Direct Observation of Biaxial Confinement of a Semi-flexible Filament in a Channel

We have studied the biaxial confinement of a semi-flexible filament in a channel by in situ video fluorescence microscopy*. As the channel width decreases, F-actin undergoes a transition from a 2D random regime to a 1D biaxially confined regime, leading to an increased effective persistence length. A theoretical calculation shows that the tangent-tangent correlation function in the confined regime shows a minimum, then reaches to a constant at long distances, indicating that confinement induces long-range order in a semi-flexible filament. The location of the minimum of the experimental correlation function is consistent with our theoretical calculation. This work was supported by KISTEP I-03-064, KISTEP IMT-2000-B3-2, MOHW 0405-MN01-0604-0007, NSF DMR 00-80034, 05-03347, 02-03755, 01-29804, NSF CTS-0404444, ONR N00014-05-1-0540, and DOE W-7405-ENG-36. M.C.Choi acknowledges partial support from the Korea Research Foundation Grant KRF-2005-214-C00202. *M.C.Choi et al., \textit{Macromolecules}, 38, 9882 (2005)