Search Results (72)

In this study, we investigate the electrochemical performance of a carboxyl-functionalized pencil graphite (CFPG) electrode for chloride ion oxidation and its subsequent application in dye degradation. The graphite electrode was chemically modified using acetic acid to introduce –COOH functional groups, enhancing surface polarity and chloride adsorption capacity. Surface characterization by SEM, EDX, and XPS confirmed morphological changes and oxygen enrichment following functionalization. Electrochemical measurements demonstrated a positive shift in open circuit potential (OCP) and significantly enhanced chloride oxidation activity, as evidenced by cyclic voltammetry (CV) in 0.1 M KCl. The functionalized electrode facilitated the in situ generation of reactive chlorine species (RCS), with spectral features near ~240 nm consistent with HOCl/ClO⁻ and a broader band around ~450 nm attributable to chlorine-derived intermediates rather than exclusively to molecular chlorine. These species played a central role in degrading structurally diverse dyes—Kenacid Green and Brilliant Green—via oxidative pathways. The results highlight the potential of low-cost, –COOH-modified graphite electrodes as effective platforms for the RCS-mediated electrochemical treatment of organic contaminants. Full article

COVID-19, caused by SARS-CoV-2, has created unprecedented global health challenges, necessitating rapid and reliable diagnostic strategies. The spike (S) protein, particularly its S1 subunit, plays a critical role in viral entry, making it a prime biomarker for early detection. In this study, we present a disposable, low-cost, and portable electrochemical biosensor employing specifically optimized aptamers (Optimers) for SARS-CoV-2 S1 recognition. The sensing approach is based on aptamer–protein complex formation in solution, followed by immobilization onto pencil graphite electrodes (PGEs). The key parameters, including aptamer concentration, interaction time, redox probe concentration, and immobilization time, were systematically optimized by performing electrochemical measurement in redox probe solution containing ferri/ferrocyanide using differential pulse voltammetry (DPV) technique.Under optimized conditions, the biosensor achieved an ultralow detection limit of 18.80 ag/mL with a wide linear range (10⁻¹–10⁴ fg/mL) in buffer. Importantly, the sensor exhibited excellent selectivity against hemagglutinin antigen and MERS-CoV-S1 protein, while maintaining high performance in artificial saliva with a detection limit of 14.42 ag/mL. Furthermore, its integration with a smartphone-connected portable potentiostat underscores strong potential for point-of-care use. To our knowledge, this is the first voltammetric biosensor utilizing optimized aptamers (Optimers) specific to SARS-CoV-2 S1 on disposable PGEs, providing a robust and field-deployable platform for early COVID-19 diagnostics. Full article

The paper presents experimental results for a modified pulsed plasma thruster (PPT) with solid propellant, using a coaxial anode–cathode design. Graphite from pencil leads served as propellant, and a tungsten trigger electrode was tested to reduce carbonization effects. Experiments were performed in a vacuum chamber at 0.001 Pa, employing diagnostics such as discharge current/voltage recording, power measurement, ballistic pendulum, time-of-flight (TOF) method, and a Faraday cup. Current and voltage waveforms matched an oscillatory RLC circuit with variable plasma channel resistance. Key discharge parameters were measured, including current pulse duration/amplitude and plasma channel formation/decay dynamics. Impulse bit values, obtained with a ballistic pendulum, reached up to 8.5 μN·s. Increasing trigger capacitor capacitance reduced thrust due to unstable “pre-plasma” formation and partial pre-discharge energy loss. Using TOF and Faraday cup diagnostics, plasma front velocity, ion current amplitude, current density, and ion concentration were determined. Tungsten electrodes produced lower charged particle concentrations than graphite but offered better adhesion resistance, minimal carbonization, and stable long-term performance. The findings support optimizing trigger electrode materials and PPT operating modes to extend lifetime and stabilize thrust output. Full article

