Micro- and Nanoelectrodes

Monopolar recordings in the intracellular space are made with a small transmembrane electrode in contact with the cytoplasm, and a larger extracellular electrode in the interstitial liquid. The tip of the electrode must be small enough to penetrate the membrane without too much damage and not too much plasma/electrolyte leakage. Squid giant axons have diameters up to 1000 pm, and in such studies the diameter of the penetrating part may be of the order of 50 pm. For ordinary cell sizes, tips down to 1 pm diameter are used. 

The metal needle can be made of tungsten, stainless steel, platinum alloys, etc., and it is possible to fabricate tip diameters down to 1 pm. It is necessary to isolate the shaft except the tip. A lacquer or glass coating can do this. A description of how to make them can be 

The ordinary use of a micropipette electrode is monopolar. Double pipette electrodes are sometimes used with only one penetration of the cell membrane. One pipette is current carrying and the other is recording in a three-electrode set-up. 

Another example of the use of small electrodes is Jahnke et al. (2013), who used a flexible microelectrode array to separate between brain and tumor tissue in vivo. 

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A persistent problem with micro- and nanoelectrodes is the sealing of the conductive element to the insulating material that surrounds the element such that solution does not creep into this junction [25,68,75]. This solution creeping is undesirable because it causes the double layer charging currents... 

In the direct mode the resolution is governed by the electric field distribution, which therefore requires that the UME be brought very close to the surface. At the same time, the direct mode does not require a UME with a disc shape insulated in an inert matrix, as long as the active part of the UME is small and close to the surface. As described above, high-resolution modification of surfaces by the direct mode of the SECM is basically an STM-driven approach. On the other hand, the resolution of the feedback mode is presently limited by our ability to produce micro- and nanoelectrodes with well-defined shapes. Recently, Mirkin and Lewis reported (45) the preparation and characterization of nanoelectrodes that are suitable for SECM (see Chapter 3). This development may pave the way for a substantial increase in feedback mode resolution. 

The application field of bioimpedance is very wide—from single-cell measurements with micro- and nanoelectrodes to whole-body composition analysis from healthy to ischemic, pathological, and dead tissue. We have selected some typical bioimpedance application examples. 

A. Molina, E. Laborda, J. Gonzalez, and R. G. Compton. Effects of convergent diffusion and charge transfer kinetics on the diffusion layer thickness of spherical micro- and nanoelectrodes, Phys. Chem. Chem. Phys. 15, 7106-7113 (2013). 

Micro- and Nanoelectrodes, Fig. 2 The cyclic voltammograms in 5-mM ferrocene corresponding to different stages in the fabrication of a 60-nm-radius An nanoelectrode, a Pt nanoelectrode (radius) 60 nm,... 

Micro- and Nanoelectrodes, Fig. 5 (a) Schematic of a single-nanoparticle Au electrode and the radial-type diffusion profile, (b) Transmission electron microscope image of a single-Au nanoparticle (Au NP) immobilized on a Pt nanoelectrode, (c) Voltammetric responses in an 02-saturated 0.10 M KOH solution of an 18-nm Au single-nanoparticle electrode (SNPE) (black), a 3-aminopropyltrimethoxysilane (APrMS)-modified Pt... 

Henstridge MC, Compton RG (2012) Mass transport to micro- and nanoelectrodes and their arrays a review. Chem Rec 12 63-71... 

A general template method for preparing nanomaterials has been investigated by Martin and others for the formation of micro- and nanoelectrode arrays (140). The method entails synthesis of the desired metal (or polymer, protein, semiconductor, carbon nanowire) within the cylindrical and monodisperse pores of a membrane or another porous material (Figure 10.9) (see also Section 16.2 in Chapter 16). 

Forster R (2014) Micro- and nanoelectrodes. In Kreysa G, i Ota K, SavineU RF (eds) Encyclopedia of applied electrochemistry. Springer, Heidelberg, pp 1248-1256 (Online)... 

Said NAM, Twomey K, Ogurstov VI, Anigan DWM, Herzog G (2011) Fabrication and electrochemical characterization of micro- and nanoelectrode arrays for sensor applications. J Phys Conf Ser 307 012052... 

Lugstein, A., E. Bertagnolli, C. Kranz, A. Kueng, and B. Mizaikoff, Integrating micro-and nanoelectrodes into atomic force microscopy cantilevers using focused ion beam techniques, Appl. Phys. Lett., Vol. 81, 2002 pp. 349-351. 

FIGURE 22.1 Membrane components and ionophores used in ion-selective micro- and nanoelectrodes. 

Besides the obvious practical advantage of the small size, allowing smaller sample volumes to be used and application to in vivo measurements, microelectrodes offer a number of advantages such as high current density, low backgroimd charging current, and enhanced mass transport efficiency. For an in-depth discussion about macro- micro- and nanoelectrodes see Chap. 15. 

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