PEDOT/Superoxide Dismutase Electrode Surface Modification for Superoxide Bioelectrochemical Sensing

An amperometric biosensor for the sensitive detection of superoxide was designed utilizing a drop‐coating approach for immobilizing the superoxide dismutase enzyme on Pt electrode modified with a thin layer of poly (3,4‐ethylenedioxythiophene) (PEDOT). The layer electrodeposited on Pt was characterized by cyclic voltammetry and atomic force microscopy (AFM). Then, drop‐coating procedure was chosen for the immobilization of superoxide dismutase (SOD), which was incorporated at the electrode surface using a solution containing SOD, glutaraldehyde and bovine serum albumin (optimized composition: SOD 0.1 % – BSA 2 % – GA 2.5 %.) This simple procedure allows forming a reproducible enzymatic biocomposite layer that allows optimal sensitivity and limit of detection for superoxide sensing. The synergistic effect integrates an effective conductivity and permselectivity attributed to the PEDOT layer, as well as the specificity and selectivity of SOD for the detection of superoxide. A high sensitivity (0.82±0.01 μA/μM) and a low detection limit of 11 nM were obtained, as well as good selectivity against main interfering biological compounds such as uric acid and ascorbic acid. Our results suggest that the biosensor could be used for the detection and quantification of in vitro and in vivo.     

Clinoptilolite‐based Conductometric Sensors for Detection of Ammonium in Aqueous Solutions

New clinoptilolite‐based conductometric sensors were developed and optimized for selective detection of ammonium in the buffered aqueous solutions. The sensors’ selective elements were prepared by subsequent drop‐casting of zeolite and Nafion on the gold electrode surface. Electrochemical impedance spectroscopy and differential conductometry were used to investigate the sensor performance. As determined in the phosphate buffer solution, the detection limit of the sensors was 30 μM and the linear range 0–1.5 mM. The developed sensors were featured with a simple preparation procedure, high selectivity to , and storage stability for not less than 126 days.     

Silver Selective Electrode Based on Hybrid Mesoporous Silica (MCM‐41) Modified Material

A silver selective electrode based on TEPQA‐MCM‐41 material was developed and used for the selective determination of Ag⁺ ion in various samples. The effect of various plasticizers i. e. dimethyl phthalate (DMP), Tris(ethylhexyl)phosphate (TEP), bis‐(2‐ethylhexyl)sebacate (BEHS), bis‐(2‐ethylhexyl)adipate (BEHA) was investigated. The electrode of the composition of 2 : 1 : 77 : 12 : 8 (w/w, %) of TEPQA‐MCM‐41 : NaTPB : Graphite powder : paraffin oil : DMP respectively, works satisfactorily in a wide concentration range of 1.3×10^?9 M–1.0×10^?1 M for Ag⁺ ion with a lower detection limit (LOD) of 1.0×10^?9 M and has Nernstian slope of 63.4 1 mV/decay. The electrode can be used in a pH range of 2.3 to 6.7 for a period of 3 months without any divergence in potential response. The selectivity coefficient calculated by fixed interference method indicates the high selectivity of the electrode towards Ag⁺ ion over other tested cations.     

Centri‐Voltammetric Folic Acid Detection

The need for practical detection of folic acid (FA) has been increased day by day. For this reason in this work, a two steps electroanalytical technique, centri‐voltammetry was utilized for FA detection for the first time. In order to get rid of the slow electrode kinetics of FA oxidation, the working electrode was modified with graphene‐Pt hibrid nanomaterial. Also for increasing the sensitivity, 1‐Chloro‐2‐[2‐(2‐methoxyethoxy) ethoxy]ethane (TEG?Cl) and 1,2‐di{2‐[2‐(2‐methoxyethoxy)ethoxy] ethoxy}‐4‐nitrobenzene (4NC?NO₂) was used as a carrier material. After the characterization of graphene‐Pt hybrid nanomaterial, experimental parameters like, 4NC?NO₂ amount, adsorption time, centri‐voltammetric parameters like centrifuge time and speed were optimized. After that, analytical characteristics such as linear range, relative standard deviation (R.S.D), limit of detection (LOD) and limit of quantification (LOQ) values were found. In this manner, linear range was obtained for FA between 1.0 μM–1000 μM with the equations of (R²=0.9977). R.S.D value was calculated for 0.83 mM FA (n=3) as 1.86 % while LOD and LOQ values were found as 1.00 μM and 3.34 μM respectively. After the examination of interference effect of substances like ascorbic acid and uric acid, established centri‐voltammetric technique was enforced for FA detection in pharmateutical tablets. As a result, the recovery value was calculated as 96.4 %.     

