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Fluorescence bandpass filter is a special optical filter mainly used in fluorescence detection system (such as fluorescence microscope, flow cytometer, biochemical analyzer, etc.), whose core function is to selectively transmit the fluorescence signal of a specific band while blocking the excitation light and other stray light, in order to improve the signal-to-noise ratio and detection sensitivity.
| Parameter | Typical Value | Influence |
| CWL | Selection based on fluorescent dye (e.g. Cy5: ~670 nm) | It must match the fluorescence emission peak or the signal is lost. |
| FWHM | 10~40nm (narrow band) | The narrower the bandwidth, the higher the signal-to-noise ratio, but the signal strength may be reduced. |
| Cut-off Range | OD4~OD6 (excitation light band) | Ensure complete blocking of excitation light (e.g., 488 nm laser) to avoid background interference. |
| AOI | 0° (vertical incidence optimal) | Tilted incidence may result in a CWL offset (requires selection of an angle-compensated design). |
Center Wavelength (CWL): The wavelength at which the filter has the highest transmittance, which needs to match the emission peak of the fluorescent dye (e.g. FITC: ~525 nm, DAPI: ~460 nm).
Full Width at Half Maximum (FWHM): The wavelength range in which the transmittance is ≥50%, commonly narrowband (10~40 nm) or broadband (50~100 nm).
Peak Transmittance (Tpeak): Usually >90% (up to 95% or more for high quality filters).
Blocking Range: Optical density (OD) in the non-passband region (e.g., excitation band) should be ≥ OD4 (i.e., transmittance < 0.01%).
| Common fluorescent dyes and filters matching | |||
| Dye/Probe | Excitation Wavelength | Emission Wavelength | Recommended Filter Combination |
| SYBR® Green | 497 nm | 520 nm | 480–500 nm Ex / 510–540 nm Em |
| FAM | 494 nm | 520 nm | 480–500 nm Ex / 510–540 nm Em |
| HEX/VIC | 535 nm | 556 nm | 520–550 nm Ex / 550–580 nm Em |
| CY5 | 640 nm | 670 nm | 630–650 nm Ex / 660–690 nm Em |
| Texas Red | 589 nm | 615 nm | 570–600 nm Ex / 610–630 nm Em |
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