Surface Conductivity Sensors Mode

Zourob et al.22 constructed a flow-cell incorporating the MCLW and ITO electrode as shown in Fig. 15.25. Initial experiments were conducted after treating the surface with BSA overnight. BG bacterial spores were introduced to the sensor system at a constant flow rate of 200 pL min 1 in 50 mM histidine buffer, and the sensor system was operated in real-time scattering mode using a CCD camera. 

The emphasis on the thickness of the selective layer is linked to the mode of interaction between the analyte and the selective layer. If this interaction takes place exclusively at the surface of the selective layer, then the bulk conductivity does not contribute and represents only a shunt which decreases the signal-to-noise ratio. This is a typical case of chemiresistors based on inorganic materials (Fig. 8.6). On the other hand in chemiresistors based on organic semiconductors, the signal usually originates in the bulk of the selective layer. In that case, the response time of the sensor is affected by its thickness. 

The response of piezoelectric devices propagating shear horizontal acoustic plate modes (SH-APMs) has been modeled and experimentally characterized for variations in surface mass, liquid rheological properties, and solution dielectric coefficient and electrical conductivity. The nature of the SH-APM and its propagation characteristics are outlined and used to describe a range of Interactions at the solid/liquid interface. Sensitivity to sub-monolayer mass changes is demonstrated and a Cu sensor is described. The APM device is compared to the surface acoustic wave device and the quartz crystal microbalance for liquid sensing applications. 

Conducting polymers have been used to modify the surface properties of metallic electrodes, in particular microelectrodes [49]. TTie prosthetic functional groups covalently attached to the polymer chains can be used as molecular sensors or molecular transducers that can reversibly transfer electrochemical information between the medium and the electrodes. These systems are useful for solution sensing in both amperometric and resistometric modes. Enzymes (for example, glucose oxidase) can be incorporated directly into the polymeric layer during polymerization and subsequently used as biosensors. 

In Eq. (11) Tg is the average sample temperature (see Fig. 4) and AT is the offset between bath and sample temperature. In Eq. (10) is the thermal conductance for heat flow perpendicular to the surface of the planar sample. Tj is the sample bath relaxation time and t2 is a combined (internal) relaxation time for the sample and addenda (heater, temperature sensor, and sample holder when present). T, and result, respectively, in a low and high frequency cut-off. In the normal a.c. calorimetric mode one chooses a frequency ft) so that ft)T2- 1 in order to avoid temperature gradients in the sample. In Eq. (10) the third term can then be neglected. If one further assume the thermal conductance of the sample to be much larger than Ky, also the last term can be omitted. In addition to AT one may also observe a phase shift ((p- nil) between T t) and P t), with given by [6] ... 

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