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Öğe A Binary Solvent Dispersive Liquid-Liquid Microextraction Method for the Determination of Four Endocrine Disruptor Compounds by Gas Chromatography with Flame Ionization Detector(Springer Int Publ Ag, 2022) Yaman, Burcu; Zaman, Buse Tugba; Chormey, Dotse Selali; Bakirdere, Sezgin; Dilgin, YusufThe present study reports a precise and accurate binary dispersive liquid-liquid microextraction method for the enrichment of selected endocrine disruptor compounds for determination by gas chromatography flame ionization detector. Optimal variables of influential extraction parameters (binary solvent volume, disperser solvent volume, and vortex period) were determined with a design experiment. The main effects of these parameters were examined using analysis of variance (ANOVA), and the optimum parameters of the model were obtained from the model predictor. The analytes recorded detection limits varying between 0.43 and 2.7 ng/mL under the optimum experimental conditions. All the analytes exhibited good linearity and high precision (%RSD<10%) for six replicate measurements of the lowest calibration concentrations. The enhancement in calibration sensitivity for the analytes in GC-FID was found in the range of 41.9-64.5 times for each analyte by applying the developed method. The accuracy and feasibility of the method was assessed using water samples from a well and a hospital sewer, and the percent recovery results calculated using matrix matching calibration were in the range of 90-113%. These results demonstrated that the analytes can be accurately quantified in real aqueous matrices using the developed method.Öğe A low-cost, fast, disposable and sensitive biosensor study: flow injection analysis of glucose at poly-methylene blue-modified pencil graphite electrode(Springer, 2018) Dilgin, Didem Giray; Ertek, Bensu; Dilgin, YusufIn this work, firstly methylene blue (MB) was electropolymerized onto pencil graphite electrode (PGE) surface for the electrocatalytic oxidation of NADH. Cyclic voltammograms show that oxidation potential of NADH at Poly-MB/PGE shifted to negative direction about 300 mV compared with bare PGE. These results indicate that Poly-MB/PGE exhibits a good electrocatalytic activity toward NADH oxidation. Then, a glucose biosensor study was performed based on the determination of enzymatically generated NADH by glucose dehydrogenase (GDH) which immobilized onto Poly-MB/PGE using glutaraldehyde cross-linking procedure. The biosensing of glucose in flow injection analysis (FIA) system was performed at GDH/Poly-MB/PGE for the first time. The electrocatalytic oxidation currents of enzymatically produced NADH obtained from FI amperometric current-time curves recorded at + 200 mV and in phosphate buffer solution at pH 7.0 containing 1.0 M KCl were linearly related to the concentration of glucose. Linear calibration plots are obtained in the concentration range from 0.01 to 1.0 mM. The limit of detection (LOD) was found to be 4.0 mu M. A fast, sensitive, low-cost and disposable glucose biosensor was constructed in FIA system using GDH/Poly-MB/PGE; therefore, it might provide a new perspective for the fabrication of biosensor of other compounds such as glutamate, lactate and alcohol.Öğe A new colorimetric lactate biosensor based on CUPRAC reagent using binary enzyme (lactate-pyruvate oxidases)-immobilized silanized magnetite nanoparticles(Springer Wien, 2024) Ayaz, Selen; Ersan, Teslime; Dilgin, Yusuf; Apak, ResatA novel optical lactate biosensor is presented that utilizes a colorimetric interaction between H2O2 liberated by a binary enzymatic reaction and bis(neocuproine)copper(II) complex ([Cu(Nc)2]2+) known as CUPRAC (cupric reducing antioxidant capacity) reagent. In the first step, lactate oxidase (LOx) and pyruvate oxidase (POx) were separately immobilized on silanized magnetite nanoparticles (SiO2@Fe3O4 NPs), and thus, 2 mol of H2O2 was released per 1 mol of the substrate due to a sequential enzymatic reaction of the