text: An alternative to the ensemble-based method described above is the voltage-clamp experiment.  In a voltage-clamp experiment, two compartments of electrolyte are divided by an aperture, usually between 5-250 micrometres in diameter.  A lipid bilayer is painted across this aperture, thus electrically separating the compartments; the molecular nature can be ascertained by measuring its capacitance.
  Upon the addition of an (ideal) ion channel, a defined path between the two compartments is formed.  Through this pore, ions flow down the potential and electrochemical gradient rapidly (>10/second), the maximum flux limited by the geometry and dimensions of the pore.   At some later instant the pore may close or collapse, whereupon the current returns to zero.  This open-state current, originating and amplified from a single-molecule event, is typically on the order of pA to nA, with time-resolution of approx. millisecond.  Ideal or close-to-ideal events is termed "square-tops" in the literature, and have been considered as signature for a channel-based mechanism.
  It is notable that the events observed at this scale are truly stochastic - that is, they are the result of random molecular collision and conformation changes.  As the membrane area is much larger than that of a pore, multiple copies may open and close independently of one another, giving rise to the staircase like appearance (Panel C in figure); these ideal events are often modelled as Markov processes.
  By using the activity grid notation, synthetic ion channels studied with the voltage-clamp method during the period 1982-2010 have been critically reviewed.  While the ideal traces are most frequently analyzed and reported in the literature, many records are decidedly non-ideal, with a subset was shown to be fractal.  Developing methods for analyzing these non-ideal traces and clarifying their relationship to transport mechanism is an area of contemporary research.