Indirect Electroanalysis of 3-Methyl-4-Nitrophenol in Water Using Carbon Fiber Microelectrode Modified with Nickel Tetrasulfonated Phthalocyanine Complex

Electrochemical detection of 3-methyl-4-nitrophenol (MNP) in direct phenol oxidation occurs at high potentials and generally leads to progressive passivation of the electrochemical sensor. This study describes the use of a carbon fiber microelectrode modified with a tetrasulfonated nickel phthalocyanine complex for the detection of MNP at a lower potential than that of direct phenol oxidation. The MNP voltammogram showed the presence of an anodic peak at -0.11 V vs SCE, corresponding to the oxidation of the hydroxylamine group generated after the reduction of the nitro group. The effect of buffer pH on the peak current and SWV parameters such as frequency, scan increment, and pulse amplitude were studied and optimized to have better electrochemical response of the proposed sensor. With these optimal parameters, the calibration curve shows that the peak current varied linearly as a function of MNP concentration, leading to a limit of detection (LoD) of 1.1 μg/L. These results show an appreciable sensitivity of the sensor for detecting the MNP at relatively low potentials, making it possible to avoid passivation phenomena.

An AuNPs/Mesoporous NiO/Nickel Foam Nanocomposite as a Miniaturized Electrode for Heavy Metal Detection in Groundwater

Heavy metals,notably Pb2+and Cu^(2+),are some of the most persistent contaminants found in groundwater.Frequent monitoring of these metals,which relies on efficient,sensitive,cost-effective,and reliable methods,is a necessity.We present a nanocomposite-based miniaturized electrode for the concurrent measurement of Pb2+and Cu^(2+)by exploiting the electroanalytical technique of square wave voltammetry.We also propose a facile in situ hydrothermal calcination method to directly grow binder-free mesoporous Ni O on a three-dimensional nickel foam,which is then electrochemically seeded with gold nanoparticles(Au NPs).The meticulous design of a low-barrier Ohmic contact between mesoporous Ni O and Au NPs facilitates target-mediated nanochannel-confined electron transfer within mesoporous Ni O.As a result,the heavy metals Pb2+(0.020 mg.L^(-1)detection limit;2.0–16.0 mg.L^(-1)detection range)and Cu^(2+)(0.013 mg.L^(-1)detection limit;0.4–12.8 mg.L^(-1)detection range)can be detected simultaneously with high precision.Furthermore,other heavy metal ions and common interfering ions found in groundwater showed negligible impacts on the electrode’s performance,and the recovery rate of groundwater samples varied between 96.3%±2.1%and 109.4%±0.6%.The compactness,flexible shape,low power consumption,and ability to remotely operate our electrode pave the way for onsite detection of heavy metals in groundwater,thereby demonstrating the potential to revolutionize the field of environmental monitoring.

Reduction behavior of cerium(Ⅲ) ions in NaCl-2CsCl melt

The cathodic process of cerium(III) ions in NaCl-2CsCl melt was studied bycyclic voltammetry and square wave voltammetry with tungsten and gold electrodes at 873 K. The twoelectroanalytical methods yield similar results. The cathodic process of cerium(III) ions consistsof two reversible steps: Ce^(3+)+ e^-= Ce^(2+) and Ce^(2+) + 2e^-= Ce. The half wave potentials ofCe^(3+)/Ce^(2+) and Ce^(2+)/Ce were determined as -2.525 V vs. Cl_2/Cl^- and -2.975 V vs. Cl_2/Cl^-,respectively. The diffusion coefficient of Ce^(3+) was also determined as 5.5 X 10^(-5) cm^2 centredot s^(-1).

