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.

Semidifferential Electroanalysis of Aqueous Triton X-100/Toluene/H2O Microemulsion

Semidifferential electroanalysis is used as an effective method for investigating microstructure and structural transition of Triton X-100 microemulsions.

Electroanalysis overview:Addressing the green credentials in the use of electroanalytical sensors

Electrochemical methodologies provide a wide arsenal of options for analytical sensors,providing a high sensitivity,short analysis time,low-cost,possibility for miniaturization,and are readily portable solutions.One common theme within the literature is the use of the word“green”.The use of this terminology is intended to demonstrate the development of electroanalytical sensing platforms utilizing biodegradable and sustainable materials.In many cases,the claims of“green”electroanalytical platforms is questionable.This minireview looks to address the green credentials that are utilized in the pursuit of electroanalytical sensors,offering insights into future research opportunities.

Recent Advances of Nanoelectrodes for Single-Cell Electroanalysis:From Extracellular, Intercellular to Intracellular

Detection at single-cell level plays a critical role in revealing cell behavior in different organisms.Nanoelectrodes with high temporal–spatial resolution can precisely and dynamically monitor the physiological and pathological processes of various single cells.The field of using nanoelectrodes in single-cell electroanalysis is blooming in recent years.In this review,we mainly summarize the recent advances of nanoelectrodes for single-cell electroanalysis from extracellular,intercellular to intracellular levels in the past decade.First,we introduce the main types of nanoelectrodes based on their geometry and characteristics for single-cell electroanalysis.Then,the representative works of using nanoelectrodes to investigate cellular signaling biomolecules and to understand various cellular processes from the extracellular,intercellular,and intracellular levels are introduced.Finally,the challenges and future prospects of nanoelectrodes for single-cell electroanalysis are proposed.This review gives a comprehensive summary of nanoelectrodes for single-cell electroanalysis in the prospects of monitoring cell physiological topography,understanding communication mechanism and revealing physiological functions,which can provide new insights into cell-based pharmacological screening and fundamental studies of disease development mechanisms.

Voltammetric sensor based on cobalt-poly(methionine)-modified glassy carbon electrode for determination of estriol hormone in pharmaceuticals and urine

A voltammetric sensor based on the electropolymerization of cobalt-poly(methionine)(Co-poly(Met)) on a glassy carbon electrode (GCE) was developed and applied for the determination of estriol by differential pulse voltammetry (DPV) for the first time. The electrochemical properties of the Co-poly(Met)/GCE were analysed by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to characterize the polymers on the GCE surface. The deposition of the Co-poly(Met) film on the GCE surface enhanced the sensor electronic transfer. CV studies revealed that estriol exhibits an irreversible oxidation peak at t0.58 V for the Co-poly(Met)/GCE (vs. Ag/AgCl reference electrode) in 0.10 mol/L Britton-Robinson buffer solution (pH=7.0). Different voltammetric scan rates (10-200 mV/s) suggested that the estriol oxidation on the Co-poly(Met)/GCE surface is controlled by adsorption and diffusion processes. Based on the optimized DPV conditions, the linear responses for estriol quantification were from 0.596 μmol/L to 4.76 μmol/L (R2 =0.996) and from 5.66 μmol/L to 9.90 μmol/L (R2 =0.994) with a limit of detection (LOD) of 0.0340 μmol/L and a limit of quantification (LOQ) of 0.113 μmol/L. The DPV-Co-poly(Met)/GCE method provided good intra-day and inter-day repeatability with RSD values lower than 5%. Also, no interference of real sample matrices was observed on the estriol voltammetric response, making the DPV-Copoly( Met)/GCE highly selective for estriol. The accuracy test showed that the estriol recovery was in the ranges 96.7%-103% and 98.7%-102% for pharmaceutical tablets and human urine, respectively. The estriol quantification in pharmaceutical tablets performed by the Co-poly(Met)/GCE-assisted DPV method was comparable to the official analytical protocols.