mixture of LOx-SiO2@Fe3O4 and POx-SiO2@Fe3O4 NPs with lactate and pyruvate, respectively. In the second step, the absorbance at 450 nm of the yellow-orange [Cu(Nc)2]+ complex formed through the color reaction of enzymatically produced H2O2 with [Cu(Nc)2]2+ was recorded. The results indicate that the developed colorimetric binary enzymatic biosensor exhibits a broad linear range of response between 0.5 and 50.0 mu M for lactate under optimal conditions with a detection limit of 0.17 mu M. The fabricated biosensor did not respond to other saccharides, while the positive interferences of certain reducing compounds such as dopamine, ascorbic acid, and uric acid were minimized through their oxidative removal with a pre-oxidant (NaBiO3) before enzymatic and colorimetric reactions. The fabricated optical biosensor was applied to various samples such as artificial blood, artificial/real sweat, and cow milk. The high recovery values (close to 100%) achieved for lactate-spiked samples indicate an acceptable accuracy of this colorimetric biosensor in the determination of lactate in real samples. Due to the increase in H2O2 production with the bienzymatic lactate sensor, the proposed method displays double-fold sensitivity relative to monoenzymatic biosensors and involves a neat color reaction with cupric-neocuproine having a clear stoichiometry as opposed to the rather indefinite stoichiometry of analogous redox dye methods.Öğe A New Redox Mediator (Cupric-Neocuproine Complex)-Modified Pencil Graphite Electrode for the Electrocatalytic Oxidation of H2O2: A Flow Injection Amperometric Sensor(Wiley-V C H Verlag Gmbh, 2020) Emir, Gamze; Dilgin, Yusuf; Apak, ResatThis paper introduces the cupric-neocuproine complex ([Cu(Nc)(2)](2+)) as a new redox mediator for the electrocatalytic oxidation of H2O2. For this purpose, [Cu(Nc)(2)](2+) was modified onto a disposable pencil graphite electrode (PGE) surface by using Nafion (Nf) as a cation-exchange membrane for the effective adsorption of complex. The modified electrode was prepared by immersing Nf-adsorbed PGE into [Cu(Nc)(2)](2+) complex solution (0.40 mM of Cu2+ and 0.80 mM of Nc prepared at pH 4.76 in 0.10 M acetate buffer). SEM images and EDX spectra of electrodes were presented for the elucidation of their surface morphologies. Cyclic voltammetric results showed that H2O2 was electrocatalytically oxidized at [Cu(Nc)(2)](2+)/Nf/PGE, because both the increase in current and the potential shift to a more negative direction were observed for oxidation of H2O2 at [Cu(Nc)(2)](2+)/Nf/PGE in comparison to bare PGE. Then, the electrocatalytic activity of [Cu(Nc)(2)](2+)/Nf/PGE toward H2O2 oxidation was utilized for amperometric determination of H2O2 in flow injection analysis (FIA) system. Flow injection (FI) amperometric studies showed two linear calibration ranges (1.0-1000.0 mu M (R-2=0.9958) and 1000.0-10000.0 mu M (R-2=0.9902) with a detection limit of 0.4 mu M H2O2 which is considered good for electroanalytical determinations, especially for electrocatalytic oxidation. To test the applicability of the developed FI amperometric hydrogen peroxide sensor, H2O2 contents of some relevant samples were determined.Öğe A novel acetylcholinesterase inhibition based colorimetric biosensor for the detection of paraoxon ethyl using CUPRAC reagent as chromogenic oxidant(Elsevier B.V., 2024) Ayaz, Selen; Ulucay, Sude; Uzer, Ayşem; Dilgin, Yusuf; Apak, ReşatA novel colorimetric biosensor for the sensitive and selective detection of an organophosphate pesticide, paraoxon ethyl (POE), was developed based on its inhibitory effect on the acetylcholine esterase (AChE) enzyme. The bis-neocuproine copper (II) complex ([Cu(Nc)2]2+) known as the CUPRAC reagent, was used as a chromogenic oxidant in the AChE inhibition-based biosensors for the first time. To initiate the biosensor, an enzymatic reaction takes place between AChE and its substrate acetylthiocholine (ATCh). Then, enzymatically produced thiocholine (TCh) reacts with the light blue [Cu(Nc)2]2+ complex, resulting