| Solid-state nanopores are routinely used as single-molecule detectors and show considerable promise as the framework for rapid DNA sequencing technology, but their performance is limited by conductance fluctuations. In this work, experimental studies with solid-state nanopores identify two major sources of conductance fluctuations: excess white noise in the 0.1--10 kHz frequency band used for single-molecule detection, and 1/f noise.Excess white noise is found to have two basic mechanisms. Fluctuations in the number of mobile ions in the pore arise from the diffusive motion of ions. These ionic number fluctuations are a fundamental limit to the equilibrium conductance noise. Protonation reactions of the silanol groups on the nanopore surface give rise to surface charge fluctuations , which can be measured to determine the protonation reaction rates.Two distinct mechanisms of 1/f noise are also present. The first type of 1/f noise, associated with "noisy" pores, may be the result of uncharged contaminants in the nanopore. The experiments in this thesis cannot distinguish among nanobubbles, phonon scattering, and charge traps as possible sources of the second type of 1/f noise.Finally, the implications of the various conductance noise sources for single-molecule detection are discussed. Detection of DNA molecules by ionic current measurements is straightforward, but angstrom-scale variations in a single molecule are indistinguishable from the conductance noise for all feasible pore geometries. |
