High-performance electrochemical sensor with a hollow iron oxide-modified carbon paste electrode (HIO/CPE) for selective clindamycin detection

Porous metals have recently attracted much attention in both academia and industry. They have many potential applications ranging from light weight structure, thermal management and sound absorption, because of their unique structural, mechanical, thermal and acoustic properties. Open-cell porous metal can be an ideal material for electrochemical applications due to its high surface area, permeability and electric conductivity. The electro-active surface area of porous electrodes is the most important factor in electrochemical applications, such as fuel cells, because it largely determines the current density in the electrode. However, most research to date on the surface area of porous metals has been focused on the geometric and real surface areas. Very little research has been conducted to study the electro-active surface area. The mass transfer coefficient of a solid electrode is a very important factor in flow cell applications, such as flow battery and wastewater treatment, because high mass transfer coefficient means high reaction performance. However, very little research has been carried out on the mass transfer coefficient of open-cell porous metal manufactured by the space-holder method. The main objective of this study is to investigate the electrochemically relevant structural properties of porous Cu and Ni fabricated by the Lost Carbonate Sintering (LCS) process, which is a cost-effective process for manufacturing open-cell porous metals with controlled porosity, pore size and pore shape. In this project, the geometric, electro-active and real surface areas of porous Cu and Ni have been measured by quantitative stereology, cyclic voltammetry (peak current) and cyclic voltammetry (double layer capacitance) methods, respectively. The mass transfer coefficient of porous Ni has been measured by linear sweep voltammetry, using a purpose-built flow cell. The tortuosity of porous Cu has been measured by a diffusion method, using a purpose-built diaphragm cell. The geometric, electro-active and real surface areas of porous metal are due to the contributions from the primary porosity, the primary and secondary porosities, and the surfaces of metal particles, respectively. The geometric, electro-active and real surface areas of porous Cu and Ni samples with pore sizes 75-1500 µm and porosities 0.53-0.81 were in the ranges of 18-110 cm-1, 24-369 cm-1 and 700-1200 cm-1, respectively. Both the geometric and electro-active surface area increased with porosity and decreased with pore size. The real surface area decreased with porosity but the effect of pore size was not pronounced. The values of electro-active surface area of LCS porous metal can be similar to and often greater than those of the existing porous metals, e.g. incofoam Ni. The mass transfer coefficient of porous Ni with pore sizes 250-1500 µm and porosities 0.63-0.81 at different flow rates from 0.24 ml/s to 2.8 ml/s was in the range of 0.0035-0.0727 cm/s. Both the limiting current and mass transfer coefficient increased with flow rate and had the maximum values at a porosity of around 0.65-0.70. The maximum limiting current decreased and the maximum mass transfer coefficient increased with pore size. Compared with a smooth Ni plate at the same flow velocity, the mass transfer coefficient of the LCS porous Ni was increased by up to 9 times. The enhancement is due to the Ni particles providing a rough surface for the cell walls and the tortuous pore structure resulting in a high level of fluid turbulence. The tortuosity of the porous Cu samples, with pore sizes 250-1500 µm and porosities 0.56-0.84, was in the range of 1.33-1.78. It increased with pore size and decreased with porosity, agreeing with an empirical formula for porous media. This research has successfully applied cyclic voltammetry to the measurement of electro-active surface area of porous metals for the first time. It is the first systematic study of the structural properties of relevance to electrochemical applications of porous metals manufactured by LCS process.

