A boron-doped diamond interdigital sensor with an alternating excitation strategy for integrated conductivity and free chlorine measurement

Abstract

Real-time free chlorine measurement through wearable-integrated sensors is critical for swimmer safety. However, existing sensors face reliability challenges for wearable integration due to excessive bulk, insufficient stability, and accuracy degradation from unaddressed conductivity interference in complex aqueous environments. This paper proposes a miniaturized sensor with an alternating excitation strategy based on boron-doped diamond (BDD) interdigitated electrodes, enabling high-precision in situ free chlorine measurement. The sensor was batch-fabricated via micro-electro-mechanical system (MEMS) technology, achieving a compact form factor (8 × 8 mm). By implementing an alternating excitation strategy, the sensor alternately applies electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA) to achieve simultaneous detection of conductivity (σ) and free chlorine response current (I). These dual-input parameters feed a multiple linear regression (MLR) model that dynamically corrects conductivity-induced measurement errors. The experimental results showed that the sensor exhibited a good linear response to the conductivity in the range of 0–2 mS cm⁻¹ and to free chlorine in the range of 0–1 mg L⁻¹. The constructed dual-input model achieves a goodness-of-fit of R² = 0.99, with residuals controlled within ±0.05 mg L⁻¹, effectively improving free chlorine measurement accuracy. Therefore, this sensor demonstrates the potential for accurate measurement of free chlorine in complex dynamic environments, providing critical technical support for integrating external risk-sensing functionality into wearable devices.