Sensitive electrochemical determination of epinephrine at poly(L-aspartic acid)/electro-chemically reduced graphene oxide modified electrode by square wave voltammetry in pharmaceutics

Detection of epinephrine using a K2Fe4O7 modified glassy carbon electrode

Iron-based electrochemical catalysts used to modify electrodes for biosensing have received more attention from biosensor manufacturers because of their excellent biocompatibility and low cost. In this work, a fast-ion conductor potassium ferrite (K2Fe4O7) modified glassy carbon electrode (GCE) was prepared for detecting epinephrine (EP) by electrochemical techniques. The obtained K2Fe4O7/GCE electrode exhibited not only a wide linear range over EP concentration from 2 μM to 260 μM with a detection limit of 0.27 μM (S/N = 3) but also high selectivity toward EP in the presence of common interferents ascorbic acid (AA) and uric acid (UA), as well as good reproducibility and stability.

Laccase-Conjugated Nanostructured ZnFe2O4/rGO-Modified Electrode-Based Interfaces for Electrochemical Impedance Monitoring of Adrenaline: A Promising Biosensor for Management of Neurodegenerative Disorders

A propitious biosensor for adrenaline (AD) detection in bovine serum albumin (BSA) real samples, which can be used for diagnosis and treatment of neurodegenerative disorders, is reported here. The biosensor consists of a La/ZF/rGO/ITO bioelectrode, which is fabricated by electrophoretic deposition of zinc ferrite/reduced graphene oxide (ZF/rGO) nanohybrid followed by drop casting of laccase (La) enzymes. The material characterization and electrochemical studies revealed that the ZF/rGO nanohybrid enhanced the electroactive surface and facilitated direct electron transfer between the electrode and electrolyte interface, resulting in enhanced electrocatalytic performance. The cyclic voltammetry and electrochemical impedance spectroscopy results asserted that the ZF/rGO nanohybrid decreased the charge-transfer resistance (Rct) and increased the surface adsorption, leading to a high diffusion coefficient (D) of 0.192 cm2/s. The biosensor exhibited a high sensitivity of 0.71 Ω/μM cm2, a good linear range (0.1 to 140 μM with R2 = 0.98), and a low limit of detection (LOD) is 12.5 μM, demonstrating the synergic effect of ZF and rGO in the La/ZF/rGO/ITO bioelectrode with AD. The biosensor also exhibited high selectivity and stability (55 days) in the presence of interfering substances and in BSA samples, with a recovery percentage close to 100 ± 5% RSD, indicating its potential biosensing applications for real-world applications in disease diagnostics, monitoring, and treatment.

New approaches in antibiotics detection: The use of square wave voltammetry

Antibiotics belongs to a class of pharmaceutical compounds widely used due to their effectiveness against bacterial infections. However, if consumed or inappropriately disposed of in the environment can results in environmental and public health problems, because they are considered emerging contaminants and their residues represent damage, whether in the long or short term, to different terrestrial ecosystems, in addition to bringing potential risks to agricultural sectors, such as livestock and fish farming. For this, the development of analytical methods for low-concentration detection and identification of antibiotics in natural waters, wastewaters, soil, foods, and biological fluids is necessary. This review shows the applicability of square wave voltammetry for the analytical determination of antibiotics from different chemical classes and covers a variety of samples and working electrodes that are used as voltammetric sensors. The review involved the analysis of scientific publications from the Science Direct® and Scopus® databases, with scientific manuscripts covering the period between January 2012 and May 2023. Various manuscripts were discussed indicating the applicability of square wave voltammetry in antibiotics detection in urine, blood, natural waters, milk, among other complex samples.

A novel, extreme low-cost poly (Erythrosine) modified pencil graphite electrode for determination of Adrenaline

A simple, novel, and less cost yellow (Erythrosine) modified pencil graphite electrode (Po-ERY/MGPE) was successfully fabricated via electropolymerization method using cyclic voltammetric techniques. The fabricated Po-ERY/MGPE opted as a sensor for the detection of Adrenaline (ADR) in 0.2 M PBS (7.4 pH). This reported senor displayed excellent electrocatalytic activity, increased sensitivity, high stability, superior electron transfer kinetics in the oxidation of ADR once relative to BGPE. The significance of pH, scan rate, and impact of concentration was assessed at the sensor. As per the pH and scan rate study, redox routes carry the same number of electrons and protons, and electro-oxidation of ADR was adsorption controlled respectively. The LOD of ADR was found to be 0.499 µM. The DPV data indicate that there is a significant peak divergence among ADR and uric acid (UA) which could make it easier to determine them alone and simultaneously on the sensor. The described method has been employed for the determination of ADR in injection sample. Good recovery values indicate the efficacy and applicability of the sensor in detecting ADR.

