We investigate experimentally the effects of electrostatic interactions and topological constraints on DNA dynamics in nanoslit confinement by studying the equilibrium shape and dynamics of single linear and circular lambda-DNA confined in a silicon/glass nanoslit. Having examined the dependence of chain radius of gyration R-parallel to, shape asphericity A, and relaxation time tau on chain topology, slit height h (20-782 nm), and solvent ionic strength I (8.2-268.8 mM), it is found that the chain shape becomes more aspherical as h and I decrease. Moreover, in strong sub-Kuhn length confinement, the DNA relaxation time increases with decreasing h in a smooth and broad transition. Our results provide experimental evidence to confirm that the scaling exponents of radius of gyration and of relaxation time are the same for linear and circular DNA and help resolve conflicting observations of the qualitative dependencies of chain radius of gyration and relaxation time in sub-Kuhn length slits.