Measuring Solvent Exchange in Silica Nanoparticles with Rotor-Based Fluorophore

Area of Science:

• Materials Science
• Physical Chemistry
• Nanotechnology

Background:

• Measuring molecular diffusivity is crucial for understanding and controlling diffusion processes.
• Challenges in diffusivity measurements increase with smaller molecules, especially non-fluorescent and non-reactive ones like solvents.
• Silica micropores present a highly viscous microenvironment influenced by solvent polarity.

Purpose of the Study:

• To demonstrate a method for monitoring solvent exchange within silica micropores with millisecond time resolution.
• To develop a technique for measuring the diffusion coefficients of solvents in silica.
• To validate the effectiveness and sensitivity of the developed method.

Main Methods:

• Embedding a rotor-based fluorophore (thioflavin T) within colloidal silica nanoparticles.
• Monitoring solvent exchange processes by analyzing fluorescence intensity changes over time.
• Fitting fluorescence intensity traces to the Fickian diffusion model for analytical solutions.

Main Results:

• Successfully demonstrated millisecond time-resolution monitoring of solvent exchange in silica micropores.
• Obtained diffusion coefficients by fitting fluorescence data to the Fickian diffusion model.
• Validated the method through water-to-ethanol and ethanol-to-water exchange experiments, varying drying conditions and silica cross-linking.

Conclusions:

• The developed method enables sensitive and effective characterization of diffusion dynamics in silica micropores.
• High temporal resolution tracking of solvent exchange over short distances opens new avenues for diffusion studies.
• This technique is valuable for studying diffusion of non-fluorescent and non-reactive molecules in confined environments.