We propose a method for the separation of long DNA molecules, based on elastomeric nanochannels with tunable cross section. These nanoconfinement structures can be used to stretch DNA molecules and lower their conformational entropy. The sieving mechanism of entropic recoil, proposed by Cabodi et al. [1], will be implemented using an array of elastomeric nanocheannels. Structures of various dimensions are fabricated taking advantage of replica molding techniques, starting from Focused Ion Beam (FIB) patterned silicon substrates. Poly(dimethylsiloxane) (PDMS) and hard-PDMS [2] are used to replicate the features on the silicon mold. After plasma oxidation the nanochannels are sealed using a glass cover slip. A piezoelectric system will be integrated on the device in order to exploit the elastomeric propertis of PDMS, reversibly deform the nanochannels and tune their cross section. This system will allow a dynamic variation of the confinement conditions affecting molecules mobility inside the nanochannels.