Enzymatic Biosensor Based on One-step Electrodeposition of Graphene-gold Nanohybrid Materials and its Sensing Performance for Glucose

RGO/Au/Ni electrode was manufactured by a convenient, controllable, and environmental process, which was carried out by cyclic voltammetry (CV), and in this process, graphene-gold nanohybrid materials were simultaneously deposited on the nickel foam. Then the GOx was immobilized on the RGO/Au/Ni electrode by covalent bonding, and obtained the enzymatic biosensor. Scanning electron microscope (SEM) and Raman spectroscopy were adopted to confirm the microstructure of the fabricated RGO/Au/Ni electrode. Fourier transform infrared spectroscopy (FT-IR) was used to characterize the prepared enzymatic electrode. CV, chronoamperometry, and electrochemical impedance spectroscopy (EIS) were used to characterize the electrochemical performance of the fabricated enzymatic biosensor. It is found that AuNPs were well dispersed on the wrinkled RGO sheets, and the biosensor had a high sensitivity to glucose (32.83 μA ⋅ mM⁻¹ ⋅ cm⁻²) with a wide linear range (0.15 26.15 mM), the strengths of anti-interference ability, good stability, and repeatability, etc.     

Development of a Perchlorate Chemical Sensor Based on Magnetic Nanoparticles and Silicon Nitride Capacitive Transducer

We report in this work the development of a novel capacitance electrochemical sensors based on silicon nitride substrate (Si₃N₄) chemically modified with a structure of Cobalt phthalocyanine, C,C,C,C‐tetracarboxylic acid‐Polyacrylamide (Co(II)Pc‐PAA). This sensitive layer was tested with and without magnetic nanoparticles (MNP) for perchlorate ( ) detection. The developed chemical sensor with Si₃N₄/APTES‐MNP/Co(II)Pc‐PAA structure has shown a better performance when compared to the other structure based on Si₃N₄/Co(II)Pc‐PAA. Contact angle measurements (CAM) and atomic force microscopy (AFM) characterizations have been performed to characterize the functionalization of the chemical sensors surface. Under the optimized structure of the chemical sensor, electrochemical measurements were carried out using Mott‐Schottky analysis for detection within the large range of 10⁻¹⁰ to 10⁻⁴ M with a very low detection limit of 2×10⁻¹⁰ M. The chemical sensor has demonstrated a high selectivity toward when compared to other interfering anions such as Cl⁻, SO₄²⁻, and CO₃²⁻. The present capacitive chemical sensor is very promising for sensitive and rapid detection of for environmental applications.     

Ruthenium-based Conjugated Polymer and Metal-organic Framework Nanocomposites for Glucose Sensing

