title: Electrochemical characterization of polyelectrolyte/gold nanoparticle multilayers self-assembled on gold electrodes.
abstract: Polyelectrolyte/gold nanoparticle multilayers composed of poly(l-lysine) (pLys) and mercaptosuccinic acid (MSA) stabilized gold nanoparticles (Au NPs) were built up using the electrostatic layer-by-layer self-assembly technique upon a gold electrode modified with a first layer of MSA. The assemblies were characterized using UV-vis absorption spectroscopy, cyclic and square-wave voltammetry, electrochemical impedance spectroscopy, and atomic force microscopy. Charge transport through the multilayer was studied experimentally as well as theoretically by using two different redox pairs [Fe(CN)(6)](3-/4-) and [Ru(NH(3))(6)](3+/2+). This paper reports a large sensitivity to the charge of the outermost layer for the permeability of these assemblies to the probe ions. With the former redox pair, dramatic changes in the impedance response were obtained for thin multilayers each time a new layer was deposited. In the latter case, the multilayer behaves as a conductor exhibiting a strikingly lower impedance response, the electric current being enhanced as more layers are added for Au NP terminated multilayers. These results are interpreted quite satisfactorily by means of a capillary membrane model that encompasses the wide variety of behaviors observed. It is concluded that nonlinear slow diffusion through defects (pinholes) in the multilayer is the governing mechanism for the [Fe(CN)(6)](3-/4-) species, whereas electron transfer through the Au NPs is the dominant mechanism in the case of the [Ru(NH(3))(6)](3+/2+) pair.
authors.affiliation: Departamento de Química da Faculdade de Ciências da Universidade do Porto, Rua do Campo Alegre 687, 4169-007 Porto, Portugal. mariana.chirea@fc.up.pt
authors.forename: Mariana
authors.initials: M
authors.lastname: Chirea
authors.forename: Vladimir
authors.initials: V
authors.lastname: García-Morales
authors.forename: José A
authors.initials: JA
authors.lastname: Manzanares
authors.forename: Carlos
authors.initials: C
authors.lastname: Pereira
authors.forename: Rubin
authors.initials: R
authors.lastname: Gulaboski
authors.forename: Fernando
authors.initials: F
authors.lastname: Silva
mesh_terms: D004563:Electrochemistry; D004566:Electrodes; D004573:Electrolytes / Q000737:chemistry*; D006046:Gold / Q000737:chemistry*; D053768:Metal Nanoparticles / Q000737:chemistry*; D015394:Molecular Structure; D010316:Particle Size; D011107:Polylysine / Q000737:chemistry; D011108:Polymers / Q000737:chemistry*; D055672:Static Electricity; D013499:Surface Properties; D013870:Thiomalates / Q000737:chemistry
chemical_list: D004573:Electrolytes; D011108:Polymers; D013870:Thiomalates; D011107:Polylysine; D006046:Gold; C046062:2-thiomalic acid