We report a theoretical study of electron transport along helical molecules under an external electric field, which is perpendicular to the helix axis of the molecule. Our results reveal that the topological states could appear in single-helical molecule and double-stranded DNA in the presence of the perpendicular electric field. And these topological states guarantee adiabatic charge pumping across the helical molecules by rotating the electric field in the transverse plane and the pumped current at zero bias voltage is quantized. In addition, the quantized current constitutes multiple plateaus by scanning the Fermi energy as well as the bias voltage, and hold for various model parameters, since they are topologically protected against perturbations. These results could motivate further experimental and theoretical studies in the electron transport through helical molecules, and pave the way to detect topological states and quantized current in the biological systems.PACS numbers: 87.14.-g, 87.14.gk, 87.15.Pc, 82.39.JnIntroduction.-Helix structures are ubiquitous both in the biological world[1-3] and for synthetic materials [4][5][6]. The electron transport along helical molecules, such as DNA and α-helical protein, has been receiving much attention among the scientific communities [7][8][9][10][11][12][13][14][15][16][17], because this subject can enrich our knowledge regarding the electronic properties of low-dimensional systems due to the unique helix structure and provides valuable information for understanding the biological processes in living organisms [18][19][20]. It was reported by direct charge transport experiments that double-stranded DNA (dsDNA) could exhibit fascinating physical phenomena, such as the proximity-induced superconductivity [21], the negative differential resistance [22], and the piezoelectric effect [23]. Additionally, it was shown that both dsDNA and α-helical protein can behave as electric field-effect transistors [24][25][26][27] and as efficient spin filters [28][29][30][31][32][33][34][35].