Improving plasma bonding of PDMS to gold-patterned glass for electrochemical microfluidic applications

Abstract

Plasma-treated poly(dimethylsiloxane) (PDMS) bonds irreversibly to Si-containing substrates. In electrochemical microfluidic cells, commonly used gold electrodes are inert to this bonding method, causing leaks in the PDMS$|$Au interface. In this work, the effect of the electrode connector width on the leak was studied. Leak pressure tests show that higher leak pressures can be obtained using narrower electrode connectors. A 4 $\mathrm{\mu }$m connector width presents a leak pressure of 238±22 kPa, comparable to the typical failure pressures reported for PDMS$|$glass devices without electrodes. Finite element modeling suggests that the deformation of the PDMS under the pressure in the channel is the mechanism responsible for the sharp increase in leak resistance observed at narrow gold structures. To ensure that narrow connectors are suitable for faradaic electrochemical measurements, a model analyte was evaluated in cells with different electrode connector width. Voltammograms show that even when using the 4 $\mathrm{\mu }$m structure, ohmic drop is negligible. We propose the use of narrow electrode connectors to reliably use the simple and widespread plasma bonding method while minimizing the solution leaking.