The alarming rise in foodborne illnesses, particularly those associated with microbial contamination in meat products, presents a serious challenge to global food safety. Among these microbial threats, Pseudomonas aeruginosa (P. aeruginosa) poses a critical threat due to its biofilm-forming capability and prevalence in contaminated beef, highlighting its effective real-time detection. Herein, we report the fabrication of a novel electrochemical aptasensor based on multimetal perovskite (FeCoCuNiO) doped with urea-derived graphitic carbon nitride (g-C₃N₄), synthesized via a sol–gel combustion method. The FeCoCuNiO-g-C₃N₄ nanocomposite was then coated onto a graphitic pencil electrode and functionalized with a DNA-based aptamer specific towards P. aeruginosa. The resulting aptasensor exhibited a low detection limit of 3.03 CFU mL⁻¹ with high selectivity and sensitivity, and was successfully applied to real-time detection of P. aeruginosa in food samples. To the best of our knowledge, this work presents the first FeCoCuNiO-g-C₃N₄-based aptasensor for bacterial detection, offering a promising platform for food safety assurance and public health protection. Full article

Lignin, the second most abundant biopolymer in nature after cellulose, has attracted attention for its compatibility with carbon-based materials. In this study, lignin-modified single-use pencil graphite electrodes (PGE/LG) were developed for the electrochemical detection of fish sperm DNA (fsDNA), the anticancer drug Mitomycin C (MC), and their interaction. The modified electrodes were characterized using field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) techniques. Differential pulse voltammetry (DPV) in ferri/ferrocyanide redox probe solution was employed for signal monitoring. The detection limits were calculated as 2.95 ng/mL for fsDNA between 10¹ and 10⁵ ng/mL and 0.22 pg/mL for MC between 1 and 10⁶ pg/mL. Furthermore, the interaction of DNA with MC was evaluated by DPV and EIS techniques. The cross-linking between MC and the guanine bases of DNA inhibited electron transfer, resulting in a decrease in current response and an increase in charge transfer resistance. These results demonstrate the potential of the PGE/LG platform as a cost-effective, sensitive, and rapid biosensor for DNA detection, anticancer drug analysis, and drug–DNA interaction studies. Full article

The BRCA-1 protein, recognized for its diagnostic relevance in a wide spectrum of malignancies, has been the focus of extensive investigation. In this study, an electrochemical immunosensor specifically designed for BRCA-1 detection was fabricated. The sensing platform utilizes disposable pencil graphite electrodes modified with a nanocomposite composed of gold nanoparticles (AuNPs), molybdenum disulfide (MoS₂), and chitosan (CS). This multifunctional nanostructure significantly promotes electron transfer efficiency and supports the effective immobilization of antibodies. The constructed immunosensor exhibited excellent analytical performance, with a linear detection range between 0.05 and 20 ng/mL for BRCA-1 and a notably low limit of detection at 0.04 ng/mL. The device maintained a relative standard deviation of 3.59% (n = 3), indicating strong reproducibility. In addition, a high recovery rate of 98 ± 3% was achieved in spiked serum samples, even in the presence of common electroactive interferents such as dopamine and ascorbic acid. These findings highlight the sensor’s promising applicability for the clinical detection of BRCA-1 and potentially other cancer-related biomarkers. Full article

Exciton generation and separation play an important role in the photoelectric properties and the luminescence performance of materials. In order to tailor the defects and grain boundaries and improve the exciton separation and light harvesting of the graphitic carbon nitride (g-C₃N₄) nanosheets, a C₃N₄/bismuth sulfide (Bi₂S₃) nanocomposite was synthesized. The photoelectric properties of the 405, 532, 650, 780, 808, 980 and 1064 nm light sources were studied using Au electrodes and graphite electrodes with 4B and 5B pencil drawings. The results indicate that the C₃N₄/Bi₂S₃ nanocomposite exhibited photocurrent switching behavior in the broadband light spectrum range. It is noted that even with zero bias applied, a good photoelectric signal was still measured. The resulting nanocomposite exhibited good photophysical stability. Physical mechanisms are discussed herein. It is suggested that the interfacial interaction of C₃N₄ and Bi₂S₃ in the nanocomposite creates a strong built-in electric field, which accelerates the separation of excitons. Therefore, as a dynamic process of photoexcitation, fluorescence, the photoelectric effect, and scattering are three main competing processes; the separation of excitons and the extraction of free photogenerated charge can be used as a reference for the fluorescent materials or other photoelectric materials studies as photophysical properties. This study also serves as an important reference for the design, defect and grain boundary modulation or interdisciplinary application of functional nanocomposites, especially for the bandgap modulation and suppression of photogenerated carrier recombination. Full article

