Development of carbon nanotube-based polymer-modified electrochemical sensor for the voltammetric study of Curcumin

Microwave plasma treated Sn/SnO2 and graphite nanocomposites to synergistically promote electrochemical sensing performance toward dopamine and uric acid

BACKGROUND

The investigation of biomolecules is essential due to abnormalities in biological metabolism in the human body. Dopamine (DA) and uric acid (UA) are important chemicals that coexist in biological systems and play crucial roles in various physiological processes related to human metabolism. This study explores the application of carbon and SnO2 nanoparticles for DA and UA sensing, focusing on the preparation of Sn/SnO2 nanocomposites through electrospinning and plasma treatment. The research aims to measure these concentrations quickly and accurately, offering advantages such as low manufacturing costs and environmental friendliness.

RESULT

This study presents a novel Sn/SnO2 nanocomposites as an electrocatalyst for the detection of dopamine (DA) and uric acid (UA) levels. Sn/SnO2 nanocomposites were effectively obtained by argon microwave plasma (ArMP) treatment, a dry and green process, on electrospun fibers containing SnCl2 within 120 s. The resultant Sn/SnO2 nanocomposites provide excellent electrochemical catalytic effects to quantify the levels of DA and uric acid UA, which are the two important physiological molecules. To further incorporate graphite into ArMP-Sn/SnO2 can modulate precise differentiation of the oxidation peaks of DA, UA, and ascorbic acid (AA), solving the problems of overlapped oxidation potential among biomolecules. The as-established nanocomposites revealed excellent applicability to be incorporated onto difference substrates including gold electrode (AuE), screen-printed carbon electrodes (SPCE), and flexible carbon electrodes (FCE), providing great potential for building point-of-care sensing platform.

SIGNIFICANCE

The 1%g-120s-ArMP-Sn/SnO2@AuE resulting the highest sensing performance for DA and UA, which the linear detection range was 0.1-400 μM and 0.1-900 μM, with sensitivity of 473.72 and 169.21 μA/mM.cm2, and LOD 0.003 and 0.010 μM, respectively. Additionally, in the areal human fluid matrix the sensor obtains a recovery rate between 95.28 % and 102.72 % with a high selectivity (less than 5 %) upon the presence of common interferences in body fluid.

Exploiting the Electrostatic Binding of Ruthenium Hexamine Molecular Redox Nanowires onto DNA/OGCN Biohybrid Electrodes toward the Electrochemical Detection of COVID-19

The Coronavirus Disease 2019 (COVID-19) recently emerged as a life-threatening global pandemic that has ravaged millions of lives. The affected patients are known to frequently register numerous comorbidities induced by COVID-19 such as diabetes, asthma, cardiac arrest, hypertension, and neurodegenerative diseases, to name a few. The expensiveness and probability of false negative results of conventional screening tests often delay timely diagnosis and treatment. In such cases, the deployment of a suitable biosensing platform can readily expedite the rapid diagnosis process for enhanced patient outcomes. We report the development of an electrochemical genosensor based on DNA/OGCN (DNA/oxygenated graphitic carbon nitride) nanohybrids for the quantification of severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) DNA─the key biomarker for COVID-19. This is achieved by exploiting the molecular nanowire-formation capability of the [Ru(NH3)6]2+/3+ redox probe onto the DNA phosphate backbone via electrostatic interactions. The microstructural characterization of OGCN was performed using scanning electron microscopy (SEM) coupled with an energy-dispersive X-ray (EDX) module, X-ray diffraction (XRD), and Fourier transform infrared spectroscopy. The electrochemical analyses were performed using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), while the analytical performance of the sensor was evaluated using square wave voltammetry (SWV). The developed sensor exhibited a wide linear detection range within 10 fM-10 μM, with a limit of detection (LoD) of ∼7.23 fM with a high degree of selectivity toward SARS-CoV-2 target DNA, thereby indicating its potential to be employed in a point-of-care scenario toward providing affordable healthcare to the global populace.

