Label-free nanofluidic preconcentration with multi-operational modes by loop currents monitoring for biological application

A novel method, "loop currents monitoring", was proposed for interpreting the onset of preconcentration mechanism and the behaviors of a preconcentrated plug of a nanofluidic preconcentrator without fluorescent labeling. Three operational modes of preconcentrated plugs during the preconcentration process were explained by loop currents of the chip and flow profiles including electroosmotic flow (EOF) and nanochannel-induced backflow (EOF of the second kind). It is demonstrated that our nanofluidic preconcentrator has the capability to precisely control and rapidly preconcentrate label-free proteins.