Ultrafast Modulation of Thermoplasmonic Nanobubbles in Water

Enabling Continuous and Improved Solar-Driven Atmospheric Water Harvesting with Ti3C2-Incorporated Metal-Organic Framework Monoliths

Solar-powered atmospheric water harvest (SAWH) with metal-organic frameworks (MOFs) represents one of the most sustainable, energy-efficient, and low-cost ways to alleviate water shortage stress in arid regions. However, the daily water productivity of previously developed SAWH devices remains low as they are merely allowed to be operated in batch mode and complete one water harvest cycle every day. This inevitably makes it rather challenging to deploy MOF-based SAWH for water production at scales. To overcome this challenge, MXene Ti₃C₂-incorporated UiO-66-NH₂ (TUN) cylindrical monoliths (13 mm diameter, 4 mm thickness) with vertically aligned porous networks have been prepared and exhibited greatly enhanced solar heating capacity and atmospheric water adsorption/desorption kinetics. Using TUN monoliths as atmospheric water adsorbents, a novel SAWH device containing a flippable adsorbent stage with dual TUN monolith layers attached on both sides has been fabricated. Such a novel design enables the prototype to produce water in a continuous mode under sunlight irradiation, delivering 57.8 mL_H2O kg_MOF^-1 h^-1 of water productivity in a simulated indoor arid environment (20% relative humidity, 298 K). This is the first exploration in continuous water production with MOF-based SAWH, demonstrating a promising way to achieve scalable and low-cost SAWH in arid areas.

Behavior of Thermally Induced Nanobubbles during Instantaneous Particle Heating by Pulsed Laser Melting in Liquid

Pulsed laser melting in liquid (PLML) is a technique to produce submicrometer spherical particles (SMPs). In this process, raw particles dispersed in liquid are selectively heated, and thermally induced nanobubbles (TINBs) at the particle surface are generated and act as a thermal barrier to enhance the temperature increase during heating. However, monitoring TINBs is difficult since PLML is a low-temperature, nonplasma process. Simple transmittance measurements of monodisperse Au SMP (250 nm) colloidal solutions on a transient time scale were used to monitor the temporal dependence of the TINB thickness and the pressure within the bubble. By applying this technique for ZnO and Sn SMP formation, TINBs in the PLML process are important in promoting the formation of large particles via particle merging during laser heating.

Strong Transient Flows Generated by Thermoplasmonic Bubble Nucleation

The challenge of inducing and controlling localized fluid flows for generic force actuation and for achieving efficient mass transport in microfluidics is key to the development of next-generation miniaturized systems for chemistry and life sciences. Here we demonstrate a methodology for the robust generation and precise quantification of extremely strong flow transients driven by vapor bubble nucleation on spatially isolated plasmonic nanoantennas excited by light. The system is capable of producing peak flow speeds of the order mm/s at modulation rates up to ∼100 Hz in water, thus allowing for a variety of high-throughput applications. Analysis of flow dynamics and fluid viscosity dependence indicates that the transient originates in the rapid bubble expansion that follows nucleation rather than being strictly thermocapillary in nature.

Directed Concentrating of Micro-/Nanoparticles via Near-Infrared Laser Generated Plasmonic Microbubbles

Directed concentrating of micro- and nanoparticles via laser-generated plasmonic microbubbles in a liquid environment is an emerging technology. For effective heating, visible light has been primarily employed in existing demonstrations. In this paper, we demonstrate a new plasmonic platform based on nanoporous gold disk (NPGD) array. Thanks to the highly tunable localized surface plasmon resonance of the NPGD array, microbubbles of controlled size can be generated by near-infrared (NIR) light. Using NIR light provides several key advantages over visible light in less interference with standard microscopy and fluorescence imaging, preventing fluorescence photobleaching, less susceptible to absorption and scattering in turbid biological media, and much reduced photochemistry, phototoxicity, and so forth. The large surface-to-volume ratio of NPGD further facilitates the heat transfer from these gold nanoheaters to the surroundings. While the microbubble is formed, the surrounding liquid circulates and direct microparticles randomly dispersed in the liquid to the bottom NPGD surface, which can be made to yield a unique collection of 3D hollow dome microstructures with bubbles larger than 5 μm. Such capability can also be employed in concentrating suspended colloidal nanoparticles at desirable sites and with the preferred configuration enhancing the sensor performance. Specifically, the interaction among concentrated nanoparticles and their interactions with the underlying substrate have been investigated for the first time. These collections have been characterized using optical microscopy, scanning electron microscopy, hyperspectral localized surface plasmon resonance imaging, and hyperspectral Raman imaging. In addition to various micro- and nanoparticles, the plasmonic microbubbles are also shown to collect biological cells and extracellular nanovesicles such as exosomes. By using a spatial light modulator to project the laser in arbitrary patterns, parallel concentrating can be achieved to fabricate an array of clusters.

Optical Rotation and Thermometry of Laser Tweezed Silicon Nanorods

Optical rotation of laser tweezed nanoparticles offers a convenient means for optical to mechanical force transduction and sensing at the nanoscale. Plasmonic nanoparticles are the benchmark system for such studies, but their rapid rotation comes at the price of high photoinduced heating due to Ohmic losses. We show that Mie resonant silicon nanorods with characteristic dimensions of ∼220 × 120 nm² can be optically trapped and rotated at frequencies up to 2 kHz in water using circularly polarized laser light. The temperature excess due to heating from the trapping laser was estimated by phonon Raman scattering and particle rotation analysis. We find that the silicon nanorods exhibit slightly improved thermal characteristics compared to Au nanorods with similar rotation performance and optical resonance anisotropy. Altogether, the results indicate that silicon nanoparticles have the potential to become the system of choice for a wide range of optomechanical applications at the nanoscale.