A photoinduced nanoparticle separation in microchannels via pH-sensitive surface traps

Area of Science:

• Microfluidics and Nanotechnology
• Photochemistry and Polymer Science

Background:

• Developing precise methods for capturing and separating nanoparticles in microfluidic devices is crucial for various applications.
• Existing methods often lack spatial control or rely on complex surface modifications.

Purpose of the Study:

• To develop a microfluidic surface trap for capturing pH-sensitive nanoparticles.
• To utilize a photoinitiated proton-releasing reaction for controlled pH changes within microchannels.
• To achieve spatially localized particle capture using controlled UV irradiation.

Main Methods:

• Fabrication of a microfluidic device with o-nitrobenzaldehyde (o-NBA) coated walls.
• Modification of nanoparticles and surface trap with a pH-responsive polymer, poly(N-isopropylacrylamide-co-propylacrylic acid) (P(NIPAAm-co-PAA)).
• Photoinitiation of proton release using UV light to alter local pH and induce polymer hydrophobicity for nanoparticle capture.
• Utilized photomask for spatially controlled UV irradiation and particle separation.

Main Results:

• UV irradiation rapidly decreased microchannel pH from 7.4 to 4.5 within 60 seconds.
• The pH change induced a hydrophobic transition in the P(NIPAAm-co-PAA) polymer, enabling capture of pH-sensitive nanobeads.
• Spatially confined UV exposure using a photomask successfully restricted particle capture to specific regions.

Conclusions:

• The developed microfluidic surface trap effectively captures pH-sensitive nanoparticles via photoinitiated pH changes.
• This technique offers precise temporal and spatial control over particle manipulation in microfluidic systems.
• The method provides a versatile platform for targeted molecule capture and separation in microfluidic devices.