in the oxidation of TCh to its disulfide form. On the other hand, [Cu(Nc)2]2+ reduces to a yellow-orange cuprous complex ([Cu(Nc)2]+) which gives maximum absorbance at 450 nm. However, the absorbance of [Cu(Nc)2]+ proportionally decreased with the addition of POE because the inhibition of AChE by the organophosphate pesticide reduced the amount of TCh that would give a colorimetric reaction with the CUPRAC reagent. Based on this strategy, the linear response range of a colorimetric biosensor was found to be between 0.15 and 1.25 μM with a detection limit of 0.045 μM. The fabricated biosensor enabled the selective determination of POE in the presence of some other pesticides and metal ions. The recovery results between 92% and 104% were obtained from water and soil samples spiked with POE, indicating that the determination of POE in real water and soil samples can be performed with this simple, accurate, sensitive, and low-cost colorimetric biosensor.Öğe A novel enzyme-free FI-amperometric glucose biosensor at Cu nanoparticles modified graphite pencil electrode(Elsevier, 2020) Ayaz, Selen; Karakaya, Serkan; Emir, Gamze; Dilgin, Didem Giray; Dilgin, YusufIn this work, graphite pencil electrode (GPE) was modified with Cu nanoparticles (CuNPs) for enzyme-free flow injection (FI) amperometric detection of glucose. To modify electrode, CuNPs were electrodeposited onto GPE surface by recording 10 successive cyclic voltammograms (CVs) of 2.0 mM Cu(NO3)(2) in 100 mM KNO3. The electrochemical characterizations of the electrodes were realized by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry techniques. The SEM images and EDX spectra of the pencil leads were recorded to investigate the surface morphologies of the electrodes. Then, the electrochemical response of both unmodified GPE and CuNPs/GPE towards electrochemical oxidation of glucose was performed by recording CVs in the supporting electrolyte consisted of 100 mM NaOH and 100 mM KCl. CVs recorded at GPE showed that the electron transfer rate of glucose is relatively slow and oxidation of glucose irreversibly observed with very low current at a high positive potential (+ 0.70 V). On the other hand, glucose oxidized at more negative potential value ( + 0.45 V) than that of unmodified GPE with a view of sharp peak at CuNPs/GPE. These results show that CuNPs/GPE exhibits excellent electrocatalytic activity and high electrochemical response towards oxidation of glucose because electron transfer rate of glucose was remarkably enhanced by modification of GPE with CuNPs. In the flow injection (FI) amperometric experiments, + 0.45 V and 2.5 mL/min were used as optimal values for applied potential (E-ap) and flow rate (f(r)), respectively. A linear calibration curve was obtained in the range from 0.10 to 400 mu M glucose with a detection limit and sensitivity of 0.04 mu M and 0.830 mu A mu M-1 cm(-2), respectively. The selectivity of glucose sensor was tested in the presence of various interferences. At last step, constructed glucose biosensor was successfully tested on some real glucose samples.Öğe A novel flow injection amperometric method for sensitive determination of total antioxidant capacity at cupric-neocuproine complex modified MWCNT glassy carbon electrode(Springer Wien, 2022) Ayaz, Selen; Uzer, Aysem; Dilgin, Yusuf; Apak, ResatA novel amperometric method is presented for the determination of total antioxidant capacity in flow injection analysis (FIA) system using copper(II)-neocuproine complex modified on Nafion-functionalized multi-walled carbon nanotube-glassy carbon electrode ([Cu(Ncp)(2)(2+)]/Nf@f-MWCNT/GCE). Cyclic voltammetric studies showed that the modified electrode exhibits a very well-formed reversible redox couple for Cu(II)-/Cu(I)-complex. In addition, the [Cu(Ncp)(2)(2+)]/[Cu(Ncp)(2)(+)] redox pair shows very good electrocatalytic activity towards the oxidation of polyphenolic compounds (PPhCs) such as trolox, catechin, and quercetin due to the enhancement of the anodic peak current of the redox