Chemical and Electronic Properties of DNA-immobilized Indium Arsenide for Biosensor applications

Single-stranded DNA immobilized on an III–V semiconductor has potential as 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 and electronic properties of DNA-immobilized InAs surfaces were determined through high-resolution X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure (NEXAFS), and ultraviolet photoelectron spectroscopy (UPS). Prior to DNA functionalization, sulfur passivation and HF- and NH4OH- based aqueous etches were used to alter the surface chemistry of the InAs surface. The initial chemical states of the surface resulting from these chemical treatments were characterized prior to functionalization. F-tagged thiolated single-strand 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 NaCl in the functionalization solution substantially increased the density of immobilized DNA on the InAs surface. The interfacial chemistry was studied using an analysis of the As 3 d and In 3d spectra indicating 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 NaCl 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. The electronic properties of DNA-immobilized InAs surfaces such as band bending and work function were also studied using XPS and UPS. The DNA functionalization method determines not only the interface chemistry, but also a surface state density and surface band bending. The surface potential influenced by the density of the immobilized-DNA. The influence of the DNA attachment on the chemical and electronic structure of InAs surfaces provides insight into how the chemical and electronic properties of the InAs surfaces modulated with the DNA immobilization showing the potential use of InAs substrate for biosensor applications.