The central challenge the team addressed is a familiar one in analytical electrochemistry. Thiocyanate and sulfide ions are both difficult to oxidize directly at electrode surfaces, because the heterogeneous electron transfer between the electrode and these anions is intrinsically slow and often accompanied by fouling of the surface by oxidation products such as elemental sulfur. Direct anodic oxidation of sulfide, for example, has long been known to deposit sulfur films on electrodes, degrading their performance over time. Mediated electrocatalysis offers an elegant workaround: instead of forcing the analyte to surrender electrons directly to the solid electrode, a dissolved redox-active mediator is first oxidized at the electrode and then chemically oxidizes the analyte in solution, regenerating the reduced form of the mediator and completing a catalytic cycle. In electrochemical notation this is the classic EC′ mechanism, where an electrode reaction (E) is followed by a homogeneous chemical reaction (C′) that consumes the electrogenerated species.

Chlorpromazine is exceptionally well suited to this role. The phenothiazine core undergoes a well-defined, reversible one-electron oxidation in aqueous media, converting the parent compound into a stable radical cation that is a potent chemical oxidant. Because the redox couple sits at a potential that is accessible on many electrode materials, the oxidized form can be generated cleanly and reproducibly. The Iranian team chose boron-doped diamond as the working electrode, a material prized in electrochemistry for its extraordinary chemical inertness, wide potential window in water, and resistance to fouling. These properties make BDD an ideal substrate for studying mediated oxidation reactions without the complicating background chemistry that plagues more reactive carbon or metal surfaces. Using cyclic voltammetry, the researchers first characterized the redox behavior of chlorpromazine itself in aqueous buffer, establishing the standard potential and the kinetic parameters that govern the electron transfer at the diamond surface.

The crucial methodological innovation of the study lies in its use of digital simulation software, specifically DigiSim 3, to fit simulated cyclic voltammograms to the experimental curves. Digital simulation works by numerically solving the coupled partial differential equations that describe mass transport, electron transfer, and homogeneous chemical kinetics in the diffusion layer adjacent to the electrode. The researcher proposes a mechanism, assigns plausible values for the diffusion coefficients, heterogeneous electron-transfer rate constants, charge-transfer coefficients, and catalytic rate constants, and the software generates a predicted voltammogram. By iteratively adjusting these parameters until the simulated curve overlays the experimental data, the team could extract quantitative kinetic information that would be nearly impossible to obtain from peak currents and peak potentials alone. The quality of the fit then becomes a stringent test of the proposed mechanism: if the assumed reaction scheme is wrong, no reasonable parameter set will reproduce the observed peak shapes, positions, and scan-rate dependence.

When thiocyanate was added to the solution containing chlorpromazine, the cyclic voltammograms changed in a manner diagnostic of electrocatalysis. The anodic peak current for the oxidation of the mediator increased substantially, while the corresponding cathodic peak on the reverse scan diminished, exactly the signature expected when the electrochemically generated oxidized chlorpromazine is consumed by a fast chemical reaction with thiocyanate in the diffusion layer. The same behavior appeared with sulfide. The team systematically varied the analyte concentration and the potential scan rate, mapping out how the catalytic response evolved across both dimensions. At slow scan rates, the chemical step has more time to consume the oxidized mediator, amplifying the catalytic enhancement; at fast scan rates, the voltammetry increasingly reflects the intrinsic kinetics of the mediator redox couple itself. This scan-rate dependence, combined with concentration dependence, provided the experimental scaffolding on which the digital simulations were built.

The fitted parameters tell a quantitative story. The diffusion coefficient of thiocyanate was determined to be (2.08 ± 0.05) × 10⁻⁵ cm² s⁻¹, while sulfide diffused somewhat faster at (5.08 ± 0.16) × 10⁻⁵ cm² s⁻¹, consistent with the smaller hydrodynamic radius of the hydrated sulfide species. The heterogeneous electron-transfer rate constant for the chlorpromazine couple on boron-doped diamond came out at 0.0066 cm s⁻¹ for both analyte systems, indicating a moderately fast but not diffusion-limited surface reaction. The charge-transfer coefficients, which describe the symmetry of the energy barrier for electron transfer, were 0.605 ± 0.037 for the thiocyanate system and 0.550 ± 0.025 for sulfide, values close to the idealized 0.5 that characterizes a well-behaved outer-sphere electron transfer. Most strikingly, the catalytic rate constants, which quantify how rapidly the oxidized mediator attacks the analyte in solution, reached (4.05 ± 0.42) × 10⁴ M⁻¹ s⁻¹ for thiocyanate and (5.34 ± 1.92) × 10⁴ M⁻¹ s⁻¹ for sulfide, confirming that the homogeneous chemical steps are genuinely fast and efficient.

The satisfactory agreement between simulated and experimental voltammograms across the full range of conditions gives the authors confidence that the EC′ mechanism they propose is the correct description of the chemistry. In other words, the oxidized chlorpromazine radical cation formed at the diamond surface diffuses into the solution, transfers oxygen-equivalent oxidizing power to thiocyanate or sulfide, and is reduced back to its parent form, ready to be re-oxidized at the electrode. This catalytic turnover is what produces the amplified anodic currents that underpin potential analytical applications. The study builds on the group’s earlier work, including a 2017 investigation of chlorpromazine-mediated oxidation of arsenic(III) and iron(II) and a 2024 study that revealed more complex EEC and EC′EC mechanisms when the mediator operates in the presence of the amino acid L-cysteine. Together, these papers sketch a versatile mediator chemistry whose mechanism shifts depending on the identity and reactivity of the target analyte.

Why does this matter beyond the electrochemistry community? Thiocyanate is a clinically and forensically significant biomarker. It is the principal metabolite of cyanide exposure, and elevated salivary thiocyanate levels are associated with tobacco smoking, making it a target for noninvasive screening methods ranging from ion-selective electrodes to colorimetric assays. Sulfide, meanwhile, occupies a dual identity: hydrogen sulfide is a notorious toxic gas and an environmental pollutant in wastewater and food spoilage, yet it is also increasingly recognized as a biologically produced signaling molecule, or gasotransmitter, whose concentration in living cells is actively regulated. Analytical methods for sulfide therefore span environmental monitoring, food safety, and biomedical research, employing everything from nanoporous gold electrodes to fluorescent probes and smartphone-based colorimetry. A robust, mechanistically understood electrocatalytic route to oxidizing both species could feed into the design of simpler, cheaper electrochemical sensors that do not suffer from the fouling problems of direct oxidation.

The study also contributes to a broader renaissance of interest in the electrochemistry of phenothiazines. Recent work has mapped the surprisingly complex three-electron oxidation pathway of chlorpromazine, and other groups have developed nanostructured electrodes, from nickel phosphate to antimony vanadate nanospheres, for detecting the drug itself in biological samples. The Ionics paper inverts that perspective: rather than detecting chlorpromazine, it deploys the drug as an active catalytic agent. The combination of a fouling-resistant diamond electrode, a cheap and commercially available mediator, and the mechanistic rigor of digital simulation offers a template for how mediated electrocatalysis can be characterized quantitatively rather than merely demonstrated. As sensor developers seek mediators whose kinetics are fully understood and whose behavior can be predicted computationally, this fusion of experiment and simulation may prove to be the study’s most lasting contribution, turning a vintage antipsychotic into a precision tool for environmental and analytical chemistry.

Subject of Research: Electrocatalytic oxidation mechanisms of thiocyanate and sulfide mediated by chlorpromazine at boron-doped diamond electrodes, characterized by digital electrochemical simulation

Article Title: A comprehensive experimental and theoretical elucidation of the electrocatalytic oxidation mechanisms of thiocyanate and sulfide mediated by chlorpromazine: supported by digital electrochemical simulations

Article References: Salimi, A., Amini, N., & Naderi, K. (2026). A comprehensive experimental and theoretical elucidation of the electrocatalytic oxidation mechanisms of thiocyanate and sulfide mediated by chlorpromazine: supported by digital electrochemical simulations. Ionics. https://doi.org/10.1007/s11581-026-07571-3

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07571-3

Keywords: chlorpromazine, thiocyanate, sulfide, electrocatalysis, boron-doped diamond electrode, cyclic voltammetry, digital simulation, EC′ mechanism, reaction kinetics, phenothiazine, electrochemical sensing, redox mediator

The synthesis itself is strikingly simple. One gram of guaraná seed material was soaked in 100 milliliters of distilled water for 24 hours, filtered, and stored cold. When 50 milliliters of a dilute silver nitrate solution were mixed with a small aliquot of this extract, the reaction medium changed from colorless to yellowish-brown within minutes, the classic visual signature of colloidal silver forming. Ultraviolet-visible spectroscopy confirmed the transformation, revealing a surface plasmon resonance band at 418 to 420 nanometers, the optical fingerprint of silver nanoparticles. The plasmon intensity grew over the first two hours, indicating ongoing nanoparticle formation, before shifting slightly toward 410 nanometers, a change the authors interpret cautiously as evidence of evolving colloidal populations rather than proof of any specific particle shape.

