A liposome-based size calibration method for measuring microvesicles by flow cytometry

Area of Science:

• Extracellular vesicle research
• Flow cytometry applications
• Nanoparticle characterization

Background:

• Accurate sizing of microvesicles is crucial for understanding their biological roles.
• Existing methods for microvesicle size determination by flow cytometry lack a standardized gold standard.
• The need for reliable calibrators in flow cytometry-based vesicle analysis is increasingly recognized.

Purpose of the Study:

• To establish a more accurate method for determining microvesicle sizes using flow cytometry.
• To evaluate the suitability of fluorescently labeled liposomes as size calibrators.
• To compare the performance of liposome-based calibrators against traditional polystyrene beads.

Main Methods:

• Preparation of fluorescently labeled liposomes with defined sizes (200-1000 nm) via extrusion.
• Measurement of side scattering (SSC) signals from liposomes and microvesicles using flow cytometry.
• Correlation analysis between liposome size, fluorescence intensity, and SSC signals.

Main Results:

• Fluorescent liposomes demonstrated a reliable correlation between SSC and vesicle size.
• Polystyrene beads showed significant inaccuracies, with 110 nm beads correlating to ~400 nm vesicles.
• The SSC-based size assessment method exhibits a resolution limit of approximately 60-200 nm.

Conclusions:

• Fluorescent liposomes offer a more accurate size calibration method for microvesicles in flow cytometry.
• Liposome-based calibration improves the reliability of microvesicle size estimation compared to polystyrene beads.
• The study highlights the limitations and potential improvements for flow cytometry-based vesicle sizing.