A microfluidic sensor chip with renewable in-situ copper modified microelectrode for continuous monitoring of nitrate

Miniaturized on-chip electrochemical sensors fabricated by MEMS techniques have been demonstrated to have sufficient sensitivity for environmental sample analysis. However, due to the surface cumulative passivation effects, the decreasing sensitivity towards analytical targets has restricted the low-cost and long term applications of these devices. In this paper, a microfluidic electrochemical sensor with a renewable copper modified micro working-electrode for nitrate measurements is demonstrated. A microchannel and a micro three-electrode-system chip were fabricated to implement sensitive, reproducible and continuous nitrate measurements under an optimal potential protocol. Based on this microfluidic chip, the continuous renewal of the microelectrode surface allowed each measurement to be performed at a fresh and active copper surface, which guaranteed that sensitive and reproducible nitrate determination was achieved for a long period of time. The response of the microsensor towards nitrate was linear over the range from 40 to 3500 μmolL^-1 with a detection limit of 10 μmolL^-1 (S/N=3). The difference of 30 times measurements was determined as 4.8% at the best conditions, which shows good repeatability of the microsensor.