This study aimed to optimize the electrochemical pretreatment and functionalization of pencil graphite electrodes (PGEs) for the performance evaluation of a transducer applied in initial studies in the development of an immunosensor for vaccinia virus (VACV) detection. The effects of the applied potential, duration, and supporting electrolyte type and concentration on PGE activation were investigated. Functionalization using a polymeric film derived from 2-hydroxybenzamide (2-HXB) was optimized by varying the applied potential, deposition time, and monomer concentration. Optimal activation conditions were found to be +0.90 V in 0.02 M of H₂SO₄ for 300 s, promoting the formation of hydrogenated groups and increasing electrode wettability. For electropolymerization, +1.20 V for 300 s with a 2-HXB concentration of 2.50 mM provided the best results, ensuring proper film formation and adhesion. Scanning electron microscopy revealed a rough, sheet-like surface on the polished PGE, while energy dispersive spectroscopy confirmed poly(2-HXB) adsorption through increased oxygen and nitrogen content on the functionalized electrode. The optimized pretreatment and functionalization conditions significantly influenced the response of the transducer used for VACV detection, demonstrating its crucial role in device development. These findings contribute to the advancement of inexpensive and effective electrochemical transducers and highlight the importance of pretreatment and modification of PGEs in biosensing applications. Full article

Curcumin (CU, turmeric), a polyphenolic phytochemical that is largely used as a food spice, has benefits for human health, which have led to increased interest in its therapeutic applications and its analysis from different matrices. The two guaiacol moieties of CU are responsible for its antioxidant properties and allow for its voltammetric quantification. Cyclic and differential pulse voltammetry (DPV) investigations at a single-use pencil graphite electrode (PGE) emphasized complex pH-dependent electrode processes, involving an equal number of protons and electrons. Theoretical calculations predicted a folded geometry for the β-diketone CU conformers, which interact with the PGE surface, exposing the electroactive moieties of only one aromatic ring. The Gibbs energy variations of the structures involved in CU electro-oxidation and the theoretical electrochemical potential values were calculated. CU’s DPV cathodic peak intensity recorded at an HB-type PGE in 0.05 mol × L⁻¹ H₂SO₄ varied linearly in the range 5.00 × 10⁻⁸–5.00 × 10⁻⁶ mol × L⁻¹ CU. The method’s detection and quantification limits were 2.12 × 10⁻⁸ mol × L⁻¹ and 6.42 × 10⁻⁸ mol × L⁻¹, respectively. The practical applicability of the developed method, successfully tested by CU assessment in dietary supplements, provided a recovery of 99.28 ± 2.04%. Full article

The development of electrochemical DNA biosensors occurred by applying different organically coated Mn-NPs such as MnCO₃@OAm, MnCO₃@TEG and MnO₂/Mn₂O₃@TEG, as well as naked MnCO₃ NPs (where OAm = oleylamine and TEG = tetraethylene glycol). The detection performances of PGEs were modified with different types of Mn-NPs, according to the guanine signal magnitudes obtained after double-stranded DNA (dsDNA) or single-stranded DNA (ssDNA) immobilization at these surfaces. DNA interaction studies were realized using UV-vis, circular dichroism (CD), electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV) techniques. In addition, a 3- to 5.4-fold increase in guanine response in the presence of dsDNA and a 2.3-fold increase in the presence of ssDNA were obtained with the developed biosensor. The increased signals in DNA immobilization at the electrode surfaces modified with Mn-NPs compared to bare PGE clearly show that the modification of Mn-NPs increases the electroactive surface area of the electrode. The detection limit (LOD) of dsDNA was calculated as 7.86 μg·L⁻¹ using the MnO₂/Mn₂O₃@TEG type of the Mn-NP-modified biosensor, while the detection limit of ssDNA was calculated as 3.49 μg·L⁻¹ with the MnCO₃@OAm type Mn-NP-modified biosensor. The proposed sensor was applied to a human DNA sample where the amount of dsDNA extract was found to be 0.62 ± 0.03 mg·L⁻¹ after applying the MnO₂/Mn₂O₃@TEG type of Mn-NP-modified biosensor. Full article

