In this work new designed, highly sensitive electrochemical method is developed for the determination of nitrites in tap water using glassy carbon electrode modified with graphene nanoribbons ...(GNs/GCE). Graphene nanoribbons (GNs) have been newly synthetized and aligned to the surface of glassy carbon electrode (GCE) and exhibited excellent electrocatalytic activity for nitrite oxidation with a very high peak currents. Studies about electrochemical behavior and optimization of the most important experimental conditions were done using cyclic voltammetry (CV), while quantitative studies were done with amperometric detection. Nitrite provides a well-defined, oxidation peak at +0.9V (vs. Ag/AgCl, 3.0M KCl) in Britton-Robinson buffer solution (BRBS) at pH 3. The influence of most possible interferent ions has been examined and was found to be negligible. Under optimized experimental conditions in BRBS at pH 3 linear calibration curves were obtained in the range from 0.5 to 105µM with the detection limit of 0.22µM. Reproducibility of ten replicate measurements of 1µM of nitrite was estimated to be 1.9%. Proposed method and constructed sensor is successfully applied for the determination of nitrite present in tap water samples without any pretreatment. This developed method represents inexpensive analytical alternative approach compared to other analytical methods.
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•Graphene nanoribbons were synthetized and used as a sensing material.•Glassy carbon electrode modified with graphene nanoribbons was fabricated.•Determination of nitrite in tap water samples was studied.•Wide dynamic range from 0.5 to 105µM with a detection limit of 0.22µM was achieved.
A nonenzymatic hydrogen-peroxide sensor was developed by utilization of silver nanoparticles and graphene nanoribbons. The mentioned composite was inflicted on a screen-printed carbon electrode which ...provides disposable, ready-to-use sensor. The structure and morphology of the nanocomposite were analyzed by scanning electron microscopy and X-ray diffraction. The sensor has excellent performance toward H2O2 amperometric detection. Figures of merit include dynamic response range from 0.05 to 5mM and detection limit of 20μM (at S/N=3). The fabricated sensor was used for the determination of H2O2 in milk samples. The obtained results showed that the proposed AgNp@GNR/SPCE sensor can be used for the determination of hydrogen peroxide in real samples.
•New enzyme-less sensor for the determination of hydrogen peroxide is proposed.•Disposable sensor based on silver nanoparticles and graphene nanoribbons composite supported on screen printed electrode.•Satisfactory selectivity, sensitivity and precision of proposed method are obtained.
A carbon paste electrode bulk was modified with MnO
2
and investigated for use as an electrochemical sensor for riboflavin (vitamin B
2
) using differential pulse voltammetry (DPV). Riboflavin ...displays a well expressed oxidation peak at −0.15 V (versus Ag/AgCl) in solutions with a pH value of 2. Effects of pH value, pulse amplitude and pulse time were optimized by employing DPV. The signals obtained are linearly related to the concentrations of riboflavin in the range from 0.02 to 9 μM. Other features include a 15 nM detection limit, and good reproducibility (±3 %) and repeatability (±2 %). Interferences by common compounds were tested, and the method was successfully applied to the determination of riboflavin in pharmaceutical formulations where is gave recoveries in the range from 95 to 97 %.
Graphical abstract
Manganese(IV) oxide was used as a modifier for the carbon paste electrode (MnO
2
/CPE) for improving its performance toward riboflavin oxidation. Cyclic voltammetry and differential voltammetry were used for characterization and determination of riboflavin, respectively.
Essential oil of Carum copticum seeds, obtained from a local shop, was extracted and content of thymol was analyzed using square-wave voltammetry at boron-doped diamond electrode. The effect of ...various parameters, such as pH of supporting electrolyte and square-wave voltammetric parameters (modulation amplitude and frequency), was examined. In Britton–Robinson buffer solution (pH 4), thymol provided a single and oval-shaped irreversible oxidation peak at +1.13 V versus silver/silver chloride potassium electrode (3M). Under optimal experimental conditions, a plot of peak height against concentration of thymol was found to be linear over the range of 4 to 100μM consisting of two linear ranges: from 4 to 20μM (R2=0.9964) and from 20 to 100μM (R2=0.9993). The effect of potential interferences such as p-cymene and γ-terpinene (major components in essential oil of C. copticum seeds) was evaluated. Thus, the proposed method displays a sufficient selectivity toward thymol with a detection limit of 3.9μM, and it was successfully applied for the determination of thymol in essential oil of C. copticum seeds. The Prussian blue method was used for validation of the proposed electroanalytical method.
