Disposable Amperometric Biosensor Based on Poly‐L‐lysine and Fe3O4 NPs‐chitosan Composite for the Detection of Tyramine in Cheese

An amperometric tyramine biosensor based on poly‐L‐lysine (PLL) and Fe₃O₄ nanoparticles (Fe₃O₄NP) modified screen printed carbon electrode (SPCE) was developed. PLL was formed on the SPCE by the electropolymerization of L‐lysine. Subsequently, Fe₃O₄NP suspension prepared in chitosan (CH) solution was casted onto the PLL/SPCE. Tyrosinase (Ty) enzyme was immobilized onto the modified Fe₃O₄?CH/PLL/SPCE and the electrode was coated with Nafion to fabricate the Ty/Fe₃O₄?CH/PLL/SPCE. Different techniques including scanning electron microscopy, chronoamperometry (i–t curve), cyclic voltammetry and electrochemical impedance spectroscopy were utilized to study the fabrication processes, electrochemical characteristics and performance parameters of the biosensor. The analytical performance of the tyramine biosensor was evaluated with respect to linear range, sensitivity, limit of detection, repeatability and reproducibility. The response of the biosensor to tyramine was linear between 4.9×10^?7–6.3×10^?5 M with a detection limit of 7.5×10^?8 M and sensitivity of 71.36 μA mM^?1 (595 μA mM^?1 cm^?2). The application of the developed biosensor for the determination of tyramine was successfully tested in cheese sample and mean analytical recovery of added tyramine in cheese extract was calculated as 101.2±2.1 %. The presented tyramine biosensor is a promising approach for tyramine analysis in real samples due to its high sensitivity, rapid response and easy fabrication.     

Fabrication of Fe3O4 Nanoparticles Modified Electrode and Its Application for Voltammetric Sensing of Dopamine

Magnetic nanoparticles of Fe₃O₄ approximately 5nm in size were synthesized and characterized by XRD and TEM. A novel gold electrode modified with Fe₃O₄ nanoparticles was then constructed and was characterized by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The modified electrode exhibited strong promoting effect and high stability toward the electrochemical oxidation of dopamine (DA), which gave reversible redox peaks with a formal potential of 0.192 V (vs. Ag/AgCl) electrode in pH 7.0 phosphate buffer solution (PB). The anodic peak currents (measured by constant potential amperometry) increased linearly with the concentration of dopamine in the range of 1.5×10^?7 to 4.0×10^?4 M. The detection limit (S/N=3) obtained was 3.0×10^?8 M. The relative standard deviation (RSD) of 8 successive scans was 3.41% for 1.5×10^?6 M DA. The interference of ascorbic acid (AA) could be eliminated efficiently. The proposed method showed excellent sensitivity and recovery.     

Chitosan–iron oxide nanobiocomposite based immunosensor for ochratoxin-A

The rabbit immunoglobulin antibodies (IgGs) have been immobilized onto nanobiocomposite film of chitosan (CH)–iron oxide (Fe₃O₄₎ nanoparticles prepared onto indium–tin oxide (ITO) electrode for detection of ochratoxin-A (OTA). Excellent film forming ability and availability of –NH₂ group in CH and affinity of surface charged Fe₃O₄ nanoparticles for oxygen support the immobilization of IgGs. Differential pulse voltammettry (DPV) studies indicate that Fe₃O₄ nanoparticles provide increased electroactive surface area for loading of IgGs and improved electron transport between IgGs and electrode. IgGs/CH–Fe₃O₄ nanobiocomposite/ITO immunoelectrode exhibits improved characteristics such as low detection limit (0.5 ng dL⁻¹), fast response time (18 s) and high sensitivity (36 μA/ng dL⁻¹ cm⁻²) with respect to IgGs/CH/ITO immunoelectrode.     

