A one-step process for multi-gradient wettability modification on a polymer surface

Area of Science:

• Materials Science
• Surface Chemistry
• Microfluidics

Background:

• Poly(dimethylsiloxane) (PDMS) microfluidic devices require surface modification for tunable wettability and flow control.
• Existing methods for PDMS surface modification are limited to altering single areas at a time.

Purpose of the Study:

• To introduce a novel Controlled Gradient Oxygen Plasma Modification (CGPM) technique for creating spatially controlled wettability gradients on PDMS surfaces.
• To investigate the influence of mask properties on CGPM effectiveness.
• To demonstrate the application of CGPM in an integrated microfluidic device for enhanced D-dimer detection.

Main Methods:

• Developed CGPM by layering porous resin masks on PDMS surfaces to control oxygen plasma density.
• Utilized COMSOL plasma module simulations to analyze the effect of mask porosity, hole size, distribution, and distance on wettability.
• Characterized CGPM performance using contact angle measurements.
• Integrated the CGPM technique into a microfluidic device for D-dimer identification.

Main Results:

• CGPM achieved a continuous change in PDMS surface contact angle from 8.77° to 76.98° within 25 seconds.
• Simulations provided insights into optimizing mask parameters for precise wettability control.
• The D-dimer assay in the integrated device was completed in 10 minutes, showing a dynamic range of 1-1000 ng mL⁻¹.
• Observed a 78.3% peak and 31.1% average increase in fluorescence signal for D-dimer detection compared to standard treatments.

Conclusions:

• CGPM offers a versatile and efficient method for creating tunable wettability gradients on PDMS surfaces.
• The technique significantly improves the performance of microfluidic assays, as demonstrated by enhanced D-dimer detection.
• CGPM holds promise for advancing microfluidic device applications in diagnostics and beyond.