Tracking Bulk and Interfacial Diffusion Using Multiplex Coherent Anti-Stokes Raman Scattering Correlation...

Area of Science:

• Chemical Physics
• Spectroscopy
• Materials Science

Background:

• Label-free chemical analysis is crucial for understanding molecular dynamics.
• Monitoring particle mobility in complex environments like solutions and interfaces presents challenges.
• Coherent anti-Stokes Raman scattering (CARS) spectroscopy provides chemical specificity.

Purpose of the Study:

• To demonstrate multiplex CARS correlation spectroscopy (CARS-CS) as a label-free method for monitoring particle molecular mobility.
• To quantify particle diffusion coefficients in solution and at various interfaces.
• To distinguish and track different lipid vesicle compositions within a mixture.

Main Methods:

• Utilizing multiplex CARS correlation spectroscopy (CARS-CS) with broadband excitation.
• Measuring particle diffusion coefficients for polymer beads (100 nm–1.1 μm) and comparing with Stokes-Einstein predictions.
• Analyzing diffusion rates at bulk liquid, liquid/glass, and air/liquid interfaces.
• Employing multivariate curve resolution for spectral analysis of lipid vesicles.

Main Results:

• Measured diffusion coefficients for polymer beads align with Stokes-Einstein predictions (10⁻⁸–10⁻⁹ cm²/s).
• Particle diffusion rates vary across interfaces: fastest in bulk, slower at liquid/glass, and slowest at air/liquid.
• Multivariate analysis successfully distinguished and tracked lipid vesicles of different compositions in a mixture.

Conclusions:

• Multiplex CARS-CS is a versatile, label-free technique for studying particle diffusion.
• The method provides millisecond timescale insights into molecular mobility at interfaces.
• CARS-CS is effective for analyzing complex mixtures and diverse chemical species.