Doctor of Philosophy (PhD)


Electrical and Computer Engineering

Document Type



The goal of this research was to develop enhanced signal detection mechanisms for immunosensing using carbon nanotubes (CNTs). The utilization of CNT labels for direct electrical measurement was implemented on lateral flow system and microfluidic integrated interdigitated array microelectrodes. These sensing mechanisms in simple and miniaturized system provided higher sensitivity and autonomous flow control for rapid detection aimed at point-of-care diagnostics. Specific functionalization protocols were carried out to chemically modify the surface of the CNTs for uniform dispersion and antibody conjugation in aqueous solution. Surfactant assisted dispersion of the CNTs was studied using PVP and PEG. Covalent conjugation of antibodies on the carboxyl groups of the CNTs was accomplished using EDC/Sulfo-NHS coupling chemistry. The adsorption of surfactant and antibodies were manipulated in order to optimize immunoassay detection capability based on electrical measurements. Following surface functionalization methods, CNTs as a sensing label were employed on a lateral flow system. Competitive and sandwich immunoassay formats were demonstrated based on antibody and antigen binding. The lateral flow system was used for immobilization of capture molecules and passive sample transport by capillary action. CNTs conjugated to antibodies formed conductive network at the capture zone providing a visual indication corresponding to the amount of binding. Most importantly, significant change in electrical conductance was measured for varying low antigen concentrations, detecting anti-human Immunoglobulin G concentration below 1 ng/ml. Research was also conducted to obtain on-chip immunoassay detection using CNT labels. An IDA microelectrode was used as a binding surface and integrated within a PDMS microfluidic system. The sample and reagents were delivered to the sensing area through a microchannel. The capture of target analyte was indicated by the conjugated CNTs that formed a conducting matrix across the IDA. The detection was based on the selective binding between HSA and anti-HSA, where the conductimetric signal of the binding reaction was monitored through the IDA. The developed miniaturized system provided simple and sensitive immunosensing with detection capability below 1 ng/ml concentration using only 5 ìl of sample volume. Simulation was performed in order to understand the influence of the parameters in the microfluidic detection system.



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