Sensitive and Rapid Flow Injection Amperometric Hydrazine Sensor using an Electrodeposited Gold Nanoparticle Graphite Pencil Electrode

A gold (Au) nanoparticle-modified graphite pencil electrode was prepared by an electrodeposition procedure for the sensitive and rapid flow injection amperometric determination of hydrazine (N₂H₄). The electrodeposited Au nanoparticles on the pretreated graphite pencil electrode surface were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction spectroscopy, and electrochemical impedance spectroscopy. Cyclic voltammograms showed that the Au nanoparticle-modified pretreated graphite pencil electrode exhibits excellent electrocatalytic activity toward oxidation of hydrazine because the highly irreversibly and broadly observed oxidation peak at +600?mV at the pretreated graphite pencil electrode shifted to ?167?mV at the Au nanoparticle pretreated graphite pencil electrode; in addition, a significant enhancement in the oxidation peak current was obtained. Thus, the flow-injection (FI) amperometric hydrazine sensor was constructed based on its electrocatalytic oxidation at the Au nanoparticle-modified pretreated graphite pencil electrode. The Au nanoparticle-modified pretreated graphite pencil electrode exhibits a linear calibration curve between the flow injection amperometric current and hydrazine concentration within the concentration range from 0.01 to 100?µM with a detection limit of 0.002?µM. The flow injection amperometric sensor has been successfully used for the determination of N₂H₄ in water samples with good accuracy and precision.     

Electrochemical Design of Ultrathin Palladium Coated Gold Nanoparticles as Nanostructured Catalyst for Amperometric Detection of Formaldehyde

An underpotential deposition (UPD) replacement tactic was employed to design a Pd overlayer on gold (Au) nanoparticles electrodeposited on a carbon ionic liquid electrode (CILE). Pd/Au/CILE was applied as an amperometric sensor for the determination of formaldehyde in aqueous solutions. The sensor displayed two linear ranges from 15 µM–1.4 mM and 1.4–56.7 mM of formaldehyde. The limit of detection was 3 µM of formaldehyde and the sensitivity of the sensor was 2.35 µA mM^?1, using the calibration graph in the lower range. The presence of 20 mM of formic acid and methanol and 10 mM ethanol did not interfere with the determination of formaldehyde solution.     

Fabrication of Hemoglobin/Ionic Liquid Modified Carbon Paste Electrode Based on the Electrodeposition of Gold Nanoparticles/CdS Quantum Dots and Its Electrochemical Application

A novel H₂O₂ amperometric biosensor based on the electrodeposition of gold nanoparticles (AuNPs) and CdS quantum dots (CdS QDs) onto a carbon paste electrode (CPE) and immobilizing hemoglobin (Hb) with ionic liquid (IL), is presented in this article. The modification process of the electrode was monitored by scanning electron microscopy (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Due to synergistic effects of AuNPs, CdS QDs and IL, the biosensor exhibited high stability and good bioelectrocatalytic ability to H₂O₂ with a linear concentration range from 10 to 750 µM and a detection limit of 4.35 µM (S/N=3).     

Fabrication of Bienzymatic Glucose Biosensor Based on Novel Gold Nanoparticles‐Bacteria Cellulose Nanofibers Nanocomposite

An exploration of gold nanoparticles–bacterial cellulose nanofibers (Au‐BC) nanocomposite as a platform for amperometric determination of glucose is presented. Two enzymes, glucose oxidase (GOx) and horseradish peroxidase (HRP) were immobilized in Au‐BC nanocomposite modified glassy carbon electrode at the same time. A sensitive and fast amperometric response to glucose was observed in the presence of electron mediator (HQ). Both of GOx and HRP kept their biocatalytic activities very well in Au‐BC nanocomposite. The detection limit for glucose in optimized conditions was as low as 2.3 µM with a linear range from 10 µM to 400 µM. The biosensor was successfully applied to the determination of glucose in human blood samples.     

