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Many biological assays require effectively and sensitively sorting DNA fragments. Here, we demonstrate a solid-state nanopore platform for label-free detection and separation of short single-stranded DNA (ssDNA) fragments (<100 nt), based on their length-dependent translocation behaviors. Our experimental data show that each sized pore has a passable length threshold. The negative charged ssDNA fragments with length smaller than the threshold can be electrically facilitated driven through the correspondingly sized nanopore along the direction of electric field. In addition, the passable length threshold increases with the pore size enlarging. As a result, this phenomenon is able to be applicable for the controllable selectivity of ssDNA by tuning nanopore size, and the selectivity limitation is up to 30nt. Numerical simulation results indicate the translocation direction of ssDNA is governed by the competition of …