Visualization and dynamic size evaluation of nanoparticles in solution by single optical fiber-illuminated video microscope analysis.

Aim: It is hoped that nanoparticles will become ever more useful in the development of nanomedicine. To evaluate the behavior of nanoparticles in solution, we aimed to establish a single optical fiber-illumination method that is easy to integrate with a conventional microscope at low cost.

Methods: Solutions of gold nanoparticles and carbon nanotubes were analyzed in a single optical fiber-illuminated video microscope and the tracks of Brownian motion of these nanoparticles were traced using video images. Their diffusion coefficient was measured by the mean square displacement of the movement. Using the diffusion coefficient in the Stokes-Einstein equation, the hydrodynamic diameter of the nanoparticles in solution was evaluated.

Results: The visualization of gold nanoparticles clearly in a high signal-to-noise ratio was achieved. The evaluated particle sizes of gold nanoparticles were similar to those obtained by a transmission electron microscope and the aggregation process of the carbon nanotubes following incubation was also observed and similar size estimation of the aggregates was performed.

Conclusion: The single fiber-illumination method was applicable to visualize nanoparticle movement clearly and to estimate their sizes in solution. This simple method is suitable for the in situ observation of the nanoparticle-binding process to target cells.