Molecular Devices ImageXpress Pico Installation Manual page 19

Chapter 1: ImageXpress Pico Automated Cell Imaging System
Filter Cubes
In the ImageXpress Pico system, the filter cube contains the excitation and emission filters and
the dichroic mirror. These optical components are essential parts of an epi-illumination
fluorescence imaging system in which the illumination and imaging optical paths overlap at the
objective lens.
A bandpass filter in the illumination optical path (called the excitation filter, since it filters the
excitation light) is used to restrict the illumination spectrum to a narrow range of wavelengths.
A dichroic mirror is a specially designed beam splitter that transmits light above a certain cutoff
wavelength and reflects light at shorter wavelengths. In the illumination path, the dichroic
mirror reflects shorter wavelengths from the light source up through the objective onto the
specimen.
Similarly, when imaging the illuminated sample, it is desirable to collect only the emission
photons from the target fluorophore, rejecting as much as possible any reflected or scattered
excitation light, any light from other dyes, and autofluorescence from the sample and
substrate. This is done by placing a filter in the collection light path, called the emission filter, to
restrict the wavelength range.
The optics in a filter cube are interference filters made by depositing thin film coatings on a
glass support. These components are delicate and can be easily damaged. Always use care
when handling a filter cube.
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