Immersed AC electrospray (iACE) for monodispersed aqueous droplet generation

Area of Science:

• Biotechnology
• Microfluidics
• Physical Chemistry

Background:

• Droplet generation is crucial for various applications, including diagnostics and drug delivery.
• Existing microfluidic methods often require complex setups and controlled fluid flows.
• Generating stable, monodispersed droplets from viscous or high ionic strength samples remains challenging.

Purpose of the Study:

• To develop a novel, chip-free electrospray method for generating monodispersed water-in-oil droplets.
• To enable droplet generation from challenging samples, such as raw physiological fluids.
• To provide a high-throughput and easily tunable droplet generation system.

Main Methods:

• Utilized an immersed alternating current (AC) electrospray technique with a glass micropipette nozzle.
• Employed a small back pressure and AC electric Maxwell pressure for droplet ejection.
• Incorporated polyethylene oxide to suppress undesirable electrical phenomena and promote monodispersity.
• Developed a scaling theory to correlate droplet size with applied pressure and frequency.

Main Results:

• Successfully generated monodispersed water-in-oil droplets with diameters from 5 to 150 μm.
• Achieved high throughput and precise droplet size control by adjusting back pressure.
• Demonstrated compatibility with viscous aqueous phases and high ionic strength samples.
• Validated the method's utility in a digital loop-mediated isothermal amplification assay with minimal biomolecule damage.

Conclusions:

• The new AC electrospray method offers a simple, chip-free alternative for monodispersed droplet generation.
• This technique is robust for handling complex biological samples and enables precise control over droplet characteristics.
• The method shows significant potential for applications in digital assays and other areas requiring controlled micro-droplet production.