Comparison of three cell fixation methods for high content analysis assays utilizing quantum dots.

Area of Science:

• Cell biology
• Nanotechnology
• Biophysics

Background:

• Semiconductor nanoparticles, or quantum dots (QDs), are increasingly used as fluorescent probes in live and fixed cell assays.
• QDs offer potential for multiplexing assays on high-content screening systems.
• Experimental requirements vary, necessitating studies on cells with intact membranes or fixed/permeabilized cells.

Purpose of the Study:

• To quantitatively compare the effects of three common fixation techniques on quantum dot localization, emission properties, and stability.
• To evaluate these effects across two different cell lines exposed to carboxylic acid-stabilized CdTe quantum dots.
• To provide guidance on optimal sample processing for high-content imaging assays utilizing quantum dots.

Main Methods:

• Utilized a high-content analysis platform for quantitative comparative analysis.
• Tested three common fixation techniques (glutaraldehyde, methanol, paraformaldehyde) on two cell lines.
• Investigated quantum dot (QD) behavior in both prefixed/permeabilized cells and live cells followed by fixation.

Main Results:

• In prefixed cells, QDs were readily internalized, with intracellular location determined by QD properties.
• Fixation procedures performed after QD incubation significantly influenced QD fluorescence characteristics.
• All fixatives negatively affected QD fluorescence intensity; 2% paraformaldehyde emerged as the preferred fixative.
• Protein presence in media did not significantly alter QD fluorescence.

Conclusions:

• The choice of fixative is critical when processing live cells incubated with quantum dots.
• Fixation significantly impacts QD fluorescence intensity, necessitating careful consideration.
• While QDs are powerful tools for high-content cell imaging, basic sample processing steps require optimization.