Fabrication of New Magnetic Nanoparticles (Fe3O4) Grafted Multiwall Carbon Nanotubes and Heterocyclic Compound Modified Electrode for Electrochemical Sensor

Magnetic Fe₃O₄ nanoparticles functionalized multiwalled carbon nanotubes (nano‐Fe₃O₄ MWNTs) were prepared for electrochemical sensors. 2‐amino‐5‐mercapto‐1,3,4‐thiadiazole was used as a connecter to form a network that connected nano‐Fe₃O₄ MWNTs to the Au electrode surface. Modified process of the electrode was studied with SEM, TEM and cyclic voltammetry. Cyclic voltammetry and amperometric i‐t curve were used to investigate characteristics of the obtained electrode. The sensor has been successfully used on the direct detection of catechol and showed excellent performances. The linear regression equation was I_pa(μA)=0.07763+0.16739 C (μmol/L); R=0.9993 and the detection limit was 5.38×10^?8 mol/L. The modified electrode showed good reproducibility and stability.     

Carbon Paste Electrode Modified with ZrO<Subscript>2</Subscript> Nanoparticles and Ionic Liquid for Sensing of Dopamine in the Presence of Uric Acid

A novel carbon paste electrode modified with ZrO₂ nanoparticles and an ionic liquid (n-hexyl-3- methylimidazolium hexafluorophosphate) was fabricated. The electrochemical study of the modified electrode, as well as its efficiency for simultaneous voltammetric oxidation of dopamine and uric acid is described. The electrode was also employed to study the electrochemical oxidation of dopamine and uric acid, using cyclic voltammetry, chronoamperometry and square wave voltammetry as diagnostic techniques. Square wave voltammetry exhibits linear dynamic range from 1.0 × 10^?6 to 9.0 × 10^?4 M for dopamine. Also, square wave voltammetry exhibits linear dynamic range from 9.0 × 10^?6–1.0 × 10^?3 M for uric acid. The modified electrode displayed strong function for resolving the overlapping voltammetric responses of dopamine and uric acid into two well-defined voltammetric peaks. In the mixture containing dopamine and uric acid, the two compounds can be well separated from each other with potential difference of 155 mV, which is large enough to determine dopamine and uric acid individually and simultaneously. Finally, the modified electrode was used for determination of dopamine and uric acid in real samples.     

Electrocatalysis of Horseradish Peroxidase Immobilized on Cobalt Nanoparticles Modified ITO Electrode

Abstract

It is the first time that Horseradish peroxidase (HRP) was successively immobilized on the magnetic cobalt nanoparticles modified ITO (indium tin oxide) electrode. Morphologies of electrode surface were featured by the field emission‐scanning electron microscope (FSEM). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to characterize the modified process of electrode. Direct electrochemistry and electrocatalysis of HRP immobilized on nano‐Co/ITO were investigated. The biosensor exhibited high sensitivity, good stability, and excellent electrocatalytic activity to the reduction of H₂O₂. Under the optimized experimental conditions, a calibration curve over 2.0×10^?9～2.0×10^?8 mol l^?1 and 2.0×10^?7～2.0×10^?6 mol l^?1, with a limit of detection of 1.9×10^?9 mol l^?1 was obtained. The apparent Michaelis‐Menten constant (K _M ^app ) for HRP/nano‐Co/ITO electrode was calculated to be 0.79 mmol l^?1, indicating a higher affinity of HRP attached on the modified electrode.     

Electrochemical determination of NADH using a glassy carbon electrode modified with Fe3O4 nanoparticles and poly-2,6-pyridinedicarboxylic acid, and its application to the determination of antioxidant capacity

We have prepared a glassy carbon electrode modified with poly-2,6-pyridinedicarboxylic acid and with magnetic Fe₃O₄ nanoparticles. This modification enhances the effective surface area and the electrocatalytic oxidation of nicotinamide adenine dinucleotide (NADH) in addition to providing positively charged groups for electrostatic assembly of the phosphate group of NADH. The modified electrode responds linearly to NADH in the range from 5?×?10^?8 to 2.5?×?10^?5?M and gives a lower detection limit of 1?×?10^?8?M. It displays satisfactory selectivity and reproducibility. The sensor was applied to rapid screening of plant extracts for their antioxidant properties.

