Chemical Characterization of DNA-Immobilized InAs Surfaces Using X-ray Photoelectron Spectroscopy and Near-Edge X-ray Absorption Fine Structure

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• 作者：EunKyung Cho ; April Brown ; Thomas F. Kuech
• 刊名：Langmuir
• 出版年：2012
• 出版时间：August 14, 2012
• 年：2012
• 卷：28
• 期：32
• 页码：11890-11898
• 全文大小：386K
• 年卷期：v.28,no.32(August 14, 2012)
• ISSN：1520-5827

文摘

Single-stranded DNA immobilized on an III鈥揤 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 NH₄OH- 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鈥揝 and As鈥揝 are present on the surface after DNA functionalization. The amount of In鈥揝 and As鈥揝 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.