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.