Poly(aniline) Nanowires in Sol–Gel Coated ITO: A pH-Responsive Substrate for Planar Supported Lipid Bilayers

Abstract

Facilitated ion transport across an artificial lipid bilayer coupled to a solid substrate is a function common to several types of bioelectronic devices based on supported membranes, including biomimetic fuel cells and ion channel biosensors. Described here is fabrication of a pH-sensitive transducer composed of a porous sol-gel layer derivatized with poly(aniline) (PANI) nanowires grown from an underlying planar indium-tin oxide (ITO) electrode. The upper sol-gel surface is hydrophilic, smooth, and compatible with deposition of a planar supported lipid bilayer (PSLB) formed via vesicle fusion. Conducting tip AFM was used to show that the PANI wires are connected to the ITO, which convert this electrode into a potentiometric pH sensor. The response to changes in the pH of the buffer contacting the PANI nanowire/sol-gel/ITO electrode is blocked by the very low ion permeability of the overlying, fluid PSLB. The feasibility of using this assembly to monitor facilitated proton transport across the PSLB was demonstrated by doping the membrane with lipophilic ionophores that respond to a transmembrane pH gradient, which produced an apparent proton permeability several orders of magnitude greater than values measured for undoped lipid bilayers.

ITO/Poly(Aniline)/Sol-Gel Glass: An Optically Transparent, pH-Responsive Substrate for Supported Lipid Bilayers

“…Just prior to vesicle fusion, ITO/PANI/sol-gel electrodes were oxidized in an air plasma for 10 seconds to generate a hydrophilic surface. Vesicle fusion was performed using procedures described previously [28] to generate a PSLB on the electrode, followed by rinsing away unfused vesicles with buffer.…”

“…Fluorescence imaging and fluorescence recovery after photobleaching (FRAP) measurements on PSLBs deposited on ITO/PANI/sol-gel electrodes were performed as described in [28, 32] and in Supplementary Material. For FRAP, PSLBs composed of egg PC (the blank) or NBD-PC/egg PC (the sample, 0.05/0.95 mol/mol)) were formed on pairs of ITO/PANI/sol-gel electrodes mounted in the two compartments of a liquid cell.…”

“…For example, doping/dedoping of poly(aniline) (PANI) can be accomplished by changing the pH of the surrounding medium, and this property makes PANI useful as a pH-sensing material [24]. Both electrochemical and optical pH sensors based on PANI have been reported [22, 23, 25–27], which suggests the possibility of using a PANI-coated electrode as a proton-selective substrate for a planar supported lipid bilayer (PSLB) [28, 29]. …”

“…One strategy to overcome these problems is overcoating the PANI-modified electrode with a material that promotes vesicle fusion. Recently we used this strategy to prepare PANI-modified ITO substrates [28]. PANI nanowires were grown electrochemically in the pores of a sol-gel glass layer that was spin coated on ITO.…”

A unified bottom up multiscale strategy to model gas sensors based on conductive polymers

“…Polyaniline in its forms (see Fig. 1) emeraldine base (PANI EB) or salt (PANI ES) are most widely used ICPs because of its ease of synthesis, high chemical and environmental stability and tunable properties [6,[9][10][11][12][13][14].…”