Electrochemical detection of methyl-paraoxon based on bifunctional cerium oxide nanozyme with catalytic activity and signal amplification effect

A new electrochemical sensor for organophosphate pesticide(methyl-paraoxon)detection based on bifunctional cerium oxide(CeO_(2))nanozyme is here reported for the first time.Methyl-paraoxon was degraded into p-nitrophenol by using CeO_(2) with phosphatase mimicking activity.The CeO_(2) nanozymemodified electrode was then synthesized to detect p-nitrophenol.Cyclic voltammetry was applied to investigate the electrochemical behavior of the modified electrode,which indicates that the signal enhancement effect may attribute to the coating of CeO_(2) nanozyme.The current research also studied and discussed the main parameters affecting the analytical signal,including accumulation potential,accumulation time,and pH.Under the optimum conditions,the present method provided a wider linear range from 0.1 to 100 mmol/L for methyl-paraoxon with a detection limit of 0.06 mmol/L.To validate the proof of concept,the electrochemical sensor was then successfully applied for the determination of methyl-paraoxon in three herb samples,i.e.,Coix lacryma-jobi,Adenophora stricta and Semen nelumbinis.Our findings may provide new insights into the application of bifunctional nanozyme in electrochemical detection of organophosphorus pesticide.

Voltammetry and fluorescence studies on the interaction between Eu(phen)_3^(+3)and DNA

The binding mode of Eu(phen)_3^(3+) with DNA is studied by fluorescence andvoltammetric methods. From the Scatchard graph and the fluorescence quenching phenomenon, it isconcluded that the mode of interaction between Eu(phen)_3^(3+) and DNA is intercalation bind byinserting the phen pi-pi conjugate surface between the base pairs of the DNA duplex. Voltammetry wasused to confirm the results obtained from the fluorescence method, the result from both methodsagrees with each other. The binding constant (K) and the binding site size (n_s) were calculatedfrom voltammetric data such as the shifts in potential and limiting currents in the process ofadding DNA, according to the positive shifts of peak potential. It was considered that the complexof the +2 ion interacted more favorably with the nucleotide bases than that of the +3 ion byhydrophobic interaction.

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.

Investigation on a Small Oscillogram

A small oscillogram, one end of which was substituted by a bright point caused by the redox of an appropriate depolarizer and the other end of which was the redox of Hg or the redox of supporting electrolyte cation, was investigated in this paper. Experimental results of application of the small oscillogram to oscillographic determination of cefoperazone showed that the small osciUogram was more stable, sensitive, and less interference than classical oscillogram.

Electrochemical detection of hydrogen peroxide at a waxed graphite electrode modified with platinum-decorated carbon nanotubes

Platinum-decorated carbon nanotubes （CNT-Pt） were produced by the chemical reduction method. A novel modified electrode was fabricated by intercalated CNT-Pt in the surface of waxed graphite, which provided excellent electrocatalytic activity and selectivity for both oxidation and reduction of hydrogen peroxide. The current response of the modified electrode for hydrogen peroxide was very rapid and the detection limits in amperometry are 2.5×10^-6 mol/L at reduction potential and 4.8×10^-6 mol/L at oxidation potential. It was desmonstrated that the electrode with high electro-activity was a suitable basic electrode for preparing enzyme electrode.

Fullerene/MWCNT/Nafion Modified Glassy Carbon Electrode for the Electrochemical Determination of Caffeine

Herein, a convenient method based on a fullerene/multiwalled carbon nanotube/Nafion modified glassy carbon electrode (fullerene/MWCNT/Naf/GCE) for the electrochemical determination of caffeine (CAF) is reported. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to study ionic exchange properties and conductivity the proposed electrode using [Fe(CN)6]3-/4- redox couple. Caffeine gave an irreversible oxidation peak around +1.33 V (vs. Ag/AgCl reference electrode) in HClO4 (pH 1). The linear dependence of the peak current with the square root of the scan rate showed that the electron transfer process is controlled by diffusion. After optimization of key analytical parameters involved in differential pulse voltammetry (DPV), the oxidation peak current varied linearly with CAF concentration in the range of 10 to 1000 μM. A detection limit of 7.289 × 10-8 M (S/N = 3) was found. Kinetic and chronocoulometric studies were also performed to characterize the diffusion of CAF. The developed electrode exhibited good stability and was easily regenerated. The influence of some potential interfering compounds such as dopamine, uric acid, glucose and sulfite ions on the anodic peak current of CAF was also examined. The proposed method was successfully employed in the determination of CAF in some commercial drugs.

