A new type of micro amperometric sensing chip based on gold interdigitated microband array (IDA) electrode for trace nitrate determination was developed in this paper. The IDA as working electrode was fabricated with micro-electro-mechanical systems (MEMS) technology. Three-dimensional (3D) nano-structured dendritic silver was electrochemically deposited on the IDA electrode surface, which showed superior electrocatalytic reduction of nitrate than silver nanoparticle modified IDA and regular silver wire electrode. The experiment results demonstrated that the proposed chip showed high sensitivity (9.5 nA/(μmol/L), within a concentration range of 25～1000 μmol/L (R²＝0.9998) and low detection limit (10 μmol/L) using square-wave voltammetry method. Interference analysis with 8 kinds of ions ( NO₂^-, F^-, PO₄^3- , SO₄^2- , CO₃^2- , NH₄⁺ , Na⁺and K⁺) commonly found in surface water indicated that the microchips in this paper had good selectivity to NO₃^- . It was noteworthy that the 3D nano-structured dendritic silver as sensing film modified on IDA electrode could electrochemically reduce nitrate at a pH range of 5.0～9.0 which is important for further study of field and real-time monitoring nitrate ions in natural water.

Key words: three-dimensional (3D) nano-structured silver, interdigitated microband array (IDA) electrode, natural water environment, nitrate determination