High-tech microscope makes molecules move.

High-tech microscope makes molecules move

Like the early microscopists of the 17th century, who peered at anything that fit under their lenses, modern scientists are just beginning to explore the power of the atomic force microscope to image atoms and molecules, and even to move molecules. That power may one day lead to a new generation of biosensors and microchips, they suggest.

Developed in 1985, the atomic force microscope features a scanning tip that "reads" surfaces with atomic resolution. A computer monitors the tip's varying vertical positions as it sweeps over the molecular features of a surface, and then generates images of the underlying landscape. Scientists now report they have used the device to see how different molecules arrange themselves on a catalytic crystal. What's more, they say they manipulated some of those molecules.

Researchers at the University of California, Santa Barbara, began by looking at how two types of molecules bind to the surface of a zeolite catalyst. Zeolite crystals are often used to break down crude oil and to convert methanol to gasoline. With the atomic force microscope, the team observed molecular interactions on a zeolite used to remove ammonium and phosphate ions during wastewater treatment. They found that molecules bind to the zeolite surface differently depending on whether they are charged. Positively charged t-butyl ammonium ions formed clumps, while neutral t-butanol molecules arranged themselves in an orderly sheet, the group reports in the March 16 SCIENCE.

Visualizing molecular interactions on zeolite surfaces will give chemists a clearer picture of how zeolites speed reactions. Armed with such knowledge, scientists might learn how to alter zeolites to catalyze new reactions and to boost the efficiency of known reactions, says coauthor James E. MacDougall.

More dramatically, the researchers demonstrated that they could move molecules by increasing the force with which the microscope tip scans. To achieve this effect, they used the tip to carve an "X" on the zeolite surface. Like a snowplow, the tip shoved aside molecules in its path.

"The binding and movement of molecules on zeolite crystals justifies hope that in the future it may be possible to see biologically important molecules binding to receptor sites," says physicist Paul K. Hansma, also of the Santa Barbara team. With the atomic force microscope, researchers might someday use arrays of receptor molecules as biosensors, monitoring how they bind other biological molecules and how long the bonds last, he suggests.

In addition, the ability to manipulate smaller and smaller particles may eventually lead to more compact microchips, although such applications would require years of research, Hansma says.

John Foster of the IBM Almaden Research Center in San Jose, Calif., who is also investigating molecular manipulation with the atomic force microscope, comments: "Anytime you can work on a molecular scale it's terrific, but it's too early to predict how this technology may be used by scientists and industry."