Biological nanofibers in a standing wave optical trap
To explain fundamental processes in molecular and cell biology a detailed description of the interaction of the relevant components involved is required. Hence, single molecule experiments have to be carried out in order to omit averaging of the interaction. For observation of small particles in a non-intrusive fashion optical traps can be used for immobilization and manipulation. The proposed design of a Gaussian standing wave optical trap, feasible to trap unprecedently small particles due to steep intensity gradients and the depletion of the scattering force is presented. In its realization with a reflective slide, it is used to demonstrate the capability of this tool to trap small biological particles. Nanofibers model a reduction in dimensionality, thus leading the way to single molecules. The high ratio of axial-to-lateral trap stiffness in the standing wave optical trap causes the nanofibers to lay in the focal plane. Microtubules with a diameter of 25nm were trapped and moved in the focal plane. Long time observation of microtubule bundles using darkfield microscopy is achieved and used to characterize the trapping efficiency. Bundles of three microtubules were held in focus over a time period of hours using a trapping power of only 6mW. The suitable conditioning of the sample chamber with a heating system is demonstrated by polymerizing microtubules inside the sample chamber, pointing the way to a controlled assembly of microtubule bundles.