Feedback mode, scanning electrochemical

Nakano, K., Nakamura, K., Iwamoto, K., Soh, N., Imato, T. Positive-feedback-mode scanning electrochemical microscopy imaging of redox-active DNA-poly(l,4-benzoquinone) conjugate film deposited on carbon fiber electrode for micrometer-sized hybridization biosensor applications. J Electroanal Chem 2009, 628, 113-118. 

Selzer Y and Manler D 2000 Scanning electrochemical microscopy. Theory of the feedback mode for hemispherical ultramicroelectrodes steady-state and transient behavior Anal. Chem. 72 2383... 

In scanning electrochemical microscopy (SECM) a microelectrode probe (tip) is used to examine solid-liquid and liquid-liquid interfaces. SECM can provide information about the chemical nature, reactivity, and topography of phase boundaries. The earlier SECM experiments employed microdisk metal electrodes as amperometric probes [29]. This limited the applicability of the SECM to studies of processes involving electroactive (i.e., either oxidizable or reducible) species. One can apply SECM to studies of processes involving electroinactive species by using potentiometric tips [36]. However, potentio-metric tips are suitable only for collection mode measurements, whereas the amperometric feedback mode has been used for most quantitative SECM applications. 

The SECM can be used in the feedback mode to probe lateral mass-charge transfer [79-83]. The theory of SECM feedback surveyed in Section IV.A.2 assumes that the substrate surface is uniformly reactive. When lateral mass and/ or charge transfer occurs on the substrate surface, or within a thin film, the surface reactivity of the substrate becomes non-uniform and the SECM feedback theory must be modified. Unwin and Bard [79] developed the theory for adsorption-desorption of a redox species at the substrate that allowed for surface diffusion of the adsorbate. They introduced a new approach, the scanning electrochemical microscope induced desorption (SECMID), as a way to probe surface diffusion. The set of differential equations for the diffusion problem comprise Eqs. (8a,b), and Eq. (26), which relates the redox concentration at the substrate surface and the surface coverage by adsorbed species... 

Scanning electrochemical microscopy (SECM) - Direct mode - Feedback mode - Generation/collection mode Scanning reference electrode technique (SRET) Scanning vibrating electrode technique (SVET) Scanning photoelectrochemical microscopy (SPECM) Scanning electrochemical induced desorption (SECMID)... 

Bard and co-workers have reported on the attainment of equilibrium between the nanosized particles and an electrode in the presence of a redox mediator [25a]. The study refers to the production of a mediator (methyl viologen radical cation) that reduces water in the presence of colloidal gold and platinum metal catalyst. An electrochemical model based on the assumption that the kinetic properties are controlled by the half-cell reactions is proposed to understand the catalytic properties of the colloidal metals. The same authors have used 15 nm electrodes to detect single molecules using scanning electrochemical microscopy (SECM) [25b]. A Pt-Ir tip of nm size diameter is used along with a ferrocene derivative in a positive feedback mode of SECM. The response has been found to be stochastic and Ear-adaic currents of the order of pA are observed. 

Kwak, J. Bard, A. J., Scanning electrochemical microscopy - theory of the feedback mode, Anal. Chem. 1989, 61, 1221-1227... 

K wak J and Bard A J 1989 Scanning electrochemical microscopy— theory of the feedback mode Anal. Chem. 61 1221... 

Unwin P R and Bard A J 1991 Scanning electrochemical microscopy—theory and application of the feedback mode to the measurement of following chemical-reaction rates in electrode processes J. Phys. Chem. 95 7814... 

Scanning electrochemical microscopy (SECM) sustains great interest for biomolecular recognition detection [29, 30]. This comes from the versatility of SECM methodology that offers versatile detection principles, e.g., positive or negative feedback modes together with collection mode that are compatible with unlabeUed hybridization detection as well as with redox amplification strategies of DNA hybridization [31, 32]. 

Mandler D, Bard AJ (1989) Scanning electrochemical microscopy - the application of the feedback mode for high-resolution copper etching. J Electrochem Soc 136(10) 3143-3144. doi 10.1149/ 1.2096416... 

Mandler D, Bard AJ (1990) High-resolution etching of semiconductors by the feedback mode of the scanning electrochemical microscope. J Electrochem Soc 137(8) 2468-2472. doi 10.1149/ 1.2086965... 

Martin RD, Unwin PR (1997) Scanning electrochemical microscopy theory and experiment for the positive feedback mode with unequal diflusion coefficients of the redox mediator couple. J Electroantil Chem 439 123—136... 

Bard AJ, Mirkin MV, Unwin PR, Wipf DO (1992) Scanning electrochemical microscopy. 12. Theory and experiment of the feedback mode with finite heterogeneous electron-transfer kinetics and arbitrary substrate size. J Phys Chem 96 1861-1868... 

FIGURE 1.16 Scheme of nanogap-based SECM measurements of a fast electron-transfer reaction at a macroscopic snbstrate in the (a) steady-state feedback mode and in quasi-steady-state (b) feedback and (c) SG/TC modes, (d) Quasi-steady-state i-j- — Eg voltammograms of TCNQ in acetonitrile (solid cnrves). The tip was held at —0.235 or 0 V versus an Ag quasireference electrode for feedback or SG/TC modes, respectively. Snbstrate potential was cycled at 50 mV/s. Closed circles and dotted lines are theoretical cnrves for quasi-reversible (k = 7 cm/s and a = 0.5) and reversible snbstrate reactions, respectively, with EP = -88 mV. The inset shows a reversible voltammogram with a peak separation of 61 mV simultaneously measured at the substrate. (Reprinted with permission from Nioradze, N. et al.. Quasi-steady-state voltammetry of rapid electron transfer reactions at the macroscopic substrate of the scanning electrochemical microscope. Anal. Chem., Vol. 83, 2011 pp. 828-835. Copyright 2011, American Chemical Society.)... 

Xiong, H., J. Guo, and S. Amemiya, Probing heterogeneous electron transfer at an unbiased conductor by scanning electrochemical microscopy in the feedback mode. Anal. Chem., Vol. 79, 2007 pp. 2735-2744. 

Combellas, C., Ghilane, J., Kanoufi, R, and Mazouzi, D. 2004. Surface modification of halogenated pol5miers. 7. Local reduction of p>olytetrafluoroethylene and polychlorotrifluoroefhylene by the scanning electrochemical microscop>e in the feedback mode. T.Phus.Chem. BIOS 6391-6397. 

Finally, Hapiot and coworkers used scanning electrochemical microscopy (SECM) in feedback mode to investigate electronic and permeation properties of the polymeric films obtained from the mono-substituted ZnOEPfbpy)" monomer and ZnOEP monomer in the presence of free bipyridine [143]. The results showed that the polymer obtained from the EPOP process (namely from the commercial ZnOEP) was more permeable and had a lower conductivity than the one prepared using the mono-substituted ZnOEPfbpy)" monomer. These two observations were... 

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