Nanovortex-Driven All-Dielectric Optical Diffusion Boosting and Sorting Concept for Lab-on-a-Chip Platforms

Optothermal Needle-Free Injection of Vaterite Nanocapsules

The propulsion and acceleration of nanoparticles with light have both fundamental and applied significance across many disciplines. Needle-free injection of biomedical nano cargoes into living tissues is among the examples. Here a new physical mechanism of laser-induced particle acceleration is explored, based on abnormal optothermal expansion of mesoporous vaterite cargoes. Vaterite nanoparticles, a metastable form of calcium carbonate, are placed on a substrate, underneath a target phantom, and accelerated toward it with the aid of a short femtosecond laser pulse. Light absorption followed by picosecond-scale thermal expansion is shown to elevate the particle's center of mass thus causing acceleration. It is shown that a 2 µm size vaterite particle, being illuminated with 0.5 W average power 100 fsec IR laser, is capable to overcome van der Waals attraction and acquire 15m sec-1 velocity. The demonstrated optothermal laser-driven needle-free injection into a phantom layer and Xenopus oocyte in vitro promotes the further development of light-responsive nanocapsules, which can be equipped with additional optical and biomedical functions for delivery, monitoring, and controllable biomedical dosage to name a few.

Superscattering emerging from the physics of bound states in the continuum

We study the Mie-like scattering from an open subwavelength resonator made of a high-index dielectric material, when its parameters are tuned to the regime of interfering resonances. We uncover a novel mechanism of superscattering, closely linked to strong coupling of the resonant modes and described by the physics of bound states in the continuum (BICs). We demonstrate that the enhanced scattering occurs due to constructive interference described by the Friedrich-Wintgen mechanism of interfering resonances, allowing to push the scattering cross section of a multipole resonance beyond the currently established limit. We develop a general non-Hermitian model to describe interfering resonances of the quasi-normal modes, and study subwavelength dielectric nonspherical resonators exhibiting avoided crossing resonances associated with quasi-BIC states. We confirm our theoretical findings by a scattering experiment conducted in the microwave frequency range. Our results reveal a new strategy to boost scattering from non-Hermitian systems, suggesting important implications for metadevices.

Polarization-Dependent Forces and Torques at Resonance in a Microfiber-Microcavity System

Spin-orbit interactions in evanescent fields have recently attracted significant interest. In particular, the transfer of the Belinfante spin momentum perpendicular to the propagation direction generates polarization-dependent lateral forces on particles. However, it is still elusive as to how the polarization-dependent resonances of large particles synergize with the incident light's helicity and resultant lateral forces. Here, we investigate these polarization-dependent phenomena in a microfiber-microcavity system where whispering-gallery-mode resonances exist. This system allows for an intuitive understanding and unification of the polarization-dependent forces. Contrary to previous studies, the induced lateral forces at resonance are not proportional to the helicity of incident light. Instead, polarization-dependent coupling phases and resonance phases generate extra helicity contributions. We propose a generalized law for optical lateral forces and find the existence of optical lateral forces even when the helicity of incident light is zero. Our work provides new insights into these polarization-dependent phenomena and an opportunity to engineer polarization-controlled resonant optomechanical systems.

Special scattering regimes for conical all-dielectric nanoparticles

All-dielectric nanophotonics opens a venue for a variety of novel phenomena and scattering regimes driven by unique optical effects in semiconductor and dielectric nanoresonators. Their peculiar optical signatures enabled by simultaneous electric and magnetic responses in the visible range pave a way for a plenty of new applications in nano-optics, biology, sensing, etc. In this work, we investigate fabrication-friendly truncated cone resonators and achieve several important scattering regimes due to the inherent property of cones-broken symmetry along the main axis without involving complex geometries or structured beams. We show this symmetry breaking to deliver various kinds of Kerker effects (generalized and transverse Kerker effects), non-scattering hybrid anapole regime (simultaneous anapole conditions for all the multipoles in a particle leading to the nearly full scattering suppression) and, vice versa, superscattering regime. Being governed by the same straightforward geometrical paradigm, discussed effects could greatly simplify the manufacturing process of photonic devices with different functionalities. Moreover, the additional degrees of freedom driven by the conicity open new horizons to tailor light-matter interactions at the nanoscale.

