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Chemical characterization of DNA-immobilized InAs surfaces using X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure.

Authors
  • Cho, EunKyung1
  • Brown, April
  • Kuech, Thomas F
  • 1 Department of Chemical and Biological Engineering, University of Wisconsin-Madison, 1415 Engineering Drive, Madison, Wisconsin 53706, USA.
Type
Published Article
Journal
Langmuir
Publisher
American Chemical Society
Publication Date
Aug 14, 2012
Volume
28
Issue
32
Pages
11890–11898
Identifiers
DOI: 10.1021/la302313v
PMID: 22809291
Source
Medline
License
Unknown

Abstract

Single-stranded DNA immobilized on an III-V semiconductor is a potential high-sensitivity biosensor. The chemical and electronic changes occurring upon the binding of DNA to the InAs surface are essential to understanding the DNA-immobilization mechanism. In this work, the chemical properties of DNA-immobilized InAs surfaces were determined through high-resolution X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS). Prior to DNA functionalization, HF- and NH(4)OH- based aqueous etches were used to remove the native oxide from the InAs surface. The initial chemical state of the surface resulting from these etches were characterized prior to functionalization. F-tagged thiolated single-stranded DNA (ssDNA) was used as the probe species under two different functionalization methods. The presence of DNA immobilized on the surface was confirmed from the F 1s, N 1s, and P 2p peaks in the XPS spectra. The presence of salt had a profound effect on the density of immobilized DNA on the InAs surface. To study the interfacial chemistry, the surface was treated with thiolated ssDNA with and without the mercaptohexanol molecule. An analysis of the As 3d and In 3d spectra indicates that both In-S and As-S are present on the surface after DNA functionalization. The amount of In-S and As-S was determined by the functionalization method as well as the presence of mercaptohexanol during functionalization. The orientation of the adsorbed ssDNA is determined by polarization-dependent NEXAFS utilizing the N K-edge. The immobilized ssDNA molecule has a preferred tilt angle with respect to the substrate normal, but with a random azimuthal distribution.

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