Rapid and inexpensive method for the simple fabrication of PDMS-based electrochemical sensors for detection in microfluidic devices.

The fabrication of PDMS microfluidic structures through soft lithography is widely reported. While this well-established method gives high precision microstructures and has been successfully used for many researchers, it often requires sophisticated instrumentation and expensive materials such as clean room facilities and photoresists. Thus, we present here a simple protocol that allows the rapid molding of simple linear microchannels in PDMS substrates aiming microfluidics-based applications. It might serve as an alternative to researchers that do not have access to sophisticated facilities such as clean rooms. The method developed here consists on the use of pencil graphite leads as template for the molding of PDMS channels. It yields structures that can be used for several applications, such as housing support for electrochemical sensors or channels for flow devices. Here, the microdevices produced through this protocol were employed for the accommodation of carbon black paste, which was utilized for the first time as amperometric sensor in microchip electrophoresis. This platform was successfully used for the separation and detection of model analytes. Ascorbic acid and iodide were separated within 45 s with peak resolution of 1.2 and sensitivities of 198 and 492 pA/μM, respectively. The background noise was ca. 84 pA. The analytical usefulness of the system developed was successfully tested through the quantification of iodide in commercial pharmaceutical formulations. It demonstrates good efficiency of the microfabrication protocol developed and enables its use for the easy and rapid prototyping of PDMS structures over a low fabrication cost.