title: Charge-signal multiplication mediated by urea wires inside Y-shaped carbon nanotubes.
abstract: In previous studies, we reported molecular dynamics (MD) simulations showing that single-file water wires confined inside Y-shaped single-walled carbon nanotubes (Y-SWNTs) held strong and robust capability to convert and multiply charge signals [Y. S. Tu, P. Xiu, R. Z. Wan, J. Hu, R. H. Zhou, and H. P. Fang, Proc. Natl. Acad. Sci. U.S.A. 106, 18120 (2009); Y. Tu, H. Lu, Y. Zhang, T. Huynh, and R. Zhou, J. Chem. Phys. 138, 015104 (2013)]. It is fascinating to see whether the signal multiplication can be realized by other kinds of polar molecules with larger dipole moments (which make the experimental realization easier). In this article, we use MD simulations to study the urea-mediated signal conversion and multiplication with Y-SWNTs. We observe that when a Y-SWNT with an external charge of magnitude 1.0 e (the model of a signal at the single-electron level) is solvated in 1 M urea solutions, urea can induce drying of the Y-SWNT and fill its interiors in single-file, forming Y-shaped urea wires. The external charge can effectively control the dipole orientation of the urea wire inside the main channel (i.e., the signal can be readily converted), and this signal can further be multiplied into 2 (or more) output signals by modulating dipole orientations of urea wires in bifurcated branch channels of the Y-SWNT. This remarkable signal transduction capability arises from the strong dipole-induced ordering of urea wires under extreme confinement. We also discuss the advantage of urea as compared with water in the signal multiplication, as well as the robustness and biological implications of our findings. This study provides the possibility for multiplying signals by using urea molecules (or other polar organic molecules) with Y-shaped nanochannels and might also help understand the mechanism behind signal conduction in both physical and biological systems.
authors.affiliation: Department of Mathematics, and Institute of Systems Biology, Shanghai University, Shanghai 200444, China.
authors.forename: Mei
authors.initials: M
authors.lastname: Lv
authors.affiliation: School of Computer Engineering and Science, Shanghai University, Shanghai 200444, China.
authors.forename: Bing
authors.initials: B
authors.lastname: He
authors.affiliation: Department of Mathematics, and Institute of Systems Biology, Shanghai University, Shanghai 200444, China.
authors.forename: Zengrong
authors.initials: Z
authors.lastname: Liu
authors.affiliation: Department of Engineering Mechanics, and Soft Matter Research Center, Zhejiang University, Hangzhou 310027, China.
authors.forename: Peng
authors.initials: P
authors.lastname: Xiu
authors.affiliation: Department of Mathematics, and Institute of Systems Biology, Shanghai University, Shanghai 200444, China.
authors.forename: Yusong
authors.initials: Y
authors.lastname: Tu
mesh_terms: D004583:Electrons; D056004:Molecular Dynamics Simulation; D037742:Nanotubes, Carbon / Q000737:chemistry*; D014508:Urea / Q000737:chemistry*
chemical_list: D037742:Nanotubes, Carbon; D014508:Urea