Dielectric metasurfaces have recently attracted much attention due to their ability to efficiently control light propagation, that is, its amplitude, phase and polarization, on micro- and macro- levels. Such metasurfaces also naturally allow for integration in compact optical setups due to their small sizes. An important issue of energy losses is also addressed by employing all-dielectric platform. Advancements in nanofabrication have enabled realization of metasurface-based high-resolution wavefront engineering devices, which have been employed in different imaging applications, for example, as metalenses, polarization filters, metaholograms, etc. Quantitative phase imaging is a powerful tool for the optical inspection of transparent samples in connection with biological and technical applications. By measuring thickness and/or refractive index profiles, phase imaging facilitates, for example, the observation of dynamic events in unstained cells. As such, it has become indispensable in biological imaging, wavefront correction and metrology. However, conventional cameras and photodetectors are inherently not sensitive to the phase of an incident lightwave. As a consequence, direct phase detection is challenging. Only by multiple intensity measurements or application of specialized interferometric schemes, the phase profile of an object can be in principle reconstructed. In this paper, we report on the ability of metasurfaces to contribute to quantitative phase imaging by independent control of the phase profiles in two orthogonal polarization states of an incident beam.
The generalized phase contrast method is employed as an efficient “phase-only” laser beam-shaping technique in an optical setup built for catapulting microspheres through simple mucus models. The influence of the laser power and mucin concentration on the motion of the microspheres is investigated in terms of instant and average velocities on a 250-μm trajectory, corresponding to the mucus thickness in the human gastrointestinal tract. Increasing the laser power leads to higher velocities in all the tested samples, while increasing the mucin concentration leads to significant velocity decrease for similar laser input power. However, velocities of up to 95 μm · s − 1 are demonstrated in a 5% mucin simple mucus model using our catapulting system. This study contributes to understanding and overcoming the challenges of optical manipulation in mucus models. This paves the way for efficient optical manipulation of three-dimensional-printed light-controlled microtools with the ability to penetrate the mucus biobarrier for in vitro drug-delivery studies.
Microfluidic systems have gained much interest in the past decade as they tremendously reduce sample volume requirements for investigating different phenomena and for various medical, pharmaceutical and defense applications. Rapid heat transfer and efficient diffusive material transport are among the benefits of miniaturization. These have been achieved so far by tediously designing and fabricating application-specific microfluidic chambers or by employing microdevices that can be difficult to integrate in microfluidic systems. In this work, we present the fabrication and functionalization via two-photon polymerization and physical vapor deposition of microstructures that serve as heat sources in microfluidic devices upon laser illumination. In contrast to other existing methods that rely on photo-thermal effects, our microtools are amenable to optical manipulation and can be actuated in specific locations where heat generation is desired. Heating effects manifest in the presence of a temperature gradient, induced fluid flow and the formation of microbubbles.
Light Robotics is one of the newest progenies of the robotics family, bringing together advances in microfabrication and optical manipulation with intelligent control ideas from robotics and Fourier optics. The development of lightcontrollable microrobots capable of performing specific tasks at the microscale requires the ability to sculpt the two protagonists of the story: the light and the microrobots. Complex light sculpting for optical trapping has been in focus for over three decades, and its importance for controlling microscopic objects is well understood. Designing intricate microrobots for the task is a more recent development facilitated by state-of-the-art microfabrication techniques, and particularly by two-photon polymerization. The full 3D design freedom offered by two-photon polymerization opens the door for imagination, while at the same time bringing the responsibility of rationally designing microrobots tailored to specific tasks. In addition to shape and topology features, the surface chemistry of the microrobots can also help steer them towards specific applications. This paper will discuss strategies for the design and fabrication of light-controllable microrobots as a toolbox for biomedical applications.
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