, two bands of adsorbed CO2 are observed, whereas these bands are absent in C–NiO, indicating clearer pathways for ion–electron exchange. Compared to undoped NiO (55 F/g at 50 mV/s), C–NiO exhibits a more than tenfold increase in specific capacitance (1079 F/g at 50 mV/s).

Initial Research on the 1%CuO – 6CeO2 – 4ZrO2 Catalysts by TPR-H2 for the Carbon Monoxide Preferential Oxidation (CO-PROX Reaction)

The 1wt%CuO – 6CeO2 – 4ZrO2 catalysts were synthesized by sol-gel method with two different procedures: (i) impregnating CuO on CeO2-ZrO2 support (CuO/CeO2-ZrO2), (ii) sol-gel of the Cu, Ce and Zr precursor together (CuO-CeO2-ZrO2). These catalysts were applied for the preferential oxidation of carbon monoxide (CO-PROX) to remove a small quantity of CO in an H2-rich stream (the new research direction in Viet Nam), fueling the proton exchange membrane fuel cell (PEMFC) energy system. The findings of the TPR-H2 experiment indicated that the catalyst produced through the first method exhibited an α reduction peak at 174 °C, which shows the effective dispersion of copper species. In combination with EPR results, the author anticipates a significant dispersion arising from isolated copper, which is recognized as a pivotal site in the CO-PROX reaction per numerous reputable studies. The catalyst synthesized by the second method did not provide a clear indication of the oxidation behavior of Cu-species. Therefore, it can be inferred that this catalyst is inappropriate for the low-temperature CO-PROX reaction.

Predictive power fluctuation mitigation in grid-connected PV systems with rapid response to EV charging stations

Currently, renewable energies and electric vehicle charging stations are essential for energy sustainability. However, the variable generation from renewable sources, such as photovoltaic systems, can lead to power peaks that impact the stability of the grid. This challenge is exacerbated by the increasing demand in fast-charging stations. Addressing these demand peaks is crucial to ensure the stability of the electrical grid. This paper introduces the predictive-flex smoother, an innovative method designed to mitigate power fluctuations in grid-connected photovoltaic systems while optimizing energy management in electric vehicle charging stations. The predictive-flex smoother method incorporates a hybrid energy storage system comprising supercapacitors and vanadium redox flow batteries to respond rapidly to electric vehicle charging stations demands, enhance grid electricity purchase optimization, and improve energy quality delivery. The proposed method integrates two control strategies: photovoltaic fluctuation reduction strategy and peak demand reduction strategy for electric vehicle charging stations. By leveraging prediction algorithms and machine learning techniques, the predictive-flex smoother method achieves precise power fluctuation forecasts, allowing efficient utilization of supercapacitors and vanadium redox flow batteries to smooth photovoltaic power fluctuations and reduce electrical vehicles peak demand. Comprehensive experimental investigations and simulations validate the method's performance under various operational conditions. The results demonstrate the effectiveness of the predictive-flex smoother method, significantly improving the quality of power delivered to the grid while reducing costs. The experimental platform, validates the real-time response of the proposed method, with response times under 500 ms. The experimental results further confirm the efficiency of the method in power smoothing and charging strategies with varying electrical vehicles models and connection coefficients.

Broadband RCS reduction metasurface based on vortex singularities generated by Spin-to-Orbital angular momentum conversion

A broadband radar cross-section (RCS) reduction employed by the vortex metasurface is proposed. The underlying physics is associated with the Pancharatnam-Berry geometrical phases involved in spin-to-orbital angular momentum conversion. The proposed metasurface generates spin-controlled vortex waves with different topological charges. The vortex singularity implements specular extremely low RCS reduction. The prototypes are fabricated and measured to verify the wideband performance of the RCS reduction. The simulated results illustrate that −10 dB broadband RCS reduction from 9 GHz to 22.5 GHz and the RCS reduction has peak values −37.2 dB, −40.8 dB, and −42.5 dB at 9.8 GHz, 13.1 GHz, and 20.8 GHz, respectively. The measurement results illustrate that −10 dB RCS reduction over 9.1–18 GHz is realized, and the RCS reduction peak −53 dB at 10.1 GHz. The measured electric field intensities and phase distribution of the vortex metasurface also be displayed. Due to the limitation of experimental conditions, no test was done in the range greater than 18 GHz. Far-field results achieve good agreement between simulations and experiments, and the near-field measurements are a subtle difference in the experimental results. This work reveals the potential advantages of vortex waves in the fields of multifunctional electromagnetic stealth, beamforming for communication systems, etc.