Electroanalytical performance of self-assembled monolayer gold electrode for chloramphenicol determination

Monolayers of 2-mercapto-5-methylbenzimidazole (MMB) were prepared on a polycrystalline gold electrode via a self-assembly process to produce a self-assembled monolayer. The resulting electrode was investigated by cyclic voltammetry and electrochemical impedance spectroscopy, and applied to the determination of chloramphenicol (CAP) in a pharmaceutical formulation using flow injection analysis along with amperometric detection. The amperometric cell was operated at ?0.75 V (vs Ag/AgCl) at a flow rate of 3 mL min^?1. The method was applied to the determination of CAP in ophthalmic solutions, and its performance was compared to a previously validated HPLC method. The response to CAP is linear in the range from 0.050 to 1.000 µmol L^?1 (r?=?0.9990), and the limit of detection is 44 µmol L^?1.     

Ascorbic acid amperometric sensor using a graphene-wrapped hierarchical TiO<Subscript>2</Subscript> nanocomposite

An ascorbic acid (AA) amperometric sensor was fabricated based on a glassy carbon electrode (GCE) modified with a reduced graphene oxide-wrapped hierarchical TiO₂ (RGO—TiO₂) nanocomposite. The RGO—TiO₂ nanocomposite was synthesized via the facial wet chemical method and characterized by scanning electron microscopy and X-ray diffraction. Cyclic voltammetry and amperometric techniques were employed to investigate its electrocatalytic performance towards the AA oxidation. The combined advantages of RGO and TiO₂ provide the electrode with higher current response and lower oxidation potential compared with those of bare GCE and TiO₂ modified GCE. The proposed electrode can be used for the determination of AA in the wide concentration range from 1 to 1500 µM with the detection limit of 0.5 µM. The proposed electrode was successfully used to determine AA in vitamin C tablets and spiked fruit juice.     

Electrocatalytic Determination of Traces of Hydrazine by a Glassy Carbon Electrode Modified with Palladium‐Gold Nanoparticles

A glassy carbon electrode modified with palladium/gold nanoparticles was successfully prepared by an electrodeposition process. It efficiently oxidizes hydrazine at a low overpotential of ?0.26 V versus SCE. The Pd‐AuNPs with an average size of 50–80 nm are uniformly dispersed at the GCE. The Pd‐AuNPs/GCE was used for determination of hydrazine in phosphate buffer solution of pH 7.0. The amperometric current response of the electrode was increased linearly over a hydrazine concentration of 0.1–500 µM with a limit of detection of 0.07 µM .The prepared hydrazine sensor exhibited high sensitivity, good selectivity reproducibility and long term stability.     

A novel amperometric inhibition biosensor based on HRP and gold sononanoparticles immobilised onto Sonogel-Carbon electrode for the determination of sulphides

A novel inhibition biosensor used for the detection of sulphides (Na₂S) has been developed. The biosensor is based on the immobilisation of horseradish peroxidase (HRP) on the Sonogel-Carbon (SNGC) electrode using glutaraldehyde, Poly(4-vinylpyridine) and gold sononanoparticles (AuSNPs). The Poly(4-vinylpyridine) was used due to its high affinity for sulphide anions, while the presence of gold sononanoparticles enhances the electron transfer reaction and improves the analytical performance of the biosensor. The amperometric measurements were performed at an applied potential of ?0.15 V vs. Ag/AgCl in 50 mM sodium acetate buffer solution pH = 6.0. The apparent kinetic parameters (K_mapp, V_max) of immobilised HRP were calculated in the absence of inhibitor (sulphide) using caffeic acid as substrate. Under the optimal experimental conditions, the determination of sulphide can be achieved in a dynamic range of 0.4–2.8 µM with a low limit of detection of 0.15 µM. The electrochemical impedance spectroscopy (EIS) was also used to characterise the interactions of substrate and inhibitor with the enzyme-modified electrode. The developed biosensor exhibited high sensitivity, selectivity and stability, and can be successfully applied to the detection of sulphide in water.     

