Relatively recently it has been demonstrated that nanopores can be used for label-free detection of single biomolecules. Conceptually this is similar to a classical Coulter counter, where the passage of a bacterial cell through a micropore causes a temporary partial blockage of the pore, which is detected as a short-lived decrease in electrical current (~aqueous electrolyte) flowing through the micropore, with the frequency of current block events ('pulses') correlating to the bacterium concentration. In this project, the biological nanopore a-hemolysin is used for the detection of nucleic acid biomarkers by resistive pulse sensing. The nanopore is incorporated in aperture-suspended lipid bilayers and nucleic acids are made to traverse the pore by application of a transmembrane potential. Probe DNA is added to the sample to create probe-target duplexes that cause a deeper and longer-lifetime current block than non-complexed non-target molecules, enabling specific single-molecule detection of the biomarker in a complex sample.