Two-photon induced polymerization of photo-driven microsensors

Abstract

We report on the fabrication of photo-driven polymer microsensors for viscosimetry, velocimetry and micropump applications. They are readily made with a low-cost polymerization technique based on two-photon absorption. Microsensors are free-floating in the liquid to be characterized. A linearly-polarized optical tweezers is used to trap one sensor at the laser focal point and to generate the optical torque needed for local hydrodynamic measurements. Viscosity and velocity microsensors have slab shapes that align in the polarization direction. The local viscosity is deduced from the maximum rotation frequency generated by the rotating linear polarization, while the fluid velocity is obtained by measuring the maximum angle that equilibrates the optical torque and drag torque. Experimental results are in good agreement with theoretical calculations. The micropump is based on a micron-size Archimedes screw that rotates around its long axis when it is trapped at the focal point. The laser-induced rotation is due to the optical torque that is transferred by the laser scattering on the screw.