From Seashells to Nanocomputers

CAMBRIDGE, Mass. — What can a humble seashell tell us about how to build biocomputers at the nanoscale level— 50,000 times smaller than the width of a human hair? Plenty, according to Angela M. Belcher, Professor of Materials Science and Engineering and Bioengineering at the Massachusetts Institute of Technology.

Belcher kicked off the Whitehead Institute’s BioFrontiers seminar series on new, mutidisciplinary areas of scientific research with a talk on how nature can be harnessed to build complex structures, which can be used to make new devices for optics and electronics.

Abalone shell, bones, magnetic bacteria, and other natural materials exert biological control over the way chemicals such as calcium carbonate and silica form crystals. By imitating and modifying nature’s methods, Belcher and others are developing new materials with extraordinary electronic and optical properties.

Her talk covered recent work that will be able to probe biological processes in novel ways, build biocompatible medical devices, develop biosensors for medical and antiterror applications, and assemble semiconductors of various sizes.

Belcher’s early studies focused on the abalone shell, which has evolved a complex control mechanism for self-assembling into an appropriate form and thickness. It does this by combining protein and a chemical called calcium chloride in very precise and complex ways at the nanoscale, where building blocks can be as small as a few atoms. Imitating nature, she and others are creating biological-electronic hybrid materials in a controlled manner, not possible by current manufacturing methods.

Belcher described studies she recently published in the May 3, 2002, issue of Science in which she used genetically engineered viruses that are noninfectious to humans to mass produce tiny materials for next-generation optical, electronic and magnetic devices.

In this case, they took advantage of the viruses’ genetic makeup and physical shape to not only grow the material but also to help them assemble themselves into liquid crystal structures that are several centimeters long.

Identify, Analyze, and Alter

Whether simply building crystal structures or developing semiconductors that assemble themselves, Belcher’s approach takes advantage of systems such as bacteriophages, which have evolved over millions of years to work at the nanoscale level. These bacteriophages—viruses that infect bacteria—are induced to work on technologically useful materials.

Belcher first identifies bacteriophages that bind to a particular synthetic material and the phage proteins that play a critical role in binding. She uses a well-known technique called phage display to screen a library of 100 million phage proteins, discovers which of these can recognize and bind to the synthetic material being studied, and identifies the DNA that makes these proteins. Belcher’s lab is then able to introduce the DNA for these proteins into bacteriophages. This forces the bacteriophage to produce the proteins of interest in desired quantities and in desired places, either at one end of the bacteriophages or along their protein coats.

Belcher’s lab has showed that engineered bacteriophages can recognize specific semiconductor surfaces, and these recognition properties can be used to organize molecules in nanocrystals, forming ordered arrays. The system can be easily manipulated to create an enormous variety of biomaterials. The length of the bacteriophage and the type of synthetic materials the viruses are grown on can be customized through genetic modification and selection. One can easily modulate and align different types of inorganic nanocrystals in three-dimensional layered structures. In previous work, Belcher showed how specially selected bacteriophages could potentially recognize different sites on a semiconductor and spontaneously build such structures.

The work of Belcher and her colleagues integrates a wide span of disciplines, including materials chemistry, inorganic synthesis, surface chemistry, molecular biology, biochemistry, and electrical engineering. It served as a fitting introduction to the BioFrontiers series of seminars, which will feature speakers whose work challenges the boundaries of disciplines and conventional approaches to biological research.