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SPR is real-time, label-free measurements of binding kinetics and affinity. This has distinct advantage over radioactive or fluorescent labeling methods, in terms of 1) ligand-analyte binding kinetics, that can be probed without the costly and time-consuming labeling process that may interfere with molecular binding interactions; 2) binding rates and affinity can be measured directly and 3) low affinity interactions in high protein concentrations for can be characterized with less reagent consumption than other equilibrium measurement techniques; 4) Label-free detection of molecular interactions presents an attractive alternative.

This is particularly true for protein targets where labels can compromise protein function. Label-free methods are also desirable because they are typically compatible with real-time detection, enabling the determination of rates of association. The success of SPR biosensors was indicated by the growing number of commercially available instruments. Since Biacore AB (originally Pharmacia Biosensor AB) launched the first commercial SPR biosensor on market in 1990, there have been many more competing SPR instruments including IASys (Affinity Sensors), SPR-670 (Nippon Laser Electronics), IBIS (IBIS Technology BV), TISPR (Texas Instruments), etc.
Plasmon resonance techniques such as SPR, SPR-imaging, SPR-MS (mass spectrometry) and PWR, trends in protein array technology and a potential use of SPR biosensors in proteome and optics based research will be reviewed in terms of their fundamentals, and in the latest applications with emphasis in studies performed with membrane proteins.

This work will also throw light on SPR sensors (from typical Kretschmann prism configurations to fiber sensor schemes) with micro- or nano-structures for local light field enhancement, extraordinary optical transmission, interference of surface plasmon waves, plasmonic cavities, etc. Additionally, a note on covalent and non-covalent immobilization methods for the attachment of the molecules to the sensor surface is also reviewed for the functional reconstitution of membrane proteins in the various types of lipid mono/bilayers. Advantages and disadvantages of each methodology are provided along with some of the latest accomplishments with emphasis on the area of GPCRs.

With everincreasing advances in high-throughput proteomics and systems biology, there is a growing demand for the instruments that can precisely quantitate a wide range of receptor-ligand binding kinetics in a high-throughput fashion. The ability to quantify kinetics and affinities of receptor-ligand binding interactions is essential for basic biology, viz. ligand screening, immunology, cell biology, signal transduction, and nucleotide-nucleotide, nucleotide-protein, protein-protein and protein-lipid interactions biomarker discovery, proteomics, pharmaceutical development and drug discovery, among others.

Optical biosensors that utilize surface plasmon waves (SPs) –electromagnetic waves propagating on the interface between a metallic film and a dielectric medium – have been widely used for this purpose. Techniques based on surface plasmons such as Surface Plasmon Resonance (SPR), SPR Imaging, Plasmon Waveguide Resonance (PWR) and others, have been increasingly used to determine the affinity and kinetics of a wide variety of real time molecular interactions such as protein-protein, lipid-protein and ligand-protein, without the need for a molecular tag or label. (Imprint: Novinka)