A modular microfluidic approach to nano high-performance liquid chromatography with electrochemical detection

Abstract

The field of microfluidics faces many challenges that must be overcome before wide-spread use of microfluidic devices can be achieved. Chief among these challenges are the need for reliable, user-friendly packaging and robust, reconfigurable, and reusable microfluidic systems. A modular microfluidic design approach to microfluidic systems is developed and a prototype modular nano high-performance liquid chromatography (nHPLC) system with electrochemical detection is demonstrated. The modular microfluidic system requires high operating pressure, low dead volume interconnects, and assembly into a simple, reliable package. The modular approach differs from the classic monolithic approach to microfluidic systems by offering increased system flexibility, reduced individual device fabrication complexity, and increased independence of component fabrication technologies at the cost of an additional microfluidic interconnect component. Microgaskets and MEMS O-rings based on a new, commercial, photodefinable silicone are developed and characterized to provide the necessary low dead volume interconnects. The microgaskets and MEMS O-rings are shown to work well at typical operating pressures and did not leak under operating pressures up to 250 psi. The modular nHPLC system is used to separate a nitrate/nitrite sample with efficiencies favorably comparable to commercial macro HPLC systems and other nano HPLC systems reported in the literature. Finally, new electrochemical working electrode materials are presented for use in electrochemical detectors. One material is a thin-film carbon based on pyrolyzed Parylene-C that can conformally coat high-aspect-ratio structures to achieve better than a ten-fold increase in effective electrode area relative to geometric surface area. The second material is a carbon nanotube (CNT) nanoarray that uses a Parylene-C stabilization and insulation matrix. The CNT nanoarray shows a bifurcated sensitivity profile that indicates possible application to trace analyte detection. The combination of trace analyte detection and high-efficiency analyte separation in modular microfluidic systems places applications, such as near real-time, single cell small molecule secretion monitoring, within reach.