Many studies have focused on effective ways to exploit enzyme immobilization on an electrode surface to help improve the performance of enzymatic electrochemical biosensors. Herein, a novel glucose sensor was fabricated by immobilizing glucose oxidase (GOx) onruthenium-based conjugated polymer (CP) and metal-organic framework (MOF) nanocomposites. This has not only reduced the applied potential to 0.2 V (vs. Ag/AgCl), but also improved the effective surface area for enzyme immobilization.PPG@Ru@UiO-66-NH₂ was tailored by controlled chemical synthesis from a pre-synthesized water-soluble conjugated polymer (poly(N-phenylglycine)) and metal-organic framework (UiO-66-NH₂). The resulting nanocomposites were characterized using Fourier transform infrared spectroscopy, X-ray fluorescence, scanning electron microscopy, and cyclic voltammetry. The PPG@Ru@UiO-66-NH₂/GOx coated electrodedisplayed a linear measurementrange for glucose from 1 mM to 10 mM, with a sensitivity of 45.92 μA ⋅ mM⁻¹cm⁻¹ and limit of detection of5 μM( ). Furthermore, the practical application of the fabricatedglucosesensor was tested in simulative blood samples with satisfactoryaccuracy. This approach alsoopens a new door for applications regarding both enzymatic electrochemical biosensors and enzymatic biofuel cells (EBFCs).     

Enzyme‐free Cu2O@MnO2/GCE for Hydrogen Peroxide Sensing

A novel composite material of copper (I) oxide at manganese (IV) oxide (Cu₂O@MnO₂), was synthesized and applied for modification on the glassy carbon electrode (GCE) surface (Cu₂O@MnO₂/GCE) as a hydrogen peroxide (H₂O₂) sensor. The composite material was characterized regarding its structural and morphological properties, using field emission scanning electron microscopy (FE‐SEM), energy‐dispersive X‐ray spectroscopy (EDX), X‐ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The Cu₂O@MnO₂/GCE showed an excellent electrocatalytic response to the oxidation of H₂O₂ which provided a 0.56 s^?1 charge transfer rate constant (K_s), 1.65×10^?5 cm² s^?1 diffusion coefficient value (D), 0.12 mm² electroactive surface area (A_e) and 1.04×10^?8 mol cm^?2 surface concentration ( ). At the optimal condition, the constructed sensor exhibited a wide linear range from 0.5 μM to 20 mM with a low limit of detection (63 nM, (S/N=3) and a good sensitivity of 256.33 μA mM^?1 cm^?2. It also presented high stability (ΔI_response±15 %, n=100), repeatability (1.25 %RSD, n=10) and reproducibility (3.55 %RSD, n=10). The results indicated that the synthesized Cu₂O@MnO₂ was successfully used as a new platform for H₂O₂ sensing.     

Nano‐sensor Based on MoS2 Nanosheet mixed with Au quantum dot: Role of Layer Number and Temperature

The performance of nano‐sensor based on MoS₂ nanosheet mixed with Au particle is tested based electrochemical test involving cyclic voltammogram and impedance spectroscopy, where the Fe^III(CN)₆^3?/Fe^II(CN)₆^4? and dopamine (DA) are chosen as research object to verify the role of layer number of MoS₂ nanosheet and the temperature. The electrochemical test shows the Au nanoparticle would improve the electron exchange reaction occurring on the electrode. In the solution of Fe^III(CN)₆^3?/Fe^II(CN)₆^4?, the electrode reaction follows , where increasing the layer number of MoS₂ nanosheet would restrict the reaction. In the DA system, the reaction of occurs on the electrode and increasing the layer number of MoS₂ nanosheet would facilitate the reaction. The difference as mentioned above is assigned to the energy level shift originated from variance of layer number of MoS₂ nanosheet and the changing of reaction mechanism. In addition, temperature would mainly facilitate the kinetics of electron exchange reaction, which is assigned to the diffusion acceleration of DA molecule. Simultaneously, the desorption process of reactant in the electrolyte would enhance. The role of layer number of MoS₂ nanosheet and the temperature is clarified with the thermodynamic and kinetic properties of electron exchange reaction based on MoS₂ nanosheet, which would improve the understanding of nano‐sensor based on MoS₂ nanosheet.     