Why guaraná? The seeds of P. cupana are rich in caffeine, phenolics, and other redox-active metabolites, compounds that previous phytochemical studies have identified in guaraná-derived matrices. The authors are careful to note that the extract was not chromatographically profiled in this study, so these constituents are cited as literature-supported candidate reducing and stabilizing agents rather than directly measured ones. Still, the chemistry is plausible: plant phenolics can reduce silver ions to metallic silver while simultaneously adsorbing onto particle surfaces, providing an organic corona that helps keep the colloid dispersed. After testing different temperatures and pH values, the team settled on pH 9.0 at 30 degrees Celsius as the optimal working condition for subsequent preparations.

Dynamic light scattering painted a nuanced picture of the resulting colloid. The mean hydrodynamic diameter came out at 429.5 plus or minus 14.0 nanometers, with a polydispersity index of 0.229, indicating a moderately polydisperse system rather than a uniform one. The intensity-weighted distribution actually contained two populations: a minor population centered at 21.7 nanometers accounting for roughly 2 percent of the scattered-light intensity, and a dominant population near 452 nanometers making up the remaining 98 percent. Because light scattering is intensity-weighted, larger entities dominate the signal even when they represent a small fraction of the particle count. The authors therefore interpret the large value as the hydrodynamic size of hydrated, associated colloidal entities, metallic domains wrapped in extract-derived organic material, rather than the size of individual silver cores. The zeta potential of minus 10.93 millivolts, modest in magnitude, suggests limited electrostatic repulsion, with steric stabilization from the organic corona likely helping the dispersion persist.

To make the nanoparticles electrochemically useful, the team immobilized the silver phase onto Vulcan XC-72R carbon black using two routes. In the in situ route, the carbon was present during nanoparticle formation; in the ex situ route, pre-formed nanoparticles were combined with carbon afterward. Ultraviolet-visible analysis of the supernatants showed a marked suppression of the plasmon band after contact with the support, consistent with retention of the silver-containing phase on the carbon surface. X-ray diffraction patterns were dominated by the broad carbon reflections at 24.5 and 43.7 degrees two-theta, with a weak additional reflection near 37.9 degrees assigned to a silver-containing phase, supportive but not exhaustive evidence of immobilization. Scanning electron microscopy showed that both materials preserved the particulate morphology of the carbon support, while energy-dispersive X-ray spectroscopy detected carbon, oxygen, and a low but detectable silver signal. Transmission electron microscopy in dark-field mode revealed high-contrast nanodomains distributed across the carbon matrix, tentatively associated with the silver phase.

Textural measurements added an important control dimension. Pristine Vulcan carbon displayed a specific surface area of 150.73 square meters per gram, while the in situ and ex situ composites measured 131.10 and 133.04 square meters per gram respectively, with pore diameters remaining in a narrow 2.03 to 2.18 nanometer range. The key insight is that the two supported materials are texturally almost identical yet electrochemically distinct, which means their different behaviors cannot be explained by gross porosity differences and likely reflect route-dependent interfacial organization, how the silver and organic residues are arranged at the surface.

The electrochemical experiments used the commercial emulsifiable concentrate Decis 25 EC, a Bayer product containing 25 grams per liter of deltamethrin, as the pesticide source. Deltamethrin is a synthetic pyrethroid widely used against insect pests, but its environmental persistence and potential effects on non-target organisms have raised toxicological concern, making detection methods valuable. The researchers deposited their AgNPs@C materials onto polished gold disk electrodes and ran cyclic voltammetry at scan rates from 0.01 to 0.30 volts per second in pH 8.0 phosphate buffer with potassium chloride. In blank electrolyte, the ex situ material showed a better-resolved anodic process around 1.0 volt and a corresponding cathodic process between 0.9 and 0.8 volts, tentatively associated with silver redox chemistry, while the in situ material gave a broader response with a stronger capacitive contribution.

In the presence of the deltamethrin formulation, both materials exhibited two irreversible cathodic processes. For the ex situ composite, the peaks appeared near 0.42 and 0.55 volts versus a normal hydrogen electrode, with currents of approximately minus 3.556 and minus 4.491 milliamperes. The in situ material showed peaks near 0.32 and 0.60 volts, with a substantially stronger first cathodic response of about minus 16.177 milliamperes. Regression analysis of peak current against scan rate and the square root of scan rate showed that the latter relationships were generally more linear, particularly for the second cathodic process, indicating diffusion-influenced transport rather than ideal surface-confined behavior. The authors stress an important interpretive caveat: because a commercial emulsifiable concentrate was used rather than analytical-grade deltamethrin, the voltammograms reflect the behavior of the whole formulation, coformulants included, in the presence of the electrode material. The study is therefore framed as a comparative behavior investigation at a fixed formulation concentration, not as analytical validation of a deltamethrin sensor.

The biological half of the study revealed a different kind of duality. In germination bioassays, gherkin (Cucumis anguria) and coriander (Coriandrum sativum) seeds were exposed to the aqueous guaraná extract and the biosynthesized nanoparticle dispersions at low (0.1 percent) and high (1.0 percent) concentrations, with distilled water and a Tween vehicle as controls. Each treatment comprised three replicates of 25 surface-disinfected seeds maintained for 14 days under a 12-hour dark and light photoperiod, with germination scored daily and root length measured at the end. The parameters tracked included germination percentage, mean germination time, mean germination rate, germination rate index, and mean root length, with statistical analysis by ANOVA followed by the Student–Newman–Keuls test.

The results were clearly concentration- and species-dependent. For gherkin, the low-dose nanoparticle treatment maintained high germination and a higher germination rate index than the extract treatments, while the high-dose nanoparticle treatment caused a marked reduction in final germination. Coriander followed a different pattern: the low-dose extract remained comparable to the controls, whereas both high-dose treatments were clearly inhibitory. Root growth data reinforced the trend, with the strongest negative effects associated with the highest nanoparticle concentration, especially for coriander. Notably, the low nanoparticle dose was in some cases compatible with a more favorable early response than the corresponding extract treatment alone. Because the dispersions were applied as complete systems, the authors interpret these effects as properties of the dispersions as applied rather than attributing them exclusively to an isolated nanoparticulate fraction. The findings align with a broader literature in which silver nanoparticles can either stimulate or impair germination depending on dose, particle properties, and plant species, ranging from biostimulation to phytotoxicity. Taken together, the study positions guaraná-mediated silver nanoparticles as green multifunctional materials, one part sustainable synthesis, one part pesticide-relevant electrochemistry, and one part dose-sensitive biology, while leaving open the question of which interfacial and molecular mechanisms underlie each response.

Subject of Research: Green synthesis of guaraná-mediated silver nanoparticles for electrochemical response to deltamethrin and effects on seed germination

Article Title: Green synthesized silver nanoparticles mediated by Paullinia cupana extract exhibit electrochemical behavior toward a commercial deltamethrin formulation and concentration related effects on seed germination

Article References: da Encarnação, J. R., Flores, S. M., da Silva, E. M., Ribeiro, C. R., de Souza, E. A., Neiva, E. G. C., Perotti, G. F., & Maia, P. J. S. (2026). Green synthesized silver nanoparticles mediated by Paullinia cupana extract exhibit electrochemical behavior toward a commercial deltamethrin formulation and concentration related effects on seed germination. Discover Chemistry, 3(1), Article 483. https://doi.org/10.1007/s44371-026-00946-5

Image Credits: AI Generated

DOI: 10.1007/s44371-026-00946-5

Keywords: silver nanoparticles, green synthesis, Paullinia cupana, guaraná, deltamethrin, electrochemistry, cyclic voltammetry, carbon black, seed germination, phytotoxicity, nanotechnology, pyrethroid

The research team, led by Dipali Potdar of Jaysingpur College and Shivaji University together with colleagues including corresponding authors Shivaji Sadale and Prashant Chikode, electrodeposited nickel thin films onto 304-grade stainless steel substrates from simple sulfate baths. They systematically varied three parameters that any plating shop can control: the applied deposition potential, the pH of the electrolyte, and the concentration of nickel ions in solution. By sweeping nickel sulfate concentrations from 25 to 50 millimolar and adjusting pH from 4 to 8 with ammonium hydroxide, they created a matrix of deposition conditions whose effects could be traced all the way from current signatures to crystal structure.

