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The release of the cargo from soft vesicles, an essential process for chemical delivery, is mediated by multiple factors. Among them, the regulation by the interaction between the chemical cargo species and the vesicular membrane, widely existing in all vesicles, has not been investigated to date. Yet, these interactions hold the potential to complicate the release process. We used liposomes loaded with different monoamines, dopamine (DA) and serotonin (5-HT), to simulate vesicular release and to monitor the dynamics of chemical release from isolated vesicles during vesicle impact electrochemical cytometry (VIEC). The release of DA from liposomes presents a longer release time compared to 5-HT. Modelling the release time showed that DA filled vesicles had a higher percentage of events where the time for the peak fall was better fit to a double exponential (DblExp) decay function, suggesting multiple kinetic steps in the release. By fitting to a desorption–release model, where the transmitters adsorbed to the vesicle membrane, the dissociation rates of DA and 5-HT from the liposome membrane were estimated. DA has a lower desorption rate constant, which leads to slower DA release than that observed for 5-HT, whereas there is little difference in pore size. The alteration of vesicular release dynamics due to the interaction between the chemical cargo and vesicle membrane lipids provides an important mechanism to regulate vesicular release in chemical and physiological processes. It is highly possible that this introduces a fundamental chemical regulation difference between transmitters during exocytosis., The release of the cargo from soft vesicles, an essential process for chemical delivery, is mediated by multiple factors.

International audience; Since the early work of Bernard Katz, the process of cellular chemical communication via exocytosis, quantal release, has been considered to be all or none. Recent evidence has shown exocytosis to be partial or 'subquantal' at single-cell model systems, but there is a need to understand this at communicating nerve cells. Partial release allows nerve cells to control the signal at the site of release during individual events, where the smaller the fraction released, the greater the range of regulation. Here we show that the fraction of the vesicular octopamine content released from a living Drosophila larval neuromuscular neuron is very small. The percentage of released molecules was found to be only 4.5% for simple events and 10.7% for complex (i.e., oscillating or flickering) events. This large content, combined with partial release controlled by fluctuations of the fusion pore, offers presynaptic plasticity that can be widely regulated. Two works published in 2010 suggested that the Katz principle, [1] was incorrect for all-or-none release and that only part of the chemical load of vesicles was released during exocytosis, at least as measured as a full spike during amperometry. [2] The combination of electrochemical methods to measure both release and vesicle content in 2015 added a wealth of information to support the concept of partial release in exocytosis. [3] Additionally, this has recently been supported by work with TIRF microscopy showing 'subquantal' release from vesicles in adrenal chromaffin cells and using super-resolution STED microscopy. [4] It appears that the full event generally involves release of only part of the load of chemical messenger in single-cell model systems like adrenal chromaffin and PC12 cells. Is this also true at living neurons in a nervous system and to what extent? To answer this critical question, we quantified the number of octopamine molecules in the neuromuscular neurons of Drosophila larvae by adapting an amperometric technique developed in our

We used liposomes loaded with different monoamines, dopamine (DA) and serotonin (5-HT), to simulate vesicular release and to monitor the dynamics of chemical release from isolated vesicles during vesicle impact electrochemical cytometry (VIEC). The release of DA from liposomes presents a longer release time compared to 5-HT. Modelling the release time showed that DA filled vesicles had a higher percentage of events where the time for the peak fall was better fit to a double exponential (DblExp) decay function, suggesting multiple kinetic steps in the release. By fitting to a desorption-release model, where the transmitters adsorbed to the vesicle membrane, the dissociation rates of DA and 5-HT from liposome membrane were estimated. DA has a lower desorption rate constant, which leads to slower DA release than that observed for 5-HT, whereas there is little difference in pore size. The alteration of vesicular release dynamics due to the interaction between chemical cargo and vesicle membrane lipids provides an important mechanism to regulate vesicular release in chemical and physiological processes. It is highly possible that this introduces a fundamental chemical regulation difference between transmitters during exocytosis.

Studying brain function and neuronal communication has been always crucial due to the complexity of these systems. A great deal of technology and model systems have been developed to study this subject. Yet, very small invertebrate systems such as the fruit fly, Drosophila are excellent models and often have better defined and more easily manipulated genetics. This review focuses on in vivo, ex vivo, and in vitro measurements of biogenic amines by electrochemical techniques on the fly nervous system. The methods include capillary electrophoresis, fast scan cyclic voltammetry, and chronoamperometry have been used to study both larval and adult central nervous systems. Better understanding of brain function in model systems should aid in finding solutions to biological and bioanalytical challenges related to human brain function and also neurodegenerative disease.