Radical Scavenging Activity of Antioxidants by Cyclic Voltammetry

This work investigates the reactivity of individual antioxidants with the free radicals generated by 2,2′-azobis(isobutironitrile) (AIBN). The consumption of antioxidants was followed by cyclic voltammetry. The fitting of such decay with a kinetic model yielded the rate constant of radical formation and the rate constant of radical inhibition exerted by each antioxidant. The antioxidant efficiency was defined as the ratio between and . The following ranking of antioxidants was obtained: α-tocopherol≫catechin≫retinyl acetate≫hydroxytyrosol≫oleuropein≫caffeic acid. Overall, the approach shows the utility of cyclic voltammetry to investigate the kinetic rates at which antioxidants react with radicals.     

Cauliflower‐like NiCo2O4−Zn/Al Layered Double Hydroxide Nanocomposite as an Efficient Electrochemical Sensing Platform for Selective Pyridoxine Detection

In the present study, a cauliflower‐like NiCo₂O₄?Zn/Al layered double hydroxide (NiCo₂O₄?Zn/Al LDH) nanocomposite was used as a novel electrode material for the sensitive and selective determination of pyridoxine (vitamin B₆). The structure and morphology of the as‐prepared nanocomposite were characterized by X‐ray diffraction (XRD), FT‐IR, field emission scanning electron microscopy (FESEM) and energy dispersive X‐ray spectroscopy (EDX). The NiCo₂O₄?Zn/Al LDH nanocomposite exhibited excellent electrocatalytic ability in the oxidation of pyridoxine, which could result from the synergistic effect of the two components. The developed sensor also provided a selective determination of pyridoxine in the presence of other species such as vitamins (B₁, B₂, B₁₂ and ascorbic acid), inorganic ions and biomolecules. The fabricated sensor showed a good linear response for pyridoxine over the concentration ranges 2×10^?7–2.0×10^?4 mol L^?1 with a low detection limit of 8.6×10^?8 mol L^?1. Finally, the proposed method was successfully applied for the determination of pyridoxine in commercial tablets and plasma samples with satisfactory results. Furthermore, this novel sensor displayed superior benefits in terms of stability, sensitivity, repeatability and cost. The present work aims to expand NiCo₂O₄ based nanocomposites to sensor fields and promote the development of pyridoxine sensors.     

Carbon‐based Nanosensors for Salicylate Determination in Pharmaceutical Preparations

Thiourea derivative‐based carbon paste electrode (TUD1‐CPE) was constructed as a potentiometric sensor for the determination of salicylate anion in pharmaceutical formulations, Aspocid® and Aspirin®. The optimized CPE contained 45.5 % graphite, 0.5 % reduced graphene oxide (rGO), 46.0 % nitrophenyl octyl ether (NPOE) plasticizer, 5.0 % TUD1 ionophore, and 3.0 % tridodecylmethyl ammonium chloride as additive. The incorporation of NPOE of high dielectric constant, and rGO in electrode caused better performance of the sensor; Nernstian response of 59.0 mV decade^?1 in the concentration range of 10^?1–10^?5 mole L^?1, a detection limit of 1×10^?5 mole L^?1 in a very short response time of 6 seconds. The prepared sensor showed high selectivity against similar anions (i. e. , benzoate, I^?, SCN^?). Selectivity was confirmed by calculating the formation constant (K_β) using sandwich membrane method, where K_β for TUD1‐salicylate is 10^0.43. Theoretical calculations at DFT‐B3LY/6‐31G** level of theory were performed to find interaction mechanism, Energies of HOMO and LUMO orbitals, non‐linear optical (NLO) properties (the electronic dipole moment (μ), first‐order hyperpolarizability (β), the hyper‐Rayleigh scattering (β_HRS) and the depolarization ratio (DR)), and other global properties; these calculations showed lower values of β and DR, higher value of β_HRS, and the shortest lengths of the four N?H bonds between TUD1 and salicylate which confirm their strong complexation and salicylate‐selectivity. Also, all the studied anion‐TUD1 exhibited relatively high NLO properties, and these results were considered as a preliminary study for investigating new types of NLO bearing materials. The sensors were applied successfully for the determination of salicylate anion in Aspocid® and Aspirin®.     