Amperometric Determination of Maltol using a Cobalt Oxide-Assembled MCM-41 Composite-Modified Glassy Carbon Electrode

A sensitive and selective amperometric method for maltol is reported based on a nanostructural Co₃O₄-assembled Mobil composite material (MCM-41). The amperometric sensor was characterized by scanning electron microscopy, energy-dispersive X-ray spectrometry, cyclic voltammetry, electrochemical impedance spectroscopy, and ultraviolet–visible absorption spectroscopy. The obtained calibration curve showed that the oxidative peaks increased linearly with the maltol concentration from 1.66?×?10^?6?M to 1.15?×?10^?4?M with a detection limit of 0.42?µM. Furthermore, the mechanism of oxidation of the analyte on the modified electrode surface was investigated using electrochemical techniques. The modified electrode was used for the determination of maltol using the method of standard addition with satisfactory results.     

A Novel Amperometric Immunosensor for Phytohormone Abscisic Acid Based on In Situ Chemical Reductive Growth of Gold Nanoparticles on Glassy Carbon Electrode

Abstract

An amperometric immunosensor for phytohormone abscisic acid was developed based on in situ chemical reductive growth of gold nanoparticles on glassy carbon electrode. First, an approximate 10 nm gold layer was sputtered uniformly onto the electrode surface, and then gold nanoparticles were grown directly on the gold layer for antibody adsorption by immersing the electrode into the H₂AuCl₄ solution. Determination was based on an enzyme-linked competitive immunoreaction between free and enzyme-labeled abscisic acid to bind on immobilized antibody on electrode. The linear response was from 10 ng/ml to 10 µg/ml with a detection limit of 5 ng/ml.     

Determination of Total Monoamines in Rat Brain via Nanotubes Based Human Monoamine Oxidase B Biosensor

A specific and sensitive electrochemical biosensor with human monoamine oxidase B (hMAO B) as biological receptor and a MnO₂ modified nanomaterial based transducer system has been developed and optimised. Best results for the biosensor were achieved when using enzyme immobilisation with a dialysis membrane (regenerated cellulose, molecular weight cut‐off 14000) and a 20 % (m/m) MnO₂ modified multi‐walled carbon nanotubes (MWCNTs, ratio of fluid to solid compounds of 1 : 0.7 (m/m)) paste electrode smoothed with a glassy carbon paste (GCP, ratio 1 : 3.6 (m/m)) containing the same mediator concentration. The biosensor was operated in a flow injection analysis (FIA) system with Sørensen phosphate buffer (33 mM, pH 7.5) and amperometric detection at a fixed potential of +400 mV vs. Ag/AgCl. The developed sensor underwent validation using phenylethylamine (PEA) as standard substrate showing linearity between 5.0 and 400 µM PEA and limits of detection and quantification of 1.5 and 5.0 µM PEA, respectively. The sensor was successfully tested for the determination of total monoamines in rat brain calculated as PEA equivalents showing a result of 1.2 µg/g brain tissue (n=3, relative standard deviation 4.4 %).     

Electrochemical Determination of Hydrogen Peroxide Using a Glassy Carbon Electrode Modified with Three-Dimensional Copper Hydroxide Nanosupercages and Electrochemically Reduced Graphene Oxide

Three-dimensional copper hydroxide nanosupercages and electrochemically reduced graphene oxide were used to modify the glassy carbon electrode for the selective determination of hydrogen peroxide. The morphology and electrochemistry properties of copper hydroxide nanosupercage/electrochemically reduced graphene oxide/glassy carbon electrode were characterized using transmission electron microscopy, scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectra, Raman spectra, cyclic voltammetry, and electrochemical impedance spectroscopy. The resulting copper hydroxide nanosupercage/electrochemically reduced graphene oxide/glassy carbon electrode showed favorable performance for the electrocatalytic reduction of hydrogen peroxide. The amperometric current–time curve of the electrochemical sensor exhibited a wide linear range from 0.5 to 1030?µM with a limit of detection of 0.23?µM at a signal-to-noise ratio of three. Moreover, the sensor provided favorable selectivity, reproducibility, and stability and was used for the determination of H₂O₂ in tap water.     