Three new tools are discussed for understanding chemical communication between cells and primarily to delve into the content and structure of nanometer transmitter vesicles. These are amperometric measurements of exocytosis, vesicle impact electrochemical cytometry, and intracellular vesicle impact electrochemical cytometry. These are combining in the end nanoscale mass spectrometry imaging to begin determination of vesicle structure. These methods have provided solid evidence for the concept of open and closed exocytosis leading to partial release of the vesicle content during normal exocytosis. They have also been used to discover cases where the fraction of transmitter released is not changed, and other cases where the vesicle transmitter fraction released is altered, as with zinc, thought to alter cognition. Overall, the combination of these methods is showing us details of vesicular processes that would not be measureable without these micro and nano electrochemical methods.

We applied electrochemical techniques with nano-tip electrodes to show that micromolar concentrations of zinc not only trigger changes in the dynamics of exocytosis, but also vesicle content in a model cell line. The vesicle catecholamine content in PC12 cells is significantly decreased after 100 μM zinc treatment, but, catecholamine release during exocytosis remains nearly the same. This contrasts the number of molecules stored in the exocytosis vesicles, which decreases, and we find that the amount of catecholamine released from zinc-treated cells reaches nearly 100 percent content being expelled. Further investigation shows that zinc slows down exocytotic release allowing time for this to occur. Our results provide the missing link between zinc and the regulation of neurotransmitter release processes, which might be important in memory formation and storage.

Secretory cells respond to hypertonic stress by cell shrinking, which causes a reduction in exocytosis activity and the amount of signaling molecules released from single exocytosis events. These changes in exocytosis have been suggested to result from alterations in biophysical properties of cell cytoplasm and plasma membrane, based on the assumption that osmotic stress does not affect the secretory vesicle content and size prior to exocytosis. To further investigate whether vesicles in secretory cells are affected by the osmolality of the extracellular environment, we used intracellular electrochemical cytometry together with transmission electron microscopy imaging to quantify and determine the catecholamine concentration of dense core vesicles in situ before and after cell exposure to osmotic stress. In addition, single cell amperometry recordings of exocytosis at chromaffin cells were used to monitor the effect on exocytosis activity and quantal release when cells were exposed to osmotic stress. Here we show that hypertonic stress hampers exocytosis secretion after the first pool of readily releasable vesicles have been fused and that extracellular osmotic stress causes catecholamine filled vesicles to shrink, mainly by reducing the volume of the halo solution surrounding the protein matrix in dense core vesicles. In addition, the vesicles demonstrate the ability to perform adjustments in neurotransmitter content during shrinking, and intracellular amperometry measurements in situ suggest that vesicles reduce the catecholamine content to maintain a constant concentration within the vesicle compartment. Hence, the secretory vesicles in the cell cytoplasm are highly affected and respond to extracellular osmotic stress, which gives a new perspective to the cause of reduction in quantal size by these vesicles when undergoing exocytosis.

Adenosine triphosphate (ATP) is the main energy source for cellular metabolism. Besides that, ATP is a neurotransmitter and a cotransmitter that acts on purinergic receptors present either pre- or postsynaptically. Almost all types of secretory vesicles from any neuron or animal species contain high concentrations of ATP, being an essential factor in the accumulation of neurotransmitters. In this work, we studied the effects of ATP on quantum catecholamine release and vesicular storage in chromaffin cells. We combined three electrochemical methods: conventional amperometry with intracellular vesicle impact electrochemical cytometry and vesicle impact electrochemical cytometry. We found that extracellular ATP increased the released quantal fraction of catecholamine but not its vesicular content. Studying the dynamics of exocytosis events in ATP treated cells showed that ATP affects the release fusion pore. To elucidate the mechanisms of the observed ATP effects, cells and vesicles were pharmacologically treated with suramin (a purinergic blocker) and ARL-67156 (an antagonist of ecto-ATPases). The data indicate that the catecholamine content of vesicles increased compared to control after these drugs. Our data suggest that ATP acting on purinergic receptors increases the quantum releasable size through an increased fusion pore opening and that ARL-67156 and/or suramin protect the vesicle from neurotransmitter leakage by functioning as competitive inhibitors to ATP.

