Contrast enhancement of coherent brightfield (COBRI) microscopy for high-speed imaging and tracking of very small single nanoparticles

Ching-Ya Cheng^1*, Yi-Hung Liao¹, Chia-Lung Hsieh¹

¹Institute of Atomic and Molecular Science, Academia Sinica, Taipei, Taiwan

* Presenter:Ching-Ya Cheng, email:samu172004@gmail.com

We demonstrate contrast-enhanced coherent brightfield (COBRI) microscopy for imaging and tracking eight nanoparticle samples of different materials and sizes (as small as 10 nm gold and silver nanoparticles). The optical detection of COBRI is based on interference between transmitted reference beam and forward scattering of nanoparticle. Contrast enhancement is achieved by inserting a dot-shaped attenuator at the conjugate back focal plane of objective, which selectively weakens the intensity of reference beam and leaves the intensity of forward scattering signal nearly unchanged. The quantitative relationship of measured COBRI contrast and scattering cross section of nanoparticles is obtained. We successfully detect single nanoparticle of scattering cross section as small as 10-16 cm2. Moreover, we show high-speed tracking (1000 fps) of 10 nm gold nanoparticle diffusing on supported lipid bilayer membranes. The recorded trajectories show free diffusion, indicating the homogeneity of lipid bilayers that we prepared.

Keywords: high-speed imaging, nanoparticles, single-particle tracking, coherent brightfield microscopy, interference