Effect of the Refractive Index on the Light Scattering Detection

Based on the theory of Rayleigh scattering, the scattering cross-section of a nanoparticle is not only determined by the particle size but also influenced by the refractive index contrast, which is the ratio of the refractive index of the particle to that of the medium. A silica nanoparticle scatters 3.8 times less light than a polystyrene nanoparticle of the same size at a wavelength of 532 nm and with refractive indices of 1.46 and 1.59, respectively. The exact refractive index of the virus is not known, but it can be assumed to be 1.45 or 1.46, similar to that of proteins and DNA. The effect of the refractive index on the light scattering detection of single viruses is examined using the bacteriophage T7, a bacterial virus with an icosahedral capsid head of ~60 nm in diameter, along with silica nanospheres and polystyrene nanobeads of a comparable size.

Figure 1. Light scattering analysis of single nanoparticles with similar diameters.

The comparable burst height/burst area for the T7 virions and 60 nm silica nanospheres confirms that the virus and silica nanoparticles exhibit comparable refractive indices. This demonstrates that the Flow NanoAnalyzer can quickly analyze the influence of different materials on the scattered light of particles.

Angew. Chem. Int. Edit., 2016, 55(35), 10239-10243.