Imaging in the far-red with electronic light microscopy: requirements and limitations

Area of Science:

• Confocal microscopy
• Fluorescence imaging
• Optical filter design

Background:

• Simultaneous dual confocal imaging using red and far-red light offers benefits like reduced autofluorescence but presents challenges.
• Understanding system requirements is crucial for high-quality image acquisition and accurate data interpretation.

Purpose of the Study:

• To demystify filter set design for confocal microscopy.
• To guide users in constructing filter sets beyond commercial multi-purpose designs.
• To detail considerations for using cyanine 3.18 (Cy3) and cyanine 5.18 (Cy5) reagents.

Main Methods:

• Evaluating objective lens transmittance and chromatic aberration in the far-red spectrum.
• Designing high-transmission optical filters with sharp bandpass cutoffs.
• Considering light path mirror efficiency and its impact on signal detection.

Main Results:

• Optimizing filters maximizes collectable fluorescence, especially for cyanine 3.18 (Cy3) excited at 568 nm.
• Acceptable loss of cyanine 5.18 (Cy5) signal at longer wavelengths due to fluorophore brightness and aberration concerns.
• Far-red light offers greater penetration and less scattering, enabling high-quality deep-specimen imaging despite reduced resolution.

Conclusions:

• Careful filter set design is essential for successful dual-color confocal imaging.
• Custom filter sets can overcome limitations of commercial options.
• Far-red imaging provides advantages for deep tissue visualization in fluorescence microscopy.