Elucidating the complete oxidation mechanism of betanidin in an aqueous solution

An important point to take advantage of the use of antioxidants in industrial applications in a more efficient way is to know in depth their oxidation mechanism. This is not always a simple task and requires an in-depth study that is often insufficient to precisely describe all the structures and processes involved. This is the case of betanidin, a natural pigment employed in the drug, food, and cosmetic industries. In the present work, we seek to unravel the complete oxidation mechanism of betanidin with the use of computational techniques, supported by experimental data. For this aim, the pK_as and oxidation potentials of the reactions involved at different pHs were analyzed using density functional theory (DFT) with the B3LYP/6-31+G(d,p)/SMD approach. Moreover, the decomposition mechanism of the intermediate products (decarboxylation reactions) was studied deeply. The analysis of DFT results allowed the proposal of a tentative mechanism that was put to test using the digital simulations of cyclic voltammetry by comparing the results of these simulations with an experimental case. Based on the rigorous experimental analysis, DFT, and simulations of cyclic voltammetry, the complete mechanism of the oxidation of betanidin in an aqueous medium was proposed. The dimerization of the oxidation products was also considered to explain the voltammetric response of betanidin.

A nonenzymatic reduced graphene oxide-based nanosensor for parathion

Organophosphate-based pesticides (e.g., parathion (PT)) have toxic effects on human health through their residues. Therefore, cost-effective and rapid detection strategies need to be developed to ensure the consuming food is free of any organophosphate-residue. This work proposed the fabrication of a robust, nonenzymatic electrochemical-sensing electrode modified with electrochemically reduced graphene oxide (ERGO) to detect PT residues in environmental samples (e.g., soil, water) as well as in vegetables and cereals. The ERGO sensor shows a significantly affected electrocatalytic reduction peak at -0.58 V (vs Ag/AgCl) for rapid quantification of PT due to the amplified electroactive surface area of the modified electrode. At optimized experimental conditions, square-wave voltammetric analysis exhibits higher sensitivity (50.5 μA·μM^-1·cm^-2), excellent selectivity, excellent stability (≈180 days), good reproducibility, and repeatability for interference-free detection of PT residues in actual samples. This electrochemical nanosensor is suitable for point-of-care detection of PT in a wide dynamic range of 3 × 10^-11-11 × 10^-6 M with a lower detection limit of 10.9 pM. The performance of the nanosensor was validated by adding PT to natural samples and comparing the data via absorption spectroscopy. PT detection results encourage the design of easy-to-use nanosensor-based analytical tools for rapidly monitoring other environmental samples.

Fabrication of a label-free electrochemical aptasensor to detect cytochrome c in the early stage of cell apoptosis

A label-free direct electrochemical aptasensor is presented for the identification of cytochrome c (Cyt c) at the nM concentration level. Carbon nanofibers (CNF), as a highly conductive material, were used to modify a glassy carbon electrode (GCE) and thus increase its conductivity. Moreover, to enhance the immobilization of aptamers (Apt) on the electrode surface, graphene oxide functionalized with aspartic acid (GOAsp) was added to the surface. Aspartic acid with countless carboxyl groups (-COOH) on its surface caused more aptamers to be immobilized on the electrode surface. Electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and differential pulse voltammetry (DPV) were used to monitor the step-by-step fabrication of the label-free direct electrochemical aptasensor. The label-free quantification of Cyt c was also done by the direct electron transfer between the Fe(III)/Fe(II)-heme redox-active sites which were selectively bound to the aptamers on the GCE and the surface of the electrode. Under optimum conditions, the peak currents of differential pulse voltammograms at 0.26 V (vs. Ag/AgCl) were used for calibration. The proposed aptasensor performs in a wide dynamic range from 10 nM to 100 µM with a low detection limit of 0.74 nM for cytochrome c. It also has high selectivity as well as acceptable stability. These advantages make the biosensor capable of detecting early-stage apoptotic cells that contribute to early cancer diagnosis.

Electrochemically reduced graphene oxide/Cu-MOF/Pt nanoparticles composites as a high-performance sensing platform for sensitive detection of tetracycline