Electro-polymerization of modified carbon paste sensor for detecting azithromycin

Azithromycin (AM) is one of the prescribed drugs in pandemic medication treatment which has paid great attention. We developed in this study a simply modified carbon paste electrode (CPE) to detect AM using poly-threonine (PT). PT or similar polymers are used as carriers to enhance the delivery and effectiveness of AM. The work was characterised via Cyclic Voltammetry (CV), electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). We take into consideration the effects of pH, scan rate, accumulation time, interference, and calibration curve.A very sensitive response to the oxidation of 1.0 mM from AM in phosphate buffer solution (PBS) over a pH range of 5.0 to 10.0 was observed using the developed poly-threonine carbon paste electrode (PTCPE). The impact of different AM concentrations was investigated resulting in a detection limit of 0.32 µM and a quantification limit of 1.07 µM at PBS (pH 7.4). Finally, the recently used electrode realized acceptable sensitivity and consistency for AM detection in pharmaceutical drugs.

Oatmeal-derived carbon loaded with Pt nanoparticles using a "two-fold benefit approach" for sensitive detection of the biomolecule adrenaline

In this study, we innovatively synthesized nitrogen-doped carbon microspheres (NCS) derived from oatmeal. By utilizing polyoxometalates (POM) as both reducing and linking agents, we achieved uniform loading of platinum nanoparticles (Pt NPs) onto the surface of the NCS. The composite nanoparticles constructed from Pt/polyoxometalate/nitrogen-doped carbon microspheres (Pt/POM/NCS) fully exploit the synergistic catalytic effect, demonstrating superior performance in adrenaline detection. The method has a linear range of 2.59 to 1109.59 μM, a detection limit as low as 0.25 μM (S/N = 3), and a sensitivity of 0.74 μA μM-1 cm-2. Additionally, it exhibits high stability and strong anti-interference ability. The recoveries in human serum were 98.51 % to 101.25 %.

CoWO4/Reduced Graphene Oxide Nanocomposite-Modified Screen-Printed Carbon Electrode for Enhanced Voltammetric Determination of 2,4-Dichlorophenol in Water Samples

Water pollution with phenolic compounds is a serious environmental issue that can pose a major threat to the water sources. This pollution can come from various agricultural and industrial activities. Phenolic compounds can have detrimental effects on both human health and the environment. Therefore, it is essential to develop and improve analytical methods for determination of these compounds in the water samples. In this work, the aim was to design and develop an electrochemical sensing platform for the determination of 2,4-dichlorophenol (2,4-DCP) in water samples. In this regard, a nanocomposite consisting of CoWO4 nanoparticles (NPs) anchored on reduced graphene oxide nanosheets (rGO NSs) was prepared through a facile hydrothermal method. The formation of the CoWO4/rGO nanocomposite was confirmed via different characterization techniques. Then, the prepared CoWO4/rGO nanocomposite was used to modify the surface of a screen-printed carbon electrode (SPCE) for enhanced determination of 2,4-DCP. The good electrochemical response of the modified SPCE towards the oxidation of 2,4-DCP was observed by using cyclic voltammetry (CV) due to the good properties of CoWO4 NPs and rGO NSs along with their synergistic effects. Under optimized conditions, the CoWO4/rGO/SPCE sensor demonstrated a broad linear detection range (0.001 to 100.0 µM) and low limit of detection (LOD) (0.0007 µM) for 2,4-DCP determination. Also, the sensitivity of CoWO4/rGO/SPCE for detecting 2,4-DCP was 0.3315 µA/µM. In addition, the good recoveries for determining spiked 2,4-DCP in the water samples at the surface of CoWO4/rGO/SPCE showed its potential for determination of this compound in real samples.