Microfluidic synthesis of optically responsive materials for nano- and biophotonics

Recently, nanomaterials demonstrating optical response under illumination, the so-called optically responsive nanoparticles (NPs), have found their broad application as optical switchers, gas adsorbents, data storage devices, and optical and biological sensors. Unique optical properties of such nanomaterials are strongly related to their chemical composition, geometrical parameters and morphology. Microfluidic approaches for NPs' synthesis allow overcoming the known critical stages in conventional synthesis of NPs due to a high rate of heat/mass transfer and precise regulation of synthesis conditions, which results in reproducible synthesis outcomes with the desired physico-chemical properties. Here, we review the recent advances in microfluidic approach for synthesis of optically responsive nanomaterials (plasmonic, photoluminescent, shape-changeable NPs), highlighting the general background of microfluidics, common considerations in the design of microfluidic chips (MFCs), and theoretical models of the NPs' formation mechanisms. Comparative analysis of microfluidic synthesis with conventional synthesis methods is provided further, along with the recent applications of optically responsive NPs in nano- and biophotonics.

Cell nucleus as endogenous biological micropump

Micropumps can generate directional microflows in blood vessels or bio-capillaries for targeted transport of nanoparticles and cells in vivo, which is highly significant for biomedical applications from active drug delivery to precision clinical therapy. Meanwhile, they have been extensively used in the biosensing fields with their unique features of autonomous motion, easy surface functionalization, dynamic capture and effective isolation of analytes in complex biological media. However, synthetic devices for actuating microflows, including pumps and motors, generally exhibit poor or limited biocompatibility with living organisms as a result of the invasive implantation of exogenous materials into blood vessels. Here we demonstrate a method of constructing endogenous micropumps by extracting nuclei from red blood cells, thus making them intrinsically and completely biocompatible. The nuclei are extracted and then driven by a scanning optical tweezing system. By a precise actuation of the microflows, nanoparticles and cells are navigated to target destinations, and the transport velocity and direction is controlled by the multifunctional dynamics of the micropumps. With the targeted transport of functionalized micro/nanoparticles followed by a dynamic mixing in microliter blood samples, the micropumps provide considerable promises to enhance the target binding efficiency and improve the sensitivity and speed of biological assays in vivo. Furthermore, multiplexing by simultaneously driving an array of multiple nuclei is demonstrated, thus confirming that the micropumps could provide a bio-friendly high-throughput in vivo platform for the treatment of blood diseases, microenvironment monitoring, and biomedical analysis.

Multipole interplay controls optical forces and ultra-directional scattering

We analyze the superposition of Cartesian multipoles to reveal the mechanisms underlying the origin of optical forces. We show that a multipolar decomposition approach significantly simplifies the analysis of this problem and leads to a very intuitive explanation of optical forces based on the interference between multipoles. We provide an in-depth analysis of the radiation coming from the object, starting from low-order multipole interactions up to quadrupolar terms. Interestingly, by varying the phase difference between multipoles, the optical force as well as the total radiation directivity can be well controlled. The theory developed in this paper may also serve as a reference for ultra-directional light steering applications.

Optical Potential-Well Array for High-Selectivity, Massive Trapping and Sorting at Nanoscale

Optical tweezers are versatile tools capable of sorting microparticles, yet formidable challenges are present in the separation of nanoparticles smaller than 200 nm. The difficulties arise from the controversy on the requirement of a tightly focused light spot in order to create strong optical forces while a large area is kept for the sorting. To overcome this problem, we create a near-field potential well array with connected tiny hotspots in a large scale. This situation can sort nanoparticles with sizes from 100 to 500 nm, based on the differentiated energy depths of each potential well. In this way, nanoparticles of 200, 300, and 500 nm can be selectively trapped in this microchannel by appropriately tuning the laser power. Our approach provides a robust and unprecedented recipe for optical trapping and separation of nanoparticles and biomolecules, such that it presents a huge potential in the physical and biomedical sciences.