The present disclosure describes methods, devices, reagents, and kits for the detection of one or more target molecules that may be present in a test sample. The described methods, devices, kits, and reagents facilitate the detection and quantification of a non-nucleic acid target (e.g., a protein target) in a test sample by detecting and quantifying a nucleic acid (i.e., an aptamer). The methods described create a nucleic acid surrogate for a non-nucleic acid target, thus allowing the wide variety of nucleic acid technologies, including amplification, to be applied to a broader range of desired targets, especially protein targets. The disclosure further describes aptamer constructs that facilitate the use of aptamers in a variety of analytical detection applications.