Creative synthesis of pH-dependent nanoporous pectic acid grafted with acrylamide and acrylic acid copolymer as an ultrasensitive and selective riboflavin electrochemical sensor in real samples

In current research, an innovative pectic acid was grafted with poly (acrylamide-co-acrylic acid) [PA-g-poly (AAm-co-AA)] nanoporous membrane using a free radical-mediated grafting copolymerization process. The optimized parameters for the grafting copolymerization reaction such as initiator concentration, monomer concentrations, polymerization reaction time, and temperature were studied. Additionally, the solid content, graft percentage, and conversion were calculated. The unique polymeric membrane was characterized using Fourier-transform infrared spectroscopy (FT-IR), thermal gravimetry (TG), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) supported by energy dispersive X-ray spectroscopy (EDX). The formulated novel PA-g-poly (AAm-co-AA) had a nanoporous structure with a diameter of 113 nm. pH-dependent swelling and biodegradation measurements were also studied. The electrochemical characterizations of PA-g-poly (AAm-co-AA) were conducted through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Furthermore, the screen-printed electrode (SPE) was modified with pure PA and the new generation of its grafted polymeric nanoparticles to detect and quantify the concentration of riboflavin (RF) in real samples using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques. The modified electrode showed two linear concentration ranges from 0.01 - 2 nM and 2 - 90 nM with low detection limits (LODs) of 0.004 and 0.97 nM, respectively, demonstrating high sensitivity. Besides, the fabricated sensor exhibited more selectivity, simplicity, great reproducibility, repeatability, and good stability. Finally, the PA-g-poly (AAm-co-AA)-modified SPE based sensor was effectively used in real sample analysis of egg yolk, milk, and vitamin B2 drugs with good recovery rates.

Simultaneous Determination of Sulfamethoxazole and Trimethoprim from Clinical Urine and Blood Serum Samples by the Application of Poly(Cu2P4BCL4)/GCE

Synthetic antibiotics known as sulfonamides suppress the synthesis of tetrahydrofolic acid, which cures respiratory tract infections and protozoal infections by preventing the creation of dihydrofolic acid. Electrochemical sensors based on tetrakis(1,10-phenanthroline)-μ-(4,4'-bipyridine) dicopper(II) chloride monohydrate ([P2Cu-Bip-CuP2]Cl4·H2O or simply Cu2P4BCl4) have been successfully applied for the determination of sulfamethoxazole (SMX) and trimethoprim (TMP) from samples. The experimental conditions and parameters were optimized to achieve the best electrode performances for simultaneous quantification of SMX and TMP. Based on the analysis of the effect of scan rate on the peak parameters, the R 2 for the peak current vs square root of the scan rate was greater than that of the peak current vs scan rate, indicating diffusion-controlled behavior of both species. The current intensities of both SMX and TMP were highly improved due to surface activation of the electrodes by electropolymerization. For SMX, the limit of detection was determined to be 27.94 nM, while for TMP, it was 21.56 nM, and the limit of quantifications was 71.88 nM, and the corresponding relative standard deviation for each was 0.74% and 0.11%. The constructed electrode was stored for varying durations ranging from two h to 2 days, and it was found to be above 97% stable after storing for 15 days. The real applicability of the suggested sensor for the simultaneous determination of SMX and TMP was verified by sensing clinical serum and urine samples and their spike recovery studies.

Investigation of green synchronous spectrofluorimetric approach for facile sensitive estimation of two co-administered anti-cancer drugs; curcumin and doxorubicin in their laboratory-prepared mixtures, human plasma, and urine

Recently, phytochemicals play an important role in cancer management. Curcumin (CUR), a natural phytochemical, has been co-administered with widespread chemotherapeutic agents such as doxorubicin (DOX) due to its excellent antitumor activity and the ability to lower the adverse reactions and drug resistance cells associated with DOX use. The present study aims to determine DOX and CUR utilizing a label-free, selective, sensitive, and precise synchronous spectrofluorimetric method. The obvious overlap between the emission spectra of DOX and CUR prevents simultaneous estimation of both analytes by conventional spectrofluorimetry. To solve such a problem, synchronous spectrofluorimetric measurements were recorded at Δλ = 20 nm, utilizing ethanol as a diluting solvent. Curcumin was recorded at 442.5 nm, whereas DOX was estimated at 571.5 nm, each at the zero-crossing point of the other one. The developed method exhibited linearity over a concentration range of 0.04-0.40 μg/mL for CUR and 0.05-0.50 μg/mL for DOX, respectively. The values of limit of detection (LOD) were 0.009 and 0.012 µg/mL, while the values of limit of quantitation (LOQ) were 0.028 and 0.037 µg/mL for CUR and DOX, respectively. The adopted approach was carefully validated according to the guidelines of ICH Q2R1. The method was utilized to estimate CUR and DOX in laboratory-prepared mixtures and human biological matrices. It showed a high percentage of recoveries with minimal RSD values. Additionally, three different tools were utilized to evaluate the greenness of the proposed approach.