The central analytical tool was the Scharifker-Hills model, a theoretical framework developed in 1983 that remains the workhorse for interpreting nucleation during electrodeposition. The model distinguishes between two limiting behaviors. In instantaneous nucleation, all active sites on the electrode surface are occupied essentially at once, so the number of nuclei is fixed from the start and each nucleus simply grows. In progressive nucleation, new sites continue to activate throughout the deposition, so the population of nuclei keeps increasing. The shape of the current-time transient, recorded when a fixed potential is applied, carries the fingerprint of whichever mechanism dominates, and comparing normalized experimental curves against the model’s dimensionless predictions reveals the mechanism at work.

Before diving into transients, the team used cyclic voltammetry to establish the electrochemical landscape of their bath. Sweeping the potential from 0.7 volts down to minus 1 volt against a silver-silver chloride reference electrode, they observed a stable current until an onset potential near minus 0.7 volts, followed by a rapid rise and a cathodic peak at minus 0.88 volts, which they attribute to the reduction of nickel ions on the stainless steel surface. A further surge at more negative potentials signaled the onset of the hydrogen evolution reaction, the parasitic process that plagues nickel plating by generating gas bubbles at the electrode. Two crossover points on the reverse scan, at minus 0.78 and minus 0.43 volts, marked the initiation of nucleation and the adsorption of nickel ions on the surface, while an anodic peak at minus 0.2 volts reflected nickel oxidation.

The voltammetry also revealed that the deposition reaction is diffusion-controlled. Recording curves at scan rates of 10, 20, and 30 millivolts per second, the researchers found that the anodic peak current density scaled linearly with the square root of the scan rate, exactly the relationship predicted by the Randles-Sevcik equation for a process limited by how fast nickel ions can travel to the electrode. This diffusion control proved crucial for interpreting everything that followed, because when ions arrive at the surface faster than they can be replenished from the bulk solution, the geometry of the depletion zones around growing nuclei shapes both the current response and the final film morphology.

Chronoamperometry, the recording of current as a function of time at a fixed applied potential, then exposed the three-act drama of nickel electrocrystallization. In the first fraction of a millisecond, a sharp spike and decay of current reflects double-layer charging and ion adsorption. A rapid rise follows as new nuclei form and each one draws a hemispherical diffusion zone around itself, pushing the current to a maximum. Beyond that peak, the current decays in a manner governed by the Cottrell equation, the classic signature of diffusion-limited mass transfer, before settling into a plateau where the supply of nickel ions from the bulk solution constrains everything. This characteristic profile confirmed that nickel deposition on stainless steel follows a three-dimensional nucleation process, with hemispherical clusters growing and eventually coalescing into a continuous film.

The comparison with the Scharifker-Hills model produced the study’s most striking finding: the nucleation mechanism is not fixed but shifts with deposition conditions. At underpotentials, where the driving force is modest, the transients tracked the progressive nucleation curve, because the nucleation rate lagged behind the growth rate and new sites kept activating. At overpotentials, the curves aligned closely with instantaneous nucleation, since the nucleation barrier is overcome quickly and a large population of nuclei forms simultaneously. At the reduction potential itself, a mixed mechanism appeared. Raising the bath pH from 4 to 8 pushed the system toward progressive nucleation, which the authors attribute to pH-dependent changes in hydroxide species and surface energetics that favor the continuous creation of new nucleation sites over time.

Concentration played an equally decisive role. Films grown from the most dilute 25 millimolar bath followed the instantaneous nucleation curve, while the 37 and 50 millimolar baths produced mixed instantaneous and progressive behavior, echoing earlier observations of silver deposition on glassy carbon. The team notes that experimental curves deviated from ideal theory in places, with a slower current decay than predicted, which they attribute to side processes such as hydrogen evolution, adsorption, and charge-transfer resistance. These deviations are a reminder that real plating baths are chemically messy systems, and that the clean limiting cases of nucleation theory blend into one another under practical conditions.

What makes the study compelling is that the electrochemical fingerprints translated directly into physical film quality. X-ray diffraction confirmed the cubic crystal structure of nickel in every film, with a prominent reflection from the (111) planes at 44.5 degrees, and the Williamson-Hall analysis of peak broadening revealed compressive microstrain induced by the stainless steel substrate. Notably, crystallite size, lattice constant, and texture coefficient barely changed across the parameter range, but strain and dislocation density dropped to negligible levels at the highest pH and concentration. Meanwhile, field-emission scanning electron microscopy showed a dramatic morphological transition: films from acidic, dilute baths were rough and cracked, riddled with grain boundaries, while films from alkaline, concentrated baths were smooth, uniform, and compact. The culprit behind the cracking is the hydrogen evolution reaction, whose disruptive bubbles and induced internal stress scar the growing film at low pH but are largely suppressed in alkaline conditions.

The practical implications ripple outward from the plating bath. The authors point out that cracked, fine-grained films with abundant grain boundaries resist dislocation movement and are therefore harder, but the same boundaries promote corrosion, whereas the coarser, compact films grown at higher pH and concentration conduct electricity better and resist corrosion. Because nickel coatings serve industries ranging from metal decoration and electronic components to catalysis and energy storage, the ability to dial in a specific nucleation mechanism and morphology through nothing more exotic than pH, concentration, and potential offers a low-cost route to tailored coatings. The researchers acknowledge support from the Mahatma Jyotiba Phule Research and Training Institute, and their work stands as a reminder that some of the most consequential physics in manufacturing happens in the first milliseconds, when a handful of atoms decides what kind of surface the world will see.

Subject of Research: Nucleation and growth kinetics during the electrodeposition of nickel thin films on stainless steel

Article Title: Studies on nucleation and growth kinetics during electrodeposition of nickel thin films

Article References: Potdar, D., Patil, S., Kulkarni, Y., Pawar, N., Banne, S., Sadale, S., & Chikode, P. (2026). Studies on nucleation and growth kinetics during electrodeposition of nickel thin films. Discover Electrochemistry, 3(1), Article 29. https://doi.org/10.1007/s44373-026-00115-4

Image Credits: AI Generated

DOI: 10.1007/s44373-026-00115-4

Keywords: electrodeposition, nickel thin films, nucleation kinetics, Scharifker-Hills model, chronoamperometry, cyclic voltammetry, stainless steel substrate, hydrogen evolution reaction, X-ray diffraction, FESEM, bath pH, crystal growth

The synthesis relied on the polyol method, a versatile wet-chemical technique in which ethylene glycol serves simultaneously as solvent and reducing agent. The researchers preheated the glycol to 160 degrees Celsius, then introduced silver nitrate together with polyvinylpyrrolidone, a polymer that caps the growing crystals and steers them into long, straight wires. Seed particles formed first, and anisotropic growth followed, yielding silver nanowires with diameters of roughly 60 to 75 nanometres and lengths on the micrometre scale. Zinc acetate solutions of two different concentrations, 0.1 and 0.3 molar, were then added to grow the zinc oxide coating, producing samples labelled Z1 and Z3. For the mixed-oxide variants, zinc acetate and nickel acetate were injected together, giving the ZNM1 and ZNM3 nanocables.

Scanning electron microscopy revealed how dramatically the shell chemistry reshapes the architecture. Pure silver nanowires displayed smooth surfaces and diameters up to about 75 nanometres, while zinc-coated cables thickened to 75–85 nanometres, their surfaces studded with cubic nanoparticles and spherical particles ranging from around 100 nanometres to a micron. Adding nickel pushed the diameters to 85–95 nanometres and produced a striking zoo of morphologies, including irregular hexagonal crystals, quadrangular pyramidal crystals and clustered spheres spanning one to three microns. The team attributes this heterogeneity to nickel’s influence on nucleation dynamics and to synergistic effects between the two oxide-forming metals that alter surface energy minimisation during growth.

Transmission electron microscopy confirmed the coaxial design at higher resolution. The images showed elongated one-dimensional structures with a crystalline metallic silver core and a continuous oxide shell, with uniform contrast along their lengths indicating homogeneous composition. At low precursor concentrations, isotropic shapes such as cubes and triangular bipyramids dominated, whereas higher concentrations favoured elongated rods and wires. Some samples showed partial fragmentation and aggregation attributed to mechanical stress during grid preparation, and the thickest cables reached diameters near 85 nanometres with lengths up to ten micrometres, sometimes bundling together with ultrathin companions attached.

