Volume 87, Number 4, August 2009
Article Number 48006
Number of page(s) 6
Section Interdisciplinary Physics and Related Areas of Science and Technology
Published online 07 September 2009
EPL, 87 (2009) 48006
DOI: 10.1209/0295-5075/87/48006

Condensation of isolated semi-flexible filaments driven by depletion interactions

A. W. C. Lau1, A. Prasad2 and Z. Dogic3, 4

1   Department of Physics, Florida Atlantic University - Boca Raton, FL 33431, USA
2   Department of Chemical and Biological Engineering, Colorado State University - Fort Collins, CO 80523, USA
3   Department of Physics, Brandeis University - Waltham, MA 02454, USA
4   Rowland Institute at Harvard, Harvard University - Cambridge MA 02143, USA

received 23 April 2009; accepted in final form 5 August 2009; published August 2009
published online 7 September 2009

Using fluorescence microscopy, we directly visualize the condensed structures of individual semi-flexible actin filaments in a poor solvent. The condensation of filaments into either ring-like or racquet-like structures is driven by non-adsorbing polymers which induce attractive interactions between filaments via the well-known depletion mechanism. A quantitative analysis of the racquet structures yields a direct measurement of the adhesion strength between a pair of filaments. We also compare our experimental data with a theoretical model, demonstrating that in the limit of weak binding, thermal fluctuations can renormalize the effective strength of the attractive depletion interactions. Our experimental methods can be applied to other filamentous structures to directly measure their attractive intermolecular potentials.

82.70.Dd - Colloids.
87.16.Ka - Filaments, microtubules, their networks, and supramolecular assemblies.
82.35.Pq - Biopolymers, biopolymerization.

© EPLA 2009