Spatiotemporal Control of Electrokinetic Transport in Nanofluidics Using an Inverted Electron-Beam Lithography System

Manipulation techniques of biomolecules have been proposed for biochemical analysis which combine electrokinetic dynamics, such as electrophoresis or electroosmotic flow, with optical manipulation to provide high throughput and high spatial degrees of freedom. However, there are still challenging problems in nanoscale manipulation due to the diffraction limit of optics. We propose here a new manipulation technique for spatiotemporal control of chemical transport in nanofluids using an inverted electron-beam (EB) lithography system for liquid samples. By irradiating a 2.5 keV EB to a liquid sample through a 100-nm-thick SiN membrane, negative charges can be generated within the SiN membrane, and these negative charges can induce a highly focused electric field in the liquid sample. We showed that the EB-induced negative charges could induce fluid flow, which was strong enough to manipulate 240 nm nanoparticles in water, and we verified that the main dynamics of this EB-induced fluid flow was electroosmosis caused by changing the zeta potential of the SiN membrane surface. Moreover, we demonstrated manipulation of a single nanoparticle and concentration patterning of nanoparticles by scanning EB. Considering the shortness of the EB wavelength and Debye length in buffer solutions, we expect that our manipulation technique will be applied to nanomanipulation of biomolecules in biochemical analysis and control

Spatiotemporal Control of Electrokinetic Transport in Nanofluidics Using an Inverted Electron-Beam Lithography System

Manipulation techniques of biomolecules have been proposed for biochemical analysis which combine electrokinetic dynamics, such as electrophoresis or electroosmotic flow, with optical manipulation to provide high throughput and high spatial degrees of freedom. However, there are still challenging problems in nanoscale manipulation due to the diffraction limit of optics. We propose here a new manipulation technique for spatiotemporal control of chemical transport in nanofluids using an inverted electron-beam (EB) lithography system for liquid samples. By irradiating a 2.5 keV EB to a liquid sample through a 100-nm-thick SiN membrane, negative charges can be generated within the SiN membrane, and these negative charges can induce a highly focused electric field in the liquid sample. We showed that the EB-induced negative charges could induce fluid flow, which was strong enough to manipulate 240 nm nanoparticles in water, and we verified that the main dynamics of this EB-induced fluid flow was electroosmosis caused by changing the zeta potential of the SiN membrane surface. Moreover, we demonstrated manipulation of a single nanoparticle and concentration patterning of nanoparticles by scanning EB. Considering the shortness of the EB wavelength and Debye length in buffer solutions, we expect that our manipulation technique will be applied to nanomanipulation of biomolecules in biochemical analysis and control

Room Temperature Operable Autonomously Moving Bio-Microrobot Powered by Insect Dorsal Vessel Tissue

<div><p>Living muscle tissues and cells have been attracting attention as potential actuator candidates. In particular, insect dorsal vessel tissue (DVT) seems to be well suited for a bio-actuator since it is capable of contracting autonomously and the tissue itself and its cells are more environmentally robust under culturing conditions compared with mammalian tissues and cells. Here we demonstrate an autonomously moving polypod microrobot (PMR) powered by DVT excised from an inchworm. We fabricated a prototype of the PMR by assembling a whole DVT onto an inverted two-row micropillar array. The prototype moved autonomously at a velocity of 3.5×10⁻² µm/s, and the contracting force of the whole DVT was calculated as 20 µN. Based on the results obtained by the prototype, we then designed and fabricated an actual PMR. We were able to increase the velocity significantly for the actual PMR which could move autonomously at a velocity of 3.5 µm/s. These results indicate that insect DVT has sufficient potential as the driving force for a bio-microrobot that can be utilized in microspaces.</p> </div

Measurement of deformation distance of the PMR base powered by contraction force of the dorsal vessel tissue.

<p>(a) Microscopic images of the prototype from the side. The inset shows an enlarged view of the area surrounded by the white rectangle in the main picture. Movies showing the whole prototype and the inset area, respectively, are available as <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0038274#pone.0038274.s003" target="_blank">Movies S3</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0038274#pone.0038274.s004" target="_blank">S4</a> in the SI. (b) Time course of deformation distance of the base. The graph was obtained by image analysis processing of <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0038274#pone.0038274.s004" target="_blank">Movie S4</a>. (c) The model to estimate the contractile force of the DVT.</p

Measurement of displacement of micropillars powered by contraction force of the dorsal vessel tissue.

<p>(a) Microscopic image of the prototype PMR. The PMR was not inverted and its base was stuck to the bottom of the petri dish. Micropillars deformed in the direction of the yellow arrows and were divided into two groups (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0038274#pone.0038274.s001" target="_blank">Movie S1</a> in the SI). The groups are surrounded by the dotted line ellipses. (b) Time courses of deformation of pillars A and B marked in (a). (c) Peak intervals obtained from periods between the contraction peaks marked in (b). There was a significant difference between the peak intervals of pillars A and B.</p

Trajectory measurement of the actual PMR powered by contraction force of the dorsal vessel tissue.

<p>(a) An image of the whole actual PMR after inversion. (b) Enlarged view of the area surrounded by the dotted rectangle marked in (a). A movie of this area was taken for 1 min (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0038274#pone.0038274.s006" target="_blank">Movie S6</a> in the SI) and analyzed with image analysis. The moving direction was set as the Y axis and the axis perpendicular to the Y axis was set as the X axis, the same as for the prototype. In (a) and (b), the red arrows show the designed moving direction. (c) Trajectories and time courses of moving distances along X and Y axes of the prototypes for the 1 min movie period. The moving distances in the first, second, and third experiments were 199, 256, and 175 µm, respectively.</p

Principle of the prototype Polypod Microrobot (PMR).

<p>(a) Schematic illustration of the prototype PMR. (b) Principle of the PMR movement in a lateral view. (c) Schematic illustration of the actual PMR.</p