Sensors multiple-electrode sensor array

Multiple electrodes have been used to obtain selectivity in electrochemical detection. An early example involved the separation of catecholamines from human plasma using a Vydac (The Separation Group Hesperia, CA) SCX cation exchange column eluted with phosphate-EDTA.61 A sensor array using metal oxide-modified surfaces was used with flow injection to analyze multicomponent mixtures of amino acids and sugars.62 An example of the selectivity provided by a multi-electrode system is shown in Figure 2.63... 

Different miniaturized flow injection analyzers have been constructed using spectrophotometry as a leading detection technique. Besides, electrochemical techniques such as amperometry and potentiometry with chemically modified solidstate electrodes and tubular membrane-based ISEs, respectively, have been proved to be well adapted to multiparametric measurements of inorganic species present in wastewater, using multiple sensor arrays. 

During the 1980s, Raytheon Company manufactured a selected number of towed array sensors [Sj. These sensors consisted of multiple homopolymer PVDF elements connected electrically in parallel to form an extended line sensor. The individual elements were constructed from electroded and bonded PVDF sheets stacked in mechanical series and electrically in parallel to simultaneously boost both the capacitance and sensitivity. The anisotropy of the homopolymer is exploited in these extended sensors by aligning the low (3,2) axis sensitivity along the towed axis. This results in an array that, by design, will suppress flow noise and vibration strum while being most sensitive in the normal direction. 

In addition to the modified electrodes described in the previous sections, which usually involve a conductive substrate and a single film of modifying material, more complicated structures have been described. Typical examples (Figure 14.2.4) include multiple films of different polymers (e.g., bilayer structures), metal films formed on the polymer layer (sandwich structures), multiple conductive substrates under the polymer film (electrode arrays), intermixed films of ionic and electronic conductor (biconductive layers), and polymer layers with porous metal or minigrid supports (solid polymer electrolyte or ion-gate structures) (6,7). These often show different electrochemical properties than the simpler modified electrodes and may be useful in applications such as switches, amplifiers, and sensors. 

A miniaturized sensor for heavy-metal ions consisting of a nontoxic bismuth working electrode, an integrated Ag/AgCl reference electrode, and a gold counter electrode, has been proposed by Zou et al." Pb(II) and Cd(II) are positioned in a microchamber of 4.5 pL in which a planar array of multiple sensors can be located for multiple measurements using different sensor son one chip (Fig. 21.7). 

For real-time multiple analyte monitoring, a group of sensors must be brought together, typically in an array format. We have demonstrated small arrays of IL sensors using both amperometric and impedance approaches. An array of four IL-coated glassy carbon electrodes was tested for the voltammetric detection of DNT and TNT, and a correlation (with 100 % classification accuracy) between the redox properties and the physiochemical parameters of the species involved was revealed (Fig. 2.18) [204]. Detection limits in liquid phase of 190 nM and 230 nM for TNT and DNT, respectively, and a linear range up to 100 jM were obtained. 

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