Electrochemical microRNA biosenosrs

To develop point of care devices for cancer by detecting blood-based biomarkers, there are several challenges that the current research aims to overcome including higher sensitivity, greater selectivity, and rapid assaying time. To achieve these goals, the results of three research chapters are presented in this PhD dissertation. The first two chapters aim to establish a detection method for microRNA while also seeks to advance fundamental insight into the impact of surface chemistry on the performance of nucleic acids biosensors. In the first chapter, the effect of interfacial design on the mismatch discrimination capability from methylene blue, as a non-covalently bound redox label, at low-density DNA films was studied. A decrease in the ability of the double helix to access the electrode surface was found to result in an improvement in the single mismatch discrimination. Although selective discrimination of the target microRNA from single base pair mismatch was achieved, the detection scheme required multi incubation and rinsing steps, which is not desirable. To address this issue, the applied sensing method in the second chapter involves the use of methylene blue covalently attached to probe nucleic acid, whose distance from the electrode surface is altered as a result of the conformational changes of probe upon hybridization. Using this method, the impact of surface chemistry of nucleic acids duplexes (the choice of probe and target being DNA or RNA) on their electrochemical properties has been investigated. It was found that DNA/RNA has a unique and highly bent conformation, compared to the well-studied DNA/DNA duplex. The optimal conditions for the construction of microRNA detection have been identified using this system. To achieve ultralow concentration detection, the third chapter reports on combining the developed detection method for microRNA in the second chapter, with the concept of using gold coated magnetic particles as dispersible electrodes. This is to address the limited mass transfer rates at the nanoscale. Using this combination, an ultrasensitive and rapid detection of microRNA, with a lowest detected concentration of 1 aM and a response time of 30 min, was achieved