A dual-signal output electrochemical aptasensor for glypican-3 ultrasensitive detection based on reduced graphene oxide-cuprous oxide nanozyme catalytic amplification strategy

Glypican-3 (GPC3) is an essential reference target for hepatocellular carcinoma detection, follow-up and prediction. Herein, a dual-signal electrochemical aptasensor based on reduced graphene oxide-cuprous oxide (RGO-Cu2O) nanozyme was developed for GPC3 detection. The RGO-Cu2O nanoenzyme displayed excellent electron transport effect, large specific surface area and outstanding peroxidase-like ability. The differential pulse voltammetry (DPV) signal of Cu2O oxidation fraction and the chronoamperometry (i-t) signal of H2O2 decomposition catalyzed by RGO-Cu2O nanozyme were used as dual-signal detection. Under optimal conditions, the log-linear response ranges were 0.1 to 500.0 ng/mL with the limit of detection 0.064 ng/mL for DPV technique, and 0.1-50.0 ng/mL for i-t technique (detection limit of 0.0177 ng/mL). The electrochemical aptasensor has remarkably analytical performance with wide response range, low detection limit, excellent repeatability and specificity, good recovery in human serum samples. The two output signals of one sample achieve self-calibration of the results, effectively avoiding the occurrence of possible leakage and misdiagnosis of a single detection signal, suggesting that it will be a promising method in the early biomarker detection.

Real samples sensitive dopamine sensor based on poly 1,3-benzothiazol-2-yl((4-carboxlicphenyl)hydrazono)acetonitrile on a glassy carbon electrode

Herein, a novel electrochemical sensor that was used for the first time for sensitive and selective detection of dopamine (DA) was fabricated. The new sensor is based on the decoration of the glassy carbon electrode surface (GC) with a polymer film of 1,3-Benzothiazol-2-yl((4-carboxlicphenyl)hydrazono)) acetonitrile (poly(BTCA). The prepared (poly(BTCA) was examined by using different techniques such as 1H NMR, 13C NMR, FTIR, and UV-visible spectroscopy. The electrochemical investigations of DA were assessed using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The results obtained showed that the modifier increased the electrocatalytic efficiency with a noticeable increase in the oxidation peak current of DA in 0.1 M phosphate buffer solution (PBS) at an optimum pH of 7.0 and scan rate of 200 mV/s when compared to unmodified GC. The new sensor displays a good performance for detecting DA with a limit of detection (LOD 3σ), and limit of quantification (LOQ 10σ) are 0.28 nM and 94 nM respectively. The peak current of DA is linearly proportional to the concentration in the range from 0.1 to 10.0 µM. Additionally, the fabricated electrode showed sufficient reproducibility, stability, and selectivity for DA detection in the presence of different interferents. The proposed poly(BTCA)/GCE sensor was effectively applied to detect DA in the biological samples.