couple in the presence of these analytes. This electrocatalytic oxidation current at the [Cu(Ncp)(2)(2+)]/Nf@f-MWCNT/GCE was used for flow injection (FI) amperometric determination of PPhCs. FI amperometric-time curves recorded under optimized conditions (applied potential: + 0.6 V vs. Ag/AgCl/KCl(0.10 M), flow rate: 2 mL/min) showed that the proposed electrode had a wide linear range (LR) with a very low detection limit (LOD) for PPhCs. LR and LOD were 0.5-800 and 0.2 mu M for trolox, respectively and 0.50-250 and 0.14 mu M, respectively, for both quercetin and catechin. This sensitive method was successfully applied to the amperometric measurement of total antioxidant capacity (TAC) of some herbal teas, giving compatible results with the spectrophotometric CUPRAC method. The proposed method gave higher rank to fast-reacting antioxidants; it was equally precise but had a wider linear range and lower LOD than the spectrophotometric CUPRAC assay (e.g., LOD for ascorbic acid and gallic acid were 0.07 and 0.08 mu M, respectively), and similar electroanalytical methods using the CUPRAC reagent.Öğe A novel impedimetric sensor based on molecularly imprinted polypyrrole modified pencil graphite electrode for trace level determination of chlorpyrifos(Elsevier Science Sa, 2013) Uygun, Zihni Onur; Dilgin, YusufA chlorpyrifos (CPF) templated molecularly imprinted film was electrochemically synthesized on a pencil graphite electrode (PGE) by electropolymerization of pyrrole (Py) in the presence of CPF. The fabricated modified electrode was used as a novel impedimetric sensor for the determination of an important organophosphorus pesticide, CPF. The binding performance of CPF toward the polypyrrole (PPy) film was examined using electrochemical impedance spectroscopy (EIS). The surface morphology of the imprinted film was characterized by scanning electron microscopy (SEM). Results obtained from the impedance measurements show that imprinted PPy modified PGE offers a disposable, low cost, selective and sensitive electrochemical sensor for the determination of CPF. Under experimental conditions, the proposed impedimetric sensor has a linear response range from 20 to 300 mu g L-1 CPF with a detection limit of 4.5 mu g L-1 (based on 3(sb)). Furthermore, the fabricated sensor was successfully applied to determine CPF in CPF-added artificial samples. (C) 2013 Elsevier B.V. All rights reserved.Öğe A Self-Powered Enzymatic Glucose Sensor Utilizing Bimetallic Nanoparticle Composites Modified Pencil Graphite Electrodes as Cathode(Springer, 2024) Emir, Gamze; Dilgin, Yusuf; Sahin, Samet; Akgul, CahitEnzymatic biofuel cells (EBFC) are promising sources of green energy owing to the benefits of using renewable biofuels, eco-friendly biocatalysts, and moderate operating conditions. In this study, a simple and effective EBFC was presented using an enzymatic composite material-based anode and a nonenzymatic bimetallic nanoparticle-based cathode respectively. The anode was constructed from a glassy carbon electrode (GCE) modified with a multi-walled carbon nanotube (MWCNT) and ferrocene (Fc) as a conductive layer coupled with the enzyme glucose oxidase (GOx) as a sensitive detection layer for glucose. A chitosan layer was also applied to the electrode as a protective layer to complete the composite anode. Chronoamperometry (CA) results show that the MWCNT-Fc-GOx/GCE electrode has a linear relationship between current and glucose concentration, which varied from 1 to 10 mM. The LOD and LOQ were calculated for anode as 0.26 mM and 0.87 mM glucose, respectively. Also the sensitivity of the proposed sensor was calculated as 25.71 mu\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mu$$\end{document}A/mM. Moreover, the studies of some potential interferants show that there is no significant interference for anode in the determination of glucose except ascorbic acid (AA), uric acid (UA), and dopamine (DA). On the other hand, the cathode consisted of a disposable pencil graphite electrode (PGE) modified with