The motivation for the work lies in the well-known weaknesses of enzyme-based glucose sensors, which dominate the commercial market but degrade when exposed to fluctuations in pH, temperature, or humidity. Enzymes are fragile biological molecules, and their activity drifts over time, complicating long-term monitoring. Nonenzymatic sensors replace the enzyme with an inorganic catalyst, trading some biochemical specificity for dramatically improved stability and shelf life. Among inorganic catalysts, nickel-based materials have long been favored because they are cheap, abundant, and highly active toward glucose oxidation in alkaline media, but their performance depends critically on how much catalytic surface area can be packed onto an electrode.

The Iranian team, led by Mohadeseh Haghkhah and Rahim Mohammad-Rezaei, addressed that surface-area problem with a two-step electrochemical strategy. First, they electrodeposited a nickel-copper alloy onto a flat graphitic electrode that had been coated with a composite of acid-treated carbon nanofibers and sulfur-nitrogen co-doped graphene quantum dots. The deposition was performed at minus 0.9 volts for 120 seconds in a solution containing nickel chloride, copper chloride, and boric acid. Then came the crucial dealloying step: applying a positive potential of 0.2 volts for 180 seconds selectively dissolves copper from the alloy while nickel, which rapidly forms a protective passive oxide layer, stays behind.

The choice of dealloying potential proved decisive. At 0.1 volts, substantial copper remained on the surface, confirmed by residual copper redox peaks in cyclic voltammetry. At 0.5 volts, the process became too aggressive and significant nickel leached away alongside the copper. Energy-dispersive X-ray spectroscopy and amperometric current-time traces both pointed to 0.2 volts as the sweet spot, where copper removal was nearly complete while nickel loss was minimized. Scanning electron microscopy revealed the dramatic morphological consequence: the spherical NiCu nanoparticles collapsed into needle-like nickel structures with vastly increased electroactive surface area, a transformation that simply did not occur when the dealloying step was skipped.

The underlying scaffold is just as important as the nanoneedles themselves. Carbon nanofibers, roughly 60 to 100 nanometers in diameter, were activated with a sulfuric and nitric acid treatment that replaced surface-bound oxides with hydroxyl groups, boosting hydrophilicity. The graphene quantum dots, synthesized hydrothermally from citric acid and thiourea, were confirmed by infrared spectroscopy and fluorescence measurements, showing characteristic blue emission at 443 nanometers. Raman spectroscopy tracked the whole transformation: copper oxide vibrational bands visible in the alloyed electrode vanished almost entirely after dealloying, while bands associated with nickel oxyhydroxide and hydroxide phases emerged, providing direct spectroscopic evidence that the copper had been stripped and the nickel converted to its active form.

Electrochemical impedance spectroscopy quantified the synergy between the components. The charge-transfer resistance of the full composite shrank progressively as carbon nanofibers and then quantum dots were added, and dropped again after copper removal. Cyclic voltammetry showed quasi-reversible nickel(II)/nickel(III) redox peaks at approximately 0.29 and 0.5 volts, and the electroactive surface area, calculated by charge integration, told a striking story: 0.146 square centimeters for nanoneedles on bare graphite, 2.49 square centimeters with carbon nanofibers, and 6.00 square centimeters with the full carbon nanofiber-quantum dot composite. In other words, the nanostructured scaffold multiplied the effective catalytic area more than fortyfold relative to the plain electrode.

Glucose oxidation on the finished electrode follows a well-understood electrochemical-chemical mechanism. In the anodic scan, surface nickel hydroxide is electrochemically oxidized to nickel oxyhydroxide, the true catalytic species. Glucose then reduces nickel oxyhydroxide back to nickel hydroxide while being converted to gluconolactone, and the regenerated nickel hydroxide is oxidized again, sustaining a continuous catalytic cycle that amplifies the anodic current. Scan-rate studies confirmed that peak currents scaled linearly with scan rate, consistent with this surface-confined redox cycle. Crucially, the un-dealloyed NiCu electrode showed essentially no sensitivity to glucose, demonstrating that residual copper participates in parasitic side reactions and disrupts the nickel redox kinetics that the sensing mechanism depends on.

The analytical figures of merit are impressive. Operating at 0.40 volts in 0.1 molar potassium hydroxide, the optimized sensor achieved a sensitivity of 2105.95 microamperes per millimolar per square centimeter, a linear range spanning 0.012 to 12 millimolar, and a detection limit of 3.13 micromolar, with a response time of about five seconds. That sensitivity represents a 240 percent improvement over electrodes lacking either the quantum dots or the dealloying treatment, and it compares favorably with recently reported nickel-based nonenzymatic sensors built on MoS2, MXenes, and layered double hydroxides. Selectivity tests showed that physiologically relevant concentrations of ascorbic acid, dopamine, citric acid, uric acid, and sodium chloride produced negligible signal changes, with interference fluctuations staying below five percent.

