Aptamer-based biosensors for protein biomarkers

The technique of “systematic evolution of ligands by exponential enrichment” has transformed biorecognition to encompass nucleic acids in addition to antibodies. Aptamers are DNA or RNA strands that have been selected through in vitro selection to bind with affinity to analytes of choice. In this thesis, the voltammetric aptamer-based detection of lysozyme was first explored based on charge density changes on aptamer-modified electrodes upon analyte binding. Different optical and electrochemical methods were then tested for the detection of MUC1, a glycoprotein overexpressed in elevated concentrations in the serum of patients with epithelial adenocarcinomas. Optical biosensors for MUC1 had quantum dot-based fluorescence readout. Electrochemical methods were based on either direct attachment of methylene blue (MB), or adding free MB molecules to aptamer strands. To improve the sensitivity, a biochemical assay was explored featuring the fusion of anti-thrombin and anti-MUC1 aptamers via the MUC1-dependent allosteric upregulation of the proteolytic activity of thrombin.