Integrated label-free protein detection and separation in real time using confined surface plasmon resonance imaging

We demonstrate a label-free protein detection and separation technology for real-time monitoring of proteins in micro/nanofluidic channels, confined surface plasmon resonance imaging (confined-SPRi). This was achieved by fabricating ultrathin fluidic channels (500 nm high, 500 microm wide) directly on top of a specialized SPRi sensor surface. In this way, SPRi is uniquely used to detect proteins deep into the fluidic channel while maintaining high lateral accuracy of separated products. The channel fluid and proteins were driven electrokinetically under an external electric field. For this to occur, the metallic SPR sensor (46 nm of Au on 2 nm of Cr) was segmented into an array of squares (each 200 microm x 200 microm in size and spaced 8 microm apart) and coated with 30 nm of CYTOP polymer. In this work, we track label-free protein separation in real time through a simple cross-junction fluidic device with an 8-mm separation channel length under 30 V/cm electric field strength.