Assays can be used to detect mutations found in neoplasms of the pancreas, as well as for other neoplasms and other uses. Nucleic acids can be captured from body fluids such as cyst fluids. Thousands of oligonucleotides can be synthesized in parallel, amplified and ligated together. The ligated products can be further amplified. The amplified, ligated products are used to capture complementary DNA sequences, which can be analyzed, for example by massively parallel sequencing.