Tollens Reaction-Based Integration of Thin Film Wall Electrodes into Microfluidic PDMS Devices

The integration of electrodes into microfluidic devices is a prerequisite for several key technologies such as electrophoresis, dielectrophoresis, electrowetting, or analysis and manipulation of biological cells in organ-on-a-chip applications. However, conventional sputtering or metal deposition methods result in electrodes on the top or the bottom of the microfluidic device leading to either an inhomogeneous electrical field or considerable restrictions regarding optical analysis methods. Here, a novel method for integrating electrodes into microfluidic devices based on the deposition of silver films on the sidewalls of microfluidic channels by Tollens reaction is presented. Aldehydes diffuse readily through polydimethylsiloxane walls and reduce noble metal ions such as silver, which in turn precipitate and deposit on the phase border as homogeneous thin layers. The process results in sidewall electrodes that adopt the channel's geometry and offer a highly homogeneous electrical field in the case of a rectangular channel. The electrodes were analyzed by dissipative X-ray (EDX) and electrical impedance spectroscopy, while the electrical field was visualized by particle image velocimetry. The method can fabricate electrodes in different shapes rendering the process highly promising for a wide range of different electrochemical applications in the field of microfluidics, while simultaneously enable optical analysis methods.

Automated summary

By depositing silver films on the sidewalls of microfluidic channels, a highly homogeneous electrical field can be achieved in the case of a rectangular channel, overcoming the limitations of conventional electrode integration methods while enabling optical analysis methods.