Direct measurement of self-diffusiophoretic force generated by active colloids of different patch coverage using...

Area of Science:

• Materials Science
• Nanotechnology
• Biomedical Engineering

Background:

• Synthetic micro/nanomotors are crucial for biomedical applications like drug delivery.
• Controlling propulsion speed, direction, and force is key for their feasibility.
• Diffusiophoretic micro/nanomotors offer tunable motion characteristics.

Purpose of the Study:

• To engineer diffusiophoretic micro/nanomotors by controlling self-propulsion speed and force.
• To investigate the effect of patch coverage and adhesion layers on micro/nanomotor performance.
• To compare force measurement techniques for active colloids.

Main Methods:

• Microswimmers fabricated with varying catalytic patch coverages (10°, 30°, 90°) using glancing angle metal deposition (GLAD).
• Patches were deposited with (Ti/Pt) and without (Pt) an adhesion layer.
• Self-propulsion parameters (speed, angular speed) determined via mean-square displacement (MSD) analysis.
• Self-propulsive force measured using optical tweezers (OT) from force power spectral density.

Main Results:

• Maximal self-propulsion speed (4.61±0.3μm/s) and force (345±57fN) observed for Pt 10° micro-motors without an adhesion layer in 5% H₂O₂.
• Propulsion speed and force decreased with increasing patch size, contradicting theoretical predictions.
• MSD-derived forces were 2-4 times lower than OT-measured forces, attributed to surface interactions.
• OT-based force measurements are deemed more reliable than MSD-based estimates due to avoiding particle-substrate interactions.

Conclusions:

• Adhesion layers are unnecessary for optimal catalytic micro/nanomotor performance.
• Patch size significantly influences micro/nanomotor speed and force.
• Optical tweezers offer a more accurate method for measuring self-propulsive forces compared to MSD analysis.
• This research provides a foundation for designing efficient micro/nanomotors for biomedical applications.