A Sensitive Enzymatic Electrochemical Biosensor for Cholesterol Based on Cobalt Ferrite@Molybdenum Disulfide/Gold Nanoparticles

Cholesterol is essential in biological systems, and the level of cholesterol in the body of a person acts as a diagnostic marker for a variety of diseases. So, in this work, we fabricated an enzymatic electrochemical biosensor for cholesterol using cobalt ferrite@molybdenum disulfide/gold nanoparticles (CoFe2O4@MoS2/Au). The synthesized composite was used for the determination of cholesterol by voltametric methods. The electroactive material CoFe2O4@MoS2/Au was successfully verified from the physiochemical studies such as XRD, Raman, FT-IR, and XPS spectroscopy along with morphological FESEM and HRTEM characterization. CoFe2O4@MoS2/Au showed outstanding dispersion in the aqueous phase, a large effective area, good biological compatibility, and superior electronic conductivity. The microflower-like CoFe2O4@MoS2/Au was confirmed by scanning electron microscopy. The image of transmission electron microscopy showed decoration of gold nanoparticles on CoFe2O4@MoS2 surfaces. Furthermore, a one-step dip-coating technique was used to build the biosensor used for cholesterol detection. In addition to acting as an enabling matrix to immobilize cholesterol oxidase (ChOx), CoFe2O4@MoS2/Au contributes to an increase in electrical conductivity. The differential pulse voltammetry method was used for the quantitative measurement of cholesterol. The calibration curve for cholesterol was linear in the concentration range of 5 to 100 μM, with a low limit of detection of 0.09 μM and sensitivity of 0.194 μA μM-1 cm-2. Furthermore, the biosensor demonstrates good practicability, as it was also employed for identifying cholesterol in real samples with acceptable selectivity and stability.

Novel reusable and switchable deep eutectic solvent for extraction and determination of curcumin in water and food samples

For the first time, a fast and easy extraction method based on a unique reusable and switchable deep eutectic solvent (made of octylamine, succinic acid, and water as precursors) was presented and utilized for the microextraction and determination of curcumin as a model analyte. The main factors used to induce a phase transition in the as-prepared deep eutectic solvent were solutions of NaOH and HCl. Among the standout characteristics of the suggested deep eutectic solvent are the removal of toxic organic solvents like THF, the lack of a need for centrifugation, and the ability to be reused in subsequent extractions. The influence of effective parameters (i.e., proportions of deep eutectic solvent structure components, volume of prepared deep eutectic solvent, volume and concertation of NaOH, volume of HCl, and salt effect) on the extraction procedure were investigated. The calibration curve also was linear in the range of 35-500 μg L-1 with coefficients of determination (R2) of 0.9976. Limit of detection (S/N = 3) 10.0 μg L-1, the limit of quantification (LOQ) of 35.0 μg L-1, the relative standard deviations (RSDs %) composed of intra-day RSD (4.7) and inter-day RSD (6.4), preconcentration factor of 40.0, enrichment factor of 38.68, and relative recovery of 92.6%-100.3 % were achieved. The reusable and switchable deep eutectic solvent based-dispersive liquid-liquid microextraction technique was proficiently employed to expedite easy and fast extraction of curcumin from water and food samples.

Electrochemical Sensing of Curcumin: A Review

Curcumin is a natural polyphenol derived from turmeric (Curcuma longa) root that has been used for centuries as a spice, coloring agent, and medicine. Curcumin presents anti-inflammatory, antioxidant, anticarcinogenic, antimicrobial, antiviral, antimalarial, hepatoprotective, thrombosuppressive, cardiovascular, hypoglycemic, antiarthritic, and anti-neurodegenerative properties. It scavenges different forms of free radicals and acts on transcription factors, growth factors and their receptors, cytokines, enzymes, and genes, regulating cell proliferation and apoptosis. Curcumin is electroactive, and a relationship between its electron transfer properties and radical-scavenging activity has been highlighted. The objective of this review is to provide a comprehensive overview of the curcumin electron transfer reactions, with emphasis on the controversial aspects related to its oxidation mechanism. The final sections will focus on the electroanalysis of curcumin in natural products, highlighting the most important sensing strategies, based on functional electrodes and nanostructured materials, essential for the development of more efficient in vitro methods of detection and quantification of curcumin in food samples, supplements, and nutripharmaceuticals.

