Virus particles are captured and transported using kinesin‐driven, antibody‐functionalized microtubules. The functionalization was achieved through covalent crosslinking, which consequently enhanced the microtubule stability. The capture and transport of the virus particles was subsequently demonstrated in gliding motility assays in which antibody‐coated microtubules functioned as capture elements, and antibody‐coated microspheres served as fluorescent reporters (see Figure).

Recently, kinesin biomolecular motors and microtubules filaments (MTs) were used to transport metal and semiconductor nanoparticles with the long-term goal of exploiting this active transport system to dynamically assemble nanostructured materials. In some cases, however, the presence of nanoparticle cargo on MTs was shown to inhibit transport by interfering with kinesin-MT interactions. The primary objectives of this work were (1) to determine what factors affect the ability of kinesin and MTs to transport nanoparticle cargo, and (2) to establish a functional parameter space in which kinesin and MTs can support unimpeded transport of nanoparticles and materials. Of the factors evaluated, nanoparticle density on a given MT was the most significant factor affecting kinesin-based transport of nanoparticles. The density of particles was controlled by limiting the number of available linkage sites (i.e., biotinylated tubulin), and/or the relative concentration of nanoparticles in solution. Nanoparticle size was also a significant factor affecting transport, and attributed to the ability of particles < 40 nm in diameter to bind to the "underside" of the MT, and block kinesin transport. Overall, a generalized method of assembling and transporting a range of nanoparticle cargo using kinesin and MTs was established.

Thermodynamic relaxation can generate complex nanostructured materials via self-assembly; these structures, however, are ultimately limited by chemical equilibria and diffusional transport processes. [1] In contrast, living systems use a concerted combination of thermodynamic and energydissipating processes to remove these functional limitations, and generate complex, structured materials with a wide range of adaptive and emergent behaviors. An underlying principle of such systems involves the dynamic self-assembly of materials, which occurs outside of thermodynamic equilibrium, requires a source of energy, and bridges multiple length scales. [2][3][4] Analogous principles have been applied to assemble a broad range of artificial ''dissipative'' structures [5] through electrorheological, [6] magnetohydrodynamic, [7] electrohydrodynamic, [8] and magnetorheological, [9] interactions that induce spatiotemporal ordering. Efforts to understand these effects have led to significant insights into fundamental nonequilibrium physics.[10] While these approaches expand the practical range of materials, they rely on programmed or user-defined stimuli to drive the assemblies out of equilibrium. The next major step in developing materials assemblies will involve selfregulating systems that define the dynamic assembly and adaptive behavior of materials. Such feedback-regulated systems will extend the functional nature of nanostructured materials to include revolutionary behaviors (e.g., adaptive reconfiguration and self-healing), currently unattainable by conventional self-assembly methods.There are few examples of dynamic self-assembly in which the energy component is intrinsic to the system, as opposed to externally applied (e.g., electromagnetic fields). One system involves the dynamic assembly of nanospools [11,12] and nanocomposite rings [13] wherein assembly is achieved through a stochastic interaction of energy-dissipation and thermodynamic processes. One remarkable characteristic of both structures is the significant energy (i.e., >10 5 kT) that is required for their formation, which is based on the relatively high bending rigidity of the microtubules. [11] This energy input is cooperatively supplied through the hydrolysis of ATP by kinesin (energy dissipation) and the formation of multiple biotin-streptavidin bonds (thermodynamic). In addition, the nanospools display a highly nonequilibrium existence in which the unzipping of biotin-streptavidin bonds by kinesin motor leads to the spontaneous unspooling for the structures.[11] A unique aspect of the nanocomposite rings concerns the ability to assemble quantum dots across multiple length scales. The microtubules in these structures serve as a nanoscale scaffold for assembling the quantum dots; the quantum dot-laden microtubules subsequently self-organize into microscale, optically active structures. [13] While the properties of these nonequilibrium structures have been described, the mechanism of their formation is unknown and may provide valuable insight with respect t...