Metal ion pollution is a major environmental concern, with toxic metals like lead (Pb) and mercury (Hg) contaminating water, soil and air, which poses serious risks to human health and the ecosystem. Thus, effective monitoring is essential to assess and mitigate their harmful impact. Electrochemical metal ion sensing has emerged as a promising real-time technique for quantifying metal ions through electrode reactions with high accuracy, sensitivity and selectivity. For this purpose, a thiol-functionalized silica supported material, FMS-TA-ATT, has been synthesized for the electrochemical sensing of Pb2+ and Hg2+ simultaneously and individually in 0.2 M acetate buffer solution and is found to hold promising detection ability in neutral medium (pH = 7). The comprehensive characterization of the synthesized materials has been performed by powder X-ray diffraction, electron microscopy, nitrogen adsorption/desorption studies, thermogravimetric analysis, FT-IR, and solid state 29Si and 13C CP MAS NMR spectroscopy, and the electrochemical behavior has been evaluated by cyclic voltammetry and electrochemical impedance spectroscopy. The sensing ability of the glassy carbon electrode prepared with FMS-TA-ATT (FMS-TA-ATT/GCE) has been examined by differential pulse voltammetry. This material shows good selectivity and sensitivity towards Pb2+ and Hg2+ in 0.2 M acetate buffer solution at pH = 7 with a very low limit of detection (LOD) (13 nM for Pb2+ and 29 nM for Hg2+). Additionally, FMS-TA-ATT/GCE is efficient at detecting Pb2+ and Hg2+ in the presence of other metal ions and it also displays sensing ability with real water samples.

Combustion synthesis of Pr6O11 nanoparticles as an effective and sensitive sensor for detection of vanillin in the presence of uric acid

Safranin amplified carbon paste electrode sensor for analysis of paracetamol and epinephrine in presence of folic acid and ascorbic acid

Effects of dynamic polarization on boron-doped NCD properties and on its performance for electrochemical-analysis of Pb (II), Cu (II) and Hg (II) in aqueous solution via direct LSV

In electroanalytical chemistry, it is often observed that square wave voltammetry (SWV) and differential pulse voltammetry (DPV) are more sensitive techniques compared to linear sweep voltammetry (LSV), due to their method of sampling which minimises the charging current (non‐faradaic processes). In this work, a comparison of the three techniques (LSV, DPV and SWV) is performed for ammonia (NH3) gas oxidation (a chemically and electrochemically irreversible redox process) in an ionic liquid over a concentration range of 10–100 ppm. Four different platinum electrodes are employed: a screen‐printed electrode (SPE), a thin‐film electrode (TFE), a microarray thin‐film electrode (MATFE) and a Pt microdisk electrode (μ‐disk). Calibration plots (current vs concentration) for all three different electrochemical techniques on all four surfaces showed excellent linearity with increased concentrations of NH3 gas and relatively low limits of detection (LODs). On the larger mm‐sized surfaces (SPE and TFE), the current responses for LSV and SWV were quite similar, but DPV gave the lowest currents. Whereas for the smaller micron sized electrodes (MATFE and μ‐disk), currents were of the order LSV>SWV>DPV, with LSV being far superior to the pulse techniques. These findings suggest that the pulse techniques of SWV and DPV may not be the optimum methods, particularly on microelectrodes, for the detection of analytes such as ammonia in RTILs.

A sensitive electrochemical sensor for hydroxylamine determination: Using multiwall carbon nanotube paste electrode (MWCNTPE) and promazine hydrochloride as homogenous mediator

The electrochemical oxidation of the antineoplastic agent etoposide was studied at carbon paste electrode in Britton-Robinson buffer solutions over the pH range 2.0-10.0 using cyclic, linear sweep and differential pulse voltammetry. Oxidation of the drug was effected in a single reversible, diffusion-controlled step within the pH range 2.0-4.0, a second oxidation process was produced above pH 4.0. Using differential pulse voltammetry (DPV), the drug yielded a well-defined voltammetric response in Britton-Robinson buffer, pH 3.0 at 0.500 V (vs. Ag/AgCl) on carbon paste electrode. This process could be used to determine etoposide concentrations in the range 2.5 x 10(-7) to 2.5 x 10(-5) M with a detection limit of 1.0 x 10(-7) M. The method was successfully applied to the determination of the drug in spiked human serum.

Multifunctional nanoplatforms with the synergistic effects of multiple therapeutic modalities have become a research focus due to their superior anti-tumor properties over single therapeutic modalities. Herein, we developed around 14 nm porous hollow copper iron oxide nanoparticles (PHCuFeNPs) with pore sizes of around 2-3 nm as a cisplatin carrier and photothermal therapeutic agent. The PHCuFeNPs were synthesized via a galvanic reaction between Cu2S nanoparticles and iron pentacarbonyl (Fe(CO)5) followed by etching in the organic phase to make the pores. They were stable under normal physiological conditions, but the pores were etched in a weak acidic tumor microenvironment, resulting in the controlled release of Cu and Fe ions for enhanced chemodynamic therapy and accelerated cisplatin release for chemotherapy. Under 980 nm laser irradiation, the PHCuFeNPs could effectively heat up to further promote the release process for synergistic therapy. Besides, they were proved to mediate immunogenic cell death to activate the immune system for potential immunotherapy. Together with their ability to degrade into fragments for fast renal metabolism, we believe that these PHCuFeNPs could provide a biocompatible and efficient multi-antitumor therapeutic approach.