Direct Electrochemistry of Hemoglobin Based on Fe3O4@SiO2 Nanoparticles Modified Electrode

A biosensor based on hemoglobin‐Fe₃O₄@SiO₂ nanoparticle bioconjunctions modified indium‐tin‐oxide (Hb/Fe₃O₄@SiO₂/ITO) electrode was fabricated to determine the concentration of H₂O₂. UV‐vis absorption spectra, fourier transform infrared (FT‐IR) spectroscopy, cyclic voltammetry (CV) and high‐resolution transmission electron microscopy (HRTEM) were used to characterize the bioconjunction of Fe₃O₄@SiO₂ with Hb. Experimental results demonstrate that the immobilized Hb on the Fe₃O₄@SiO₂ matrix retained its native structure well. In addition, Fe₃O₄@SiO₂ nanoparticles (NPs) are very effective in facilitating electron transfer of the immobilized enzyme, which can be attributed to the unique nanostructure and larger surface area of the Fe₃O₄@SiO₂ NPs. The biosensor displayed good performance for the detection of H₂O₂ with a wide linear range from 2.03×10^?6 to 4.05×10^?3 mol/L and a detection limit of 0.32 µmol/L. The resulting biosensor exhibited fast amperometric response, good stability, reproducibility, and selectivity to H₂O₂.     

Nanostructured Iron Oxide Platform for Impedimetric Cholesterol Detection

A nanostructured iron oxide (NanoFe₃O₄, particle size ca. 25 nm and roughness ca. 21 nm) film deposited onto a hydrolyzed indium‐tin‐oxide (ITO) coated glass plate has been used to immobilize cholesterol oxidase (ChOx) to fabricate an impedimetric cholesterol sensor. Electrochemical studies reveal that surface charged Fe₃O₄ nanoparticles provide better conformation for ChOx loading resulting in enhanced electron transfer between ChOx and the electrode. Impedimetric response studies of the ChOx/NanoFe₃O₄/ITO bioelectrode exhibit improved linearity (2.5–400 mg/dL), low detection limit (0.25 mg/dL), fast response time (25 s), high sensitivity (86 Ω/mg dL^?1/cm^?2) and a low value of the Michaelis‐Menten constant (K_m, 0.8 mg/dL) with a regression coefficient of 0.997.     

A Simple and Sensitive Square Wave Stripping Pathway for the Analysis of Desmedipham Herbicide by Modified Carbon Paste Electrode Based on Hematite (α‐Fe2O3 Nanoparticles)

In the present study, desmedipham, used as an herbicide to control broad leaf weed in commonly sugar beet crops, was analyzed at the first time by cyclic voltammetry (CV) and square wave stripping voltammetry (SWSV) with the modified carbon paste electrode based on hematite nanoparticles (α‐Fe₂O₃?CPE). The modified α‐Fe₂O₃?CPE prepared by hematite (α‐Fe₂O₃ nanoparticles), which is very sensitive to carbon paste electrode (CPE) and glassy carbon electrode (GCE). Morphology of electrode surface detailed by scanning electron microscopy (SEM) and energy dispersive X‐ray analysis (EDX). The oxidation of desmedipham created irreversible well‐done two peaks at nearly +1.1 and +1.3 V. In order to obtain the best calibration graph, various important parameters such as pH, accumulation time, puls amplitude and frequency etc. were investigated. Under the optimum conditions, electrochemical behavior of desmedipham presented two linear working ranges at 0.15–1.20 mg/L and 1.20–4.50 mg/L. The limits of detection (LOD) for the desmedipham were calculated as 41.00 and 50.00 μg/L for the peak I and II, respectively. Furthermore, desmedipham was analyzed at high recovery in the presence of rizolex, fluometuron, teflubenzuron and some heavy metal ions. Consequently, the developed SWSV was successfully applied to evaluate desmedipham in spiked commercial strawberry juices at recoveries of 96.00–104.00 % with satisfactory relative standard deviations.     