Flow‐Injection Pulsed‐Amperometric Determination of Free Glycerol in Biodiesel at a Gold Electrode

This work reports the highly‐sensitive amperometric determination of free glycerol in biodiesel at a gold electrode adapted in a flow‐injection analysis (FIA) cell. The amperometric method involved the continuous application of three sequential pulses to the working electrode (+250 mV, +700 mV, and ?200 mV, for 100 ms each). This sequence of potential pulses eliminated electrode passivation and dramatically increased the analytical signal. The proposed FIA‐amperometric method presented low relative standard deviation between injections (1.5 %, n=15), high analytical frequency (85 h^?1), satisfactory recovery values (93–118 %) for spiked samples, wide linear range (from 1 to 300 µmol L^?1), and low detection limit (0.5 µmol L^?1).     

Room temperature fabrication of magnetic covalent organic frameworks for analyzing sulfonamide residues in animal-derived foods

A magnetic solid phase extraction method based on magnetic covalent organic frameworks (TpBD@Fe₃O₄; 2,4,6-triformylphloroglucinol (Tp) and benzidine (BD)) combined with high performance liquid chromatography has been developed to detect the sulfonamides including sulfadiazine, sulfamerazine, sulfamethazine, and sulfamethoxazole in milk and meat. TpBD@Fe₃O₄ were synthesized at room temperature under mild reaction conditions with a simple and rapid operation. The TpBD@Fe₃O₄ exhibited higher extraction efficiency because of the π–π and electrostatic interactions between the benzene ring structure of the TpBD and the sulfonamide molecules. The extraction conditions including the dosage of adsorbents, the type and dosage of eluent, the elution time, and the pH of the sample solution were fully optimized. The detection results showed good linearity over a wide range (50–5 × 10⁴ ng/mL) and low detection limits (3.39–5.77 ng/mL) for the sulfonamide targets. The practicability of this magnetic solidphase extraction-high-performance liquid chromatography method was further evaluated by analyzing milk and meat samples, with recoveries of the targets of 71.6–110.8% in milk and 71.9–109.7% in pork. The successful detection of sulfonamides residues has demonstrated the TpBD@Fe₃O₄ excellent practical potential for analyzing pharmaceutical residues in animal-derived foods.     

Electrocatalytic Oxidation of Tryptophan at Gold Nanoparticle‐Modified Carbon Ionic Liquid Electrode

The electrochemical behavior of tryptophan was studied at the carbon ionic liquid electrode (CILE) modified with gold nanoparticle (GNP). This electrode has a stable and excellent response toward tryptophan. Under optimum experimental conditions, the calibration curve was linear in the tryptophan concentration range of 5 to 900 µM with an excellent correlation coefficient (0.995). The experimental limit of detection was 4 µM. Contrary to many other electrodes, the oxidation of tryptophan on GNP/CILE does not result in electrode fouling. GNP/CILE has been effectively applied to the determination of tryptophan in composite amino acid injection.     

Protein‐Directed In Situ Synthesis of Gold Nanoparticles on Reduced Graphene Oxide Modified Electrode for Nonenzymatic Glucose Sensing

A novel nonenzymatic glucose sensor was developed based on well‐dispersed gold nanoparticles, which were in situ grown under direction of protein on a reduced graphene oxide modified electrode. This electrode exhibited high electrocatalytic activity towards glucose oxidation without use of any enzyme or mediator. In application for the amperometric detection of glucose, a wide linear range of 0.02–16.6 mM, low detection limit of 5 µM and good selectivity were obtained. The attractive analytical performances of the proposed glucose sensor, coupled with the facile preparation method, provide a promising electrochemical platform for the development of effective nonenzymatic sensors.     

