Sample preconcentration is an important step that increases the accuracy of subsequent detection, especially for samples with extremely low concentrations. Due to the overlap of electrical double layers in a nanofluidic channel, the concentration polarization effect can be generated by applying an electric field. A nonlinear electrokinetic flow is induced, which results in the fast accumulation of proteins in front of the induced ionic depletion zone, the so-called exclusion- enrichment effect. In this way, a protein sample can be driven by electroosmotic flow and accumulated at a specific location. In the present study, a nanofluidic preconcentrator fabricated with the help of junction gap electric breakdown was integrated with microelectrodes for immunoassay. The preconcentration chip for proteins was fabricated using simple standard soft lithography with a polydimethylsiloxane replica. Human galectin-1 proteins from the cell lysate of T24 cells were concentrated and immunoassayed in the proposed microchip. The capability of the proposed microchip for concentrating multiple proteins from cell lysates and immunoassays after preconcentration was demonstrated. Immunosensing was evaluated by measurements of both fluorescence intensities and impedance, which proved the enhancement of preconcentration for immunoassay.
Wu, Hsuan Franziska, Tamara G. Amstislavskaya, Pin-Hsuan Chen, Ting-Feng Wu, Yu-Hung Chen, Chun-Ping Jen