Design and Fabrication of Ag / AgCl Composite Reference Electrode Based on Microfluidic Chip

Abstract

Polydimethylsiloxane (PDMS) has been widely used in chip fabrication. However, PDMS itself is a non-conducting polymer, and the adhesion between metal and PDMS is also really weak. Hence, integrating microelectrodes on PDMS microchips has become a technical bottleneck in many applications such as miniaturized electrochemical (EC) sensing systems. A new method was presented to integrate Ag/AgCl electrode on microfluidic chips by using a new conductive composite. It was made of the mixture of PDMS and silver powders, so good electrical conductivity was achieved. Two chloridizing methods were selected to fabricate Ag/AgCl reference electrode. In the electrolysis method, Ag-PDMS composite electrode (as anode) was electrolyzed for 24 hours in saturated KCl solution. In the second one, silver chloride powder was uniformly mixed with silver powders and PDMS pre-polymer, and then cured 1 hour at 90 oC. These composite materials could be efficiently shaped as different electrode structures. Its potential response was measured in different chloride solutions, and its stability was also measured in water (10 days) and 3 mol/L KCl solution (14 days), respectively. Electrochemical characteristics of the electrode were also analyzed in potentiometric and amperometric measurements. SEM pictures showed that the surface of the electrode was fluffy and of rough morphology, which might increase its contacting area with solution, so as to improve the measuring adequacy and accuracy. The electrodes had a fast and stable potential response toward Cl− concentration change.The much tiny potential fluctuation indicated that the composite electrode was stable, which could be served as a good reference for EC measurements. Its CV curves showed its performance was almost as good as a standard reference electrode. Based on its excellent properties, the composite material can be widely applied in microfluidic field. The new method has many advantages such as simple operation, low cost and no special environmental requirements.