Nanowires from biomolecules
doi:10.1038/nindia.2011.61 Published online 28 April 2011
Peptides, tiny molecules made of amino acids, have been successfully used to make nanosized conducting wire. Such wires could help design hi-tech nanosized electronic devices.
Conventionally, biomolecules have been known to be non-conducting. However, in recent years experiments have found that it is possible to transfer charge through biomolecules such as DNA and peptides. This has prompted a flurry of research to create tiny conducting wires out of biomolecules.
"Peptides have the potential to become building blocks for the next generation of molecular electronics," says Lam Yeng Ming, lead researcher of the team working on the peptide wires. The global team is drawn from the Nanyang Technological University and Institute of Materials Research and Engineering (both in Singapore), the Institute of Microbial Technology in Chandigrah, India and US-based Northwestern University.
Earlier experiments have studied charge transfer in peptides by dissolving them in water or attaching them to iron containing molecules such as ferrocenoyl. Such experiments showed low conductivity through the peptide backbone.
To design a peptide which can conduct electrons in a dry state over longer distance, the researchers synthesized peptides with a sequence of amino acids with tyrosine in the beginning and alanine at the end. The sequence was carefully chosen to facilitate self-assembly of peptide molecules.
The tyrosine in the beginning helped form a hydrogen bond with neighboring peptide molecules. Alanine, in the end of the chain, has a carboxyl group which helped attach the peptide onto a silicon substrate using a linker called aminopropyltriethoxysilane (APTES). The researchers constructed a channel using gold contacts with this assembled layer to measure electrical properties.
The team found electrical conduction over hundreds of nanometers along the length of peptides in dry state unlike previous studies which showed electron conduction over a few nanometers. This was "very likely due to the electron transport between the phenyl rings in the tyrosine amino acid residue of the peptide."
Peptide assemblies have shown the potential to self-assemble into electron transport channels and may be considered as alternatives to one-dimensional conductors such as nanotubes and nanowires.
"Since the power consumed is too small in the biological world, more efficient biomolecular electronic devices could be generated using these types of molecular wires and other analogues," Vijayamohanan Pillai of the National Chemical Laboratory, Pune, told Nature India while commenting on the potential of the research.
The approach might be successful in making nanowire of molecular diameter, said Nikhil Jana of the Indian Association for the Cultivation of Science in Kolkata. "If it works in a device form, it can help in greater understanding of those natural phenomenon where conduction is important", Jana added.