When liquid meets gas, a unique zone forms. Variable by nature, molecules can cross from one state to another, combining in unique ways to either desirable or unwanted ends. From heat escaping a mug of coffee to increasing molecular concentrations in chemical solutions, gas-liquid interfaces are ubiquitous across nature and engineering. But a lack of tools capable of precisely controlling such gas-liquid interfaces limit their applications—until now.

“Whether it’s engineered or occurs in nature, gas-liquid interfaces play an important role in numerous chemical and biological processes,” said paper author Yan Xu, associate professor of chemical engineering in the Graduate School of Engineering at Osaka Prefecture University. “Nanoscale gas-liquid interfaces have been randomly generated in carbon nanotubes and porous membranes, for example, but fabricating controllable, nanoscale versions is still challenging because nanofluidic channels are too small to make use of conventional approaches to surface control.”

Fluidic devices help researchers capture target molecules and examine specific properties, as well as force interactions through nanoscale channels designed with precisely controlled geometry, Xu said.

In microfluidic devices, which contain channels about 1,000 times larger than those in nanofluidic devices, the surface of the channels can be changed to attract or reject specific molecules.

“Such surface modification is commonly used for microfluidic channels, but its applicability for nanofluidic channels is almost never explored,” Xu said.

While microfluidic devices can be made from a variety of materials, nanofluidic devices require a glass substrate. According to Xu, glass properties, such as optical transparency, thermal stability and mechanical robustness, make it a favorable material for applications in a wide range of disciplines and an ideal material in nanofluidics.

While hydrophilic in nature, glass can be made hydrophobic, a technique used in surface modification to help stop molecules in the sample liquid from bonding to molecules in the glass. The researchers also made glass nanochannels—which are roughly the width of 1/1,000 a sheet of paper —with hydrophilic gold nanopatterns precisely placed to locally attract liquid molecules at the entrance of nanochannels. The gold nanopatterns were fabricated using a technique called “Nano-in-Nano” integration, which was developed by the researchers and allows for precise patterning of much smaller functional nanopatterns in the tiny nanofluidic channels.

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