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 μm 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.