Investigating axial diffusion in cylindrical pores using confocal single-particle fluorescence correlation...

Area of Science:

• Physical Chemistry
• Nanotechnology
• Biophysics

Background:

• Studying nanoparticle diffusion in confined geometries is crucial for understanding transport phenomena.
• Confocal fluorescence correlation spectroscopy (FCS) is a powerful technique for analyzing molecular dynamics.

Purpose of the Study:

• To assess the feasibility of using FCS to study nanoparticle diffusion in cylindrical pores.
• To differentiate and analyze one-dimensional (1D) axial and two-dimensional (2D) lateral diffusion dynamics.
• To investigate nanoparticle diffusion in experimentally relevant pore sizes and materials.

Main Methods:

• Computational modeling of single particle diffusion in confined 3D space.
• Confocal fluorescence correlation spectroscopy (FCS) measurements.
• Analysis of autocorrelation functions (ACFs) using 1D diffusion models.

Main Results:

• FCS successfully distinguished between 1D axial and 2D lateral diffusion of nanoparticles in pores.
• Experimental data for 45 nm nanoparticles in 300 nm alumina pores matched simulation predictions.
• A 1D diffusion model with a Lorentzian axial collection profile accurately determined the axial diffusion coefficient.
• Nanoparticle diffusion slowed by approximately twofold in PEG-passivated pores, attributed to hydrodynamic friction.

Conclusions:

• Confocal FCS is a viable method for studying multi-dimensional diffusion in nanopores.
• The technique allows for separate analysis of diffusion dynamics in different dimensions.
• Hydrodynamic interactions significantly influence nanoparticle diffusion within confined environments.