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This thesis describes a novel approach to the fabrication and characterisation of metallic nanopores and their application for the detection of single DNA molecules. Metallic nanopores with apparent diameters below 20 nm are produced using electrochemical deposition and real-time ionic current feedback. Beginning with large nanopores (diameter 100-200 nm) milled into gold silicon nitride membranes using a focused ion beam, platinum metal is electrodeposited onto the gold surface, thus reducing the effective pore diameter. By simultaneously observing the ion current feedback, the shrinking of the nanopore can be monitored and terminated at any pre-defined value of the pore conductance in a precisely controlled and reproducible way. The ion transport properties of the metallic nanopore system are investigated by characterising the pore conductance at varying potentials across the nanopore and concentrations of electrolyte. The results are compared to conventional bare silicon nitride nanopore systems. Chemical modification at the nanopore surface is also studied using thiolisation to reduce the capacitive charging effects observed with metallic nanopores. Further to this, impedance measurements are carried out to study the resistive behaviour exhibited in these systems. An equivalent circuit model is proposed to validate the results obtained from the experimental studies. To evaluate the suitability of these nanopores for applications in single-molecule biosensing, translocation experiments using λ-DNA are performed. DNA molecules are electrokinetically driven through the nanopore under an applied electric field, hence as the DNA translocates through the pore, current blockade events are detected. Each event is the result of a single molecular interaction of DNA with the nanopore and is characterised by its dwell time and amplitude. Characterisation studies and noise analysis towards the applicability of metallic nanopores as single molecule detectors are also studied and compared to current bare silicon nitride pore systems. |
