Project 17: Self-assembly of Polymers into NEMS Force Sensors (Prof. Robert Cohn, ECE)

Advanced Manufacturing Topic: Visco-elastic instabilities of stressed polymeric  liquids  (including biomaterials of fibrin, actin and DNA) can be used to self-assemble suspended nanofiber air-bridges (top figure) that have aspect ratios exceeding 10,000:1 [1-6]. The fabrication process is quite robust, enabling defect-free arrays of identical structures [3-4] to be produced by even hand-application. The relatively large bead enables both simple observation and nanomanipulation of the structure under a light microscope. Force detection limits of under a piconewton are estimated, making visual sensing under a light microscope a possible alternative to traditional atomic force microscopy and laser trapping for detection of single molecule [7] and biomolecular [8-11] forces. The REU intern will personally explore the intimate connections between the everyday world and the nanoworld by learning how to fabricate the nanofibers by hand (as in bottom figure) and then actuate and view under a light microscope the motions (simple/coupled displacements and torsions) of the structures to forces produced by applied magnetic fields and laminar air flows. This project is suited for students interested in Physics, Chemistry, Biology, Material Science, ME or ChE. Please view more project details at:

Self-assembly of bead-on-a-string (BOS) fibers from saliva (top left) and a PEO-water-glycerol solution (top right). The sequential time-lapse images in PEO-water-glycerol are at 25ms/frame [12,13].

Brush-on fabrication of BOS nanofibers on top of MEMS micropillars


[1] S. A. Harfenist, S. D. Cambron, E. W. Nelson, S. M. Berry, A. W. Isham, M. M. Crain, K. M. Walsh, R. S. Keynton and R. W. Cohn, “Direct drawing of suspended filamentary micro- and nano- structures from liquid polymers,” Nano Letters 4, 1931-1937 (2004)

[2] S. Pabba, A. N. Sidorov, S. M. Berry, M. M. Yazdanpanah, R. S. Keynton, G. U. Sumanasekera and R. W. Cohn, “Oriented nanomaterial air-bridges formed from suspended polymer-composite nanofibers,” ACS Nano 1, 57-62 (2007)

[3] S. Pabba “Generalization and extensions of capillary thinning driven self-assembly of nanostructured air bridges,” Dissertation, University of Louisville (2009)

[4] S. Pabba, M. M. Yazdanpanah, B. H. Fasciotto, V. V. Dobrokhotov, J. M. Rathfon, G. N. Tew and R. W. Cohn, “Biopolymerization-driven self-assembly of nanofiber air-bridges,” Soft Matter 5, 1378–1385 (2009)

[5] C. H. Lin, J. Guan, S. W. Chau, S. C. Chen and L. J. Lee, “Patterning nanowire and micro-/nanoparticle array on micropillar-structured surface: Experiment and modeling,” Biomicrofluidics 4, 034103 (2010)

[6] S. Grilli, S. Coppola, V. Vespini, F. Merola, A. Finizio and P. Ferraro, “3D lithography by rapid curing of liquid instabilities at nanoscale,” Proc. National Academy of Sciences 108, 15106-15111 (2011).

[7] P. Lussis, T. Svaldo-Lanero, A. Bertocco, C.-A. Fustin, D. A. Leigh and A.-S. Duwez, “A single synthetic small molecule that generates force against a load,” Nature Nanotech. 6, 553 (2011)

[8] T. R. Strick, J. F. Allemand, D. Bensimon, A. Bensimon and V. Croquette, "The elasticity of a single supercoiled DNA molecule," Science 271, 1835-1837 (1996)

[9] W. J. Greenleaf, M. T. Woodside, S. M. Block, “High-resolution, single-molecule measurements of biomolecular motion,” Ann. Rev. Biophysics and Biomolecular Structure 36, 171 (2007)

[10] C. Bustamante, J. C. Macosko and G. J. L. Wuite, “Grabbing the cat by the tail: Manipulating molecules one by one,” Nature Reviews: Molecular Cell Biology 1, 130-136 (2000)

[11] K. C. Neuman and A. Nagy, “Single-molecule force spectroscopy: Optical tweezers, magnetic tweezers and atomic force microscopy,” Nature Methods 5, 491-505 (2008)

[12] P. P. Bhat, S. Appathurai, M. T. Harris, M. Pasquali, G. H. McKinley and O. A. Basaran, “Formation of beads-on-a-string structures during breakup of viscoelastic filaments,” Nature Physics 6, 625 - 631 (2010)

[13] M. S. N. Oliveira, R. Yeh and G. H. McKinley, “Iterated stretching, extensional rheology and formation of beads-on-a-string structures in polymer solutions,” J. Non-Newtonian Fluid Mechanics 137, 137-148 (2006)