Aptamers are single-stranded nucleic acids or peptides that can bind target molecules with high affinity and specificity. The conformation of an aptamer usually changes upon binding to its target analyte, and this property has been used in a wide variety of sensing applications, including detections based on fluorescence, electrochemistry, mass, or color change. Because native nucleic acids do not possess signaling moieties required for most detection methods, aptamer sensors usually involve labeling of external signaling groups. Among the many kinds of labels, inorganic nanoparticles are emerging as highly attractive candidates because some of their unique properties. Here, we describe protocols for the preparation of aptamer-linked gold nanoparticles (AuNPs) that undergo fast disassembly into red dispersed nanoparticles upon binding of target analytes. This method has been proven to be generally applicable for colorimetric sensing of a broad range of analytes. The sample protocols have also been successfully applied to quantum dots and magnetic nanoparticles. Finally, to increase the user friendliness of the method, the sensors have been converted into simple dipstick tests using lateral flow devices.