The energy carrying molecule adenosine triphosphate (ATP) has been implicated for its role in modulation of chemical signaling for some time. Despite this, the precise effects and mechanisms of action of ATP on secretory cells are not well-known. Here, bovine chromaffin cells have been used as a model system to study the effects of extracellular ATP in combination with the catecholamine transmitter norepinephrine (NE). Both transmitter storage and exocytotic release were quantified using complementary amperometric techniques. Although incubation with NE alone did not cause any changes to either transmitter storage or release, coincubation with NE and ATP resulted in a significant increase that was concentration dependent. To probe the potential mechanisms of action, a slowly hydrolyzable version of ATP, ATP-γ-S, was used either alone or together with NE. The result implicates two different behaviors of ATP acting on both the purinergic autoreceptors and as a source of the energy needed to load chromaffin cell vesicles.

Electrochemical cytometry is a method developed recently to determine the content of an individual cell vesicle. The mechanism of vesicle rupture at the electrode surface involves the formation of a pore at the interface between a vesicle and the electrode through electroporation, which leads to the release and oxidation of the vesicle's chemical cargo. We have manipulated the membrane properties using excited fluorophores conjugated to lipids, which appears to make the membrane more susceptible to electroporation. We propose that by having excited fluorophores in close contact with the membrane, membrane lipids (and perhaps proteins) are oxidized upon production of reactive oxygen species, which then leads to changes in membrane properties and the formation of water defects. This is supported by experiments in which the fluorophores were placed on the lipid tail instead of the headgroup, which leads to a more rapid onset of vesicle opening. Additionally, application of DMSO to the vesicles, which increases the membrane area per lipid, and decreasing the membrane thickness result in the same enhancement in vesicle opening, which confirms the mechanism of vesicle opening with excited fluorophores in the membrane. Light-induced manipulation of membrane vesicle pore opening might be an attractive means of controlling cell activity and exocytosis. Additionally, our data confirm that in experiments in which cells or vesicle membranes are labeled for fluorescence monitoring, the properties of the excited membrane change substantially.

The mechanism of mammalian vesicle rupture onto the surface of a polarized carbon fiber microelectrode during electrochemical vesicle cytometry is investigated. It appears that following adsorption to the surface of the polarized electrode, electroporation leads to the formation of a pore at the interface between a vesicle and the electrode and this is shown to be potential dependent. The chemical cargo is then released through this pore to be oxidized at the electrode surface. This makes it possible to quantify the contents as it restricts diffusion away from the electrode and coulometric oxidation takes place. Using a bottom up approach, lipid-only transmitter-loaded liposomes were used to mimic native vesicles and the rupture events occurred much faster in comparison with native vesicles. Liposomes with added peptide in the membrane result in rupture events with a lower duration than that of liposomes and faster in comparison to native vesicles. Diffusional models have been developed and suggest that the trend in pore size is dependent on soft nanoparticle size and diffusion of the content in the nanometer vesicle. In addition, it appears that proteins form a barrier for the membrane to reach the electrode and need to move out of the way to allow close contact and electroporation. The protein dense core in vesicles matrixes is also important in the dynamics of the events in that it significantly slows diffusion through the vesicle.

Amperometry recording of cells subjected to osmotic shock show that secretory cells respond to this physical stress by reducing the exocytosis activity and the amount of neurotransmitter released from vesicles in single exocytosis events. It has been suggested that the reduction in neurotransmitters expelled is due to alterations in membrane biophysical properties when cells shrink in response to osmotic stress and with assumptions made that secretory vesicles in the cell cytoplasm are not affected by extracellular osmotic stress. Amperometry recording of exocytosis monitors what is released from cells the moment a vesicle fuses with the plasma membrane, but does not provide information on the vesicle content before the vesicle fusion is triggered. Therefore, by combining amperometry recording with other complementary analytical methods that are capable of characterizing the secretory vesicles before exocytosis at cells is triggered offers a broader overview for examining how secretory vesicles and the exocytosis process are affected by osmotic shock. We here describe how complementing amperometry recording with intracellular electrochemical cytometry and transmission electron microscopy (TEM) imaging can be used to characterize alterations in secretory vesicles size and neurotransmitter content at chromaffin cells in relation to exocytosis activity before and after exposure to osmotic stress. By linking the quantitative information gained from experiments using all three analytical methods, conclusions were previously made that secretory vesicles respond to extracellular osmotic stress by shrinking in size and reducing the vesicle quantal size to maintain a constant vesicle neurotransmitter concentration. Hence, this gives some clarification regarding why vesicles, in response to osmotic stress, reduce the amount neurotransmitters released during exocytosis release. The amperometric recordings here indicate this is a reversible process and that vesicle after osmotic shock are refilled with neurotransmitters when placed cells are reverted into an isotonic environment.

