NiO-CNT Nanocomposites for Non-Enzymatic Electrochemical Lactate Sensor

Abstract

Introduction: Non-enzymatic electrochemical sensors are crucial in biomedical applications, especially for the real-time monitoring of lactate concentrations in biological fluids such as saliva. In this work, NiO-coated stacked-cut carbon nanotube (NiO/SCCNT) nanocomposites were fabricated via atomic layer deposition (ALD) to enhance lactate-sensing performance.

Methods: Carbon nanotubes (CNTs) were coated with NiO of varying thicknesses (0, 50, 200, and 700 ALD cycles) to form core–shell nanocomposites. These were then integrated into screen-printed carbon electrodes (SPCEs) for non-enzymatic lactate detection. Electrochemical experiments, i.e., cyclic voltammetry (CV), chronoamperometry, and electrochemical impedance spectroscopy (EIS), were carried out to characterize the sensor properties.

Results: Compared with bare SPCE, the NiO(x)/CNT-modified electrode presented a marked decrease in charge transfer resistance, indicating significantly improved electron transfer. The NiO thickness influenced the electrochemical response, with 200 ALD cycles exhibiting the most favourable characteristics. In the 0–4 mM range, the optimized composite achieved a sensitivity of 138.44 μAmM⁻¹cm⁻² and a limit of detection (LOD) of 0.067 mM (S/N = 3). Excellent sensitivity, selectivity, stability, and reproducibility supported the rapid and accurate detection of lactate in real salivary samples.

Conclusions: NiO-coated CNT nanocomposites demonstrate high potential as non-enzymatic lactate sensors for saliva-based measurements. They deliver strong electrochemical performance, low LOD, and high sensitivity, highlighting their suitability for real-time lactate monitoring in biomedical applications.