Directional transport by nonprocessive motor proteins on fascin-cross-linked actin arrays.

In this study, the unidirectional transport of heavy meromyosin (HMM)-coated beads is demonstrated on fascin-cross-linked actin arrays. The streptavidin-coated surface was properly blocked to prevent nonspecific binding of F-actin and, as a result, a high population of long gelsolin-actin complexes was suspended in the medium for subsequent processes. A flow field was utilized to lay down F-actin aligned along the direction of the flow and fascin cross-linked laid F-actin to prevent F-actin resuspension. When HMM-coated beads came into contact with the fascin-cross-linked actin arrays, they started to move in the same direction over long distances. Because of the nonprocessive nature of myosin II motor protein, the bead size limited the number of HMM heads on the area in contact with F-actin arrays, which resulted in beads traveling at different velocities according to their sizes. Furthermore, this study demonstrates the patterning of actin arrays, which could serve as a basis for the development of applications.

The movement of actin-myosin biomolecular linear motor under AC electric fields: an experimental study.

The role of actin-myosin as a biomolecular linear motor is considered a transport system at nanoscale because of their size, efficiency and functionality. To utilize the ability to transport, it is essential to control the random movement of actin filaments (F-actin) on myosin coated substrate. In the presence of an alternating current (AC) electric field, the direction of F-actin movement is regulated by electro-orientation torque and, as a result, its movement is perpendicularly toward the electrode edges. Our data confirm such aligned movement is proportional to the strength of applied electric field. Interestingly, the aligned movement is found frequency-dependent and the electrothermal effect is observed by means of the velocity measurement of aligned F-actin movement. The findings in this study may provide constructive information for manipulating actin-myosin nanotransport system to build functional nanodevices in future work.

A visualized observation of calcium-dependent gelsolin activity upon the surface coverage of fluorescent-tagged actin filaments.

Gelsolin regulates the dynamics of F-actin by binding to F-actin to sever and cap. In the present study, a novel approach is introduced to observe gelsolin activity through the coverage of surface-bound F-actin. Gelsolin was immobilized on streptavidin coated surface using biotinylation and, as a result, the interaction between gelsolin and F-actin was visualized. Consequently, the coverage of F-actin reflects the activity of gelsolin as a function of free Ca(2+) concentrations. In order to prevent non-specific binding of F-actin, the combinations of BSA and Tween-20 as blocking agents were investigated. Moreover, the measurement of the length of F-actin with actin-gelsolin mixtures at various ratios provided the verification of gelsolin activity after biotinylation. The data shows the increase in Ca(2+) concentration leads to a proportional increase in F-actin coverage, giving to half-maximal coverage at ~2.9 µM. Furthermore, the length of bound F-actin was found to decrease along with increasing Ca(2+) concentration, and full-length F-actin was rarely observed. This may suggest that severing and capping activities of gelsolin occur without more additional Ca(2+) for subsequent activation after full-length gelsolin binds to a side of F-actin. This finding may provide a key to understand gelsolin activity.

Rapid and efficient sonochemical formation of gold nanoparticles under ambient conditions using functional alkoxysilane.

Gold nanoparticles (NPs) are rapidly and efficiently formed under ambient conditions with a novel and highly-efficient sonochemical promoter. Despite of the presence of free oxygen, 3-glycidoxypropyltrimethoxysilane (GPTMS) showed remarkable efficiency in promoting the reduction rate of Au (III) than that of conventional promoters (primary alcohols). This is likely attributed to the formation of a variety of radical scavengers, which are alcoholic products from sonochemical hydrolysis of the epoxide group and methoxysilane moieties of GPTMS under weakly acidic conditions. Interestingly, the promotion is quenched by amine- or thiol-functionalized alkoxysilane, thereby producing marginal amounts of gold NPs. Furthermore, products of hydrolyzed GPTMS were confirmed to attach on the surface of gold NPs by attenuated total reflectance-Fourier transform infrared spectroscopy. However, according to transmission electron microscopy images, gold NPs that were produced in the presence of GPTMS tend to fuse with each other as condensation of silanols occurs, forming worm- or nugget-like gold nanostructures. The use of long chain surfactants (i.e. polyethylene glycol terminated with hydroxyl or carboxyl) inhibited the fusion, leading to mono-dispersed gold NPs. Additionally, the fact that this approach requires neither an ultrasound source with high frequency nor anaerobic conditions provides a huge advantage. These findings could potentially open an avenue for rapid and large-scale green-synthesis of gold NPs in future work.

Transport of single cells using an actin bundle-myosin bionanomotor transport system.

The potential of using actin bundles for the transport of liposomes and single cells across myosin-coated surfaces is investigated. Compared to that observed with filamentous actin, the liposome transport using actin bundles was more linear in nature and able to occur over longer distances. Bundles, but not filamentous actin, were capable of moving single cells. Cargo unloading from bundles was achieved by incubation with Triton X-100. These data suggest that actin bundling may improve the ability of the myosin motor system for nanotransport applications.

Selective attachment of F-actin with controlled length for developing an intelligent nanodevice.

Development of the nanodevice that myosin-coated beads "walk" on actin filaments (F-actin) tracks for in vitro nanotransportation was hindered due to the difficulty of assembling large-area well-orientated F-actin tracks on the surface. In this work, we present a selective attachment of F-actin with controlled length on a patterned surface by employing biotinylated capped protein gelsolin as intermediate anchoring bridge. A patterned streptavidin layer was formed via coupling with a biotin layer that photo-actively attached to an amine-functionalized glass surface. The patterned film was found stable and homogenous compared to that obtained by microcontact printing method, according to the profiling with fluorescence microscopy. By a secondary blocking process, non-specific binding of F-actin to the patterned surface through electrostatic adsorption can be resisted. The length variation of F-actin as a function of gelsolin concentration was also investigated, implying that F-actin is appropriately of 2.5 µm in average length once F-actin/gelsolin molar ratio is 4:1. Finally, the selective attachment of F-actin was well characterized with quantifying the number of attached F-actin per unit area in the patterned areas over that in blocked areas. The density of F-actin was estimated at c.a. 2 µm(2) per actin filament molecule so that the distance between one another actin filament is estimated as c.a. 1.41-1.97 µm. The unique properties of F-actin, e.g. well flexibility or electrical conductivity, make it feasible to lay them down and form unidirectional aligned tracks by fluidic flow or electrical field. This may open a possibility for the long-distant movement of myosin-coated beads, offering a novel discipline for the development of micro-biochip in vitro.

Application of capillary electrophoresis to predict crossover frequency of polystyrene particles in dielectrophoresis.

CE is used to calculate the zeta potential of polystyrene particles in order to estimate the surface conductivity of the particles. These values are used to predict the dielectrophoretic behavior, including the crossover frequency of particles under the influence of an AC electric field. Predictions for fluorescent polystyrene particles that are unmodified, carboxylate-modified, or streptavidin-modified are tested using miniaturized dielectrophoresis cells containing patterned gold quadrupole electrodes. The particle surface conductivities derived from CE separations differ from those derived from dielectrophoresis experiments by < or =0.003 S/m and serve as a guide to effectively select the suspending medium to generate a crossover frequency approximately 0.5 MHz. Prediction of dielectrophoresis crossover frequency is limited by several factors, especially the accuracy and precision of the conductivity measurements for the particle and suspending medium. A rapid analysis of particles by CE is a viable alternative to determine zeta potential.