Three-dimensional hydrodynamic focusing in a microfluidic Coulter counter

Area of Science:

• Biomedical Engineering
• Microfluidics
• Analytical Chemistry

Background:

• Electrical impedance sensing, or Coulter counting, is a lab-on-chip compatible method for flow cytometry.
• Conventional Coulter apertures are prone to clogging, limiting device performance and reliability.
• Hydrodynamic focusing offers a solution by creating fluid-walled channels to increase sensitivity and prevent blockages.

Purpose of the Study:

• To develop a novel 3D hydrodynamic focusing technique for electrical impedance-based particle detection.
• To enhance the sensitivity and reduce the risk of clogging in microfluidic flow cytometry devices.
• To create a more portable, lower-cost, and lower-power alternative to fluorescence-based flow cytometry.

Main Methods:

• Fabrication of a microfluidic device with a stepped outlet channel using soft lithography.
• Implementation of three-dimensional hydrodynamic focusing to create a narrow sample stream.
• Integration of sensing electrodes for electrical impedance measurements.
• Comparison of particle sensing performance with and without 3D focusing.

Main Results:

• The 3D hydrodynamic focusing design successfully created a narrow sample stream on the channel floor for optimal electrode interaction.
• The new design requires minimal substrate alignment, simplifying fabrication and use.
• Experiments demonstrated a 2.5-fold increase in percentage conductivity change compared to devices with only horizontal focusing.
• The device showed high sensitivity to cell-size particles in larger channels, mitigating clogging issues.

Conclusions:

• Three-dimensional hydrodynamic focusing significantly enhances the sensitivity of electrical impedance-based particle detection.
• The developed microfluidic device offers a clog-resistant and highly sensitive platform for flow cytometry.
• This technology presents a promising advancement for portable, cost-effective particle analysis in various scientific applications.