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    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, Resat
    A 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.
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    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, Reşat
    A 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.
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    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, Yusuf
    In 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.
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    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, Resat
    A 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.
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    Aromatik sülfonik asit boyar maddeleriyle modifiye elektrot kullanılarak akışa enjeksiyon analiz sisteminde hidrazinin elektrokatalitik tayini
    (Çanakkale Onsekiz Mart Üniversitesi, 2018) Ayaz, Selen; Dilgin, Yusuf
    Bu çalışmada kalmagit (Clm), kromotropik asit (Cta), tropeolin (Trp), pirokatekol violet (Pcv) gibi iyi bir redoks mediyatör özelliğine sahip aromatik sülfonik asit boyar maddelerin elektropolimerizasyon ve adsorpisyon yoluyla modifiye kalem grafit elektrot yüzeyine modifikasyonu gerçekleştirilmiş ve hazırlanan bu modifiye elektrotlar ile hidrazinin elektrokatalitik yükseltgenmesi hem döngüsel voltammetri hem de amperometrik tekniklerle incelenmiştir. 0,1 M pH 9,0 fosfat çözeltisinde kaydedilen döngüsel voltammogramlara göre hidrazin, yalın PGE'de yaklaşık 600 mV gibi yüksek bir potansiyelde yayvan bir şekilde yükseltgenirken, Clm ve Pcv modifiye elektrotlarda sırasıyla 300 mV ve 150 mV gibi daha negatif potansiyellerde keskin şekilde yükseltgenmiştir. Bu özellikler, bu iki organik molekülün hidrazinin yükseltgenmesine iyi bir elektrokatalitik aktivite gösterdiğini yansıtmaktadır. Ancak Trp ve Cta ile modifiye PGE'lerde hidrazinin elektrokatalitik yükseltgenmesine iyi yanıt alınamamıştır. Poli-Clm/PGE ve Pcv/PGE ile birlikte daha önceki çalışmalarda ilk defa PGE için geliştirilen fotoelektrokimyasal akış hücresi kullanılarak hidrazinin akış enjeksiyon (Flow Injection, FI) amperometrik tayini de gerçekleştirilmiştir. FI amperometrik çalışmalardan, doğrusal kalibrasyon aralığı/gözlenebilme sınırı (limit of detection, LOD) değerleri Poli-Clm/PGE ve Pcv/PGE için sırasıyla 0,1-100 µM (R2=0,9999)/0,038µM ve 0,25-500 µM (R2=0,9995)/0,08 µM hidrazin olarak bulunmuştur. Geliştirilen FI amperometrik hidrazin sensörünün su örneklerine uygulanabilirliği test edilmiş ve çeşme ve deniz suyu örneklerine ilave edilen hidrazinin %98-102 arasında bir geri kazanımla tayin edilebileceği sonucuna varılmıştır. Ayrıca hidrazinin elektrokatalitik yükseltgenmesine girişim yapan bazı katyonların girişimleri, çözeltiye EDTA ve etilen glikol ilave edilerek giderilmiştir. Bu çalışma sonucunda Poli-Clm/PGE ve Pcv/PGE modifiye elektrotlar kullanılarak, duyarlığı, seçiciciliği ve doğruluğu yüksek amperometrik hidrazin sensörü ilk defa FIA sisteminde geliştirilmiştir.
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    Bis-neokuproin bakır(II) kompleksine dayalı optik ve elektrokimyasal sensör/biyosensörlerin geliştirilmesi ve biyoteknolojik uygulamaları
    (Çanakkale Onsekiz Mart Üniversitesi, 2024) Ayaz, Selen; Dilgin, Yusuf
    Bu tez çalışmasında, bakır(II) bis neokuproin kompleksinin (CUPric Reducing Antioxidant Capacity, CUPRAC reaktifi) kullanımına dayalı elektrokimyasal ve optik olmak üzere iki farklı sensör/biyosensör çalışması geliştirilmiştir. Tez çalışmanın ilk kısmında, elektrokimyasal olarak tersinir davranış sergileyen CUPRAC reaktifi çok duvarlı karbon nanotüp (Multi walled carbon nanotube, MWCNT) modifiye camımsı karbon elektrot (Glassy carbon electrode, GCE) yüzeyine modifiye edilerek, antioksidan kapasite tayini akışa enjeksiyon analizi (Flow injection analysis, FIA) sistemiyle amperometrik olarak ilk defa bu tez kapsamında gerçekleştirilmiştir. Model olarak seçilen trolox, kuersetin ve kateşin antioksidan örnekleri için optimize edilen koşullarda 21 farklı antioksidan için doğrusal çalışma aralığı, LOD ve LOQ değerleri hesaplanmış, girişim ve gerçek örnek çalışmaları elektrokimyasal olarak FIA sisteminde amperometri yöntemi kullanılarak gerçekleştirilmiştir. Çalışmanın ikinci kısımında, CUPRAC reaktifi kullanılarak üç farklı enzim grubu için i) O2 ve substrat varlığında H2O2 üreten oksidaz (Glukoz oksidaz-GOx, Kolesterol oksidaz-KOx, Laktat oksidaz-LOx ve Pirüvat oksidaz-POx), enzimlerine dayalı glukoz, kolesterol ve laktat tayini için; ii) kofaktör NAD+ ve substrat varlığında NADH üreten dehidrogenaz Glukoz dehidrogenaz-GDH) enzimine dayalı glukoz tayini