A microchip device to enhance free flow electrophoresis using controllable pinched sample injections

Area of Science:

• Analytical Chemistry
• Microfluidics
• Separation Science

Background:

• Micro free flow electrophoresis (µFFE) offers high-throughput microscale separations under mild conditions.
• A key limitation of µFFE is stream broadening, which negatively impacts separation performance.
• This broadening arises from sample stream deflection inherent in free-flow electrophoresis techniques.

Purpose of the Study:

• To introduce a novel microfluidic device for controlling injection bandwidth in µFFE.
• To investigate the impact of injection bandwidth control on separation performance and resolution.
• To demonstrate the applicability of this technique for various analytical separations.

Main Methods:

• Development of a microfluidic device enabling pinched injection in a µFFE system.
• Systematic variation of the sample flow rate ratio (r) to control initial sample bandwidth.
• Theoretical modeling and experimental validation of stream broadening reduction.
• Assessment of separation resolution using a dye mixture and amino acid analysis.

Main Results:

• Initial sample bandwidth at the separation chamber entrance was reduced from 800 µm to 30 µm by increasing r from 1 to 256.
• Stream broadening at the chamber exit was reduced by approximately 96% for r values from 4 to 128.
• Separation resolution for a dye mixture improved by a factor of 4 with increased r (16 to 128), correlating with an 80% reduction in initial bandwidth.
• Similar resolution enhancements were observed for amino acid separations.

Conclusions:

• The developed microfluidic device effectively controls injection bandwidth in µFFE.
• Injection bandwidth control significantly reduces stream broadening and enhances separation resolution.
• This method offers a simple yet powerful approach to improve µFFE performance for diverse analytical applications.
• The technique is readily integrable into online/offline sample preparation and downstream analysis workflows.