Fluorophore Spectrum Viewer

Spectral overlap occurs when the emission spectrum of one fluorochrome extends into the detection range of a channel assigned to a different fluorochrome. In multicolor flow cytometry, every fluorochrome emits photons across a range of wavelengths — not just at its emission peak. When two fluorochromes share part of their emission range, the detector for one will also capture signal from the other.

For example, FITC (emission max ~520nm) and PE (emission max ~575nm) both emit photons in the 530–560nm range. A 530/30 bandpass filter designed for FITC will also capture some PE emission. This unwanted signal is called spillover, and the process of mathematically removing it is called compensation.

The degree of spectral overlap depends on the specific fluorochrome pair and the bandpass filters on your instrument. This tool calculates spillover coefficients for your selected fluorochromes using their full spectral curves, helping you identify problematic combinations before you run your experiment.

A spillover table (also called a compensation matrix) shows how much signal from each fluorochrome spills into each detector channel. Rows represent the source fluorochrome (the one emitting photons), and columns represent the receiving detector channel.

Spillover is asymmetric — the amount FITC spills into the PE channel is different from how much PE spills into the FITC channel. This is because spillover depends on the shape of each fluorochrome's emission spectrum relative to the receiving detector's bandpass filter.

In this tool, spillover values are color-coded: green (<5%) indicates minimal spillover, yellow (5–15%) indicates moderate spillover, orange (15–30%) indicates significant spillover, and red (>30%) indicates high spillover. High spillover pairs increase spreading error and should be avoided when possible.

Compensation is the traditional method for removing spillover in conventional flow cytometry. It uses single-stained controls to calculate how much signal from each fluorochrome leaks into adjacent channels, then mathematically subtracts the spillover. Compensation works well for panels with moderate spectral overlap but reaches its limits with large panels (>10 colors) where cumulative spreading error degrades resolution.

Spectral unmixing is the approach used by spectral cytometers (e.g., Cytek Aurora, Sony ID7000). Instead of detecting fluorescence through discrete bandpass filters, spectral instruments capture the full emission spectrum across many narrow channels. An unmixing algorithm then decomposes the combined signal into individual fluorochrome contributions using reference spectra.

Spectral unmixing can resolve fluorochromes with very similar emission peaks that conventional compensation cannot separate, enabling panels of 30+ colors. However, it requires accurate reference spectra and is sensitive to autofluorescence, which must be treated as an additional component in the unmixing model.

Effective multicolor panel design balances antigen expression levels with fluorochrome brightness, minimizes spectral overlap between channels that carry functionally important markers, and accounts for instrument-specific detector configurations.

• Bright fluorochromes for dim antigens: Pair very bright fluorochromes (PE, APC, BV421) with low-abundance markers. Reserve dimmer fluorochromes for highly expressed antigens where signal strength is less critical.
• Minimize spillover between critical channels: If two markers define your key population (e.g., CD4 and CD8), assign them to fluorochromes with minimal spectral overlap to preserve resolution at the population boundary.
• Tandem dye awareness: Tandem conjugates like PE-Cy7 and APC-Cy7 are susceptible to lot-to-lot variability and degradation. Always run single-stained compensation controls with each new lot. Store conjugates at 4°C, protected from light.
• Autofluorescence considerations: Cell types with high autofluorescence (myeloid cells, tissue-derived samples) emit most strongly in the green/yellow range (500–580nm). Avoid assigning dim markers to FITC or other green-channel fluorochromes when working with these samples.
• Match your instrument: Use this tool's instrument presets to see which detectors are available on your cytometer. Choose fluorochromes whose emission peaks align with your instrument's bandpass filters for optimal signal capture.