Methods, assays, and products for the detection of small molecules are provided. In one aspect, for example, a method of detecting a small molecule in a sample can include reacting together a first half of a DNA split aptamer having a first reactive group coupled thereto, a second half of a DNA split aptamer having a second reactive group coupled thereto, where the DNA split aptamer is selective for the small molecule, and a sample containing the small molecule. The first half and the second half bind to the small molecule and the first reactive group and the second reactive group react to form an aptamer ligation product of the first half and the second half. The method can also include assaying for the aptamer ligation product in order to detect the small molecule presence in the sample.