Damage-free light-induced assembly of intestinal bacteria with a bubble-mimetic substrate

Plasmon dephasing time and optical field enhancement in a plasmonic nanobowl substrate studied by scanning near-field optical microscopy

Plasmonic substrates have been extensively investigated due to their potential applications in fluorescence microscopy, chemical sensing, and photochemical reactions. The optical properties of the substrate depend on the spatial and temporal features of the plasmon excited. Hence, the ability to directly visualize plasmon dynamics is crucial. In this study, we investigated the spatial and temporal properties of plasmon excitation in a plasmonic nanobowl substrate consisting of a periodic hexagonal array of nanoscale bowl-like structures developed with self-assembly. Near-field transmission imaging revealed that multiple plasmon resonance bands are observed from visible to near-infrared spectral region, and the optical contrast of the image is dependent on the observed band. Near-field two-photon photoluminescence microscopy revealed that the probability of excitation inside each nanoscale bowl-like structure is greater than that in the surrounding area. Near-field time-resolved imaging revealed that the nanobowl substrate exhibited a substantially long plasmon dephasing time, exceeding 12 fs. Based on the spectral features of the near-field and far-field spectra, we found that optically dark plasmon mode is excited by the near-field illumination and only partly contributes to the long dephasing time observed. This fact indicates that the dephasing time is extended by some other mechanism in the periodic substrate. We revealed from this study that the enhanced optical fields induced in the nanobowl structure originate from the photosynergetic effect of the cavity mode and plasmon mode excited.

Opto-thermal manipulation with a 3 µm mid-infrared Er:ZBLAN fiber laser

Water has significantly high absorption around 3 µm wavelength region, originated by its fundamental OH vibrational modes. Here, we successfully demonstrate an opto-thermal manipulation of particles utilizing a 3 µm mid-infrared Er:ZBLAN fiber laser (adjustable from 2700 to 2826 nm) that can efficiently elevate the temperature at a laser focus with a low laser power. The 3 µm laser indeed accelerates the formation of the particle assembly by simply irradiating the laser into water. By altering the laser wavelengths, the assembling speed and size, instantaneous particle velocity, particle distribution, trapping stiffness and temperature elevation are evaluated systematically. We propose that the dynamics of particle assembly can be understood through thermo-osmotic slip flows, taking into account the effects of volume heating within the focal cone and point heating at the focus.

Adaptive and Dissipative Hierarchical Population Crowding of Synthetic Protocells through Click-PISA under Gradient Energy Inputs

The ability of living objects to respond rapidly en masse to various stimuli or stress is an important function in response to externally applied changes in the local environment. This occurs across many length scales, for instance, bacteria swarming in response to different stimuli or stress and macromolecular crowding within cells. Currently there are few mechanisms to induce similar autonomous behaviors within populations of synthetic protocells. Herein, we report a system in which populations of individual objects behave in a coordinated manner in response to changes in the energetic environment by the emergent self-organization of large object swarms. These swarms contain protocell populations of approximately 60 000 individuals. We demonstrate the dissipative nature of the hierarchical constructs, which persist under appropriate UV stimulation. Finally, we identify the ability of the object populations to change behaviors in an adaptive population-wide response to the local energetic environment.

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.

Light-Induced Condensation of Biofunctional Molecules around Targeted Living Cells to Accelerate Cytosolic Delivery

The light-induced force and convection can be enhanced by the collective effect of electrons (superradiance and red shift) in high-density metallic nanoparticles, leading to macroscopic assembly of target molecules. We here demonstrate application of the light-induced assembly for drug delivery system with enhancement of cell membrane accumulation and penetration of biofunctional molecules including cell-penetrating peptides (CPPs) with superradiance-mediated photothermal convection. For induction of photothermal assembly around targeted living cells in cell culture medium, infrared continuous-wave laser light was focused onto high-density gold-particle-bound glass bottom dishes exhibiting plasmonic superradiance or thin gold-film-coated glass bottom dishes. In this system, the biofunctional molecules can be concentrated around the targeted living cells and internalized into them only by 100 s laser irradiation. Using this simple approach, we successfully achieved enhanced cytosolic release of the CPPs and apoptosis induction using a pro-apoptotic domain with a very low peptide concentration (nM level) by light-induced condensation.

Review of Bubble Applications in Microrobotics: Propulsion, Manipulation, and Assembly

In recent years, microbubbles have been widely used in the field of microrobots due to their unique properties. Microbubbles can be easily produced and used as power sources or tools of microrobots, and the bubbles can even serve as microrobots themselves. As a power source, bubbles can propel microrobots to swim in liquid under low-Reynolds-number conditions. As a manipulation tool, microbubbles can act as the micromanipulators of microrobots, allowing them to operate upon particles, cells, and organisms. As a microrobot, microbubbles can operate and assemble complex microparts in two- or three-dimensional spaces. This review provides a comprehensive overview of bubble applications in microrobotics including propulsion, micromanipulation, and microassembly. First, we introduce the diverse bubble generation and control methods. Then, we review and discuss how bubbles can play a role in microrobotics via three functions: propulsion, manipulation, and assembly. Finally, by highlighting the advantages and current challenges of this progress, we discuss the prospects of microbubbles in microrobotics.

Interfacial Flows and Interfacial Shape Modulation Controlled by the Thermal Action of Light Energy

The review covers the research on thermocapillary convection caused by the thermal action of laser radiation in single-layer and bilayer liquid systems of capillary thickness. The advantages of using optical radiation are the instantaneous delivery of thermal energy to a place on demand (a bulk phase, interfaces); low radiation power required; concentrating heat flux on a spot of a few micrometers; the production of arbitrary spatial distributions of radiation intensity; and, as a result, corresponding thermal fields at a liquid interface and their fast reconfiguration. Thermocapillary stresses at the liquid interfaces lead to the transfer of the liquid and a change in the shape of the interface, in accordance with the distribution of the light-induced thermal field. Studies concerned with the methods of non-destructive testing of liquid media and solids, which are based on a photothermocapillary signal emitted by a laser-induced concave deformation of a thin layer, are considered. Features of thermocapillary deformation of a liquid–air interface caused by local heating of thin and thick (exceeding the capillary length) layers are demonstrated. A part of the review addresses the results of the study of thermocapillary rupture of films in the heating zone and the application of this effect in semiconductor electronics and high-resolution lithography. The works on the light-induced thermocapillary effect in bilayer (multilayer) liquid systems are analyzed, including early works on image recording liquid layer systems, liquid IR transducers, and nonlinear optical media.

Switching between laser-induced thermophoresis and thermal convection of liquid suspension in a microgap with variable dimension

Phoretic motion of particles along a temperature gradient formed in a fluid, known as thermophoresis, often takes place under the influence of bulk motion caused by thermal convection. In this paper, using a laser heating method, the significance of two competing effects, that is, thermophoresis and thermal convection, for the particle transport in a liquid phase confined in a microgap is investigated experimentally by changing the gap size as a control parameter. It is found that there is a threshold of the gap size, above which the particles tend to accumulate around the heated spot, forming a ring-like particle distribution. On the contrary, if the gap size is below the threshold, the particles are depleted from the heated spot. Switching between these accumulation and depletion modes is expected to develop novel manipulation techniques.