We study the immobilization of single-stranded DNA (ssDNA) probe on indium arsenide (InAs) surface and its characterization for diagnostic application. In contrast to other semiconductors, the Fermi level in InAs is typically pinned above the conduction band minimum, resulting two-dimensional electron gas (2DEG) located immediately below the surface. The InAs based system forms the basis of a DNA sensing platform because hybridization of complimentary DNA sequence with the immobilized DNA probes on InAs surface causes the conductivity changes due to negativity charges on the phosphorus backbone of DNA sequences. The DNA immobilization was done using weakly basic solution and characterized by X-ray photoelectron spectroscopy (XPS) and hall measurement. The DNA probe is modified with thiol for 5’ end to anchor the DNA probes on InAs surface and fluoro adenosine for 3’ end to reveal the existence of DNA on the InAs surface. The XPS spectrum of F 1s and N 1s peaks verify that the DNA is successfully attached on InAs surfaces. The As 3d peak shows that there are considerable amount of As-S observed with no As-Ox after exposing the basic DNA solution. In contrast, In-S is not found in the In 3d core-level. The XPS data suggest that the DNA probes are attached to the InAs surface exclusively via thiolate bonds to As atoms and the DNA functionalization effectively removes InAs oxide as well. This result is not consistent with what has been observed on InAs (100) surfaces, where the thiolate bond is predominantly anchored to Indium atoms. For example, it has been shown a predominance of In-S bonds of alkanethiols and thioacetamide self-assembled monolayer (SAM) on InAs [1, 2]. However, the bonding chemistry of thiolate to III-V surface has been of great debate in literature [3]. The predominance of As-S bonds has been shown with octadecanethiol SAM on GaAs (100) surfaces driven by kinetic competitions [3] even though Ga-S bonds are energetically more favorable than As-S bonds [4]. In addition, the sheet resistivity of initial InAs surface and DNA immobilized surface is measured, and the response of a DNA functionalized InAs surface with complimentary DNA sequence is monitored.

 

[1] D. Y. Petrovykh et al., Surf. Interface Anal. 2005, 37, 989-997.

[2] D. Y. Petrovykh et al., Langmuir 2009, 25, 12185-12194.

[3] C. L. McGuiness et al., J. Phys. Chem. C 2007, 111, 4226-4234.

[4] T. Scimeca et al., Phys. Rev. B 1991, 44, 12927-12932.