Artificial Muscles from Fishing Line and Sewing Thread

Carter S. Haines, Márcio D. Lima, Na Li, Geoffrey M. Spinks, Javad Foroughi, John D. W. Madden, Shi Hyeong Kim, Shaoli Fang, Mônica Jung de Andrade, Fatma Göktepe, Özer Göktepe, Seyed M. Mirvakili, Sina Naficy, Xavier Lepró, Jiyoung Oh, Mikhail E. Kozlov, Seon Jeong Kim, Xiuru Xu, Benjamin J. Swedlove, Gordon G. Wallace, Ray H. Baughman

The high cost of powerful, large-stroke, high-stress artificial muscles has combined with performance limitations such as low cycle life, hysteresis, and low efficiency to restrict applications. We demonstrated that inexpensive high-strength polymer fibers used for fishing line and sewing thread can be easily transformed by twist insertion to provide fast, scalable, nonhysteretic, long-life tensile and torsional muscles. Extreme twisting produces coiled muscles that can contract by 49%, lift loads over 100 times heavier than can human muscle of the same length and weight, and generate 5.3 kilowatts of mechanical work per kilogram of muscle weight, similar to that produced by a jet engine. Woven textiles that change porosity in response to temperature and actuating window shutters that could help conserve energy were also demonstrated. Large-stroke tensile actuation was theoretically and experimentally shown to result from torsional actuation.

DOI

Journal: Science

Chemical mapping of a single molecule by plasmon-enhanced Raman scattering

R. Zhang, Y. Zhang, Z. C. Dong, S. Jiang, C. Zhang, L. G. Chen, L. Zhang, Y. Liao, J. Aizpurua, Y. Luo,  J. L. Yang, and J. G. Hou

Visualizing individual molecules with chemical recognition is a longstanding target in catalysis, molecular nanotechnology and biotechnology. Molecular vibrations provide a valuable ‘fingerprint’ for such identification. Vibrational spectroscopy based on tip-enhanced Raman scattering allows us to access the spectral signals of molecular species very efficiently via the strong localized plasmonic fields produced at the tip apex1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11. However, the best spatial resolution of the tip-enhanced Raman scattering imaging is still limited to 3−15 nanometres5, 12, 13, 14, 15, 16, which is not adequate for resolving a single molecule chemically. Here we demonstrate Raman spectral imaging with spatial resolution below one nanometre, resolving the inner structure and surface configuration of a single molecule. This is achieved by spectrally matching the resonance of the nanocavity plasmon to the molecular vibronic transitions, particularly the downward transition responsible for the emission of Raman photons. This matching is made possible by the extremely precise tuning capability provided by scanning tunnelling microscopy. Experimental evidence suggests that the highly confined and broadband nature of the nanocavity plasmon field in the tunnelling gap is essential for ultrahigh-resolution imaging through the generation of an efficient double-resonance enhancement for both Raman excitation and Raman emission. Our technique not only allows for chemical imaging at the single-molecule level, but also offers a new way to study the optical processes and photochemistry of a single molecule.

DOI

Journal: Nature

Single-Molecule Reconstruction of Oligonucleotide Secondary Structure by Atomic Force Microscopy

Alice Pyne, Ruth Thompson, Carl Leung, Debdulal Roy and Bart W. Hoogenboom

Based on soft-touch atomic force microscopy, a method is described to reconstruct the secondary structure of single extended biomolecules, without the need for crystallization. The method is tested by accurately reproducing the dimensions of the B-DNA crystal structure. Importantly, intramolecular variations in groove depth of the DNA double helix are resolved, which would be inaccessible for methods that rely on ensemble-averaging.

DOI

Journal: Small

Observation of Brownian Motion in Liquids at Short Times: Instantaneous Velocity and Memory Loss

Simon Kheifets, Akarsh Simha, Kevin Melin, Tongcang Li, Mark G. Raizen

Measurement of the instantaneous velocity of Brownian motion of suspended particles in liquid probes the microscopic foundations of statistical mechanics in soft condensed matter. However, instantaneous velocity has eluded experimental observation for more than a century since Einstein’s prediction of the small length and time scales involved. We report shot-noise–limited, high-bandwidth measurements of Brownian motion of micrometer-sized beads suspended in water and acetone by an optical tweezer. We observe the hydrodynamic instantaneous velocity of Brownian motion in a liquid, which follows a modified energy equipartition theorem that accounts for the kinetic energy of the fluid displaced by the moving bead. We also observe an anticorrelated thermal force, which is conventionally assumed to be uncorrelated.

