  We study the spin transport and polarization properties of manganese-doped
dual-guanine molecules connected to graphene leads using non-equilibrium
Green's function method. It is shown that a manganese doped dual-guanine
molecule is a biological semiconductor and behaves as a prefect spin filter. We
show that this semiconductor can behave as a spin switch when the Rashba
spin-orbit interaction is considered. In addition, it is shown that, a large
conductance is observed due to the Fano-Kondo-Rashba resonance effect.
