ISAC Panel Design and Fluorochrome Selection 1 — Questions and Answers
Question 1: What is the primary consideration when selecting fluorochromes for a multicolor flow cytometry panel?
- Cost of the reagents
- Spectral overlap between fluorochromes (Correct answer)
- Color preference of the researcher
- Availability of secondary antibodies
Correct answer: Spectral overlap between fluorochromes
Spectral overlap between fluorochromes is the primary concern because emission bleed-through into neighboring channels requires compensation, which can degrade resolution.
Question 2: In panel design, a bright fluorochrome like PE should ideally be assigned to which type of marker?
- Highly expressed surface markers
- Markers used only as lineage dump
- Dimly expressed or rare markers (Correct answer)
- Markers with bimodal expression only
Correct answer: Dimly expressed or rare markers
Assigning bright fluorochromes like PE to dimly expressed antigens maximizes signal from those targets and improves their detection above background.
Question 3: What is spectral spillover in flow cytometry?
- Loss of signal caused by laser power fluctuations
- Detection of one fluorochrome's emission in another fluorochrome's detection channel (Correct answer)
- Cross-contamination of samples in the flow cell
- Autofluorescence signal produced by unlabeled cells
Correct answer: Detection of one fluorochrome's emission in another fluorochrome's detection channel
Spectral spillover occurs when a fluorochrome's emission spectrum extends beyond its primary detection channel into channels designated for other fluorochromes.
Question 4: Which parameter is most important for evaluating fluorochrome brightness in the context of panel design?
- Molecular weight of the fluorochrome
- Excitation wavelength alone
- Staining index (Correct answer)
- The visible color of the fluorochrome solution
Correct answer: Staining index
The staining index quantifies the separation between positive and negative populations relative to background spread, making it the most practical measure of effective brightness for panel decisions.
Question 5: What is a tandem dye in flow cytometry?
- Two separate antibodies used simultaneously against the same antigen
- A fluorochrome consisting of two energy-coupled dyes that shift emission to a longer wavelength (Correct answer)
- A dual-laser instrument configuration
- A detection filter paired with a dichroic mirror
Correct answer: A fluorochrome consisting of two energy-coupled dyes that shift emission to a longer wavelength
Tandem dyes couple a donor fluorochrome to an acceptor via FRET, so energy absorbed by the donor is transferred and emitted at the acceptor's longer wavelength.
Question 6: Why is minimizing spectral overlap between fluorochromes a key goal in panel design?
- It reduces the cost of reagents per experiment
- It simplifies gating hierarchies in the analysis software
- It reduces compensation requirements and preserves signal resolution (Correct answer)
- It allows the use of fewer antibody clones
Correct answer: It reduces compensation requirements and preserves signal resolution
Less spectral overlap means less spillover to correct, and since compensation mathematically increases variance, minimizing it preserves the resolution between positive and negative populations.
Question 7: Which laser is most commonly used to excite FITC and propidium iodide (PI) in flow cytometry?
- Red laser (633 nm)
- Violet laser (405 nm)
- Blue laser (488 nm) (Correct answer)
- Yellow-green laser (561 nm)
Correct answer: Blue laser (488 nm)
The 488 nm blue laser efficiently excites FITC and PI because both fluorochromes have strong absorption peaks near this wavelength.
ISAC Panel Design and Fluorochrome Selection 1
What is the primary consideration when selecting fluorochromes for a multicolor flow cytometry panel?