Enhancing a Novel Robust Multicomposite Materials Platform for Glucose Biosensors

An effective, stable enzymatic glucose biosensor was fabricated on a glassy carbon electrode (GCE) surface using simple multicomposite materials (MCM): a solution of prepared poly(diallyldimethylammonium chloride)‐capped gold nanoparticles‐nickel ferrite particles‐carbon nanotubes‐chitosan (PDDA‐AuNPs‐NiFe₂O₄‐CNTs‐CHIT), electropolymerization of poly(o‐phenylenediamine) (PoPD) and immobilization of glucose oxidase (GOx). Biocompatibility and synergy of the MCM enhanced the immobilization and the reaction of GOx and as well as the electron transfer from an oxidation reaction of hydrogen peroxide in the system. The NiFe₂O₄ was synthesized by co‐precipitation and calcined at 700 °C. Characterization was carried out by field emission scanning electron microscopy (FE‐SEM), energy‐dispersive X‐ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR) and X‐ray diffraction (XRD) which presented both tetrahedral and octahedral metal stretching with a cubic NiFe₂O₄ crystal phase. The GOx/PoPD/MCM/GCE yielded a 0.77 s^?1 charge transfer rate constant (K_s), a 2.28×10^?6 cm² s^?1 diffusion coefficient value (D), a 0.21 mm² electroactive surface area (A_e) and a 1.93×10^?8 mol cm^?2 surface concentration ( ) as determined by cyclic voltammetry. The modified electrode showed a durable operation time (n=97, more than 50 % I), repeatability (%RSD=0.38, n=10), reproducibility (%RSD=1.60, n=10), high sensitivity (853.07 μA mM^?1 cm^?2), selectivity without effects of electroactive species (aspirin, uric acid, caffeine, cholesterol, ascorbic acid and dopamine) and two linear ranges from 0.5 to 10 μM (R²=0.998) and 10 to 15,000 μM (R²=0.991) with a low detection limit (0.35 μM, S/N=3). Its Michaelis‐Menten constant (K_m) was calculated as 93.51 μM with 46.30 μA maximum current (I_max). This proposed simple method was successfully applied for glucose determination in human blood samples.     

Amperometric Tyrosinase Biosensor Based on Carbon Black Paste Electrode for Sensitive Detection of Catechol in Environmental Samples

In this work, a renewable tyrosinase-based biosensor was developed for the detection of catechol, using a carbon black paste electrode, without any mediator. The effect of pH, type of electrolyte, and amount of tyrosinase enzyme were explored for optimum analytical performance. The best-performing biosensor in amperometric experiments at potential −0.2 V vs. Ag/AgCl (3 mol L⁻¹ KCl) was obtained using a 0.1 mol L⁻¹ phosphate buffer solution (pH 7.0) as electrolyte. Under optimized conditions, the proposed biosensor had two concentration linear ranges from 5.0×10⁻⁹ to 4.8×10⁻⁸ and from 4.8×10⁻⁸ to 8.5×10⁻⁶ mol L⁻¹ and a limit of detection of 1.5×10⁻⁹ mol L⁻¹. The apparent Michaelis-Menten constant ( ) was calculated by the amperometric method, and the obtained value was 1.2×10⁻⁵ mol L⁻¹ whose result was similar when compared with other studies previously. The biosensor was applied in river water samples, and the results were very satisfactory, with recoveries near 100 %. In addition, the response of this biosensor for different compounds, taking into account their molecular structures was investigated and the results obtained showed no interference with the response potential of catechol. The electrochemical biosensor developed in this work can be considered highly advantageous because it does not require the use of a mediator (direct detection) for electrochemical response, and also because it is based on a low-cost materials that can be used with success to immobilise other enzymes and/or biomolecules.     

