Scanning Electrochemical Microscopy (SECM) has been successfully used for the imaging of modified surfaces revealing localized chemical information such as immobilized enzyme activity, electron-transfer kinetics etc. [1]. Previously, we have used enzyme microstructures visualized by SECM for compensating for potentially interfering compounds or determination of more than one substrate [2].

It is usually considered that by integration of many differently modified structures the amount of information about a measured sample can be significantly increased as compared to using a single structure. Sensor arrays usually consist of a number of individually and by purpose differently modified sensor surfaces, thus potentially allowing for the evaluation of complex multi-component samples. In contrast, each defined surface area modified with a sensing chemistry exhibits spatial inhomogeneity and could hence be treated similar to a sensor array, provided the possibility to extract localized information.

In order to demonstrate this approach enzyme/polymer layers were fabricated on surfaces and the localized sensor response upon addition of the enzyme's substrate was visualized with high lateral resolution using SECM, in the generator/collector mode (Fig. 1).

Fig. 1 SECM image of the localized sensor response [nA] of an enzyme/polymer
microspot in the presence of enzyme's substrate.

The SECM images obtained at different substrate concentrations were used as a basis for investigation of spatial variability of surface activity with feature extraction techniques.

[1] Ch. Zhao, G. Wittstock, Biosens. Bioelelectron., 20 (2005) 1277.
[2] S. Gaspar, M. Mosbach, L. Wallman, T. Laurell, E. Csöregi, W. Schuhmann, Anal. Chem., 73 (2001) 4254.