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12 Apr 2010

Volume 96, Issue 15, Articles (15xxxx)

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Appl. Phys. Lett. 96, 153701 (2010); http://dx.doi.org/10.1063/1.3385388 (3 pages)

Sinan Keten and Markus J. Buehler
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Atomistic model of the spider silk nanostructure

Sinan Keten and Markus J. Buehler

Appl. Phys. Lett. 96, 153701 (2010); http://dx.doi.org/10.1063/1.3385388 (3 pages) | Cited 17 times

Online Publication Date: 12 April 2010

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Spider silk is an ultrastrong and extensible self-assembling biopolymer that outperforms the mechanical characteristics of many synthetic materials including steel. Here we report atomic-level structures that represent aggregates of MaSp1 proteins from the N. Clavipes silk sequence based on a bottom-up computational approach using replica exchange molecular dynamics. We discover that poly-alanine regions predominantly form distinct and orderly beta-sheet crystal domains while disorderly structures are formed by poly-glycine repeats, resembling 31-helices. These could be the molecular source of the large semicrystalline fraction observed in silks, and also form the basis of the so-called “prestretched” molecular configuration. Our structures are validated against experimental data based on dihedral angle pair calculations presented in Ramachandran plots, alpha-carbon atomic distances, as well as secondary structure content.
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87.14.E- Proteins
87.15.-v Biomolecules: structure and physical properties
87.15.ap Molecular dynamics simulation
87.15.La Mechanical properties

Behavior of Caenorhabditis elegans in alternating electric field and its application to their localization and control

Pouya Rezai, Asad Siddiqui, Ponnambalam Ravi Selvaganapathy, and Bhagwati P. Gupta

Appl. Phys. Lett. 96, 153702 (2010); http://dx.doi.org/10.1063/1.3383223 (3 pages) | Cited 6 times

Online Publication Date: 14 April 2010

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Caenorhabditis elegans is an attractive model organism because of its genetic similarity to humans and the ease of its manipulation in the laboratory. Recently, it was shown that a direct current electric field inside microfluidic channel induces directed movement that is highly sensitive, reliable, and benign. In this letter, we describe the worm’s movement response to alternating electric fields in a similar channel setup. We demonstrate that the 1 Hz and higher frequency of alternating current field can effectively localize worms in the channel. This discovery could potentially help design microfluidic devices for high throughput automated analysis of worms.
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87.50.ct Therapeutic applications
87.85.D- Applied neuroscience
87.19.Ff Muscles
87.85.Ox Biomedical instrumentation and transducers, including micro-electro-mechanical systems (MEMS)

Observation of an anomalous mass effect in microcantilever-based biosensing caused by adsorbed DNA

Seonghwan Kim, Dechang Yi, Ali Passian, and Thomas Thundat

Appl. Phys. Lett. 96, 153703 (2010); http://dx.doi.org/10.1063/1.3399234 (3 pages) | Cited 6 times

Online Publication Date: 15 April 2010

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Quantifying adsorbed mass using resonance frequency variation in a microcantilever is an established technique. However, when applied to adsorbed mass determination in liquids, the resonance frequency variations represent several contributions. While the discrepancy between the apparent and real adsorbed mass is negligible for measurements in air, it can be significant in liquids. Here we present an anomalous effect of adsorbed DNA on the resonance frequency of microcantilevers which cannot be explained using current models. Our findings suggest that the measured frequency shifts may be explained on the basis of a hydrodynamic interaction caused by the adsorbed molecules on the cantilever.
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87.80.Ek Mechanical and micromechanical techniques
87.14.gk DNA
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Rapid inactivation of Penicillium digitatum spores using high-density nonequilibrium atmospheric pressure plasma

Sachiko Iseki, Takayuki Ohta, Akiyoshi Aomatsu, Masafumi Ito, Hiroyuki Kano, Yasuhiro Higashijima, and Masaru Hori

Appl. Phys. Lett. 96, 153704 (2010); http://dx.doi.org/10.1063/1.3399265 (3 pages) | Cited 12 times

Online Publication Date: 15 April 2010

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A promising, environmentally safe method for inactivating fungal spores of Penicillium digitatum, a difficult-to-inactivate food spoilage microorganism, was developed using a high-density nonequilibrium atmospheric pressure plasma (NEAPP). The NEAPP employing Ar gas had a high electron density on the order of 1015 cm−3. The spores were successfully and rapidly inactivated using the NEAPP, with a decimal reduction time in spores (D value) of 1.7 min. The contributions of ozone and UV radiation on the inactivation of the spores were evaluated and concluded to be not dominant, which was fundamentally different from the conventional sterilizations.
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52.77.-j Plasma applications
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
87.90.+y Other topics in biological and medical physics (restricted to new topics in section 87)
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