Differential Normal Pulse Voltammetry Research Articles

Controllable Synthesis of a Porous PEI-Functionalized Co3O4/rGO Nanocomposite as an Electrochemical Sensor for Simultaneous as Well as Individual Detection of Heavy Metal Ions.

The present study focuses on the strategy of employing an electrochemical sensor with a porous polyethylenimine (PEI)-functionalized Co3O4/reduced graphene oxide (rGO) nanocomposite (NCP) to detect heavy metal ions (HMIs: Cd2+, Pb2+, Cu2+, and Hg2+). The porous PEI-functionalized Co3O4/rGO NCP (rGO·Co3O4·PEI) was prepared via a hydrothermal method. The synthesized NCP was based on a conducting polymer PEI, rGO, nanoribbons of Co3O4, and highly dispersed Co3O4 nanoparticles (NPs), which have shown excellent performance in the detection of HMIs. The as-prepared PEI-functionalized rGO·Co3O4·PEI NCP-modified electrode was used for the sensing/detection of HMIs by means of both square wave anodic stripping voltammetry (SWV) and differential normal pulse voltammetry (DNPV) methods for the first time. Both methods were employed for the simultaneous detection of HMIs, whereas SWV was employed for the individual analysis as well. The limits of detection (LOD; 3σ method) for Cd2+, Pb2+, Cu2+, and Hg2+ determined using the rGO·Co3O4·PEI NCP–modified electrode were 0.285, 1.132, 1.194, and 1.293 nM for SWV, respectively. Similarly, LODs of Cd2+, Pb2+, Cu2+, and Hg2+ were 1.069, 0.285, 2.398, and 1.115 nM, respectively, by DNPV during simultaneous analysis, whereas they were 0.484, 0.878, 0.462, and 0.477 nM, respectively, by SWV in individual analysis.

A Nanometer-Sized Graphite/Boron-Doped Diamond Electrochemical Sensor for Sensitive Detection of Acetaminophen.

A boron-doped diamond (BDD) has been widely used as an outstanding electrode for constructing high-performance electrochemical biosensors. In this paper, we fabricated a novel electrode combined of nanometer-sized graphite-BDD film (NG-BDD) by chemical vapor deposition. The nanometer-sized graphite (NG) is formed on the (111) facet of BDD via converting an sp3 diamond structure to an sp2 graphitic phase at high temperature in boron-rich ambient. The electrode was characterized by means of scanning electron microscopy, Raman spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. This NG-BDD was performed as an electrode of electrochemical biosensor to detect trace acetaminophen (APAP) accurately. Cyclic voltammetry and differential normal pulse voltammetry are used to investigate the overall performance of the electrochemical device. The sensor has a linear electrochemical response to APAP in the concentration range of 0.02–50 μM, and the detection limit is estimated to be as low as 5 nM. The research has resulted in a solution of constructing a reusable NG-BDD sensor to detect APAP with stability and show potential in extensive application.

Electrocatalytic determination of Reduced Glutathione using rutin as a mediator at acetylene black spiked carbon paste electrode

The electrocatalytic oxidation of glutathione based on rutin as a mediator was studied at acetylene black (AB) modified carbon paste electrode (CPE). The results of cyclic voltammetric experiments showed that rutin could catalyze oxidation of GSH in PBS (pH 7.0) and the oxidation current was greatly increased by using AB-CPE compared to the nonmodified CPE. The kinetic parameters such as catalytic rate constant and diffusion coefficient were obtained using double potential step chronoamperometry. Under the optimum conditions, the electrocatalytic oxidation peak current was linear to the glutathione concentration range from 0.5μM to 3.5μM and 2.5μM to 25μM with the detection limit of 0.080μM (S/N=3) by differential normal pulse voltammetry (DNPV). The proposed method has been applied to the determination of glutathione in pharmaceutical sample with satisfactory results.

