Metastatic tumors can spread via release of circulating tumor cells (CTCs) into the bloodstream. Early detection of these CTCs could greatly improve cancer survival rates by enabling diagnosis, and therefore treatment, before secondary tumors arise. However, tumor cells are typically present in very low concentrations, making them difficult to detect in a fluid dominated by red blood cells (RBCs), leukocytes and serum proteins. Separation of CTCs from blood plasma, leukocytes and RBCs is predicted to improve cell capture via antibody-based methods and reduce interference in capture/detection assays. Previously, members of our team have demonstrated microfluidic, size-based separation of blood components, but have yet to integrate this sorting capability with an affinity-based detection technology. To this end, we have developed a microfluidic platform to separate CTCs from mouse blood and detect them using grating coupled surface plasmon resonance (GCSPR). We have implemented a size-based sorting array, which separates objects based upon their diameter, within a microfluidic channel. Separation of beads (2 μm, 6 μm, 10 μm) has been demonstrated, as well as separation of white blood cells and CTCs from blood. The resulting stream of large blood cells (including CTCs) is then directed onto an integrated SPR grating for affinity based capture and detection. Using GCSPR vs. conventional SPR enables detection of multiple cell types across the grating in an array-based format. We have demonstrated differential capture and detection of cells on GCSPR gratings following size-based separation of blood. Using capture antibodies specific to unique CTC surface proteins enables identification of cell types and may provide prognostic capability, beyond the diagnostic capacity of this system.