In this paper, we present an innovative optofluidic system that leverages cascaded bowtie photonic crystal (BPhC) to achieve subwavelength-scale control of temperature and fluid motion. The strong electromagnetic field enhancement of the bowtie structure can generate a hotspot at the resonance of BPhC, due to the absorption of bulk water in the infrared wavelength range (around 1600 nm). With the assistance of a cationic surfactant, cetyltrimethylammonium chloride (CTAC), a thermoelectric field is established to attract particles towards the hot region. Our experiments show that suspended particles as small as 800 nanometers can be rapidly transported to bowtie region and become trapped at the bowtie cavity on the resonance of BPhC. The trapped particles can be released simply by tuning the wavelength from on to off resonant conditions. Our work paves the way for non-plasmonic nanophotonics to manipulate microfluidic dynamics and precisely control trapping by tuning the wavelength
In this study, a novel method is proposed for low-power trapping of nanoparticles that employs resonant bowtie nano-antennas, which generate high temperature gradients upon laser illumination. The approach involves the integration of the depletion attraction force and the near-field optical gradient force, which results in highly efficient trapping of small extracellular vesicles (EVs) and 100nm polystyrene beads with low power consumption (less than 5mW). Additionally, we demonstrate that rapid transport can be achieved in less than 10 seconds, facilitated by the long-range nature of the depletion attraction force.
We propose a platform that can transport, trap, and manipulate nanoscale particles using a combination of diffusiophoretic and near-field optical gradient forces. This platform operates with an anapole state under 532 nm laser illumination. The anapole antenna enhances the electromagnetic field through a slot that also makes the field accessible, and simultaneously operates as a nanoscale heat source to induce thermophoretic depletion of PEG, creating a diffusiophopretic force that delivers particles to the region of enhanced field for additional trapping by the optical gradient force. Our preliminary results have demonstrated transportation, agglomeration, and tweezing action of 300 nm particles in a 10% PEG solution.
We have proposed and systematically studied a cascaded bowtie photonic crystal nanobeam system that can achieve multiplexed long-range electrohydrodynamic transport and optical trapping of nanoscale particles. Ultra-high quality factor and ultra-low mode volume has been demonstrated, providing a strong field gradient ideal for trapping sub-20 nm particles. Combined with an applied alternating current electric field, the localized water absorption induces the electrothermal flow that can efficiently transport nanoparticles to the vicinity of a given bowtie region by switching the input wavelength. We envision this system will be promising in many fields, including single molecule characterization and assembly of single photon emitters.
The trapping and dynamic manipulation of nanoscale biological molecules such as proteins and exosomes using the conventional optical tweezer technology have been met with challenges. This arises because of the substantial optical intensity required, which poses photo-induced damage to the biomolecules. In this talk, I will introduce a new kind of optically controlled nanotweezers termed Opto-Thermo-Electrohydrodynamic Tweezers (OTET) that enables the stable trapping and dynamic manipulation of sub-10 nm biomolecules at locations that are several microns away from the high-intensity laser focus, where they experience both negligible photothermal heating and light intensity.
This novel non-invasive optical nanotweezer is expected to open new horizons in life science and medicine by offering an unprecedented level of control of tiny nano-sized biological objects in solution without photo-induced damage.
Optical tweezers have emerged as a powerful technique for non-invasive trapping and manipulation of microscopic objects. The diffraction limit precludes the low power trapping of nanoscale objects with optical tweezers. Plasmonic optical tweezers, which employ resonant plasmonic nanoantenna to confine electromagnetic fields to the nanoscale have been developed to enable the optical trapping of nanoscale objects. A peculiar advantage of plasmonic tweezers is the capability to not only trap nanoscale objects and biomolecules but also to perform spectroscopy on the trapped object. Such new capability would benefit from high throughput trapping and sorting of nanoscale objects on a plasmonic substrate. To meet this need, we present a thermoplasmonic nanohole metasurface platform for high throughput trapping and size-based sorting of nanoscale particles. The thermoplasmonic metasurface comprises of sub-wavelength nanoholes patterned on a gold film. A microfluidic channel is constructed over the nanohole metasurface region and another substrate is placed over it, to create a parallel plate capacitor configuration. The illumination of the thermoplasmonic nanohole metasurface causes photothermal heating and a thermal gradient in the fluid. The application of an AC electric field across the fluid element creates an electrothermoplasmonic microfluidic vortex. This vortex enables the long-range capture of the nanoparticles for rapid trapping and assembly. Additionally, the thermoplasmonic nanohole metasurface structure creates a distortion of the applied AC electric field. The tangential component of the AC electric field induces an AC electro-osmotic flow. By harnessing the interplay of these forces with the optical gradient force, we demonstrate several features including trapping, dynamic manipulation of nanoparticles, and size-dependent sorting of nanoscale particles.
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