Detection of Dexamethasone Sodium Phosphate in Blood Plasma: Application of Hematite in Electrochemical Sensors

We studied sensor application of a graphene oxide and hematite (α‐Fe₂O₃/GO) composite electrode well‐characterized by the SEM and XRD. Through differential pulse voltammetry (DPV), oxidation of dexamethasone sodium phosphate (DSP) was studied at the surface of a glassy carbon electrode (GCE) modified with graphene oxide nanosheets (GO) and the α‐Fe₂O₃/GO composite. The values of the transfer coefficient (α) and the diffusion coefficient (D) of DSP were 0.5961 and 4.71×10^?5 cm² s^?1 respectively. In the linear range of 0.1–50 μM, the detection limit (DL) was 0.076 μM. In the second step, a GCE was modified with α‐Fe₂O₃/GO composite and the DSP measurement step was repeated to analyzed and compare the effects of hematite nanoparticles present on graphene oxide surfaces. According to the results, α and D were 0.52 and 2.406×10^?4 cm² s^?1 respectively and the DL was 0.046 μM in the linear range of 0.1–10.0 μM. The sensor is simple, inexpensive and uses blood serum.     

Construction of an Amperometric Glucose Biosensor by Immobilization of Glucose Oxidase on Nanocomposite at the Surface of FTO Electrode

Fluorine? tin oxide (FTO) nanostructure was developed on the surface of a glass plate using spray payroliziz method. A new electrochemical biosensor was fabricated based on a layer by layer process. In this process chitosan? Fe₃O₄ (CH? Fe₃O₄) nanocomposite film was prepared at the surface of FTO electrode by dip? coating method. In the next step, the glucose oxidase (GOx) was immobilized on the CH? Fe₃O₄/FTO nanocomposite electrode. The GOx/CH? Fe₃O₄/FTO bioelectrode has a linear range of 10–270 µM and a detection limit of 5 µM. The highest sensitivity was obtained at 1.2 µA mM^?1 cm^?2.     

Fe3O4@SiO2‐PANI‐Au Nanocomposite Prepared for Electrochemical Determination of Quercetin in Food Samples and Biological Fluids

A new electrochemical sensor based on Fe₃O₄@SiO₂‐PANI‐Au nanocomposite was fabricated for modification of glassy carbon electrode (Fe₃O₄@SiO₂‐PANI‐Au GCE). The Fe₃O₄@SiO₂‐PANI‐Au nanocomposite was characterized by TEM, FESEM‐EDS‐Mapping, XRD, and TGA methods. The Fe₃O₄@SiO₂‐PANI‐Au GC electrode exhibited an acceptable sensitivity, fast electrochemical response, and good selectivity for determination of quercetin. Under optimal conditions, the linear range for quercetin concentrations using this sensor was 1.0×10^?8 to 1.5×10^?5 mol L^?1, and the limit of detection was 3.8×10^?9 mol L^?1. The results illustrated that the offered sensor could be a possible alternative for the measurement of quercetin in food samples and biological fluids.     

Self-assembly of ultra-small gold nanoparticles on an indium tin oxide electrode for the enzyme-free detection of hydrogen peroxide

A novel enzyme-free electrochemical sensor for H₂O₂ was fabricated by modifying an indium tin oxide (ITO) support with (3-aminopropyl) trimethoxysilane to yield an interface for the assembly of colloidal gold. Gold nanoparticles (AuNPs) were then immobilized on the substrate via self-assembly. Atomic force microscopy showed the presence of a monolayer of well-dispersed AuNPs with an average size of ~4 nm. The electrochemical behavior of the resultant AuNP/ITO-modified electrode and its response to hydrogen peroxide were studied by cyclic voltammetry. This non-enzymatic and mediator-free electrode exhibits a linear response in the range from 3.0?×?10^?5 M to 1.0?×?10^?3 M (M?=?mol?·?L^?1) with a correlation coefficient of 0.999. The limit of detection is as low as 10 nM (for S/N?=?3). The sensor is stable, gives well reproducible results, and is deemed to represent a promising tool for electrochemical sensing.

