Detection of DNA Bases and Oligonucleotides in Plasmonic Nanoslits Using Fluidic SERS

Raman spectroscopy is a widely used vibrational spectroscopic technique to identify and study chemical compounds. The signal can be strongly enhanced in the presence of metal nanostructures resulting in so-called surface-enhanced Raman scattering (SERS). Here, we describe the use of SERS for the molecular characterization of DNA molecules inside a nanoslit across a thin, metal-coated membrane. Nanoslits with two different dimensions were examined. More specifically, relatively long nanoslits (over 700 nm) with a strong, broad plasmonic coupling mode as well as short nanoslits (100 nm) with a strong Fabry-Pérot resonance for a specific wavelength. Both geometries were fabricated using standard lithographic processes and were coated with gold to enable the excitation of surface plasmons, needed for SERS. Using electrophoresis to actuate the analytes across the nanoslits, we were able to record SERS spectra of a typical DNA base, namely adenine. Similarly, short DNA oligonucleotides were also successfully detected. It is expected that the nanoslit-based fluidic SERS will become a promising real-time detection tool, especially for DNA.