CuO-nanoparticles modified carbon paste electrode for square wave voltammetric determination of lidocaine: Comparing classical and Box–Behnken optimization methodologies

In this research, copper oxide nanoparticles modified carbon paste electrode was developed for the voltammetric determination of lidocaine. The square wave voltammogram of lidocaine solution showed a well-defined peak between ＋0.5 and ＋1.5 V. Instrumental and chemical parameters influencing voltammetric response were optimized by both one at a time and Box–Behnken model of response surface methodology. The results revealed that there was no significant difference between two methods of optimization. The linear range was 1–2500 μmol L^-1（Ip= 0.11 C（LH）＋ 17.38, R^2= 0.999）. The LOD and LOQ based on three and ten times of the signal to noise（S/N） were 0.39 and 1.3 μmol L^-1（n = 10）,respectively. The precision of the method was assessed for 10 replicate square wave voltammetry（SWV）determinations each of 0.05, 0.5 and 1 μmol L^-1 of lidocaine showing relative standard deviations 4.1%,3.7% and 2.1%, respectively. The reliability of the proposed method was established by application of the method for the determination of lidocaine in two pharmaceutical preparations, namely injection and gel.

Electrochemical Assay of Effects of Organophosphate Poisoning on Acetylcholinesterase from Pheretima via 2,6-Dimethyl-p-benzoquinone

Electroanalytical techniques could be a reliable and promising alternative to classical and sophisticated methods because of their simplicity（small and portable）,easy use,the ability to deliver fast response with high sensitivity and selectivity.A square wave voltammetric method was developed for the assessment of organophosphorus（OPs） compound impact on acetylcholinesterase（AChE） of Pheretima with 2,6-dimethyl-p-benzoquinone（2,6DMBQ） as a redox indicator.The substrate of acetylthiocholine is hydrolyzed by AChE and the produced thiocholine reacts with 2,6-DMBQ to give an obvious shift of electrochemical signal.The reduction peak of 2,6-DMBQ is located at around 0.18 V which is far away from the oxidation potential of possible interference components often present in biosample.The decreased rate of reduction current was related with the activity of AChE.The inhibition of parathion-methyl on AChE was assessed.The inhibiton rate of OPs on AChE activity increased quickly during the first 10 min inhibition,and after that the value of inhibition rate approached to be constant.AChE lost almost 29.3% of activity after 10 min incubation with 1 μg/mL parathion-methyl and 67.5% of activity with 10 μg/mL parathion-methyl,while the activity that corresponds to 40 μg/mL parathion-methyl was nearly completely inhibited（94.9%）.Compared to cyclic voltammetry and amperometry,Square wave voltammetry（SWV） method is a high sensitive electroanalysis with fast scan-rate（only several seconds for one signal value） which is useful to prevent the electrodes from possible fouling or passivation.This method can be employed to assess the inhibition of organophosphate on AChE and investigate OPs impact on environmental animals.

Mechanistic insights into homogeneous electrocatalytic reaction for energy storage using finite element simulation

The application of homogeneous electrocatalytic reactions in energy storage and conversion has driven surging interests of researchers in exploring the reaction mechanisms of molecular catalysts.In this paper,homogeneous electrocatalytic reaction between hydroxymethylferrocene(HMF)and L-cysteine is intensively investigated by cyclic voltammetry and square wave voltammetry for which,the secondorder rate constant(k_(ec))of the chemical reaction between HMF^(+)and L-cysteine is determined via a 1D homogeneous electrocatalytic reaction model based on finite element simulation.The corresponding k_(ec)(1.1(mol·m^(-3))^(-1)·s^(-1))is further verified by linear sweep voltammograms under the same model.Square wave voltammetry parameters including potential frequency(f),increment(Estep)and amplitude(ESW)have been comprehensively investigated in terms of the voltammetric waveform transition of homogeneous electrocatalytic reaction.Specifically,the effect of potential frequency and increment is in accordance with the potential scan rate in cyclic voltammetry and the increase of pulsed potential amplitude results in a conspicuous split oxidative peaks phenomenon.Moreover,the proposed methodology of k_(ec)prediction is examined by hydroxyethylferrocene(HEF)and L-cysteine.The present work facilitates the understanding of homogeneous electrocatalytic reaction for energy storage purpose,especially in terms of electrochemical kinetics extraction and flow battery design.

