Measurement of particle distribution in microchannel flow using a 3D-TIRFM technique
The presence of bio-substances in the near-wall region in micro bio-chemical analysis chips is an important topic but one which is difficult to investigate directly. In this paper we developed an accurate 3D-TIRFM technique, which was used to investigate the three-dimensional positions of nano-particles. The depth was calibrated using a piezo stage. As an example of an application of this technique, the concentration profile of nano-particles near a wall surface was investigated. The results showed that the concentration profile was non-uniform and lower than that in the bulk. In addition the ionic strength of the solvent strongly influenced the concentration profile. It was concluded that the non-uniform concentration profile is due to the influence of the electric double layer around the particles and the surface. This demonstrates the importance of selecting suitable electric characteristics, since a non-uniform and low concentration profile near the wall will affect the reaction efficiency and the sensitivity in micro bio-chemical analysis.
microchannel flow 3d-tirfm concentration profile evanescent light near wall