X-ray diffraction established the crystallographic foundations of the composites. Peaks at 38.2 and 44.7 degrees corresponded to the (111) and (200) planes of face-centred cubic silver, with no impurity phases detected. Additional reflections at 31.82 and 34.33 degrees matched the (100) and (002) planes of crystalline zinc oxide. Applying the Debye–Scherrer equation gave average crystallite sizes of about 35 to 36 nanometres, and the analysis showed that crystallite size shrank as the zinc and zinc/nickel salt content increased. Because the silver ion radius of 114 picometres exceeds that of zinc at 74 picometres, substituting silver into the lattice expands the unit cell, and the measured lattice parameters tracked these substitutions. An intense peak at 38.02 degrees signalled anisotropic growth of silver along the (111) direction, with the nickel/zinc shell growing coaxially in the same phase, evidence of atomic-level alloying between the metals.

Optical measurements highlighted the plasmonic fingerprints of the silver core and the electronic tuning imposed by the shells. The bare nanowires showed sharp surface plasmon resonance peaks at 356 and 386 nanometres from the transverse mode, while the zinc-coated cables shifted these features, with a peak at 319 nanometres and a prominent band at 358 nanometres, and a slight redshift appearing as zinc concentration rose. Band gap energies fell steadily with increasing metal doping, from 3.220 electronvolts for Z1 down to 2.8 electronvolts for the most heavily doped mixed-oxide sample, a narrowing that reflects deliberate modification of the electronic structure. Photoluminescence spectroscopy added further nuance: band-edge emission sat at 380 nanometres for Ag@Zn and shifted marginally to 383 nanometres with nickel, while deep-trap emission linked to defect states moved from 522 to 513 nanometres. Crucially, the composite catalysts showed much weaker photoluminescence intensity than the bare wires, indicating that the silver cores suppress electron–hole recombination and lengthen the lifetime of photoexcited charge carriers, a property that directly benefits catalysis.

The catalytic showcase was the reduction of p-nitrophenol to p-aminophenol by sodium borohydride, a benchmark reaction for water treatment because p-nitrophenol is a persistent organic pollutant. In the untreated mixture, the yellow p-nitrophenolate ion absorbs strongly at 400 nanometres; as the reaction proceeds, this peak fades. The uncoated silver nanowires needed 44 minutes to complete the conversion, the zinc-coated cables cut this to 30 and 24 minutes for Z1 and Z3, and the nickel-containing composites performed best of all, finishing in 16 and 12 minutes for ZNM1 and ZNM3. A clear isosbestic point near 314 nanometres appeared in all spectra, a spectroscopic signature of a clean, direct conversion pathway. The team notes that these catalysts compare favourably with previously reported systems for the same transformation, and they emphasise that zinc offers a cheap, abundant and comparatively non-toxic alternative to more hazardous transition-metal catalysts.

Electrochemical testing painted an equally encouraging picture for energy storage. Cyclic voltammetry in potassium hydroxide electrolyte, using a three-electrode configuration with the nanocables deposited on nickel foam, revealed distinct redox peaks characteristic of pseudocapacitive behaviour. Bare silver nanowires produced current responses of roughly 20 microamperes with symmetrical peaks around the zero-current axis, corresponding to reversible silver oxidation and reduction. The zinc oxide coating raised the current density to about 35 microamperes, improving electron transfer kinetics, while the Ag@Zn/Ni composites delivered the highest response at approximately 60 microamperes, with a broad reduction peak near minus 0.8 volts and multiple oxidation peaks extending up to plus 1.4 volts, reflecting overlapping redox processes from silver, zinc oxide and nickel oxide. Electrochemical impedance spectroscopy, spanning frequencies from 10^-2 to 10^5 hertz, reinforced the story: the silver-coated composites showed the lowest equivalent series resistance, the smallest high-frequency semicircles indicating minimal charge transfer resistance, and shallow low-frequency slopes consistent with low Warburg resistance, all hallmarks of fast, efficient electron transport.

Taken together, the results argue that the whole of these nanocables exceeds the sum of their parts. The silver core supplies conductivity, plasmonic light harvesting and charge-separation assistance; the zinc oxide shell contributes wide-band-gap semiconducting behaviour, chemical stability and catalytic sites; and the nickel oxide component adds high redox activity that multiplies the pseudocapacitive response. Because the shell thickness and composition can be tuned simply by adjusting precursor concentrations, the platform offers a tunable route to bimetallic and mixed-oxide nanostructures without exotic equipment or scarce raw materials, and the polyol approach could plausibly be extended to other metal combinations. The authors suggest the nanocables could serve as electrodes for advanced electronic and energy storage devices, with potential reach into medical, environmental and fuel-cell technologies. For a field searching for ways to stretch precious silver further while squeezing more performance out of earth-abundant oxides, these cable-like hybrids offer a compelling blueprint.

Subject of Research: Synthesis and characterization of silver-core zinc/nickel oxide coaxial nanocables for catalytic and electrochemical applications

Article Title: Hybridized Ag@Zn/Ni nanocables: synergistic enhancements in optical, catalytic, and electrochemical behaviour

Article References: Sharif, S., Ahmad, Z., Choudhary, M. A., Irshad, M. A., Nisar, F., Al-Hussain, S. A., Irfan, A., & Zaki, M. E. A. (2026). Hybridized Ag@Zn/Ni nanocables: synergistic enhancements in optical, catalytic, and electrochemical behaviour. Journal of Saudi Chemical Society, 30(2), Article 21. https://doi.org/10.1007/s44442-026-00069-7

Image Credits: AI Generated

DOI: 10.1007/s44442-026-00069-7

Keywords: nanocables, silver nanowires, zinc oxide, nickel oxide, core-shell nanostructures, polyol method, p-nitrophenol reduction, pseudocapacitance, cyclic voltammetry, electrochemical impedance spectroscopy, surface plasmon resonance, photoluminescence

The molecule at the center of the study, 5-[(Z)-1,3-thiazol-2-yldiazenyl]quinolin-8-ol, abbreviated TDQ, belongs to the azo dye family, compounds defined by their signature nitrogen-nitrogen double bond, the azo group, which gives them their intense colors. Azo dyes have historically dominated textiles, leather, paints, and printing, but researchers have increasingly explored them in solar cells, optical systems, and even pharmacology, where azo-bearing heterocycles show antibacterial, antiviral, and antifungal activity. Quinoline, the second structural element of TDQ, brings its own electrochemical pedigree: the redox behavior of quinoline derivatives has attracted sustained research interest, making the pairing of a quinoline scaffold with a thiazole-linked azo bridge a logical candidate for electrode modification.

Synthesis of the dye followed a classic diazotization-coupling route performed under carefully controlled cold conditions. The team dissolved 2-aminothiazole in concentrated hydrochloric acid and rapidly chilled the mixture in an ice-salt bath to roughly 0 to 5 degrees Celsius before adding nitrosylsulfuric acid to generate the diazonium salt. After two hours of stirring at the same low temperature, the diazonium solution was combined with an alkaline solution of 8-hydroxyquinoline, with the pH held between 5 and 6 throughout the coupling step. Thin-layer chromatography tracked the reaction to completion, and the resulting dark red solid was filtered, washed, dried, and recrystallized from ethanol, delivering a 70 percent yield with a melting point of 95 to 96 degrees Celsius.

Structural confirmation relied on a battery of spectroscopic techniques. Infrared spectroscopy revealed the hydroxyl stretch of the quinoline group at 3382 inverse centimeters, aromatic carbon-hydrogen stretches at 2929, carbon-nitrogen and carbon-sulfur vibrations at 1602 and 778, and, critically, the azo linkage at 1454 inverse centimeters. Proton nuclear magnetic resonance in DMSO-d6 showed the expected hydroxyl singlet near 9.0 ppm alongside aromatic signals between 6.82 and 7.37 ppm. Ultraviolet-visible spectra recorded in DMSO, DMF, ethanol, and acetone displayed sharp absorptions at 414, 396, 386, and 409 nanometers respectively, with DMSO giving the strongest response, while mass spectrometry produced a molecular ion peak at m/z 257.3, consistent with the formula C12H8N4OS.

To build the sensor, the researchers ground one milligram of TDQ with graphite powder and silicon oil in a 70:30 ratio for half an hour, then packed the paste into a 3-millimeter electrode cavity. Electrochemical benchmarking against a bare carbon paste electrode used the standard potassium ferrocyanide redox probe in 1 M potassium chloride. The bare electrode showed weak redox peaks and large peak separations, hallmarks of slow electron transfer and a limited active surface. The TDQ-modified version, by contrast, delivered markedly higher peak currents at reduced overpotential, and calculations based on the Randles-Sevcik equation put the electroactive surface area at 0.04526 square centimeters, well above the 0.0267 square centimeters of the unmodified paste.