platinum-palladium bimetallic nanoparticles (Nps) which exhibit excellent conductivity and electron transfer rate for the oxygen reduction reaction (ORR). The constructed EBFC was optimized and characterized using various electroanalytical techniques. The EBFC consisting of MWCNT-Fc-GOx/GCE anode and Pt-PdNps/PGE cathode exhibits an open circuit potential of 285.0 mV and a maximum power density of 32.25 mu W cm-2 under optimized conditions. The results show that the proposed EBFC consisting of an enzymatic composite-based anode and bimetallic nanozyme-based cathode is a unique design and a promising candidate for detecting glucose while harvesting power from glucose-containing natural or artificial fluids.Öğe Adsorption and deposition-assisted anodic stripping voltammetry for determination of antimony(III) in presence of hematoxylin on glassy carbon electrode(Elsevier Science Bv, 2017) Sezgin, Hanife Vardar; Dilgin, Yusuf; Gokcel, H. IsmetA validated simple, reliable and sensitive adsorptive anodic stripping voltammetric procedure is suggested for the accurate determination of antimony(III) on a glassy carbon electrode (GCE) in the presence of hematoxylin (HT), used as a chemical receptor in antimony analysis for the first time. Under optimized conditions, the plot of stripping peak current versus Sb(III) concentration showed two dynamic linear ranges, 1.0x10(-4) - 0.01 mu m (R-2 =0.9986) and 0.01 - 1.0 mu m (R-2 =0.9973) with a detection limit of 9.5x10(-11) mol (11.57 ng L-1). The RSD values of intra-day precision and inter-day precision (n =5) for 5.0x10(-7) mol L-1 Sb(III) were calculated as 1.63% and 2.27%, respectively, indicating that the proposed method has a good precision. Recoveries for Sb(III) in water samples were found to be between 97% and 102% for the 5.0x10(-7) mol L-1 Sb(III), proving the reliability and accuracy of the method proposed.Öğe Adsorption and removal of Cu (II) ions from aqueous solution using pretreated fish bones(Elsevier Science Bv, 2010) Kizilkaya, Bayram; Tekinay, A. Adem; Dilgin, YusufPretreated fish bones obtained from engraulis European anchovy (Engraulis encrasicolus), European anchovy (Sardine pilchardus), bogue (Boops boops), bluefish (Pomatomus saltatrix) and gilthead seabream (Sparus aurata) were used as natural, cost-effective, waste sorbents for the adsorption and removal of copper from aqueous systems. The removal efficiency of the adsorbent was investigated as a function of pH, contact time, initial metal concentration, temperature, cleaning process, fish species and adsorbent dose. The maximum adsorption capacity was 150.7 mg/g at optimum conditions. The kinetic results of adsorption obeyed a pseudo-second-order model. Copper adsorption fitted the Langmuir isotherm. Delta H-0 value was 12.9 kJ/mol indicating that the adsorption mechanism was endothermic. The activation energy, E-a, was determined as 52.9 kJ/mol. Weber-Morris and Urano-Tachikawa diffusion models were also applied to experimental equilibrium data. The fish bones were effectively used as a sorbent for the removal of Cu ions from aqueous solution. (C) 2010 Elsevier B.V. All rights reserved.Öğe Adsorptive anodic stripping voltammetric determination of antimony(III) on a glassy carbon electrode using rivastigmine as a new chemical receptor(Elsevier Science Sa, 2015) Sezgin, Hanife Vardar; Gokcel, H. Ismet; Dilgin, YusufA very simple and sensitive adsorptive anodic stripping voltammetric method was developed for determination of antimony(III) on a glassy carbon electrode (GCE), using rivastigmine (RIV) as the chemical receptor. No study on the usage of antimony(III) for metal determination as a modifier/complexing agent/chemical receptor was found in the literature review. The proposed method is based on the accumulation of the Sb-RIV complex on GCE under stirring conditions using optimized accumulation potential and time following the recording of a differential pulse (DP) voltammogram in anodic direction. The calibration graph consisted of two linear segments of 