Scanning electrochemical microscopy has open up new direction for functional characterization of materials for the exploration of new concepts in electrochemistry and for the optimization of sensors and sensor components and biomimetic surfaces.¹ While the initial phase of SECM has seen progress mainly in the establishment of new imaging modes and demonstration of their applicability to classes of problems using well-defined model samples and connection to numerical simulation of idealized experiments, the focus is currently shifting considerably towards more complex samples and less ideal reactions (irreversible reactions in fuel cells and in corrosion). Almost all imaging principles have found application in biochemical or biological context.^2-6 This opens up more direct relation to application but also poses new difficulties for the quantitative understanding of the experiments.⁷ New instrumental developments aim for providing complementary information that allows a meaningful investigation of such samples. Critical to the success is the proper choice of control experiments.

This trend will be illustrated by examples for increasing the lateral resolution and the associated differences in maintaining the quantitative rigor of SECM that has been considered as one of its main advantages. A vivid development takes place in the field of new imaging modes that are able to follow irreversible reaction at the sample surface. This is driven by the need of the fuel cell development but also by other application requiring (bio)electrocatalytic reactions of small molecules (O₂, H₂O₂, H₂). In this context pulsed generation-collection experiments^{8, 9} and local reagent delivery see a revival and expansion¹⁰ and the redox competition is applied in different variations for local analysis.^{4, 11} In order to carry out these experiments in a sensible way, patterning of samples with material libraries, e.g. electrocatalysts becomes increasingly important. Many complex materials can only be analysed by using complementing microscopic techniques that provide spatially correlated topographic, optical and reactivity information from exactly the same sample region. In many cases confocal laser scanning microscopy is an interesting complementing technique because of the similar resolution and scanning ranges and because of its ability for mapping three-dimensional concentration distributions.

Finally, analysing samples under conditions that are close to practically relevant conditions but far from ideal SECM imaging conditions is an area where careful judgement between the possibilities and requirements of SECM as a method and the relevance for the application in question must be made.

(1)           Wittstock, G.; Burchardt, M.; Pust, S. E.; Shen, Y.; Zhao, C. Angew. Chem. Int. Ed. 2007, 46, 1584-1617.

(2)           Wilhelm, T.; Wittstock, G. Angew. Chem. Int. Ed. 2003, 42, 2247-2250.

(3)           Zhao, C.; Wittstock, G. Anal. Chem. 2004, 76, 3145-3154.

(4)           Nogala, W.; Burchardt, M.; Opallo, M.; Rogalski, J.; Wittstock, G. Bioelectrochemistry 2008, 72, 174-182.

(5)           Burchardt, M.; Wittstock, G. Bioelectrochemistry 2008, 72, 66-76.

(6)           Wittstock, G.; Burchardt, M.; Nunes Kirchner, C. In Electrochemical Sensor Analysis; Alegret, S., Merkoci, A., Eds.; Elsevier: Amsterdam, 2007; Vol. 49, pp 907-939.

(7)           Pust, S. E.; Maier, W.; Wittstock, G. Z. Phys. Chem. 2008, 222, 1463-1517.

(8)           Shen, Y.; Träuble, M.; Wittstock, G. Anal. Chem. 2008, 80, 750-759.

(9)           Shen, Y.; Träuble, M.; Wittstock, G. Phys. Chem. Chem. Phys. 2008, 10, 3635-3644.

(10)         Zhao, C.; Zawisza, I.; Nullmeier, M.; Burchardt, M.; Träuble, M.; Witte, I.; Wittstock, G. Langmuir 2008, 24, 7605-7613.

(11)         Eckhard, K.; Schuhmann, W. Electrochim. Acta 2007, 53, 1164-1169.

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