Defocused dark-field orientation imaging of single gold microrods on synthetic membranes.

Plasmonic gold microrods (AuMRs) are promising optical probes because of direct observation of their in-plane orientations and motions under an optical microscope. However, our understanding of the optical properties of AuMRs is still very limited to the single particle level, and their out-of-plane orientations cannot be resolved by eye with high accuracy. Herein, we present the scattering properties of 1 μm-long AuMRs under a defocused DF microscope. The characteristic defocused scattering patterns of single AuMRs allowed us to resolve both in-plane and out-of-plane angles of single AuMRs. We further demonstrate the feasibility of using the defocused orientation imaging technique to track rotational motions and out-of-plane angles of single AuMRs on synthetic membranes.