Acoustic Waves Used to Drive Fluids at the Nanoscale

A group of mechanical engineers at the University of California San Diego have effectively used acoustic waves to transport fluids via small channels at the nanoscale. This innovative method is a first step toward the manufacturing of small, portable devices that may be used for microrobotics applications and drug discovery.

The devices could be combined in a lab on a chip to arrange cells, transport liquids, control particles and sense other biological parts. For instance, it could be used to filter particles, such as bacteria, to perform quick diagnosis.

The research findings were published in the November 14 issue of Advanced Functional Materials. This research is the first time that surface acoustic waves were used at the nanoscale.

James Friend, a professor and materials science expert at the Jacobs School of Engineering at UC San Diego stated that the field of nanofluidics has struggled for long time with transporting fluids within channels that are 1000 times smaller in comparison to the width of a hair.

In addition to high temperatures, current techniques need bulky and costly equipment. Moving fluid out of a channel that measures only a few nanometers high requires pressures of 1 MPa, or the equivalent of 10 atmospheres.

A team led by Friend had tried to apply acoustic waves to transport the fluids along at the nanoscale for many years. They also focused on performing this using a device that could be produced at room temperature.

Following a year of experimenting, post-doctoral researcher Morteza Miansari, now at Stanford, was successful in constructing a device made of lithium niobate with nanoscale channels where fluids can be transported using surface acoustic waves. This was achieved by a new technique formulated by Miansari to bond the material to itself at room temperature.

The fabrication technique is quite simple to scale up, which would minimize manufacturing costs. Constructing a single device would cost $1000 but constructing 100,000 would push the price down to $1 each.

The device is well-matched with biological materials, molecules, and cells.

The researchers used acoustic waves with a frequency of 20 MHz to control fluids, particles, and droplets in nanoslits that measure 50 to 250 nm in height. To fill the channels, the team used the sound waves in the same direction as the fluid traveling into the channels. To drain the channels, the sound waves were used in the reverse direction.

By altering the height of the channels, the device could be used to filter a number of particles such as even large biomolecules e.g., siRNA, which cannot fit in the slits. The acoustic waves can be used to move fluids containing the particles into these channels. While the fluid would pass through, the particles would get filtered and form a dry mass. This could be used for speedy diagnosis in the field.