Reliability testing reinforced the platform’s practical credentials. Three independently fabricated electrodes gave responses with a relative standard deviation of just 3.5 percent, and repeated measurements on a single electrode yielded 4.15 percent. The amperometric signal remained stable for more than 1500 seconds of continuous operation, and the electrode retained its performance over four weeks of storage with only 3.19 percent variation. In real-world validation, the team deproteinized human serum with acetonitrile, added just 15 microliters of the treated serum to the micro-drop cell, and measured a glucose concentration of 4.90 millimolar using the standard addition method, with spike recoveries between 97.22 and 102.82 percent. Commercial glucometers read the same samples at 5.01 millimolar, a statistically indistinguishable result.

The micro-drop platform itself may prove as consequential as the nanomaterials. Built from air-dry modeling clay, epoxy resin, and flat graphitic electrodes arranged radially around a well of at most 800 microliters, it is inexpensive, reusable, and ideally suited to clinical samples where volume is scarce. Unlike disposable screen-printed electrodes, the flat platform can be regenerated and monitored over the long term. The authors suggest the combination of low cost, straightforward fabrication, micro-volume capability, and serum-level accuracy positions the sensor for point-of-care diagnostics and sample-limited biomedical assays, offering a glimpse of how rational nanoscale engineering, in this case the simple act of etching copper out of an alloy, can translate into clinically meaningful analytical performance.

Subject of Research: Nonenzymatic electrochemical glucose sensing using alloying-dealloying activated NiOOH nanoneedles on carbon nanofiber-graphene quantum dot composites

Article Title: Electrochemical alloying-dealloying driven activation of NiOOH nanoneedles on carbon nanofiber-graphene quantum dot composites for nonenzymatic glucose sensing on a micro-drop flat platform

Article References: Electrochemical alloying-dealloying driven activation of NiOOH nanoneedles on carbon nanofiber-graphene quantum dot composites for nonenzymatic glucose sensing on a micro-drop flat platform. (n.d.). https://doi.org/10.1016/j.rechem.2026.103905

Image Credits: AI Generated

DOI: 10.1016/j.rechem.2026.103905

Keywords: glucose sensor, nonenzymatic sensing, NiOOH nanoneedles, dealloying, carbon nanofibers, graphene quantum dots, electrodeposition, micro-drop electrode, electrocatalysis, human serum, point-of-care diagnostics, electrochemical biosensor

The rationale behind the design rests on the complementary strengths of its two nanomaterials. Polyaniline is prized among conducting polymers for its mechanical robustness, low cost, electrical conductivity and chemically active conjugated backbone of alternating diamine and diimine units. However, its conductivity drops markedly at neutral pH, precisely the condition under which environmental water samples are typically analysed. Quantum dots, by contrast, offer quantum confinement effects, abundant edge sites and favourable electronic properties. By marrying the two, the researchers aimed to create a synergistic nanocomposite in which the quantum dots act as electron mediators, reducing charge transfer resistance and compensating for polyaniline’s weakness at neutral pH.

Fabrication began with the aqueous synthesis of the quantum dots themselves. Gadolinium chloride was combined with 3-mercaptopropionic acid in an alkaline solution, where the deprotonated thiol groups coordinated to the rare-earth metal, a transition signalled by the solution turning from clear to white. Separate sodium borohydride reductions of tellurium and selenium powders generated the chalcogenide precursors, which were injected sequentially into the gadolinium solution, the more reactive tellurium first. After refluxing at 100 degrees Celsius for an hour under anaerobic conditions, the reaction was quenched in an ice bath and the product washed and centrifuged. The result was a water-soluble, thiol-capped quantum dot suitable for biological interfacing.

The polyaniline layer was grown directly on a glassy carbon electrode by electropolymerising aniline in hydrochloric acid over thirty cyclic voltammetry cycles, producing the thin green deposit characteristic of the emeraldine salt form. This form matters: of polyaniline’s three redox states, only the emeraldine salt is both electrically conductive and stable in air and moisture, unlike the fully oxidised pernigraniline or the fully reduced leucoemeraldine. The nanocomposite was then co-deposited from a solution containing aniline, the quantum dots and acid, with the carboxylic acid termini of the capping ligand activated by EDC and NHS chemistry to form stable amide bonds with the amine groups of the polymer.

