Electrochemically Reduced Graphene Oxide as Screen‐printed Electrode Modifier for Fenamiphos Determination

Emerging carbonaceous material based on residual grape seed applied in selective and sensitive electrochemical detection of fenamiphos

Fenamiphos (FNP) is a pesticide applied for soil pest control, particularly nematodes, and sucking insects, including aphids and thrips. Despite its use being banned in several countries due to its highly toxic nature for living beings, including mammals, because of its acetylcholine-inhibiting action, it is still marketed for use in agriculture. Therefore, a carbon paste electrode modified with residual grape seed biochar (bSU), served as an electrochemical sensor (E-bSU) for the quantification of fenamiphos in grape juice, tap water, and river water samples. The bSU underwent comprehensive characterization employing elemental, morphological, and spectroscopic analysis techniques. The impact of electrode modification and the electrochemical behavior of the FNP were systematically assessed through cyclic voltammetry, electrochemical impedance spectroscopy and differential pulse voltammetry. The biochar manifested a microporous surface adorned with dispersed functional groups, enhancing its affinity for organic compounds, particularly the investigated pesticide. Electrode modification and the optimization of analysis parameters resulted in a notable 6-fold amplification of the electrochemical signal of FNP relative to initial conditions, underscoring the efficacy of the E-bSU. The developed methodology attained limits of detection and quantification of 0.3 and 0.9 nmol L⁻1, respectively. Repeatability and reproducibility assays demonstrated relative standard deviations below 5%, underscoring the reliability of the applied electrode. The sensor showcased recoveries ranging from 99.75% to 109.9% across the analyzed samples, highlighting the utility of this selective, stable, and reproducible sensor for fenamiphos determination.

Precision phenylalanine sensing in blood with nanomaterial-enhanced electrodes

Phenylketonuria (PKU) is a genetic disorder associated with the metabolic dysfunction of the phenylalanine hydroxylase enzyme, which catalyses the conversion of l-phenylalanine (Phe) to l-tyrosine. Elevated levels of phenylalanine disrupt the central nervous system by impairing the myelination process and leading to mental retardation. Currently, commonly used diagnostic methods for PKU include the Guthrie test, liquid chromatography, and tandem mass spectrometry, all of which necessitate sophisticated infrastructure and costly equipment. Conversely, electrochemical detection methods hold promise in clinical diagnosis due to their high accuracy, rapid response time, and user-friendly nature. The choice of electrodes in electrochemical methods significantly influences sensitivity and analytical performance. In this study, we evaluated the performance of various nanomaterial-modified electrodes and compared their responses to the redox reaction of phenylalanine, focusing on detection capabilities in blood samples. Specifically, we examined carbon nanotube-gold nanoparticle modified carbon electrode (C-CNT-GNP), graphene-gold nanoparticle modified carbon electrode (C-GPH-GNP), electrochemically reduced graphene oxide (ERGO) modified carbon electrode (C-ERGO), bare carbon electrode (C-BARE), ERGO modified gold electrode (Au-ERGO), and bare gold electrode (Au-BARE) using amperometric detection. The performance of these electrodes was compared in terms of their limit of detection (LOD), limit of quantification (LOQ), and sensitivity. Among all electrodes, ERGO gold electrode showed the lowest LOD, LOQ, and highest sensitivity. This study highlights the potential of ERGO-modified gold electrodes for enhancing electrocatalytic activity, thus offering promising prospects for further diagnostic applications.

Carbon Nanomaterials-Based Screen-Printed Electrodes for Sensing Applications

Electrochemical sensors consisting of screen-printed electrodes (SPEs) are recurrent devices in the recent literature for applications in different fields of interest and contribute to the expanding electroanalytical chemistry field. This is due to inherent characteristics that can be better (or only) achieved with the use of SPEs, including miniaturization, cost reduction, lower sample consumption, compatibility with portable equipment, and disposability. SPEs are also quite versatile; they can be manufactured using different formulations of conductive inks and substrates, and are of varied designs. Naturally, the analytical performance of SPEs is directly affected by the quality of the material used for printing and modifying the electrodes. In this sense, the most varied carbon nanomaterials have been explored for the preparation and modification of SPEs, providing devices with an enhanced electrochemical response and greater sensitivity, in addition to functionalized surfaces that can immobilize biological agents for the manufacture of biosensors. Considering the relevance and timeliness of the topic, this review aimed to provide an overview of the current scenario of the use of carbonaceous nanomaterials in the context of making electrochemical SPE sensors, from which different approaches will be presented, exploring materials traditionally investigated in electrochemistry, such as graphene, carbon nanotubes, carbon black, and those more recently investigated for this (carbon quantum dots, graphitic carbon nitride, and biochar). Perspectives on the use and expansion of these devices are also considered.

