UC Riverside

Modern diagnostics strive to be accurate, fast, and inexpensive and aim to properly identify the presence of a disease, infection, or illness. Early diagnosis is key to earlier therapeutic intervention, which can improve prognosis and reduce mortality. The challenge with many diseases is that detectability of the disease scales with disease progression. Modern diagnostic techniques exhibit a specific threshold to be surpassed for accurate, reliable tests to be performed. Often, symptoms do not appear until disease progression has reached a significant stage. Since single molecule sensors, e.g., nanopores, can sense biomolecules at extremely low concentrations, they have the potential to become clinically relevant in many of today’s medical settings. The nanopore-detected current measurements can be used to identify disease biomarkers, determine the presence of pathogens, and monitor the efficacy of drugs. Specifically, solid-state nanopores offer several advantages over traditional diagnostic tools such as speed, accuracy, and cost-effectiveness. As a result, they have become an increasingly popular tool in the diagnostic field and are expected to play a critical role in the development of personalized medicine. In the first chapter, we investigate the origins of current enhancing events under low ionic strength conditions and propose an alternative theory for the observation of conductive events. Utilizing electroosmotic flow, we show that a flux imbalance in favor of cations allows for detection of DNA and protein to be divergent. In the second chapter, we expand upon low ionic strength conditions to high and asymmetric electrolyte conditions to examine differences in signal-to-noise ratio, molecule dwell time, and configuration. In asymmetric salt, we show the ability of detecting differences in DNA configuration as well as protein alone and bound to DNA complexes, superior to that of the gold standard sensing conditions. Following that, several denaturing agents are integrated into the nanopore system, serving to linearize and provide a uniform negative charge to both whole proteins and peptides of varying lengths. With this, a novel electrolyte sensing condition is introduced that allows for peptide length to be distinguishable by changes in the current amplitude upon molecule translocation via electrophoretic forces. Lastly, we critically analyze peptide fragments generated by protease digestion in whole blood using a portable device. The utilization of nanopores in this study goes beyond serving as only a sensing device; rather, it represents a breakthrough in the field of diagnostics, as it opens up the possibility of monitoring protease activity levels within the body.