This document provides methods and materials involved in collecting and processing complex macromolecular mixtures (e.g., stool samples). For example, stool collection devices, buffers for stabilizing nucleic acid and polypeptides present in stool, and kits for using sequence-specific capture probes (e.g., nucleic acid sequences designed to hybridize with particular target nucleic acids) to capture target nucleic acids directly from complex macromolecular mixtures (e.g., stool samples) without the need to perform prior steps to enrich, isolate, or purify the nucleic acid component are provided.