The modular molecular composite nanosystems (MMCNs) route to atomically precise productive nanosystems could benefit from a new modular method of constructing DNA nanotubes that provides control of the geometry of the nanotube cross-section (for example, triangular or square) and may enable real-time modulation of the stiffness and porosity of the nanotube. From McGill University, via AAAS EurekAlert “DNA ‘tricked’ to act as nano-building blocks“:
McGill researchers find new ways to manufacture nanotubes of controlled geometry, stiffness and porosities
McGill researchers have succeeded in finding a new way to manufacture nanotubes, one of the important building blocks of the nanotechnology of the future.
Their building material? Biological DNA.
A team of researchers, led by Prof. Hanadi Sleiman in collaboration with Prof. Gonzalo Cosa, both of McGill University’s Department of Chemistry, can now tailor different geometries, rigidities and porosities into these nanotubes through the clever introduction of non-DNA molecules. This work [was published online 12 April in] Nature Nanotechnology [abstract].
Nanotubes are infinitesimally small, measuring six or seven nanometers across. (A nanometre, one-billionth of a metre, is one ten-thousandth the diameter of a human hair.) One of the important features of these tubes is their extreme length, at about 20,000 nanometres. While they are tiny, they offer an incredibly versatile potential to solve a number of key problems facing nanotechnology researchers. This includes the design of drug delivery vehicles, the manufacture of electronic nanowires, medical implants and scaffolds for solar energy conversion among others.
“It looks like our fabrication is in place,” Sleiman said. “We are now looking at potential applications of these materials in drug delivery. It’s too early to tell for sure, but this is certainly something worth exploring.
“DNA is an incredible scaffold for making nanotubes.”
Nanotechnology’s tremendous potential to affect social and economic development is dependent on scientists first being able to make the necessary molecules and materials. To make this happen, nanotechnologists are now using nature’s code of life, DNA. With its simple A, T, C and G alphabet, DNA is able to direct the formation of an astounding array of proteins that work collectively to create life. It is precisely this property of chemical information stored in DNA that nanotechnology is now exploiting.
In this case, DNA strands are programmed to assemble into complex one- two- and three-dimensional structures. By incorporating synthetic molecules into such strands of DNA, the Sleiman group provided nature’s workhorse with further specific dialed-in structural and functional properties.
Using this method, Faisal Aldaye, Peggy Lo, Pierre Karam and Chris McLaughlin in the Sleiman and Cosa laboratories have demonstrated the first examples of DNA nanotubes with deliberately controlled geometry. Remarkable triangular and square-shaped tubes spontaneously form using these new techniques.
These nanotubes offer great potential, for example, for the construction of metal nanowires of different geometries. The DNA tube can be used as a mold into which metals are grown, creating microscopically thin wires that may have a wide variety of applications.
The team has also shown how these nanotubes can be created in an ‘open’, single-stranded form and ‘closed’ double-stranded form. These forms will be especially interesting for the encapsulation and selective release of drugs near the site of diseased cells.
The key to the programmable properties of these modular DNA nanotubes is the introduction of rigid organic molecules as vertices (three for a triangular cross section; four for a square, etc.) to connect single strand segments of DNA (three for a triangular cross section; four for a square, etc.) to form a flexible cyclic molecule. To take the triangular nanotube case, the cyclic molecule is made rigid by hybridization with three long single strand DNA segments, each of which has a central region which hybridizes to one DNA segment in the cycle to make that segment rigid, leaving long single strand tails at each end of the rigid segment. The rigid triangles now form modules that can be stacked like rungs in a ladder, one on top of another, by hybridizing to double strand linker DNA segments that have single strand tails complementary to the tails from each vertex. Examination of the resulting DNA nanotubes using atomic force microscopy (AFM) reveals DNA nanotubes thousands of nanometers long with a distance between each rung of about 15 nanometers (remember the DNA double helix is about 2 nm in diameter), and with each rung rotated 40 ° with respect to the next rung. Thus the method produces DNA nanotubes that are geometrically well-defined. By replacing some of the double strand linker segments with single strand linker segments, the rungs can be connected to form nanotubes with looser connections between rungs so that the nanotubes are less stiff and the space between rungs is more accessible to other “guest” molecules. Adding and removing DNA to interconvert the partially single strand linker DNA and fully double strand linker DNA would thus allow real-time control of stiffness and whether the guest molecules are encapsulated or released. (Credit: KurzweilAI.net and PhysOrg.com)