ИСТИНА

Magnetic particles actuated by rotating magnetic fields are commonly used as controllable nano- and micromotors and microfluidic mixers. Rotating microparticles are also utilized to twist biological molecules to probe their torsional stiffness as well as to rotate the surrounding fluid to probe the mechanical properties of liquid media [1]. Optical tweezers have emerged as a unique technique allowing for the precise manipulation of the positions of microparticles, thereby making the distance between interacting particles a controllable parameter. Furthermore, optical tweezers are a powerful tool for directly measuring the interaction forces between microparticles and measuring their displacements from the traps and rotation rate [2]. Here we show that rotating magnetic microparticles in optical traps can be used as local microscale heaters and mixers for liquids with volumes on the order of a few picoliters. The temperature of such a trapped microparticle can be controlled with a precision of approximately 1 °C, which may be very useful for studying thermal effects in a variety of biological and chemical microsystems. Also the determination of the influence of Brownian torque on the rotation of a spherical magnetic microparticle using optical tweezers is reported. The experimental dependences of the microparticle rotation on the external magnetic field strength and the rotational frequency clarify the microparticle dynamics near the transition between the synchronous and asynchronous rotational modes. The results are in agreement with numerical Brownian dynamics simulations of microparticle rotation in the presence of Brownian torques. The last part of research is devoted to experimental study of the thermophoresis-assisted Magnus force acting on an optically trapped magnetic microparticle rotating in a liquid flow. The results show, that the thermophoretic Magnus force is significant enough to contribute to the motion of the trapped microparticle.