Fast and precise Laguerre-Gaussian beam steering with acousto-optic deflectors.

Novel fluorescence microscopy techniques and two-color laser direct imaging photolithography methods that enable resolution an order of magnitude beyond the diffraction limit require Laguerre-Gaussian beams and a fast and precise laser beam steering device to obtain images and produce microstructures. An acousto-optic deflector (AOD) is a suitable choice and provides high-speed random access beam positioning with subnanometer precision as well as beam intensity control in a single element. In high-resolution applications, the impact of an AOD on beam quality plays a major role.

Measurement of fluid flow generated by artificial cilia.

We observed and measured the fluid flow that was generated by an artificial cilium. The cilium was composed of superparamagnetic microspheres, in which magnetic dipole moments were induced by an external magnetic field. The interaction between the dipole moments resulted in formation of long chains-cilia, and the same external magnetic field was also used to drive the cilia in a periodic manner.

Analysis of fluid flow around a beating artificial cilium.

Biological cilia are found on surfaces of some microorganisms and on surfaces of many eukaryotic cells where they interact with the surrounding fluid. The periodic beating of the cilia is asymmetric, resulting in directed swimming of unicellular organisms or in generation of a fluid flow above a ciliated surface in multicellular ones. Following the biological example, externally driven artificial cilia have recently been successfully implemented as micropumps and mixers.

A microfluidic diffusion chamber for reversible environmental changes around flaccid lipid vesicles.

The reversible environmental changes around flaccid lipid vesicles represent a considerable experimental challenge, particularly because of remarkable softness of flaccid membranes, which can warp irreversibly under the slightest hydrodynamic flow. As a result, we have developed a microfluidic device for the controlled analysis of individual flaccid, giant lipid vesicles in a changing chemical environment. The setup combines the advantages of a flow-free microfluidic diffusion chamber and optical tweezers, which are used to load the sample vesicles into the chamber.

Self-assembled artificial cilia.

Due to their small dimensions, microfluidic devices operate in the low Reynolds number regime. In this case, the hydrodynamics is governed by the viscosity rather than inertia and special elements have to be introduced into the system for mixing and pumping of fluids. Here we report on the realization of an effective pumping device that mimics a ciliated surface and imitates its motion to generate fluid flow.