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    Design of an electrochemical sensor based on 3-thiophene methanol and 3-methylthiophene supported molecularly imprinted polymer for the sensitive and selective detection of levothyroxine
    (Elsevier, 2025) Yayan, Emrah; Kazici, Dilek; Savan, Ebru Kuyumcu
    Levothyroxine (L-T4) is the most frequently prescribed drug to treat thyroid hormone deficiency. Herein, a levothyroxine-specific sensor was designed using the molecular imprinting method to increase the selectivity of the target molecule on the electrode surface and prevent interference effects. 3-thiophene methanol (3-TMeOH) and 3-methyl thiophene (3-MT) monomers were electro-polymerized as molecularly imprinted polymer (MIP) on the surface of a glassy carbon electrode (GCE) in the presence of L-T4. Gaps were created on the surface of the designed electrode to fit the target molecule by removing L-T4 molecules. This way, L-T4-specific selective structures were formed on the sensors' surface. The results showed that under optimized conditions, the fabricated modified sensor (3-TMeOH/3-MT@MIP/GCE) exhibited a linear response in the concentration range of 1.0-5.7 mu M with limit of determination, limit of quantitation, and sensitivity values of 1.83 nM, 5.50 nM, and 0.0023 A.L.mmol- 1.cm- 2, respectively. The analytical method validation process of the voltammetric determination method using the sensor selective to L-T4 was completed following the method's intended use. The designed modified sensor exhibited high sensitivity, repeatability, excellent stability, selectivity, and high precision and accuracy.
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    Electrochemical and in Silico Investigations of the Interaction between Nitro Blue Tetrazolium Chloride and Bovine Serum Albumin
    (Eurasia Acad Publ Group (Eapg), 2022) Kazici, Dilek; Alagoz, Mehmet Abdullah; Savan, Ebru Kuyumcu
    The binding ability of the drug on its interaction with the protein will also significantly affect the apparent volume of distribution of the drugs and, in many cases the rate of elimination of the drugs. The interactions of proteins and other molecules are a fascinating topic applied to surface technologies and sensors. Therefore, it is aimed to determine the NBTCand to elucidate its interaction with Bovine Serum Albumin (BSA) by electrochemical and in silico studies in this paper. The reduction in BSA oxidation signals measured by differential pulse voltammetry upon incubation with different NBTC concentrations indicated that NBTC was bound to BSA. In addition, in silico (molecular modeling and molecular dynamics) studies have been conducted on the interactions of NBTC with proteins in plasma. As a result of the in silico studies investigated the interactions of NBTC with serum albumin, its binding affinity, and the dynamic process in the binding state. In silico studies showed that NBTC binds to BSA with high affinity (with-7.986 kcal/mol docking score), and this binding was stable (with a 3.0 average RMSD value). Eventually, the results of the electrochemical and modeling studies were perfectly matched.
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    Electrochemical and in silico study of the interaction between phenazopyridine and bovine serum albumin
    (Springer, 2024) Kazici, Dilek; Alagoez, Mehmet Abdullah; Savan, Ebru Kuyumcu
    In this study, an electrochemical sensor was developed using a simple methodology to investigate for the first time the interaction of phenazopyridine with bovine serum albumin (BSA). The modified sensor was fabricated by electropolymerized diphenylamine-4-sulfonic acid barium salt onto the glassy carbon electrode surface by the cyclic voltammetry technique. Very low detection limit and quantification limit values were obtained by differential pulse voltammetry (DPV) in 0.1 M NaClO4 as 0.13 mu M and 0.43 mu M, respectively. In addition, the interference effect was studied, and recovery studies were performed in urine samples achieving dramatic recovery values. Selective and reproducible determinations of phenazopyridine were performed perfectly with the developed sensor. The reduction in BSA oxidation signals as measured by DPV upon incubation with different phenazopyridine concentrations indicated that phenazopyridine was bound to BSA. The currents of the BSA peaks decreased linearly with the phenazopyridine concentration in the linear concentration range (2.00-22.60 mu M). The results of the DPV experiments showed the formation of the BSA-Phenazopyridine complex. Binding parameters such as binding constants and binding free energy were calculated with the voltammetric data. Molecular docking and molecular dynamics simulation studies were performed to learn more about the interaction mechanism between phenazopyridine and BSA. Residues in the active gorge of BSA playing an important role in binding were determined by in silico studies. In silico studies showed that phenazopyridine binds to BSA with high affinity and this binding was stable. Eventually, the results of the electrochemical and modeling studies were perfectly matched.
