pH- and Ionic Strength-Controlled Cation Permselectivity in Amine-Modified Nanoporous Opal Films

Abstract

The influence of pH and ionic strength on permselective transport in nanoporous opal films prepared from 440 nm silica spheres was investigated by cyclic voltammetry in aqueous and acetonitrile solutions. Three-layer opal films were deposited from a 1.5 wt % colloidal solution of silica spheres onto 25-microm-diameter Pt microdisk electrodes shrouded in glass. The films were chemically modified by immersing them in a dry acetonitrile solution of 3-aminopropyl triethoxysilane. When the surface amino groups of the modified opal films are protonated and there is little or no supporting electrolyte present in solution, the flux of cationic redox species through the opal membrane is blocked because of electrostatic repulsion. The permselectivity is pH-dependent and can be modulated by adjusting the Debye screening length within the nanopores of the opal by changing the ionic strength of the contacting solution.

Biosensing with Nanopores

“…Introduction of amine-terminated silane provides an opportunity for further modification (Figure 15.5). Single silica nanopores [64,65], single nanochannels [66,67], alumina membranes [35,68,69,72], and reverse opals [74] are aminated easily.…”

pH‐Responsive Nanoporous Silica Colloidal Membranes

“…Previously, we modified thin colloidal crystalline films with chargeable moieties, such as amines [29,30] and sulthonic acid groups, [31,32] as well as with a variety of neutral molecules, such as chiral selector moieties, [33,34] thiacalixarenes, [35] and spiropyran molecules. [36] In these studies molecular transport has been successfully controlled either by electrostatics or by molecular recognition.…”

Ultrasensitive Specific Stimulant Assay Based on Molecularly Imprinted Photonic Hydrogels

“…The 3D, highly-ordered, interconnected macropores within the polymer matrix can accelerate alkaline drugs diffusing from bulk solutions into films and accessing nanocavities to specifically rebind with their complementary binding sites when soaking the IPPs in their buffers. Once they rebind to the residual carboxyl groups of the hydrogel, the gel is negatively charged and binds ephedrine by ion exchange, and theophylline by hydrogen bonding, both assisted by hydrophobic interactions, [16,18,40] since alkaloids easily lose a proton leading to the anion (in this case, the acidic dissociation constants, pKa, of theophylline and ephedrine are 8.8 and 9.96, respectively). [41,42] The extremely-thin wall between the macropores, as well as the giant specific surface area (estimated as about 66.76 m 2 g À1 ), make these IPP films highly sensitive to environment stimuli even in a much-dilute concentration of analytes.…”

“…[12,13] Many works have been reported about colloidal crystals to develop photonic-sensitive polymers with three-dimensional (3D) highly-ordered macroporous structures, [14] which can be used to optically determine analytes by means of the shift of the Bragg diffraction due to a change of the periodic lattice spacing. [15][16][17][18] In particular, if these photonic polymers consist of hydrogels, they enable easy swellings or shrinkage in response to chemical stimuli and give rise to volume changes to easily implement a rapid and sensitive assay, judged only by a visually-perceptible colour change. [19] Currently, various photonic sensitive polymers have been reported, to measure various chemical and environmental stimuli such as pH, [20] analytes, [21] metal ions, [22,23] humidity [24] and other physical deformation.…”