Abstract
Plasmon waveguide resonance (PWR) is a variant of surface plasmon resonance (SPR) that was invented about two decades ago at the University of Arizona. In addition to the characterization of the kinetics and affinity of molecular interactions, PWR possesses several advantages relative to SPR, namely, the ability to monitor both mass and structural changes. PWR allows anisotropy information to be obtained and is ideal for the investigation of molecular interactions occurring in anisotropic-oriented thin films. In this review, we will revisit main PWR applications, aiming at characterizing molecular interactions occurring (1) at lipid membranes deposited in the sensor and (2) in chemically modified sensors. Among the most widely used applications is the investigation of G-protein coupled receptor (GPCR) ligand activation and the study of the lipid environment’s impact on this process. Pioneering PWR studies on GPCRs were carried out thanks to the strong and effective collaboration between two laboratories in the University of Arizona leaded by Dr. Gordon Tollin and Dr. Victor J. Hruby. This review provides an overview of the main applications of PWR and provides a historical perspective on the development of instruments since the first prototype and continuous technological improvements to ongoing and future developments, aiming at broadening the information obtained and expanding the application portfolio.
Highlights
The first observation of surface plasmons (SPs) was made by Wood in 1902, who reported anomalies in the spectrum of light diffracted on a metallic diffraction grating [1]
Two different possible scenarios of changes in protein conformation and orientation that result from ligand addition are presented: ligand X leads to a small decrease in thickness and a decrease in anisotropy, which could be explained by the tilting of the receptor; and ligand Y leads to large decrease in bilayer thickness and a decrease in anisotropy and could be explained by a lateral receptor expansion and a decrease in molecular ordering as a result of helix rearrangements
This strategy was applied by Salamon to detect lateral lipid segregation in proteolipid bilayers [31,32]; (3) moving Plasmon waveguide resonance (PWR) into an imaging technique allow to circumvent this limitation at the price of a higher complexity and bigger data processing
Summary
The first observation of surface plasmons (SPs) was made by Wood in 1902, who reported anomalies in the spectrum of light diffracted on a metallic diffraction grating [1]. SPs are coherent electron oscillations that exist at the interface between any two materials where the real part of the dielectric function changes signs across the interface, typically a metal–dielectric interface These are light waves that are trapped on the surface because of their interaction with the free electrons of the metal. The SPR phenomenon occurs on the surface of a metal (or another conducting materials) located at the interface of two media (usually glass and liquid) when it is illuminated by polarized light at a specific angle. In the 1990s, there was a burst in terms of SPR sensor development in a way to characterize molecular interactions directly (without labelling) and with high sensitivity Among those are optical waveguide resonance techniques, which have been used simultaneously to measure the refractive index and the anisotropy of biomaterials. Instrument development and applications to specific and challenging scientific questions moved side by side, resulting in great advances, especially in the field of membrane proteins, as further discussed in Sections 2 and 3
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