also negative) values. This result appears to hold also at frequencies that are relatively smaller than those re- quired to observe the first memory regime, namely at frequencies that are on the order of tens of MHz or less (see Fig. 4). Therefore, with appropriate control of the external circuit, at these frequencies one should at least be able to observe non-trivial changes (manifested, e.g., in fast jumps between positive and negative values) of the capacitance when the bias crosses its zero value. We thus expect that by simultaneously measuring the elec- tric charge on the external electrodes as shown in Fig. 1 (or, equivalently, the current at the electrodes) in the presence of an applied time-dependent voltage should al- low a direct verification of our predictions for both types of memory. 

Conclusions — We have shown, using molecular dy- namics simulations, that a nanopore sequencing setup acts as a memcapacitor, namely a capacitor with mem- ory [4]. The latter is due to two types of effects, and thus arises at very different frequencies of the external bias. At high frequencies the finite mobility of ions in water and hence the slow polarizability of the ionic solution give rise to one type of memory. Memcapacitive effects, however, may also occur as a result of the ion transport through the pore at very low frequencies. These pro- cesses occur internally in the system and, from the point of view of an external circuit, the whole system behaves as an unusual capacitor. These effects may potentially play a role in nanopore DNA sequencing proposals, es- pecially those based on ac-electric fields [18], as well as in other nanopore sensing applications. Moreover, the effect of the charge buildup on the nanopore surface may influence DNA translocation and its structure in proxim- ity to the pore. Finally, due to the ubiquitous nature of nanopores in biological processes, these results may be relevant to specific ion dynamics when time-dependent fields are of importance, such as in the action potential formation and propagation during neuronal activity. We thus hope this work will motivate studies in this direc- tion. 

We thank Heiko Appel for useful discussions. Finan- cial support from the NIH-National Human Genome Re- search Institute is gratefully acknowledged. 

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