Surface plasmon resonance applied to DNA-protein complexes.

Abstract

Surface plasmon resonance (SPR) measures refractive index changes (Δn) at or near a surface and relates these to changes in mass at the surface Fig 1). This relationship is given by the Clausius Mossotti form (Eq. 2) of the Debye equation (Eq. 1): Open image in new window (1) Open image in new window Fig. 1. Schema showing the principle of surface plasmon resonance. Light from a laser source arriving through a prism at a gold surface at the angle of total internal reflection (θ) induces a nonpropagative evanescent wave that penetrates into the flow cell opposite the prism. The intensity of the reflected light is continuously monitored. At a given angle (λ) dependent on the refractive index of the solution in the flow cell, resonance between the evanescent wave and free electrons in the gold layer results in a reduction in the intensity of reflected light. The change in angle of reduced intensity (Δλ) reflects changes in the refractive index (n) of the solution in the flow cell immediately adjacent to the gold layer. A dextran surface coupled to the gold layer allows immobilization of ligands (e.g., DNA) within the evanescent field. where ɛ is the real part of the dielectric constant or permittivity constant related to the refractive index by ɛ = n 2, N is the number density given by N Aρ/Ma (N A is Avogadro’s number, ρ is the density and M a is the molecular mass). It is assumed that Δn/ΔC is a constant.