Scientists recently discovered that DNA can be used as a molecular scaffold to make metal contacts to organic semiconductors. A key step in this process involves being able to tether the DNA to various surfaces and stretch the molecule to varying lengths.

Zhenan Bao and colleagues' new strategy involves synthesizing hybrid DNA-organic molecule-DNA (DOD) structures, then stretching and tethering the DOD assemblies between two microscopic metal electrodes. The researchers then make metal electrode-organic molecule-metal electrode (MOM) structures by further metallizing the DNA segments within the DOD structures.

The team then exploited so-called biotin-Streptavidin linkage chemistry to tether the DNA assemblies to device surfaces (quartz in this case). The basic steps are as follows: functionalizing the surface with amine (-NH2) terminated silanes; reacting the amines with N-hydroxysuccinimide (NHS) functionaliszed polyethylene glycol (PEG) chains terminated with biotin; and using Streptavidin to create a link to biotin-terminated DNA molecules.

A crucial step
"We have made progress in synthesizing these DOD hybrid structures and have now developed a reproducible surface chemistry technique to tether DNA molecules of different lengths to substrate surfaces," team member Guihua Yu told nanotechweb.org. "We have also developed a shear flow processing method to control DNA stretching and alignment. This represents a crucial step in making large-scale nanoelectronic devices based on DOD array structures."

Aside these practical applications, the technique could also be used to study single DNA molecules and how they rotate. DNA tethering and stretching may also help in manipulating nucleotides in single DNA molecules for genetic applications and to study how DNA reacts with proteins at the single-molecule level, said Yu. Other single-molecule technologies, such as DNA sequencing could also benefit.

Spurred on by these first results, the team is now working on a controllable, double-tethering process while developing in situ DNA metallization for ultimately making larger-scale nanoelectronic devices based on single organic molecules. "We will then perform electrical transport measurements on these device arrays to probe how charge travels through single molecules with different chemical functionalities and length," added Yu.

The work was reported in ACS Nano.