Dual-Wavelength Detection of Rotational Diffusion of Single Anisotropic Nanocarriers on Live Cell Membranes

Single-particle rotational tracking is of great importance to monitor orientation changes of biomolecules and to understand their functions and mechanisms in biological systems. Differential interference contrast (DIC) microscopy has been found to be an excellent tool to measure polarization anisotropy for tracking rotational dynamics of gold nanorod (AuNR) probes. DIC polarization anisotropy can be conveniently obtained from the bright and dark intensities of a single DIC image of an AuNR. Here, DIC microscopy-based dual-wavelength detection of rotational motions of AuNRs at both transverse and longitudinal surface plasmon resonance (SPR) wavelengths is demonstrated. The transverse SPR mode was successfully used to track fast rotational dynamics of individual AuNRs on live cell membranes. This is important since the transverse SPR mode is mostly insensitive to the medium refractive index, AuNR aspect ratio, and adsorption of biomolecules. DIC polarization anisotropy was simultaneously obtained from the two SPR wavelengths during the dynamic process. wavelengths showed good agreement and provided accurate and reliable measurement of AuNR orientation. Both