Label-free high-resolution 3-D imaging of gold nanoparticles inside live cells using optical diffraction tomography.

Doyeon Kim,Kyoohyun Kim,Yongkeun Park,Nuri Oh,Sangyun Lee,Ji-Ho Park,Chan-Gi Pack

doi:10.1016/j.ymeth.2017.07.008

Abstract

Delivery of gold nanoparticles (GNPs) into live cells has high potentials, ranging from molecular-specific imaging, photodiagnostics, to photothermal therapy. However, studying the long-term dynamics of cells with GNPs using conventional fluorescence techniques suffers from phototoxicity and photobleaching. Here, we present a method for 3-D imaging of GNPs inside live cells exploiting refractive index (RI) as imaging contrast. Employing optical diffraction tomography, 3-D RI tomograms of live cells with GNPs are precisely measured for an extended period with sub-micrometer resolution. The locations and contents of GNPs in live cells are precisely addressed and quantified due to their distinctly high RI values, which was validated by confocal fluorescence imaging of fluorescent dye conjugated GNPs. In addition, we perform quantitative imaging analysis including the segmentations of GNPs in the cytosol, the volume distributions of aggregated GNPs, and the temporal evolution of GNPs contents in HeLa and 4T1 cells.

Highlights

Gold nanoparticles (GNPs) have been widely applied to biological cell studies in various research fields because of their distinctive properties which differentiate them from conventional biomolecules and even from other metal nanoparticles[1]
We present a label-free 3-D imaging method for measuring the 3-D spatial distribution of GNPs inside live cells by employing optical diffraction tomography (ODT)
The 3-D refractive index (RI) distribution of GNPs inside live cells reconstructed via ODT shows significantly high RI values (n > 1.375) compares to surrounding cytoplasm, which was confirmed by fluorescence images of the same GNPs

Summary

Introduction

Gold nanoparticles (GNPs) have been widely applied to biological cell studies in various research fields because of their distinctive properties which differentiate them from conventional biomolecules and even from other metal nanoparticles[1]. GNPs show relatively high chemical stability compared to other metal nanoparticles With these unique properties, the current uses of GNPs can be listed from photodiagnostics to photothermal therapy[2,3,4,5,6]. While transmission electron microscopy (TEM) conventionally provides high spatial resolution images of GNPs, TEM requires the extremely vacuum and high-intensity electron beam, incompatible with live cells[7, 8]. Fluorescence imaging techniques, such as epifluorescence microscopy and confocal microscopy, have been utilized for observing the spatial distribution of GNPs inside biological cells. Three-dimensional (3-D) fluorescence imaging requires the axial scanning scheme, which suffers long acquisition time for 3-D images[13]

Methods

Results

Conclusion