Raman enhancement in bowtie-shaped aperture-particle hybrid nanostructures fabricated with DNA-assisted lithography.

We report on efficient surface-enhanced Raman spectroscopy (SERS) supporting substrates, which are based on deoxyribonucleic acid (DNA)-assisted lithography (DALI) and a layered configuration of materials. In detail, we used nanoscopic DNA origami bowtie templates to form hybrid nanostructures consisting of aligned silver bowtie-shaped particles and apertures of similar shape in a silver film. We hypothesized that this particular geometry could facilitate a four-fold advantage in Raman enhancement compared to common particle-based SERS substrates, and further, we verified these hypotheses experimentally and by finite difference time domain simulations. In summary, our DALI-fabricated hybrid structures suppress the background emission, allow emission predominantly from the areas of high field enhancement, and support additional resonances associated with the nanoscopic apertures. Finally, these nanoapertures also enhance the fields associated with the resonances of the underlying bowtie particles. The versatility and parallel nature of our DNA origami-based nanofabrication scheme and all of the above-mentioned features of the hybrid structures therefore make our optically resonant substrates attractive for various SERS-based applications.

Optical characterization of DNA origami-shaped silver nanoparticles created through biotemplated lithography.

Here, we study optically resonant substrates fabricated using the previously reported BLIN (biotemplated lithography of inorganic nanostructures) technique with single triangle and bowtie DNA origami as templates. We present the first optical characterization of BLIN-fabricated origami-shaped silver nanoparticle patterns on glass surfaces, comprising optical transmission measurements and surface-enhanced Raman spectroscopy. The formed nanoparticle patterns are examined by optical transmission measurements and used for surface enhanced Raman spectroscopy (SERS) of Rhodamine 6G (R6G) dye molecules. Polarization-resolved simulations reveal that the higher SERS enhancement observed for the bowties is primarily due to spectral overlap of the optical resonances with the Raman transitions of R6G. The results manifest the applicability of the BLIN method and substantiate its potential in parallel and high-throughput substrate manufacturing with engineered optical properties. While the results demonstrate the crucial role of the formed nanogaps for SERS, the DNA origami may enable even more complex nanopatterns for various optical applications.

Double resonant plasmonic lattices for Raman studies.

We demonstrate radiation induced enhancement of both the in coupling of Raman excitation wavelength and Raman signal in plasmonic nanoparticle lattices. Rectangular nanoparticle lattices show two independently controllable lattice resonances, which we tune to be resonant with both the Raman excitation wavelength and the Raman transitions of rhodamine 6G molecules. We demonstrate that these narrow and intense resonances produced by the nanoparticle lattices allow for Raman transition specific enhancements. The system allows for independent tuning of both resonance conditions, enabling an efficient and versatile platform for Raman studies of various molecules.