Plasmon resonances

When the interface between a thin ( 50nm) film of free-electron metal (e.g., Au, Ag, or Al) and a glass prism is irradiated with a TM polarized coherent light, correlated motion of free electrons in the metal leads to the formation of oscillating charge at the metal/glass interface (Fig. 9.16) 

Collectively the two oscillating vectors are known as surface plasmon (Homola, 2004, 2008), which moves along the surface, but does not radiate energy. Its intensity decays exponentially to the dielectric (sample) in the direction perpendicular to the interface. In that respect, it is similar to the evanescent field. 

Thus the value of the dielectric constant at the sample/metal interface determines the shift of the resonance. When adsorption of molecules at the metal surface results in the change of the refractive index or of the local value of the dielectric constant, the change of reflectivity is observed. This phenomenon has been used as the mechanism for detection of gases (Fig. 9.18a) and of adsorbed biomolecules (Fig. 9.18b). The depth of penetration of the surface plasmon is comparable to that of the evanescent field, that is, 100-500 nm for the visible-near infrared range. 

It is important to realize that for the plasmon resonance to occur the condition of two matching plasmons at the opposite interfaces of the thin metal must be met. In other words there must be a dielectric/metal interface at which an evanescent field is created. In the Kretschmann geometry that interface is created by having the metal coated on the glass prism. Likewise, the SPR condition can also be realized in a fiberoptic format with a thin metal layer deposited on a flattened single-mode optical 

Related to the plasmon resonance physics is the micromirror optical sensor for hydrogen (Butler, 1991). Like gold and silver, palladium is a free-electron gas metal in which charge groupings such as phonons or plasmons are likely to occur. As we have seen already, palladium has a natural selectivity due to its sorption of monoatomic hydrogen. In that sensor, the reflectivity of the thin Pd film mirror mounted at the end of cladded optical fiber (Fig. 9.19) is modulated by absorption of hydrogen. 

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There are a few other surface-sensitive characterization techniques that also rely on the use of lasers. For instance surface-plasmon resonance (SPR) measurements have been used to follow changes in surface optical properties as a fiinction of time as the sample is modified by, for instance, adsorption processes [ ]. SPR has proven usefiil to image adsorption patterns on surfaces as well [59]. 

Klar T ef a/1998 Surface-plasmon resonances in single metallic nanoparticles Phys. Rev. Lett. 80 4249... 

Bulk and surface imprinting strategies are straightforward tools to generate artificial antibodies. Combined with transducers such as QCM (quartz crystal microbalance), SAW (surface acoustic wave resonator), IDC (interdigital capacitor) or SPR (surface plasmon resonator) they yield powerful chemical sensors for a very broad range of analytes. 

Surface plasmon resonance (SPR) Interaction strength (molar dissociation constant, K ). One member of the reacting pair needs to be immobilised onto an inert surface. Not suitable for selfassociation analysis. [7]... 

Hartmann T, Ober D (2000) Biosynthesis and Metabolism of Pyrrolizidine Alkaloids in Plants and Specialized Insect Herbivores. 209. 207-243 Haseley SR, Kamerling JP, Vliegenthart JFG (2002) Unravelling Carbohydrate Interactions with Biosensors Using Surface Plasmon Resonance (SPR) Detection. 218 93-114... 

More recently, the method of scanning near-field optical microscopy (SNOM) has been applied to LB films of phospholipids and has revealed submicron-domain structures [55-59]. The method involves scanning a fiber-optic tip over a surface in much the same way an AFM tip is scanned over a surface. In principle, other optical experiments could be combined with the SNOM, snch as resonance energy transfer, time-resolved flnorescence, and surface plasmon resonance. It is likely that spectroscopic investigation of snbmicron domains in LB films nsing these principles will be pnrsned extensively. 

Under i-polarization light, the optical spectra of 5-nm nanoparticles (Fig. 7A), recorded at various incident angles 0 do not change with increasing 0. They are characterized by a maximum centered at 2.9 cV, which is similar to that observed for isolated particles (Fig. 5B). Flowever, the plasmon resonance peak remains asymmetrical, as observed under nonpolarized light (Fig. 6). 

The interaction between c Fusarium moniliforme and PGIP from Phaseolus vulgaris L. was investigated using a biosensor technique based on sur ce plasmon resonance (BIAlite). This new analytical system provides information on the strength and the kinetics of biomolecular interactions. 

Averitt, R.D., Sarkar, D. and Halas, N.J. (1997) Plasmon resonance shifts of Au-coated AU2S nanoshells Insight into multicomponent nanopartide growth. Physical Review Letters, 78, 4217-4220. 

El-Sayed, I.H., Huang, X. and El-Sayed, M.A. (2005) Surface plasmon resonance scattering and absorption of anti-EGFR antibody conjugated gold nanopartides in cancer diagnostics Applications in oral cancer. Nano Letters, 5, 829-834. 

Hutter, E. and Fendler, J.H. (2004) Exploitation of localized surface plasmon resonance. Advanced Materials, 16, 1685-1706. 

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