Modular and Selective Arylation of Aryl Germanes (C−GeEt3) over C−Bpin,C−SiR3 and Halogens Enabled by Light‐Activated Gold Catalysis

Selective C –C couplings are powerful strategies for the rapid and programmable construction of bi‐ or multiaryls. To this end, the next frontier of synthetic modularity will likely arise from harnessing the coupling space that is orthogonal to the powerful Pd‐catalyzed coupling regime. This report details the realization of this concept and presents the fully selective arylation of aryl germanes (which are inert under Pd⁰/Pd^II catalysis) in the presence of the valuable functionalities C?BPin, C?SiMe₃, C?I, C?Br, C?Cl, which in turn offer versatile opportunities for diversification. The protocol makes use of visible light activation combined with gold catalysis, which facilitates the selective coupling of C?Ge with aryl diazonium salts. Contrary to previous light‐/gold‐catalyzed couplings of Ar–N₂⁺, which were specialized in Ar–N₂⁺ scope, we present conditions to efficiently couple electron‐rich, electron‐poor, heterocyclic and sterically hindered aryl diazonium salts. Our computational data suggest that while electron‐poor Ar–N₂⁺ salts are readily activated by gold under blue‐light irradiation, there is a competing dissociative deactivation pathway for excited electron‐rich Ar–N₂⁺, which requires an alternative photo‐redox approach to enable productive couplings.     

Hydrodynamic Rocking Disc Electrode Study of the TEMPO‐mediated Catalytic Oxidation of Primary Alcohols

The hydrodynamically thinned diffusion layer at a sinusoidally rocking disc is approximately uniform and can be expressed in terms of a diffusion layer thickness with D, the diffusion coefficient of the redox active species, v, the kinematic viscosity, Θ, the total rocking angle (here 90 degrees), and f, the rocking frequency (ranging here from 0.83 to 25 Hz). For the one‐electron oxidation of 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) in aqueous carbonate buffer pH 9.5, it is shown that there is quantitative agreement between the expression for the diffusion layer thickness and experimental data. Next, for seven primary alcohols, the catalytic TEMPO‐mediated oxidation mechanism is investigated under rocking disc conditions. Chemical rate constants are evaluated (by varying the diffusion layer thickness) employing the DigiElch4.F simulation package. Trends in the chemical rate constants (compared with DFT calculations) suggest enhanced reactivity for methanol versus higher primary alcohols and for aromatic versus non‐aromatic primary alcohols. Rocking disc voltammetry allows quantitative mechanistic analysis in the laminar flow regime.     

Gold(II) Porphyrins in Photoinduced Electron Transfer Reactions

In the context of solar-to-chemical energy conversion, inspired by natural photosynthesis, the synthesis, electrochemical properties and photoinduced electron-transfer processes of three novel zinc(II)-gold(III) bis(porphyrin) dyads [Zn^II(P)–Au^III(P)]⁺ are presented (P: tetraaryl porphyrin). Time-resolved spectroscopic studies indicated ultrafast dynamics (k >10¹⁰ s⁻¹) after visible-light excitation, which finally yielded a charge-shifted state [Zn^II(P ^{⋅ +})–Au^II(P)]⁺ featuring a gold(II) center. The lifetime of this excited state is quite long due to a comparably slow charge recombination (k ≈3×10⁸ s⁻¹). The [Zn^II(P ^{⋅ +})–Au^II(P)]⁺ charge-shifted state is reductively quenched by amines in bimolecular reactions, yielding the neutral zinc(II)–gold(II) bis(porphyrin) Zn^II(P)–Au^II(P). The electronic nature of this key gold(II) intermediate, prepared by chemical or photochemical reduction, is elucidated by UV/Vis, X-band EPR, gold L₃-edge X-ray absorption near edge structure (XANES) and paramagnetic ¹H NMR spectroscopy as well as by quantum chemical calculations. Finally, the gold(II) site in Zn^II(P)–Au^II(P) is thermodynamically and kinetically competent to reduce an aryl azide to the corresponding aryl amine, paving the way to catalytic applications of gold(III) porphyrins in photoredox catalysis involving the gold(III/II) redox couple.     

