Submitted to the Department of Chemical Engineering.
Thesis (Ph.D.)--Stanford University, 2014.
Organic field-effect transistors (OFETs) are unique platforms for the detection of chemical and biomolecular species. However, in order to define sensitivity for a particular molecule of interest, integration of a receptor group into the device's architecture is necessary. Unfortunately, the direct chemical modification of the organic semiconductor to incorporate specific recognition sites has been demonstrated to diminish the electronic performance of OFETs. To address this issue, we developed a novel OFET sensor platform capable of stable operation in an aqueous environment that permits the selective detection of user-defined analytes. Sensitivity for the targeted analyte is conferred by virtue of an ordered array of gold nanoparticles (AuNPs) decorating the OFET's surface that is deposited through a block-copolymer templating process. This highly versatile platform is compatible with a large, previously existing library of thiolated receptor groups that can functionalize the AuNPs through the well-known gold-thiol (Au--S) linkage. As a proof-of-concept demonstration of chemical detection, we used this platform to demonstrate the highly selective detection of toxic mercury(II) ion in water. We then expanded the sensing capabilities of the AuNP-decorated OFET platform for biodetection applications by demonstrating the selective and highly sensitive detection of thrombin. Using thrombin detection as a model system, we built a comprehensive picture of biodetection with OFETs by performing a thorough and empirical investigation of the effects of varying the pH of the buffer, the average center-to-center distance between the receptor sites, and the ionic strength of the buffer. During this comprehensive investigation, we elucidated that electrostatic screening, caused by operation of the OFET sensors in highly ionic media (mimicking the physiological environment), restricted our ability to observe charge-based detection events. We therefore adapted a traditional enzyme-linked immunosorbent assay (ELISA) to be compatible with electronic readout using an OFET. Using this assay, we demonstrated the multiplexed detection of a panel of three biomarkers in serum at clinically relevant concentrations in order to build a predictive screening tool for preeclampsia, a potentially fatal pregnancy disorder. To take advantage of the full potential offered by these biosensors, we fabricated an inkjet printed OFET sensor capable of detecting the preeclampsia biomarkers in undiluted buffer, revealing that inexpensive, potentially disposable OFET biosensors for point-of-care applications could be a possibility in the near future.