Measuring concentration fields in microfluidic channels in situ with a Fabry-Perot interferometer

Area of Science:

• Chemical Engineering
• Analytical Chemistry
• Biophysics

Background:

• Microfluidic technologies enable complex chemical gradient generation.
• Measuring these gradients in situ without fluorescent labels remains a challenge.

Purpose of the Study:

• To develop a general, label-free technique for measuring spatio-temporal concentration profiles.
• To demonstrate the technique's capability in analyzing diffusion in various media.

Main Methods:

• Utilized a Fabry-Perot interferometric technique to track Fringes of Equal Chromatic Order (FECO).
• Achieved in situ, label-free concentration measurements with high sensitivity (10⁻⁵ RIU) and spatial resolution (1 μm).
• Recorded concentration field evolution at a rate of approximately 20 Hz.

Main Results:

• Demonstrated the ability to measure local solute changes as low as ~0.05% (w/w).
• Successfully measured binary diffusion coefficients for various solutes and solvents.
• Quantified concentration-dependent diffusion in both free solutions and PEG-DA hydrogels.

Conclusions:

• The developed interferometric technique offers a sensitive, label-free method for analyzing chemical gradients.
• This technique is valuable for studying diffusion dynamics in complex systems, including hydrogels.
• Provides a new tool for in situ, real-time characterization of chemical transport phenomena.