Abstract
Calf thymus DNA adsorbed on a rough gold substrate or on an atomically smooth gold (111) surface has been investigated by collecting its unique Raman fingerprints using either surface-enhanced Raman scattering (SERS) or tip-enhanced Raman scattering (TERS). A monolayer coverage of DNA strands adsorbed at both the irregular rough edges of evaporated gold grids and at gold nanoparticles is detected by SERS. Highly improved sensitivity down to single DNA strand spectroscopic determination is accomplished by TERS providing an enhancement factor of at least 1400. Based on our experimental results, we propose that TERS is a promising technique to study the DNA–drug molecule interaction on the level of a single DNA strand.
Highlights
Comprehension of biomolecular interaction is crucial for the development and improvement of drugs [10]
The edges of the gold appear bright due to the random formation of gold clusters, some of which are resonantly excited by the 632.8 nm helium-neon laser
The bands can be assigned to literature values: among others there is the typical adenine band at 735 cm−1, the O–P–O vibrational stretching around 800 cm−1, the PO2− band at 1100 cm−1 and at 1246 cm−1 a band assigned to both adenine and cytosine
Summary
Comprehension of biomolecular interaction is crucial for the development and improvement of drugs [10]. TERS [1] is a fairly new spectroscopic technique It makes use of the same fundamental principle of LSP excitation as SERS does; the geometry is turned upside down: Instead of providing a rough substrate below the molecules, the plasmonic mode is excited in a custom shaped noble metal tip which approaches the molecules from above. This tip is the crucial element that turns TERS into a highly versatile combination of Raman spectroscopy and topographical scanning probe microscopy. We will show strongly enhanced TERS spectra of DNA strands adsorbed on an atomically flat gold (111) crystal and discuss the enhancement factor obtained
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