Single Cigar-Shaped Nanopores Functionalized with Amphoteric Amino Acid Chains: Experimental and Theoretical Characterization

Abstract

We present an experimental and theoretical characterization of single cigar-shaped nanopores with pH-responsive carboxylic acid and lysine chains functionalized on the pore surface. The nanopore characterization includes (i) optical images of the nanostructure obtained by FESEM; (ii) different chemical procedures for the nanopore preparation (etching time and functionalizations; pH and electrolyte concentration of the external solution) allowing externally tunable nanopore responses monitored by the current-voltage (I-V) curves; and (iii) transport simulations obtained with a multilayer nanopore model. We show that a single, approximately symmetric nanopore can be operated as a reconfigurable diode showing different rectifying behaviors by applying chemical and electrical signals. The remarkable characteristics of the new nanopore are the sharp response observed in the I-V curves, the improved tunability (with respect to previous designs of symmetric nanopores) which is achieved because of the direct external access to the nanostructure mouths, and the broad range of rectifying properties. The results concern both fundamental concepts useful for the understanding of transport processes in biological systems (ion channels) and applications relevant for tunable nanopore technology (information processing and drug controlled release).

Net currents obtained from zero-average potentials in single amphoteric nanopores

“…The results are reminiscent of those found in ratchet systems [9] and constitute a significant extension with respect to previous studies by Siwy et al [11,12,29]. The observed effects could be enhanced further by exploiting pH gradients [35]. Rectification and signal averaging of weak electric fields (in particular, the problem of dc currents generated by external ac signals [36,37]) are important for biological cells and then this study may also have some bio-electrochemical relevance.…”

Current rectification by nanoparticle blocking in single cylindrical nanopores

“…1,2,9,10 In the multi-pore membranes, Au nanowires are fabricated via replica method to image the internal pore geometry with field emission scanning electron microscopy (FESEM), 2,10 as shown in Figs. 1(a)-(c).…”

Nernst-Planck model of photo-triggered, pH–tunable ionic transport through nanopores functionalized with “caged” lysine chains

“…10,11 Polymer samples containing single asymmetric nanopores and multipore arrays obtained by track-etching 12 are of particular interest because they mimic some of the transport properties of biological ion channels. [13][14][15][16][17][18][19] Recent advances concerning the fabrication processes and the tailoring of the surface properties have permitted to control the pore geometry [20][21][22][23] and the response to external stimuli such as voltage, 24,25 temperature, 26,27 pH [28][29][30] or the presence of a given analyte in the pore solution. [31][32][33][34] These features have allowed the fabrication of nanofluidic devices [35][36][37][38] with potential applications in sensing, 34,39,40 energy harvesting 41,42 and information processing.…”