Determination of Oxytetracycline in Food Using a Disposable Montmorillonite and Acetylene Black Modified Microelectrode

Oxytetracycline is a broad-spectrum antibiotic used in animal husbandry that may cause the occurrence of antibiotic residues in food-producing animals. A detailed study of the electrochemical properties of oxytetracycline was carried out at montmorillonite and acetylene black modified carbon paste microelectrode. The oxytetracycline underwent an irreversible oxidation at montmorillonite-acetylene black/carbon paste microelectrode, which was an adsorption-controlled process with one proton and one electron. Using differential normal pulse voltammetry with accumulation at a fixed potential of 0.3 V for 120 s, oxytetracycline yielded a well-defined voltammetric response at 0.6 V in pH 7.4 citric acid–Na2HPO4 buffer. Furthermore, the oxidation peak current of oxytetracycline at the montmorillonite–acetylene black/carbon paste microelectrode linearly increased with concentration in the range of 0.5–50 µM with a low detection limit of 87 nM (S/N = 3). This methodology was successfully applied to the determination of oxytetracycline from food samples, suggesting that it has practical applications in monitoring oxytetracycline.

Clay Composite Modified Electrodes I: Voltammetric Method for Selective Analysis of Dopamine and Ascorbic Acid

Clay Composite Modified Electrodes I: Voltammetric Method for Selective Analysis of Dopamine and Ascorbic Acid

Modification of platinum microelectrode with molecularly imprinted over-oxidized polypyrrole for dopamine measurement in rat striatum

Abstract A highly sensitive and selective electrochemical microelectrode using the molecularly imprinted (MIP) electropolymer of over-oxidized polypyrrole (OPPy) was proposed for in vivo detection of dopamine (DA) which process is different from current approaches for in vitro DA detection using MIP-based macroelectrode. The proposed MIP electrosynthesized by our present method under a DA/pyrrole-monomer concentration ratio of 1 mM/10 mM yielded the best results for DA adsorption, reaching 2.6-fold that of similar microelectrodes without imprinting. Differential normal pulse voltammetry techniques was used to evaluate the DA-imprinted OPPy microelectrodes for demonstrating high selectivity for in vitro DA detection under conditions with various competitive electroactive molecules. The validity of the modified OPPy-MIP thin-film microelectrodes was further verified with amperometric i – t measurements, which showed a lower DA levels of detection (10–100 nM) and the low detection limit of 4.5 nM with signal to noise ratio of 3. Good reproducibility with relative standard deviation of 5.45% and long-term stability within two weeks were also observed. The developed OPPy-MIP microelectrode has been successfully applied for acute in vivo DA detection in the striatum of anesthetized rats with 3,4-dihydroxy -l -phenylalanine ( l -DOPA) administration, which can be used for future evaluation of novel therapeutic treatments in Parkinsonian rats.

Current Literature Review

To assess whether intracavernosal injections of prostaglandin E1 (PGE1) can influence nitric oxide (NO) release in the corpora in a rat model of penile erection.The extracellular levels of NO were monitored at 100 seconds intervals in the corpus cavernosum of anesthetized rats by using differential normal pulse voltammetry with porphyrin-Nafion coated carbon fiber microelectrodes. The intracavernosal pressure (ICP) was simultaneously recorded. PGE1 was given either as a single dose (ranging from 0.2 to 15 μg.) or as repeated 2 μg. injections in alternate days for two weeks. The NO and ICP responses to electrostimulation of the cavernosal nerve (SCN) was studied in the animals in the repeated treatment schedule at 1, 7, 15 and 30 days after its termination. The levels of the three NO synthase (NOS) isoforms in the cavernous tissue were measured by immunoblotting.Acute PGE1 treatment dose-relatedly increased NO levels in the corpora, with a concomitant ICP increase with the highest dose. Repeated 2 μg. PGE1 injections increased the NO and ICP responses to SCN as compared with intact or vehicle-injected animals. This treatment also increased the penile content of the neuronal and endothelial NOS proteins. The inducible NOS isoform remained unchanged after either vehicle or PGE1 injections. The effects of the repeated PGE1 treatment were greater in the group studied 24 hours after the last injection and decreased progressively thereafter.Stimulation of NO release can contribute to the erectogenic effect of intracavernous PGE1 injections. The increased levels of constitutive NOS isoforms in the corpora could contribute to the improvement of the erectile function reported by some patients following repeated treatment with vasorelaxant agents.