Detection of Thiols by o‐Quinone Nanocomposite Modified Electrodes

A chemically modified glassy carbon (GC) electrode was developed as an amperometric sensor for detection of biological thiols. The electrode was modified by inclusion of co‐enzyme pyrroloquinoline quinone (PQQ) and a co‐catalyst of oxidized single wall carbon nanotubes (Ox‐SWNT) into a gold polypyrrole (Au‐PPy) nanocomposite matrix. The electrode (PQQ/Ox‐SWNT/Au‐PPy/GC) was characterized using scanning electron microscopy and cyclic voltammetry. Optimal conditions for the PQQ/Ox‐SWNT/Au‐PPy/GC electrode were determined and then utilized for the amperometric detection of L‐cysteine, N‐acetyl‐L‐cysteine, L‐penicillamine and D, L‐glutathione. The electrochemical response for each thiol in pH 3.2 citrate phosphate buffer at +450 mV (vs. Ag/AgCl) was found to be linear with limit of detections (LOD, S/N=3) ranging from 0.50 µM for L‐penicillamine to 1.55 µM for D, L‐glutathione with sensitivities of 30.2 nA/µM and 3.6 nA/µM respectively. The electrode design is simple and easy to construct using a minimum amount of co‐enzyme and co‐catalyst, resulting in detection methods with very good stability and improved sensitivity for thiol detection.     

Rapid Determination of Hydrogen Peroxide in Milk with Non-enzymatic Amperometric Sensor Based on Porous Gold Modified Screen-printed Electrode in Online Dialysis System

A rapid method for determination of hydrogen peroxide based on a non-enzymatic amperometric sensor with an online dialysis unit was developed for analysis of sample with complicated matrices. A porous gold modified gold screen-printed electrode was prepared by a simple method using 9 V-battery electrodeposition. Based on data from amperometry, a linear dynamic range can be obtained in the range of 10 to 1000 μmol L⁻¹, with a limit of detection of 0.37 μmol L⁻¹. The proposed system was successfully applied to determine H₂O₂ in various milk samples with rapid analysis, high electrode stability, and excellent repeatability (1.95 % RSD with 100 replications).     

Determination of the anticancer drug 5-fluorouracil added to blood serum by liquid chromatography with anodic amperometric detection

Liquid chromatography with on-line anodic amperometric detection is used after a liquid/solid extraction step for the determination of the anticancer drug 5-fluorouracil added to blood serum. A detection limit of 15 ng ml^?1 can be achieved. The anodic electrochemical behaviour of the drug at a mercury electrode, which is the basis of the detection principle, is also described. Anodic amperometric detection at a mercury electrode is compared with detection at a glassy carbon electrode in terms of sensitivity, linearity and selectivity.     

Amperometric Biosensor for Hydrogen Peroxide,Using Supramolecularly Immobilized Horseradish Peroxidase on the β‐Cyclodextrin‐Coated Gold Electrode

Horseradish peroxidase, previously modified with 1‐adamantane moieties, was supramolecularly immobilized on gold electrodes coated with perthiolated β‐cyclodextrin. The functionalized electrode was employed for the construction of an amperometric biosensor device for hydrogen peroxide using 1 mM hydroquinone as electrochemical mediator. The biosensor exhibited a fast amperometric response (6 s) and a good linear response toward H₂O₂ concentration between 12 μM and 450 μM. The biosensor showed a sensitivity of 1.02 mA/M cm², and a very low detection limit of 5 μM. The electrode retained 97% of its initial electrocatalytic activity after 30 days of storage at 4 ⁰C in 50 mM sodium phosphate buffer, pH 7.0.