Synthesis of carbon nanosheet from barley and its use as non-enzymatic glucose biosensor

In this work,carbon nanosheet（CNS） based electrode was designed for electrochemical biosensing of glucose.CNS has been obtained by the pyrolysis of barley at 600-750℃ in a muffle furnace：it was then purified and functionalized.The CNS has been characterized by scanning electron microscopy（SEM）.X-ray diffraction（XRD） and Raman spectroscopic techniques.The electrochemical activity of CNS-based electrode was investigated by linear sweep vollammetry（LSV） and square wave voltammetry（SWV）,for the oxidation of glucose in 0.001 M H2SO4（pH 6.0）.The linear range of the sensor was found to be 10-4-10-6M（1-100 μM） within the response time of 4 s.Interestingly,its sensitivity reached as high as 26.002±0.01 μA/μM cm2.Electrochemical experiments revealed that the proposed electrode offered an excellent electrochemical activity towards the oxidation of glucose and could be applied for the construction of non-enzymatic glucose biosensors.

Ac voltammetric and square wave voltammetric study of the self-assembled monolayers of thiol-functionalized viologen derivative

Electroactive self-assembled monolayers (SAMs) containing viologen group are formed through the adsorption of thiol-functionalized viologen compound CH3(CH2)(9)V2+(CH2)(8)SH, where V2+ is N,N'-dialkylbipyridinium (i.e. a viologen group), onto gold electrodes from methanol/water solution and its electrochemical behavior is investigated ty Ac voltammetry and square wave voltammetry, which have the high sensitivity against background charging. The viologen SAM formed is a sub-monolayer and the normal potentials corresponding to the two successive one-electron transfer processes of the active centers (viologen) are -360 mV and -750 mV (vs. Ag/AgCl) in 0.1 mol/L phosphate buffer solutions (pH 6.96) respectively, and the standard electron transfer rate constant is 9.0 s(-1). The electrochemical behavior of this SAM in various solutions has been preliminarily discussed.

Paracetamol Sensitive Cellulose-Based Electrochemical Sensors

Electrochemical determination of paracetamol(PCT)was successfully performed using carbon paste electrodes(CPEs)modified with treated coffee husks(CHt)or cellulose powder(Ce).Scanning electron microscopy was used to characterize unmodified or modified CPEs prior to their use.The electrochemical oxidation of PCT was investigated using square wave voltammetry(SWV)and cyclic voltammetry(CV).The oxidation current density of PCT was two-fold higher with the CPE-CHt sensor and 30%higher with CPE-Ce in comparison with the unmodified CPE,and this correlated with the higher hydrophilicity of the modified electrodes.Using SWV for the electrochemical analysis of PCT,carbon paste electrode modified with raw coffee husks(CPE-CHr)showed the presence of impurities at+0.27 V/SCE,showing the interest in using pure cellulose for the present analytical application.Furthermore,CPE-Ce presented a higher real area compared to CPE-CHr,which explains the increase in the limit of saturation from 400 mg/L to 950 mg/L.The better saturation limit exhibited by CPE-Ce justifies its choice for electroanalysis of PCT in commercialized tablets.The proposed method was successfully applied in the determination of PCT in commercialized tablets(DolipraneR 500)with a recovery rate close to 100%,and no interference with the excipients contained in the tablets analyzed was observed.This novel sensor opens the way for sustainable development of electroanalytical control of drugs sold individually in developing countries.

A Simple Over-Oxidized Molecularly Imprinted Polypyrrole for the Sensitive Detection of Dopamine in Human Serum

A simple electrochemical sensor for dopamine detection, is based on molecularly imprinted and electropolymerized over-oxidized polypyrrole (OPPy). The MIP-based electrode is obtained by electrocopolymerization of pyrrole (0.1 M) in the presence of the template molecular (dopamine, DA) (10-3 M). The square wave voltammetry (SWV) is used for the detection of dopamine in buffer solution. The current peak obtained at the MIP electrode was proportional to the logarithm of the DA concentration in the range of 10-11 to 5 × 10-8 M with a detection limit of 10-11 M. The proposed sensor was used for the detection of DA in spiked blood serum, satisfactory results were obtained.