Impedance spectroscopy reinforced that story. Nyquist plots showed a semicircle at high frequencies whose diameter reflects charge transfer resistance: the bare electrode registered 234.82 ohms, while the TDQ-modified electrode dropped to 177.47 ohms, indicating faster interfacial electron transport and more efficient ion pathways. Bode plots added a capacitive dimension, with the modified electrode displaying more negative phase angles at low frequencies, a sign of stronger charge retention and better energy storage behavior. The authors note that this combination of lower resistance and enhanced capacitance makes the dye-modified surface attractive not only for sensing but potentially for energy storage applications as well.

With the platform validated, the team turned to the three target analytes in 0.2 M phosphate buffer. pH optimization across the range 5.8 to 7.4 showed peak currents rising to a maximum at pH 7.0, the physiological value, which was adopted for all subsequent experiments. Scan rate studies then probed the underlying mechanism: for dopamine, a log-log slope of 1.012 indicated an adsorption-controlled process, while uric acid’s slope of 0.370 pointed to diffusion control, and paracetamol’s slope of 0.474 likewise suggested diffusion-dominated behavior. Concentration studies from 10 to 100 micromolar produced calibration curves with correlation coefficients of 0.9979 for dopamine, 0.9982 for uric acid, and 0.98 for paracetamol.

The detection limits, calculated as three times the standard deviation divided by the calibration slope, came out at 6.86 micromolar for dopamine, 10.28 micromolar for uric acid, and 15.93 micromolar for paracetamol, with corresponding quantification limits of 21.15, 34.29, and 42.58 micromolar. The most striking result, however, came from simultaneous detection. In cyclic voltammetry, the modified electrode resolved three distinct oxidation peaks at 0.265 volts for dopamine, 0.554 volts for uric acid, and 0.875 volts for paracetamol, giving peak-to-peak separations of 0.289 and 0.321 volts. Differential pulse voltammetry sharpened the discrimination further, with separations of 0.227 and 0.362 volts, allowing all three compounds to be identified and quantified in a single run.

Practical durability and real-world performance rounded out the evaluation. Across five identically prepared electrodes, the relative standard deviation was just 0.85 percent, and the sensor retained 94 percent of its original dopamine response after twenty days of laboratory storage. When the team applied the standard addition method to a commercially available dopamine hydrochloride injection diluted into buffer, recoveries of spiked samples ranged from 97 to 102 percent, demonstrating that the sensor can deliver accurate measurements in a genuine pharmaceutical matrix rather than only in idealized solutions.

The broader significance lies in the simplicity and economy of the approach. Carbon paste electrodes are cheap, easy to prepare, and easy to refresh, and a milligram-scale dye modifier transforms their otherwise mediocre electrochemistry into a selective, stable sensing platform. Because dopamine imbalances are linked to Parkinson’s disease, Alzheimer’s disease, schizophrenia, and Huntington’s disease, uric acid levels flag kidney failure, pneumonia, and metabolic disorders, and paracetamol monitoring underpins safe use of one of the world’s most common analgesics, a single low-cost electrode that reads all three simultaneously could find a home in clinical labs, pharmaceutical quality control, and point-of-care diagnostics. The Davangere team’s work adds a quinoline-azo dye to the growing toolbox of molecular modifiers, showing that sometimes the fastest route to better biosensing runs through the chemistry of color.

Subject of Research: Electrochemical detection of dopamine, uric acid, and paracetamol using a quinoline-azo dye modified carbon paste electrode

Article Title: Electrochemical sensing of dopamine, uric acid, and paracetamol using a quinoline-azo dye modified carbon paste electrode

Article References: Paalaplara, K. H., Chinnagiri, K. T., Chinnagiri, R. T., & Thippandegowdru, R. M. (2026). Electrochemical sensing of dopamine, uric acid, and paracetamol using a quinoline-azo dye modified carbon paste electrode. Discover Electrochemistry, 3(1), Article 42. https://doi.org/10.1007/s44373-026-00127-0

Image Credits: AI Generated

DOI: 10.1007/s44373-026-00127-0

Keywords: electrochemical sensor, azo dye, quinoline, carbon paste electrode, dopamine, uric acid, paracetamol, cyclic voltammetry, differential pulse voltammetry, electrocatalysis, detection limit, pharmaceutical analysis

The novelty of the work lies in its discipline. Rather than varying several synthesis parameters at once, the team isolated manganese precursor molarity as a single, independent lever—the variable that controls how supersaturated the solution becomes with Mn2+ ions at the moment of nucleation. Because the resulting powders contain no conductive scaffold or composite additives, the measured electrochemical behavior reflects the intrinsic properties of the β-MnO2 itself. That makes the study a unusually clean probe of a question that has long hovered over pseudocapacitor research: how exactly do structural defects govern whether charge is stored quickly at surfaces or slowly through bulk diffusion?

Electron microscopy revealed that the precursor concentration directly sculpted the material’s architecture. All three samples formed flower-like agglomerates of nanorods, but their mean diameter grew steadily with concentration, from 171 nanometers at 0.05 M to 268 nanometers at 0.20 M. Higher molarity means more Mn2+ supersaturation, faster nucleation and growth, and consequently larger, more developed structures. Morphology, however, turned out to be only half the story. Raman spectroscopy told a subtler tale about what was happening inside the crystal lattice.

The Raman ν2 vibrational mode of the material shifted from 647.1 to 638.5 inverse centimeters as the precursor concentration rose, while the peak broadened from 36.8 to 47.4 inverse centimeters. In the language of vibrational spectroscopy, that combination of shifting and broadening is a fingerprint of increasing oxygen-vacancy-related disorder—missing oxygen atoms in the crystal lattice that disturb the local bonding environment. Oxygen vacancies are not mere imperfections; in manganese dioxide they are known to enhance electronic conductivity and can open additional pathways for cation storage. The Indonesian team had, in effect, tuned the defect density of their electrodes simply by choosing how concentrated the starting solution should be.

To quantify how those defects translated into charge-storage behavior, the researchers turned to cyclic voltammetry and analyzed the current response using the well-established power-law framework, extracting the kinetic exponent known as the b-value at a fixed anodic potential. The b-value is a diagnostic dial: a value of 1.0 indicates ideal capacitive behavior, where current scales linearly with scan rate and charge is stored at surfaces, while 0.5 signals diffusion-controlled processes, where ions must slowly intercalate into the bulk. A b-value of 0.96 for the lowest-concentration sample (Mn-0.05) meant that electrode behaved almost like an ideal capacitor. The intermediate sample (Mn-0.10) dropped to 0.62, deep into diffusion-limited territory, and the highest concentration (Mn-0.20) recovered only partially to 0.74.

That non-monotonic pattern is the study’s most striking result. If morphology alone dictated kinetics, the trend should have been smooth. Instead, the intermediate composition was the most kinetically crippled of the three. The authors’ independent Dunn deconvolution analysis—which separates the current at each potential into surface-capacitive and diffusion-controlled contributions—reproduced the same ordering. At a scan rate of 10 millivolts per second, the capacitive fraction of stored charge was 80 percent for Mn-0.05, only 23 percent for Mn-0.10, and 44 percent for Mn-0.20. Those percentages are consistent with the values of 2b−1 predicted from the power-law exponents, a cross-check that lends confidence to the kinetic picture.

Electrochemical impedance spectroscopy filled in the mechanistic details. Fitting the spectra to an equivalent circuit comprising solution resistance, a charge-transfer resistance in parallel with a double-layer constant phase element, and a low-frequency constant phase element, the team achieved excellent fits with chi-squared values at or below 4.9 × 10−3. The charge-transfer resistance told a dramatic story: it plummeted from 3471 ohms for the intermediate sample and 174 ohms for the lowest concentration down to just 25 ohms for Mn-0.20. Meanwhile, the low-frequency exponent nL approached the Warburg limit of 0.53—the signature of semi-infinite diffusion—only for the highest-concentration material. In other words, the defect-rich, larger-structure Mn-0.20 moved charge across its interface with ease but then throttled it in slow, diffusion-limited storage.

The capacitance rankings added a final layer of nuance. Mn-0.20 delivered the highest specific capacitance, roughly 13 farads per gram, but its impedance was dominated by Warburg diffusion, meaning that capacity comes at the price of sluggish kinetics. Mn-0.05, by contrast, exhibited more ideal capacitive phase behavior, with phase angles near 70 degrees, but at a lower total capacity. Notably, capacitances derived independently from cyclic voltammetry, galvanostatic charge–discharge, and impedance spectroscopy ranked the three samples identically, and the galvanostatic and impedance values agreed to within 1.0 farad per gram—a level of internal consistency that strengthens the reliability of the conclusions.