The coronavirus disease (COVID-19) pandemic has created an urgent need for rapid, accurate, and cost-effective diagnostic tools. In this study, an economical electrochemical immunosensor for the rapid diagnosis of COVID-19 was developed and optimized based on charge transfer resistance (Rct) values obtained by electrochemical impedance spectroscopy (EIS) from the interaction between antibodies (anti-SARS-CoV-2) immobilized as a bioreceptor and the virus (SARS-CoV-2). The sensor uses modified pencil graphite electrodes (PGE) coated with poly(4-hydroxybenzoic acid), anti-SARS-CoV-2, and silver nanoparticles. The immobilization of anti-SARS-CoV-2 antibodies was optimized at a concentration of 1:250 for 30 min, followed by blocking the surface with 0.01% bovine serum albumin for 10 min. The optimal conditions for virus detection in clinical samples were a 1:10 dilution with a response time of 20 min. The immunosensor responded linearly in the range of 0.2–2.5 × 10⁶ particles/μL. From the relationship between the obtained signal and the concentration of the analyzed sample, the limit of detection (LOD) and limit of quantification (LOQ) obtained were 1.21 × 10⁶ and 4.04 × 10⁶ particles/μL, respectively. The device did not cross-react with other viruses, including Influenza A and B, HIV, and Vaccinia virus. The relative standard deviation (RSD) of the six immunosensors prepared using the shared-pool sample was 3.87. Decreases of 22.3% and 12.4% were observed in the response values of the ten immunosensors stored at 25 °C and 4.0 °C, respectively. The sensor provides timely and accurate results with high sensitivity and specificity, offering a cost-effective alternative to the existing diagnostic methods. Full article

The disinfection of drinking water is essential for eliminating pathogens and preventing waterborne diseases. However, this process generates various disinfection byproducts (DBPs), which toxicological research indicates can have detrimental effects on living organisms. Moreover, the safety of these DBPs has not been sufficiently assessed, underscoring the need for a comprehensive evaluation of their toxic effects and associated health risks. Compared to traditional methods for studying the toxicity of pollutants, emerging electrochemical sensing technologies offer advantages such as simplicity, speed, and sensitivity, presenting an effective means for toxicity research on pollutants. However, challenges remain in this field, including the need to improve electrode sensitivity and reduce electrode costs. In this study, a pencil graphite electrode (PGE) was modified with carboxylated multi-walled carbon nanotubes (MWCNT-COOH) and nano-iron (III) oxide (α-Fe₂O₃) to fabricate a low-cost electrode with excellent electrocatalytic performance for cell-active substances. Subsequently, a novel cellular electrochemical sensor was constructed for the sensitive detection of the toxicity of three drinking water DBPs. The half inhibitory concentration (IC₅₀) values of 2-chlorophenylacetonitrile (2-CPAN), 3-chlorophenylacetonitrile (3-CPAN), and 4-chlorophenylacetonitrile (4-CPAN) for HepG2 cells were 660.69, 831.76, and 812.83 µM, respectively. This study provides technical support and scientific evidence for the toxicity detection and safety assessment of emerging contaminants. Full article

