High-speed three-dimensional tracking of individual 100 nm polystyrene standard particles in multi-wavelength evanescent fields

摘要

The nanoparticle phenomena concern three-dimensional motion in a fluid in which the nanoparticles move at ultra-high-speed with Brownian motion. However, current commercial methods for nanoparticle position tracking are only able to determine a two-dimensional position, and are not able to define the longitudinal axisZas the third dimension. We have therefore proposed a method and have observed the three-dimensional tracking of individual nanoparticles with nanometer localisation precision and high temporal resolution. In this paper, 100 nm polystyrene standard particles were used to investigate our three-dimensional tracking method. Evanescent fields have been used to obtain a scattering light from the observed particle near the reference surface. The single wavelength could determine the localisation tracking of theX,Ycoordinates, but was not available for tracking the heightZ, because the particle size is usually unknown. Thus, we have employed multi-wavelength evanescent fields to achieve higher localisation tracking of the heightZ. TheX,Ycoordinates of an individual nanoparticle were determined by the centre of mass of the scattering light intensities, and the heightZwas evaluated from the detected scattering light intensities, then plotted with an exponential relationship. The penetration height ability of our method was approximately 250 nm from the reference surface (Z= 0). The outcomes of this study can provide information explaining some of the phenomena during nanoscale processes on a surface, such as in a semiconductor wet process.