Activated Screen-Printed Boron-Doped Diamond Electrode for Rapid and Highly Sensitive Determination of Curcumin in Food Products

Due to a great interest in the beneficial properties of polyphenolic antioxidant curcumin (CCM), sensitive and accurate methods for determining CCM are needed. The purpose of our research was to develop a very simple, fast, and sensitive differential pulse adsorptive stripping voltammetric (DPAdSV) procedure using an electrochemically activated screen-printed boron-doped diamond electrode (aSPBDDE) for the determination of CCM. The activation of the SPBDDE was accomplished in a solution of 0.1 mol/L NaOH by performing five cyclic voltammetric scans in the range of 0-2 V, at ν of 100 mV/s. The changes in surface morphology and the reduction of the charge transfer resistance due to the activation of the electrode resulted in the amplification of the CCM analytical signal on the aSPBDDE. As a result, an extremely sensitive measurement tool was formed, which under optimized conditions (0.025 mol/L PBS of pH = 2.6, Eacc of 0.3 V, tacc of 90 s, ΔEA of 100 mV, ν of 150 mV/s, and tm of 10 ms) allowed us to obtain a limit of detection (LOD) of 5.0 × 10-13 mol/L. The aSPBDDE has proven to be a highly effective tool for the direct determination of CCM in food samples with high accuracy and precision. The results are in agreement with those obtained using ultra-high-performance liquid chromatography coupled with mass spectrometry and electrospray ionization (UHPLC-ESI/MS).

Greener Stability-Indicating HPLC Approach for the Determination of Curcumin in In-House Developed Nanoemulsion and Curcuma longa L. Extract

Despite the fact that several analytical methodologies have been reported for the determination of curcumin (CCM) in a wide range of sample matrices, the greener liquid chromatographic approaches to determine CCM are scarce in the literature. Therefore, this research is designed to develop and validate a greener stability-indicating “high-performance liquid chromatography (HPLC)” methodology to determine CCM in an in-house developed nanoemulsion, Curcuma longa L. extract, and commercial tablets. CCM was measured on a Nucleodur (150 mm × 4.6 mm) RP C18 column with 5 µm-sized particles. Ethanol and ethyl acetate (83:17 v/v) made up the greener eluent system, which was pumped at a flow speed of 1.0 mL/min. At a wavelength of 425 nm, CCM was detected. The greener HPLC methodology was linear in the 1–100 µg/mL range, with a determination coefficient of 0.9983. The greener HPLC methodology for CCM estimation was also rapid (Rt = 3.57 min), accurate (%recoveries = 98.90–101.85), precise (%CV = 0.90–1.11), and sensitive (LOD = 0.39 µg/mL and LOQ = 1.17 µg/mL). The AGREE approach predicted the AGREE score of 0.81 for the established HPLC technique, indicating an outstanding greenness profile. The utility of the greener HPLC methodology was demonstrated by determining CCM in the in-house developed nanoemulsion, Curcuma longa extract, and commercial tablets. The % amount of CCM in the in-house developed nanoemulsion, Curcuma longa extract, and commercial tablets was found to be 101.24%, 81.15%, and 78.41%, respectively. The greener HPLC methodology was able to detect its degradation product under various stress conditions, suggesting its stability-indication characteristics. These results suggested that CCM in developed nanoemulsion, plant extract samples, and commercial tablets may be routinely determined using the greener HPLC methodology.

Synthesis and Characterization of NiCoPt/CNFs Nanoparticles as an Effective Electrocatalyst for Energy Applications

