Tip-enhanced
Raman scattering (TERS) is a promising optical and
analytical technique for chemical imaging and sensing at single molecule
resolution. In particular, TERS signals generated by a gap-mode configuration
where a silver tip is coupled with a gold substrate can resolve a
single-stranded DNA (ssDNA) molecule with a spatial resolution below
1 nm. To demonstrate the proof of subnanometer resolution, we show
direct nucleic acid sequencing using TERS of a phage ssDNA (M13mp18).
M13mp18 provides a known sequence and, through our deposition strategy,
can be stretched (uncoiled) and attached to the substrate by its phosphate
groups, while exposing its nucleobases to the tip. After deposition,
we scan the silver tip along the ssDNA and collect TERS signals with
a step of 0.5 nm, comparable to the bond length between two adjacent
DNA bases. By demonstrating the real-time profiling of a ssDNA configuration
and furthermore, with unique TERS signals of monomeric units of other
biopolymers, we anticipate that this technique can be extended to
the high-resolution imaging of various nanostructures as well as the
direct sequencing of other important biopolymers including RNA, polysaccharides,
and polypeptides.
Gold nanoplates (AuNPLs) enable the gap-mode configuration of tipenhanced Raman spectroscopy (TERS). This allows for low-concentration molecular sensing and high-resolution imaging. Compared with non-gap-mode TERS, the gap plasmon provides significantly higher enhancement factors. In addition, AuNPLs exhibit a lightning rod or edge effect, further enhancing the laser field and increasing the spectroscopic sensitivity. In this study, we investigate the relationship between the thickness of AuNPLs and the intensity of the spontaneous Raman signal produced by 4-nitrobenzenethiol, a reporter molecule used in TERS. Our experimental and theoretical results show that the intensity of TERS spectra increases with an increase in the thickness of the AuNPLs. This study of the thickness dependence of AuNPL allows us to find a configuration with maximal nanoplasmonic effects. Moreover, the electromagnetic interaction of the AuNPL with the tip, positioned near the AuNPL's edge, results in a plasmonic nanoantenna configuration for field enhancement, with important promise for future applications to nanobioimaging and biosensing.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.