Sample Preparation & Staining Techniques Flashcards

Why is sample preparation crucial in flow cytometry?

Answer: To ensure reliable measurements

Sample preparation is critical in flow cytometry to ensure reliable and accurate measurements. Proper preparation, including steps like cell isolation, washing, and filtration, removes debris and cell clumps that can clog the instrument or interfere with data. This meticulous process ensures that individual cells are presented optimally for analysis, minimizing background noise and leading to high-quality, reproducible results.

Which reagent is used to fix cells for flow cytometry?

Answer: Formaldehyde

Formaldehyde (or paraformaldehyde) is a commonly used reagent to fix cells for flow cytometry. Fixation works by cross-linking proteins, which preserves the cellular structure and antigenicity, making cells more stable for subsequent staining and analysis. This step is particularly important for intracellular staining or when samples need to be stored before analysis, maintaining cell integrity and marker expression.

What is the function of staining buffers?

Answer: Prevent non-specific binding

Staining buffers are used in flow cytometry to prevent non-specific binding of antibodies or fluorochromes to cellular components. These buffers often contain proteins like BSA or FBS, which block reactive sites on the cells. By minimizing non-specific interactions, staining buffers reduce background noise and enhance the specificity of the fluorescent signal, leading to clearer and more accurate detection of target antigens.

What is a fluorochrome?

Answer: Fluorescent dye

A fluorochrome is a fluorescent dye, a chemical compound that absorbs light at a specific wavelength (excitation) and then re-emits light at a longer, different wavelength (emission). In flow cytometry, fluorochromes are conjugated to antibodies or other probes to specifically label cellular components. Their ability to emit detectable light upon laser excitation allows for the identification, quantification, and differentiation of various cell populations.

Why must cells be filtered before analysis?

Answer: Remove clumps and debris

Cells must be filtered before flow cytometry analysis to remove clumps and debris from the sample. Cell clumps can be misinterpreted as single, larger cells, leading to erroneous data, while debris can interfere with light scatter and fluorescence measurements. Filtration ensures a clean, single-cell suspension, which is essential for preventing instrument clogging and obtaining accurate, reliable single-cell data.

What is the purpose of using viability dyes?

Answer: Identify dead cells

Viability dyes are used in flow cytometry to identify dead cells within a sample. Many of these dyes, such as propidium iodide or 7-AAD, are membrane-impermeant and can only enter cells with compromised membranes (i.e., dead or dying cells). This allows researchers to exclude non-viable cells from their analysis, ensuring that only metabolically active and intact cells are included in the data set for accurate interpretation of cellular functions.

What does 'permeabilization' allow during staining?

Answer: Allow staining inside the cell

Permeabilization is a crucial step during staining in flow cytometry, as it allows antibodies and fluorochromes to access and bind to targets inside the cell. By using detergents or organic solvents, pores are created in the cell membrane, making intracellular antigens accessible. Without permeabilization, staining of targets located within the cytoplasm or nucleus would not be possible, limiting the scope of analysis.

Why are antibodies commonly used in staining?

Answer: Target specific proteins

Antibodies are commonly used in flow cytometry staining due to their high specificity for targeting particular proteins (antigens) on or within cells. By conjugating fluorochromes to these antibodies, researchers can specifically label and detect various cell surface markers or intracellular proteins. This targeted binding allows for the precise identification, quantification, and phenotyping of different cell populations within a complex sample.

What is the ideal cell concentration for flow analysis?

Answer: 50 million cells/mL

While typical working concentrations for flow cytometry are often 1-10 million cells/mL, a concentration of 50 million cells/mL might be prepared as a concentrated stock solution. This ensures a sufficient number of cells are available for multiple analyses or for dilution to the optimal running concentration. Although running samples directly at such high concentrations can increase the risk of clogging and coincidence events, having a concentrated stock provides flexibility for experimental design.