Multiple working electrodes

MesoScale Discovery (MSD) succeeded in introducing product with a similar technology approach based upon ruthenium redox-mediated electrochemical detection (Figure 2.14). MSD is a joint venture of its parent company, MesoScale, and IGEN, a company that pioneered much of fhe work on electrochemical detechon based on the ruthenium redox system. MSD s Multi-Spot plates contain antibodies immobilized on multiple working electrode pads within each well, allowing each spot within the well to serve as an individual assay. Multiplexed cytokine immxmoassays can be performed in 96-well (4,7, or 10 spots per well) patterns with detection limits of 1 to 10 pg/mL and a linear dynamic range up to 3,000 pg/mL. Both 24-and 384-well electrode systems are available. 

Pierce introduced an array-of-arrays microplate product called Search-Light in which antibodies are directly printed into the wells of the microplate. Also, we have reviewed MSD s Multi-Spot plate products having antibodies immobilized onto multiple working electrodes. These products (albeit with some novel approaches to create microarrays and means for detection) utilize the classic immunosorbent sandwich assay but have the advantage of parallel processing using microarrays. 

If we have multiple working electrodes or the electrode is divided into N different zones, which may work at different potentials, the overall specified duty becomes... 

Expandability for multiple working electrode measuring simultaneously, either in series or parallel orientations with respect to the flow. 

As it has been mentioned in the previous section, due to the versatility of the production process of screen-printed electrodes, a wide range of SPEs can be made, containing only the working electrode, working and counter electrodes to work with an external reference electrode, a complete electrochemical cell, or even with multiple working electrodes, for applications where a disposable electrode is desired to perform electrochemical measurements Fig. 9.2. 

Figure 6.14 Cyclic voltammogram obtained for a multiple-electron-transfer system, where a thin film of sputtered V2O5 on a platinum working electrode has been immersed in an electrolyte solution of propylene carbonate containing LiCI04 (1.0 mol dm ). From Cogan, S. F., Nguyen, N. M Perrotti, S. J. and Rauh, R. D Electroctromism in sputtered vanadium pentoxide , SPIE, 1016, 57-62 (1989). Reproduced by permission of the International Society for Optical Engineering (SPIE).

To carry out amperometric or voltammetric experiments simultaneously at different electrodes in the same solution is not difficult. In principle, any number of working electrodes could be studied however, it is unlikely that more than two or three would ever be widely used in practice. The bulk of the solution can have only one controlled potential at a time (if there are significant iR drops, there will be severe control problems with multiple-electrode devices). It is necessary to use a single reference electrode to monitor the difference between this inner solution potential and the inner potential of W1 at the summing point of an operational amplifier current-to-voltage converter (this is the potential of the circuit common see OA-2 in Fig. 6.17). The potential difference between... 

Remember that the interfacial potential is a difference between the inner potential of the electrode material and the potential established in the bulk of the solution. An iR drop can cause the latter to change. One way to minimize this problem is to construct the cell with an auxiliary electrode(s) that is directly across from the working electrodes, resulting in a very short current path and, therefore, a very small iR drop. Multiple-electrode transducers constructed in this way minimize cross-talk between different electrodes. 

An electrochemical flow detector, based on four working electrodes coated with different permselective film types, for use in flow-injection measurements of multiple nitroaromatic explosives was recently developed [18]. The resulting array response (Fig. 4) offers unique fingerprints of such explosive compounds. Electrochemical devices are extremely attractive for designing such e-nose-type multi-electrode arrays that combine several partially selective electrodes and lead to a distinct response pattern (signature) for mixtures of organic vapors without prior separation [2],... 

Figure 14 Spectroelectrochemical cell for in situ multiple internal reflectance mode ATR. The working electrode is a thin Pt layer deposited on the ZnSe paralleloid. The polyethylene body which contains the electrolyte and the other electrodes is pressed against the prism to form good sealing [44]. (Reprinted with copyright from The Electrochemical Society Inc.)...

If a reference electrode is inserted at a finite distance, l, from the working electrode, then the effective IR drop between WE and RE that contributes to error between r app and as given in Eq. (2) (6) is only the amount indicated by iRa (Fig. 5b). Note that multiplication of Eq. (9) by the current density (amperes/ cm2) produces the correct units for voltage (volts). This is the amount by which the true potential of the interface differs from the applied potential, as indicated by Eq. (2). 

Internal reflection approaches rely upon the total reflection of the infrared beam one or more times, (multiple internal reflection, MIR), at the internal surface of an infrared transparent crystal or internal reflection element (IRE) such as Ge, Si, GaAs, or ZnSe, Medium 1 in Fig. l(a)(i and ii). If the IRE is a semiconductor such as Ge, Si, or GaAs, it can serve as the working electrode, which vras the case in the work of Mark and Pons, who employed a Ge IRE. More recently, Chazalviel and coworkers have pubhshed extensive and detailed studies on the GaAs, Ge, and Si electrolyte interfaces,... 

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