Surface-Plasmon Resonance

Surface-plasmon resonance (SPR) has been used to detect surface-bound chemical species. SPR is achieved to detect the binding events of antibody and antigens in immunoassays. A gold-coated PMMA chip that was sealed by a PDMS channel plate was used. The antibodies were first immobilized on the gold layer. Upon binding with benzo[a]pyrene (BaP) 2-hydroxybiphenyl (HBP), the SPR signal was recorded [740]. 

In another report, binding of IgG to anti-IgG immobilized on a Au-coated BK7 chip (sealed by PDMS) was detected by SPR [741]. Lactate was also determined using the SPR method. First, lactate was oxidized by LOX immobilized on an osmium redox polymer to produce H202. This molecule was then reduced by HRP immobilized in the same redox polymer. This surface reaction was detected by SPR [741]. 

A binding kinetics study of rabbit IgG to protein A was also carried out based on SPR detection. Protein A was immobilized on the Au layer in the channel wall in a PDMS-glass chip [511], Antibody binding on peptides was also followed by SPR. The peptides were immobilized in cross-PDMS channels on a Au-coated chip [742], 

The surface plasmon resonance (SPR) is the analytical technique widely applied in the field of characterizing adsorption to surfaces. The big advantage of this method is the high sensitivity in detecting substances adsorbed on a surface (Ipg/pm of protein molecules) and the possibility of label-free measurements also in the in situ mode. The resulting graph is presented in the arbitrary units and called sensogram. 

In general, the system comprises the light source, detector, optical system (mostly prism), and a sensor chip (mostly thin gold film) (Fig. 4.23). The sensor chip, depending on the method, can stay in direct contact with the prism surface (Kretschmann configuration) or close to the surface (Otto configuration). 

The SPR is operated imder total internal reflection conditions. It means no light is transmitted through the reflecting surface and all light is reflected. To achieve total reflection condition, the RI of the crystal has to be significantly 

FIGURE 4.23 Setup and principle of surface plasmon resonance (Kretschmann 

The term surface plasmon resonance (SPR) can refer to the phenomenon itself or to the use of this phenomenon to measure biomolecules binding to surfaces. This method is now widely used in the biosciences and provides a generic approach to measurement of bio molecule interactions on surfaces. 

The phenomenon of SPR is directly related to Snell s Law (see fig. 18). In fact when radiation passes to a medium with lower dielectric constant there is a critical angle beyond which the refracted beam cannot propagate in the other medium. 

The decrease in reflectivity at the SPR angle (2sp) is due to absorption of the incident light at this particular angle of incidence. At this angle the incident light is absorbed and excites electron oscillations on the metal surface. 

It is important to understand why reflectivity is sensitive to the refractive index of the aqueous medium if the light is reflected by the gold film. This sensitivity is due to an evanescent field which penetrates approximately 200 nm into the solution [5]. 

The evanescent field appears whenever there is resonance between the incident beam and the gold surface and is not present when there is no plasmon resonance, that is, where the reflectivity is high. 

At certain incident angles the wavelength of the light matches the plasmon frequency and resonance occurs. This reduces the intensity of the reflected light, and the magnitude of the effect depends on the refractive index of the material into which the evanescent wave penetrates. 

This is the basis for SPR biosensor chips for measuring the binding kinetics of biological molecules. The biosensor consists of a thin metal 

Another technique used for the analysis of receptor-ligand interaction is surface plasmon resonance (SPR), with its first commercially available application in the BIAcore instruments [44] (Fig. 5.8). Like PCS, it allows the determination of kinetics by monitoring the association and dissociation of a receptor-ligand complex in real time. The interaction partners do not necessarily have to be labeled, which is an advantage of the technique. The principle of SPR measurements is based on an optical phenomenon. The core unit in this technique is a sensor chip consisting of a thin gold film with a modified surface attached on one side. One reactant is attached to the modified sensor surface, whereas the other reaction partner flows past this surface in solution. When the two interaction partners form a com- 

As mentioned in Sect. I, there are several diiferent mechanisms that operate in a well-designed NFT for enhancing the FOM. For the purposes of this article either the peak E intensity in the medium or the dissipated power in the medium will be chosen as the FOM for studying these enhancement mechanisms for HAMR. Depending on the specific NFT design, the order of importance of these mechanisms may vary, but in general the best NFTs will combine most or all of these mechanisms. The ones we will consider in this section are localized surface plasmon resonance (LSPR), the lightning rod effect, and the dual-dipole effect. 

Small metallic particles are well known to exhibit LSPRs. Surface plasmons are collective excitations of surface charge which under suitable conditions can be excited by an external optical field. Localized surface plasmons (LSPs) are oscillations of surface charge on a finite structure with fields that decay exponentially from the surface of the structure in both directions normal to the surface. The structure may be composed of a metal surrounded by a dielectric, or it may be composed of a dielectric surrounded by a metal. Examples include metallic nanoparticles and nanobubbles embedded in metals. Nanoholes in metal films also support LSPRs even though a hole is not entirely surrounded by the metal film. The surface plasmon resonance wavelength is determined by the size, shape, and material of the stmcture and the surrounding medium. 

2 Oblique-Incidence Optical Reflectivity Difference Microscopy 

3 Surface-Enhanced Laser Desorption/ionization Mass Spectrometry 

In recent years, various MS technologies have evolved as the dominant tools for identification and characterization of bound proteins. In the future, microarrays in combination with MS will provide new directions in biotechnology research. The microchip development for MS microarray and its application have 

These results should be compared with those of Vlatakis et al. [23]. As determined by an equilibrium binding method using radio-labelled substrates, their theophylline MIP reached binding equilibrium after 8 h, displayed negligible crossreactivity with theobromine (but 7% with 3-methylxanthine), gave a linear response from 14-224 /rM r = 0.999) and had a detection limit of 3.5 /rM (0.6 /ig/mL) theophylline. 

While the MIPs used in this work were inherently stable for at least 1 year, the silver films were prone to atmospheric degradation. Indeed, it was found that the application of the MIPs to the film protected it to some extent, but even when stored in vacuo these substrates were only stable for 5 days. The use of gold substrates is reportedly under investigation. Finally, it must be noted that the equipment used in this work was not a simple off-the-shelf commercial SPR system. These custom-made systems employed either highly sensitive photothermal deflection spectroscopy or a photodiode array to detect the changes in resonance 

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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. 

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. 

Futamata, M., Maruyama, Y. and Ishikawa, M. (2003) Local electric field and scattering cross section of Ag nanopartides under surface plasmon resonance by finite difference time domain method. J. Phys. Chem. B, 107, 7607-7617. 

There are several other techniques Uke the fluorescent dye displacement assays, footprinting, Fourier transform infrared spectroscopy. X-ray crystallography, electron microscopy, confocal microscopy, atomic force microscopy, surface plasmon resonance etc used for hgand-DNA interactions that are not discussed here. 

Regression correlation coefficient Regression coefficient of determination Rolling circle amplification Water solubility Sodium dodecyl sulfate Supercritical fluid extraction Standard operating procedure Solid-phase extraction Surface plasmon resonance Thymine... 

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