Tip-enhanced Raman spectroscopy: plasmid-free vs. plasmid-embedded DNA.

Tip-enhanced Raman spectroscopy (TERS) provides greatly enhanced Raman signals along with ultra-high lateral spatial resolutions and has been demonstrated to be a technique of choice to study a variety of biochemical specimens such as DNA and RNA at the single chain level. However, the sensitivity of TERS to demonstrate the influence of the nanoscale environment on DNA properties has not been investigated. Herein, we used a gap-mode TERS as an ultra-sensitive label-free technique to investigate the influence of the local plasmid on the DNA properties of a ß2-adrenergic receptor (ß2AR). Remarkable lateral spatial resolutions down to 8 nm were also acquired for the collected Raman signals under ambient conditions. This approach offers not only a tool to examine the influence of the local nanoscale environment surrounding the DNA structure, but also the localization of the majority of nucleic acid base(s) present in selected regions on the DNA strand.

Tip-enhanced Raman spectroscopy of graphene-like and graphitic platelets on ultraflat gold nanoplates.

In this study, tip-enhanced Raman spectroscopy (TERS) is used to characterize graphene-like and graphitic platelets composed of a few layers of graphene. Specifically, gap-mode TERS geometry provides a larger enhancement of the local electromagnetic field at the junction formed by a gold sharp tip and a gold substrate. Graphene-like platelets are deposited onto ultra-flat thin gold nanoplates using a surfactant-assisted method. Au-coated atomic force microscopy (AFM) tips are used to probe specific substrate regions coated by the platelets. TERS spectra are collected on distinctive points on the graphene-like layers and surrounding substrate using radially or linearly polarized light, with an excitation wavelength of 632.8 nm. The position, width and intensity of G, D, and 2D Raman-active modes of graphene are discussed as a function of the incident light polarization and for distinct positions on the graphene layer. We report here on the nature of the collected TERS spectra focusing in particular on the edges of the graphene platelets.