Yazar "Apak, Reşat" seçeneğine göre listele
Listeleniyor 1 - 4 / 4
Sayfa Başına Sonuç
Sıralama seçenekleri
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; Erşan, Teslime; Dilgin, Yusuf; Apak, ReşatA 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 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 Amperometric sensor for total antioxidant capacity measurement using Cu (II)-neocuproine/carrageenan-MWCNT/GCE(Elsevier, 2024) Şen, Furkan Burak; Elmas, Ervanur; Dilgin, Yusuf; Bener, Mustafa; Apak, ReşatDetermination 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 Flow injection amperometric sensing of hydroxylamine at a Cu(ii)-neocuproine-functionalized multiwalled carbon nanotube/screen printed carbon electrode(Royal Society of Chemistry, 2021) Ayaz, Selen; Dilgin, Yusuf; Apak, ReşatThis work describes a flow injection analysis (FIA) method for a sensitive, selective and fast detection of hydroxylamine (NH2OH) at a multiwalled carbon nanotube/screen-printed carbon electrode (MWCNT/SPCE) modified with an effective redox mediator of bis-neocuproine Cu(ii) complex ([(Cu(Ncp)(2)](2+)). To fabricate the modified electrode ([(Cu(Ncp)(2)](2+)/Nf-MWCNT/SPCE), negatively charged Nafion (Nf) molecules and [(Cu(Ncp)(2)](2+) complex were consecutively adsorbed onto MWCNT/SPCE through pi-pi stacking and electrostatic interactions, respectively. Cyclic voltammograms of the modified electrodes displayed an efficient redox pair, attributed to the reversible oxidation of Cu(i)-Ncp to Cu(ii) chelate complexes. Moreover, this redox couple showed superior electrocatalytic activity towards NH2OH oxidation compared to bare SCPE and Nf-MWCNT/SPCE due to the synergistic combination of MWCNT with the redox mediator. The FI amperometric current response towards electrocatalytic oxidation of NH2OH at +0.35 V vs. Ag/AgCl (0.10 M KCl) exhibited two linear dynamic concentration ranges between 0.25 and 100.0 mu M with a detection limit of 0.08 mu M (3 sigma) and between 100.0 and 3000.0 mu M. The FI amperometric sensor had high precision and stability, with RSD values of 2.7 and 4.8% (n = 3) for intra-day and inter-day repeatability, respectively. The developed method owes its high sensitivity and selectivity to the 2-e(-) oxidation of NH2OH to N2O catalyzed by [(Cu(Ncp)(2)](2+) as the redox mediator, with no side reactions, excellent electrode stability and low pH dependence, unlike other similar literature studies. The proposed electrode was also successfully used for the selective determination of NH2OH in two different real sample types (water and pharmaceutical samples) with satisfactory results.