5.0 x 10(-4)-0.5 mu M (i(p)(mu A) = 7.45C(Sb(III)) (mu M) + 0.05, R-2 = 0.9974) and 0.5-2.5 mu M (i(p)(mu A) = 10.45C(Sb(III)) (mu M) - 0.76, R-2 = 0.9959) with a detection limit of 7.1 x 10(-11) mol L-1. The RSD (n = 5, intra-day) for 1.0 x 10(-6) mol L-1 Sb(III) and 5.0 x 10(-7) mol L-1 Sb(III) were calculated as 1.53% and 2.62%, respectively. Inter-day precision (n = 5) was also calculated as 2.16% for 1.0 x 10(-6) mol L-1 Sb(III), indicating that the proposed method has good precision. The spiked water sample analyses were evaluated using the described method and a good recovery of Sb(III) was obtained with results in the range from 95.0% to 97.6%. (C) 2014 Elsevier B.V. All rights reserved.Öğe Amperometric determination of sulfide based on its electrocatalytic oxidation at a pencil graphite electrode modified with quercetin(Elsevier, 2012) Dilgin, Yusuf; Kizilkaya, Bayram; Ertek, Bensu; Erena, Nuri; Dilgin, Didem GirayThis study describes a new approach for the investigation of electrocatalytic oxidation of sulfide using a pencil graphite electrode modified with quercetin (PGE/QH(2)). Adsorption procedure was used for the preparation of the modified electrodes. It was observed that PGE/QH(2) showed a significant electrocatalytic activity toward sulfide oxidation. Cyclic voltammetric studies show that the peak potential of sulfide shifts from +450 mV at bare PGE to +280 mV at PGE/QH(2). The electrocatalytic currents obtained from amperometric measurements at +300 mV vs. Ag/AgCl/KClsat and at pH 8.0 BR buffer solution containing 0.1 M NH4Cl were linearly related to the concentration of sulfide. The calibration graph consisted of two linear segments of 1-20 mu M and 20-800 mu M with a detection limit of 0.3 mu M (based on 3s(b)). The proposed method was successfully applied to the determination of sulfide in waste waters and was compared with the spectrophotometric method. (C) 2012 Elsevier B.V. All rights reserved.Öğe Amperometric nonenzymatic glucose biosensor based on graphite rod electrode modified by Ni-nanoparticle/polypyrrole composite(Elsevier Inc., 2021) Emir, Gamze; Dilgin, Yusuf; Ramanaviciene, Almira; Ramanavicius, ArunasThis study reports non-ezymatic electrocatalytic amperometric glucose biosensor based on a graphite rod electrode (GRE) modified with biomimetic-composite consisting of Ni nanoparticles (Ni-NPs) and polypyrrole (Ppy) prepared by 1 cycle electro polymerization of pyrrole monomer (Ni-NPs/Ppy(1)/GRE). During the modification of GRE, the electropolymerization of pyrrole and the electrodeposition of Ni-NPs onto GRE surface were consequentially performed by potential cycling. Surface morphology of Ni-NPs/Ppy(1)/GRE electrode was evaluated by atomic force microscopy and scanning electron microscopy based imaging, and electrochemical characterization of electrodes was performed by electrochemical impedance spectroscopy and cyclic voltammetry. Cyclic voltammograms recorded in the presence of glucose show that Ni-NPs/Ppy(1)/GRE at + 500 mV vs Ag/AgCl exhibits efficient electrocatalytic oxidation activity towards glucose, while the oxidation of glucose was not observed at a bare GRE. Amperometric sensing of glucose was performed by Ni-NPs/Ppy(1)/GRE at constant + 450 mV vs Ag/AgCl electrode potential in 0.10 mol L−1 NaOH. Ni-NPs/Ppy(1)/GRE-based sensor, which was characterized by a wide linear glucose determination range between 1.0 and 1000 µmol L−1 with a limit of detection of 0.4 µmol L−1 and a sensitivity of 2873 µA mmol−1 L cm−2. The applicability of here reported Ni-NPs/Ppy(1)/GRE-based sensor has been demonstrated by the determination of glucose concentrations in real samples.