Optical Spectroscopy

Surface Plasmon Resonance (SPR)

SPR arises when photons are reflected from a conducting film at the interface between two media of different refractive indices. This phenomenon can be utilized by measuring a change in the angle of reflection of polarized near infra-red light on a gold surface, which occurs when the index of refraction of the surface changes. The Biacore 3000 instrument is used to measure biomolecular interactions, specifically the association rate and dissociation rate of analytes from a biomolecule immobilized on one side of a gold film. In the instrument, light is reflected on the opposite side of a gold film to excite the surface plasmons, that is, the oscillations of free electrons propagating along the film's surface. The angle of reflection of polarized light reflecting off this surface is measured. When the immobilized biomolecules are bound by their ligands, an alteration in surface plasmons on the opposite side of the film is created that is directly proportional to the change in bound, or absorbed, mass. The HTSRC hosts a Biacore 3000 SPR instrument and can provide guidance and support in its use.

Fourier Transform Infrared (FTIR) Spectroscopy

An infrared spectrum represents a fingerprint of a sample with absorption peaks which correspond to the frequencies of vibrations of the bonds of the atoms making up the material. The specific absorption pattern of infrared (IR) photons by the atomic bonds within a molecule correlates with its composition and structure. The presence of absorption peaks at specific IR-wavelengths can be attributed to the presence and orientation of specific functional groups. Thus, an IR spectrum can be used to identify and quantify a material.

The HTSRC hosts a Nicolet Magna IR-560 Fourier Transform Infrared Spectrometer and can provide training and guidance in its use.

Circular Dichroism

Circular dichroism (CD) spectrometry measures very small differences in the absorption of right- and left-circularly polarized photons. This differential absorption correlates with the phenomenon of chirality. Changes in the CD spectrum correlate with protein secondary structure such as alpha-helixes or beta-sheets. Thus, CD spectrometry can be used to monitor changes in the secondary structure of biomolecules that possess chiral centers.

The HTSRC hosts an Aviv model 202 CD spectrometer and can provide guidance and training for its use.