The quantification of vesicular transmitter content is important for studying the mechanisms of neurotransmission and malfunction in disease, and yet it is incredibly difficult to measure the tiny amounts of neurotransmitters in the attoliter volume of a single vesicle, especially in the cell environment. We introduce a novel method, intracellular vesicle electrochemical cytometry. A nanotip conical carbon-fiber microelectrode was used to electrochemically measure the total content of electroactive neurotransmitters in individual nanoscale vesicles in single PC12 cells as these vesicles lysed on the electrode inside the living cell. The results demonstrate that only a fraction of the quantal neurotransmitter content is released during exocytosis. These data support the intriguing hypothesis that the vesicle does not open all the way during the normal exocytosis process, thus resulting in incomplete expulsion of the vesicular contents.

Dimethyl sulfoxide (DMSO) is frequently used as a solvent in biological studies and as a vehicle for drug therapy; but the side effects of DMSO, especially on the cell environment, are not well understood, and controls with DMSO are not neutral at higher concentrations. Herein, electrochemical measurement techniques are applied to show that DMSO increases exocytotic neurotransmitter release, while leaving vesicular contents unchanged. In addition, the kinetics of release from DMSO-treated cells are faster than that of untreated ones. The results suggest that DMSO has a significant influence on the chemistry of the cell membrane, leading to alteration of exocytosis. A speculative chemical mechanism of the effect on the fusion pore during exocytosis is presented.

A composite electrode comprised of graphite, Nujol, and nanoparticles of Fe2O3 core–cobalt hexacyanoferrate shell was prepared and the charge transport processes in the bulk of this composite were studied. The electrode/solution interface was assumed as a binary electrolyte whose charge transport occurred between redox sites of the nanoparticles present in the composite and counter cations present in the solution. Using cyclic voltammetry, the diffusion of counter cation in the shell was investigated. Using chronoamperometry, an effective diffusion coefficient and its dependency on the applied potential was obtained. In the Nyquist diagrams, different time constants were appeared with relation to different physical and electrochemical processes. Percolation of electron in the shell of the nanoparticles appeared at very high frequencies and exhibited the feature of a diffusion process with a transmissive boundary condition at interface of core–shell structure/graphite particles. The diffusion coefficients of electron and counter cation and the standard rate constants of each individual electrochemical reaction were obtained.

A facile precipitation route was developed for the synthesis of cobalt hexacyanoferrate (CoHCF) as a thin shell around cores of nanoparticles of iron(III) oxide, forming nanoparticles of iron(III) oxide@CoHCF (n-Fe2O3@NaCo[Fe(CN)6]). The morphology and structure of the as-prepared n-Fe2O3@NaCo[Fe(CN)6] were characterized by the techniques of electron microscopies, X-ray diffraction measurements, X-ray photoelectron spectroscopy, infrared spectroscopy and thermogravimetry. Carbon composite electrodes of n-Fe2O3@NaCo[Fe(CN)6] were prepared and the electrochemical behavior of the nanoparticles was evaluated using cyclic voltammetry. The redox couples of n-Fe2O3@NaCo[Fe(CN)6] were investigated and the diffusion coefficients of counter cation in the shell of CoHCF were obtained. The effect of size of particles and the structure of CoHCF was also evaluated. n-Fe2O3@NaCo[Fe(CN)6] represented prominent electrocatalytic activity toward the oxidation of some biologically active compounds.