Öğe Amperometric sensor for total antioxidant capacity measurement using Cu (II)-neocuproine/carrageenan-MWCNT/GCE(Elsevier, 2024) Sen, Furkan Burak; Elmas, Ervanur; Dilgin, Yusuf; Bener, Mustafa; Apak, ResatDetermination of total antioxidant capacity (TAC) in foods is very important for combating oxidative stressinduced diseases. For this purpose, an amperometric sensor was developed for TAC determination by manufacturing a new electrode consisting of a copper(II)-neocuproine (Cu(II)-Nc) and carrageenan-multi-walled nanotube suspension functionalized on a glassy carbon electrode, named as Cu(II)-Nc/Car-MWCNT/GCE. Cyclic voltammetric studies showed that the modified electrode exhibits a very well-formed reversible redox couple for the Cu(II)-Nc/Cu(I)-Nc complex. For amperometric sensor preparation, the Cu(II)-Nc cationic chelate was electrostatically retained on the electrode with the anionic groups of Car (a sulfated biopolymer of low cost) and immobilized on the surface. Cu(II)-Nc was reduced to Cu(I)-Nc on the electrode with the addition of antioxidants under constant potential, thereby functioning as an electron-transfer mediator. Thus, the individual antioxidant compounds were not measured at their own peak potentials but were indirectly measured at a common potential through their ability to reduce cupric-to-cuprous neocuproine. The reoxidation current of Cu(I)-Nc showing a proportional increase with antioxidant concentration was recorded, resulting in increased sensitivity and selectivity. This anodic current intensity of Cu(I)-Nc correlated with the total antioxidant capacity (TAC) of real samples such as plant extracts, reflecting the combined reducing ability of all antioxidants in the sample. Calibration graphs of antioxidants were obtained by optimizing the working conditions. The current intensity of Cu (I)-Nc arising from trolox varied linearly with concentration in the range of 4.98-84.39 mu M. The limit of detection and limit of quantification values for trolox were found to be 0.59 and 1.99 mu M, respectively. The developed method selectively responded to food antioxidants, and was not affected by potential interferent ions and molecules commonly found in foods. The TAC values of real samples such as herbal teas, plant extracts, and fruit juices were calculated and compared with those found by the conventional spectrophotometric CUPRAC method.Öğe Aromatik Sülfonik Asit Boyar Maddeleriyle Modifiye Elektrot Kullanılarak Akışa Enjeksiyon Analiz Sisteminde Elektrokimyasal Sensör ve Biyosensör Tasarımı(2017) Dilgin, YusufBu çalışmada yapısındaki fenolik ya da naftol gruplardan dolayı iyi bir redoks mediyatör olma potansiyeline sahip olan aromatik sülfonik asit boyar maddelerden kalmagit (Clm), kromotropik asit (Cta), tropeolin (Trp), pirokatekol violet (Pcv) ile modifiye kalem grafit elektrot (pencil graphite electrode, PGE) hazırlanmış ve hazırlanan bu modifiye elektrotlarla NADH (B nikotin amid dinükleotid in indirgenmiş hali), sülfür ve hidrazin gibi moleküllerin elektrokatalitik yükseltgenmesi incelenmiştir. İlk defa PGE için geliştirilen fotoelektrokimyasal akış hücresi kullanılarak akışa enjeksiyon analiz (flow injection analysis, FIA) sisteminde NADH, sülfür ve hidrazinin organik redoks boyar maddeleriyle modifiye PGE’lerde elektrokatalitik yükseltgenmesine bağlı amperometrik sensörleri geliştirilmiştir. Bunun yanında modifiye elektrotlar yüzeyine dehidrogenaz enzimi immobilize edilerek NAD+/NADH redoks çiftine bağlı glukoz biyosensörü tasarlanmış ve FIA sisteminde ilk defa aromatik sülfonik asit boyar madde modifiye PGE ile FI amperometrik glukoz biyosensörü geliştirilmiştir. Hazırlanan modifiye elektrotlar arasında, Trp ve Cta modifiye PGE’ler ve adsorpsiyon yoluyla hazırlanmış Clm modifiye PGE ilgili analitlerin yükseltgenmesine iyi bir elektrokatalitik etkinlik göstermemiş, bunun yanında elektropolimerizasyon yoluyla hazırlanan modifiye Clm/PGE’ler ise iyi bir elektrokatalitik etkinlik sağlamıştır. Bunun yanında en iyi elektrokatalitik etkinlik Pcv modifiye elektrotlarda elde edilmiştir. Tasarlanan FI amperometrik sensörle hidrazin ve sülfür tayini için su örneklerinde geri kazanım çalışmaları gerçekleştirilmiş ve tasarlanan FI amperometrik sensörün su örneklerinde yüksek bir doğrulukla sülfür ve hidrazin tayininde uygulanabileceği sonucu elde edilmiştir. Biyosensörün uygulanabilirliği ise ticari olarak satılan dekstroz çözeltisindeki glukoz tasarlanan biyosensörle başarılı bir şekilde tayin edilerek test edilmiştir. İlgili analitlere iyi yanıt veren Clm ve Pcv modifiye PGE’lerin, yalın PGE ile birlikte SEM ve AFM görüntüleri, Raman spektrumları alınarak yüzey morfolojileri incelenmiş, döngüsel voltammogramları ve elektrokimyasal impedans eğrileri alınarak da elektrokimyasal karakterizasyonları gerçekleştirilmiştir.