Microfluidic sensor integrated with nanochannel liquid conjunct Ag/AgCl reference electrode for trace Pb(II) measurement

Highlights: • An integrated sensor based on "sandwich" structure for Pb²⁺ detection was proposed. • The reference electrode with nanochannel was compatible and showed a good stability. • The working electrode with micropillar array reached 0.13 μg L⁻¹ of detection limit. • The sensor achieved trace Pb²⁺ in different water samples with high recovery rate. Pollution due to heavy metals is becoming increasingly hazardous; therefore, demand for the large-scale deployment of sensor nodes for water quality monitoring has increased. The development of integrated and miniaturised sensors for detecting heavy metals is necessary. Herein, an integrated microfluidic sensor based on a "glass-silicon-glass" sandwich structure is proposed for Pb²⁺ detection. This micro-sensor consists of a nanochannel liquid conjunct Ag/AgCl reference electrode(RE), a working electrode with a three-dimensional Au micropillar array, and a detection chamber for sample measurement. The potential fluctuation of the RE in this sensor was only 0.62% over seven days, remaining relatively stable. Under optimal conditions, the limit of detection and sensitivity for lead were 0.13 μg L⁻¹ (S/N = 3) and 52.30 nA (μg L⁻¹)⁻¹, respectively. The linearity of the sensor for detecting lead was good in the concentration range of 0.50–150 μg L⁻¹ (R² = 0.9989). Moreover, the proposed microsensor showed high selectivity for Pb²⁺ and achieved sensitive detection of trace Pb²⁺ in different water samples. Therefore, this integrated and miniaturised sensor is a practical tool for trace lead detection, allowing the development of large scale sensor network for water monitoring.