Spectroscopic characterisation confirmed the chemistry. Fourier transform infrared spectra of the nanocomposite showed a new band at 881 wavenumbers assigned to the gadolinium-sulfur stretching vibration, alongside shifts at 2977 and 1639 wavenumbers consistent with conversion of the carboxylic acid group into an amide linkage. Raman spectroscopy of the modified electrode revealed the characteristic D and G bands of graphitic carbon, with a decreasing defect-to-graphitic ratio indicating that the polymer coating dominated over disordered carbon sites. X-ray diffraction confirmed a cubic crystal structure for the quantum dots with crystallite sizes between 10 and 32 nanometres, averaging 17 nanometres.

Imaging and scattering analyses added further detail. Scanning electron microscopy showed quantum dot nanocrystals bound along the polymer nanofibres in a well-defined distribution, and energy-dispersive X-ray spectroscopy detected carbon, oxygen, sulfur, nitrogen, tellurium and selenium, with gadolinium present only in trace amounts, a limitation the authors attribute to the detection threshold of the EDS system. Small-angle X-ray scattering revealed that the quantum dots adopt core-shell shapes while the composite takes on a dumbbell geometry, and that introducing the dots onto polyaniline actually reduced particle size, improving dispersion and preventing the agglomeration that could otherwise impair conductivity and sensing performance.

The sensing element itself is a thiolated aptamer, a short single-stranded DNA sequence that folds into a defined three-dimensional structure upon binding its target. The team compared thiolated and non-thiolated versions of the CoV-RBD-4C aptamer and found the thiolated variant superior, reaching optimal electrocatalytic performance after just seven minutes of incubation in the presence of 10 nanomolar spike glycoprotein, compared with eleven minutes for the non-thiolated version. The rapid response reflects the strong covalent attachment achieved through thiol-ene chemistry between the aptamer’s thiol group and alkene functionalities on the nanocomposite surface, which produces a well-oriented monolayer with improved accessibility and stability. Bovine serum albumin was then applied to block any remaining non-specific binding sites.

When the finished sensor was exposed to increasing concentrations of spike glycoprotein, the anodic current decreased in proportion to concentration, an inverse relationship the authors explain through the aptamer’s conformational switch. Upon binding the spike protein, the aptamer folds into its three-dimensional recognition structure, and the resulting electrostatic repulsion hinders electron transfer through the film. Using square wave voltammetry across a concentration range of 0 to 0.95 femtomolar in phosphate-buffered saline, the team obtained a linear response between 0.45 and 0.80 femtomolar, with a limit of detection of 0.04 femtomolar and a limit of quantification of 0.4 femtomolar, alongside a sensitivity of 7.55 times ten to the minus four microamperes per femtomolar.

The critical test came with real environmental samples. Effluents from two South African wastewater treatment plants, Darville and Goudkoppies, were spiked with spike glycoprotein at three concentrations spanning 0.40 to 0.80 femtomolar. The sensor achieved recoveries of 98.6 to 101.4 percent with relative standard deviations below 1.4 percent in the Darville samples, and 91.5 to 103.1 percent with deviations up to 2.5 percent at Goudkoppies, performance figures that demonstrate the device can function in the chemically complex matrix of treated wastewater rather than only in idealised buffer solutions.

The implications extend beyond the current pandemic. Wastewater-based epidemiology has relied largely on reverse transcription polymerase chain reaction, the gold standard, but that approach requires laboratory infrastructure that many low-income and rural regions lack. Because the aptasensor is portable, inexpensive and amenable to miniaturisation, the authors suggest it could serve as an alternative environmental or clinical diagnostic tool during future disease outbreaks, and potentially be adapted to other biomarkers. They note that further work should optimise the number of electropolymerisation cycles to probe stability, and test the sensor against structurally similar proteins to fully establish its selectivity and durability in the field.

Subject of Research: An electrochemical aptasensor combining polyaniline and gadolinium telluride selenide quantum dots for ultrasensitive detection of SARS-CoV-2 spike glycoprotein in wastewater

Article Title: Polyaniline metal dichalcogenide-based amplified aptasensor for SARS-CoV-2 spike glycoprotein detection in wastewater

Article References: Gazu, N. T., Fuku, X., Cabunda, Z. N., Mamba, B. B., & Feleni, U. (2026). Polyaniline metal dichalcogenide-based amplified aptasensor for SARS-CoV-2 spike glycoprotein detection in wastewater. Discover Electrochemistry, 3(1), Article 59. https://doi.org/10.1007/s44373-026-00146-x

Image Credits: AI Generated

DOI: 10.1007/s44373-026-00146-x

Keywords: aptasensor, SARS-CoV-2, spike glycoprotein, wastewater surveillance, polyaniline, quantum dots, electrochemical biosensor, nanocomposite, thiolated aptamer, gadolinium telluride selenide, femtomolar detection, waterborne epidemiology