Mesoporous silica nanoparticles decorated with C3N4 framework as a novel electrocatalyst for the design of a selective clonazepam sensor

In this study, a new chemical modifier based on copper nitrate hydroxide-containing mesoporous silica decorated with a C3N4 framework (MSN/C3N4/CNH) was developed to design a modified sensor for the determination of clonazepam (CZP). The resulting composite was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), energy-dispersive X-ray spectroscopy (EDS), simultaneous thermal analysis (STA), Brunauer-Emmett-Teller (BET) and Barrett Joyner–Halenda (BJH) analyses. The fabricated electrochemical sensor which was designed with a new modified glassy carbon electrode (GCE) for CZP analysis, exhibits outstanding electrocatalytic activities toward the reduction of CZP. The results showed that significant sensitivity compared to existing methods improved with an excellent detection limit of 2.50 nmol L−1 for the CZP detection, and the modified electrode has high activity toward the oxidation and reduction of CZP, with an oxidation peak around 0.32 V, and a lower reduction peak around −0.78 V; at pH = 7.0. The effect of experimental and instrumental factors on the electrochemical sensor response was examined, and the cyclic voltammetric results confirmed the 4H+/4e− process in the electrochemical studies. Moreover, in differential pulse voltammetry, the reduction peak current was proportional toward the CZP concentration from 0.82 to 76.90 μmol L−1, at optimum conditions. The modified electrode showed good reproducibility, and repeatability with relative standard deviation values of 2.7% and 1.2%, respectively. The proposed method can be applied as a simple, selective, and precise method to determine CZP drug in real samples, with satisfactory results.

Dual-mode detection of antibiotic drugs using ytterbium molybdate/porous carbon nanocomposite

Monitoring the levels of metronidazole (MTZ) is crucial to ensure the desired therapeutic effectiveness and to prevent potential harm to patients. However, MTZ exhibits concentration-dependent antimicrobial activity and has a narrow therapeutic range. In this study, “one stone two mango” strategy was influenced for the electrochemical and UV–vis spectroscopy detection of antibiotic residues of MTZ. The successfully synthesized ytterbium molybdate nano petals (YbMO) with porous carbon (PC) nanocomposite (NC) using ultrasonication method. The YbMO/PC NC, as well as other modified electrodes, were identified and targeted as molecules using natural pH as the probe to indicate current intensity. Also, examined the morphology and physicochemical properties of the synthesized materials. Furthermore, conducted cycling voltammetry (CV) and linear sweep voltammetry (LSV) on the modified electrodes to model MTZ analytes. Among them, the YbMO/PC NC/GCE exhibited larger reduction peak current and lower potential compared to other modified electrodes due to the synergistic effect between YbMO and PC, resulting in effective detection of MTZ. The YbMO/PC NC/GCE demonstrated exceptional sensitivity (3.28 µA µM−1 cm−2), a wide linear range (0.01–10.61 and 20.61–1630.61 µM), and a remarkably low detection limit (LOD: 0.006 µM). The proposed YbMO/PC NC/GCE exhibits the successfully analyzed MTZ in serum (101%), urine (97.9%), tablets (99.15%), lake (99.1%), and river water (99.8%). On the other hand, a UV–vis spectrometric method was employed to detect MTZ. The results showed a wide linear range (0.05–57.2 µM) and an impressive LOD (70 nM). These results are attributed to the heightened sensitivity, selectivity, repeatability, and durability of the sensor.

