Electrical detection of the biological interaction of a charged peptide via gallium arsenide junction-field-effect transistors

Kangho Lee, Purdue University
Pradeep R. Nair, Birck Nanotechnology Center, School of Electrical and Computer Engineering, Purdue University
Muhammad A. Alam, Birck Nanotechnology Center, School of Electrical and Computer Engineering, Purdue University
David B. Janes, Purdue University
Heeyeon P. Wampler, Purdue University - Main Campus
Dmitry Zemlyanov, Birck Nanotechnology Center, Purdue University
Albena Ivanisevic, Birck Nanotechnology Center, Purdue University

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GaAs junction-field-effect transistors (JFETs) are utilized to achieve label-free detection of biological interaction between a probe transactivating transcriptional activator (TAT) peptide and the target trans-activation-responsive (TAR) RNA. The TAT peptide is a short sequence derived from the human immunodeficiency virus-type 1 TAT protein. The GaAs JFETs are modified with a mixed adlayer of 1-octadecanethiol (ODT) and TAT peptide, with the ODT passivating the GaAs surface from polar ions in physiological solutions and the TAT peptide providing selective binding sites for TAR RNA. The devices modified with the mixed adlayer exhibit a negative pinch-off voltage (V-P) shift, which is attributed to the fixed positive charges from the arginine-rich regions in the TAT peptide. Immersing the modified devices into a TAR RNA solution results in a large positive V-P shift (>1 V) and a steeper subthreshold slope (similar to 80 mV/decade), whereas "dummy" RNA induced a small positive V-P shift (similar to 0.3 V) without a significant change in subthreshold slopes (similar to 330 mV/decade). The observed modulation of device characteristics is analyzed with analytical modeling and two-dimensional numerical device simulations to investigate the electronic interactions between the GaAs JFETs and biological molecules.