Microfabrication and characterization of three dimensional electrode systems for electrochemical detection

Abstract

Interdigitated array (IDA) electrodes have been researched extensively because they are one of the most effective structures for detecting electroactive species. Redox recycling of the species enables the signal to be amplified on repeated anode and cathode of IDA electrode. The key to the sensitivity of IDA electrode is narrow gap between anode and cathode. Moreover, IDA electrode applicable to flow systems is in the spotlight due to the high sensitivity. The change of the structure from planar to 3D watches for two advantages. One is that the electrode at each side forms space which becomes a channel for sample flow. The other is that the gap can be controlled up to nanoscale not by patterning but by thickness of sacrificial layer between electrodes. Two approaches were proposed for the advantages; the first electrode was designated as channel integrated electrode and the last as air bridge type electrode. Channel integrated electrode was made by high nickel electroplating. There is a channel between electrodes which has fingers. The fingers act as obstacles to generate turbulent flow, which results in amplified signal. The lengths of the fingers are 10, 20, 30, and 40um. Electrochemical techniques for characterizations were cyclic voltammetry and chronoamperometry. The chronoamperometric curve proved higher sensitivity of longer finger channel. The slopes of current with respect to concentration curve at chronoamperometry were $1.06×10^{-3}$ and $5.43×10^{-4}$ in 40㎛ and 10 ㎛ finger, respectively. During the experiment the flow rate was 0.5ml/h which was optimized value from 0 to 10ml/h. The mixing effect was established by the experiment as well as computer simulation by CFD. Air bridge type electrode was completed by the following procedures; gold patterning for lower electrode, copper electroplating, gold deposition for upper electrode, PR patterning for gold support, and copper etching for gap formation. The thickness of copper electroplating is that o...