Interdigitated Microelectrode

The determination of ammonium, arsenic, thiosulfate, allyl alcohol, and iodide has been achieved with a bromine redox mediator. Tomcik etal. [156] employ interdigitated microelectrodes at which bromine is generated at one set of electrodes and collected at a second set of electrodes. The reaction of the bromine with the analytes allows quantitative determination down to a micromolar level. 

Figure 1. Schematic representations and dimensions of interdigital microelectrodes that were coated with phthalocyanines.

Anion detection at microelectrodes has not been studied widely. Amongst the first was the work of de Beer et al. [ 111 ] who manufactured a nitrite sensor with a tip just a few microns in diameter, which could detect nitrite ions down to 1 pM. This proved to be suitable for profiling the concentrations of nitrite anion within biofilms less than 1-mm thick inside water treatment plants. Other workers have found that use of an interdigitated microelectrode array [ 112] allows measurement of iodide via monitoring of its redox peak down to sub-micromole levels, making it a suitable technique for analysing mineral water. Carbon nanotubes coated onto Pt microdiscs have been utilised to make a nitrite sensor [113,114] with detection levels of 0.1 pM. Sulphide has also been detected at nickel microdiscs (50 pm diameter) [115]. 

Heterogeneous immunoassay has also been conducted with the antibody immobilized on beads. For instance, mouse IgG (50-100 ng/mL) was detected by ELISA in a glass chip. First, mouse IgG (antigen) was captured by magnetic beads coated with sheep anti-mouse antibody (1.02 x 107 beads/mL). Then the secondary antibody, which was rat anti-mouse conjugated with alkaline phosphatase (0.7 pg/mL), was delivered. Thereafter the substrate, PAPP, was added. It was enzymatically converted to p-aminophenol (PAP), which was electrochem-ically detected by the on-chip interdigital microelectrodes [1016]. 

DEP can be used to create regular patterns of particles on a surface or in a microfluidic channel. For example, two-dimensional (2D) patterns of polystyrene latex microbeads were fabricated on glass substrates using n-DEP, and the line- and grid-patterned microparticles, which formed due to the repulsive force of this n-DEP, were covalently bound on the substrate via cross-linking agents (Suzuki et al., 2004). In this work, interdigitated microelectrodes were incorporated into a fluidic channel in order to direct the particles into very specific patterns. 

S. Park, A. Beskok, Alternating current electrokinetic motion of colloidal particles on interdigitated microelectrodes, Analytical Chemistry, 80(8) 2832-2841 (2008). 

Field flow fraction (FFF) describes a method for separating particles based on combining a deterministic force with hydrodynamic separation. A typical configuration is shown in Fig. 11. The system consists of a channel with interdigitated microelectrodes patterned on the bottom substrate. Particles are introduced into the system and when the field is switched on they experience nDEP, moving to equilibrium positions which are defined according to the balance of dielectrophoresis (DEP) and gravity (buoyancy). Different types of particles move to different equilibrium positions in the... 

F. F. Becker, X-B. Wang, Y. Huang, R. Pethig, J. Vykoukal and P. R. C. Gascoyne, The removal of human leukaemia cells from blood using interdigitated microelectrodes, J. Phys. D Appl. Phys. 27,2659-2662 (1994). 

Polymetallorotaxanes 7.24 (M = Zn" or Cu ) have been prepared by electropolymerization, which involved anodic oxidation of the pre-assembled metallorotaxane precursors (Scheme 7.2) [48]. Importantly, studies of these materials have allowed an evaluation of the individual contributions of the organic backbone and the metal-centered redox process to the overall conductivity measured on interdigitated microelectrodes. The Zn and Cu polymers behave quite differently. The Zn polymer behaves in a similar fashion to the metal-free material 7.25, whereas the matching of the polymer and Cu-centered redox potentials in 7.24 (M=Cu ) leads to enhancement of the communication between these two units resistance drops by a factor of 10 for the Cu polymer 7.24 relative to metal-free 7.25. In a further development in this general area, two-step electropolymerizations have been used to generate three-stranded conducting ladder polymetallorotaxanes 49]. 

Sun, G., J. An, C. K. Chua, H. Pang, J. Zhang, and P. Chen. 2015. Layer-by-layer printing of laminated graphene-based interdigitated microelectrodes for flexible planar micro-supercapacitors. Electrochemistry Communications 51 33-36. 

There are a number of instmments for skin hydration assessment on the market. Most of them measure at rather high frequencies, which means that they measure deep into the viable skin. Some instmments use closely spaced interdigitated microelectrodes. This somewhat reduces the contribution from viable skin layers, but the chance of only measuring in redundant moisture on the skin surface is obvious for such systems. Rationales for using a low-frequency electrical susceptance method for skin hydration assessment and description of a method for absolute calibration of the measurements can be found elsewhere (Martinsen et al., 1998b, 2008 Martinsen and Grimnes, 2001). 

Yang L (2008) Electrical impedance spectroscopy for detection of bacterial cells in suspensions using interdigitated microelectrodes. Talanta 74(5) 1621-1629... 

Figure 7 shows the detection principle of an impedimetric IME biosensor for bacterial detection [8]. It is based on measurements of electrochemical faradic impedance in the presence of [Fe(CN)6] " as a redox probe. When a bare interdigitated microelectrode is immersed into an electrolyte solution containing the redox couple and a small-amplitude AC potential (5 mV) is applied to the electrode, the faradic process of oxidation and reduction of the redox couple occurs, and then electrons are transferred between the two sets of array electrodes through the redox couple (Fig. 7a). When antibodies are immobilized onto the electrode surface (Fig. 7b) they form a layer that can inhibit the electron transfer between the electrodes, and thus an increase in the electron transfer resistance can be expected. If bacterial cells attach to the antibody-modified electrode surface (Fig. 7c), the intact cells can create a further barrier for...

Earlier studies of indirect conductimetric biosensors based on CEPs have been described by Wrighton and coworkers. The devices of Wrighton and coworkers [34] used an ingenious connection to a third electrode to potentiate the response of the CEP that was set between a pair of interdigitated microelectrodes (Figure 12.3). In this configuration, when the applied voltage to the microelectrodes is zero... 

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