The electrocatalytic oxidation of N-acetyl- l -cysteine (NAC) was studied on nanoparticles of iron(III) oxide core–cobalt hexacyanoferrate shell (Fe 2 O 3 @CoHCF)-modified carbon paste electrode (cs-MCPE). Voltammetric studies indicated that NAC was oxidized via a surface mediation electrocatalytic mechanism by Fe 2 O 3 @CoHCF. The catalytic rate constant, the electron-transfer coefficient and the diffusion coefficient involved in the electrooxidation process of NAC on Fe 2 O 3 @CoHCF were reported. Based on the electrocatalytic efficiency of Fe 2 O 3 @CoHCF, cs-MCPE was employed for the ultrasensitive sensing of the trace amounts of NAC. Linear sweep voltammetry (LSV) and amperometry techniques were developed for the analysis of NAC. For the former method, a linear dynamic range from 12.2 to 66.7 μM with calibration sensitivity of 7.88 × 10 −2 A M −1 cm −2 and for the latter one, a linear dynamic range from 20 to 432 μM with calibration sensitivity of 1.67 × 10 −2 A M −1 cm −2 resulted for NAC. Also, according to the proposed LSV and amperometry methods, NAC was determined with detection limits of 205 and 20.9 nM, respectively. The proposed amperometry method was also applied to the analysis of commercial tablets and injection samples.

Electrocatalytic oxidation of deferoxamine was studied on carbon paste electrodes modified with nanoparticles of iron(III) oxide core-cobalt hexacyanoferrate-shell using cyclic voltammetry and chronoamperometry. Voltammetric curves represented two quasi-reversible redox transitions which in the presence of deferoxamine, the two anodic peak currents increased, followed by decreases in the corresponding cathodic currents. This indicated that deferoxamine was oxidized on the immobilized cobalt hexacyanoferrate via two electrocatalytic steps. The rate constants, the electron transfer coefficients and the diffusion coefficient involved in the electrocatalytic oxidation of deferoxamine were reported. A sensitive and time-saving determination procedure was developed for the analysis of the drug in both batch and flow systems, and the corresponding analytical parameters were reported. The proposed amperometric method was also successfully applied to the direct assays of spiked human serum with iron–drug complex.

The electrooxidation of dextromethorphan on a composite constructed with carbon nanotube–ionic liquid–carbon microparticles was investigated by cyclic voltammetry in a 100 mM phosphate buffer solution, pH 7.40. In the voltammograms, an irreversible diffusion-controlled anodic peak appeared. The diffusion coefficient of dextromethorphan, the electron-transfer coefficient, and the standard rate constant of the electrooxidation process were found to be 3.45 × 10−6 cm2 s−1, 0.65, and 1.67 × 10−3 cm s−1, respectively. A sensitive and timesaving determination procedure was developed for the analysis of dextromethorphan, and the corresponding analytical parameters were reported. Using this method, dextromethorphan was determined with an LOD and LOQ of 8.81 and 29.36 μM in a linear range of 2.5 × 10−4 to 3.3 × 10−3 M, respectively. The proposed amperometric method was successfully applied to the analysis of commercial pharmaceutical products (syrup and oral drop), and the results were in good agreement with the declared values.

The electrooxidation of several non-steroidal anti-inflammatory drugs (indomethacin, mefenamic acid, and diclofenac) was investigated on nanoparticles of Ni–curcumin-complex-modified glassy carbon (n-GC) electrode in alkaline solution. Surfaces studies were performed by scanning electron micrographs and atomic force microscopy. The oxidation process and its kinetics were studied using cyclic voltammetry and chronoamperometry techniques and also pseudo-steady-state polarization measurements. Voltammetric studies indicated that, in the presence of drugs, the anodic peak current of low-valence nickel species increases, followed by a decrease in the corresponding cathodic current. This pattern indicates that drugs were oxidized on the redox mediator immobilized on the electrode surface via an electrocatalytic mechanism. A mechanism based on the electrochemical generation of Ni(III)-active sites and their subsequent consumption by drugs was proposed. The rate constants of the catalytic oxidation of drugs and the electron-transfer coefficient are reported. A sensitive, simple, and time-saving amperometric procedure was developed for the analysis of these drugs in bulk form and for the direct assay of tablets, using the n-GC electrode.

