Credit: © 2007 Wiley

Controlling the growth of semiconductor materials into organized structures is essential for making functional nanoscale systems that could be used in applications ranging from biosensing to electronics. One approach involves the use of a scaffold on which nanostructures of controlled dimensions can be grown. Biopolymers — DNA in particular — are attractive templates because they have well-defined structures and are readily available.

Andrew Houlton and co-workers1 from the University of Newcastle in the UK have shown that different CdS nanostructures can be made using DNA templates. When the DNA was bonded to a mica surface, regularly sized and spaced CdS nanoparticles were formed along the rigid double helical strands resulting in a bead-like structure. In contrast, it was found that DNA molecules aligned on alkyl monolayers on a silicon surface were poor templates because they move during the deposition process.

DNA molecules floating freely in solution and not fixed to a surface were also studied in templating reactions. Under the right conditions, CdS nanowires could be made that had fairly uniform diameters (approximately 14 nm) along their length. Although bead-like structures were formed initially, adjacent particles eventually fused together to form continuous wires. Using a combing technique that has been developed to align DNA strands, the CdS nanowires could be located across electrodes and their electrical transport properties were measured.