This paper summarizes the main findings of a study which aimed to examine the electrochemical oxidation of homovanillic acid (HVA), the final metabolite of dopamine. A pencil graphite electrode (PGE) was used as working electrode and the measurements were performed by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The type and the composition of the graphite leads used as PGE, the pH of the supporting electrolyte, as well as the scan rates were optimized by CV. The analyte was irreversibly oxidized in Britton–Robinson buffer (BRB) solutions. The interpretation of the voltammetric signals and the correlation of the acquired information were the key to addressing the electrode process undergone by HVA at the PGE. The outcomes of the pH and scan rate studies led to the conclusion that two electrons and two protons were involved in the diffusion-controlled process. Using the PGE, a linear relationship between peak current and HVA concentration was obtained between 1.0 × 10⁻⁶ M and 5.0 × 10⁻⁵ M by DPV in BRB with pH 2.0. The detection limit of 3.84 × 10⁻⁷ M was calculated. The accuracy, the precision, and the selectivity of the quantitative method have successfully undergone evaluation. The practical application of the developed voltammetric method was checked by determining the HVA concentration in spiked plasma samples, yielding good recovery values. Full article

In this study, we introduce a novel electrochemical sensor combining reduced graphene oxide (rGO) sheets with a bismuth–mercury (Bi/Hg) film, electroplated onto pencil graphite electrodes (PGEs) for the high-sensitivity detection of trace amounts of gallium (Ga³⁺) and indium (In³⁺) in water samples using square wave anodic stripping voltammetry (SWASV). The electrochemical modification of PGEs with rGO and bimetallic Bi/Hg films (ERGO-Bi/HgF-PGE) exhibited synergistic effects, enhancing the oxidation signals of Ga and In. Graphene oxide (GO) was accumulated onto PGEs and reduced through cyclic reduction. Key parameters influencing the electroanalytical performance, such as deposition potential, deposition time, and pH, were systematically optimized. The improved adsorption of Ga³⁺ and In³⁺ ions at the Bi/Hg films on the graphene-functionalized electrodes during the preconcentration step significantly enhanced sensitivity, achieving detection limits of 2.53 nmol L⁻¹ for Ga³⁺ and 7.27 nmol L⁻¹ for In³⁺. The preferential accumulation of each post-transition metal, used in transparent displays, to form fused alloys at Bi and Hg films, respectively, is highlighted. The sensor demonstrated effective quantification of Ga³⁺ and In³⁺ in tap water, with detection capabilities well below the USEPA guidelines. This study pioneers the use of bimetallic films to selectively and simultaneously detect the post-transition metals In³⁺ and Ga³⁺, highlighting the role of graphene functionalization in augmenting metal film accumulation on cost-effective graphite rods. Additionally, the combined synergistic effects of Bi/Hg and graphene functionalization have been explored for the first time, offering promising implications for environmental analysis and water quality monitoring. Full article

A new molecularly imprinted polymer (MIP)-based disposable electrochemical sensor for dipyridamole (DIP) determination was obtained. The sensor was rapidly prepared by potentiodynamic electrochemical polymerization on a pencil graphite electrode (PGE) using curcumin (CUR) as a functional monomer and DIP as a template molecule. After the optimization of the conditions (pH, monomer–template ratio, scan rate, number of cyclic voltammetric cycles applied in the electro-polymerization process and extraction time of the template molecule) for MIP formation, DIP voltammetric behavior at the modified electrode (MIP_PGE) was investigated. DIP oxidation took place in a pH-dependent, irreversible mixed diffusion-adsorption controlled process. Differential pulse voltammetry (DPV) and adsorptive stripping differential pulse voltammetry (AdSDPV) were used to quantify DIP from pharmaceutical and tap water samples. Under optimized conditions (Britton–Robinson buffer at pH = 3.29), the obtained linear ranges were 5.00 × 10⁻⁸–1.00 × 10⁻⁵ mol/L and 5.00 × 10⁻⁹–1.00 × 10⁻⁷ mol/L DIP for DPV and AdSDPV, respectively. The limits of detection of the methods were 1.47 × 10⁻⁸ mol/L for DPV and 3.96 × 10⁻⁹ mol/L DIP for AdSDPV. Full article