In the present study, a simple electrochemical sensor for trace determination of Hg(II) ions in aqueous solutions was introduced. The proposed sensor was designed by incorporation of the 4-methyl-piperidine-carbodithioate capped gold nanoparticles (GNPs) into the carbon paste electrode (CPE), which provides a remarkably improved sensitivity for stripping voltammetric determination of Hg(II). Differential pulse voltammetry (DPV) was applied for quantitative determinations. The resulting electrode exhibited a linear relationship towards Hg(II) concentrations ranging from 0.4 to 100.0 μg L-1. The detction limit was found to be 0.2 μg L-1 (S/N = 3) that is lower than the permitted value of Hg(II) reported by the Environmental Protection Agency (EPA) limit for drinkable water. The relative standard deviation (RSD) for 7 successive measurements at different electrodes was also found to be 3.8%. The interference studies showed that the several common metal ions did not interfere with the quantitative mercury determination. The designed sensor was further utilized for the determination of mercury ions in real water samples with satisfactory results.

A novel chemically modified electrode was constructed based on the electrodeposition of palladium nanoparticles (PdNps) on to a poly(solochrome cyanine) (polySCCy) film coated carbon paste electrode (CPE). Cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS) were used to characterize the properties of the modified electrode. The polySCCy/PdNPs/CPE was used for the impressionable, individualized determination and simultaneous resolution of dopamine (DA), ascorbic acid (AA) and uric acid (UA) in 0.1 M acetate buffer solution (ABS) of pH 5.0 by employing CV and DPV. The polySCCy/PdNPs/CPE exhibited strong electrocatalytic activity towards the oxidation of a mixture solution of DA, AA and UA with obvious redox potentials. The overlapping voltammetric response of biomolecules were separated into three well resolved oxidation peaks for DA, AA and UA with lower oxidation potentials and significant increase in the anodic peak currents in the presence of polySCCy/PdNPs/CPE by using CV and DPV. The results showed good sensitivity, selectivity and high reproducibility of the electrosynthesized polymer nanoparticles inclusion electrode. The limit of detection, limit of quantification and correlation coefficient of DA at polySCCy/PdNPs/CPE were 1.87 μM, 6.24 μM and 0.99375, respectively. The developed chemical sensor is ideal for the analysis of DA in pharmaceutical formulations providing satisfactory results. The interfacial electron transfer rate of DA was studied by EIS.

