Measuring aptamer equilibria using gradient micro free flow electrophoresis

Gradient micro free flow electrophoresis ([mu]FFE) was used to observe the equilibria of DNA aptamera with their targets (IgE or HIVRT) across a range of ligand concentrations. A continuous stream of aptamer was mixed online with an increasing concentration of target and introduced into the [mu]FFE device, which separated ligand--aptamer complexes from the unbound aptamer. The continuous nature of [mu]FFE allowed the equilibrium distribution of aptamer and complex to be measured at 300 discrete target concentrations within 5 min. This is a significant improvement in speed and precision over affinity capillary electrophoresis (ACE) assays. The dissociation constant of the aptamer--IgE complex was estimated to be 48 [+ or -] 3 nM. The high coverage across the range of ligand concentrations allowed complex stoichiometries of the aptamer--HIVRT complexes to be observed. Nearly continuous observation of the equilibrium distribution from 0 to 500 nM HIVRT revealed the presence of complexes with 3:1 (aptamer/HIVRT), 2:1, and 1:1 stoichiometries. 10.1021/ac902877v