"With increasing urban runoff, sewage spills and blooms of harmful algae off heavily populated coastal areas, it is very important to be able to sense, and then identify, particular ocean microorganisms quickly," said Ari Requicha, a USC professor of computer science and the project's principal investigator. "The quicker we learn that a pathogen is present in the water, the sooner we can warn people and begin action to correct the situation."

The project spans the fields of nanotechnology, robotics, computer science and marine biology, but is centered on the development of the ultra-small robotic sensors and software systems to control them.

Requicha directs the USC School of Engineering's Laboratory for Molecular Robotics where his team has been experimenting with nanometer-scale structures for nearly seven years. 

(One nanometer is one/one-billionth of a meter. A nanometer is to a meter what a small grape is to the entire Earth.)

In the 1980s, scientists discovered that the sharp silicon tip of the newly invented scanning probe microscope not only produced images revealing individual atoms and molecules, but it sometimes moved them. 

The computer-controlled microscope scans microscopic samples, sensing their minute atomic forces and precisely mapping the surface at a molecular or even atomic level.

Working with colloidal gold and silver balls as small as two nanometers, and string-like organic molecules called dithiols that tether the balls to each other, Requicha's group has programmed their atomic force microscope -- a particular kind of scanning probe-microscope -- to slide the "nanoscale" particles into precise positions on tiny slabs of mica or silicon. 

They can chemically link the particles to form crude assemblies, and they can make "nanowires" by depositing metals on strings of carefully positioned balls.

"We do this at room temperature and at normal air pressure, and we can also work in water and other liquids, which is crucial for biological applications," said Requicha.

The group has made a nanoscale single-electron transistor and an optical waveguide, which is a structure used to guide light. They are working on an actuator, or switch, and are starting to fabricate more complex 3D "nanostructures" by building up successive layers of nanoscale assemblies. Each layer is surrounded by a "sacrificial" material that holds it in place and that is removed when all the layers are complete to leave a tiny nanoelectromechanical device. 

Substances being investigated for use as the sacrificial material include charged polymers, zinc phosphonate films and organic compounds containing silicon known as silanes.

Requicha said it will be possible to build nanoscale devices with electrical and mechanical components so that the devices could propel themselves, send electronic signals and even compute. While individual nanoscale devices would have far less computing power and capability than full-sized devices, the plan is to have vast numbers of them operating in concert.

It often takes Requicha's team weeks to assemble even a simple nanoscale object, but the procedure can be automated once the computer programming is perfected. Other labs are working on atomic force microscopes with more than one tip. Requicha said a single atomic force microscope could theoretically have an array containing thousands or even millions of tips, all controlled by the same computer program to manufacture large numbers of nanoscale devices.

David Caron, professor of biological sciences and a co-investigator on the project, said ocean robots needn't be terribly complicated or powerful to be useful. A single robot might sense only whether the water is fresh or saline and communicate by a faint radio signal only with other robots closest to it, which would then relay the information to other robots in the network linked to the Internet by still more robots.

In the next year, Caron hopes to attach an antibody to a microscope tip. He recently created an antibody that binds to Aureococcus anophagefferens, the toxic algae known as Brown Tide. With the same procedure widely used to test for HIV and other diseases, he can reliably test for the algae.

"That test takes a day in the lab, which is an improvement over current testing, but it's still not fast enough," said Caron. The microscope should detect the algae the instant a microorganism binds to the antibody on its tip.

Requicha estimates that it will be a decade before the researchers can build and deploy nanoscale robots in the ocean capable of the kind of instant and specific test like Caron's for Brown Tide. Along the way, he hopes the project will spin off technology in marine biology and other areas.

"Suppose we put 15-nanometer particles on a grid with 100-nanometer spacing, which we can routinely do in our lab today. If we interpret the presence of a particle as a binary one and its absence as a zero, we have a scheme to store data," he said. "The bit density is 10 gigabytes per square centimeter, which means we have data storage that is 100 times better than today's compact disks. And it could be even greater with smaller particles and spacing."

The USC researchers will first build small robots that will move, sense and communicate while tethered in a tank of water in a laboratory. They will gradually progress to building and controlling increasingly larger numbers of increasingly smaller freely moving robots. The end goal of the project will be to create robots that are as small as the microorganisms that they seek to monitor.

"Today, we commonly do experiments with five or ten robots," said Gaurav Sukhatme, USC assistant professor of computer science and a co-investigator on the project. "But we'll need algorithms to coordinate a million or more robots. That is a daunting problem, and we must start laying out the foundations for large numbers of robots long before they are a reality."

Requicha said that nanotechnology today is at the same stage of development as the Internet was in the late 1960's.

"The idea that we'll have swarms of nanorobots in the ocean is no more far-fetched than the idea of connecting millions of computers was then," he said. "I don't think these robots will be confined to the ocean. We will eventually make robots to hunt down pathogens or repair cells in the human body."

The grant is from the National Science Foundation's Information Technology Research program. Maja Mataric, associate professor of computer science and director of the USC School of Engineering's Robotics Research Laboratories, and Deborah Estrin, a computer networking specialist from UCLA, are also co-investigators on the project. - By Bob Calverly
 

[Contact: Bob Calverley]
 

14-Jan-2002