title: Alignment of biological microparticles by a polarized laser beam.
abstract: The optical alignment of biological samples is of great relevance to microspectrometry and to the micromanipulation of single particles. Recently, Bayoudh et al. (J. Mod. Opt. 50:1581-1590, 2003) have shown that isolated, disk-shaped chloroplasts can be aligned in a controlled manner using an in-plane-polarized Gaussian beam trap, and suggested that this is due to their nonspherical shape. Here we demonstrate that the orientation of various micrometer-sized isolated biological particles, trapped by optical tweezers, can be altered in a controlled way by changing the plane of linear polarization of the tweezers. In addition to chloroplasts, we show that subchloroplast particles of small size and irregular overall shape, aggregated photosynthetic light-harvesting protein complexes as well as chromosomes can be oriented with the linearly polarized beam of the tweezers. By using a laser scanning confocal microscope equipped with a differential polarization attachment, we also measured the birefringence of magnetically oriented granal chloroplasts, and found that they exhibit strong birefringence with large local variations, which appears to originate from stacked membranes. The size and sign of the birefringence are such that the resulting anisotropic interaction with the linearly polarized laser beam significantly contributes to the torque orienting the chloroplasts.
authors.affiliation: Institute of Plant Biology, Hungarian Academy of Sciences, P.O. Box 521, 6701 Szeged, Hungary. gyozo@brc.hu
authors.forename: Gyozo
authors.initials: G
authors.lastname: Garab
authors.forename: Péter
authors.initials: P
authors.lastname: Galajda
authors.forename: István
authors.initials: I
authors.lastname: Pomozi
authors.forename: Laura
authors.initials: L
authors.lastname: Finzi
authors.forename: Tünde
authors.initials: T
authors.lastname: Praznovszky
authors.forename: Pál
authors.initials: P
authors.lastname: Ormos
authors.forename: Herbert
authors.initials: H
authors.lastname: van Amerongen
mesh_terms: D000818:Animals; D001703:Biophysics / Q000379:methods*; D002460:Cell Line; D002736:Chloroplasts / Q000528:radiation effects* / Q000648:ultrastructure; D002875:Chromosomes / Q000378:metabolism; D006224:Cricetinae; D007834:Lasers; D008027:Light; D008677:Metaphase; D051379:Mice; D018613:Microscopy, Confocal; D015233:Models, Statistical; D016011:Normal Distribution; D018532:Pisum sativum; D013053:Spectrophotometry / Q000379:methods*; D013997:Time Factors