Chapter 5:Electrochemical applications of nanopore systems

Nanopore sensors are a new class of single-molecule biosensors that allow for the detection of DNA, RNA, proteins, their complexes, as well as non-biological polymers, nanoparticles and small molecules. In their simplest form, such sensors feature a thin membrane that separates an electrolyte-filled cell into two compartments with one electrode each. A nanometre-scale pore connects the two parts of the cell for the transport of liquid, ions, and analyte molecules. Since the pore is so small - diameters range from 1 to about 100 nm - it typically represents the largest source of resistance in the cell (MΩ to GΩ). Application of a bias voltage between the two electrodes results in an ion current through the cell, which to a first approximation depends on the dimensions of the pore; the bias voltage applied; and the conductivity of the electrolyte. Transport of, say DNA through the pore (“translocation”), changes the pore conductance and hence the ion current - which can be detected with fast low-current detection electronics. The duration, magnitude and details of the modulation event may then be related back to the identity of the analyte molecule. For example, the longer the DNA, the longer the translocation event; the larger its magnitude, the larger the relative pore volume temporarily blocked by the DNA; the more feature-rich the current modulation, the more complex the structure of the analyte (e.g. due to specific binding of proteins to the DNA) and so forth