Optical Visualization Method for High Speed Tracking of a Transparent Floating Cell

Abstract

This paper describes an optical visualization method for a transparent object that is capable of realizing high speed tracking of a motile cell without the need to use fluorescent labeling. This method visualizes a non-labeled cell as a periodic light intensity distribution by deriving the diffracted light of a single frequency from the sample. Using this periodic pattern, a high response photodiode can be employed to measure the velocity of a transparent cell. We propose an optical spatial-filtering method to select the spatial frequency component, which introduces two pinholes in the optical Fourier-transform plane. The positions of these pinholes are the two focusing points of the ±1^st-order diffracted light for the selected spatial frequency. By blocking the 0^th-order diffracted light, which includes the regular reflection component from the surface of the cover glass that is the main source of stray light, a laser of high coherence and high power can be used as the light source. We could clearly observe three kinds of transparent cell (lymph cell: JURKAT, white blood cell: K562, breast cancer cell: YMB-1-E) as periodic light intensity distributions. In addition, we confirmed that this pattern moves in accordance with the translational movement of the cell.