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