In this work, three nanoparticle samples, Ni4Co2Pt/CNFs, Ni5CoPt/CNFs and Ni6Pt/CNFs, were designed according to the molar ratio during loading on carbon nanofibers (CNFs) using electrospinning and carbonization at 900 °C for 7 h in an argon atmosphere. The metal loading and carbon ratio were fixed at 20 and 80 wt%, respectively. Various analysis tools were used to investigate the chemical composition, structural, morphological, and electrochemical (EC) properties. For samples with varying Co%, the carbonization process reduces the fiber diameter of the obtained electrospun nanofibers from 200-580 nm to 150-200 nm. The EDX mapping revealed that nickel, platinum, and cobalt were evenly and uniformly incorporated into the carbonized PVANFs. The prepared Ni-Co-Pt/CNFs have a face-centered cubic (FCC) structure with slightly increased crystallite size as the Co% decreased. The electrocatalytic properties of the samples were investigated for ethanol, methanol and urea electrooxidation. Using cyclic voltammetry (CV), chronoamperometry, and electrochemical impedance measurements, the catalytic performance and electrode stability were investigated as a function of electrolyte concentration, scan rate, and reaction time. When Co is added to Ni, the activation energy required for the electrooxidation reaction decreases and the electrode stability increases. In 1.5 M methanol, the Ni5CoPt/CNFs electrode showed the lowest onset potential and the highest current density (30.6 A/g). This current density is reduced to 28.2 and 21.2 A/g for 1.5 M ethanol and 0.33 M urea, respectively. The electrooxidation of ethanol, methanol, and urea using our electrocatalysts is a combination of kinetic/diffusion control limiting reactions. This research provided a unique approach to developing an efficient Ni-Co-Pt-based electrooxidation catalyst for ethanol, methanol and urea.

Electrocatalytic Determination of Hydroxychloroquine Using Sodium Dodecyl Sulphate Modified Carbon Nanotube Paste Electrode

Selective, sensitive, easy, and fast voltammetric techniques were developed for the analysis of Hydroxychloroquine (HCQ). These analysis were carried out at sodium dodecyl sulphate modified carbon nanotube paste electrode (SDSMCNTPE) using an aqueous 0.2 M phosphate buffer solution as supporting electrolyte. The field emission-scanning electron microscopy, cyclic voltammetry (CV), and electrochemical impedance spectroscopy were used for material characterization. A minute quantity of the SDS surfactant was sufficient to convey an outstanding electrocatalytic action to the electrochemical oxidation nature of HCQ. The HCQ molecule parades only electrochemical oxidation (irreversible) with the transfer of two electrons. The detection of HCQ was carried out through CV method at SDSMCNTPE and bare carbon nanotube paste electrode (BCNTPE). The corresponding analytical curve offered a decent linear nature in the considered HCQ concentration range (10-40 µM) and the detection limit was found to be 0.85 µM. The significant peak to peak split-up was observed between HCQ and interferents with a decent sensitivity and stability. The SDSMCNTPE to be an approachable electrode for the usage in the examination of HCQ independently and in the presence of paracetamol (PC) and ascorbic acid (AA). Thus, they were used to determine HCQ in pharmaceutical formulations and the results that showed good agreement with comparative methods. Furthermore, a mechanism for HCQ electro-oxidation was proposed.

Electro-Polymerized Titan Yellow Modified Carbon Paste Electrode for the Analysis of Curcumin

A modest, efficient, and sensitive chemically modified electrode was fabricated for sensing curcumin (CRC) through an electrochemically polymerized titan yellow (TY) modified carbon paste electrode (PTYMCPE) in phosphate buffer solution (pH 7.0). Cyclic voltammetry (CV) linear sweep voltammetry (LSV) and differential pulse voltammetry (DPV) approaches were used for CRC detection. PTYMCPE interaction with CRC suggests that the electrode exhibits admirable electrochemical response as compared to bare carbon paste electrode (BCPE). Under the optimized circumstances, a linear response of the electrode was observed for CRC in the concentration range 2 × 10−6 M to 10 × 10−6 M with a limit of detection (LOD) of 10.94 × 10−7 M. Moreover, the effort explains that the PTYMCPE electrode has a hopeful approach for the electrochemical resolution of biologically significant compounds. Additionally, the proposed electrode has demonstrated many advantages such as easy preparation, elevated sensitivity, stability, and enhanced catalytic activity, and can be successfully applied in real sample analysis.

