Pressure injection on a valved microdevice for electrophoretic analysis of submicroliter samples

Area of Science:

• Microfluidics
• Analytical Chemistry
• Biotechnology

Background:

• Diaphragm pumps are crucial for fluid manipulation in microfluidic devices.
• Previous work established reversible valves for on-chip pumping.
• Integrated pumping systems are needed for advanced microchip applications.

Purpose of the Study:

• To demonstrate integrated diaphragm pump functionality for pressure injections on a hybrid PDMS-glass microchip.
• To compare pressure injection with electrokinetic (EK) injection for electrophoretic separations.
• To evaluate the accuracy and reproducibility of sample handling using different injection methods.

Main Methods:

• A hybrid PDMS-glass microchip was designed to incorporate a diaphragm pump.
• A model system of fluorescein and ROX dyes in borate buffer was used.
• Electrophoretic separations were performed using both pressure and EK injections.

Main Results:

• Electrokinetic injections showed an electrophoretic bias, altering sample composition by 20% over 20 runs.
• Pressure injections maintained sample composition with a 3.6% coefficient of variation over 20 runs.
• The system demonstrated the ability to switch between injection modes and perform accurate pressure injections on small sample volumes (as low as 500 nL).

Conclusions:

• Integrated diaphragm pumps provide accurate and reproducible sample injection for microchip electrophoresis.
• Pressure injection overcomes the bias associated with EK injection, ensuring sample integrity.
• This technology supports integrated systems for precise small-volume sample analysis.