Interaction of Self-Assembled Monolayers of DNA with Electrons: HREELS and XPS Studies

Abstract

We present results from high-resolution electron energy loss spectroscopy (HREELS) and XPS studies of self-assembled monolayers of DNA. The monolayers are well-organized and display sharp vibrational peaks in the HREEL spectra. The electrons interact mainly with the backbone of the DNA. The XPS results indicate that, in most of the samples studied, the phosphates on the DNA are not charged.

X-ray Photoelectron Spectroscopy Analysis of Gold Surfaces after Removal of Thiolated DNA Oligomers by Ultraviolet/Ozone Treatment

“…For the freshly deposited 5S-ds DNA film studied in Fig. 2, the maximum photoelectron yield of the N 1s manifold is observed at a binding energy (BE) of 399 eV, which, considering the possible multiple sites for nitrogen atoms within long DNA samples, is consistent with earlier XPS measurements of DNA SAM films (e.g., [17,18,21,30]). It is apparent from Fig.…”

Fabrication of patterned surfaces by photolithographic exposure of DNA hairpins carrying a novel photolabile group

“…Dynamic contact angle measurements of ÀSCN terminated surfaces revealed an increase in contact angle upon formation of ÀSCN terminated surfaces, which is in good agreement with previously seen behaviour (Table 1) [30]. Ellipsometry of the ÀSCN terminated surfaces revealed a thickness of 1.2 nm AE 0.2 nm, which is comparable to the estimated thickness of the molecule (1.6 nm, Chem3D Software).…”

“…The APTMS SAM (-NH 2 , Scheme 1, Step 1) surfaces were then treated with PDITC to form isothiocyanate terminated surfaces (-SCN, Scheme 1, Step 2) [30][31][32]. These surfaces were then coupled to the -NH 2 terminated photolabile hairpin oligonucleotide A to form the -OLIGO terminated surfaces (Scheme 1, Step 3).…”

“…The peak at approximately 400 eV is thought to originate from the NH 2 species of the APTMS and the second peak at approximately 401.5 eV is thought to originate from the protonated form of the APTMS SAM (NH þ 3 ) [30]. The two peaks are approximately in a ratio 1 : 1, indicating a 50/50 split in terms of both at the surface.…”

“…It is believed however that such spacing of the PDITC moieties may be advantageous, as there will be a suitable spacing achieved for the oligonucleotide grafting. Examination of the addition of the oligonucleotide to the silicon surfaces was inconclusive due to broadening of the nitrogen peak, especially in the region between the NH 2 and NH þ 3 regions, consistent with the addition of multiple nitrogen species and especially (N-(C¼O)-N) from the high levels of thymine present in the oligonucleotide [30].…”