Picoliter liquid operations in nanofluidic channel utilizing an open/close valve with nanoscale curved structure mimicking glass deflection

Microfluidics has downscaled to nanofluidics to achieve state-of-the-art analyses at single/countable molecules level. In nanofluidic analytical devices, switching and partitioning reagents in nanochannels without contamination are essential operations. For such operations, we have developed a nanochannel open/close valve utilizing elastic glass deformation. However, owing to a rectangular-shaped nanospace, sample leakage due to diffusion through the remaining open space in the closed valve occurs and causes contamination. Herein, we propose a fabrication method of nanoscale curved structure resembling the glass deflection shape to develop the nanofluidic valve for switching and partitioning operations in nanochannels. After fabricating a four-stepped rectangular nanospace by electron beam lithography and dry etching, the space was plastically deformed using an impulsive force by pressing the chamber more than 20 000 times. A smoothly curved structure with a high aspect ratio of 750 (75 mu m width and 100 nm depth) fitting the glass deflection shape, which has been difficult for conventional methods, was successfully fabricated. Utilizing a valve with the curved structure, the solute leakage through the closed valve was reduced to less than 0.5% with a 94% decreased diffusion flux compared to previous valve with the rectangular-shaped structure. The developed valve realized switching of 72 pl reagents in a nanochannel with a response time of 0.4 s, which is sufficient for nanofluidic-chromatography, and it correctly worked even after an interval of 30 min, which is required for repeatable nanofluidic analyses. The newly developed valve will contribute to realizing versatile nanofluidic analytical devices.

Automated summary

This research presents a method for fabricating nanoscale curved structures for switch and partition operations. By utilizing a valve with a curved structure, solute leakage can be significantly reduced and response time can be improved, contributing to the realization of versatile nanofluidic analytical devices.