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    Electrochemical determination of anti-müllerian hormone level at antibody-based biosensor
    (Elsevier Science Sa, 2025) Kazici, Dilek; Savan, Ebru Kuyumcu
    Anti-m & uuml;llerian hormone (AMH) test is used for polycystic ovary syndrome (PCOS) diagnosis, early menopause risk assessment, determination of ovarian reserve in fertility treatments, and, sometimes, evaluation of testicular function. In this study, an antibody-based biosensor surface was designed to detect AMH, a biomarker of PCOS. The glassy carbon electrode surface was electropolymerized with 4-aminobenzenesulfonic acid, and then AMH antibodies were attached to its surface. Afterward, AMH and bovine serum albumin were immobilized as a blocking agent. The characterization of the biosensor surfaces and their morphologies were examined by cyclic voltammetry, electrochemical impedance spectroscopy, and scanning electron microscopy. The newly produced biosensor exhibited a linear response in the 6.95-50.4 pg/mL concentration range in pH 7.4 phosphate buffer solution containing [Fe(CN)6]3-/4- by differential pulse voltammetry. With a sensitivity of 8.88 x 10-3 A.mL/pg. cm2 in this linear range, the limit of detection and quantitation values were calculated as 0.19 pg/mL and 0.62 pg/mL, respectively. The applicability of the developed biosensor gave excellent results with 98 % recovery in synthetic urine and 99 % recovery in blood serum.
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    Preparation of MWCNT-based poly (methacrylic acid) hybrid film modified sensors and their use in selective determination of levothyroxine
    (Pergamon-Elsevier Science Ltd, 2025) Yayan, Emrah; Kazici, Dilek; Savan, Ebru Kuyumcu; Ozcan, Imren; Koytepe, Suleyman
    Herein, the novel functional multi-walled carbon nanotube (MWCNT) hybrid material capable of rapid, ultra-sensitive, and accurate levothyroxine (L-T4) detection was synthesized for preparing modified sensors. Firstly, MWCNT was functionalized with triethoxyvinylsilane (TEVS). Vinyl functionalized MWCNT structures (MWCNT@TEVs) were treated with methacrylic acid (MA) and MA/divinylbenzene to synthesize two different hybrid polymers. These sensor materials were characterized in detail using Fourier transform infrared spectroscopy, energy dispersive X-ray analysis, scanning electron microscopy, and thermal analysis. The polymers were modified onto the glassy carbon electrode (GCE) surface by the drop-casting technique. The best-responsing sensor (MA-MWCNT@TEVS/GCE) was used for the rapid and sensitive detection of l-T4 in a wide concentration range using differential pulse voltammetry. The limit of detection for l-T4 was calculated as 0.26 nmol L--(1). The calibration curve R-2 value was determined as 0.9904 with a sensitivity of 0.408 A L nmol(-1) cm(-2) in the linear 4.0 - 44.0 mu mol L--(1) concentration range. Eventually, it was seen that poly (MA) based sensor materials could be an important alternative for the stable, sensitive, and reproducible determination of levothyroxine.
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    Preparation of pyridoxine-based polyurethane modified sensors and their use in simultaneous determination of Cu(II) - Co(II) ions
    (Elsevier, 2024) Savan, Ebru Kuyumcu; Kazici, Dilek; Ozcan, Imren; Bayram, Songuel; Koytepe, Sueleyman
    In this study, pyridoxine-based polyurethane-modified electrodes were prepared to simultaneously and sensitively measure copper (Cu(II)) and cobalt (Co(II)) ions in complex matrix samples. For the production of the electrodes, firstly, the synthesis of pyridoxine-based polyurethane structures was carried out. In these syntheses, the polymer structure was diversified by using different isocyanates. Polyethyleneglycol-200 (PEG), pyridoxine (B6), and beta- cyclodextrin ( beta- CD) groups were used as the source of polyol. The synthesized polyurethane structures were characterized by different instrumental techniques and used in gold electrode surface modification. Modified sensor surfaces were examined by scanning electron microscopy and atomic force microscopy techniques. The prepared modified sensors were used for the simultaneous detection of Cu(II) and Co(II) ions using the differential pulse voltammetry technique. The limit of detection (LOD), limit of quantitation (LOQ), and R 2 values for Cu(II) ions were calculated as 8.81 mu M, 29.4 mu M, and 0.993, respectively. LOD, LOQ, and R 2 values for Co(II) ions were calculated as 9.84 mu M, 32.8 mu M, and 0.9935, respectively. For repeatability, the relative standard deviation (RSD %) of the prepared simultaneous sensors was determined as 1.54 and 1.71 for Cu(II) and Co(II), respectively. As a result, Cu(II) and Co(II) ions were measured independently and simultaneously with high sensitivity. According to these results, it is predicted that pyridoxine-based polyurethane-modified sensors may be suitable for the simultaneous detection of Cu(II) and Co(II) in medical, food, and agricultural samples.