Visual DNA test

A new method could make it easier to test for the DNA base changes known as single-nucleotide polymorphisms, or SNPs, in a point-of-care setting without the instrumentation that is currently required. Dmitry M. Kolpashchikov of Columbia University reports that a previously identified DNA aptamer with peroxidase-like activity can provide a visual readout for SNPs (J. Am. Chem. Soc., DOI: 10.1021/ja711192e). He splits the aptamer in two pieces and attaches analyte-binding arms to both halves. The aptamer acquires its peroxidase activity only when it binds its target DNA sequence, which brings the two aptamer halves back together and allows the re-formed enzyme to catalyze the oxidation of a colorless substrate to a colored product. To demonstrate the method, Kolpashchikov used a DNA fragment that encodes a protein known as MAPT, which has been shown to be associated with the risk of Alzheimer's disease. The solution turned brown in the presence of the perfectly matched DNA sequence but not with a mismatched sequence.