A Single Drop Fabrication of the Cholesterol Biosensor Based on Synthesized NiFe2O4NPs Dispersed on PDDA‐CNTs

A cholesterol biosensor based on cholesterol oxidase‐poly(diallyldimethylammonium chloride)‐carbon nanotubes‐nickel ferrite nanoparticles (ChOx‐PDDA‐CNTs‐NiFe₂O₄NPs) solution is easily fabricated by using a single dropping step on a glassy carbon electrode (GCE) surface. This technique is an alternative way to reduce complexity, cost and time to produce the biosensor. The uniformly dispersed materials on the electrode surface enhance the catalytic reaction of cholesterol oxidase and electron transfer from the oxidation of hydrogen peroxide in the system. The nickel ferrite nanoparticles were synthesized by co‐precipitation and calcination at various temperatures. These nanoparticles were then characterized using field emission scanning electron microscopy (FE‐SEM), energy‐dispersive X‐ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV) and X‐ray diffraction (XRD). The synthesized material calcined at 700 °C was well defined and presented the octahedral metal stretching with cubic NiFe₂O₄NPs phase. In cyclic voltammetric study, the ChOx‐PDDA‐CNTs‐NiFe₂O₄NPs/GCE showed 0.43 s⁻¹ charge transfer rate constant (K _s), 7.79×10⁻⁶ cm² s⁻¹ diffusion coefficient value (D ), 0.13 mm² electroactive surface area (A _e) and 3.58×10⁻⁸ mol cm⁻² surface concentration ( ). This modified electrode exhibits stability in term of percent relative standard deviation (%RSD=0.62 %, n=10), reproducibility (%RSD=0.81, n=10), high sensitivity (25.76 nA per mg L⁻¹ cm⁻²), linearity from 1 to 5,000 mg L⁻¹ (R²=0.998) with a low detection limit (0.50 mg L⁻¹). Its Michaelis‐Menten constant (K _m) was 0.14 mM with 0.92 μA maximum current (I _max) and demonstrated good selectivity without the effects of electroactive species such as ascorbic acid, glucose and uric acid. The cholesterol biosensor was successfully applied to determine cholesterol levels in human blood samples, showing promise due to its simplicity and availability.     

Rotating-disc electrode studies of the anodic oxidation of iodide in concentrated iodine + iodide solutions

The anodic oxidation of iodide on platinum in concentrated iodine + iodide solutions has been investigated using a rotating disc electrode. The conventional limiting diffusion current, which is produced by the diffusion of iodide ions towards the electrode, was not observed due to the formation of an iodine film on the electrode. On the other hand, the steady-state anodic current after a current/time transient is the genuine limiting diffusion current in the anodic oxidation due to diffusion of iodine species from the electrode surface towards the bulk solution. Thus, the dissolution-diffusion control mechanism of the iodine film is confirmed. This is interesting as a typical example of an anodic process in a redox system governed by diffusion of the anodic product species from the electrode surface towards the bulk solution. When an iodine film is formed on the electrode, the maximum driving force of the iodine species is Δm_I2,max, which is defined as the extent of unsaturation of the iodine, and the limiting current of the anodic oxidation of iodide is always directly proportional to Δm_I2,max, regardless of the forms of iodine species in the solution, which may be I₂, I⁻₃, i₅⁻, etc. δm_I2,max is clearly determined by the solution composition and temperature, and it is different in definition and value from the usual degree of unsaturation of iodine.     

Electrochemical Detection of As(III) via Iodine Electrogenerated at Platinum,Gold, Diamond or Carbon‐Based Electrodes

The reaction of iodine, electrogenerated from iodide, is used for the detection of As(III) via electrocatalytic reaction in the diffusion layer of a boron‐doped diamond electrode. The merits of this electrode material for this purpose (over platinum, gold or glassy carbon) are demonstrated and the kinetics of the reaction between I₂ and As(III) in acid reported.