A resonant capacitive test structure for biomolecule sensing

Date of Award


Degree Name

M.S. in Electrical Engineering


Department of Electrical and Computer Engineering


Advisor: Guru Subramanyam


Detection of biomolecules in aqueous or vapor phase is a valuable metric in the assessment of health and human performance. For this purpose, resonant capacitive sensors are designed and fabricated. The sensor platform used is a resonant test structure (RTS) with a molecular recognition element (MRE) functionalized guanine dielectric layer used as the sensing layer. The sensors are designed such that the selective binding of the biomarkers of interest with the MREs is expected to cause a shift in the test structures resonant frequency, amplitude, and phase thereby indicating the biomarkers presence. This thesis covers several aspects of the design and development of these biosensors. Guanine biopolymer is characterized using capacitive test structures (CTSs) and RTSs with guanine dielectric layers. From this characterization, the dielectric constant and loss tangent of guanine are found to be 5.345± 0.294 and 0.015 ± 0.001 respectively. The resonance of the RTS with guanine dielectric layer is 3.148 ± 0.079 GHz with a notch depth of 7.472 0.330 dB. To further characterize guanine, contact angle measurements with water were performed to determine the hydrophobic/hydrophilic properties. The contact angle is 62.07 3.029 indicating the guanine thin films are slightly hydrophobic in comparison to glass (contact angle is 41.4° ± 2.72°). Additionally, a chemical functionalization method for guanine is developed. In this method, a cross-linker is simultaneously and covalently bound to the surface of the guanine and to the biomolecule thereby creating a covalent tether. Tests employing a biotin-streptavidin model indicate the chemical functionalization method is viable. In addition to the resonant capacitive sensor, two radio frequency (RF) test structures are developed: an RF bridge and a half-wavelength resonator. Both of these test structures have gaps in the transmission lines that will be bridged with MRE functionalized carbon nanotubes (CNTs). Any binding event between an analyte of interest and MRE is expected to cause a shift in the resonance of the test structures. The test structures are designed for a resonance at 8 GHz and are simulated in Applied Wave Research Design Environment (AWR) software. For the RF bridge, the simulation's resonance is at 9.2 GHz with a notch depth of 20.31 dB. The simulation of the half-wavelength resonator shows a resonance at 8 GHz with a pass band peak of 0.3395 dB. Additionally, the RF bridge test structure is fabricated. Measurements pre-CNT integration reveal a resonance at 13.23 GHz with a notch depth of 29.42 dB. The resonance of the fabricated test structures post-CNT integration have varying resonances (16.43 GHz with a notch depth of 31.2 dB for one test structure and 13.58 GHz with a notch depth of 30.1 dB for the other). The variation is due to non-uniform CNT bridges across the transmission line.


Resonance Measurement, Biochemical markers Vibration, Biosensors Design and construction, Capacitors, Electrical Engineering, Biology, Resonant capacitive sensor, resonant test structure, capacitive test structure, guanine characterization, molecular recognition element functionalization, carbon nanotube-integrated test structures, biosensors

Rights Statement

Copyright 2015, author