Optical trapping of coated microspheres

Area of Science:

• Optical physics
• Biophysics
• Materials science

Background:

• Optical traps use focused laser beams to hold dielectric particles.
• Optical forces include gradient (attractive) and scattering (destabilizing) components.
• Reducing scattering is key to improving optical trap stability and stiffness.

Purpose of the Study:

• To investigate the effect of anti-reflection coatings on microsphere trapping efficiency.
• To determine optimal microsphere properties for enhanced optical trapping.
• To validate the utility of coated microspheres in biophysical applications.

Main Methods:

• Fabrication and characterization of homogeneous and coated microspheres.
• Optical trapping experiments to measure trap stiffness.
• Mie scattering calculations for theoretical validation.
• DNA stretching and motor protein assays for biophysical application testing.

Main Results:

• Homogeneous microspheres showed maximum trap stiffness at a diameter matching the laser wavelength (approx. 800 nm).
• Silica coating on polystyrene microspheres significantly improved trapping for larger diameters.
• Homogeneous spheres of specific sizes exhibited inherent anti-reflective properties.
• Coated microspheres demonstrated a large linear range for force and detection, suitable for biophysical assays.

Conclusions:

• Anti-reflection-coated microspheres provide enhanced optical trapping performance.
• Optimized microsphere design, including coatings, is crucial for advanced optical trapping applications.
• Coated microspheres are compatible with demanding biophysical measurements, validating their practical utility.