In 2006, Anderson and his colleagues unveiled a bacterium they had engineered to invade nearby cells. Importantly, the invasion only occurred under chosen conditions, including lack of oxygen, which often occurs near tumors. Rather than directly combining sensing, computation, and actuation into a single DNA or RNA molecule, Anderson’s genetic modules communicate using smaller molecules, in much the same way as normal cells. When the researchers insert new DNA into the bacteria, they include special sequences that respond to other chemicals in the cell or the environment. They “connect” their modules by inducing this sensitivity to the products of other genes that they insert. In addition, by requiring that two different molecules attach to adjacent regions of DNA, they created the cellular equivalent of an AND gate.

 

a need to Communicate The chemical sensitivity of genes gives cells some ability to communicate with each other. For example, one of the signals that stimulated Anderson’s bacteria to invade was the well-known “ quorum-sensing” response that kicks in for some bacteria when they are present in large numbers. Ron Weiss, a professor of electrical engineering and molecular biology at Princeton University, has used the quorum-sensing machinery to build bidirectional communication between two groups of bacteria. The collective behavior constitutes a kind

of computation that reflects the interaction between the two strains, each of which could be tuned to detect separate conditions. In some cases, Weiss says, “a cell that specializes in the detection of one condition can do it much better than a cell that tries to do too many things at once.”

From a broader perspective, says computer scientist Tatsuya Suda of the University of California at Irvine, “there’s always communication involved” in micromedicine. The sensing of the environment by the tiny agents is a kind of communication, he notes, as is the dispensing of drugs. As researchers design these tiny communications systems, he stresses, they need to pay careful attention to noise.

In addition to communicating with their environment, microscopic agents may communicate with each other. As an example, Suda cites regenerative medicine, in which the creation of a replacement organ requires coordinated response by many agents. But he admits that, for now, “the state of the art is just trying to find out how they work together as a group, as opposed to how we can take advantage of group behavior.”

For biologically based agents, as for ordinary cells, any communication is likely to occur through the emission and sensing of molecules. In contrast, artificial or hybrid systems incorporating nanometer-scale electronic components might also communicate by ultrasound or radio. In principle, as

described by researcher Tad Hogg of Hewlett-Packard Labs, they could signal to point others to medically important locations. In addition, they might be able to transmit information to the outside world.

Augmenting, rather than replacing, the diagnostic strengths of the medical community could be an important early application of micromedicine, and relaxes the demands for on-board computation and drug delivery. At a minimum, small devices might extend the capabilities of chemicals whose locations are monitored in modern medical equipment. “As those imaging devices advance,” Hogg says, “they should be able to give you some information more than just ‘here’ or ‘not here,’ but what they found” in a particular region, perhaps by combining several important local measurements.

Even before medical applications become practical, Shapiro suggests, the emerging tools could provide new resources for basic biology research. “I think that these types of molecular computing devices might be able to analyze living cells ex vivo and help researchers understand cells without killing them,” Shapiro notes. “These applications are probably measured in years rather than in decades.”

 

Don Monroe is a science and technology writer based in murray hill, nJ.

© 2009 acm 0001-0782/09/0600 $10.00

Search Technology
Kleinberg Wins ACM-Infosys Foundation Award

Jon Kleinberg, a professor of
computer science at Cornell
university, is the winner of the
2008 aCm-Infosys Foundation
award in the Computing sciences
for his contributions to improving
Web search techniques that
allow billions of Web users
worldwide to find relevant,
credible information on the ever-
evolving Internet. Kleinberg, 37,
developed models that document
how information is organized on
the Web, how it spreads through
large social networks, and how
these networks are structured
to create the small-world

phenomenon known as “six degrees of separation.”

Kleinberg’s use of mathematical models to illuminate search and social networking tools that underpin today’s social structure has created interest in computing from people not formerly drawn to this field. the aCm-Infosys Foundation award, established in 2007, recognizes personal contributions by young scientists and system developers to a contemporary innovation that exemplifies the greatest recent achievements in the computing field. Financial

support for the $150,000 award is provided by an endowment from the Infosys Foundation.

“Professor Kleinberg’s achievements mark him as a founder and leader of social network analysis in computer science,” says Professor Dame Wendy hall, president of aCm. “With his innovative models and algorithms, he has broadened the scope of computer science to extend its influence to the burgeoning world of the Web and the social connections it enables. We are fortunate to have the benefit of his profound

insights into the link between computer network structure and information that has transformed the way information is retrieved and shared online.”

the aCm-Infosys Foundation award recognizes young researchers who are currently making sizeable contributions to their fields and furthering computer science innovation. the goal is to identify scientifically sound breakthrough research with potentially broad implications, and encourage the recipients to further their research.