In this work, we investigated the morphological and electrochemical properties of gallium/bismuth mixed oxide. The bismuth concentration was varied from 0 to 100%. The correct ratio was determined ...with inductively coupled plasma-optical emission spectroscopy (ICP-OES), while surface characteristics were determined using scanning electron microscopy (SEM) and X-ray diffraction (XRD) measurement. Electrochemical characteristics were studied using electrochemical impedance spectroscopy (EIS) in the Fe
2+/3+
couple. The obtained materials were tested for adrenaline detection. After square wave voltammetry (SWV) optimization, the best electrode showed a wide linear working range from 7 to 100 µM at pH 6 of the Britton–Robinson buffer solution (BRBS) supporting electrolyte. The limit of detection (LOD) for the proposed method was calculated as 1.9 µM, with a limit of quantification (LOQ) of 5.8 µM. The excellent selectivity of the proposed method, with good repeatability and reproducibility, strongly suggests the possible application of the procedure for the determination of adrenaline in artificially prepared real samples. The practical applicability with good recovery values indicates that the morphology of the materials is closely connected with other parameters, which further suggests that the developed approach can offer a low-cost, rapid, selective, and sensitive method for adrenaline monitoring.
Graphical abstract
•First report dealing with electrochemical oxidation of flutamide is presented.•BDD electrode was used for the first time in sensing of cytostatic drug.•Advanced innovative platform for determination ...of flutamide was developed.•Submicromolar LOD values were achieved using bare BDD electrode.•Simple and effective alternative to mercury-based and modified electrodes.
An innovative, rapid and simple electrochemical approach for the reliable quantification of cytostatic drug flutamide (FLU) in various matrices is herein proposed. This platform involves coupling of differential pulse (DPV) and square-wave voltammetry (SWV) with a boron-doped diamond (BDD) electrode as the working electrode and 0.1M sulphuric acid as the supporting electrolyte. For the first time, the voltammetric profile of FLU was manifested by three irreversible and diffusion-controlled oxidation peaks at +1.1 (P1), +1.4 (P2) and +1.9V (P3). The analytical performance evaluation was assessed for all three peaks, using both pulse voltammetric techniques with the optimized operating parameters and the highest sensitivity of 1.76nA/μM was accomplished for P2 using DPV and 3.54nA/μM for P3 using SWV. The corresponding linear concentration ranges were found to be 0.99–42.9 and 4.8–35.5μM with the detection limits of 0.42 and 0.18μM, respectively. The repeatability varied, depending on the oxidation peaks of FLU, with the relative standard deviations in the range of 3.3–8.8% and 2.9–9.3% for DPV and SWV, respectively. The proposed electrochemical platform was successfully applied in the analysis of pharmaceutical formulations, spiked human urine and water samples with the significant mean recoveries. Using BDD electrode, the current work establishes an advanced, simple and rapid alternative platform to so far used toxic mercury-based electrodes and time demanding chemically modified electrodes in cytostatic sensing. Besides, BDD electrode represents a comfortable electrochemical sensor for routine analysis in pharmaceutical, clinical and environmental chemistry.
Diagnosis and treatment of some important diseased and metabolic disorders is based on successful detection of albumin. In this work, we aim to develop a simple immunosensor for the detection of ...human serum albumin in biological fluids. Anti-human albumin antibody was covalently attached to the activated surface of screen-printed carbon electrodes enriched with carboxyl graphene/gold nanoparticles composite. Microstructure (TEM, FE-SEM, XRD) and electrochemical (CV, EIS) characterization methods were used to investigate composite properties and to confirm the successful modification of the electrodes. Under the optimal conditions, linear working range and limit of detection were 2.5–500 μg/mL and 1.55 μg/mL, respectively. Additionally, the effect of some possibly interfering compounds was investigated and the immunosensor was used for real sample analysis. The results showed that the sensor exhibited accurate, precise and sensitive characteristics and can be promising replacement to the convention methods for albumin detection in clinical practice.
