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In exploring the genesis of life, liquid–liquid phase-separated coacervate droplets have been proposed as primitive protocells. Within the hydrothermal hypothesis, these droplets would emerge from molecule-rich hot fluids and thus be subjected to temperature gradients. Investigating their thermophoretic behavior can provide insights into protocell footprints in thermal landscapes, advancing our understanding of life’s origins. Here, we report the thermophilic behavior of heat-dissociative droplets, contrary to the intuition that heat-associative condensates would prefer hotter areas. This aspect implies the preferential presence of heat-dissociative primordial condensates near hydrothermal environments, facilitating molecular incorporation and biochemical syntheses. Additionally, our investigations reveal similarities between thermophoretic and electrophoretic motions, dictated by molecular redistribution within droplets due to their fluid nature, which necessitates revising current electrophoresis frameworks for surface charge characterization. Our study elucidates how coacervate droplets navigate thermal and electric fields, reveals their thermal-landscape-dependent molecular characteristics, and bridges foundational theories of early life: the hydrothermal and condensate-as-protocell hypotheses. 

Liquid–liquid interfaces hold the potential to serve as versatile platforms for dynamic processes, due to their inherent fluidity and capacity to accommodate surface-active materials. This study explores laser-driven actuation of liquid–liquid interfaces with and without loading of gold nanoparticles and further exploits the laser-actuated interfaces with nanoparticles for tunable photonics. Upon laser exposure, gold nanoparticles were rearranged along the interface, enabling the reconfigurable, small-aperture modulation of light transmission and the tunable lensing effect. Adapting the principles of optical and optothermal tweezers, we interpreted the underlying mechanisms of actuation and modulation as a synergy of optomechanical and optothermal effects. Our findings provide an analytical framework for understanding microscopic interfacial behaviors, contributing to potential applications in tunable photonics and interfacial material engineering. 

Optically resonant particles are key building blocks of many nanophotonic devices such as optical antennas and metasurfaces. Because the functionalities of such devices are largely determined by the optical properties of individual resonators, extending the attainable responses from a given particle is highly desirable. Practically, this is usually achieved by introducing an asymmetric dielectric environment. However, commonly used simple substrates have limited influences on the optical properties of the particles atop. Here, we show that the multipolar scattering of silicon microspheres can be effectively modified by placing the particles on a dielectric-covered mirror, which tunes the coupling between the Mie resonances of microspheres and the standing waves and waveguide modes in the dielectric spacer. This tunability allows selective excitation, enhancement, suppression, and even elimination of the multipolar resonances and enables scattering at extended wavelengths, providing transformative opportunities in controlling light–matter interactions for various applications. We further demonstrate with experiments the detection of molecular fingerprints by single-particle mid-infrared spectroscopy and with simulations strong optical repulsive forces that could elevate the particles from a substrate. 

Abstract Optical tweezers have profound importance across fields ranging from manufacturing to biotechnology. However, the requirement of refractive index contrast and high laser power results in potential photon and thermal damage to the trapped objects, such as nanoparticles and biological cells. Optothermal tweezers have been developed to trap particles and biological cells via opto-thermophoresis with much lower laser powers. However, the intense laser heating and stringent requirement of the solution environment prevent their use for general biological applications. Here, we propose hypothermal opto-thermophoretic tweezers (HOTTs) to achieve low-power trapping of diverse colloids and biological cells in their native fluids. HOTTs exploit an environmental cooling strategy to simultaneously enhance the thermophoretic trapping force at sub-ambient temperatures and suppress the thermal damage to target objects. We further apply HOTTs to demonstrate the three-dimensional manipulation of functional plasmonic vesicles for controlled cargo delivery. With their noninvasiveness and versatile capabilities, HOTTs present a promising tool for fundamental studies and practical applications in materials science and biotechnology. 

Abstract Charging of interfaces between water and hydrophobic media is a mysterious feature whose nature and origin have been under debate. Here, we investigate the fundamentals of the interfacial behaviors of water by employing opto-thermophoretic tweezers to study temperature-gradient-induced perturbation of dipole arrangement at water/oil interfaces. With surfactant-free perfluoropentane-in-water emulsions as a model interface, additional polar organic solvents are introduced to systematically modify the structural aspects of the interface. Through our experimental measurements on the thermophoretic behaviors of oil droplets under a light-generated temperature gradient, in combination with theoretical analysis, we propose that water molecules and mobile negative charges are present at the water/oil interfaces with specific dipole arrangement to hydrate oil droplets, and that this arrangement is highly susceptible to the thermal perturbation due to the mobility of the negative charges. These findings suggest a potential of opto-thermophoresis in probing aqueous interfaces and could enrich understanding of the interfacial behaviors of water. 

A universal platform drives out-of-plane optical rotation of arbitrary micro/nano-objects under a localized temperature field.