Simultaneous Multipass Resistive-Pulse Sensing and Fluorescence Imaging of Liposomes.

Area of Science:

• Biophysics
• Analytical Chemistry
• Materials Science

Background:

• Liposome characterization is crucial for understanding biological processes and developing drug delivery systems.
• Existing methods often lack the precision to correlate membrane properties with size for individual liposomes.
• Escherichia coli (E. coli) lipid liposomes are relevant models for bacterial membranes.

Purpose of the Study:

• To develop and validate a technique for simultaneous resistive-pulse sensing and fluorescence imaging of individual liposomes.
• To correlate the size and membrane fluorescence intensity of E. coli lipid liposomes.
• To investigate the relationship between liposome size, membrane surface area, and fluorescence.

Main Methods:

• Utilized a nanopipet as a waveguide for excitation light, enabling simultaneous resistive-pulse sensing and fluorescence imaging.
• Employed multipass resistive-pulse sensing with potential switching for subnanometer sizing precision of DiO-labeled liposomes (>50 nm radius).
• Measured fluorescence intensity as a function of liposome radius passing through the nanopipet orifice.

Main Results:

• Liposome fluorescence intensity was found to be approximately proportional to the total membrane surface area.
• Multivesicular liposomes exhibited higher fluorescence than unilamellar liposomes, indicating DiO incorporation across all membranes.
• A fluorescence 'dead zone' near the nanopipet orifice caused observable 'on/off' fluorescence during multipassing.

Conclusions:

• Simultaneous multipass resistive-pulse sensing and fluorescence imaging provide precise correlation of liposome size and membrane fluorescence.
• The method allows for distinguishing fluorescent from nonfluorescent liposomes in solution.
• Findings support the utility of this technique for detailed liposome analysis and characterization.