Dual Aptamer-Functionalized 3D Plasmonic Metamolecule for Thrombin Sensing

DNA nanotechnology offers the possibility to rationally design structures with emergent properties by precisely controlling their geometry and functionality. Here, we demonstrate a DNA-based plasmonic metamolecule that is capable of sensing human thrombin proteins. The chiral reconfigurability of a DNA origami structure carrying two gold nanorods was used to provide optical read-out of thrombin binding through changes in the displayed plasmonic circular dichroism. In our experiments, each arm of the structure was modified with one of two different thrombin-binding aptamers&mdash
thrombin-binding aptamer (TBA) and HD22&mdash
in such a way that a thrombin molecule could be sandwiched by the aptamers to lock the metamolecule in a state of defined chirality. Our structure exhibited a Kd of 1.4 nM, which was an order of magnitude lower than those of the individual aptamers. The increased sensitivity arose from the avidity gained by the cooperative binding of the two aptamers, which was also reflected by a Hill coefficient of 1.3 &plusmn
0.3. As we further exploited the strong plasmonic circular dichroism (CD) signals of the metamolecule, our method allowed one-step, high sensitivity optical detection of human thrombin proteins in solution.