Three dimensional orientational imaging of nanoparticles with darkfield microscopy

Area of Science:

• Nanotechnology
• Optical Microscopy
• Materials Science

Background:

• Gold nanorods (AuNR) are crucial nanomaterials with size- and shape-dependent optical properties.
• Precisely determining the 3D orientation of individual AuNR is essential for understanding their behavior and applications.
• Existing methods for orientation determination can be complex or lack speed.

Purpose of the Study:

• To develop a straightforward and rapid method for resolving the complete three-dimensional orientations of single gold nanorods.
• To utilize standard optical darkfield microscopy for this orientation analysis.

Main Methods:

• Deciphering the field distribution pattern in slightly defocused darkfield microscope images of single AuNR.
• Comparing experimental images with a series of simulated images varying parameters like aspect ratio, numerical aperture, defocusing distance, and polarization.
• Validating the technique with polarization modulation experiments.

Main Results:

• Successfully resolved the complete 3D orientations of single AuNR.
• Demonstrated that image patterns are dependent on AuNR aspect ratio, objective numerical aperture, defocusing distance, and incident polarization.
• Experimental data showed excellent agreement with simulated results.

Conclusions:

• The described darkfield microscopy technique provides a convenient, reliable, and rapid method for angle-resolving measurements of single AuNR.
• The ability to perform deconvolution off-line enables video-rate data acquisition.
• This approach has broad potential applications in various scientific imaging studies.