Nanochemistry is the synthesis and study of well-defined structures with dimensions of 1 to 100 nm. Nano-building blocks span the size range between molecules and materials such as nylon. Molecular biologists study nanochemistry, nanostructures, and molecular machines including the ribosome and membrane-bound signaling complexes. Icosahedral viruses are proving to be precision building blocks for nanochemistry. The icosahedral cowpea mosaic virus particle is 30 nm in diameter, and its atomic structure is known in detail. Grams of particles can be prepared easily from kilograms of infected leaves, insertional mutagenesis is straightforward, and precise amino acid changes can be introduced.
As illustrated in panel A of the figure, cysteine residues inserted in the capsid protein provide functional groups for chemical attachment of 60 precisely placed molecules, in this case, gold particles. High local concentrations of attached chemical agents, coupled with precise placement, and the propensity of virus-like particles for self-organization into two- and three-dimensional lattices of well-ordered arrays of particles enable rather remarkable nanoconstruction. For example, the surface of the filamentous bacteriophage M13 can be patterned to carry separate binding sites for gold and cobalt oxide and assembled into nanowires to form the anodes of small lithium ion batteries.
Remarkably, this bacteriophage also displays intrinsic piezoelectric properties, that is, the ability to generate an electric charge in response to mechanical deformation, and vice versa. The basis of this property is not fully understood, but modification of the sequence of the major protein to increase its dipole moment (figure, panel B) augmented the piezoelectric strength of the bacteriophage. Assembly of the modified M13 into thin films was exploited to build a piezoelectric generator that produced up to 6 mA of current and 400 mV of potential, sufficient to operate a liquid crystal display