High Background Fluorescence in All Populations (Flow Cytometry (CST Guide))

Question

Accepted Answer

All cell populations including negative controls show elevated fluorescence, reducing signal-to-noise ratio and making it difficult to distinguish positive from negative populations. Common causes: 1) Excessive antibody concentration beyond CST recommended dilution optimized for 10⁵-10⁶ cells 2) Two-step staining with biotinylated antibodies detecting endogenous intracellular biotin via streptavidin or anti-biotin secondary conjugates 3) Dead cells with compromised membranes non-specifically binding antibodies; viability dyes incompatible with fixation protocol 4) High autofluorescence in certain cell types (neutrophils) or use of autofluorescence-prone fluorochromes (FITC, Pacific Blue) instead of red-shifted alternatives Solutions: 1) Use CST recommended antibody dilution (optimized for 10⁵-10⁶ cells); perform own titration when using low cell numbers 2) Avoid biotinylated antibodies for intracellular staining due to endogenous biotin detection; whenever possible perform direct staining instead of two-step 3) Use viability dyes compatible with fixation: fixable dyes (e.g., eFluor) for fixed cells, PI or 7-AAD for live surface staining only 4) For autofluorescence-prone cells: use red-shifted fluorochromes (APC instead of FITC/Pacific Blue), or use brighter fluorochromes (Alexa Fluor 488 instead of FITC, Brilliant Violet 421 instead of Pacific Blue), or amplify signal with biotin-streptavidin/primary-secondary steps