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.

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.

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.

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.