Aqueous computing: A matter of control

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  • Published: Jun 15, 2015
  • Author: David Bradley
  • Channels: Chemometrics & Informatics
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A universe in a water droplet?

Stanford bioengineer Manu Prakash and his students have developed a synchronous computer that operates using the unique physics of moving water droplets. Still from video by Kurt Hickman

Nineteenth century, American poet Lucy Larcom suggested that a single drop of water, if it could write out its own history, would explain the universe to us. Now, US researchers have not quite explained the universe with water droplets, but they have built a synchronous computer that operates using the unique physics of moving water droplets.

Manu Prakash and colleagues Georgios "Yorgos" Katsikis and James Cybulski at Stanford University have built a kind of computer that uses water droplets rather than electrons as its computational currency. The system they have created uses microfluidics expertise to operate the essential "clock", the key to a modern computer. "In this work, we finally demonstrate a synchronous, universal droplet logic and control," Prakash says. The computer is universal and so theoretically could carry out any operation that can be done with a conventional electronic computer, but Prakash and his colleagues have bigger plans for their system.

"We already have digital computers to process information. Our goal is not to compete with electronic computers or to operate word processors on this," Prakash explains. "Our goal is to build a completely new class of computers that can precisely control and manipulate physical matter." He suggests that such a machine would not only run computations on information input to the system but also physically process the matter used to represent that information. This kind of physical manipulation with built-in computation could be exploited in high-throughput biology and chemistry and perhaps in a future realm of scalable digital manufacturing with far greater potential than 3D printing.

Ten-year muse

Prakash had been musing on the idea for a decade and eventually hit on the idea of using a rotating magnetic field to synchronize droplets of water. He recruited graduate student Katsikis, to help with making the concept a reality. The clock in a computer is responsible for running all the modern conveniences of the our world, smart phones, digital video recorders, aircraft, the Internet. The clock allows computer operations to be carried out in the necessary sequential manner, starting and stopping them at the appropriate point in time so that information synchronizes and your app works!

Katsikis and Prakash built arrays of tiny iron bars on glass slides that look something like the maze in the well-known video game "Pac-Man". They covered this with a glass slide, sandwiching a layer of oil in between. Then they carefully injected into the mix individual water droplets that had been infused with tiny magnetic nanoparticles.

When they switched on the magnetic field and flipped it, the polarity of the bars is inverted and the magnetized droplets move in a new, predetermined direction. Each "flip" is a tick in the clock's tick-tock cycle. The team records the interactions between individual droplets with a camera so that they can watch the computation in real time. The presence of a droplet is counted as a "1" in binary, the absence, a "0".

Logic gates

"We've demonstrated that we can make all the universal logic gates used in electronics [the Boolean AND, OR, NOT, NOR, XOR etc], simply by changing the layout of the bars on the chip," explains Katsikis. "The actual design space in our platform is incredibly rich. Give us any Boolean logic circuit in the world, and we can build it with these little magnetic droplets moving around." They have already demonstrated a 1-bit memory storage, "flip-flop", device using their basic building blocks. The system might also be used more immediately in high-throughput experiments where each droplet carries the requisite chemicals for a reaction of interest and acts as its own "test tube" within the system.

The system is extremely robust and uses universal design rules, which Prakash plans to make available to other researchers and the public through a design tool that would allow others to build their own logic blocks and create any complex droplet circuit they might desire. "We're very interested in engaging anybody and everybody who wants to play, to enable everyone to design new circuits based on building blocks we describe in this paper or discover new blocks," Prakash says.

Related Links

Nature Phys, 2015, online: "Synchronous universal droplet logic and control"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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