  Using all atom molecular dynamics simulations, we report spontaneous
unzipping and strong binding of small interfering RNA (siRNA) on graphene. Our
dispersion corrected density functional theory based calculations suggest that
nucleosides of RNA have stronger attractive interactions with graphene as
compared to DNA residues. These stronger interactions force the double stranded
siRNA to spontaneously unzip and bind to the graphene surface. Unzipping always
nucleates at one end of the siRNA and propagates to the other end after few
base-pairs get unzipped. While both the ends get unzipped, the middle part
remains in double stranded form because of torsional constraint. Unzipping
probability distributions fitted to single exponential function give unzipping
time (t) of the order of few nanoseconds which decrease exponentially with
temperature. From the temperature variation of unzipping time we estimate the
energy barrier to unzipping.
