High-throughput in-focus differential interference contrast imaging of three-dimensional orientations of single gold nanorods coated with a mesoporous silica shell

Plasmonic gold nanorods (AuNRs) have been widely applied as optical orientation probes in many biophysical studies. However, characterizing the various three-dimensional (3D) orientations of AuNRs in the same focal plane of the objective lens is a challenging task. To overcome this challenge, we fabricated single AuNRs (10 nm × 30 nm) coated with either an elliptical or spherical mesoporous silica shell (AuNRs@mSiO(2)). Unlike bare AuNRs and elliptical AuNRs@mSiO(2), spherical AuNRs@mSiO(2) contained randomly oriented AuNR cores in 3D space, which could be observed on the same focal plane within a single frame by differential interference contrast (DIC) microscopy. The spherical AuNRs@mSiO(2) thus achieved high-throughput detection. The proposed approach can overcome the limitations of the current gel-matrix method, which requires vertical scanning of the embedded AuNRs to capture different focal planes.