GWC Technologies

GWC
Technologies

505 S. Rosa Rd
Madison, WI 53719
USA

608.441.2726

WAVELENGTH-SCANNING SPR
Surface Plasmon Resonance (SPR) is an electro-optical effect that can be used to monitor events on metal surfaces. In life science research, applications center on monitoring biomolecular interactions. In materials science research, applications center on analysis of thin films on metal surfaces—often thinner than a molecular monolayer. The SPR response is typically monitored by measuring changes in the light reflected from the SPR sensor.

Traditional SPR Measurement
The SPR response is sensitive to many factors, including the angle and wavelength of light incident on the sample, the refractive index of materials in the light path and on the metal surface, temperature, and the mass density changes on the surfaces. Traditional SPR systems use angle-scanning detection, in which reflected light is measured over a range of angles of incidence. As the chart above shows, reflectivity falls to a minimum then rises again as the angle of incidence is increased (blue curve). The angle of minimum reflectivity (dotted line) is called the SPR angle. When material is adsorbed to the surface, such as when an antigen binds to an immobilized antibody, the curve shifts (red lines). The SPR response is traditionally expressed in terms of the change in SPR angle, though some systems do not provide this fundamental data, instead expressing measurements as arbitrary relative units or resonance units.

FT-SPR Measurements
GWC’s advanced “FT-SPR” wavelength-scanning system measures the SPR response over a range of wavelengths, using the light source and data collection function from a Fourier-Transform Infra-Red (FT-IR) spectrometer. Wavelength-scanning SPR curves have an analogous profile to angle scans (see chart at right). The minimum in reflectivity occurs at the “SPR wavelength”, or, in vibrational spectroscopy parlance, its reciprocal, the “SPR wavenumber” (dotted lines) when collected at a fixed angle. When material is adsorbed to the surface, the curve shifts in a manner similar to SPR angle plots (red lines).

FT-SPR measurements are theoretically more sensitive than angle-scanning measurements due to the very high precision of FT-IR spectrometers with respect to wavelength measurement. Trial experiments bear this out, indicating that FT-SPR can be used for the most demanding label-free applications.

The SPR100 System
The SPR 100 is configured as an accessory module for Thermo’s research grade FT-IR spectometers. This system provides direct access to fundamental data, so you can express surface changes as shifts in SPR wavenumber rather than the less satisfactory arbitrary units offered by other systems. The SPR100 is thus not only well suited to applications such as analysis of thin films and biomolecular interactions, but also to fundamental exploration of SPR spectroscopy.

Background information on FT-SPR
For more information about how FT-SPR works, please refer to our technical note or contact .