için (iii) asetiltiyokolin varlığında tiyokolin üreten Asetilkolinesteraz-AChE enziminin inhibisyonuna dayalı pestisit tayini için optik biyosensörler geliştirilmiştir. Her bir enzim silanlanmış manyetik nanopartiküllere (SiO2@Fe3O4) immobilize edilerek kullanılmıştır. Tez çalışması kapsamında GDH, GOx, KOx, ve LOx-POx enzimleriyle hidrofilik-politetrafloroetilen (H-PTFE) membrana dayalı fiber optik reflektometrik, GOx, KOx ve LOx-POx enzimleriyle şeffaf Nafyon (Nf) membrana dayalı fiber optik absorptimetrik biyosensör tasarımı gerçekleştirilmiştir. Son olarak AChE'nin inhibisyonuna bağlı pestisit biyosensörü geliştirilmiştir. Bu amaçla klorpirfos (CPF) ve paraoxon etil (POX-E) kullanılarak her iki pestisit için inhibisyon süresi optimize edilerek analitik performans çalışmaları gerçekleştirilmiştir. Sonuç olarak bu tez çalışmasıyla optik sensörlerde yaygın olarak kullanılan yararlı kromojenik yükseltgen CUPRAC reaktifi ile i) hem antioksidanların hem de diğer indirgenme ajanlarının doğrudan, ii) indirgen olmayan substratların, enzimatik tepkime sonucu oluşan CUPRAC aktif ürünlerle dolaylı ve iii) enzimleri inhibe eden pestisitlerin dolaylı olmak üzere üç farklı grubun analiz edebileceği belirlenmiştir.
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    Electrocatalytic oxidation and flow injection analysis of formaldehyde at binary metal oxides (Co3O4-NiO and CuO-Co3O4) modified pencil graphite electrodes
    (Springer, 2021) Emir, Gamze; Karakaya, Serkan; Ayaz, Selen; Dilgin, Didem Giray; Dilgin, Yusuf
    In this work, a highly efficient performance of bimetallic thin films as their oxide forms (Co3O4-NiO and CuO-Co3O4) modified on pencil graphite electrodes (PGEs) was presented for electrocatalytic oxidation of formaldehyde. In addition, a sensitive and selective amperometric determination of formaldehyde in flow injection analysis system have been first performed using binary transition metal oxides modified PGEs. Co3O4-NiO and CuO-Co3O4 films were electrochemically deposited on the PGE surface using cyclic voltammetric procedures. The recorded cyclic voltammograms in the presence of formaldehyde in 0.10 M NaOH containing 0.10 M KCl showed that the prepared binary transition metal oxides modified PGEs exhibited a higher electrocatalytic activity than single metal oxide thin films modified PGEs towards oxidation of formaldehyde. The linear responses based on electrocatalytic oxidation of formaldehyde were determined as 2.5-5000 mu M and 0.25-1000 mu M for Co3O4-NiO/PGE and CuO-Co3O4/PGE, respectively. Moreover, limit of detections and sensitivities were estimated as 0.73 mu M and 81.8 mu A mM(-1) cm(-2) and 0.09 mu M and 166 mu A mM(-1) cm(-2) for Co3O4-NiO/PGE and CuO-Co3O4/PGE, respectively. The results from real sample studies proved that the fabricated FI-amperometric sensors enable high applicability towards determination of formaldehyde in real water samples.
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    Fabrication of a Novel Optical Glucose Biosensor Using Copper(II) Neocuproine as a Chromogenic Oxidant and Glucose Dehydrogenase-Immobilized Magnetite Nanoparticles
    (Amer Chemical Soc, 2023) Ayaz, Selen; Uzer, Aysem; Dilgin, Yusuf; Apak, M. Resat
    This study describes a novel optical glucose biosensor based on a colorimetric reaction between reduced nicotinamide adenine dinucleotide (NADH) and a copper(II) neocuproine complex ([Cu(Nc)(2)](2+)) as a chromogenic oxidant. An enzymatic reaction takes place between glucose and glucose dehydrogenase (GDH)-chitosan (CS) immobilized on silanized magnetite nanoparticles (CS@SiO2@Fe3O4) in the presence of coenzyme NAD(+). The oxidation of glucose to gluconolactone via the immobilized enzyme is coupled with the reduction of NAD(+) to NADH at the same time. After the separation of GDH-immobilized SiO2@Fe3O4 with a magnet, the enzymatically produced NADH chemically reduces the chromogenic oxidant cupric neocuproine to the cuprous chelate. Thus, the glucose biosensor is fabricated based on the measurement of the absorbance of the formed yellow-orange complex ([Cu(Nc)(2)](+)) at 450 nm. The obtained results show that the colorimetric biosensor has a wide linear response range for glucose, between 1.0 and 150.0 mu M under optimized conditions. The limit of detection and limit of quantification were found to be 0.31 and 1.02 mu M, respectively. The selectivity properties of the fabricated biosensor were tested with various interfering species. This biosensor was applied to various samples, and the obtained results suggest that the fabricated optical biosensor can be successfully used for the selective and sensitive determination of glucose in real samples.