Aptamer-Based Antibiotic Electrochemical Detection Platform Using Portable Plastic Gold Electrode and Multichannel Chip

The development of accurate,rapid and practical electrochemical sensing technology for antibiotic detection has an important application prospect in many fields such as food safety,environmental monitoring,medical and health care.In this research,kanamycin specific DNA aptamer and its partially complementary short chain were self-assembled onto the surface of an integrated portable plastic gold electrode(PGE)by Au-s bond,and a simple kanamycin electrochemical biosensor interface was constructed.At the same time,the epoxy resin channel layer was designed,and the auxiliary instrument was set up independently in the laboratory,which could help to measure and analyze eight groups of samples automatically in turn.The quantitative analysis results showed that in 20 min,the sensor had a good linear relationship between the peak current change of square wave voltammetry and the negative logarithm of kanamycin concentration when kanamycin concentration was in the range of 1-10o0μmol/L,and the detection limit could reach 0.40μmol/L.In addition,the discrimination could be achieved within 5 min in the real-time analysis mode.The sensor had a simple construction method,good selectivity and stability,and could be used for rapid or real-time detection of kanamycin residues in actual water samples,which provided a new direction for the practical detection of kanamycin in environmental watersamples.

Electron transfer and interfacial behavior of redox proteins

This paper reviews the recent progress in the electron transfer and interfacial behavior of redox proteins. Significant achievements in the relevant fields are summarized including the direct electron transfer between proteins and electrodes, the thermodynamic and kinetic properties, catalytic activities and activity regulation of the redox proteins. It has been demonstrated that the electrochemical technique is an effective tool for protein studies, especially for probing into the electron transfer and interfacial behavior of redox proteins.

Graphene oxide–MnO2 nanocomposite-modified glassy carbon electrode as an efficient sensor for H2O2

In this study, a new facile preparation method of nanocomposites consisting of graphene oxide and manganese dioxide nanowires（GO/MnO2 NWs） was developed. The morphology, structure and composition of the resulted products were characterized by transmission electron microscopy, X-ray diffraction and N2 adsorption and desorption. The GO/MnO2 nanocomposite was used as an electrode material for non-enzymatic determination of hydrogen peroxide. The proposed sensor exhibits excellent electrocatalytic performance for the determination of hydrogen peroxide in phosphate buffer solution（PBS, pH7） at an applied potential of 0.75 V. The non-enzymatic biosensor for determination of hydrogen peroxide displayed a wide linear range of 4.90 mmol L^-1–4.50 mmol L^-1with a correlation coefficient of 0.9992, a low detection limit of 0.48 mmol L^-1 and a high sensitivity of 191.22μA（mmol L^-1）^-1cm^-2（signal/noise, S/N = 3）. Moreover, the non-enzymatic biosensor shows an excellent selectivity.

Facile Fabrication of a Graphene-based Electrochemical Biosensor for Glucose Detection

A simple and effective glucose biosensor based on immobilization of glucose oxidase （GOD） in graphene （GR）/Nafion film was constructed. The results indicated that the immobilized GOD can maintain its native structure and bioactivity, and the GR/Nafion film provides a favorable microenvironment for GOD immobilization and promotes the direct electron transfer between the electrode substrate and the redox center of GOD. The electrode reaction of the immobilized GOD shows a reversible and surface-controlled process with the large electron transfer rate constant （ks） of 3.42±0.08 s-1. Based on the oxygen consumption during the oxidation process of glucose catalyzed by the immobilized GOD, the as-prepared GOD/GR/Nafion/GCE electrode exhibits a linear range from 0.5 to 14mmol·L-1 with a detection limit of 0.03 mmol·L-1. Moreover, it displays a good reproducibility and long-term stability.

DNA Induced FePt Bimetallic Nanoparticles on Reduced Graphene Oxide for Electrochemical Determination of Dopamine

FePt bimetallic nanoparticles were formed on reduced graphene oxide（rGO） with the help of double-stranded DNA（dsDNA） via a simple and universal route to obtain a FePt/DNA-rGO composite. The FePt nanoparticles with an average size of about 5 nm were well dispersed on rGO. FePt/DNA-rGO modified glassy carbon electrode（GCE） exhibited excellent electrocatalytic activity for the oxidation of dopamine（DA） with a detec- tion limit of 100 nmol/L（S/N = 3）. In addition, the FePt/DNA-rGO based electrochemical sensor showed an excellent selectivity for DA in the presence of ascorbic acid（AA）, uric acid（UA） and other interference reagents. The as-prepared electrochemical biosensor shows great promise in the application of clinical diagnostics.