Microelectrode Applications

Katemann, A. Schulte, E. J. Calvo, M. KoudeUca-Hep, W. Schuhmann, Electrochem. 

Faulkner, Electrochemical Methods Fundamentals and Applications, Wiley  

The properties and applications of microelectrodes, as well as the broad field of electroanalysis, have been the subject of a number of reviews. Unwin reviewed the use of dynamic electrochemical methods to probe interfacial processes for a wide variety of techniques and applications including various flow-channel methods and scanning electrochemical microscopy (SEM), including issues relating to mass transport (1). Williams and Macpherson reviewed hydrodynamic modulation methods and their mass transport issues (2). Eklund et al. reviewed cyclic voltammetry, hydrodynamic voltammetry, and sono-voltammetry for assessment of electrode reaction kinetics and mechanisms with discussion of mass transport modelling issues (3). Here, we focus on applications ranging from measnrements in small volumes to electroanalysis in electrolyte free media that exploit the uniqne properties of microelectrodes. 

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W.R. LaCourse and S.J. Modi, Microelectrode applications of pulsed electrochemical detection, Electroanalysis, 17 (2005) 1141-1152. 

Silicon is convenient for microelectrode applications since it is widely used in the semiconductor industry and can be fabricated into complex mechanical and electrical structures. Unfortunately, silicon is chemically reactive in body fluids and corrodes, forming an insulating glass (Si02> that impedes current flow. For this reason, silicon is usually coated with thin layers of other metals such as platinum that form the electrical interface with tissue. Table 17.4 compares different types of bioelectrodes for different applications. 

Daniele S, Bergamin S (2007) Preparation and voltammetric characterisation of bismuth-modified mesoporous platinum microelectrodes. Application to the electrooxidation of formic acid. Electrochem Commun 9 1388-1393... 

S. Daniele, C. Bragato, and M.A. Baldo. An approach to the calibrationless determination of copper and lead by anodic stripping voltammetry at thin mercury film microelectrodes. Application to well water and rain. Analytica Chimica Acta 346 145-151, 1997. 

Szabo AJ (1987) Theory of the current at microelectrodes application to ring electrodes. JPhys Chem 91 3108-3111... 

This expression is the sum of a transient tenu and a steady-state tenu, where r is the radius of the sphere. At short times after the application of the potential step, the transient tenu dominates over the steady-state tenu, and the electrode is analogous to a plane, as the depletion layer is thin compared with the disc radius, and the current varies widi time according to the Cottrell equation. At long times, the transient cunent will decrease to a negligible value, the depletion layer is comparable to the electrode radius, spherical difhision controls the transport of reactant, and the cunent density reaches a steady-state value. At times intenuediate to the limiting conditions of Cottrell behaviour or diffusion control, both transient and steady-state tenus need to be considered and thus the fiill expression must be used. Flowever, many experiments involving microelectrodes are designed such that one of the simpler cunent expressions is valid. 

The apparatus consists of a tip-position controller, an electrochemical cell with tip, substrate, counter and reference electrodes, a bipotentiostat and a data-acquisition system. The microelectrode tip is held on a piezoelectric pusher, which is mounted on an inchwomi-translator-driven x-y-z tliree-axis stage. This assembly enables the positioning of the tip electrode above the substrate by movement of the inchwomi translator or by application of a high voltage to the pusher via an amplifier. The substrate is attached to the bottom of the electrochemical cell, which is mounted on a vibration-free table [, and ]. A number... 

Evans D FI 1991 Review of voltammetric methods for the study of electrode reactions Microelectrodes Theory and Applications (Nate ASI Series E vol 197) ed M I Montenegro, M A Queiros and J L Daschbach (Dordrecht Kluwer)... 

Koudelka-Flep M and Van der Wal P D 2000 Microelectrode sensors for biomedical and environmental applications Electrochim. Acta 45 2437... 

Polysiloxane based block copolymers have also been examined with respect to their transport properties, because these copolymers are of special interest as membranes in various biomedical applications 376). The combination of good mechanical, dielectric, permeation and film formation properties of siloxane-carbonate segmented copolymers have led to their use as blood oxygenation, dialysis and microelectrode membranes 392 394. ... 

Zeuthen, T. (ed.) The Application of Ion-Selective Microelectrodes, New York Elsevier/North-Holland Biomedical Press 1981... 

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. 

Tacussel and their application by Gonon et al.148 to differential pulse voltammetry (DPV) and differential normal pulse voltammetry (DNPV) in vivo, also called the biopulse technique the microelectrodes are implanted in the living animal brain and variations in the concentrations of some molecules can be followed via the Tacussel PRG 5 and BIPAD instruments (see also the selection of commercial models in Table 3.4). 

Thus the time during which the transport process attains the steady state depends strongly on the radius of the sphere r0. The steady state is connected with the dimensions of the surface to which diffusion transport takes place and does, in fact, not depend much on its shape. Diffusion to a semispherical surface located on an impermeable planar surface occurs in the same way as to a spherical surface in infinite space. The properties of diffusion to a disk-shaped surface located in an impermeable plane are not very different. The material flux is inversely proportional to the radius of the surface and the time during which stationary concentration distribution is attained decreases with the square of the disk radius. This is especially important for application of microelectrodes (see page 292). 

D Amman. (1986). Ion-Selective Microelectrodes Principles, Design, and Application. Springer Verlag, New York. 

The most extensive and refined application of microelectrodes, both in the wall of a cell and as a moveable probe, was made by LeLan and Angelino (L2, L3, L4), who charted convection patterns and mass-transfer rate distributions in cylindrical cells with and without baffles. 

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