A promising sensing platform was constructed based on an electrochemically reduced graphene oxide (ErGO)/copper metal-organic framework (Cu-MOF)/platinum nanoparticles (ErGO/Cu-MOF/PtNPs) modified glassy carbon electrode for the detection of tetracycline. The ErGO/Cu-MOF/PtNPs composite electrode possessed an excellent electrochemical performance to tetracycline detection mainly due to the synergistic effect of ErGO, Cu-MOF and PtNPs. The electrochemical kinetics and catalytical mechanism of tetracycline were systematically studied, showing that tetracycline's electrocatalytic oxidation reaction was an absorption-controlled two-step process involving two electrons and one proton transfer, respectively. Low concentration of tetracycline was detected by amperometry with the a linear range of 1 ~ 200 μM (R² = 0.9900) and a detection limit of 0.03 μM (S/R = 3). The proposed sensor was successfully applied to the detection of tetracycline in the real water samples with recoveries of 93.5% ~ 106%, and relative standard deviations (RSD) of 4.65% ~ 5.21% (n = 3). Furthermore, acceptable stability, repeatability and reproducibility were verified for continuous determination of tetracycline under optimized conditions. The ErGO/Cu-MOF/PtNPs composite electrode also demonstrated better anti-interference performance compared to other types of antibiotics than that of similar structural tetracyclines. Therefore, the proposed ErGO/Cu-MOF/PtNPs composites might provide a potential sensing platform for detecting analogous tetracyclines or total tetracyclines in the environment.

Single-Drop Analysis of Epinephrine and Uric Acid on a Screen-Printed Carbon Electrode

This work demonstrates the analysis of epinephrine (EP) and uric acid (UA) in a single drop (the volume of the test solution was only 50 µL) using a screen-printed carbon electrode (SPCE) sensor and square-wave voltammetry (SWV). The limit of detection, limit of quantification, linearity, accuracy, precision, and robustness were validated. The normality of the experimental data was tested and confirmed for both methods. Heteroscedasticity was checked by residual analysis followed by a statistical F-test. The latter was confirmed for both analytes. The low relative standard deviations (RSD) at all calibration points and repetitive slopes justified the use of a calibration curve; therefore, the standard addition methodology was avoided (the latter is common in electroanalysis, but time-consuming). Since the conditions for using an ordinary least squares (OLS) regression were not met, weighted linear regression (WLR) was used to improve the accuracy of the analytical results at low concentrations of the analytes. In this manner, the best weighted model was determined and used for the quantification. A comparison was made between the OLS and WLR methods to show the necessity of using the WLR method for EP and UA analysis. The newly developed and validated methods were also shown to be effective in the analysis of real samples. The content of EP in an EP auto-injector and UA in human urine was tested by employing the best weighted model. For EP and UA, the accuracy in terms of the average recovery value was 101.01% and 94.35%, and precision in terms of RSD was 5.65% and 2.75%, respectively. A new analytical methodology is presented that uses a low volume (a single drop), and it offers the advantage of electroanalysis for on-site analysis, where conventional chromatographic techniques cannot be easily employed. Furthermore, the developed technique has additional advantages in terms of speed, cost, and miniaturization.

Simultaneous Removal of Antibiotics and Heavy Metals with Poly(Aspartic Acid)-Based Fenton Micromotors

The discharge of diverse pollutants has led to a complex water environment and posed a huge health threat to humans and animals. Self-propelled micromotors have recently attracted considerable attention for efficient water remediation due to their strong localized mass transfer effect. However, a single functionalized component is difficult to tackle with multiple contaminants and requires to combine different decontamination effects together. Here, we introduced a multifunctional micromotor to implement the adsorption and degradation roles simultaneously by integrating the poly(aspartic acid) (PASP) adsorbent with a MnO₂ -based catalyst. The as-prepared micromotors are well propelled in contaminated waters by MnO₂ catalyzing hydrogen peroxide. In addition, the catalytic ramsdellite MnO₂ (R-MnO₂ ) inner layer is decorated with Fe₂ O₃ nanoparticles to improve their catalytic performance, contributing to an excellent degradation ability with 90% tetracycline (TC) removal in 50 minutes by enhanced Fenton-like reactions. Combining the attractive adsorption capability of poly (aspartic acid) (PASP), the composite micromotors offer an efficient removal of heavy metal ions in short time. Moreover, the designed micromotors are able to simultaneously remove antibiotic and heavy metals in mixed contaminants circumstance just in single treatment. This multifunctional micromotor with distinctive decontamination ability exhibits a promising prospective in treating multiple pollutants in the future.

Chemically synthesized chevron-like graphene nanoribbons for electrochemical sensors development: determination of epinephrine

We employ chevron-like graphene nanoribbons (GNRs) synthesized by a solution-based chemical route to develop a novel electrochemical sensor for determination of the neurotransmitter epinephrine (EPI). The sensor surface, a glassy carbon electrode modified with GNRs, is characterized by atomic force microscopy, scanning electron microscopy and Raman spectroscopy, which show that the electrode surface modification comprises of bi-dimensional multilayer-stacked GNRs that retain their molecular structure. The charge transfer process occurring at the electrode interface is evaluated by electrochemical impedance spectroscopy. The sensor is applied to the determination of EPI, employing as an analytical signal the reduction peak corresponding to the epinephrinechrome–leucoepinephrinechrome transition (E = − 0.25 V) instead of the oxidation peak usually employed in the literature (E =  + 0.6 V) in order to minimize interferences. The results obtained demonstrate that chevron-like nanoribbons synthesized by solution methods exhibit reliable electrocatalytic activity for EPI determination. Using differential pulse voltammetry, we obtain a linear concentration range from 6.4 × 10^–6 to 1.0 × 10^–4 M and a detection limit of 2.1 × 10^–6 M. The applicability of the sensor was evaluated by determining EPI in pharmaceutical samples with satisfactory results.