Characterization and investigation of cytotoxicity and antimicrobial properties of coencapsulated limonene and thymol into the Ferula assafoetida gum microparticles

Thymol (Th) and d-limonene (L) exhibit low stability and are prone to oxidation when exposed to air, light, humidity, and high temperatures. This study examined the coencapsulation of Th and L into Ferula assafoetida gum (AFG) microparticles. Scanning electron microscope (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analyzer (TGA) were done to characterize the obtained complexes. Furthermore, the encapsulation efficiency, antibacterial properties, cytotoxicity, and anticancer properties of both the free and encapsulated forms of L and Th were measured. For all samples, by increasing the percentage of bioactive compound (L, Th, and L-Th) from 2.5 to 5 % w/w, the EE was increased. FTIR and XRD analysis results demonstrated that Th and L were successfully incorporated into the AFG. Additionally, thermogravimetric analysis showed that in the thermal graphs of all samples, the first weight loss occurred between 30 °C and 160 °C, which was due to the evaporation of water. In the free L and Th graph, a sharp reduction peak was observed in which 80 % of compounds were lost. These reduction peaks disappeared in the thermal graphs of L: AFG and Th: AFG revealing that the thermal stability of Th and L was significantly increased upon their incorporation into the AFG. The inclusion of Th into the AFG also led to an increase in its antibacterial activity, while L exhibited acceptable antibacterial activity, albeit not as high as Th. Additionally, according to the MIC results, Th: AFG had the best antibacterial activity among all compounds, especially on gram-positive bacteria. According to the result of the MTT assay, there was a significant difference between the IC50 of free Th (123.4 μg/ml) and Th: AFG (2312 μg/ml), and free L (1762 μg/ml) and L: AFG (2480 μg/ml) showing that encapsulated Th and L into the AFG has decreased the cytotoxicity of free compounds against L929 cell line. Also, Th: AFG had the best anticancer activity against Hella and CT26 cell lines among all compounds. Finally, the flow cytometry analysis demonstrated that the encapsulated particles effectively eliminated cancer cells. The outcomes imply that AFG can be employed as a suitable delivery system to enhance the use of Th and L into the food and pharmaceutical industries.

Poly(L-lysine) modified glassy carbon electrode for sensitive electrochemical measurement of 2,3,5,6-tetramethylpyrazine

2,3,5,6-Tetramethylpyrazine (TMP), an organic compound with numerous potential health benefits, is extensively used in medical and food products. This research introduces a novel approach for the precise quantification of TMP by employing a poly(L-lysine) modified glassy carbon electrode (pLL/GCE). The pLL/GCE is fabricated through the electrochemical polymerization of L-lysine onto a glassy carbon electrode (GCE) surface. This modification enhances the electrode's electrocatalytic efficiency, resulting in a significant increase in the reduction peak current of TMP. Exploiting this distinctive property, we establish an electrochemical method for quantifying TMP using cyclic voltammetry (CV). Optimized conditions reveal a robust linear correlation between the reduction peak current of TMP and its concentration within two adjacent linearity ranges: 40.0 nmol/L to 1.0 μmol/L and 1.0 μmol/L to 100.0 μmol/L. Notably, this method achieves an impressive detection limit of 20.0 nmol/L. To validate the practicality of this approach, we analyzed various real-world samples, obtaining recovery rates ranging from 98.2% to 100.8%. The developed method holds significant promise for the determination of TMP in medical and food products, underscoring its potential for widespread application.

CV Performance of ZnO-Carbon Nanocomposite Based On ZIF-8 as Lithium-Ion Battery Anode

Compositing between metal oxide and carbon is strategy to improve the performance of lithium-ion battery anode. This is due to the high theoretical capacity of metal oxides, carbon acts as a lithium ion accelerator and supports the structural stability of metal oxides. The advantages of the ZnO-Carbon nanocomposite anode based on ZIF-8 are its large surface area and porosity. The method used is non-solvothermal through precipitation at room temperature. After obtaining ZIF-8 powder, then it was carbonized at temperatures 600°C. The characterization used were SEM, EDS and TEM. The samples also have a porous character with a nano-sized pore radius. Cyclic Voltammetry (CV) was carried out using 3-electrode system. The CV test showed 3 reduction peaks. The first peak indicated the conversion reaction, the second peak indicated the alloying reaction, and the third peak indicated a solid electrolyte interface (SEI) reaction. The highest diffusion coefficient is alloying reaction with 3.65 x 10−8 cm2/s.

