Silver/silver-chloride electrode fabrication in closed micro-fluidic capillaries

摘要

This paper presents a method to deposit and structure silver/silver-chloride (Ag/AgCl) electrodes inside closed micro-fluidic capillaries. Stable and pure silver layers showing a high specific conductivity (55 × 10~6Ω~(-1)m~(-1)) were deposited into rectangular micro-machined capillaries 3 μm × 3 μm in cross section and commercial glass capillaries 500 μm in radius by means of an electro-less silver plating (ELSP) solution, i.e., an improved Tollens' reagent. In order to achieve a sufficient layer thickness, multiple ELSP depositions were performed. The structuring of the electrodes was achieved by constraining the access of the ELSP solution inside the capillary with micro-fluidic stop-valves. Finally the silver layer was partially transformed into silver-chloride by an oxidation with ferric chloride. These Ag/AgCl electrodes were used as reference electrode in a pH-meter and its sensitivity was measured to 57.4 mV pH~(-1).