Ultramicroelectrode Arrays

J. Min and A.J. Baeumner, Characterization and optimization of interdigitated ultramicroelectrode arrays as electrochemical biosensor transducers. Electroanalysis 16, 724—729 (2004). 

A. Schwake, B. Ross, and K. Cammann, Chrono amperometric determination of hydrogen peroxide in swimming pool water using ultramicroelectrode array. Sens. Actuators, B B 46, 242-248 (1998). 

R. Feeney and S.P. Kounaves, Microfabricated ultramicroelectrode arrays developments, advances, and applications in environmental analysis. Electroanalysis 12, 677-684 (2000). 

Kounaves, S.P., Deng, W., Hallock, P.R., Kovacs, G.T.A. and Storment, C.W. (1994) Iridium-based ultramicroelectrode array fabricated by microlithography. Anal. Chem., 66, 418-423. 

Wang, J., Lu, J., Tian, B. and Yarnitzky, C. (1993) Screen-printed ultramicroelectrode arrays for on-site stripping measurements of trace metals. J. Electroanal. Chem., 361, 77-83. 

As it was mentioned earlier, a much larger range of micro/nanofabrication tools are utilized in the design and fabrication of micro/nanotransducers than applied in the fabrication of microfluidic systems. Standard photolithography as described above is only one of the many techniques used. Three examples will be described here the fabrication of freestanding transducers, UV-photolithography with lift-off technique for preparation of interdigitated ultramicroelectrode arrays (IDUAs), and more traditional techniques for microtransducer preparations. 

Fig. 6.6. Inter digitated ultramicroelectrode arrays (IDUAs). (a) schematic, (b) optical micrographs with 1000 x magnification. IDUAs were fabricated using standard photolithography and lift-off techniques on silicon and were made out of gold.

Fig. 6.7. Photolithography and hft-off process used for the fabrication of gold interdigitated ultramicroelectrode arrays on silicon or glass substrates.

Consider an electrode covered with a film that has continuous pores or channels from the solution to the electrode (Figure 14.4.1, process 6). We can ask how the electrolysis of a species in solution at such an electrode differs from that at the bare (unfilmed) electrode. The answer depends upon the extent of coverage of the electrode by the film, the size and distribution of the pores, and the time scale of the experiment. The situation is complicated, because the pores can have different dimensions and degrees of tortuosity, and their distribution within the film may not be uniform. Thus, theoretical treatments of such films often use idealized models. The theory for electrodes of this type is closely related to that for ultramicroelectrode arrays (Section 5.9.3), which, however, often involve a better-defined geometry and uniform distribution of active sites (81, 82). 

Zhu, M. Jiang, Z. Jing, W. Fabrication of polypyrrole-glucose oxidase biosensor based on multilayered interdigitated ultramicroelectrode array with containing trenches. Sens. Actuators B Chem. 2005, 2, 382-389. 

Much of the work done with conductive polymers follows the same trends as that with non-conductive polymers, so will not be described here. There will be important roles for conductive polymers as sophisticated microstructures are designed. One example of early work in this area is the use of poly(pyrrole) as a support for montmorillonite at the surface of electrodes, and in free-standing films (119). Also Kittlesen, White and Wrighton reported in 1984 that electropolymerized poly(pyrrole) and poly(N-methylpyrrole) could be prepared at electrodes with widths of only 1.4 microns (120). These electrodes were part of an ultramicroelectrode array used to demonstrate the possibility of combining surface chemistry with microelectronics technology to prepare microsensors. Since the conductivity of poly(pyrrole) (and many other conductive polymers) depends on redox state, the authors suggest that miniaturized redox sensors may be prepared from systems such as theirs. 

Schwake A, Ross B, Cammann K (1998) <2hrono amperometric determination of hydrogen peroxide in swimming pool wato using an ultramicroelectrode array. Sens Actuators B Chem 46 242... 

To investigate the film permeability in its neutral form, we performed CV with a mediator in solution over bare FTO and PPTZPQ/ITO. The redox potential of the mediator was chosen within die potential window where die polymer does not show an electrochemical response, and therefore, behaves solely as a blocking layer on the ITO electrode. If the thickness of the film is of the order of the diameter of the hole, the behavior of the electrode can be treated as that of ultramicroelectrode arrays and the response is modulated by the polymer film thickness, the size and distribution of the pores, and the time scale of die experiment. The reduction behavior of die me yl viologen (MV ) on... 

Zoski CG, Wijesinghe M (2010) Electrochemistry at ultramicroelectrode arrays and nanoelectrode ensembles of macro- and ultramicroelectrode dimensions. Israel J Chem 50 347-359... 

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