Image: Scanning electron microscopy image showing 10 nanometer gold nanoparticles aligned on a gold surface using DNA origins.
Such surfaces could be used to create circuits smaller than current ones (for example, pen drives with a capacity 100 times greater than now) or high resolution surfaces for sensors, with the small size of the patterns allowing many sensors to be neatly incorporated on a very small surface. With this, a hundred substances could be analyzed in a gold plate smaller than a cell.
Using DNA for nanodevices
For a few years, the use of DNA as the basis to obtain nanodevices has been under investigation, taking advantage of the fact that DNA segments are coupled together like Lego pieces. Not only that, but DNA segments can be used as ‘glue’ to connect to other functional molecules or nanomaterials. In this way, high precision multi-component structures can be generated and used to create surfaces for sensors or drug targeting systems, among other things. However, a method to easily integrate these DNA structures into other microelectronic devices has not yet been achieved.
Now, in a study led by CSIC with the participation of scientists from IBEC and the University of Barcelona, most of them integrated in the Center for Biomedical Research in Bioengineering Network, Biomaterials And Nanomedicine (CIBER-BBN), has achieved an important advance in this line. The team, led by Ramon Eritja, research professor at CSIC’s Institute of Advanced Chemistry (IQAC), has devised a process of molecular lithography to create patterns on gold surfaces. This process can be used to create small circuits within microelectronic devices.
Folding DNA like paper
The method is based on the use of the DNA origami technique, whose name is taken from the traditional oriental art that creates figures by folding a sheet of paper in different ways. In DNA origami, part of a large DNA strand of viral origin is folded naturally thanks to other small segments of DNA (oligonucleotides) that act like staples, resulting in various shapes. The structures obtained can be used as templates for placing proteins, nanoparticles, enzymes or any other functional molecule following a predetermined pattern.
Using this technique, scientists fixed a set of DNA molecules of about 10 micrometers square containing about 250 DNA segments on a gold surface. Between each of the orderly placed segments of DNA, there was a distance of few nanometers.
To generate the template – in this case, a straight line, although any other shape could be «drawn» as a pattern – 12 of the 250 oligonucleotide ‘staples’ were modified with a chemical compound that reacted with the gold surface. «That way, the marked molecules of DNA, and only those, react when they are fixed on the gold surface, which is the usual bedrock of microdevices,» explains Prof. Eritja.
When labeled DNA molecules have been bound in this way to the gold surface, unlabeled ones, as well as viral DNA, are removed. In this way, the linear pattern of oligonucleotides can be transferred to the gold surface, which in turn can attract and bind functionalized nanomaterials with complementary strands to the DNA staples.
It is like creating a seal which can be integrated into the photolithography processes that are commonly used to create microelectronic circuits, and that allows for the first time the «stamping» or integration of DNA onto gold surfaces of circuits, structures or patterns at a scale of less than 10 nanometers.
The new technology would enable the synthesis and marking of hundreds of oligonucleotides very quickly, which means the method can be easily scaled up to industrial proportions.
Reference: Gállego, I., Manning, B., Prades, J.D., Mir, M., Samitier, J., Eritja, R. (2017). DNA origami-driven lithography for patterning on gold surfaces with sub-10 nanometer resolution. Adv. Materials, doi: 10.1002/adma.201603233