Electrical and electrochemical pH sensing technologies: comparative mechanisms, performance, and applications

Reliable pH measurement remains central to chemical, biological, and environmental monitoring, yet conventional electrochemical glass electrodes face persistent challenges of fragility, slow response, and limited integrability. This study presents a comparative analysis between a conventional glass-electrode pH meter and a custom-fabricated aluminum interdigitated electrode (Al-IDE) for full-range pH sensing (pH 1–13). The Al-IDE device, fabricated via standard photolithography on thermally oxidized silicon, was evaluated under identical conditions using pure buffer systems. Electrical measurements revealed a distinct U-shaped current response, decreasing from 3107 nA at pH 1 to 1.03 nA near pH 7, before rising to 781 nA at pH 13. This behaviour reflects the amphoteric nature of the Al₂O₃ surface, governed by protonation–deprotonation equilibria that modulate interfacial charge transport. The proposed nonlinear quadratic model achieved strong segmental correlations (R² > 0.89) for both acidic and alkaline regimes. Comparative assessment against the glass electrode yielded a mean absolute deviation of ≈ 0.19 pH units, confirming excellent agreement between the two modalities. While the glass electrode followed a linear Nernstian slope (–58.6 mV pH⁻¹), the Al-IDE offered rapid, reference-free, and mechanically robust operation with repeatability (RSD) ranging up to 3.5%. These findings establish the Al-IDE as a low-cost, CMOS-compatible alternative for portable or embedded pH monitoring and provide foundational insights for hybrid electro-electrical sensing architectures that integrate the precision of electrochemical systems with the real-time responsiveness of electrical transduction.