Imaging metal oxide nanoparticles in biological structures with CARS microscopy

J. Moger, B. D. Johnston and C. R. Tyler.

Optics Express, 16 (5), 3408-3419, 2008.

  • The physiological and environmental effect of metal oxide nanoparticles is currently a topic of hot debate.
  • Currently no imaging modality is capable of image these nanoparticles and the surrounding tissues without disturbing the biological structure.
  • Metal oxide nanoparticles generate intense CARS signals due to large nonlinear susceptibility enhanced by two-photon electronic resonance of the band gap transition.

Gill Structure

  • Fish gills give information on the affect of biological particles on sensitive biological structures, can be used to indicate the presence of nanoparticles in the environment.
  • On each side of the fish there are four gill arches (a), bearing double rows of elongated, laterally projecting structures, gill filaments (b).
  • The lamella (c) are composed of two parallel sheets of epithelia separated by a narrow space through which blood circulates.
Diagram showing the Gill structure

Forwards- vs Epi-CARS

  • Figures (a) and (b) compare E-CARS and F-CARS images of the normal structure within the gills.
  • Stokes and pump wavelength were 1255 nm and 924 nm respectively, providing contrast of CH rich structures.
  • F-CARS image show high contrast of RBCs against the lamellae structure. In E-CARS RBCs are barely visible. Difference is due to spatial dependence of CARS generation.
  • Combining E- and F-CARS provides excellent visualistion of the microvasculature structure within the secondary lamellae and its interaction with the RBCs. Figures (c) & (d) show the epi- (green) and forward-CARS (blue) data from (a) and (b) combined in a single image.
Forwards- vs Epi-CARS

 3-Dimensional Imaging of Nanoparticles

  • Z-stack of 320 depth-resolved slices separated by 0.25 microns.
  • Figure (a): Multiplanar Reformated z-stack YZ cross-section - vertical dotted line. XZ cross-section - horizontal dotted line. Aggregate of nanoparticles located in blood channel. (Indicated by arrows)
  • Figure (b) 3D projection of z-stack Green = Forward-CARS Blue = Epi-CARS 
3-Dimensional images of Nanoparticles