Biomolecular motors are a unique class of intracellular proteins that are fundamental to a considerable number of physiological functions such as DNA replication, organelle trafficking, and cell division. The efficient transformation of chemical energy into useful work by these proteins provides strong motivation for their utilization as nanoscale actuators in ex vivo, meso- and macro-scale hybrid systems. Biomolecular motors involved in cytoskeletal transport are quite attractive models within this context due to their ability to direct the transport of nano-/micro-scale objects at rates significantly greater than diffusion, and in the absence of bulk fluid flow. As in living organisms, biomolecular motors involved in cytoskeletal transport (i.e., kinesin, dynein, and myosin) function outside of their native environment to dissipatively self-assemble biological, biomimetic, and hybrid nanostructures that exhibit nonequilibrium behaviors such as self-healing. These systems also provide nanofluidic transport function in hybrid nanodevices where target analytes are actively captured, sorted, and transported for autonomous sensing and analytical applications. Moving forward, the implementation of biomolecular motors will continue to enable a wide range of unique functionalities that are presently limited to living systems, and support the development of nanoscale systems for addressing critical engineering challenges.

Miniaturization of lab-on-a-chip devices to nanoscale dimensions necessitates a level of systems integration currently found primarily in biological systems. Such devices will require new modes of transporting macromolecular materials at nanometer length scales. In cells, efficient cytoplasmic transport is achieved by energy-consuming, active transport systems in which motor proteins transport cargo along cytoskeletal filaments. For example, the motor protein kinesin-1 carries cell organelles and macromolecules over considerable distances along microtubule filaments. [1,2] Microtubules are hollow protein polymeric filaments with a diameter of %25 nm and tens of micrometers in length that form a 3D transportation network within the cell. Small groups of kinesin transport cargo at rates up to %12 mm s À1 , with a catalytic efficiency (i.e., conversion of chemical energy into work) of %50%. [3][4][5] Together, this transport system provides a highefficiency means of transporting macromolecular cargo through the highly viscous medium of cytoplasm.

Synthetic interconnected lipid nanotube networks were fabricated on the millimeter scale based on the simple, cooperative interaction between phospholipid vesicles and kinesin-microtubule (MT) transport systems. More specifically, taxol-stabilized MTs, in constant 2D motion via surface absorbed kinesin, extracted and extended lipid nanotube networks from large Lα phase multilamellar liposomes (5-25 μm). Based on the properties of the inverted motility geometry, the total size of these nanofluidic networks was limited by MT surface density, molecular motor energy source (ATP), and total amount and physical properties of lipid source material. Interactions between MTs and extended lipid nanotubes resulted in bifurcation of the nanotubes and ultimately the generation of highly branched networks of fluidically connected nanotubes. The network bifurcation was easily tuned by changing the density of microtubules on the surface to increase or decrease the frequency of branching. The ability of these networks to capture nanomaterials at the membrane surface with high fidelity was subsequently demonstrated using quantum dots as a model system. The diffusive transport of quantum dots was also characterized with respect to using these nanotube networks for mass transport applications.

Biomolecular motors, such as kinesin, have been used to shuttle a range of biological and synthetic cargo in microfluidic architectures. A critical gap in this technology is the ability to controllably link macromolecular cargo on microtubule (MT) shuttles without forming extraneous byproducts that may potentially limit their application. Here we present a generalized approach for functionalizing MTs with antibodies in which covalent bonds are formed between the carbohydrate in F(c) region of polyclonal antibodies and the positively charged amino acids on the MT surface using the crosslinker succinimidyl 4-hydrazidoterephthalate hydrochloride (SHTH). Antibody-functionalized MTs (Ab-MTs) produced through this approach maintained motility characteristics and antigenic selectivity, and did not produce undesirable byproducts common to other approaches. We also demonstrate and characterize the application of these Ab-MTs for capturing and transporting bacterial and viral antigens. While this approach cannot be applied to monoclonal antibodies, which lack a carbohydrate moiety, it may be used for selectively functionalizing MT shuttles with a variety of carbohydrate-containing cargoes.

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