Universal optothermal micro/nanoscale rotors

Abstract

Rotation of micro/nano-objects is important for micro/nanorobotics, three-dimensional imaging, and lab-on-a-chip systems. Optical rotation techniques are especially attractive because of their fuel-free and remote operation. However, current techniques require laser beams with designed intensity profile and polarization or objects with sophisticated shapes or optical birefringence. These requirements make it challenging to use simple optical setups for light-driven rotation of many highly symmetric or isotropic objects, including biological cells. Here, we report a universal approach to the out-of-plane rotation of various objects, including spherically symmetric and isotropic particles, using an arbitrary low-power laser beam. Moreover, the laser beam is positioned away from the objects to reduce optical damage from direct illumination. The rotation mechanism based on opto-thermoelectrical coupling is elucidated by rigorous experiments combined with multiscale simulations. With its general applicability and excellent biocompatibility, our universal light-driven rotation platform is instrumental for various scientific research and engineering applications.

Optothermal rotation of micro-/nano-objects

“…In analogy with optical electrokinetics, where the migration of colloids is induced by the non-uniform electric field based on a photoconductive substrate, 70,71 thermoelectrokinetics describes a similar electrokinetic (EK) migration that stems from the electric fields from the temperature-responsive substrates. 44,72 Most colloids are negatively charged due to their ionized acid groups on the surface. 31 Similarly, substrates can carry surface charges by coating a thin layer of acid groups (e.g., carboxylic acids).…”

Recent Progress on Optical Micro/Nanomanipulations: Structured Forces, Structured Particles, and Synergetic Applications

“…Besides working alone, the thermal heating effect can also work together with other forces to manipulate particles. 49,86 Additional physical fields, such as fluidic field 50,51 and electric field, 49,85,119,137,152 can also be generated through heating to manipulate particles. Overall, the utilization of thermal effects affords additional degrees of freedom for more powerful and interesting optical manipulations.…”

“…Utilizing all-dielectric structures to eliminate the optical absorption and avoid heating is one direction. − ,, Different from the methods which mitigate absorption and avoid heating, another direction is to utilize the heating effect. , As stated in the theoretical section, light-induced heating effects can provide additional mechanisms to manipulate particles, such as photophoresis and thermophoresis. , Through tailoring the temperature distribution or engineering the particle’s thermal properties on the surface, particles can be trapped or pulled/levitated as demanded. Besides working alone, the thermal heating effect can also work together with other forces to manipulate particles. , Additional physical fields, such as fluidic field , and electric field, ,,,, can also be generated through heating to manipulate particles. Overall, the utilization of thermal effects affords additional degrees of freedom for more powerful and interesting optical manipulations …”

Creating stable trapping force and switchable optical torque with tunable phase of light

“…Optical rotation is easily affected when the motor is repelled from the optical field by perturbations, such as fluidic flow. The flow can sometimes be useful though; e.g., rotation of small objects can also be achieved through thermophoresis, shear flow, or harmonic acoustics (29)(30)(31).…”