Brain and cognitive impairments from burn injury in rats

Severe burn injuries affect not only the release of stress hormones but also the metabolism of nitric oxide (NO), a substance playing a large role in cognition. We investigated the effect of third-degree burns both on central NO-levels and on short-term memory in rats. Burns were administered under halothane-anesthesia by dipping 20% of the skin area in hot water. In a first experiment, NO-changes were estimated over hours by differential normal pulse voltammetry (DPNV) with a sensor implanted chronically in the frontal cortex. In a second experiment, cognitive abilities were tested over days by comparing the spontaneous time used to explore objects that the animals had, either never- or already-encountered before. Cerebral NO appeared steadily depleted for at least 12 h after the injury, not after control anesthesia. During nine days following the burn, discrimination performance was lower compared to controls. Putting together the results of the two experiments, especially on the day of burn, NO changes are likely to account for the behavioral effect. A choice of neuro-pharmacological agents involved in NO-metabolism, together with a choice of proper anesthetics, should now be tested as means to alleviate cognitive impairments following third-degree burns.

Comparing sertindole to other new generation antipsychotics on preferential dopamine output in limbic versus striatal projection regions: Mechanism of action

The effects of acute administration of sertindole on DA output were examined in the shell part of the nucleus accumbens (NACS) and the striatum (STR), areas which are associated with limbic functions and motor control, respectively, by using in vivo differential normal pulse voltammetry in rats. The effect of sertindole was compared to those obtained with the reference antipsychotic drugs clozapine and haloperidol, new generation antipsychotics represented by risperidone, olanzapine, ziprasidone, quetiapine, and aripiprazole, as well as, with those of preferential D2/3, D4, 5-HT1A, 5-HT2A, 5-HT2C, alpha1, and alpha2 receptor ligands. In similarity with the new generation antipsychotics, sertindole preferentially increase DA output in the NACS as compared to the STR whereas the opposite was true for haloperidol. The regional specific effect of the partial D2 receptor agonist aripiprazole was mainly driven by a decrease in striatal rather that by an increase in accumbal DA output. The selective 5-HT2A and D4 receptor antagonists MDL100,151 and Lu 38-012, respectively, both preferentially increased DA output in the NACS. Thus, the present results are in line with the hypothesis that 5-HT2A receptor antagonism is of importance for the observed limbic selectivity of new generation antipsychotics and, in turn, to their favorable clinical profile especially as regards extrapyramidal side effects (EPS) liability. For some compounds, blockade of D4 receptors may also play a role in this regard.

Study of a Catalytic Mechanism in Additive Differential Pulse Techniques

AbstractThe new electrochemical double pulse technique, known as additive differential normal pulse voltammetry (ADNPV) when there is no restriction on the duration of both pulses, and additive differential pulse voltammetry (ADPV) when t2≪t1, has been applied to a pseudo‐first‐order catalytic mechanism. The expressions obtained here are applicable to planar and spherical electrodes, of any radius. This is of great interest since the size of the electrode plays an important role in the preponderating of diffusive and kinetics processes. The signal obtained with this technique presents the same morphological characteristics as the triple pulse technique, double differential pulse voltammetry (DDPV) and is more advantageous than DDPV and than the double pulse one, differential pulse voltammetry (DPV).

In vivo electrochemical measurement of nitric oxide in corpus cavernosum penis

A wealth of pharmacological studies suggest that nitric oxide (NO) generated in the corpus cavernosum is a main molecular mediator of penile erection. However, the physiological levels of NO in the corpora and their possible changes during penile erection have remained unknown for want of suitable methodologies. We have adapted a voltammetric procedure, derived from Malinski's method, for assessing NO levels in the penis in vivo. Differential normal pulse voltammetry with carbon fiber electrodes (30 μm) coated with a polymeric porphyrin and Nafion was used to measure the NO oxidation current in the corpora cavernosa of urethane-anesthetized rats. The intracavernous pressure was monitored simultaneously. A NO oxidation peak was consistently detected at approximately 650 mV both in NO solutions and in the corpora in vivo. The changes in the NO signals observed in vitro were consistent with the concentration values measured by chemiluminescence. The NO signal recorded in vivo increased following cavernous nerve stimulation and was greatly decreased by intracavernous injections of several inhibitors of the neuronal and endothelial NO synthase isoenzymes. Such results agree with our previous studies using this methodology and substantiate further its validity for monitoring the physiological changes in NO levels in the penis.

