Abstract: In some examples, a structure is contacted with polynucleotides having a variety of lengths and each including first and second adapters. The structure includes a substrate including first and second regions spaced apart from one another by a gap of at least 100 nm, a first set of capture primers coupled to the first region of the substrate, and a second set of capture primers coupled to the second region of the substrate. The first adapter of the polynucleotide is hybridized to a capture primer of the first set of capture primers. Based on that polynucleotide being sufficiently long to bridge the gap, it is amplified using the first and second sets of capture primers. Based upon that polynucleotide being insufficiently long to bridge the gap, it is not amplified. Optionally, a wall may be disposed in the gap.

Abstract: In some examples, a method includes disposing a first hydrogel within a first recess of a substrate and over a pillar. The substrate may include a second recess in which the pillar is disposed, and a wall separating the first recess from the second recess. While the first hydrogel is disposed within the first recess, the pillar may be removed. After removing the pillar, a second hydrogel may be disposed within the second recess. Also provided herein are nonlimiting examples of manners in which recesses, walls, and patterned hydrogels may be formed.