Electro-oxidation of formoterol fumarate on the surface of novel poly(thiazole yellow-G) layered multi-walled carbon nanotube paste electrode

The current study explicates the electro-oxidation behavior of formoterol fumarate (FLFT) in the presence of uric acid (UA) on the surface of poly thiazole yellow-G (TY-G) layered multi-walled carbon nanotube paste electrode (MWCNTPE). The modified (Poly(TY-G)LMWCNTPE) and unmodified (MWCNTPE) electrode materials were characterized through electrochemical impedance spectroscopy (EIS), field emission scanning electron microscopy (FE-SEM), and cyclic voltammetry (CV) approaches. The characterization data confirms the good conducting and electrocatalytic nature with more electrochemical active sites on the Poly(TY-G)LMWCNTPE than MWCNTPE towards the FLFT analysis in the presence of UA. Poly(TY-G)LMWCNTPE easily separates the two drugs (FLFT and UA) even though they both have nearer oxidation peak potential. The electro-catalytic activity of the developed electrode is fast and clear for FLFT electro-oxidation in 0.2 M phosphate buffer (PB) of pH 6.5. The Poly(TY-G)LMWCNTPE offered a well-resolved peak with the highest electro-oxidation peak current at the peak potential of 0.538 V than MWCNTPE. The potential scan rate and oxidation peak growth time studies show the electrode reaction towards FLFT electro-oxidation is continued through a diffusion-controlled step. The variation of concentration of FLFT in the range from 0.2 to 1.5 µM (absence of UA) and 3.0 to 8.0 μM (presence of UA) provides a good linear relationship with increased peak current and a lower limit of detection (LOD) values of 0.0128 µM and 0.0129 µM, respectively. The prepared electrode gives a fine recovery for the detection of FLFT in the medicinal sample with acceptable repeatability, stability, and reproducibility.

A high-performance voltammetric methodology for the ultra-sensitive detection of riboflavin in food matrices based on graphene oxide-covered hollow MnO2 spheres

A high-performance voltammetric methodology was developed to achieve ultra-sensitive detection of riboflavin, employing an electrode modified by graphene oxide-covered hollow MnO₂ spheres nanocomposite with high catalytic activity, large surface area, and hierarchical layered structure. Under the optimal conditions, the current responses of the oxidation peak located at -0.39 V showed a good linear relationship versus the concentration of riboflavin in the range of 1.0 nM-4.0 μM in acetate buffer (pH 5.4). The limit of detection was determined as 0.26 nM. Moreover, the proposed electrode exhibited high reproducibility (relative standard deviation of 1.7%, n = 10) and excellent stability (97.6% sensitivity within two months), which has been successfully applied to the quantification of riboflavin in complicated food matrices, with results in good accordance with those obtained by chromatography as a reference method, indicating it is an effective sensing platform for ultra-sensitive determination of riboflavin in practical applications.

Addressing the surface coverage of Au nano-agglomerates and the electrochemical properties of modified carbon paste electrodes: Experimental and theoretical studies on ascorbic acid oxidation

This article shows the formation of Au nano-agglomerates when increasing amounts of gold nanoparticles (AuNP) are incorporated into carbon paste electrodes. The surface coverage by this agglomerates is related to the electro-oxidation of a widely studied redox compound, ascorbic acid (AA); by analyzing the effect on the oxidation peak potential (E_p,a) and oxidation peak current (i_p,a). The effects of pH and scan rate on the E_p,a and i_p,_a were investigated by cyclic voltammetry, and enabled to estimate the transfer coefficient and the number of electrons involved in the rate determining step (αn_α), the standard heterogeneous rate constant (k_s), and the diffusion coefficient of the redox compound, being 0.52 and 3.5 × 10^-3 cm s^-1 and 6.3 × 10^-6 cm² s^-1, respectively. On the other hand, the sensing ability of the modified electrode was evaluated, obtaining a sensitivity of (63.2 ± 2.5) μA mM^-1, a detection limit of 2.7 μM and a quantification limit of 8.9 μM. Additionally, a computational model based on lattice-gas model and Monte Carlo simulations in the Grand Canonical Ensemble was proposed in order to reproduce the behavior of the system, in terms of i_p,a and E_p,a shift with increasing surface coverage by Au nano-agglomerates.