Investigations of Thallium(Ⅰ) Underpotential Deposition on the Silver Rotating Disk Electrode and Its Analytical Application

The cyclic voltammetry(CV) and the square wave technique were used for the investigations of thallium(Ⅰ) underpotential deposition(UPD) on the silver electrode. A solution of 10 \{mmol/L\} HClO 4+10 mmol/L NaCl was selected as the supporting electrolyte. The calibration plots for Tl(Ⅰ) concentration in the range of 2×10 -9 -1×10 -7 mol/L were obtained. The detection limit was 5×10 -10 mol/L. For the solutions of 4 0×10 -9 mol/L thallium added before the urine sample pretreatment procedure, the average recovery was 105 6% with a relative standard deviation(RSD) of 15 5%.

Determination of Curcumin on Functionalized Carbon Nano Tube Modified Electrode and Probing its Interaction with DNA and Copper Ion

Voltammetry measurements have been employed to investigate the redox behaviour of curcumin in aqueous media using functionalized carbon nanotube(FCNTs)modified glassy carbon electrode(GCE).The electro-catalytic properties of FCNTs modified electrode are superior in comparison to the conventional electrode in generating the electrochemical response from curcumin.The oxidation process of the curcumin over the modified substrate is found to be p H dependent and shows 2e^(-)and 2H^(+)proton transfer electrochemical process.The oxidation peak is obtained at 0.37 V and the peak current is found to be linear with the varying concentration of curcumin.The limit of detection(LOD)and the limit of quantification(LOQ)for the curcumin are obtained as 60 and 200 nmol/L,respectively using the FCNTs modified GCE.The enhanced electrochemical response from the FCNTs modified GCE has been utilized in the evaluation of the chemical and biochemical behaviour of curcumin in presence of transition metal ions(Cu^(2+))and ds DNA,and the observation has been supported by the spectrochemical characteristics of the interactions.

Electrochemical response of MoS_(2) nanosheets/SiO_(2)-NH_(2) nanoparticles modified glassy carbon electrode to phenylacetic acid

Phenylacetic acid(PAA)is a primary raw material for illegal Methamphetamine(MATM)synthesis under the strong precursor chemicals supervisions of safrole and isosafrole.Therefore,trace detection of PAA at ultra-low concentration is a strategic technique and an urgent issue in the field of drug control.In this paper,trace determination of PAA at sub-nmol-L-1 concentration level is achieved by hydrogen bond adsorption and electrochemical catalysis through the prepared aminated SiO_(2)nanoparticles(SiO_(2)-NH_(2) NPs)and MoS_(2) nanosheets(NSs)modified glassy carbon electrode(GCE).The prepared MoS_(2) NS s/SiO_(2)-NH_(2) NPs modified electrode represents a detecting limit of 0.0989 nmol·L^(-1)and an obvious increasing linear range before the concentration increasement up to 60 nmol·L^(-1)in square wave voltammetry(SWV)responses of PAA.The SWV response of the modified electrode to PAA in the concentration range within 100 nmol·L^(-1)is higher than phenol,acetic acid(HOAc)and benzoic Acid(BEN).This electrochemical method for trace detection of PAA in aqueous solution with desired performance provides a feasible scheme for the detection of other drugs and aromatic precursor chemicals.

Toward point-of-care management of chronic respiratory conditions:Electrochemical sensing of nitrite content in exhaled breath condensate using reduced graphene oxide

