SVI Support Wiki Pages

The medium refractive index

The medium refractive index is the Refractive Index (r.i.) of the Specimen Embedding Medium .

A mismatch between the refractive index of the lens immersion medium ( Lens Refractive Index ) and specimen embedding medium will cause several serious problems: see Acquisition Pitfalls . For low values of r.i. such as 1.32 for water, the computed PSF for an oil immersion lens is only valid near the coverslip-medium interface due to spherical aberration effects in deeper layers. In such cases we recommend lenses optimized for the refractive index of the medium.

(This is one of the Microscopic Parameters ).

Examples of embedding media

For the frequently used medium glycerol (75%) the refractive index is 1.44. Polyvinyl alcohol has a refractive index 1.52-1.55.

The embedding medium Mowiol is manufactured by companies like Polysciences, Hoechst and Sigma. Mowiol is intended to match the refractive index of immersion oil, but values seem to range between 1.41 and 1.49. Other mounting media are Vectashield (R.I. 1.457, Vector Labs) and Prolonged Gold (R.I. increases during curing, Invitrogen).
The refractive index of Prolonged Gold can be reviewed here.

In general, we recommend to review the product data sheet or contact the vendor for specific details on what mounting media to use. Issues like the refractive index and compatibility with fluorescent dyes need to be considered.

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