The electrochemical behavior of ceftriaxone was investigated on a carbon-nanotube-modified glassy carbon (GC-CNT) electrode in a phosphate buffer solution, pH = 7.40, and the results were compared with those obtained using the unmodified one [glassy carbon (GC) electrode]. During oxidation of ceftriaxone, an irreversible anodic peak appeared, using both modified and unmodified electrodes. Cyclic voltammetric studies indicated that the oxidation process is irreversible and diffusion-controlled. The number of electrons exchanged in the electrooxidation process was obtained, and the data indicated that ceftriaxone is oxidized via a one-electron step. The results revealed that carbon nanotube promotes the rate of oxidation by increasing the peak current. In addition, ceftriaxone was oxidized at lower potentials, which thermodynamically is more favorable. These results were confirmed by impedance measurements. The electron-transfer coefficients and heterogeneous electron-transfer rate constants for ceftriaxone were reported using both the GC and GC-CNT electrodes. Furthermore, the diffusion coefficient of ceftriaxone was found to be 2.74 × 10−6 cm2 s−1. Binding of ceftriaxone to human serum albumin forms a kind of electroreactive species. The percentage of interaction of ceftriaxone with protein was also addressed. A sensitive, simple, and time-saving differential-pulse voltammetric procedure was developed for the analysis of ceftriaxone, using the GC-CNT electrode. Ceftriaxone can be determined with a detection limit of 4.03 × 10−6 M with the proposed method.

This study investigated the electrocatalytic oxidation of alanine, l- arginine, l- phenylalanine, l- lysine and glycine on poly-Ni(II)–curcumin film (curcumin: 1,7-bis [4-hydroxy-3-methoxy phenyl]-1,6-heptadiene-3,5-dione) electrodeposited on a glassy carbon electrode in alkaline solution. The process of oxidation and its kinetics were established by using cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy techniques. Voltammetric studies indicated that in the presence of amino acids the anodic peak current of low valence nickel species increased, followed by a decrease in the corresponding cathodic current. This indicates that amino acids were oxidized on the redox mediator which was immobilized on the electrode surface via an electrocatalytic mechanism. Using Laviron's equation, the values of α and k s for the immobilized redox species were determined as 0.43 ± 0.03 and 2.47 ± 0.02 × 10 6 s −1 , respectively. The rate constant, the electron transfer coefficient and the diffusion coefficients involved in the electrocatalytic oxidation of amino acids were determined.

The nerve terminals found in the body wall of Drosophila melanogaster larvae are readily accessible to experimental manipulation. We used the light-activated ion channel, channelrhodopsin-2, which is expressed by genetic manipulation in Type II varicosities to study octopamine release in Drosophila. We report the development of a method to measure neurotransmitter release from exocytosis events at individual varicosities in the Drosophila larval system by amperometry. A microelectrode was placed in a region of the muscle containing a varicosity and held at a potential sufficient to oxidize octopamine and the terminal stimulated by blue light. Optical stimulation of Type II boutons evokes exocytosis of octopamine, which is detected through oxidization at the electrode surface. We observe 22700±4200 molecules of octopamine released per vesicle. This system provides a genetically accessible platform to study the regulation of amine release at an intact synapse.

In vivo measurements of neurotransmitters and related compounds have provided a better understanding of the chemical interactions that are a major part in functioning of brains. In addition, a great deal of technology has been developed to measure chemical species in other areas of living organisms. A key part of this work has been sampling technologies as well as direct measurements in vivo. This is extremely important when sampling from the smallest animal systems. Yet, very small invertebrate systems are excellent models and often have better defined and more easily manipulated genetics. This review focuses on in vivo measurements, electrochemical methods, fluorescence techniques, and sampling and is further narrowed to work over approximately the last three years. Rapid developments of in vivo studies in these model systems should aid in finding solutions to biological and bioanalytical challenges related to human physiological functions and neurodegenerative diseases.

The electrocatalytic oxidation of aspirin has been investigated on a nickel oxide-modified nickel electrode in alkaline solution. The process of oxidation and its kinetics have been investigated by using cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy techniques and also steady-state polarization measurements. Voltammetric studies have indicated that in the presence of aspirin, the anodic peak current of low-valence nickel species increases, followed by a decrease in the corresponding cathodic current. This indicates that aspirin was oxidized on the redox mediator immobilized on the electrode surface via an electrocatalytic mechanism. The rate constant of the catalytic oxidation of aspirin and the electron transfer coefficient have been found to be 1.15×105 cm3 mol−1s−1 and 0.49, respectively. Impedance measurements show that aspirin is diffused into the bulk of the modifier film, and the oxidation process of aspirin occurs in the bulk of nickel oxide film. It has been shown that by using this modified electrode, aspirin can be determined with a detection limit of 4.8×10−5 and successfully applied for determination of aspirin in tablet.

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