DOI

Journal: Science

Radio-Wave Oscillations of Molecular-Chain Resonators

Stefan Müllegger, Mohammad Rashidi, Karlheinz Mayr, Michael Fattinger, Andreas Ney, and Reinhold Koch

We report a new type of nanomechanical resonator system based on one-dimensional chains of only 4 to 7 weakly coupled small molecules. Experimental characterization of the truly nanoscopic resonators is achieved by means of a novel radio-frequency scanning tunneling microscopy detection technique at cryogenic temperatures. Above 20 K we observe concerted oscillations of the individual molecules in chains, reminiscent of the first and second eigenmodes of a one-dimensional harmonic resonator. Radio-frequency scanning tunneling microscopy based frequency measurement reveals a characteristic length dependence of the oscillation frequency (between 51 and 127 MHz) in reasonable agreement with one-dimensional oscillator models. Our study demonstrates a new strategy for investigating and controlling the resonance properties of nanomechanical oscillators.

DOI

Journal:Physical Review Letters

Single-molecule resolution of protein structure and interfacial dynamics on biomaterial surfaces

Sean Yu McLoughlin, Mark Kastantin, Daniel K. Schwartz, and Joel L. Kaar

A method was developed to monitor dynamic changes in protein structure and interfacial behavior on surfaces by single-molecule Förster resonance energy transfer. This method entails the incorporation of unnatural amino acids to site-specifically label proteins with single-molecule Förster resonance energy transfer probes for high-throughput dynamic fluorescence tracking microscopy on surfaces. Structural changes in the enzyme organophosphorus hydrolase (OPH) were monitored upon adsorption to fused silica (FS) surfaces in the presence of BSA on a molecule-by-molecule basis. Analysis of >30,000 individual trajectories enabled the observation of heterogeneities in the kinetics of surface-induced OPH unfolding with unprecedented resolution. In particular, two distinct pathways were observed: a majority population (∼ 85%) unfolded with a characteristic time scale of 0.10 s, and the remainder unfolded more slowly with a time scale of 0.7 s. Importantly, even after unfolding, OPH readily desorbed from FS surfaces, challenging the common notion that surface-induced unfolding leads to irreversible protein binding. This suggests that protein fouling of surfaces is a highly dynamic process because of subtle differences in the adsorption/desorption rates of folded and unfolded species. Moreover, such observations imply that surfaces may act as a source of unfolded (i.e., aggregation-prone) protein back into solution. Continuing study of other proteins and surfaces will examine whether these conclusions are general or specific to OPH in contact with FS. Ultimately, this method, which is widely applicable to virtually any protein, provides the framework to develop surfaces and surface modifications with improved biocompatibility.

DOI

Journal: Proceedings of the National Academy of Sciences

High-Speed Force Spectroscopy Unfolds Titin at the Velocity of Molecular Dynamics Simulations

Felix Rico, Laura Gonzalez, Ignacio Casuso, Manel Puig-Vidal, Simon Scheuring

The mechanical unfolding of the muscle protein titin by atomic force microscopy was a landmark in our understanding of single-biomolecule mechanics. Molecular dynamics simulations offered atomic-level descriptions of the forced unfolding. However, experiment and simulation could not be directly compared because they differed in pulling velocity by orders of magnitude. We have developed high-speed force spectroscopy to unfold titin at velocities reached by simulation (~4 millimeters per second). We found that a small β-strand pair of an immunoglobulin domain dynamically unfolds and refolds, buffering pulling forces up to ~100 piconewtons. The distance to the unfolding transition barrier is larger than previously estimated but is in better agreement with atomistic predictions. The ability to directly compare experiment and simulation is likely to be important in studies of biomechanical processes.

DOI

Journal: Science