Electrocatalytic Determination of Hydrazine and Phenol Using a Carbon Paste Electrode Modified with Ionic Liquids and Magnetic Core‐shell Fe3O4@SiO2/MWCNT Nanocomposite

A carbon paste electrode was modified with 2‐(4‐Oxo‐3‐phenyl‐3,4‐dihydroquinazolinyl)‐N′‐phenyl‐hydrazinecarbothioamide, magnetic core? shell Fe₃O₄@SiO₂/MWCNT nanocomposite and ionic liquid (n‐hexyl‐3‐methylimidazolium hexafluoro phosphate). The electro‐oxidation of hydrazine at the surface of the modified electrode was studied using electrochemical approaches. This modified electrode offers a considerable improvement in voltammetric sensitivity toward hydrazine, compared to the bare electrode. Square wave voltammetry (SWV) exhibits a linear dynamic range from 7.0×10^?8 to 5.0×10^?4 M and a detection limit of 40.0 nM for hydrazine. The diffusion coefficient and kinetic parameters (such as electron transfer coefficient and the heterogeneous rate constant) for hydrazine oxidation were also determined. The prepared modified electrode exhibits a very good resolution between the voltammetric peaks of hydrazine and phenol that makes it suitable for the detection of hydrazine in the presence of phenol in real samples.     

Electrochemical Detection of Dopamine at Fe3O4/SPEEK Modified Electrode

Reported here is the design of an electrochemical sensor for dopamine (DA) based on a screen print carbon electrode modified with a sulphonated polyether ether ketone-iron (III) oxide composite (SPCE-Fe₃O₄/SPEEK). L. serica leaf extract was used in the synthesis of iron (III) oxide nanoparticles (Fe₃O₄NPs). Successful synthesis of Fe₃O₄NP was confirmed through characterization using Fourier transform infrared (FTIR), ultraviolet–visible light (UV–VIS), X-ray diffractometer (XRD), and scanning electron microscopy (SEM). Cyclic voltammetry (CV) was used to investigate the electrochemical behaviour of Fe₃O₄/SPEEK in 0.1 M of phosphate buffer solution (PBS) containing 5 mM of potassium ferricyanide (III) solution (K₃[Fe(CN)₆]). An increase in peak current was observed at the nanocomposite modified electrode SPCE-Fe₃O₄/SPEEK) but not SPCE and SPCE-Fe₃O₄, which could be ascribed to the presence of SPEEK. CV and square wave voltammetry (SWV) were employed in the electroxidation of dopamine (0.1 mM DA). The detection limit (LoD) of 7.1 μM and 0.005 μA/μM sensitivity was obtained for DA at the SPCE-Fe₃O₄/SPEEK electrode with concentrations ranging from 5–50 μM. LOD competes well with other electrodes reported in the literature. The developed sensor demonstrated good practical applicability for DA in a DA injection with good resultant recovery percentages and RSDs values.     

Electroanalytical Determination of Carbaryl in Natural Waters on Boron Doped Diamond Electrode

The anodic voltammetric behavior of carbaryl on a boron‐doped diamond electrode in aqueous solution is reported. The results, obtained by square‐wave voltammetry at 0.1 mol L^?1 Na₂SO₄ and pH 6.0, allow the development of a method to determine carbaryl, without any previous step of extraction, clean‐up, preconcentration or derivatization, in the range 2.5–30.0×10^?6 mol L^?1, with a detection limit of 8.2±0.2 μg L^?1 in pure water. The analytical sensitivity of this electrochemical method diminished slightly, from 3.07 mA mmol^?1 L to 2.90 mA mmol^?1L, when the electrolyte was prepared with water samples collected from two polluted points in an urban creek. In these conditions, the recovery efficiencies obtained were around 104%. The effect of other pesticides (fenthion and 4‐nitrophenol) was evaluated and found to exert a negligible influence on carbaryl determination. The square‐wave voltammetric data obtained for carbaryl were typical of an irreversible electrode process with mass transport control. The combination of square‐wave voltammetry and diamond electrodes is an interesting and desirable alternative for analytical determinations.     