Study of an EE mechanism in additive differential pulse techniques

Additive differential pulse techniques are applied to the study of a reversible EE mechanism. Analytical solutions are obtained in additive differential normal pulse voltammetry (ADNPV) and in additive differential pulse voltammetry (ADPV). The usefulness of these techniques in obtaining accurate simultaneous determinations of the formal potentials of both electrochemical steps when they are not completely separated is discussed and also applied to the study of the reduction of pyrazine in aqueous acid media. Excellent agreement between experimental results and theoretical predictions has been found.

Endogenous neurotensin down-regulates dopamine efflux in the nucleus accumbens as revealed by SR-142948A, a selective neurotensin receptor antagonist.

SR-142948A belongs to the second generation of potent, selective, non-peptide antagonists of neurotensin receptors. It was used to investigate the role of endogenous neurotensin in the regulation of dopamine efflux in the nucleus accumbens and striatum of anaesthetized and pargyline-treated rats. All the data were obtained using in vivo electrochemistry. Electrically evoked (20 Hz, 10 s) dopamine efflux was monitored by differential pulse amperometry, whereas variations in basal (tonic) dopamine efflux were monitored by differential normal pulse voltammetry. Like the first-generation compound SR-48692, SR-142948A did not affect the tonic and evoked dopamine efflux, but dose-dependently enhanced haloperidol (50 microg/kg, i.p.) induced facilitation of the electrically evoked dopamine release in the nucleus accumbens. In contrast to SR-48692, SR-142948A dose-dependently potentiated haloperidol (50 microg/kg, i.p.) induced increase in the basal dopamine level in the nucleus accumbens. This potentiating effect did not appear in the striatum. When dopaminergic and/or neurotensinergic transmissions were modified by a higher dose of haloperidol (0.5 mg/kg, i.p.), apomorphine, amphetamine or nomifensine, SR-142948A pre-treatment affected only the effect of apomorphine on the basal dopamine level in the nucleus accumbens. These results strengthen the hypothesis that endogenous neurotensin could exert a negative control on mesolimbic dopamine efflux.

Brain extracellular glucose assessed by voltammetry throughout the rat sleep-wake cycle.

In the present study, cortical extracellular levels of glucose were monitored for the first time throughout the sleep-wake states of the freely moving rat. For this purpose, polygraphic recordings (electroencephalogram of the fronto-occipital cortices and electromyogram of the neck muscles) were achieved in combination with differential normal pulse voltammetry (DNPV) using a specific glucose sensor. Data obtained reveal that the basal extracellular glucose concentration in the conscious rat is 0.59 +/- 0.3 m M while under chloral hydrate anaesthesia (0.4 g/kg, i.p.) it increases up to 180% of its basal concentration. Regarding the sleep-wake cycle, the existence of spontaneous significant variations in the mean glucose level during slow-wave sleep (SWS = +13%) and paradoxical sleep (PS = -11%) compared with the waking state (100%) is also reported. It is to be noticed that during long periods of active waking, glucose level tends towards a decrease that becomes significant after 15 min (active waking = -32%). On the contrary, during long episodes of slow-wave sleep, it tends towards an increase which becomes significant after 12 min (SWS = +28%). It is suggested that voltammetric techniques using enzymatic biosensors are useful tools allowing direct glucose measurements in the freely moving animal. On the whole, paradoxical sleep is pointed out as a state highly dependent on the availability of energy and slow-wave sleep as a period of energy saving.

Effects of competitive and non-competitive NMDA receptor antagonists on dopamine output in the shell and core subdivisions of the nucleus accumbens

