Optimized Assembly and Utilization of Functional Materials Towards Designing Stable and Reliable Affinity Based Biosensing Platforms

A wide variety of biomarkers are found in human sweat such as electrolytes, metabolites, small molecules and proteins. This renders human sweat to be highly suitable for non-invasive, lancet-free diagnosis of biomarkers. For reliable detection, it is essential to detect biomarkers in their native state without adversely affecting their characteristics. Affinity based non-Faradaic electrochemical detection is a label-free technique which fulfills this objective. The purpose of this dissertation is to develop an affinity based wearable diagnostic platform for detection of biomarkers present in human sweat. This work focuses on optimal utilization of functional materials to develop wearable diagnostic platforms. Firstly, nanotextured zinc oxide thin film based sensors were designed and fabricated to operate with small volumes (~5 µL) of sweat on a flexible nanoporous polyamide membrane. Nanoconfinement and nanotexturing contributed in achieving amplified response leading to an ultrasensitive detection even in small volumes of sweat. Secondly, interactions between biomolecular solutions and a zinc oxide semiconductor surface were studied using electrochemical transduction to develop robust methodologies for immunoassay immobilization for detection of biomarkers. Capacitive charge modulations at the zinc oxide/biomolecular solutions interface were found to be proportional to the concentrations of biomarkers tested on the functionalized sensor surface. Lastly, room temperature ionic liquids were tested to enhance the stability of immunoassay for sustainable sensor performance. The developed sensor prototype demonstrated sensitive and stable non-Faradaic electrochemical detection of cortisol, glucose and interleukin-6 from human sweat. Thus, a combinatorial strategy of using zinc oxide as a functional material for non-Faradaic electrochemical detection, employing nanoporous flexible substrate to enable small volume based wearable biosensing and utilizing room temperature ionic liquid to sustain stability of affinity based immunoassay is a promising approach for robust wearable biosensing.