ISAC Analytical Methods and Techniques 4

Question 1

What is the recommended approach when titrating an antibody conjugate for flow cytometry?

Accepted Answer

Test serial dilutions and select the concentration giving highest staining index

Answer

Antibody titration identifies the optimal concentration that maximizes the staining index (signal-to-noise), minimizing background while preserving specific signal.

Question 2

In fluorescence-activated cell sorting, what determines the deflection direction of a droplet containing a target cell?

Accepted Answer

The charge applied to the droplet when it breaks from the stream

Answer

A voltage applied to the stream at the precise moment of droplet formation charges the droplet, and the high-voltage deflection plates then push it left or right based on charge polarity.

Question 3

Which type of detector is most commonly used in flow cytometers to measure fluorescence emission?

Accepted Answer

Photomultiplier tube (PMT)

Answer

PMTs amplify weak fluorescence signals through photon-induced electron cascades, providing the sensitivity required to detect low-abundance molecules on individual cells.

Question 4

What is the main advantage of using tandem dyes (e.g., PE-Cy7) in multicolor panels?

Accepted Answer

They allow excitation by a shorter wavelength laser while emitting at a longer wavelength

Answer

Tandem dyes use FRET to transfer energy from a donor (e.g., PE) excited by one laser to an acceptor (e.g., Cy7) that emits further into the red, extending panel design options.

Question 5

When analyzing rare cell populations by flow cytometry, which strategy most reliably improves detection accuracy?

Accepted Answer

Collecting a higher total event count to reduce sampling error

Answer

For rare events, collecting more total events reduces the coefficient of variation and sampling error, improving statistical confidence in the detected population.

(ISAC) International Society for the Advancement of Cytometry Practice Test

(ISAC) International Society for the Advancement of Cytometry Practice Test

ISAC Analytical Methods and Techniques 4