The response of a microscopic dielectric object to an applied light field can profoundly affect its kinetic motion. A classic example of this is an optical trap, which can hold a particle in a tightly focused light beam. Optical fields can also be used to arrange, guide or deflect particles in appropriate light-field geometries. Here we demonstrate an optical sorter for microscopic particles that exploits the interaction of particles-biological or otherwise-with an extended, interlinked, dynamically reconfigurable, three-dimensional optical lattice. The strength of this interaction with the lattice sites depends on the optical polarizability of the particles, giving tunable selection criteria. We demonstrate both sorting by size (of protein microcapsule drug delivery agents) and sorting by refractive index (of other colloidal particle streams). The sorting efficiency of this method approaches 100%, with values of 96% or more observed even for concentrated solutions with throughputs exceeding those reported for fluorescence-activated cell sorting. This powerful, non-invasive technique is suited to sorting and fractionation within integrated ('lab-on-a-chip') microfluidic systems, and can be applied in colloidal, molecular and biological research.

We demonstrate controlled rotation of optically trapped objects in a spiral interference pattern. This pattern is generated by interfering an annular shaped laser beam with a reference beam. Objects are trapped in the spiral arms of the pattern. Changing the optical path length causes this pattern, and thus the trapped objects, to rotate. Structures of silica microspheres, microscopic glass rods, and chromosomes are set into rotation at rates in excess of 5 hertz. This technique does not depend on intrinsic properties of the trapped particle and thus offers important applications in optical and biological micromachines.

Primitive streak formation in the chick embryo involves large scale highly coordinated flows of over 100.000 cells in the epiblast. These large scale tissue flows and deformations can be correlated with specific anisotropic cell behaviours in the forming mesendoderm through a combined light-sheet microscopy and computational analysis. Relevant behaviours include apical contraction, elongation along the apical-basal axis followed by ingression as well as asynchronous directional cell intercalation of small groups of mesendoderm cells. Cell intercalation is associated with sequential, directional contraction of apical junctions, the onset, localisation and direction of which correlate strongly with the appearance of active Myosin II cables in aligned apical junctions in neighbouring cells. Use of a class specific Myosin inhibitors and gene specific knockdowns show that apical contraction and intercalation are Myosin II dependent and also reveal critical roles for Myosin I and Myosin V family members in the assembly of junctional Myosin II cables.

An interferometric pattern between two annular laser beams is used to construct three-dimensional (3D) trapped structures within an optical tweezers setup. In addition to being fully translatable in three dimensions, the trapped structure can be rotated controllably and continuously by introducing a frequency difference between the two laser beams. These interference patterns could play an important role in the creation of extended 3D crystalline structures.