For the supercapacitor field, the message is that precursor stoichiometry is not a dial for size alone; it is a dial for a coupled morphology–defect–kinetics relationship. Increasing manganese precursor concentration simultaneously enlarges the nanorod agglomerates and enriches the lattice with oxygen-vacancy disorder, and these two effects combine in a non-obvious way to redistribute charge between fast surface reactions and slow bulk diffusion. An electrode designer who wants rapid, high-power response might deliberately choose dilute precursor conditions to favor near-ideal capacitive behavior, while one chasing maximum capacity at moderate rates might accept the Warburg-limited regime of the concentrated recipe.

The work also speaks to a broader movement in electrochemistry toward defect engineering as a design principle. Oxygen vacancies in manganese oxides have been shown in numerous studies to boost conductivity and charge-transfer kinetics, but this study demonstrates that defect density can be controlled through something as mundane as the molarity of the starting salt—no dopants, no post-treatment, no conductive scaffolds required. Because the electrodes here are unsupported powders, the findings provide a baseline understanding of intrinsic material behavior that can later be layered onto composite and scaffold-based architectures. As demand grows for grid buffering, fast-charging electronics, and regenerative energy capture, understanding how a single synthesis variable redistributes the speed and location of charge storage brings the rational design of pseudocapacitive electrodes one concrete step closer.

Subject of Research: Effect of manganese precursor concentration on structural defects and charge-storage kinetics in hydrothermal beta-MnO2 supercapacitor electrodes

Article Title: Correlation between structural defects and charge storage kinetics in manganese oxide-based supercapacitor electrodes: the role of manganese precursor concentration

Article References: Nurfani, E., Mahardhika, L., Khamidy, N. I., Arundina, R. Y., & Marlina, R. (2026). Correlation between structural defects and charge storage kinetics in manganese oxide-based supercapacitor electrodes: the role of manganese precursor concentration. Ionics. https://doi.org/10.1007/s11581-026-07528-6

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07528-6

Keywords: supercapacitors, manganese dioxide, oxygen vacancies, hydrothermal synthesis, pseudocapacitance, charge-storage kinetics, Raman spectroscopy, electrochemical impedance spectroscopy, cyclic voltammetry, Dunn deconvolution, nanorods, defect engineering

The study, published in the journal Discover Electrochemistry, was led by Sandeep Kurundawade and Sharanappa T. Nandibewoor of KLE Technological University in Hubballi, together with colleagues at Atria Institute of Technology in Bengaluru and J.S.S. Banashankari Arts, Commerce and S.K. Gubbi Science College in Dharwad. Their choice of modifier was polyaniline, one of the oldest and best understood conducting polymers. Polyaniline is prized in materials science for its unique p-type doping chemistry, its reversible redox transitions between the leucoemeraldine, emeraldine and pernigraniline states, and its protonic conductivity, all of which allow it to alter the electronic behavior of an electrode surface. Compared with its polymeric cousins polypyrrole and polythiophene, polyaniline also offers superior environmental resilience, an essential property for a sensor intended for repeated laboratory use.

Synthesis of the polymer followed a classical route: oxidative polymerization of aniline in 1.5 molar hydrochloric acid, initiated by the gradual, drop-wise addition of ammonium persulphate while the reaction mixture was stirred. The slow addition is not decorative; it prevents over-oxidation and promotes uniform chain growth. The reaction mixture’s shift to the characteristic dark green color of polyaniline’s emeraldine salt signaled success. The researchers then characterized the product with scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction. Electron microscopy revealed a cohesive network of uniformly packed spherical agglomerates, while the diffraction pattern showed a broad peak near 2θ equal to 25 degrees, a signature of the polymer’s π-π stacked aromatic framework and its mildly crystalline, emeraldine-phase structure.

The heart of the sensor is a glassy carbon electrode, a workhorse of electroanalytical chemistry with a geometric area of just 0.09 square centimeters. A 1 milligram sample of polyaniline was dispersed in dimethylformamide by sonication and drop-cast onto the polished electrode, with the deposited volume optimized at 4 microliters after testing across a 2 to 8 microliter range. To measure how much the coating enlarged the electrochemically active surface, the team employed a ferricyanide redox probe and the Randles-Sevcik equation. The bare electrode’s active area was 0.04 square centimeters; with polyaniline it grew to 0.156 square centimeters, a 4.4-fold increase that translates into a far denser network of electroactive sites and correspondingly faster charge transfer.

Impedance measurements reinforced that picture. Nyquist plots, fitted to a Randles equivalent circuit, yielded charge transfer resistance values of 17.03 ohms for the bare electrode and 11.57 ohms for the modified one, while the calculated heterogeneous charge transfer rate constants rose from 1.56 × 10⁻⁵ to 2.3 × 10⁻⁵ centimeters per second and exchange currents climbed from 1.508 × 10⁻³ to 2.219 × 10⁻³ amperes. In plain terms, the polymer film does not merely add surface area; it actively lubricates the movement of electrons between the drug molecules in solution and the electrode beneath. An immersion-time study further showed that the analytical signal peaked after 40 seconds of accumulation, beyond which the response declined, likely because the available surface had saturated or an inhibitory molecular layer had formed.

With the hardware characterized, the team turned to the electrochemistry of oxybutynin itself. Cyclic voltammetry in phosphate buffer at pH 7.4, scanned between 0.5 and 1.5 volts, produced a single anodic peak with no counterpart on the reverse scan, marking the oxidation as irreversible. On the modified electrode the peak current reached 76.7 microamperes against 42.6 microamperes on bare glassy carbon, and the peak potential shifted slightly downward from 1.191 to 1.185 volts, evidence that polyaniline lowers the overpotential and eases the oxidation. Varying the pH from 3.0 to 9.2 revealed a maximum response at 7.4, close to physiological pH, and a peak potential that tracked pH with a slope of 64 millivolts per pH unit, near the Nernstian ideal of 59, indicating equal numbers of electrons and protons in the reaction.

Scan rate studies completed the mechanistic portrait. The peak current scaled linearly with the square root of the scan rate, and a log-log analysis produced a slope of 0.3285, close to the theoretical value of 0.5 for diffusion control. Applying the Laviron equation to the relationship between peak potential and scan rate gave a transfer-coefficient-electron product of 1.14, which resolved to approximately two electrons when the standard transfer coefficient of 0.5 was assumed. Combined with the pH result, the oxidation of oxybutynin at the modified electrode is therefore a diffusion-controlled, irreversible process involving two electrons and two protons, proceeding through successive electron-transfer and deprotonation steps toward an oxidized imine-type intermediate and ultimately an amine-based product.

The analytical performance is where the sensor earns its headline. Using square-wave voltammetry, a technique prized for its ability to reject background currents, the team recorded a linear response across 0.04 to 10 micromolar oxybutynin, with a detection limit of 9.16 nanomolar and a limit of quantification of 30.5 nanomolar, calculated by the standard equations based on the regression intercept’s standard deviation. That sensitivity compares favorably with previously reported oxybutynin sensors, which the authors note have tended to be either expensive, laborious to construct, or both. Selectivity testing with 100-fold excesses of citric acid, gum acacia, D-glucose, dopamine, L-ascorbic acid, sucrose, and common inorganic salts produced peak potential shifts all below the 2 percent tolerance limit, confirming the sensor’s robustness in messy real-world matrices.

The practical demonstrations may prove the most consequential part of the work. Pulverized commercial 5 milligram tablets, dissolved and diluted into the linear range, yielded recoveries in excellent agreement with the label claim, opening the door to routine pharmaceutical quality control. Human urine diluted 100-fold and spiked with known drug concentrations, along with tap water, Krishna River water from Belagavi in Karnataka, and RO-purified water, were all analyzed with acceptable recoveries, extending the sensor’s reach into pharmacokinetic monitoring and environmental surveillance of pharmaceutical contamination. Stability testing showed consistent within-day signals and retention of a high percentage of the initial response after 15 days of storage in a sealed container. Taken together, the results suggest that a coating of a cheap, easily synthesized conducting polymer can transform a routine glassy carbon electrode into a precision instrument, one well suited to clinical laboratories, quality control departments, and environmental monitoring programs that have historically been priced out of high-sensitivity drug analysis.