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    Flow injection amperometric determination of hydrazine at a cupric-neocuproine complex/anionic surfactant modified disposable electrode
    (Elsevier, 2020) Ayaz, Selen; Dilgin, Yusuf; Apak, Resat
    Hydrazine (N2H4) is a hazardous chemical widely used as rocket propellant and industrial intermediate, therefore its sensitive and accurate analysis in environmental samples is very important. In this study, a new approach for flow injection amperometric detection of N2H4 is proposed based on its electrocatalytic oxidation at a bis(neocuproine)copper (II) chelate complex/sodium dodecyl sulfate-modified graphite pencil electrode (Cu (II)-Ncp/SDS/GPE). The proposed electrode was prepared by consecutive adsorption of anionic surfactant (SDS) and Cu(II)-Ncp onto pencil leads and the surface morphologies of electrodes prepared were elucidated by recording of their SEM images. Cyclic voltammograms (CVs) showed that Cu(II)-Ncp exhibited an excellent redox mediator property for the electrocatalytic oxidation of N2H4, because oxidation potential of N2H4 at bare GPE shifted to more negative direction with the use of Cu(II)-Ncp/SDS/GPE. Then, flow injection (FI) electroanalysis of N2H4 was performed by utilizing the electrocatalytic oxidation of N2H4 at Cu(II)-Ncp/SDS/GPE. A wide linear range (0.25-250 mu M) with a limit of detection (LOD) of 0.07 mu M and a sensitivity of 262 mu AmM(-1)cm(-2) were obtained for the FI amperometric detection of N2H4. Satisfactory recoveries were obtained for N2H4 detection in water samples, showing that this method can be accurately applied to real water samples.
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    Flow injection amperometric determination of hydrazine based on its electrocatalytic oxidation at pyrocatechol violet modified pencil graphite electrode
    (Pergamon-Elsevier Science Ltd, 2017) Ayaz, Selen; Dilgin, Yusuf
    A disposable, low cost, commercial available electrode, Pencil graphite electrode (PGE), was modified with pyrocatechol violet (Pcv) for electrocatalytic oxidation of hydrazine. To prepare modified electrode, pencil leads were immersed into 0.01 M Pcv solution for 10 min at room temperature. Cyclic voltammetric experiments show that a broadened and highly irreversible peak attributed to oxidation of N2H4 was observed at 600 mV at the bare PGE, while a well-defined irreversible oxidation peak was observed at 100 mV at the Pcv/PGE. A shift in the overpotential to more negative direction (about 500 mV) and an enhancement in the peak current indicate that the Pcv/PGE presents an efficient electrocatalytic activity toward oxidation of hydrazine. Then, flow injection analysis (FIA) of N2H4 was performed based on its electrocatalytic oxidation at the Pcv/PGE. The recorded amperometric current-time curves in FIA under optimized conditions showed a linear dependence on the N2H4 concentration between 2.5 x 10(-4) mM and 0.50 mM with a detection limit of 0.08 mu M. This proposed modified electrode exhibits a simple, disposable, low cost, rapid and sensitive determination of hydrazine. (c) 2017 Elsevier Ltd. All rights reserved.
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    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, Reşat
    This 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.
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    Flow-Injection Amperometric Determination of Glucose Using Nickel Oxide-Cobalt (II,III) Oxide and Nickel Oxide-Copper Nanoparticle Modified Pencil Graphite Electrodes
    (Taylor & Francis Inc, 2022) Ayaz, Selen; Karakaya, Serkan; Emir, Gamze; Usakligil, Nihan; Dilgin, Didem Giray; Dilgin, Yusuf
    This study features an enzyme-free amperometric determination of glucose with flow injection analysis (FIA) using pencil graphite electrodes (PGEs) modified with nickel oxide-cobalt (II,III) oxide (NiO-Co3O4/PGE) and nickel oxide-copper nanoparticle (NiO-CuNPs/PGE). Both modified PGEs exhibited excellent electrocatalytic activity toward oxidation of glucose in strong alkaline media since they enhanced the peak current compared with the bare PGE and single metal oxide- or metal nanoparticle-modified PGEs. Flow-injection (FI) amperometry showed the linear response range, the limit of detection and sensitivity for NiO-Co3O4/PGE and NiO-CuNPs/PGE were 1.0-1000 mu M, 0.23 mu M and 586 mu A mM(-1) cm(-2), and 0.10-250 mu M, 0.03 mu M and 949 mu A mM(-1) cm(-2), respectively. Glucose was determined in real samples with good accuracy and precision.