Building miniature optical antennas using DNA as a guide

A new fabrication technique combines programmable DNA origami shapes and conventional lithography methods to create metallic nanoantennas and chiral shapes for diverse applications. The so-called DALI (DNA-assisted lithography) method has been published in the latest issue of Science Advances. The research has been funded by the Academy of Finland.

Research groups from the University of Jyväskylä and Aalto University in Finland together with researchers from the California Institute of Technology in the US and Aarhus University in Denmark have reported a new highly parallel technique to fabricate precise metallic nanostructures with designed plasmonic properties by means of different self-assembled DNA origami shapes.

“We can build virtually any nanoscale shape using a DNA origami technique, and now we've shown how to use these accurate shapes as 'stencils' to create millions of fully metallic nanostructures with 10 nm feature sizes in one go,” says Adjunct Professor Veikko Linko from Aalto University.

The trick in the DALI method is that when the DNA structures are deposited on a chip coated with silicon, silicon oxide can be selectively grown only on the bare areas of the substrate.

“By controlling this process, we can create origami-shaped openings on the grown silicon oxide layer, which can be used as a mask for the following lithography steps. Finally, we evaporate metal through these openings and create metallic structures having the same shape and size as the original DNA origami on a transparent substrate, such as sapphire,” explains Boxuan Shen from the Nanoscience Center of the University of Jyväskylä.

The tiny metallic features cover the whole transparent substrate, and therefore these surfaces have intriguing optical properties. The small dimensions of the structures – in the range of ten nanometers – allow further tuning of these properties at the visible wavelength range.

“Actually, we've demonstrated here a structure that we believe is the world’s smallest entirely metallic bowtie-shaped antenna. This extremely small size extends the operating range of optical features from infrared to visible,” says Adjunct Professor Jussi Toppari from the Molecular Electronics and Plasmonics group at the University of Jyväskylä.

These antennas can find use in dozens of optical and plasmonic applications, such as surface-enhanced Raman spectroscopy, biosensing or fluorescence enhancement. Moreover, the researchers demonstrated that the surfaces can be used as polarizers by fabricating chiral structures using DALI.

“The DALI method is highly parallel and could further enable cheap wafer-scale production of surfaces as it doesn't rely on costly patterning methods. It's also equipped for future studies to provide bioinspired surfaces and metamaterials if the customised origami structures can be arranged on the substrate before metallization,” says Professor Mauri Kostiainen from the Biohybrid Materials Group at Aalto University.

Source: University of Jyväskylä press release

DNA assisted lithography: bowtie-shaped DNA origami is transformed into a metallic nanostructure (image: M. Kostiainen)