The effects of acute intravenous administration of the non-competitive NMDA receptor antagonists, phencyclidine (PCP), dizocilpine (MK-801; (+)-5-methyl-10,11-dihydroxy-5H-dibenzo(a,b)cyclohepten-5,10-imine), and the competitive NMDA receptor antagonist CGP 39551 (DL-(E)-2-amino-4-methyl-5-phosphono-3-pentanoic acid) on extracellular dopamine concentrations were analyzed in the shell and core subdivisions of the nucleus accumbens (NAC), associated with limbic and motor functions, respectively. Extracellular dopamine concentrations were assessed utilizing differential normal pulse voltammetry in chloral hydrate anesthetized, pargyline pretreated rats. Intravenous administration of PCP (0.5 mg/kg) or MK-801 (0.1 mg/kg) both significantly elevated extracellular dopamine levels in the NAC shell but not in the core. However, administration of relatively low doses of the competitive NMDA receptor antagonist CGP 39551 (2.5 mg/kg) failed to affect dopamine output in either region. However, when a higher dose (10 mg/kg) was administered a significant elevation in dopamine output was obtained in the shell compared to the core. Our data demonstrate that non-competitive NMDA receptor antagonists evoke an accumbal dopamine output that is selective to limbic cortical related NAC regions. This profile is shared also by competitive NMDA receptor antagonists when given in high, but not low doses. Our results are compatible with the reported elicitation of PCP-like behavioral effects by competitive NMDA receptor antagonists when administered in relatively high doses. Moreover, these findings suggest that differences in the regional accumbal dopamine output between competitive and non-competitive NMDA receptor antagonists may be essentially attributable to the relative degree of NMDA receptor antagonism achieved by the drugs. This experimental model may afford a biochemical means to assess the psychotomimetic liability of NMDA receptor antagonists, a side effect that may reduce their usefulness as neuroprotective agents.

Effects of atypical antipsychotic drugs on dopamine output in the shell and core of the nucleus accumbens: role of 5-HT 2A and α 1-adrenoceptor antagonism

The effects of acute intravenous administration of several new, atypical antipsychotic drugs (APDs): olanzapine (0.05 and 1.0 mg/kg), sertindole (0.1 and 1.0 mg/kg) and quetiapine (0.25 and 2.5 mg/kg), a selective 5-HT 2A receptor antagonist, M100907 (0.03 and 0.3 mg/kg), and an α 1-adrenoceptor antagonist, prazosin (0.3 mg/kg), on regional dopamine output were examined in the two subdivisions of the nucleus accumbens (NAC), the core and shell, which seem associated with motor control and limbic functions, respectively, by using in vivo differential normal pulse voltammetry in anaesthetised, pargyline-pretreated rats. Both quetiapine and sertindole, in the two doses used, caused a more pronounced dopamine release in the shell than in the core region of the NAC. In contrast, the low dose of olanzapine increased dopamine output almost to the same extent in both regions, whereas the high dose increased dopamine output to a greater extent in the core. M100907 selectively increased dopamine output in the shell. Also, prazosin significantly increased dopamine output in the shell, but not in the core. The results indicate that both 5-HT 2A and α 1-adrenoceptor antagonism may play an important role in the preferential effect of atypical APDs on dopamine output in the shell versus the core of the NAC.

Electrochemical nitric oxide microsensors: sensitivity and selectivity characterisation

In this study, we have prepared two nitric oxide (NO) microsensors using two combinations of nickel tetrasulfonated phthalocyanine (NiTSPc), o-phenylenediamine ( o-PD) and Nafion ® based layers to modify the surface of 8 μm diameter carbon fiber electrodes. We have compared the performances of the obtained composite microsensors (carbon/NiTSPc/Nafion ®, and carbon/Nafion ®/ o-PD, respectively) in our home made operating conditions. We have developed the sessile drop contact angle measurement technique as well as the use of the electrochemical quartz crystal microbalance (EQCM), differential normal pulse voltammetry (DNPV) and differential normal pulse amperometry (DNPA) to correlate the hydrophobicity, mass deposit of the polymer coatings and the sensitivity of the examined microsensors. By comparing the permeability of the microsensors to various interfering analytes, such as L-arginine, ascorbate, nitrite, serotonine, dopamine, acetamidophenol, 4-met-catechol, epinephrine, norepinephrine, dopac and 5-hydroxyindol, we have discussed the molecular sieving exclusion of the deposited membranes in term of molecular weight cutoff (MWCO).

