A microfluidic flow cell subassembly, which may be assembled into a flow cell having fluidic connections outside of the main substrate, is described for encapsulating a sample to allow for subsequent controlled delivery of reagents to the sample, such as multiplexed in situ biomarker staining and analysis. Methods for fabricating the subassembly and assembled flow cell are also provided. The method includes the steps of adhering a gasket layer to a substrate layer, wherein the gasket layer may contain enclosed features and adhering an adherent layer to the gasket layer. The subassembly may be sealed against a solid support to form a flow cell.