Fabrication of a noveltantalum boride/vanadium carbidemodified screen-printed carbon electrode for voltammetric determination of pimonidazole in bio-fluids.

For the first time, a tumour hypoxia marker detection has been developedusing two-dimensional layered composite modified electrodes in biological and environmental samples. The concept of TaB2 and V4C3-based MXene composite materials is not reported hitherto using ball-milling and thermal methods and it remains the potentiality of the present work. Thesuccessful formation is confirmed through various characterisation techniques like X-ray crystallography, scanning electron microscopy photoelectron, and impedance spectroscopy. A reliable and repeatable electrochemical sensor based on TaB2@V4C3/SPCE was developed for quick and extremely sensitive detection of pimonidazole by various electroanalytical methods. It has been shown that the modified electrode intensifies the reduction peak current and causesa decrease in the potential for reduction, in comparison with the bare electrode. The proposed sensor for pimonidazole reduction has strong electrocatalytic activity and high sensitivity, as demonstrated by the cyclic voltammetry approach. Under the optimal experimental circumstances, differential pulse voltammetry techniques were utilised for generating the wide linear range (0.02 to 928.51µM) with a detection limit of 0.0072µM. The resultant data demonstrates that TaB2@V4C3/SPCE nano-sensor exhibits excellent stability, reliability, and repeatability in the determinationof pimonidazole. Additionally, the suggested sensor was successfully used to determine the presence of pimonidazole in several real samples, such as human blood serum, urine, water, and drugs.

Synthesis of Tin Doped Copper Oxide Nanocomposites for Electrochemical Sensor Application

Abstract Poly (Tin-doped copper oxide nanocomposites modified glassy carbon electrode) (Poly (Sn-doped CuO nanocomposite)-MGCE) made sensors were confirmed by electrochemical finding of norepinephrine (NE). The Sn-doped CuO nanocomposites were made by precipitation technique. This nanocomposite was described through scanning electron microscope and X-ray diffraction methods. To find the doped properties of the Poly (Sn-doped CuO nanocomposite)-MGCE were studied by cyclic voltammetry studies. The above studies prove that the altered electrodes have wide electroactive external area, and the reduction and oxidation peak appeared at pH 7.4 supportive electrolyte concentration 0.2 M phosphate buffer solution. Poly(Sn-doped CuO nanocomposite)-MGCE as limit of detection was low value for NE was found to be 2.22 µM and the limit of quantification values for NE was appeared as 7.41 µM, wide linear range, high sensitivity (20 to 350 µM), functional to the injection mockup analysis and the attained outcomes are acceptable, excellent reproducibility displays excessive potential in practical applications.

Electrosynthesis of toluidine blue on Fe3O4 nanoparticles modified electrodes in a deep eutectic solvent for the electrochemical determination of neurotransmitter epinephrine

