(606d) Field Effect Transistor Flow Control and Separation of Proteins in Nanofluidic Device

We have fabricated Si multiple internal reflection infrared waveguides embedded with a parallel array of nanofluidic channels (100 nm W ×500 nm D). This device enable us monitor the flow of proteins visibly using laser-scanning confocal fluorescence microscopy (LS-CFM), and serves in-situ analytical tool to probe using multiple internal reflection Fourier transform infrared spectroscopy (MIR-FTIRS). Fluidic field effect transistor (FET) method is used for protein control. A DC potential is applied to highly doped-gate area in mid-section of the channels under longitudinal electric field along the nanochannels. The gate potential controls the surface charge on SiO₂ channel walls and therefore the ξ-potential. Depending the polarity and magnitude, the gate potential can accelerate, decelerate, or reverse the flow of proteins. In addition, we probed pH variations naturally, or caused by the surface charge modulation and longitudinal electrical field. Our MIR-FTIR analysis demonstrates that Fluorescein dye molecules (pH indicator) are hydrogenated and dehydrogenated in response to the gate bias and subsequent pH shift. This pH shift study enables us to understand FET flow control and abnormal flow characteristics during the FET flow control. For separation of proteins in nanofluidic channels, we conduct isoelectric focusing and separation of proteins, which have different isoelectric point (I_p), by generating longitudinal pH gradient that is induced by controlled water electrolysis. Separation of proteins using their different valance charges and surface charge of nanochannels will be further disscussed