High affinity of AS1411 toward copper; its application in a sensitive aptasensor for copper detection.

AS1411 is a 26-mer G-rich DNA aptamer which has been broadly employed in the field of targeted drug delivery, due to its capability to bind to nucleolin protein on the surface of cancer cells. In this work, it has been shown for the first time that in addition to nucleolin, AS1411 aptamer could bind to copper ions (Cu) with high affinity and selectivity, affecting AS1411 usage in drug delivery systems as a targeting agent. In this study, besides the evaluations of the affinity of AS1411 to different ions and the impact of Cu on targeted drug delivery employed AS1411 aptamer as a targeting agent, a simple and ultra-sensitive fluorescent aptasensor was fabricated for Cu detection through applying AS1411, its complementary strand and magnetic beads coated with streptavidin. Gel Red (GR) was also used as a fluorescent dye. The fabricated aptasensor offered the possibility of condensing samples with different volumes. The detection limit of the sensor was 0.01 μM towards Cu in serum samples. The efficacy of this sensor was further confirmed by comparing Cu levels in serums of healthy people with patients suffering from Wilson's disease, Alzheimer's disease and Diabetes Mellitus using the proposed sensing platform.