An array includes a support including a plurality of discrete wells, a gel material positioned in each of the plurality of discrete wells, and a quality control tracer grafted to the gel material in each of the plurality of discrete wells. The quality control tracer comprises (a) a cleavable nucleotide sequence comprising a cleavage site and (b) a detectable label; and in some aspects, is a cleavable nucleotide sequence with a detectable label and a non-reactive nucleotide sequence or a primer nucleotide sequence.