Poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) brushes were grown using surface-initiated atom transfer radical polymerization on the nanopore surface inside the colloidal films assembled from 255 nm silica spheres. The molecular transport through PDMAEMA-modified colloidal nanopores was studied as a function of pH and ionic strength by measuring the flux of neutral and positively charged redox-active species across the colloidal films using cyclic voltammetry. Nanopores modified with PDMAEMA brushes exhibited pH-and ion-dependent behavior as follows. The diffusion rates decreased with decreasing pH as a result of electrostatic interactions and steric hindrance. At low pH (in the protonated state) the diffusion rates increased with increasing salt concentration because of the charge screening. We also quaternized the surface-grafted PDMAEMA, which led to the formation of strong polyelectrolyte brushes that hindered the diffusion of neutral molecules through the nanopores due to steric effects and the diffusion of positively charged species due to both electrostatic and steric effects.

The surface of nanopores in colloidal films, assembled from 205 nm silica spheres, was modified with poly(N-isopropylacrylamide), PNIPAAM, brushes using surface-initiated ATRP. The polymer thickness inside nanopores was controlled by the polymerization time. The diffusion through PNIPAAM-modified colloidal films was measured using cyclic voltammetry and studied as a function of temperature and polymer brush thickness. Nanopores modified with a thin PNIPAAM brush exhibited a positive gating behavior, where diffusion rates increased with increasing temperature. Nanopores modified with a thick PNIPAAM layer showed a negative gating behavior where diffusion rates decreased with increasing temperature. The observed temperature response is consistent with two transport mechanisms, one in which molecules diffuse through the nanopores whose volume increases with increasing temperature as the PNIPAAM brush collapses onto the nanopore surface (positive gating) and the second one where molecules diffuse through the porous PNIPAAM that fills the entire nanopore opening and collapses onto itself, becoming hydrophobic and impermeable (negative gating).

The surface of nanopores in opal films, assembled from 205 nm silica spheres, was modified with poly(acrylamide) brushes using surface-initiated atom transfer radical polymerization. The colloidal crystal lattice remained unperturbed by the polymerization. The polymer brush thickness was controlled by polymerization time and was monitored by measuring the flux of redox species across the opal film using cyclic voltammetry. The nanopore size and polymer brush thickness were calculated on the basis of the limiting current change. Polymer brush thickness increased over the course of 26 h of polymerization in a logarithmic manner from 1.3 to 8.5 nm, leading to nanopores as small as 7.5 nm.

Free‐standing colloidal membranes (nanofrits) with varied thickness and nanopore size are fabricated and modified with pH‐responsive poly(2‐(dimethylamino)ethyl methacrylate) brushes. The polymer‐modified nanofrits demonstrate excellent gating behavior for molecular diffusion: in the presence of acid, the diffusion rate of positively charged species significantly decreases. Increasing the polymer length and membrane thickness and decreasing the nanopore size leads to the complete acid‐controlled gating of the membranes.

We report the preparation of 20 and 65 nm radii glass nanopores whose surface is modified with DNA aptamers controlling the molecular transport through the nanopores in response to small molecule binding.Single synthetic nanopores are of interest as potential mimics of biological pores such as gated ion channels. Controlled transport through these synthetic pores can be achieved by integrating polymers responsive to chemical or physical stimuli. 1 Stimuli reported to date include pH, 2 ionic strength, temperature, 3 UV light as well as recognition of an ion, 4 a small molecule 5 or a protein. 6 The responsive components in the system can exhibit a single or a combination of several responses to the environmental conditions, such as changes in charge and conformation of surface-bound macromolecules. Here we significantly broaden the range of molecular effectors that can be employed to control the gating of such channels via the use of aptamers, DNA or RNA molecules selected for their ability to bind to, and fold in response to, specific aqueous targets, as the gating macromolecule. 7 As the substrate onto which our gating aptamers have been grafted we have employed a single glass nanopore electrode (Fig. 1, see ESI † for preparation details). 8 It consists of a platinum microdisk electrode embedded at the bottom of a conical nanopore made in glass, with the circular orifice of the pore having dimensions in the range 5 to 100 nm. Redoxactive molecules diffuse and migrate through the orifice connecting the bulk solution and nanopore interior. The deep cone shape of the nanopore results in an important transport characteristic: the steady-state flux of molecules into the pore is limited by the resistive restriction at the pore orifice and is independent of other geometrical parameters of the pore. Earlier, we have reported that surface modification of the glass nanopore electrodes with spiropyran moieties leads to the photochemical control of molecular transport through the pore orifice. 9 Specifically, we were able to electrostatically control the diffusion of a positively charged species by UV light-induced conversion of the neutral surface-bound spiropyran to its protonated merocyanine form, and restore the transport through the pore † Electronic supplementary information (ESI) orifice by irradiation of the electrode with visible light to reverse the spiropyran transformation. The present work introduces our proof-of-principle experiments where biomimetic glass nanopores are prepared with transport properties responsive to small molecules as a result of introducing aptamers as the sterically gating macromolecules.Critical to our investigation, aptamers can be engineered to undergo a large-scale conformational response to specific small molecules. 7a,b,10 For example, the aptamer A1 (Table 1) employed in the present work and based on a 32-base sequence reported by Stajonovic et al., binds and folds in response to cocaine. 10 Specifically, the aptamer remains partially unfolded in the absence of a targ...