Co- and cross-flow extensions in an elliptical optical trap.

Area of Science:

• Physics
• Soft Matter Physics
• Nanotechnology

Background:

• Particle extension in isotropic potentials is force-dependent and parallel.
• Anisotropic potentials introduce complex force-response relationships.
• Understanding particle behavior in anisotropic potentials is crucial for microfluidic and nanotechnological applications.

Purpose of the Study:

• To experimentally measure the two-dimensional extension of a trapped spherical particle in an anisotropic potential.
• To investigate the relationship between applied force and particle extension in an elliptical potential.
• To validate the compliance tensor model for describing particle dynamics in anisotropic traps.

Main Methods:

• Utilized the focal spot of a high numerical aperture zone plate to generate an elliptical trapping potential.
• Employed microfluidics to apply a calibrated, directional force to the trapped particle.
• Measured the two-dimensional trajectory and extension of the spherical particle.

Main Results:

• The particle's extension exhibited both parallel (coflow) and perpendicular (cross flow) components relative to the applied force.
• The measured extension trajectory formed a circular path as the elliptical potential's orientation was varied.
• Experimental data demonstrated a strong agreement with the predictions of a compliance tensor model.

Conclusions:

• The compliance tensor accurately describes the anisotropic response of a trapped particle to an applied force.
• This study provides a method for characterizing particle dynamics in complex, non-uniform potentials.
• The findings have implications for precise manipulation and control of particles in microfluidic devices.