Electrochemical imaging

Studies of electron transfer (ET) at micro-ITIES are scarce. Solomon and Bard first observed the ET between TCNQ (in DCE) and ferrocyanide (in water) at a micro-ITIES supported by micropipettes [5]. The pipette was used as a SECM probe for electrochemical imaging. The current was controlled by the rate of the bimolecular ET reaction at the micro-ITIES... 

The small size of nanoelectrodes also makes possible the detection of discrete electron transfer events. Fan and Bard have recently shown cou-lombic staircase response using electrodes of nanometer dimensions [63], Ingram and co-workers have also shown coulombic staircase response, in their case while studying colloids and collections of colloids [64]. Fan and Bard have also applied nanoelectrodes to achieve high-resolution electrochemical imaging and single-molecule detection [65]. 

A recent development in SPM technology is the combination of SECM and AFM to produce a hybrid high-resolution microscope that allows simultaneous topographic and electrochemical imaging.22 Figure 19 shows an example of this measurement in which pore structure and molecular transport of a redox-active molecule (Ru(NH3)e2+) were simultaneously imaged at l-nm resolution. Inspection of this image clearly shows a correlation between transport rates and pore structure. 

SECM instruments (77,78) will undoubtedly increase the scope and power of SECM. Further improvements in the power and scope of SECM has resulted from its coupling scanning probe or optical imaging techniques, such as AFM (57,79) or single-molecule fluorescence spectroscopy (80). The combined SECM-AFM technique offers simultaneous topographic and electrochemical imaging in connection to a probe containing a force sensor and an electrode component, respectively. 

Hafez, 1., Kisler, K., Berberian, K., Dernick, G., Valero, V., Yong, M.G., Craighead, H.G., and Lindau, M. (2005) Electrochemical imaging of fusion pore openings by electrochemical detector arrays. Proceedings of the National Academy of Sciences ofthe USA, 102 (39), 13879-13884. 

K., and Unwin, P.R. (2012) Definitive evidence for fast electron transfer at pristine basal plane graphite from high-resolution electrochemical imaging. Angew. Chem. Int. Ed., 51, 5405 - 5408. 

Macpherson, J.V. and Unwin, P.R. (2001) Noncontact electrochemical imaging with combined scanning electrochemical atomic force microscopy. Analytical Chemistry, 73, 550-557. 

Takahashi, Y., Shevchuk, A.I., Novak, P. etcd. (2010) Simultaneous noncontact topography and electrochemical imaging hy SECM/SICM featuring ion current feedback regulation. Journal of the American Chemical Society,132, 10118-10126. 

Palchetti I, Laschi S, Marrazza G, Mascini M (2007) Electrochemical imaging of localized sandwich DNA hybridization using scanning electrochemical microscopy. Anal Chem 79 7206-7213... 

This entry is just an introduction there have been numerous other developments of advanced micro /nanofabrication techniques including ion-assisted CVD electron beam etching, for example, to produce nanopores [50] and custom AFM/ STM probes for scanning electrochemical imaging [51] and materials for sensing at high temperatures and in corrosive environments. 

O Connell MA, Lewis JR, Wain AJ (2015) Electrochemical imaging of hydrogen peroxide generation at individual gold nanoparticles. Chem Commun 51(51) 10314—10317... 

Two different microelectrode arrays are presented the first array consists of 100 parallel connected ultramicroelectrodes. Counter as well as reference electrodes are integrated on the same chip. Although still exhibiting microelectrode features, this array yields analytical currents very similar to those of macroelectrodes. The second array consists of 400 individually addressable microelectrodes. It enables redundant as well as multianalyte measurements. Here, we demonstrate the electrochemical imaging of two-dimensional distributions of ammonium chloride as well as urea. 

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