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•New immunosensor for the determination of human serum albumin is proposed.•Disposable immunosensor based on carboxylic graphene enriched with gold nanoparticles supported on screen printed electrode.•Satisfactory selectivity, sensitivity and precision of proposed method are obtained.
In this work, we aimed to propose a newly synthesized composite material with enhanced electrocatalytic properties as a novel screen-printed sensor for the quantification of NADH. Additionally, the ...surface was modified with alcohol dehydrogenase for the preparation of an amperometric biosensor for analysis of ethanol. Synthesized material was characterized using several microstructural (FE-SEM, HR-TEM, XRD) and electrochemical (CV, EIS) techniques. The electrochemical response of the tested analytes was investigated as a function of important parameters. Under optimal conditions, the working linear range and limit of detection for ethanol sensing was 1–1800 µM and 0.19 µM, respectively. For NADH, the linear range was from 1 to 1300 µM with limit of detection of 0.52 µM. Moreover, effects of some possible interfering compounds were investigated and the developed procedure was applied to commercial alcoholic beverages. The results obtained showed satisfactory precision and accuracy of the developed method and confirm the proposed approach could be a possible replacement for the currently used techniques for ethanol and NADH quantification.
•Novel material with enhanced electrocatalytic properties was used as screen-printed sensor for the quantification of NADH.•Electrode surface was modified with alcohol dehydrogenase for the preparation of amperometric biosensor for ethanol analysis.•Material was characterized using microstructural and electrochemical techniques.•Excellent performances were achieved using suggested approach.
A reagentless third generation electrochemical glucose biosensor was fabricated based on wiring the template enzyme glucose oxidase (GOx) with graphene nanoribbons (GN) in order to create direct ...electron transfer between the co-factor (flavin adenine dinucleotide, FAD) and the electrode. The strategy involved: (i) isolation of the apo-enzyme by separating it from its co-enzyme; (ii) preparation of graphene nanoribbons (GN) by oxidative unzipping of multi-walled carbon nanotubes; (iii) adsorptive immobilization of GNs on the surface of a screen printed carbon electrode (SPCE); (iv) covalent attachment of FAD to the nanoribbons; (v) recombination of the apo-enzyme with the covalently bound FAD to the holoenzyme; and (vi) stabilization of the bio-layer with a thin membrane of Nafion. The biosensor (referred to as GN/FAD/apo-GOx/Nafion/SPCE) is operated at a potential of +0.475 V vs Ag/AgCl/{3 M KCl} in flow-injection mode with an oxygen-free phosphate buffer (pH 7.5) acting as a carrier. The signals are linearly proportional to the concentration of glucose in the range from 50 to 2000 mg⋅L
−1
with a detection limit of 20 mg⋅L
−1
. The repeatability (10 measurements, at 1000 mg⋅L
−1
glucose) is ±1.4% and the reproducibility (5 sensors, 1000 mg⋅L
−1
glucose) is ±1.8%. The biosensor was applied to the determination of glucose in human serum.
Graphical abstract
Wiring of the apo-enzyme of glucose oxidase (apo-GOx) with graphene nanoribbons (GN) bound to FAD at a screen-printed carbon electrode (SPCE). Cyclic voltammetric and amperometric responses to various glucose concentrations.
A disposable glucose biosensor was prepared using nanoparticles of MnO2 decorated on graphene nanoribbons by surface modification with drop coating with the GOx and Nafion®. Tested material was ...synthesized and characterized using several techniques. The biosensor could be operated under physiological conditions (0.1 M phosphate buffer, pH 7.4) and exhibited good reproducibility and stability. The linear range for the amperometric response of the biosensor at operating potential of +0.50 (versus Ag/AgCl) was from 0.1 to 1.4 mmol/l, with a detection limit of 0.05 mmol/l and high sensitivity of 56.32 μA/mmol cm2. Developed method was tested toward glucose quantification in real samples with satisfactory accuracy and precision.
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•New enzymatic biosensor for the determination of glucose is proposed.•Development of a disposable biosensor based on graphene nanoribbons supported with MnO2 nanoparticles.•Satisfactory selectivity, sensitivity and precision of proposed method are obtained.
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