Electrochemical Sensors Based on a Composite of Electrochemically Reduced Graphene Oxide and PEDOT:PSS for Hydrazine Detection

In this study, hydrazine sensors were developed from a composite of electrochemically reduced graphene oxide (ErGO) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), deposited onto a glassy carbon electrode (GCE). The structural properties, electrochemical characterization, and surface morphologies of this hydrazine sensor were characterized by Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM). In addition, the proposed hydrazine sensor also demonstrates good electrochemical and analytical performance when investigated using cyclic voltammetry (CV), differential pulse voltammetry (DPV), and amperometry techniques under optimal parameters. Using these investigated parameters, DPV and amperometry were chosen as techniques for hydrazine measurements and showed a linear range of concentration in the range of 0.2-100 μM. The obtained limits of detection and limits of quantitation for hydrazine measurements were 0.01 and 0.03 μM, respectively. In addition, the proposed sensor demonstrated good reproducibility and stability in hydrazine measurements in eight consecutive days. This fabricated hydrazine sensor also exhibited good selectivity against interference from Mg²⁺, K⁺, Zn²⁺, Fe²⁺, Na⁺, NO₂ ^-, CH₃COO^-, SO₄ ^2-, Cl^-, ascorbic acid, chlorophenol, and triclosan and combined interferences, as well as it depicted %RSD values of less than 5%. In conclusion, this proposed sensor based on GCE modified with ErGO/PEDOT:PSS displays exceptional electrochemical performance for use in hydrazine measurements and have the potential to be employed in practical applications.

Graphene-Binding Peptide in Fusion with SARS-CoV-2 Antigen for Electrochemical Immunosensor Construction

The development of immunosensors to detect antibodies or antigens has stood out in the face of traditional methods for diagnosing emerging diseases such as the one caused by the SARS-CoV-2 virus. The present study reports the construction of a simplified electrochemical immunosensor using a graphene-binding peptide applied as a recognition site to detect SARS-CoV-2 antibodies. A screen-printed electrode was used for sensor preparation by adding a solution of peptide and reduced graphene oxide (rGO). The peptide-rGO suspension was characterized by scanning electron microscopy (SEM), Raman spectroscopy, and Fourier transform infrared spectroscopy (FT-IR). The electrochemical characterization (electrochemical impedance spectroscopy-EIS, cyclic voltammetry-CV and differential pulse voltammetry-DPV) was performed on the modified electrode. The immunosensor response is based on the decrease in the faradaic signal of an electrochemical probe resulting from immunocomplex formation. Using the best set of experimental conditions, the analytic curve obtained showed a good linear regression (r² = 0.913) and a limit of detection (LOD) of 0.77 μg mL^-1 for antibody detection. The CV and EIS results proved the efficiency of device assembly. The high selectivity of the platform, which can be attributed to the peptide, was demonstrated by the decrease in the current percentage for samples with antibody against the SARS-CoV-2 S protein and the increase in the other antibodies tested. Additionally, the DPV measurements showed a clearly distinguishable response in assays against human serum samples, with sera with a response above 95% being considered negative, whereas responses below this value were considered positive. The diagnostic platform developed with specific peptides is promising and has the potential for application in the diagnosis of other infections that lead to high antibody titers.

An electrochemical sensor based on a Co3O4-ERGO nanocomposite modified screen-printed electrode for detection of uric acid in artificial saliva

In this study, we report the fabrication of a nanocomposite consisting of Co₃O₄ nanoparticles (Co₃O₄ NPs) and electrochemically reduced graphene oxide (ERGO) on a screen-printed electrode (SPE) and its sensing performance in the electrochemical detection of uric acid (UA). The surface modification of the electrode was confirmed by using a variety of characterization techniques (FE-SEM, XRD, AFM, EDX, WCA, FTIR, and Raman spectroscopy). In addition, the surface modification was electrochemically characterized step by step through CV, EIS and DPV techniques, and the results showed that the Co₃O₄-ERGO nanocomposite exhibited highly sensitive and selective sensing performance towards the oxidation of UA in 0.1 M (pH 7.0) phosphate buffer solution (PBS). The sensor (Co₃O₄-ERGO/SPE) signals were observed to be linear to the UA concentration in the range of 5 μM to 500 μM (R² = 0.9985). After revealing its other performance characteristics, such as repeatability, reproducibility, stability, sensitivity, and selectivity, the sensor was successfully applied to the analysis of UA in artificial saliva samples.

Label-free aptasensor for p24-HIV protein detection based on graphene quantum dots as an electrochemical signal amplifier

Human immunodeficiency virus (HIV) is still considered a pandemic, and the detection of p24-HIV protein has an important role in the early diagnosis of HIV in adults and newborns. The accessibility of these trials depends on the price and execution difficulty of the method, which can be reduced using electrochemical methods by using enzymeless approaches, disposable and accurate devices. In this work, graphene quantum dots were acquired by a simple synthesis and employed as an electrochemical signal amplifier and support for the aptamer immobilization through a feasible and stable modification of disposable screen-printed electrodes. The device has been easily assembled and used to detect p24-HIV protein without the interference of similar proteins or sample matrix. Using the best set of experimental conditions, a linear correlation between analytical signal and log of p24-HIV concentration from 0.93 ng mL^-1 to 93 μg mL^-1 and a limit of detection of 51.7 pg mL^-1 were observed. The developed device was applied to p24 determination in spiked human serum and provided distinct levels of signal for positive and negative samples, successfully identifying real samples with the target protein. This sensor is a step towards the development of point-of-care devices and the popularization of electrochemical methods for trials and diagnostics of relevant diseases.