High-performance electrochemical sensors: The impact of hydrodynamic flow and vibration on redox amplification

Interdigitated electrodes (IDEs) enhance analyte diffusion through overlapping concentration profiles, locally renewing analyte and improving signal response. As the IDE gap decreases, redox amplification (RA)—efficiency of the analyte cycling between electrodes—improves exponentially. However, fabricating sub-micron gaps is costly and complex, limiting point-of-care applicability. To address this, we demonstrated that forced convection, i.e., hydrodynamic flow and mechanical vibration, significantly enhances mass transport and signal response in gold IDEs with 10, 5, and 2 μm gaps. Using methylene blue (MB) and potassium ferricyanide/ferrocyanide as redox probes, we examined flow direction (parallel and cross) and mechanical vibration effects. Under hydrodynamic flow, RA values decreased because convection disrupted lateral diffusion; however, the signal response increased due to enhanced analyte replenishment by mass transport. For MB, RA in cross-flow was direction-dependent: one direction reduced analyte depletion, yielding an 11.9% higher RA. No significant directional effect was observed for the ferricyanide/ferrocyanide couple. Redox cycling under mechanical vibration across a 10 μm gap IDE increased the signal by 8-fold for MB and 4-fold for the ferricyanide/ferrocyanide couple compared to redox cycling under stagnant conditions. The maximum signal enhancement ratio (SER) obtained for MB (19.1) represents the highest vibration-induced value reported to date. To validate biosensing applicability, dopamine detection with redox cycling under mechanical vibration conditions achieved a detection limit (LOD) of 0.52 μM, nearly sixfold lower than in single-mode under stagnant conditions. These results show that large-gap IDEs without surface modification, combined with external convection, can achieve high RA performance and low LOD with minimal liquid volume (<20 μL). This strategy provides a cost-effective and scalable approach in electrochemical sensors for medical diagnostics and water analysis. • Mechanical vibration boosts IDE redox amplification, achieving a record 19.1-fold gain. • Flow direction affects RA for MB but has a minimal impact on ferricyanide systems. • RA reduction follows a linear trend with the cube root of the hydrodynamic flow rate. • Wider-gap IDEs remain sensitive; RA rises with vibrator input potential. • Dopamine sensing validated via redox cycling under vibration.