We present a portable non-invasive approach for measuring indicators of inflammation and oxidative stress in the respiratory tract by quantifying a biomarker in exhaled breath condensate(EBC).We discuss the fabrication and characterization of a miniaturized electrochemical sensor for detecting nitrite content in EBC using reduced graphene oxide.The nitrite content in EBC has been demonstrated to be a promising biomarker of inflammation in the respiratory tract,particularly in asthma.We utilized the unique properties of reduced graphene oxide(rGO);specifically,the material is resilient to corrosion while exhibiting rapid electron transfer with electrolytes,thus allowing for highly sensitive electrochemical detection with minimal fouling.Our rGO sensor was housed in an electrochemical cell fabricated from polydimethyl siloxane(PDMS),which was necessary to analyze small EBC sample volumes.The sensor is capable of detecting nitrite at a low over-potential of 0.7 V with respect to an Ag/AgCl reference electrode.We characterized the performance of the sensors using standard nitrite/buffer solutions,nitrite spiked into EBC,and clinical EBC samples.The sensor demonstrated a sensitivity of 0.21μAμM^(−1) cm^(−2) in the range of 20–100μM and of 0.1μAμM^(−1) cm^(−2) in the range of 100–1000μM nitrite concentration and exhibited a low detection limit of 830 nM in the EBC matrix.To benchmark our platform,we tested our sensors using seven pre-characterized clinical EBC samples with concentrations ranging between 0.14 and 6.5μM.This enzyme-free and label-free method of detecting biomarkers in EBC can pave the way for the development of portable breath analyzers for diagnosing and managing changes in respiratory inflammation and disease.

Electrochemical reduction behavior of Hf(Ⅳ) in molten NaCl–KCl–K_2HfCl_6 system

The electrochemical reduction mechanism of hafnium ion（IV） was studied in NaC1-KC1-K2HfC16 melts on a molybdenum electrode. The cyclic voltammetry study shows that Hf（IV） is reduced to hafnium metal in double two-electron process, that is： Hf（IV） ＋ 2e→Hf（II） and Hf（II） ＋ 2e- →Hf, and the electrochemical reduction of Hf（IV） pro- cess was diffusion-controlled. The diffusion coefficients were calculated at several temperatures, and the results obey the Arrhenius law. According to the relationship oflnD versus 1/T, the corresponding activation energy was determined to be 158.8 kJ.mol- x. The square wave voltammetry results further confirm the reduction mechanism of hafnium.

A Highly Efficient ZrO2 Nanoparticle Based Electrochemical Sensor for the Detection of Organophosphorus Pesticides

A sensitive electrochemical method for square-wave voltammetric detection of organophosphate （OP） com- pounds was developed based on zirconia （ZrO2） nanoparticles modified electrode. The electrode was fabricated us- ing electrochemical deposition and characterized by scanning electron microscopy （SEM）, which confirmed the successful formation of nanoparticles. Due to the strong affinity of ZrO2 with the phosphoric group, OPs can strongly bind to the surface of ZrO2 nanoparticles （ZrO2NPs）. Under optimized operational conditions, SWV was employed for Omethoate （a model of OP compounds） detection with 5 min absorption, which showed a wide detec- tion range from 98.5 pmoloL-x to 985 nmol·L^1, with a detection limit as low as 52.5 pmol·L^-1. This electrochemi- cal sensor has good selectivity, stability and reproducibility, and great potential in the detection of OP compounds in agriculture area.

Influence of pigment substitution on the electrochemical properties of Rhodobacter sphaeroides 601 reaction centers

With the help of pigment substitution, self-assembled monolayer film and square wave voltammetry, the influence of pigment substitution on the electrochemical properties of Rhodobacter sphaeroides 601 reaction centers was investigated. Results showed that the charge separation could also be driven by externally electric field, similar to the primary photochemical reaction in purple bacterial reaction center. On the surface of Au electrode, a self-assembled monolayer film (the RC-PDDA-DMSA film) was made up of 2,3-dimercaptosuccinic acid (DMSA), poly-dimeth-yldiallylammonium chloride (PDDA) and reaction center (RC). When square wave voltammetry was used to study the RC-PDDA-DMSA film, four redox pairs in the photochemical reaction of RC were observed by changing frequency. With nonlinear fitting, the standard potential of P/P+ and the corresponding electrode reaction rate constant were determined to be 0.522 V and 13.04 S-1, respectively. It was found that the redox peak at -0.02 V changed greatly when bacteriopheophytin was substituted by plant pheophytin in the reaction center. Further studies indicated that this change resulted from the decrease in electron transfer rate between Bphe-/Bphe (Phe-/Phe) and QA-/QA after pigment substitution. After investigations of spectra and electrochemical properties of different RCs and comparisons of different function groups of pigments, it was indicated that the phytyl tail, similar to other substituted groups of pheophytin, affected the efficiencies of pigment substitution.

