Frequently Asked Questions about PWR
What is PWR?
What can I measure with PWR?
Why is PWR powerful?
How does it compare with conventional SPR techniques ?
Where can I get information about PWR?
Who can I contact regarding PWR?
Is the PWR equipment commercially available?
What is PWR?
Plasmon Waveguide Resonance Spectroscopy (PWR) is an innovative experimental methodology that enables in-depth characterization of protein-protein, lipid-protein (proteolipid membranes), and receptor-ligand interactions occuring either within or at the surface of single anisotropic thin films. This is a powerful tool for probing the structural, kinetic and thermodynamic parameters resulting from such interactions.
Plasmon resonance spectroscopy combines techniques of thin film physics, surface plasmon resonance and waveguide phenomena, Maxwell's equations and solid-supported membrane biochemistry. Surface Plasmons (localized electron density oscillations) can be excited by light passing through a glass prism coated with a thin metal film (Ag), at a specific incident angle under total internal reflectance conditions. When the metal thin film is over-coated with a thicker dielectric coating such as SiO2, the plasmons can be excited by both s and p polarized light. This can be used to probe the optical properties of proteins in membrane bilayers in both the parallel and perpendicular directions with respect to the bilayer plane. Resonance can be achieved by varying the wavelength (l) at a fixed angle (a) or by varying 'a' at a fixed 'l'. The reflected light intensity, as a function of either 'l' or 'a', results in two well separated CPWR spectra corresponding to spectral parameters associated with mass density and film structure both parallel and perpendicular to the membrane normal.
Back to Top
What can I measure with PWR?
PWR permits characterization of molecular properties of anisotropic two-dimensional integral membrane protein systems both parallel and perpendicular with respect to the bilayer membrane surface. CPWR spectral analysis yields the following parameters: refractive index (n), extinction coefficient (k), and thickness (t), from which one can obtain information such as binding constants, kinetic parameters associated with binding , structural changes, molecular orientation, mass per unit surface area. These can be examined in a time-dependent fashion. Importantly, since these measurements can be performed with exciting light parallel and perpendicular to the plane of the membrane, it allows characterization of systems that are both birefringent and dichroic.
Back to Top
Why is PWR powerful?
PWR is a versatile technique with a relatively simple optical methodology with superior sensitivity. It can be used to obtain information about mass and structural parameters, including anisotropy in lipid and lipid-protein films. It is especially suited to detecting small amounts of material which may be labile and structurally heterogenous, located at the interface between two immiscible phases. It overcomes limitations of other techniques, such as using fluorescent probes, radioactive labels, and other labels that may interfere with binding or cause structural perturbations. The complete measurement system is located on the remote side from the sample system and there is no optical interference from the bulk medium. PWR observations are based solely on the dielectric properties of molecules, or their intrinsic light absorption characteristics, and thus require no specific labeling.
Back to Top
How does it compare with conventional SPR techniques?
PWR spectrosocopy allows for complete optical characterization (i.e. evaluating all optical parameters-n, k and thickness t) of both isotropic and anisotropic thin films including biological membranes.
Conventional SPR is limited in its approach to only isotropic systems which precludes its applications to biological membrane systems.
Back to Top
Where can I get information about PWR?
Information regarding PWR methodology and applications can be obtained from this website and pertinent publications.
Back to Top
Who can I contact regarding PWR?
All queries regarding PWR phenomenology and possible collaborations can be sent to Dr. Gordon Tollin.
Back to Top
Is the PWR equipment commercially available?
At present, there is no commercially available instrument. Commercial development is in progress.