AVS 53rd International Symposium
    Biomaterial Interfaces Tuesday Sessions
       Session BI2-TuM

Paper BI2-TuM2
Detection of Surface Potential Modulation Induced by Molecular Dipole Moment for Biosensor Platform Development on GaAs

Tuesday, November 14, 2006, 8:20 am, Room 2014

Session: Biodiagnostic Innovation
Presenter: K. Lee, Purdue University
Authors: K. Lee, Purdue University
H. Park, Purdue University
R. Jean, Purdue University
A. Yulius, Yale University
A. Ivanisevic, Purdue University
J. Woodall, Purdue University
D.B. Janes, Purdue University
Correspondent: Click to Email
Ultra-sensitive RNA detectors have been receiving enormous attentions with recent breakthroughs in finding RNA biomarkers for specific diseases. One way to detect a small quantity of specific biomarkers is to utilize well-established biological interactions. Generally, there are two key challenges when using bio-molecules as active sensing components: 1) reliable immobilization of bio-molecules and 2) an efficient sensing mechanism to convert a sensing event into a quantifiable signal. In this study, 1-octadecanethiol (ODT) and TAT peptides are self-assembled onto pre-fabricated GaAs-based sensor platforms, and conductivity modulation due to surface potential changes of ODT- or peptide-modified devices will be investigated. The TAT peptides used in this experiment are known to retain their recognition properties with TAR RNA after being attached on a GaAs surface. The sensor layer structure, which consists of a undoped low-temperature grown GaAs cap (3 nm), a 1e20 cm@super -3@ n-GaAs cap (10 nm), a 5e17 cm@super -3@ n-GaAs channel (50 nm), and a 5e16 cm@super -3@ p-GaAs base (100 nm) from the top, was grown by MBE on semi-insulating GaAs. The first two layers are added to achieve non-alloyed ohmic contacts with low specific contact resistivity. Deposition of Au/Ti injector/collector contacts completes the device fabrication, and the I-V curve displays ohmic characteristics with high current density. Subsequent wet-etching of the top cap layer resulted in ~20x decrease in conductivity, which is explained by surface Fermi level pinning of air-exposed GaAs. ODT-modification increased conductivity by ~30%, whereas no significant change was observed with peptide-modification, which could be attributed to either passivation or molecular dipole effect. The dip-pen nanolithography technique is being investigated to increase the surface coverage of sensing molecules on active device regions, and studies on reactivity of modified devices to TAR RNA is still in progress.