Amperometric sensors with nucleic acid amplification are expected to be useful for sensitive RNA detection. Nucleic acid amplification reaction involves current changes associated with accelerated redox reactions. Among the nucleic acid amplification methods, we have attempted to apply the signal amplification by ternary initiation complexes (SATIC) system to amperometric sensors1,2. Amperometric sensor with SATIC system detected target RNA by measuring the reduction of hydrogen peroxide by DNAzyme via ferrocene methyl alcohol (FMA). Although linear sweep voltammetry (LSV) was used in previous study, the current was included reactions other than reduction by DNAzyme, such as the charge of the electrical double layer and mass diffusion of redox species. Pulsed electrochemical measurement removes the other current by refreshing the diffusion layer of redox species with each pulse voltage. Therefore, in this study, we focused on pulsed electrochemical measurement methods to further increase the signal-to-noise ratio of amperometric sensors with SATIC system by removing the noise. Current values derived from nucleic acid amplification with the SATIC system were compared by LSV, differential pulse voltammetry (DPV), normal pulse voltammetry (NPV) and square wave voltammetry (SWV.)DNA primers and 6-merchapto-1-hexanol (MCH) were immobilized on gold electrode via gold-thiol bond. Then, the SATIC reaction proceeded (37 ºC, 2 h) on the electrode by target RNA, a circular DNA template, and φ29 DNA polymerase. After that, the electrode was placed in phosphate buffer containing hemin which iron-containing porphyrin. DNAzyme was formed by the G-quadruplex (G4) in the amplified nucleic acid by binding to hemin. The current value changes resulting from the catalytic reaction of DNAzyme before and after the SATIC reaction were measured by LSV, DPV, NPV, and SWV. The ranges of voltage scan were -0.15〜-0.4 V vs. Hg/Hg2SO4 and -0.05〜-0.4 V vs. Hg/Hg2SO4 in LSV and other pulsed electrochemical measurement, respectively. The step potential was 5 mV, pulse wide was 50 ms, and pulse periode was 100 ms. Additionally, the pulse amplitudes of DPV and SWV were 50 mV and 25 mV, respectively. The measuring points each were acquired after 40 s from applying the pulse signals.First, each electrochemical measurement methods in a simple redox reaction were compared. The current density corresponding to the reduction reaction of FMA was measured using a polished bare gold electrode. The results showed an increase in current density depending on FMA concentration in all electrochemical measurement methods. Furthermore, the slope of the current value change relative to the FMA concentration was found to be greater in the order LSV < SWV ≦ DPV ≦ NPV. As the pulse eliminated the contribution of the charging current due to the electrical double layer, the quantitative detectability of DPV, NPV and SWV was higher than LSV. Based on the above results, the signal-to-noise ratio of amperometric sensors with SATIC system was compared using each electrochemical measurement method. The amount of current density changes with the progression of the SATIC reaction to 1 µM Target RNA was measured. As a result, current density changes of LSV: 1.98 μA/cm2, DPV: 12.2 μA/cm2, NPV: 3.41 μA/cm2 and SWV: 9.04 μA/cm2 were observed (Figure 1). In NPV measurement, the variation in current density change was more varied than that using other electrochemical measurements. As the pulse signal were impressed from the open circuit potential in NPV, the current included not only electron transfer but also mass diffusion of FMA mediator, resulting in the variation of repeatability in each measurement. Moreover, in DPV and SWV measurements, the changing in current density were greater than that of LSV measurement. This result could be attributed to the fact that the contribution of the current due to the charging electrical double layer and mass diffusion of FMA mediator was removed by the impressed pulse signal. However, the signals obtained from measurements using DPV and SWV represent the slope of the current value change relative to the potential scan. Therefore, it is not advisable to compare each electrochemical measurement at a single RNA concentration point. In the presentation, we will further discuss the signal-to-noise ratio of measurement methods of amperometric sensors using the SATIC system by comparing the concentration dependence of the target RNA concentration obtained from each electrochemical measurement.Reference:[1] H.Fujita et al., Anal. Chem. 88, 7137−7144 (2016).[2] H.Saze et al., 2023 ECSJ Fall Metting, Abstr, S12_2_04, [in Japanese] Figure 1

A novel carbon paste electrode for sensitive, selective and rapid electrochemical determination of chloride ion based on three-dimensional graphene

Anodic stripping voltammetric measurement of trace cadmium at tin-coated carbon paste electrode

In this proposed work, direct green 6 (DG6) decorated carbon paste electrode (CPE) was fabricated for the efficient simultaneous and individual sensing of catechol (CA) and hydroquinone (HY). Electrochemical deeds of the CA and HY were carried out by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) at poly-DG6-modfied carbon paste electrode (Po-DG6-MCPE). Using scanning electron microscopy (SEM) studied the surface property of unmodified CPE (UCPE) and Po-DG6-MCPE. The decorated sensor displayed admirable electrocatalytic performance with fine stability, reproducibility, selectivity, low limit of detection (LLOD) for HY (0.11 μM) and CC (0.09 μM) and sensor process was originated to be adsorption-controlled phenomena. The Po-DG6-MCPE sensor exhibits well separated two peaks for HY and CA in CV and DPV analysis with potential difference of 0.098 V. Subsequently, the sensor was practically applied for the analysis in tap water and it consistent in-between for CA 93.25–100.16% and for HY 97.25–99.87% respectively.