Electrokinetic Transport, Trapping, and Sensing in Integrated Micro- and Nanofluidic Devices

Thesis (Ph.D.) - Indiana University, Chemistry, 2009Microfluidics is rapidly becoming a mature field, and improved fabrication methods now routinely produce sub-micrometer features. As device dimensions shrink, physical phenomena that are negligible at larger length scales become more important, and by integrating nanofluidic elements with microchannels, new analytical techniques can be developed based on the unique behavior of matter at the nanoscale. This work addresses the fabrication, operation, and application of in-plane nanochannels and out-of-plane nanopores in lab-on-a-chip devices. In planar nanofluidic devices, we demonstrate a method to produce micro- and nanoscale features simultaneously with a single UV exposure step and evaluate flow control and sample dispensing with nanofluidic cross structures. Modification of the pinched injection method makes it applicable to variable-volume, attoliter-scale injections, including the smallest volume electrokinetically-controlled injections to date. As an alternative approach, track-etch nanopore membranes are explored as out-of-plane nanofluidic components. The random distribution of pores in these membranes is overcome by lithographic and microchannel-based methods to isolate and address specific pores. Microfluidic isolation improves mass transport to the pore(s), provides easy coupling of electrical potentials, and facilitates additional sample processing steps up- and downstream. These integrated microchannel-nanopore devices are used for diffusion-based dispensing, electrokinetic trapping, and resistive pulse sensing. In a high pore density device, diffusion-based dispensing establishes a stable chemical gradient for bacterial chemotaxis assays. For lower pore density devices, the nanopores are the most resistive components in the fluidic circuit, and application of an electric potential produces localized regions of high electric field strength and field gradient. These high field regions are applied to electrokinetic trapping of particles and cells in multiple-pore devices and to single particle detection by resistive pulse sensing in devices with a single isolated pore. To better understand factors influencing ion current in single nanoscale conduits, we systematically examine ion current rectification as a function of pore diameter, ionic strength, and pH to improve understanding of ion current through nanopores and to characterize preferred operating parameters for sensing applications. These results are applied to detection of virus capsids, and future work is proposed to investigate capsid assembly