Subject of Research: Ultrasensitive electrochemical detection of the drug oxybutynin hydrochloride using a polyaniline-modified glassy carbon electrode sensor

Article Title: Ultrasensitive electrochemical detection of oxybutynin hydrochloride using polyaniline modified sensor

Article References: Kurundawade, S., Megalamani, M. B., Naik, K., Yaraguppi, D. A., & Nandibewoor, S. T. (2026). Ultrasensitive electrochemical detection of oxybutynin hydrochloride using polyaniline modified sensor. Discover Electrochemistry, 3(1), Article 73. https://doi.org/10.1007/s44373-026-00161-y

Image Credits: AI Generated

DOI: 10.1007/s44373-026-00161-y

Keywords: oxybutynin hydrochloride, polyaniline, electrochemical sensor, glassy carbon electrode, square-wave voltammetry, cyclic voltammetry, overactive bladder, pharmaceutical analysis, detection limit, conducting polymer, electrocatalysis, pharmacokinetics

Click chemistry has been a cornerstone of modern bioconjugation since the early 2000s, prized for reactions that run cleanly, at high yield, and with minimal side products under mild aqueous conditions. The workhorse of the family is the copper(I)-catalyzed azide-alkyne cycloaddition, or CuAAC, in which an azide group and a terminal alkyne snap together into a stable triazole ring. For biosensor makers, this offers a gentle way to tether receptors, fluorophores, or nanomaterials to a surface without damaging delicate biological molecules. The catch has always been the catalyst: copper(I) is unstable in oxygenated water, so traditional protocols add chemical reducing agents such as ascorbate to generate it in bulk, which gives little control over where or when the reaction happens.

The E-click approach solves that problem elegantly. Instead of dosing the solution with a reductant, the researchers used the electrode itself to electrochemically convert copper(II) into copper(I) right at the surface, on demand. Because the catalytic species is born only where the electrode is switched on, functionalization can be turned on and off with a potentiostat, confined to selected electrodes in an array, and tuned by adjusting the applied potential. This stands in contrast to conventional modification techniques such as physisorption, entrapment, molecular imprinting, or self-assembled monolayers, which can suffer from variable reaction efficiencies, limited site control, and sensitivity to pH, ionic strength, and temperature. It also offers an alternative to other electrochemical patterning tools such as light-activated electrochemistry and scanning electrochemical microscopy.

To test the concept, the team built a model biosensor surface step by step on gold substrates. First, they cleaned the gold electrochemically in sulfuric acid and immersed it in 11-mercaptoundecanoic acid, or MUA, which self-assembles into an ordered monolayer tipped with carboxylic acid groups. Next, standard EDC/NHS coupling chemistry was used to attach propargyl-PEG2-amine, presenting terminal alkyne groups at the surface. Finally, the stage was set for the click reaction: a fluorescent azide-tagged dye, FAM azide 6-isomer, served as a stand-in for a biological receptor, so that successful coupling could be read out directly from the surface’s emission spectrum. The copper(I) catalyst was generated in situ by applying a negative potential to the gold electrode in a solution of copper sulfate and sodium chloride.

Verifying that every step had worked required a battery of complementary techniques. X-ray photoelectron spectroscopy traced the chemical evolution of the surface, revealing carbon, nitrogen, and oxygen peaks consistent with the MUA monolayer, the EDC/NHS-coupled propargyl layer, and the final FAM attachment, along with copper oxide residues from the catalytic step. Crucially, sulfur 2p signals remained intact after the full procedure, showing that the underlying self-assembled monolayer had survived the electrochemical treatment without desorbing. Cyclic voltammetry in a ferrocyanide solution tracked the blocking of electron transfer as the monolayer formed, while electrochemical impedance spectroscopy, fitted to a Randles circuit, quantified the changing charge-transfer resistance at each step. Contact angle measurements rounded out the picture, shifting with the growing polarity and then hydrophobicity of the modified surface.

With the chemistry validated, the researchers turned to optimization, and the results carry practical lessons for anyone building sensors this way. Varying the reaction duration at a fixed potential of minus 0.35 volts showed that fluorescence, and therefore the amount of bound dye, rose linearly for the first ten minutes before saturating, indicating a rapid reaction and a surface approaching full coverage by roughly thirty minutes. The team settled on ten minutes as the sweet spot balancing signal, reproducibility, and handling time. Controls incubated without any applied potential showed only weak nonspecific adsorption, confirming that the coupling truly depends on electrochemically generated catalyst.

The applied potential proved to be the trickiest variable. Cyclic voltammetry of the copper electrolyte on the modified surface showed that the organic layers slow electron transfer, pushing the copper(II) to copper(I) reduction to more negative potentials and obscuring the peaks that would normally signal a viable condition. Potentials milder than about minus 0.25 volts failed to generate enough catalyst, while pushing beyond roughly minus 0.325 volts triggered unwanted copper deposition onto the surface, visible as nucleation loops and stripping peaks in the voltammograms. The usable window is narrow, and the authors identify minus 0.35 volts as a practical compromise that generates catalyst efficiently while minimizing surface damage. The fluorescence data confirmed that even potentials showing no obvious voltammetric signature could still drive the reaction, underscoring how subtle the choice of operating conditions can be on complex functionalized surfaces.

The most eye-catching demonstration, however, moves the catalyst off the sample altogether. In a proof of concept, the researchers used a conductive atomic force microscopy cantilever as the working electrode, scanning it over a propargyl-functionalized gold surface while holding it at minus 0.35 volts relative to the substrate. The copper(I) generated near the cantilever catalyzed click reactions along the scanned region, and subsequent fluorescence spectroscopy confirmed the characteristic FAM emission on the surface. In the current setup, functionalization was not confined to the scanned area alone, because the platinum-iridium coating covers the entire front face of the cantilever and generates catalyst over a broad zone. The authors note that cantilevers insulated everywhere except at the very tip could shrink the reaction zone to the nanoscale, enabling direct-write patterning of recognition molecules.

The implications reach well beyond a fluorescent demo. Electrode arrays for multiplexed diagnostics could have each electrode functionalized with a different receptor simply by addressing them individually, leaving neighbors untouched, a capability previously shown for microelectrodes but now extended to a scanning-probe geometry. Nanoarrays, multi-analyte sensors, and nanoengineered surfaces for fundamental studies of biomolecular recognition all come within reach if the tip-localized version matures. At the same time, the study is candid about its challenges: the narrow potential window for catalyst generation on modified surfaces, the risk of copper deposition at excessive overpotentials, and the difficulty of reading the copper reduction peak through an insulating organic layer. Solving these will matter for translating E-click from the bench to robust device fabrication.

What the Aalborg and Newcastle team has delivered is a careful, quantitative map of how an electrically triggered click reaction behaves on a realistic biosensor surface, complete with the spectroscopic fingerprints, electrochemical signatures, and wetting behavior that document every step. By showing that the same chemistry works whether the catalyst is born at the flat electrode or at the tip of an AFM cantilever, they have sketched a versatile platform for surface engineering in which a potentiostat, rather than a photomask or a chemical bath, dictates exactly where molecules attach. As biosensors push toward denser arrays, smaller samples, and higher sensitivity, the ability to write functional chemistry with spatial and temporal precision, using nothing more than a carefully chosen voltage applied for ten minutes, may prove to be one of those quiet enabling technologies that reshapes how sensing devices are made.

Subject of Research: Electrochemically driven click chemistry for controlled and localized biosensor electrode surface functionalization

Article Title: Electrochemical click chemistry for controlled and localized biosensor surface functionalization

Article References: Pedersen, T., Pike, A., Cucinotta, F., Horrocks, B. R., & Gurevich, L. (2026). Electrochemical click chemistry for controlled and localized biosensor surface functionalization. Discover Electrochemistry, 3(1), Article 74. https://doi.org/10.1007/s44373-026-00160-z

Image Credits: AI Generated

DOI: 10.1007/s44373-026-00160-z

Keywords: electrochemical click chemistry, CuAAC, biosensor functionalization, self-assembled monolayer, copper catalyst, X-ray photoelectron spectroscopy, cyclic voltammetry, electrochemical impedance spectroscopy, AFM cantilever, surface patterning, multiplexed biosensors, gold electrodes

The motivation behind the study rests on a well-known problem in electrochemical energy storage. Supercapacitors are prized for their fast charge–discharge rates, long cycle life and high power delivery, but their performance is ultimately dictated by the electrode material. Transition metal oxides such as copper oxide and nickel oxide are attractive candidates because they are abundant, environmentally benign and rich in accessible oxidation states that support pseudocapacitive, Faradaic charge storage. Copper oxide brings high theoretical capacitance, while nickel oxide contributes strong chemical stability and a highly active Ni2+/Ni3+ redox couple. Yet both materials suffer from the same Achilles heel: modest electrical conductivity and structural degradation during repeated cycling, which erode practical performance over time.

