Electrochemical sensors diffusion barrier

Amperometric sensors — A class of electrochemical sensors based on amperometry. A - diffusion-limited current is measured which is proportional to the concentration of an electrochemically active analyte. Preferred technique for - biosensors with or without immobilized enzymes (biocatalytic sensors). The diffusion layer thickness must be kept constant, either by continuous stirring or by means of an external diffusion barrier. Alternatively, micro electrodes can be... 

Amperometric sensing of gases is based on solid ion-conducting materials, as described for potentiometric gas sensors. Solid-state amperometric gas sensors measure the limiting current (ij) flowing across the electrochemical cell upon application of a fixed voltage so that the rate of electrode reaction is controlled by the gas transport across the cell. The diffusion barrier consists of small-hole porous ceramics. The limiting current satisfies the relationship ... 

Gas-permeable membranes and diffusion barriers are fields of polymer applications as well (Harsanyi 1995 Tierney 1996). A typical gas-permeable membrane is hydrophobic and has a high rate of gas transport relative to other species. The membrane may be solid or microporous. Gas-permeable membranes serve a number of functions. They provide the sensor with a selective membrane covering and, thus, reducing contamination of the sensor by incompatible materials in the environment. They allow passage of gases only, preventing excess electrolyte loss in electrochemical sensors. 

A system underpinned by commercially made screen-printed electrochemical cells was described by Palmisano et al. [19]. The cells were converted into biosensors for lactate in milk and yoghurt by addition of an electrochemically polymerised barrier to interference and a layer composed of lactate oxidase, glutaraldehyde and BSA. These steps appeared to have been carried out by hand. As there was no outer diffusion-limiting membrane, the linear range of the sensors was quite small (0-0.7 mM). They were incorporated into a FIA with a microdialysis unit based on a planar membrane and a buffer reservoir (earlier work used a microdialysis fibre with a platinum electrode [29]. The concentration of lactate was determined in various milks (0.27-1.64 mM), and in raw milk (c. 0.5-0.9 mM) left to degrade on the laboratory bench. The recovery of the microdialysis unit, 2.6%, implied that the sensor had an ability to return measurable currents for very low concentrations of lactate. A further implication is that the electro-polymerised layer was very effective at preventing interference. 

Amperometric sensors are based on the electrochemical reduction of oxygen, and are governed by the diffusion of the electroactive species through a barrier - that is, holes or porous layers 81,82], The coulometric sensors are based on a similar concept, and were developed for closed-chamber systems. Although very few amperometric and coulometric sensors have been studied to date, some relevant examples are summarized in Chapter 13. 

Amperometric sensors are based on electrochemical reactions which are governed by the diffusion of the electroactive species through a barrier. 129 The barrier usually consists of a hole (see Figure 10.11a) or a porous neutral layer. The control of the gas inflow by an electrochemical method was proposed recently. 2 The voltage is fixed on the diffiision plateau of the I(U) curve (Figure 10.1 lb). For a reaction limited by the mass transport process, the general flux equation in a one-dimensional model is... 

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