An Ethanol Biosensor Based on Simple Immobilization of Alcohol Dehydrogenase on Fe3O4@Au Nanoparticles

An ethanol biosensor based on alcohol dehydrogenase (ADH) attached to Au seeds decorated on magnetic nanoparticles (Fe₃O₄@Au NPs) is presented. ADH was immobilized on Fe₃O₄@Au NPs, which were subsequently fixed by a magnet on a carbon paste electrode modified with 5 % (m : m) MnO₂. Optimum conditions for the amperometric determination of ethanol with the biosensor were as follows: working potential +0.1 V (vs. Ag/AgCl); supporting electrolyte: 0.1 M phosphate buffer solution at pH 6.8 containing 0.25 mM of the coenzyme (NAD⁺); working electrode: carbon paste with magnetically attached Fe₃O₄@Au NPs (0.012 mg ? cm^?2 electrode area) with immobilized alcohol dehydrogenase (120 units per cm² of electrode area). Linearity between signal and concentration was found for the range from 0.1 to 2.0 M ethanol (r²=0.995) with a detection limit of 0.07 M, a sensitivity of 0.02 µA ? mM^?1 ? cm^?2, a reproducibility of 4.0 % RSD, and a repeatability of 2.7 % RSD. The results for the determination of ethanol in alcoholic beverages showed good agreement with gas chromatography (GC) with recovery of 96.0 – 108.8 %.     

Catalytic effects of [Ag(H2O)(H3PW11O39)]3− on a TiO2 anode for water oxidation

A [H₃Ag^I(H₂O)PW₁₁O₃₉]^3?-TiO₂/ITO electrode was fabricated by immobilizing a molecular polyoxometalate-based water oxidation catalyst, [H₃Ag^I(H₂O)PW₁₁O₃₉]^3? (AgPW₁₁), on a TiO₂ electrode. The resulting electrode was characterized by X-ray powder diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy. Linear sweep voltammetry, chronoamperometry, and electrochemical impedance measurements were performed in aqueous Na₂SO₄ solution (0.1 mol L^?1). We found that a higher applied voltage led to better catalytic performance by AgPW₁₁. The AgPW₁₁-TiO₂/ITO electrode gave currents respectively 10 and 2.5 times as high as those of the TiO₂/ITO and AgNO₃-TiO₂/ITO electrodes at an applied voltage of 1.5 V vs Ag/AgCl. This result was attributed to the lower charge transfer resistance at the electrode-electrolyte interface for the AgPW₁₁-TiO₂/ITO electrode. Under illumination, the photocurrent was not obviously enhanced although the total anode current increased. The AgPW₁₁-TiO₂/ITO electrode was relatively stable. Cyclic voltammetry of AgPW₁₁ was performed in phosphate buffer solution (0.1 mol L^?1). We found that oxidation of AgPW₁₁ was a quasi-reversible process related to one-electron and one-proton transfer. We deduced that disproportionation of the oxidized [H₂Ag^II(H₂O)PW₁₁O₃₉]^3? might have occurred and the resulting [H₃Ag^IIIOPW₁₁O₃₉]^3? oxidized water to O₂.     

Preparation of NiFe2O4/graphene nanocomposite and its application as a modifier for the fabrication of an electrochemical sensor for the simultaneous determination of tramadol and acetaminophen

An effective electrochemical sensor for the rapid and simultaneous determination of tramadol and acetaminophen based on carbon paste electrode (CPE) modified with NiFe₂O₄/graphene nanoparticles was developed. The structures of the synthesized NiFe₂O₄/graphene nanocomposite and the electrode composition were confirmed by X-ray diffraction (XRD) spectrometry, Fourier transform infrared (FT-IR) spectrometry and scanning electron microscopy (SEM). The peak currents of square wave voltammetry of tramadol and acetaminophen increased linearly with their concentration in the range of 0.01–9 μmol L⁻¹. The detection limit for their determination was found to be 0.0036 and 0.0030 μmol L⁻¹, respectively. The results show that the combination of graphene and NiFe₂O₄ nanoparticles causes a dramatic enhancement in the sensitivity of the sensor. The fabricated sensor exhibited high sensitivity and good stability, and would be valuable for the clinical assay of tramadol and acetaminophen.