Angle-Resolved XPS Analysis and Characterization of Monolayer and Multilayer Silane Films for DNA Coupling to Silica

Abstract

We measure silane density and Sulfo-EMCS cross-linker coupling efficiency on aminosilane films by high-resolution X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) measurements. We then characterize DNA immobilization and hybridization on these films by (32)P-radiometry. We find that the silane film structure controls the efficiency of the subsequent steps toward DNA hybridization. A self-limited silane monolayer produced from 3-aminopropyldimethylethoxysilane (APDMES) provides a silane surface density of ~3 nm(-2). Thin (1 h deposition) and thick (19 h deposition) multilayer films are generated from 3-aminopropyltriethoxysilane (APTES), resulting in surfaces with increased roughness compared to the APDMES monolayer. Increased silane surface density is estimated for the 19 h APTES film, due to a ∼32% increase in surface area compared to the APDMES monolayer. High cross-linker coupling efficiencies are measured for all three silane films. DNA immobilization densities are similar for the APDMES monolayer and 1 h APTES. However, the DNA immobilization density is double for the 19 h APTES, suggesting that increased surface area allows for a higher probe attachment. The APDMES monolayer has the lowest DNA target density and hybridization efficiency. This is attributed to the steric hindrance as the random packing limit is approached for DNA double helices (dsDNA, diameter ≥ 2 nm) on a plane. The heterogeneity and roughness of the APTES films reduce this steric hindrance and allow for tighter packing of DNA double helices, resulting in higher hybridization densities and efficiencies. The low steric hindrance of the thin, one to two layer APTES film provides the highest hybridization efficiency of nearly 88%, with 0.21 dsDNA/nm(2). The XPS data also reveal water on the cross-linker-treated surface that is implicated in device aging.

Scanning Kelvin probe blister studies of the delamination of epoxy films on organosilane modified ZnMgAl alloy coated steel

“…The N1s spectrum could be described by two components at 400.8 and 399.6 eV. The component at 399.0 eV is within the range of binding energies reported for the amine group of the aminosilane . The higher energy contribution might be assigned to amino groups which are coordinated to the metal ions in the surface or to protonated amino groups .…”

Multimode Surface Functional Group Determination: Combining Steady-State and Time-Resolved Fluorescence with X-ray Photoelectron Spectroscopy and Absorption Measurements for Absolute Quantification

“…1,2 Whereas for the latter NMR, IR, conductometry or zeta-potential measurements can be employed for direct surface group analysis, 3,4 macroscopically flat substrates are significantly more demanding to analyze due to their low surface-tovolume ratio and often require employment of a specific chemical label that can be interrogated selectively and sensitively. 5-7 Analysis of such substrates is mainly performed with sophisticated surface analytical techniques like X-ray photoelectron spectroscopy (XPS) [8][9][10][11][12][13] or time-offlight secondary ion mass spectrometry (ToF-SIMS). 14,15 Obtaining quantitative information on surface functional groups, however, is rather challenging as these techniques mostly produce relative results.…”

Synthesis and structure determination of calcium silicate‐cellulose nanograss biocomposite

“…These binding energies are sensitive to the number of O atoms bonded to Si. The binding energies at around ~103.49 eV for W1 (Figure A) and 103.5 eV for W2 (Figure A) are assigned to the Si(‐O) 4 component peak . For the W1 sample, the additional peak at 102.16 eV occurs due to the presence of the cristobalite phase(SiO 2 ) .…”