Öğe Balık ve yumuşakça kültüründe besinsel desek olarak yağ ve karotenoidler bakımından zengin mikroalgler(2013) Göksan, Tolga; Ak, İlknur; Dilgin, Yusuf[Abstract Not Available]Öğe Bazı ilaç aktif maddelerin farmasötik preparatlarda ve insan serumu gibi biyolojik sıvılarda eletktroanalitik metotlar (Voltametrik ve polarografik teknikler ile tayini(2005) Özkan, Sibel; Dilgin, Yusuf; Yılmaz, Selahattin; Süren, Esin; Yağmur, Sultan; Akgün, Nur; Uslu, BengiBu çalışmada, elektroaktif grup içeren bazı ilaçaktif maddelerin camsı karbon disk ve karbon pasta elektrotlarda farklı tampon ortamında voltametrik davranışları araştırıldı. Pik potansiyeline ve pik akımına, konsantrasyonun, pH 'nın tarama hızının etkisi incelendi. Alt tayin sınırı (LOD) ve Kantitatif tayin sınırı (|LOQ) belirlendi. Çalışılan bazı bileşikler için yükseltgenme veya indirgenme mekanizmaları da önerildi. Bu teknikler ile maksimum pik akımının gözlendiği ortamda ilaçaktif maddelerin farmasötik preparatlarda ve serum gibi biyolojik sıvılarda tayini yapıldı. Ayrıca kesinlik ve geri kazanım çalışmaları yapıldı. Bazı etken maddelerin önerilen elektroanalitik teknikler ile yapılan ilaçlardaki miktarı , UV-Spektrofotometrişininki ile karşılaştırıldı. Böylelikle önerilen elektroanalitik metodların doğruluğu ve üstünlüğü araştırıldı.Öğe Biosensing of glucose in flow injection analysis system based on glucose oxidase-quantum dot modified pencil graphite electrode(Elsevier Science Bv, 2016) Saglam, Ozlem; Kizilkaya, Bayram; Uysal, Huseyin; Dilgin, YusufA novel amperometric glucose biosensor was proposed in flow injection analysis (FIA) system using glucose oxidase (GOD) and Quantum dot (ZnS-CdS) modified Pencil Graphite Electrode (PGE). After ZnS-CdS film was electrochemically deposited onto PGE surface, GOD was immobilized on the surface of ZnS-CdS/PGE through crosslinking with chitosan (CT). A pair of well-defined reversible redox peak of GOD was observed at GOD/CT/ZnS-CdS/PGE based on enzyme electrode by direct electron transfer between the protein and electrode. Further, obtained GOD/CT/ZnS-CdS/PGE offers a disposable, low cost, selective and sensitive electrochemical biosensing of glucose in FIA system based on the decrease of the electrocatalytic response of the reduced form of GOD to dissolved oxygen. Under optimum conditions (flow rate, 1.3 mL min(-1); transmission tubing length, 10 cm; injection volume, 100 mu L; and constant applied potential, -500 mV vs. Ag/AgCl), the proposed method displayed a linear response to glucose in the range of 0.01-1.0 mM with detection limit of 3.0 mu M. The results obtained from this study would provide the basis for further development of the biosensing using PGE based FIA systems. (C) 2015 Elsevier B.V. All rights reserved.Öğe DETERMINATION OF ANTI-CANCER DRUG EMODIN USING A SILICA-GEL-MODIFIED CARBON PASTE ELECTRODE(Soc Brasileira Quimica, 2014) Vu, Dai Long; Ertek, Bensu; Dilgin, Yusuf; Cervenka, LiborIn this paper, a silica-gel-modified carbon paste electrode (Si-gel/ CPE) was used to determine the anti-cancer drug emodin by anodic stripping differential pulse voltammetry (ASDPV). The effects of the silica-gel content, the pH of the supporting electrolyte, and the scan rate on the oxidation current of emodin were investigated. The oxidation currents of emodin obtained from ASDPV measurements were linearly correlated with the concentration in the range of 5.0 x 10(-9) to 300.0 x 10(-9) mol L-1. The limit of detection was determined to be 1.5 x 10(-9) mol L-1. The current method was successfully applied to determine emodin in a knotweed root sample, with recovery rate of 92.5% to 98.3%.
