20 nm

20 nm

FIGURE 15.1 (A) Protein-based bionanomanufacturing: a nanomechanical device powered by the Fj-ATPase biomolecular motor (i) attached to a nickel nanopropeller (ii). Individual components were added stepwise and attached using different chemistries. The device was driven by ATP to continuously rotate the nanopropellers (iii) (Reprinted from Soong, R. et al., Science, 290, 1555, 2000. Copyright 2000 AAAS.) (B) DNA-based bionanomanufacturing: self-assembly of DNA molecules. Four DNA strands, which have complementary sticky-end overhangs (H, H', V and V'), self-assemble into a branched junction (i). These branched junctions can further self-assemble into a two-dimensional square unit due to the orientation of the complementary sticky ends. DNA 4 x 4 tile strand structures consisting of nine interconnected oligonucleotides can also self-assemble into DNA nanogrids, as shown in the AFM images of two-dimensional DNA lattices (ii). In addition, three-dimensional DNA cubes can be generated by interconnecting six single DNA strands with each linked to its four neighbors (iii). (Reprinted from Seeman, N.C., Nature, 421, 427, 2003. Copyright 2003 Nature Publishing Group; reprinted from Yan, H. et al., Science, 301, 1882, 2003. Copyright 2003 AAAS; reprinted from Seeman, N.C., Nature, 421, 427, 2003. Copyright 2003 Nature Publishing Group.) (C) Polymersomes: self-assembled diblock copolymers (number average molecular weight is 3900 g/mol) in water. Relative hydrophobic core thickness d of self-assembled copolymers was about 10 times that of a typical lipid bilayer (i). A cryo-TEM image indicates that the majority of polymersomes were rodlike (black arrow) and spherical (gray arrow) micelles (ii). (Reprinted from Discher, B.M. et al., Science, 284, 1143, 1999. Copyright 1999 AAAS. With permission.)

system has been constructed by introducing a bacteriorhodopsin for generating ATP using light to fuel the biomolecular motor [7].

Motor proteins that produce linear motion also exist. Myosin, kinesin, and dynein move along filaments composed of actin microtubules to generate nanoscale forces [12]. These motor proteins can be attached to surfaces to generate gliding movement of the filaments. Alternatively, the filaments can be anchored to a surface and the motor proteins can be forced to move in a unidirectional stepwise manner in the presence of ATP. Using these principles, novel applications were developed such as sensors for mercuric ions [135], gold nanowire transporters [136], and molecular shuttles for microbeads and quantum dots (QDs) on a nanopatterned surface [137-140]. Motor proteins provide a promising way of transporting nanostructures on surfaces and detecting biomolecules of interest at ultrahigh sensitivities [137,139,141,142]. In addition, bioinspired stimulus-responsive polymers that undergo large conforma-tional changes triggered by external stimuli are ideal candidates for biosensing and actuation. Their phase-transition properties can be exploited to generate molecular devices with interesting functional modalities such as biological thermal actuators and pH-sensitive molecular pumps [143].

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