ELASTIC LIGHT-SCATTERING MEASUREMENTS OF SINGLE BIOLOGICAL CELLS IN AN OPTICAL TRAP

We have developed an instrument for determination of the angular light scattering of beads and biological cells. The instrument uses radiati on pressure for levitation of particles inside a cuvette. The setup co nsists of two 780-nm diode lasers in a vertical double-beam trapping c onfiguration. In the horizontal direction a weakly focused 633-nm prob e beam is used to illuminate the trapped particle. One can detect scat tered light over the range of from -150 to 150 deg with an angular res olution of 0.9 deg using an avalanche photodiode. With this setup ligh t scattering from polystyrene beads was measured, and the obtained sca ttering patterns were compared with theoretical scattering patterns fr om Lorenz-Mie theory. The results show that the setup is stable, gives reproducible patterns, and qualitatively agrees with the calculations . Trapping of biological cells is more difficult than trapping of bead s, because smaller forces result from smaller refractive indices. We p resent an angular scattering pattern measured from a human lymphocyte measured from 20 to 60 deg. (C) 1996 Optical Society of America