Reconfigurable digital colloids

July 30, 2014

A team of researchers from Argonne, the University of Michigan, NYU, and the University of Colorado – Boulder has demonstrated how reconfigurable clusters of colloids can store data.

In the paper “Digital colloids: reconfigurable clusters as high information density elements,” published by the journal Soft Matter, the authors define digital colloids as having three essential characteristics: each cluster can switch among microstates with a known probability; the cluster’s ability to switch can be locked or unlocked; and the cluster’s state can be set deterministically so that information can be stored.

The largest of the clusters studied experimentally was a 4-cluster assembled from 1.8 micrometer-diameter colloidal particles. Digital video images showed that the cluster occasionally switched from its tetrahedral structure to an equivalent structure with mirror symmetry.

“To our knowledge, this is the first realization of a digital colloidal cluster,” said Carolyn Phillips, an Argonne scholar in the Mathematics and Computer Science Division and first author of the paper reporting the team’s results.

The cluster that the team produced can store one bit of information. But although the serial technique they used does not scale to larger numbers of clusters, the researchers believe that other approaches, such as self-assembly, may well prove capable of fabricating large volumes of the clusters.

Using simulation, the team demonstrated how larger clusters could realize even larger data storage.  The 12-cluster, for example, is ideal for information storage because it can store up to 2.86 bytes and is easy to lock; moreover, when the cluster is unlocked, every microstate can be reached through a sequence of Rubik’s Cube-like moves.

Accompanying the paper is a series of movies generated from the simulations, as well as interactive media, showing the rearrangement and transition structures for 4- to 12-clusters.  “I wanted to provide every tool I could to allow another person to interact with and experience these three-dimensional clusters as I experienced them,” said Phillips.

The next major challenge: writing to and reading from the digital colloids.  The authors discuss the potential of using florescent microscopy for reading a cluster’s configuration or employing a nonimaging technique such as Forster resonant energy transfer. Moreover, they describe ways in which they might allow or restrict transitions in structure between stored states – for example, by creating the central particle from materials sensitive to changes in temperature.

The authors state that “the ability of reconfigurable colloidal clusters to store states and the sensitive control of the rate of switching between states suggests that such digital clusters may have a rich potential set of applications as small, information-storage elements.” Among the real-world applications are a new class of sensors and novel interfaces between conventional computers and computations in the bloodstream.

The research has received considerable media attention. See, for example, the following:

For the full article, see

Carolyn L. Phillips, Eric Jankowski, Bhaskar Jyoti Krishnatreya, Kazem V. Edmond, Stefano Sacanna, David G. Grier, David J. Pine, and Sharon C. Glotzer, Digital colloids: reconfigurable clusters as high information density elements, Soft Matter, 2014, advance article, DOI: 10.1039/C4SM00796D.

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