The researchers, led by B. H. Akpeji of the Federal University of Petroleum Resources in Effurun, Delta State, attacked this limitation with a binary composite strategy. Rather than relying on either oxide alone, they combined CuO and NiO into a single heterostructured nanomaterial, betting that the interplay of the two phases would multiply electroactive sites, speed electron transport and buffer each oxide’s structural weaknesses. Their synthesis began with seeds collected in the Ukwani Local Government Area of Delta State and verified at the University of Benin herbarium under voucher number UBH-R673. A Soxhlet extraction with distilled water, run for roughly four hours, yielded a concentrated aqueous extract that was then subjected to systematic phytochemical screening.

That screening revealed a veritable chemical toolkit within the seed. Flavonoids, alkaloids, tannins, phenolic compounds, terpenoids, saponins, glycosides and reducing sugars were all present, each playing a distinct role in the nanomaterial formation that followed. Flavonoids, phenolics and alkaloids donate electrons that reduce Cu2+ and Ni2+ ions toward their oxide forms, while hydroxyl and carbonyl functional groups assist nucleation and stabilization. Tannins and saponins act as passivating agents that prevent the freshly formed nanoparticles from clumping together, a property that proved decisive for the later electrochemical results. In essence, the plant extract replaced the hazardous reducing agents and synthetic surfactants that conventional nanoparticle recipes demand.

Using the extract mixed with copper acetate and nickel acetate solutions in the presence of sodium hydroxide, the team observed characteristic color transitions, copper oxide turning from blue to dark black and nickel oxide to dark green, as the hydroxide intermediates dehydrated into the final oxides. The nanocomposite itself was assembled by combining equimolar CuO and NiO nanofluids and stirring them at 65 degrees Celsius for two hours before centrifugation and drying. A full characterization battery followed: UV–visible spectroscopy showed absorption peaks at 301 nanometers for CuO, 295 nanometers for NiO and 299 nanometers for the composite, with optical band gaps of 2.29, 3.21 and 2.40 electronvolts respectively. The composite’s band gap sits neatly between its parents, a hallmark of genuine electronic interaction and heterojunction formation between the two oxide phases.

Electron microscopy confirmed that the green route produced the fine, well-dispersed particles that high-performance electrodes require. The CuO nanoparticles averaged 21.0 nanometers and the NiO particles 14.9 nanometers, while the composite measured 16.2 nanometers with reduced agglomeration and enhanced dispersion. Powder X-ray diffraction reinforced the picture, resolving the monoclinic structure of CuO and the face-centered cubic phase of NiO and giving the composite a mean crystallite size of 19.18 plus or minus 5.40 nanometers, calculated from six indexed reflections using the Debye–Scherrer equation and verified statistically in SPSS. Energy-dispersive X-ray analysis confirmed the successful incorporation of copper at 47.30 weight percent, nickel at 32.10 percent and oxygen at 20.60 percent in the composite, while Fourier-transform infrared spectroscopy located the distinctive Cu–O and Ni–O lattice vibrations, with a clear band near 535 inverse centimeters signaling hybridization of the two oxide lattices.

The electrochemical payoff came in a three-electrode configuration using a glassy carbon working electrode, a platinum counter electrode and an Ag/AgCl reference in 2 molar potassium hydroxide. Cyclic voltammetry revealed reversible, Faradaic redox behavior for all three materials, but the composite’s integrated curve area was dramatically larger. Quantitatively, the CuO–NiO nanocomposite delivered a specific capacitance of 489.60 farads per gram and an energy density of 0.272 watt-hours per kilogram, against roughly 124 farads per gram and about 0.069 watt-hours per kilogram for each of the single oxides, a near fourfold leap in stored charge. Electrochemical impedance spectroscopy told the same story from another angle: the composite exhibited the lowest charge-transfer resistance of the set at 2.31 ohms, compared with 4.90 ohms for CuO and 2.34 ohms for NiO, alongside the highest double-layer capacitance at 126 microfarads, indicating faster electron-transfer kinetics, more accessible electroactive surface and superior interfacial charge storage.

The authors attribute this synergy to the heterojunction formed where the two oxides meet. Band alignment between the narrow-gap CuO and the wider-gap NiO redistributes charge at the interface, creating new electronic states that ease the movement of electrons, while the dual Cu2+/Cu3+ and Ni2+/Ni3+ redox couples multiply the sites available for reversible Faradaic reactions in the alkaline electrolyte. The phytochemical capping inherited from the seed extract adds further advantages, keeping particle sizes small, shortening ion diffusion pathways and preserving the porous, interconnected morphology that scanning electron microscopy revealed. Compared with previous CuO–NiO composites reported in the literature, some requiring controlled-atmosphere annealing or surfactants to reach similar capacitances, the raffia-mediated route achieved competitive figures with nothing more exotic than water, acetate salts, sodium hydroxide and plant chemistry.

Beyond the numbers, the study carries a broader sustainability argument. Raphia hookeri seeds are inedible and largely discarded, so converting them into functional nanomaterials adds value to agricultural waste without competing with food production, in line with circular-economy thinking and the growing field of biomass valorization. The work was funded by Nigeria’s Tertiary Education Trust Fund and conducted across the Federal University of Petroleum Resources and the University of Benin. The authors are careful to note that thermogravimetric analysis, which showed decomposition temperatures of 379, 394 and 355 degrees Celsius for CuO, NiO and the composite respectively, speaks to thermal behavior rather than long-term cycling stability, and that full-cell devices, rate capability testing and extended cycling remain the next milestones. Still, the demonstration that a humble palm seed can seed, quite literally, a fourfold capacitance improvement offers a compelling template for affordable, greener electrode manufacturing, and suggests that the future of energy storage may be growing in fields as much as it is being engineered in cleanrooms.

The choice of a hydrothermal route deserves particular attention when weighing the practical significance of this work. Hydrothermal processing, in which reactions proceed in a sealed aqueous medium under elevated temperature and pressure, is prized for producing crystalline oxides at relatively low temperatures without the need for post-synthesis calcination at extreme conditions. Coupling that method with a plant-derived extract means the reducing, nucleating and capping functions are all performed by biomolecules rather than synthetic reagents, which simplifies purification and reduces the environmental footprint of the entire workflow.

The electrochemical measurements also illustrate why pseudocapacitive metal oxides behave so differently from carbon-based double-layer electrodes. In a 2 molar potassium hydroxide electrolyte, hydroxide ions participate directly in the reversible redox reactions at the electrode surface, so the measured capacitance reflects genuine Faradaic charge transfer rather than simple electrostatic adsorption. The low solution resistance of 0.29 ohms recorded for the composite electrode indicates that the electrolyte and electrode interface offered minimal ohmic opposition, an important precondition for high-rate operation in practical devices.

The thermal analysis adds a complementary dimension to the characterization. Decomposition temperatures in the range of 355 to 394 degrees Celsius indicate that the organic residues inherited from the plant extract are largely removed or stabilized well below the operating temperatures of supercapacitors, which function near ambient conditions. This suggests the phytochemical capping does not introduce thermal liabilities during normal device use, even though it may influence long-term cycling behavior in ways that only extended testing can reveal.

From a materials-design perspective, the intermediate band gap of the composite relative to its parent oxides is a useful diagnostic. It signals electronic coupling across the heterojunction rather than a mere physical mixture, which is precisely the condition needed for the interfacial charge redistribution that underpins the observed synergy. Future work building on this platform could explore varying the CuO to NiO ratio, tuning annealing conditions, or pairing the composite with biomass-derived carbon substrates to push energy density further while retaining the low-cost, waste-valorizing character that makes the approach distinctive.

Subject of Research: Green synthesis of CuO–NiO nanocomposites from Raphia hookeri seed extract for supercapacitor energy storage

Article Title: Nanocomposite materials of CuO–NiO from Raphia hookeri seed for investigation of energy storage potentials

Article References: Akpeji, B. H., Iyasele, J. U., Elemike, E. E., Okhuarobo, L. O., & Akpeji, S. A. (2026). Nanocomposite materials of CuO–NiO from Raphia hookeri seed for investigation of energy storage potentials. Discover Electrochemistry, 3(1), Article 76. https://doi.org/10.1007/s44373-026-00163-w

Image Credits: AI Generated

DOI: 10.1007/s44373-026-00163-w

Keywords: CuO–NiO nanocomposite, green synthesis, supercapacitor, Raphia hookeri seed, pseudocapacitance, transition metal oxides, phytochemicals, energy storage, electrochemical impedance spectroscopy, cyclic voltammetry, nanoparticles, biomass valorization