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Scheme of the cigar-shaped nanopore functionalized with amino acid lysine chains (estimated pore opening radius 55 nm) 10 and schematic I-V curves for different pH symmetrical configurations in the left (L) and right (R) external solutions (top). The isoelectric point (pI = 5)| |acidic (pH = 2.5), pI| |basic (pH = 10.5), and basic| |acidic asymmetrical configurations are also shown (bottom). The cartoons show the distribution of fixed charges in the pore tips of the nanofluidic diode for the different pH values.
The nanopore experimental conductances 10 obtained with a 0.1 M KCl aqueous solution show a multilevel response that can be tuned by the pH values. The sign of the voltage gives additional functionalities: the pH dependence obtained for V < 0 (top) can be reversed with respect to the case V > 0 (bottom) because of the electrical rectification. The absolute value and direction of the current can be adjusted externally by the sign of the pH difference and voltage.
The complete library of logic functions realized on the basis of the experimental results for the conductance of Fig. 2 by combining the chemical (solution pH) and electrical (voltage V) inputs indicated in the axis. Logic values “0” and “1” are assigned to the lower and higher pH values used in each case (the intermediate pH value allows for increasing the pore functionality). Logic values “0” and “1” correspond to V < 0 and V > 0. The low (logic “0”) and high (logic “1”) conductance values are the outputs. All logic functions are obtained with a single reconfigurable nanopore.
A reversible logic function (Feynman gate) based on two nanopores implementing the YES and XOR functions (left). An arithmetic function (half-subtractor) with two nanopores implementing the XOR function (pHL = 5) as the difference output and the INH function (pHL = 10.5) as the borrow output (right). The basic logic functions are those of Fig. 3 operating under the common inputs pHR and V.
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