Aptamers are a class of bioreceptors intensively used in current
analytical tools dedicated to molecular diagnostics due to their ability
to perform large structural reorganization upon target binding. However,
there is a lack of methodologies allowing us to rationalize their
structure in order to improve the transduction efficiency in aptamer
sensors. We choose here, as a model system, a three-strand DNA structure
as the probe, composed of two DNA strands anchored on a gold surface
and partially hybridized with an aptamer sequence sensitive to ampicillin
(AMP). The DNA structure has been designed to show strong structural
change upon AMP binding to its aptamer. Using a set of computational
techniques including molecular dynamics simulations, we deeply investigated
the structure change upon analyte binding, taking into account the
grafting on the surface. Original analyses of ion distributions along
the trajectories unveil a distinct pattern between both states which
can be related to changes in capacitance of the interface between
these states. To our knowledge, this work demonstrates the ability
of computational investigations for the first time to drive, in silico,
the design of aptasensors.