Many discoveries in nanoscale science and engineering have been driven in large part by tools which now enable the characterization of fluids inside the nanoscale structure. We must now revolutionize nanofluidic system as a tool for environment, energy and bio-applications, and with this develop a deeper understanding of the underlying fundamental nanoscale science and electrokinetics. The objective is to use the micro/nano hybrid device as a model system for characterizing nonlinear electrokinetics and related phenomena including ion concentration polarization (ICP), and to develop novel engineering devices for seawater desalination, fuel cell and bio-sensing applications. The micro/nanofluidic system developed is ideally suited to track concentration, flow, and electric field simultaneously, in situ,