Precise tailoring of light beams with DNA origami

With a molecular 'origami' technique, researchers at the Ludwig Maximilian University of Munich can program the basic structure of their material at will by taking advantage of the structure of DNA. DNA molecules are built up of four types of subunits (A, C, G, T), which can pair with each other (A with T and G with C). By mixing DNA strands that pair with one another at specific sites, one can produce three-dimensional shapes of any required form. Liedl and colleagues formed an 85 nm long cylinder containing localized binding sites for 10-nanometer gold particles, on which the particles can be arrayed like beads on a string that wraps helically around the cylinder. The phenomenon of circular dichroism can be used to characterize the optical activity of materials. It is measured using two light beams of defined wavelength which are circularly polarized in opposite senses and modulated in different ways by passage through the material. When the response of a given sample of the metamaterial was determined at various wavelengths, the results were found to agree with calculations based on a theoretical model. Hence, the model can be used to design materials that modulate light in specific ways.