Ankara University

In recent years, important efforts have been made to elucidate the mechanisms of epigenetic regulation, and one of the most studied epigenetic modifications was DNA methylation/demethylation. In this study, the voltammetric behaviour of 5-hydroxymethylcytosine was studied in the pH range of 2.00-11.00 using pencil graphite electrodes by differential pulse and square wave voltammetry. The effect of buffer solutions, scan rate, square wave voltammetry parameters, and stripping conditions on the voltammetric responses of 5-hydroxymethylcytosine were performed. The electrochemical oxidation process of 5-hydroxymethylcytosine on the pencil graphite electrode was realized under adsorption control. In human urine, by square wave stripping voltammetry, 5-hydroxymethylcytosine was quantified in a concentration range of 1.00 × 10^-5 M-2.00 × 10^-4 M. The proposed method was tested in the presence of cytosine in human urine. The recovery value of 5-hydroxymethylcytosine was found to be 99.57 %.

This study is the first successful application of a nanomaterial-supported molecularly imprinted polymer (MIP)-based electrochemical sensor for the sensitive and selective determination of apigenin (API), which is a naturally occurring product of the flavone class that is an aglycone of several glycosides. Secondary metabolites are biologically active substances produced by plants in response to various environmental factors. The levels of these compounds can vary depending on factors such as climate, soil conditions and the season in which the plants are grown. Therefore, the analysis of these compounds is essential to properly understand the biological effects of plant extracts and to ensure their safe use. To increase the glassy carbon electrode (GCE) surface's active surface area and porosity, zinc oxide nanoparticles (ZnO NPs) were integrated into the MIP-based electrochemical sensor design. Tryptophan methacrylate (TrpMA) was selected as the functional monomer along with other MIP components such as 2-hydroxyethyl methacrylate (HEMA, basic monomer), 2-hydroxy-2-methylpropiophenone (initiator), and ethylene glycol dimethacrylate (EGDMA, crosslinking agent). The morphological and electrochemical characterizations of the developed API/ZnO NPs/TrpMA@MIP-GCE sensor were performed with scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The indirect measurement approach via 5.0 mM [Fe(CN)₆]^3-/4- solution was utilized to determine API in the linear range of 1.0x10^-13 M - 1.0x10^-12 M. The limit of detection (LOD) and limit of quantification (LOQ) for standard solutions were found to be 2.47x10^-14 and 8.23x10^-14 M, respectively. In addition, the extraction processes were carried out using ultrasound-assisted extraction (UAE) and maceration (MCR) procedures. For Apium graveolens L., Petroselinum crispum (Mill.) Fuss and herbal supplement, the API recoveries varied from 98.79 % to 102.71 %, with average relative standard deviations (RSD) less than 2.25 % in all three cases. The sensor's successful performance in the presence of components with chemical structures similar to the API was also demonstrated, revealing its unique selectivity.

Thermal polymerization (TP) and electropolymerization (EP) are the two methods used in this study to explore the molecular imprinting process. To detect the antiviral medication lopinavir (LPV), an inhibitor of enzyme HIV-1 protease that is co-formulated with ritonavir (RTV) to extend its half-life in the body, with greater precision, these methods were merged with an electrochemical sensor. The sensors were created on glassy carbon electrodes (GCE) based on molecularly imprinted polymers (MIP) using TP with methacrylic acid (MAA) functional monomer and EP with p-aminobenzoic acid (PABA) functional monomer. Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and electrochemical methods were utilized to examine the technical features of the suggested sensors. For both approaches, the necessary optimization investigations were carried out. Different LPV concentrations, ranging from 1.0 pM to 17.5 pM in drug solution and commercial human serum samples, were used to validate the analytical efficiency of the two sensors and compare their electroanalytical behaviour. For TP-LPV@MIP/GCE and EP-LPV@MIP/GCE, the corresponding limit of detection (LOD) was 2.68 × 10^-13 M (0.169 pg mL^-1) and 1.79 × 10^-13 M (0.113 pg mL^-1) in standard solutions, and 2.87 × 10^-13 M (0.180 pg mL^-1) and 2.91 × 10^-13 M (0.183 pg mL^-1) in serum samples. For the measurement of LPV in tablet form and serum samples, the proposed TP-LPV@MIP/GCE and EP-LPV@MIP/GCE sensors provide good recovery, demonstrating 99.85-101.16 % and 100.36-100.97 % recovery, respectively. The imprinting factor was utilized to demonstrate the selectivity of the suggested sensors by utilizing several anti-viral drugs that are structurally comparable to LPV. Additionally, the constructed sensors were examined for the potential impacts of interferences and the stability during the storage.