Registration of a patterned flow cell may utilize fiducials comprising sets or groupings of features (e.g., sites, sample wells, nanowells) having known locations and in which the placement of the features is not in accordance with a periodic pattern or is otherwise distinguishable from the periodic pattern of sites present in non-fiducial regions of the flow cell substrate. In certain embodiments the positioning of the sites that are part of the fiducial represent a break or discontinuity in the periodic pattern of sites that are otherwise present on the surface of a patterned flow cell.

A microfluidic device includes a plurality of reaction wells; and a plurality of solid supports, and each of the solid supports has a reagent attached thereto. The reagent is attached to the solid support via a labile reagent/support bond such that the reagent is configured to be cleaved from the support via a cleaving operation.

A microfluidic device includes a plurality of reaction wells; and a plurality of solid supports, and each of the solid supports has a reagent attached thereto. The reagent is attached to the solid support via a labile reagent/support bond such that the reagent is configured to be cleaved from the support via a cleaving operation.

A microfluidic device includes a plurality of reaction wells; and a plurality of solid supports, and each of the solid supports has a reagent attached thereto. The reagent is attached to the solid support via a labile reagent/support bond such that the reagent is configured to be cleaved from the support via a cleaving operation.

A microfluidic device includes a plurality of reaction wells; and a plurality of solid supports, and each of the solid supports has a reagent attached thereto. The reagent is attached to the solid support via a labile reagent/support bond such that the reagent is configured to be cleaved from the support via a cleaving operation.

A microfluidic device includes a plurality of reaction wells; and a plurality of solid supports, and each of the solid supports has a reagent attached thereto. The reagent is attached to the solid support via a labile reagent/support bond such that the reagent is configured to be cleaved from the support via a cleaving operation.

A microfluidic device includes a plurality of reaction wells; and a plurality of solid supports, and each of the solid supports has a reagent attached thereto. The reagent is attached to the solid support via a labile reagent/support bond such that the reagent is configured to be cleaved from the support via a cleaving operation.

Methods are provided for producing a molecular array comprising a plurality of molecules immobilized to a solid substrate at a density which allows individual immobilized molecules to be individually resolved, wherein each individual molecule in the array is spatially addressable and the identity of each molecule is known or determined prior to immobilization. The use of spatially addressable low density molecular arrays in single molecule detection and analysis techniques is also provided. Novel assays and methods are also provided.