title: Electron transfer at self-assembled monolayers measured by scanning electrochemical microscopy.
abstract: New approaches have been developed for measuring the rates of electron transfer (ET) across self-assembled molecular monolayers by scanning electrochemical microscopy (SECM). The developed models can be used to independently measure the rates of ET mediated by monolayer-attached redox moieties and direct ET through the film as well as the rate of a bimolecular ET reaction between the attached and dissolved redox species. By using a high concentration of redox mediator in solution, very fast heterogeneous (10(8) s(-1)) and bimolecular (10(11) mol(-1) cm(3) s(-1)) ET rate constants can be measured. The ET rate constants measured for ferrocene/alkanethiol on gold were in agreement with previously published data. The rates of bimolecular heterogeneous electron transfer between the monolayer-bound ferrocene and water-soluble redox species were measured. SECM was also used to measure the rate of ET through nonelectroactive alkanethiol molecules between substrate gold electrodes and a redox probe (Ru(NH(3))(6)(3+)) freely diffusing in the solution, yielding a tunneling decay constant, beta, of 1.0 per methylene group.
authors.affiliation: Department of Chemistry and Biochemistry, The University of Texas at Austin, Austin, Texas 78712, USA.
authors.forename: Biao
authors.initials: B
authors.lastname: Liu
authors.forename: Allen J
authors.initials: AJ
authors.lastname: Bard
authors.forename: Michael V
authors.initials: MV
authors.lastname: Mirkin
authors.forename: Stephen E
authors.initials: SE
authors.lastname: Creager
mesh_terms: D000473:Alkanes / Q000737:chemistry*; D004563:Electrochemistry / Q000379:methods*; D004583:Electrons; D005296:Ferrous Compounds / Q000737:chemistry; D007700:Kinetics; D000075163:Metallocenes; D008853:Microscopy / Q000379:methods*; D010084:Oxidation-Reduction; D000644:Quaternary Ammonium Compounds / Q000737:chemistry; D012428:Ruthenium / Q000737:chemistry; D017975:Ruthenium Compounds / Q000737:chemistry; D013438:Sulfhydryl Compounds / Q000737:chemistry*
chemical_list: D000473:Alkanes; D005296:Ferrous Compounds; D000075163:Metallocenes; D000644:Quaternary Ammonium Compounds; D017975:Ruthenium Compounds; D013438:Sulfhydryl Compounds; D012428:Ruthenium; C004998:ferrocene