Nanometer-scale fluidic channels have drawn tremendous research attention in recent years due to their unique electrokinetic properties and immense potential for developing novel applications. Surface charge induced electric double layer (EDL) has been demonstrated to regulate ion transport in nanochannel, especially at low ionic strength. Beyond a certain threshold concentration of electrolyte, nanofluidic channels have been reported to become ion-perm selective and causes an unusual phenomenon known as ion concentration polarization (ICP). The exclusive physical properties of ICP, nonlinear current-voltage (I-V) characteristics being the most significant one, have been extensively studied in nanoslots. However, there is a distinct lack of studies on characterization of ICP in nanochan...[ Read more ]

Nanometer-scale fluidic channels have drawn tremendous research attention in recent years due to their unique electrokinetic properties and immense potential for developing novel applications. Surface charge induced electric double layer (EDL) has been demonstrated to regulate ion transport in nanochannel, especially at low ionic strength. Beyond a certain threshold concentration of electrolyte, nanofluidic channels have been reported to become ion-perm selective and causes an unusual phenomenon known as ion concentration polarization (ICP). The exclusive physical properties of ICP, nonlinear current-voltage (I-V) characteristics being the most significant one, have been extensively studied in nanoslots. However, there is a distinct lack of studies on characterization of ICP in nanochannels imposing higher degree of confinement, such as nanocapillaries and nanopores, also known as one dimensional (1-D) channels.

This thesis presents an elaborate study of ion concentration polarization in self-enclosed cylindrical glass nanocapillaries, with a nominal diameter of 70 nm, realized through a unique process involving low resolution photolithography and standard fabrication techniques. First, numerical simulation has been conducted to evaluate the effect of surface conduction in ICP and the results indicate that a high surface charge density in the channel walls can obscure limiting current region from the I-V characteristics. Later, a microfluidic platform was designed and fabricated with varying physical parameters, such as inter-capillary separation and capillary array size. The results obtained from a single capillary device showed linear I-V characteristics for lower ionic strengths (≤10 mM), which may indicate the masking of limiting current due to strong surface conduction. The results also showed the inter-capillary separation to modulate the onset-voltage of limiting current regime in the I-V characteristics. Additionally, results obtained from high concentration KCl (≥100 mM) revealed ICP to appear without the presence of perm-selectivity in the nanochannel. Finally, a highly efficient microfluidic sample preconcentration device utilizing electrokinetic trapping mechanism enabled by the permselective glass nanocapillaries is presented in this report, which has achieved concentration factor as high as 10⁶ in less than 50 minutes.