Quantitatively controlled nanoliter liquid manipulation using hydrophobic valving and control of surface wettability

In this paper, we discuss nanoliter metering, transportation, merging, and biochemical reaction on a nanoliter fluidic chip. The proposed nanoliter fluidic handling is based on passive fluidic control using hydrophobic valving and liquid flow control by selective wettability patterning. For the selective patterning of the wettability, a hydrophobic fluorocarbon (FC) film (a mixture of Fluorad™ from 3M, USA) was spin-coated on a hydrophilic glass wafer and patterned using a lift-off process. The patterned FC film showed strong hydrophobicity, indicated by a high water contact angle (108–110°). For the fabrication of the nanoliter fluidic chip, polydimethysiloxane microchannel networks were aligned and bonded onto the glass wafer, along with the FC patterns. The proposed nanoliter metering technique showed an accuracy of 4% using a 20 nL criterion. A biochemical reaction on a chip was performed between β-galactosiadase (enzyme) and a fluorescein di-β-galactopyranoside (FDG) substrate. The FDG and the enzyme solution were manipulated on the nanoliter fluidic chip in desired volumes and mixing ratios. The reactions between different ratios of the enzyme and FDG substrate were monitored using the fluorescence intensity as a function of the reaction time. From the enzymatic reaction on the chip, we confirmed that the proposed fluidic handling was successfully performed on the chip, and that the reaction depended on the enzyme concentration.