Exploring poly-L-lysine-based particle capture for atomic force microscopy studies of extracellular vesicles.

Area of Science:

• Biophysics
• Materials Science
• Nanotechnology

Background:

• Extracellular vesicles (EVs) require precise immobilization for accurate atomic force microscopy (AFM) analysis.
• Current protocols for EV immobilization present challenges in quantitative morphometry and nanoindentation.
• Understanding substrate interactions is crucial for reliable EV characterization.

Purpose of the Study:

• To investigate the impact of experimental variables on EV immobilization for AFM.
• To introduce a quantitative measure (Q) for adsorbed material and sample concentration estimation.
• To develop an optimized AFM protocol for EV morphometry in air.

Main Methods:

• Systematic variation of experimental parameters for EV immobilization on various substrates.
• Introduction and application of parameter Q to quantify adsorbed material.
• Comparison of EV morphometry results obtained in liquid and air using optimized protocols.

Main Results:

• Parameter Q quantifies total adsorbed material and estimates relative sample concentrations in AFM experiments.
• Q shows a logarithmic dependence on substrate charge density.
• EV contact angle (CA) does not correlate with substrate charge density as expected.
• An optimized air-based AFM protocol achieves EV size distributions comparable to liquid-based methods.

Conclusions:

• The parameter Q provides a reliable method for estimating sample concentration in EV immobilization studies.
• Substrate charge density significantly influences EV adsorption, but contact angle is less predictable.
• An optimized air protocol offers a viable alternative for EV morphometry, simplifying experimental procedures.