λ-DNA through Porous Materials—Surface-Enhanced Raman Scattering in a Simple Plasmonic Nanopore

Abstract

Engineered electromagnetic fields in plasmonic nanopores enable enhanced optical detection and their use in single molecule sequencing. Here, a plasmonic nanopore prepared in a thick nanoporous film is used to investigate the interaction between the metal and a long-chain double strand DNA molecule. We discuss how the matrix of nanoporous metal can interact with the molecule thanks to: i) transient aspecific interactions between the porous surface and DNA and ii) optical forces exerted by the localized field in a metallic nanostructure. A duration of interaction up to tens of milliseconds enables to collect high signal-to-noise Raman vibrations allowing an easy label-free reading of information from the DNA molecule. Moreover, in order to further increase the event of detection rate, we tested a polymeric porous hydrogel placed beneath the solid-state membrane. This approach enables a slowdown of the molecule diffusion, thus increasing the number of detected interactions by a factor of about 20.