title: Imaging local proton fluxes through a polycarbonate membrane by using scanning electrochemical microscopy and functionalized alkanethiols.
abstract: A new application of scanning electrochemical microscopy (SECM) to probe the transport of protons through membranes is described. Herein, a probe ultramicroelectrode (UME) is modified with a self-assembled monolayer (SAM) of 11-mercaptoundecanoic acid to qualitatively image areas within different pH regions above a track-etched membrane. The current response of the modified electrode in the presence of potassium hexacyanoferrate as electroactive component is different in acidic and alkaline solutions. Depending on the pH value of the solution, the SAM-covered electrode exposes either a neutral or a negatively charged insulating monolayer at pH 3 or 7, respectively, which leads to an increase/decrease in the faradaic current due to electrostatic interactions between the neutral/charged surface and the charged redox mediator. Therefore, local pH changes in the close vicinity of a membrane-like substrate lead to different current responses recorded at the tip electrode when scanning above the surface.
authors.affiliation: Institut für Physikalische Chemie I, Albert-Ludwigs-Universität Freiburg, Albertstr. 21,D-79104 Freiburg, Germany.
authors.forename: Norman
authors.initials: N
authors.lastname: Baltes
authors.forename: Jürgen
authors.initials: J
authors.lastname: Heinze
mesh_terms: D004566:Electrodes; D005227:Fatty Acids / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D020527:Microscopy, Scanning Probe / Q000379:methods*; D010084:Oxidation-Reduction; D011076:Polycarboxylate Cement / Q000737:chemistry*; D011199:Potentiometry; D011522:Protons; D013438:Sulfhydryl Compounds / Q000737:chemistry*
chemical_list: C505222:11-mercaptoundecanoic acid; D005227:Fatty Acids; D011076:Polycarboxylate Cement; D011522:Protons; D013438:Sulfhydryl Compounds; C005506:polycarbonate