Angewandte Chemie International Edition
© WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
For full article and contact information, see Angew. Chem. Int. Ed. 2000, 39 (19), 3503 - 3506
Chains and Pyramids of Cells
Using "optical tweezers"
to build three-dimensional structures
out of single cells
Precisely defined aggregates of living cells are of interest to researchers in several fields, for example in analytical systems, in which the cells are used as sensors. In the area of basic biochemical research, they could be useful for the examination of processes such as signal transfer, adhesion, and the growth of cells. However, three-dimensional microstructures are especially difficult to generate.
Harvard researchers working with George M. Whitesides have now succeeded in building precisely defined two- and three-dimensional microstructures out of single cells and microspheres of polystyrene. The method they used for this is called "microfabrication with light", in which the cells and spheres are held by "optical tweezers" and are brought together with precision.
At first, the concept of light as a tweezer seems strange. Indeed, it is not in our day to day experience that light can exert a force on us or an object. The tiny forces exerted by quanta of light are sufficient to hold on to - and even to move - tiny objects such as biological cells, just like real tweezers. This requires a strongly focussed laser beam. If the beam hits a single, optically transparent cell, the beam is broken just as if it had hit a lens. The direction of the quanta of light is changed. This exerts a force on the cell, holding it in the center of the laser beam. If the beam is moved, the cell moves with it, trapped. These "tweezers" are so gentle that the cell is not damaged.
Even different types of cells, such as disc-shaped erythrocytes and spherical lymphocytes could be combined in different structures with this method. They were bound through polystyrene microspheres, to which the cells are stuck by unspecified interactions. Alternatively, adhesion can occur through biospecific interactions, if the spheres are coated with a biologically active substance.
"This kind of arrangement of different types of cells is suitable for the study of interactions between the individual cells and also differences in the effects of different pharmaceuticals or toxins on different types of cells at the same time," explains Whitesides. "Microfabrication with light is not limited to cells either, it can also be developed as a general tool for the construction of micro-objects out of all sorts of particles."