Suppression of acute and chronic opioid withdrawal by a selective soluble guanylyl cyclase inhibitor

Previous studies have shown that activation of N-methyl- d-aspartate (NMDA) receptors and formation of nitric oxide (NO) contributes to the hyperactivity of locus coeruleus (LC) noradrenergic neurons and behavioural symptoms seen during opioid withdrawal. However, the role of soluble guanylyl cyclase (sGC), the `physiological' target of NO, in this phenomenon is unclear. In this study, the effect of 1 H-[1,2,4]oxadiazolo[4,3- a]quinoxalin-1-one (ODQ), a highly selective sGC inhibitor, on the naloxone-precipitated morphine withdrawal was examined using differential normal pulse voltammetry (DNPV) to measure LC activity, in vivo microdialysis to measure glutamate/aspartate release response, and behavioural assessment to evaluate withdrawal symptoms. In halothane-anaesthetized rats, acute intracerebroventricular (i.c.v.) morphine (10 μg) reduced the catecholamine oxidation current (CA·OC) (54.5±4.9% of baseline). Naloxone (2 mg/kg, i.v.) reversed this action of morphine and produced a rebound increase in CA·OC (136.1±6.0% of baseline), representing acute morphine withdrawal. Administration of ODQ (200 nmol, i.c.v.) blocked this response without affecting acute morphine action. In animals chronically treated with morphine (15 μg/μl/h, i.c.v., 5 days), naloxone significantly increased both the CA·OC signal (270.0±19.6% of baseline) and the release of l-glu (193±30.4%) and l-asp (221.5±28.4%) above baseline. These responses were attenuated in animals pretreated with ODQ. In unanaesthetized chronic morphine dependent rats, ODQ treatment suppressed the signs of withdrawal precipitated by naloxone (10 mg/kg). Taken together, the results of this study suggest that sGC plays an intermediary role in the genesis of LC neuronal hyperactivity and behavioural signs of morphine withdrawal.

REPEATED PGE1 TREATMENT ENHANCES NITRIC OXIDE AND ERECTION RESPONSES TO NERVE STIMULATION IN THE RAT PENIS BY UPREGULATING CONSTITUTIVE NOS ISOFORMS

To assess whether intracavernosal injections of prostaglandin E1 (PGE1) can influence nitric oxide (NO) release in the corpora in a rat model of penile erection. The extracellular levels of NO were monitored at 100 seconds intervals in the corpus cavernosum of anesthetized rats by using differential normal pulse voltammetry with porphyrin-Nafion coated carbon fiber microelectrodes. The intracavernosal pressure (ICP) was simultaneously recorded. PGE1 was given either as a single dose (ranging from 0.2 to 15 microg.) or as repeated 2 microg. injections in alternate days for two weeks. The NO and ICP responses to electrostimulation of the cavernosal nerve (SCN) was studied in the animals in the repeated treatment schedule at 1, 7, 15 and 30 days after its termination. The levels of the three NO synthase (NOS) isoforms in the cavernous tissue were measured by immunoblotting. Acute PGE1 treatment dose-relatedly increased NO levels in the corpora, with a concomitant ICP increase with the highest dose. Repeated 2 microg. PGE1 injections increased the NO and ICP responses to SCN as compared with intact or vehicle-injected animals. This treatment also increased the penile content of the neuronal and endothelial NOS proteins. The inducible NOS isoform remained unchanged after either vehicle or PGE1 injections. The effects of the repeated PGE1 treatment were greater in the group studied 24 hours after the last injection and decreased progressively thereafter. Stimulation of NO release can contribute to the erectogenic effect of intracavernous PGE1 injections. The increased levels of constitutive NOS isoforms in the corpora could contribute to the improvement of the erectile function reported by some patients following repeated treatment with vasorelaxant agents.

Study of a catalytic mechanism in double potential step techniques at spherical electrodes

An analytical complete solution corresponding to the double potential step problem for the catalytic mechanism at spherical electrodes is presented. This solution is applicable to double potential step chronoamperometry, differential normal pulse voltammetry (DNPV), differential pulse voltammetry (DPV) and reverse pulse voltammetry (RPV). The effects of the sphericity of the electrode on the I/t and I/E responses are analysed. The equations deduced in this paper allow us to calculate smaller rate constant values than those that can be calculated by using microelectrodes when only steady state is considered. Methods for calculating kinetic and thermodynamic parameters for the catalytic mechanism in all the above mentioned techniques are proposed and applied to the system Ti (IV) oxalate complex in the presence of hydroxylamine at spherical electrodes of different radii.