The electrochemical methodology is important and challenging for rapid, simple, low-cost, sensitive, selective and reliable determination of biomolecules to diagnose and treat diseases. Our work presents the combination of the catalytic ability of a toluidine blue (TB) redox polymer and the important physical and chemical properties of Fe3O4 nanoparticles (Fe3O4NPs) to develop a new disposable sensor with advanced analytical performancecharacteristics for the determination of EP. Fe3O4NPs combined with poly(toluidine blue) (PTB) redox polymer film on a PGE support have been developed involving electropolymerization of TB in deep eutectic solvents (DES), which is a green solvent. Scanning electron microscopy (SEM) was used to evaluate the effect of the electrode composition on the surface morphology of the nanostructured PTB films, being correlated with the electrochemical characteristics observed by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV). It has been shown that combining Fe3O4NPs with PTB synthesized in DES improves the analytical properties of the sensor more than using each modifier individually due to synergistic effects. The analytical performance of PTBethaline-HCl/Fe3O4/PGE was evaluated for epinephrine (EP) reduction in the presence of an excess dopamine (DA) by DPV. The proposed sensor was used to determine EP using the reduction peak as a voltammetric signal instead of the oxidation peak usually employed to minimize possible interfering effects in biological samples. The developed sensor showed good response with high sensitivity (9.26 µA µM−1 cm−2), low detection limit (0.05 µM), wide linear range (0.19–20 µM), and excellent reproducibility (RSD 1.7 %) and repeatability (RSD 2.9 %). The practical applicability of the proposed sensor has been successfully tested for the quantification of EP in human serum and injection ampoule samples. This is a very promising analytical method for monitoring the level of EP in real samples.

Polymerase incorporation of 4-nitrophenyl modified 2′-deoxyuridine-5′-triphosphates into double-stranded DNA for direct electrochemical detection

Three novel 2′-deoxyuridine-5′-triphosphates modified with 4-nitrophenyl groups via various linkers (dUTP-N1, dUTP-N2, and dUTP-N3) were tested as bearers of reducible electroactive labels as well as substrates suitable for enzymes used in polymerase chain reaction (PCR) and recombinase polymerase amplification (RPA) with a potential application to direct electrochemical detection of double-stranded deoxyribonucleic acid (dsDNA). In cyclic and square wave voltammograms on carbon screen printed electrodes, the labeled dUTP have demonstrated distinct reduction peaks at potentials of –0.7 V to –0.9 V (phosphate buffer, pH 7.4). The reduction peak currents of dUTP-N derivatives were found to increase with their molar concentrations. The dUTP-N3 with a double bond in the linker had the lowest reduction potential (about 100 mV less negative) among the derivatives studied. Further, dUTP-N nucleotides were tested as substrates in PCR and RPA to incorporate the electroactive labels into 90, 210, or 206 base pair long dsDNA amplicons. However, only a dUTP-N1 derivative with a shorter linker without the double bond demonstrated satisfactory compatibility with both PCR and RPA, though with a low reaction output of modified dsDNA amplicons (at 100% substitution of dTTP). The dsDNA amplicons produced by PCR with 85% substitution of dTTP by the dUTP-N1 in the reaction mixture were successfully detected by square wave voltammetry at micromolar concentrations at high square wave frequency.

Oxidized carboxymethyl cellulose/polyaniline-based hybrid nanocomposite for sensitive detection of environmentally hazardous nitrophenol in real samples

Present work aims at fabricating chemically active, reproducible, and reliable electrode material by Ag nanoparticles anchored oxidized-carboxymethyl cellulose (O-CMC) embedded Pani (Ag@Pani/O-CMC) based nanocomposite for the trace detection of 4-nitrophenol. The Ag@Pani/O-CMC was physiochemically characterized in detail using FTIR, SEM, TEM, UV–vis, XPS, and XRD to analyze functional groups, structural morphology, optical properties, and chemical compositions. Differential pulse voltammetry and cyclic voltammetry were adopted to explore the electrochemical performance of Ag@Pani/O-CMC modified glassy carbon electrode (Ag@Pani/O-CMC/GCE). The observed reduction peak current was proportional to the 4-NP concentrations with a high sensitivity (2.48 µA nM−1 cm−2) and displayed a detection limit of 0.58 nM and a good linear range of 10–100 nM. In addition, the sensor exhibited comparable sensing capability in real biological samples, including milk, mixed fruit juice, and tap water, with excellent recovery from 97.20 % to 101 %. It also depicted high repeatability as the current response remained at 84.52 % after 28 days of operation for 4-NP detection. This approach can be projected to result in the electrochemical sensor for safe industrial processing and environmental monitoring, which is expected to have good stability, excellent selectivity, and sensitivity for detecting traces of 4-NP in actual samples.