Fluorescence detection system

A fluorescence detection system, comprising:

• a stage configured to support a sample holder;
• an illumination module including a plurality of discrete light sources, each light source configured to produce spectrally distinct excitation light;
• a detection module configured to detect fluorescence emission light produced, in response to the excitation light from at least one of the light sources, by a fluorescent sample positioned in the sample holder;
• and
• an optical relay structure including a beamsplitter assembly configured to direct the excitation light from the illumination module along an illumination path to the sample holder and to direct the fluorescence emission light from the sample holder along a response path to the detection module, wherein the illumination path and the response path overlap between the beamsplitter assembly and the sample holder;
• wherein:
• the optical relay structure includes a plurality of beamsplitters corresponding in number to the plurality of light sources,
• each light source is optically coupled with a unique one of the beamsplitters,
• given pairs of a light source and a beamsplitter can alternately be positioned to illuminate the sample,
• each pair of an optically coupled light source and a beamsplitter is mounted on an excitation wheel such that given pairs can alternately be positioned to illuminate the sample by rotating the wheel,
• the optical relay structure further includes a plurality of emission filters corresponding in number to the number of optically coupled pairs of a light source and a beamsplitter and configured to reduce the amount of excitation light that reaches the detection module, and
• the emission filters are mounted on an emission wheel that can be rotated in tandem with the excitation wheel.