Electrochemical-based biosensors offer relative facile fabrication procedures, label free operation and rapid in field sensing and may hold a key to point-of-care diagnosis. Interdigitated electrodes (IDE) are often employed as the main sensing platform, and they consist of alternating ‘finger-like’ electrodes that are electrically connected with a width and pitch typically in the range of 5 – 25 m. Through the sensing modality of electrochemical impedance spectroscopy (EIS), it reveals small variations in resistance/capacitance due to the binding of biological recognition agents and biological targets. This dissertation documents the innovative research in electrochemical biomarker detection with interdigitated electrode arrays that I have been working on throughout my PhD training at Iowa State University.

A label-free EIS aptasensor for rapid detection of interferon-gamma (IFN-γ) was fabricated by immobilizing a RNA aptamer capture probe, selective to IFN-γ, on a gold IDE. The Au IDE functionalized with a surface ternary monolayer was able to measure IFN-γ in actual fetal bovine serum with a linear sensing range from 22.22 pM to 0.11 nM (1-5 ng/ml) and a detection limit of 11.56 pM. The ability to rapidly sense IFN-γ within this sensing range makes the developed electrochemical platform conducive towards in-field disease detection of a variety of diseases including paratuberculosis (i.e., Johne’s Disease). Furthermore, experimental results were numerically validated with an analytical model that elucidated the effects of the sensing process and the influence of the immobilized ternary monolayer on signal output.

Carbon allotropes have revolutionized electrical, optical, thermal, mechanical., chemical and sensing phenomena., and the application of which into electrochemical-based biosensing demonstrates significantly increased sensitivity. Here, the first use of vertically aligned carbon nanotube array (VANTA) grown via chemical vapor deposition in a 2D IDE footprint with a high height-to-width aspect ratio (3:1 or 75:25 à ¯à ¿à ½m) is presented. They were utilized in two biosensing projects in this dissertation. The VANTA-IDE was first functionalized with an antibody (Ab) specific to the human cancerous inhibitor PP2A (CIP2A)—a salivary oncoprotein that is associated with a variety of malignancies such as oral, breast, and multiple myeloma cancers. The resultant immunosensor is capable of detecting CIP2A label-free across a wide linear sensing range (1 –100 pg/mL) with a detection limit of 0.24 pg/mL within saliva supernatant—a range that is more sensitive than the corresponding CIP2A enzyme linked immunosorbent assay (ELISA). These results help pave the way for rapid cancer screening tests at the point-of-care (POC) such as for the early-stage diagnosis of oral cancer at a dentist’s office.

Furthermore, VANTA with increased number of fingers and surface area was also applied for the detection of IL-10 and IFN- that are early stage biomarkers for Johnne’s disease. The resulting sensing range in diluted cattle implant supernatant covered 50-1000 pg/ml for IFN- with a theoretical detection limit of 95.87 pg/ml; while for IL-10, the sensing range included 0.1 to 30 pg/ml and a detection limit of 0.077 pg/ml. In addition, this biosensor presented convincing stability in different biological environment, which demonstrates the potential in future rapid (<35 minutes) and POC application for the diagnosis of Johnne’s disease without the need of pre-labeling or pre-concentration.