- 4:39 PM

Isotachophoresis in Nanochannels

Fabio Baldessari, Julien Sellier, Tarun Khurana, and Juan G. Santiago. Mechanical Engineering, Stanford University, Building 530, Room 224, Stanford, CA 94305-3030

Nanofabrication technology enables the application of electrokinetics as a method of performing chemical analyses in electronically-controlled fluidic chips without moving parts. Two important, demonstrated advantages of nanoscale (in which at least one dimension is a fraction of a micron) separations are that small ions can be separated based on valence, and that DNA molecules can be separated without separation matrices (e.g., gels or entagled polymers). One major challenge is to improve analyte detection limits in nanochannels as signals are typically weak due to small detection volumes. For this reason preconcentration techniques offer high sensitivity and may be required for some targeted microfluidic portable detection devices.

Isotachophoresis (ITP) is one method of achieving as much as million fold stacking on-chip in less than two minutes [1]. We will describe our on-going efforts to carry out ITP experiments in 40-1560 nm deep channels etched in fused quartz. In our experiments electroosmotic flow (EOF) is present, and no EOF suppression is adopted. Typical concentrations of the leading and trailing electrolytes are respectively 750 mM and 5 mM, and the initial concentration of the sample less than 1 mM (often several orders of magnitude less). Under these experimental conditions the electric double layer thickness can be as large as a 5-10 nm. ITP in nanochannels is therefore in a particular regime where channel depth is much smaller than ITP peak width, electric double layers are order of the channel (and may overlap), and fluid flow and concentration fields are strongly non-uniform and unsteady.

Reference: [1] Jung B, Bharadwaj R, Santiago JG, Analytical Chemistry, 2006, 78, 2319-2327