Silicon-on-insulator microfluidic device with monolithic sensor integration for μTAS applications

A novel concept for the integration of liquid phase charge sensors into microfluidic devices based on silicon-on-insulator (SOI) technology is reported. Utilizing standard silicon processing we fabricated basic microfluidic cross geometries comprising of 5 - 10-mm-long and 55-μm-wide channels of 3 μm depth by wet sacrificial etching of the buried oxide of an SOI substrate. To demonstrate the feasibility of fluid manipulation along the channel we performed electroosmotic pumping of a dye-labeled buffer solution. At selected positions along the channel we patterned the 205-nm thin top silicon layer into freely suspended, 10-μm wide bars bridging the channel. We demonstrate how these monolithically integrated bars work as thin-film resistors that sensitively probe changes of the surface potential via the field effect. In this way, a combination of electrokinetic manipulation and separation of charged analytes together with an on-chip electronic detection can provide a new basis for the label-free analysis of, e.g., biomolecular species as envisaged in the concept of micrototal analysis systems (μmTAS) or Lab-on-Chip (LOC).