DNA hybridization biosensors based on long-range electron transfer

摘要

For the successful detection of selected DNA sequences or mutated genes associated with human disease, there are several challenges that the current research aims to overcome - higher sensitivity, greater selectivity and rapid assaying time. An electrochemical device using redox-active intercalators to transduce DNA hybridization via long-range electron transfer is presented in this thesis which aims to address the above challenges. The DNA recognition interface is composed of thiolated single-stranded DNA (ss-DNA) and a diluent component both of which are self-assembled onto a gold electrode. This project seeks to advance fundamental insight into issues that impact the structure and behavior of surface-immobilized DNA towards hybridization with target complementary ss-DNA. After the optimal conditions have been identified for the construction of a reproducible DNA recognition layer, a stepwise detection scheme using an anionic intercalator, as the redox molecule is introduced for the DNA transduction. The stepwise detection relies on the absence of any electrochemistry prior to DNA hybridization. Upon hybridization, the perfectly stacked DNA is capable of mediating the electrochemical oxidation and reduction of intercalated species and hence voltammetric peaks become evident. Although excellent selectivity towards single-base mismatch detection is achieved, this detection scheme has a high detection limit and slow assaying time. However, this is overcome by a novel in situ approach where the electrochemistry is performed in the presence of both complementary target DNA and intercalator.The effect of different DNA recognition interfaces on hybridization is also investigated using electrochemical and gravimetric techniques where the hybridizationefficiency, kinetics and affinity constant of hybridization were assessed. These measurements showed that the length of the diluent layer has a large impact on the time taken to form a perfect duplex but no impact on the initial recognition of the target DNA by the immobilized probe DNA.Fundamental aspects of the DNA technology towards assaying small molecules which have binding affinity to DNA are also investigated. The probe ss-DNA sensing interface was found to be highly sensitive towards detection of Cd2+. The long-range electron transfer approach was also utilized in gaining more insight knowledge of the interaction of cisplatin, an anti-cancer drug with the DNA.