Surface plasmon resonance Subject

The reaction between the analjrte and the bioreceptor produces a physical or chemical output signal normally relayed to a transducer, which then generally converts it into an electrical signal, providing quantitative information of analytical interest. The transducers can be classified based on the technique utilized for measurement, being optical (absorption, luminescence, surface plasmon resonance), electrochemical, calorimetric, or mass sensitive measurements (microbalance, surface acoustic wave), etc. If the molecular recognition system and the physicochemical transducer are in direct spatial contact, the system can be defined as a biosensor [76]. A number of books have been published on this subject and they provide details concerning definitions, properties, and construction of these devices [77-82]. 

The nonlinear polarization Pi(fl, r ) of Eq. (10) is a pnrely local surface polarization because it only depends on the value of the fields at location r. Because it depends on the fundamental field inside the particle, it is subjected to resonances when the quantity s(ft)) + 2e , vanishes, where e(w) is the complex dielectric function of the metal and that of the surrounding medium. On the opposite, the nonlinear polarization 2( 2, E) of the form of Eq. (11) is a non local nonlinear polarization since it depends on spatially varying fields within the particle. Similarly to the first order contribution, it is subjected to resonances when the quantity 2e(w) + 3e vanishes. These resonances are the usual surface plasmon resonances of the particle. Within the condition of non magnetic media, the magnetic dipole field does not introduce any resonances. We neglect higher order terms. 

Figure 7.27 Schematic illustration of Surface Plasmon Resonance (SPR). Incident light is normally subject to total internal reflection in the prism block except for losses due to evanescent wave penetration of the hydrogel layer at the resonant angle. Changes in resonant angle due to receptor-ligand interactions are the basis for the real time observation of molecular recognition and association/dissociation events.

During the process, color changes from colorless to light yellow and yellow-brown indicating the formation of silver nanoparticles. After the process, the samples were subjected to spectrophotometric analysis. UV-Vis spectra are shown in Figure 12.3. The peak at 400—450 nm corresponds to the characteristic surface plasmon resonance of silver nanoparticles. Table 12.1 presents the results of nanoparticle size analysis. 

Nonsteady behavior of electrochemical systems was observed by Fechner as early as 1828 [ii]. Periodic or chaotic changes of electrode potential under gal-vanostatic or open-circuit conditions and similar variation of current under potentiostatic conditions have been the subject of numerous studies [iii,iv]. The electrochemical systems, for which interesting dynamic behavior has been reported include anodic or open-circuit dissolution of metals [v-vii], electrooxidation of small organic molecules [viii-xiv] or hydrogen, reduction of anions [xv, xvi] etc. [ii]. Much effort regarding the theoretical description and mathematical modeling of these complex phenomena has been made [xvii-xix]. Especially studies that used combined techniques, such as radiotracer (-> tracer methods) ig. 1) [x], electrochemical quartz crystal microbalance (Fig. 2) [vii,xi], probe beam deflection [xiii], surface plasmon resonance [xvi] surface stress [xiv] etc. have contributed considerably to the elucidation of the role of chemisorbed species ( chemisorption), surface reconstruction as well as transport phenomena in the mechanism of oscillations. 

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