Colorimetric adenosine assay based on the self-assembly of aptamer-functionalized gold nanorods

A colorimetric method is presented for ultrasensitive determination of adenosine. The assay is based on side-by-side self-assembly of aptamer-functionalized gold nanorods (Au NRs). It relies on the fact that the conjugation of the helper DNA predominantly occurs at the terminal ends of the Au NRs rather than at their sides. The adenosine aptamers consist of two pieces of ssDNA (termed C1 and C2) that were individually attached to the sides of Au NRs. In the presence of adenosine, it will be captured by C1 and C2 to form a stable sandwich structure. As a result, a side-to-side assembly of the Au NRs occurs. If the adenosine concentration is increased, the absorbance of the Au NRs at 742 nm gradually decreases, and the color changes from brick red to dark brown. Response is linear range in the 10 pM to 5 nM adenosine concentration range, and the detection limit is as low as 3.3 pM. Adenosine analogues such as uridine and cytidine do not interfere. The method was used to quantify adenosine in serum samples at concentrations as low as 10 pM.