Cascade Toehold-Mediated Strand Displacement Reaction for Ultrasensitive Detection of Exosomal MicroRNA

MicroRNA(miRNA)in exosomes is a powerful molecular signature for early diagnosis of cancers with the merits of high specificity and high stability.Herein,we report an ultrasensitive electrochemical assay to measure miRNA using a cascade toeholdmediated strand displacement reaction(SDR).In SDR,the trapped exosomal miRNA releases a large amount of single-stranded DNA in the solution.The product then triggers the downstream SDR at the electrode surface.

PSO-SVM applied to SWASV studies for accurate detection of Cd(II)based on disposable electrode

Square wave anodic stripping voltammetry(SWASV)is an effective method for the detection of Cd(II),but the presence of Pb(II)usually has some potential and negative interference on the SWASV detection of Cd(II).In this paper,a novel method was proposed to predict the concentration of Cd(II)in the presence of Pb(II)based on the combination of chemically modified electrode(CME),machine learning algorithms(MLA)and SWASV.A Bi film/ionic liquid/screen-printed electrode(Bi/IL/SPE)was prepared and used for the sensitive detection of trace Cd(II).The parameters affecting the stripping currents were investigated and optimized.The morphologies and electrochemical properties of the modified electrode were characterized by scanning electron microscopy(SEM)and SWASV.The measured SWASV spectrograms obtained at different concentrations were used to build the mathematical models for the prediction of Cd(II),which taking the combined effect of Cd(II)and Pb(II)into consideration on the SWASV detection of Cd(II),and to establish a nonlinear relationship between the stripping currents of Pb(II)and Cd(II)and the concentration of Cd(II).The proposed mathematical models rely on an improved particle swarm optimization-support vector machine(PSO-SVM)to assess the concentration of Cd(II)in the presence of Pb(II)in a wide range of concentrations.The experimental results suggest that this method is suitable to fulfill the goal of Cd(II)detection in the presence of Pb(II)(correlation coefficient,mean absolute error and root mean square error were 0.998,1.63 and 1.68,respectively).Finally,the proposed method was applied to predict the trace Cd(II)in soil samples with satisfactory results.

Review of Electrochemical Sensors and Biosensors Based on First-Row Transition Metals,Their Oxides,and Noble Metals Nanoparticles

The use of electrochemical sensors for sensitive disease diagnosis and detecting various species with pharmacological,therapeutic,industrial,food-related,and environmental origins is now widely accepted.A catalytic or binding event resulting from the sensor’s electroactive component recognizing its analyte creates an electrical signal proportionate to the analyte concentration,which is then monitored by a transducer.The development of morphologically distinct metal and metal oxide nanoparticles formed from first-row transition elements(Mn,Cr,Fe,Co,Ti,Ni,Cu,Zn)and noble metals(Pt,Au,Ag,Pd)is described in this review.The effect of these metal nanoparticles has been studied using Tetracyanoquinodimethane(TCNQ),Ferrocene,and other organic compounds as electroactive species using carbon paste-modified electrodes.Electroanalytical sensors,mostly based on ferrocene,are exceedingly sensitive,selective,affordable,and for detecting numerous biomolecules like glucose,dopamine,NADH,ascorbic acid,and a few dyes and are simple to build.In recent decades,charge transfer organic species-based chemosensors have become a prominent study area.This paper outlines current developments in electrochemical biosensors based on transition metal nanoparticles,covering glucose,ascorbic acid,uric acid,and other inorganic and organic analytes.The importance of transition metal and transition metal oxide nanoparticles as potential electrode modifiers for developing sensors is highlighted.A discussion of the present problem and possible solutions,and plausible future directions marks the review’s conclusion.