Optical resonances produced by photonic crystal surfaces can be designed to substantially amplify the electric field excitation of fluorophores while at the same time increasing the collection efficiency of emitted photons. Because PC surfaces can be produced inexpensively over large areas by replica molding, they offer an effective means for increasing sensitivity for broad classes of surface-based fluorescent assays. In this talk, the design and fabrication of photonic crystal surfaces and detection instrumentation for fluorescent enhancement will be described, along with demonstrated applications in gene expression microarrays and protein biomarker microarrays.