Detection of Ferric Ions and Catecholamine Neurotransmitters via Highly Fluorescent Heteroatom Co-Doped Carbon Dots

Carbon dots (CDs) demonstrate very poor fluorescence quantum yield (QY). In this study, with the help of a hydrothermal method, we combined CDs with nitrogen and phosphorus elements belonging to the VA group (in the periodic table) to form heteroatom co-doped CDs, i.e., nitrogen and phosphorus co-doped carbon dots (NPCDs). These displayed a significant improvement in the QY (up to 84%), which was as much as four times than that of CDs synthesized by the same method. The as-prepared NPCDs could be used as an "off-on" fluorescence detector for the rapid and effective sensing of ferric ions (Fe3+) and catecholamine neurotransmitters (CNs) such as dopamine (DA), adrenaline (AD), and noradrenaline (NAD). The fluorescence of NPCDs was "turned off" and the emission wavelength was slightly red-shifted upon increasing the Fe3+ concentration. However, when CNs were incorporated, the fluorescence of NPCDs was recovered in a short response time; this indicated that CN concentration could be monitored, relying on enhancing the fluorescence signal of NPCDs. As a result, NPCDs are considered as a potential fluorescent bi-sensor for Fe3+ and CN detection. Particularly, in this research, we selected DA as the representative neurotransmitter of the CN group along with Fe3+ to study the sensing system based on NPCDs. The results exhibited good linear ranges with a limit of detection (LOD) of 0.2 and 0.1 µM for Fe3+ and DA, respectively.

An amperometric biosensor based on poly(L-aspartic acid), nanodiamond particles, carbon nanofiber, and ascorbate oxidase-modified glassy carbon electrode for the determination of L-ascorbic acid

An amperometric L-ascorbic acid biosensor utilizing ascorbate oxidase (AOx) immobilized onto poly(L-aspartic acid) (P(L-Asp)) film was fabricated on carbon nanofiber (CNF) and nanodiamond particle (ND)-modified glassy carbon electrode (GCE). Effects of AOx, ND, and CNF amounts were investigated by monitoring the response currents of the biosensor at different amounts of AOx, ND, and CNF. The electropolymerization step of L-aspartic acid on CNF-ND/GCE surface was also optimized. Scanning electron microscopy (SEM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) techniques were used to enlighten the modification steps of the biosensor. The effects of pH and applied potential were studied in detail to achieve the best analytical performance. Under optimized experimental conditions, the AOx/P(L-Asp)/ND-CNF/GCE biosensor showed a linear response to L-ascorbic acid in the range of 2.0 × 10^-7-1.8 × 10^-3 M with a detection limit of 1.0 × 10^-7 M and sensitivity of 105.0 μAmM^-1 cm^-2. The novel biosensing platform showed good reproducibility and selectivity. The strong interaction between AOx and the P(L-Asp)/ND-CNF matrix was revealed by the high repeatability (3.4%) and good operational stability. The AOx/P(L-Asp)/ND-CNF/GCE biosensor was successfully applied to the determination of L-ascorbic acid in vitamin C effervescent tablet and pharmaceutical powder containing ascorbic acid with good results, which makes it a promising approach for quantification of L-ascorbic acid. Graphical abstract.

Electroanalysis of Catecholamine Drugs using Graphene Modified Electrodes

Background:

Catecholamine drugs are a family of electroactive pharmaceutics, which are widely analyzed through electrochemical methods. However, for low level online determination and monitoring of these compounds, which is very important for clinical and biological studies, modified electrodes having high signal to noise ratios are needed. Numerous materials including nanomaterials have been widely used as electrode modifies for these families during the years. Among them, graphene and its family, due to their remarkable properties in electrochemistry, were extensively used in modification of electrochemical sensors.

Objective:

In this review, working electrodes which have been modified with graphene and its derivatives and applied for electroanalyses of some important catecholamine drugs are considered.

A polyoxy group branched diazo dye as an alternative material for the fabrication of an electrochemical epinephrine sensor

A polyoxy group attached diazo dye on an electrode surface improved the voltammetric response of epinephrine.