Induced hydraulic pumping via integrated submicrometer cylindrical glass capillaries

Area of Science:

• Microfluidics
• Electrokinetics
• Analytical Chemistry

Background:

• Submicrometer capillaries exhibit unique electrical conductance behavior deviating from bulk and nanoslit models.
• Understanding surface charge dynamics in these capillaries is crucial for microfluidic device design.

Purpose of the Study:

• To develop a novel micropump based on electroosmotic flow (EOF) rate mismatch.
• To characterize the performance of submicrometer capillaries in terms of electrical conductance.
• To demonstrate the micropump's utility in micro liquid chromatography (LC).

Main Methods:

• Integration of submicrometer glass capillaries with microchannels on silicon.
• Fabrication of a cross-junction micropump with parallel capillaries (750 nm diameter, 3 mm length).
• Application of 700 V to generate hydraulic pressure and flow.
• Demonstration using open tubular LC separation of fluorescently labeled amino acids.

Main Results:

• Generated hydraulic pressure up to 5 kPa with flow velocity of nearly 3 mm/s.
• Observed gradual decrease in capillary conductance at low salt concentrations, explained by variable surface charge density.
• Achieved rapid LC separation (<20 s) with minimal plate heights (3–7 μm).
• Submicrometer capillaries fabricated without advanced lithography or wafer bonding.

Conclusions:

• The developed micropump effectively utilizes EOF mismatch for hydraulic pressure generation.
• The study provides insights into electrical transport phenomena in submicrometer capillaries.
• The micropump demonstrates a viable, efficient, and potentially low-cost solution for micro-LC applications.