ABSTRACT: Optical manipulation of plasmonic nanoparticles provides opportunities for fundamental and technical innovation in nanophotonics. Optical heating arising from the photon-to-phonon conversion is considered as an intrinsic loss in metal nanoparticles, which limits their applications. We show here that this drawback can be turned into an advantage, by developing an extremely low-power optical tweezing technique, termed opto-thermoelectric nanotweezers (OTENT). Through optically heating a thermoplasmonic substrate, alight-directed thermoelectric field can be generated due to spatial separation of dissolved ions within the heating laser spot, which allows us to manipulate metal nanoparticles of a wide range of materials, sizes and shapes with single-particle resolution. In combination with dark-field optical imaging, nanoparticles can be selectively trapped and their spectroscopic response can be resolved in-situ. With its simple optics, versatile low-power operation, applicability to diverse nanoparticles, and tuneable working wavelength, OTENT will become a powerful tool in colloid science and nanotechnology.
Project description:Optical manipulation of colloidal nanoparticles and molecules is significant in numerous fields. Opto-thermoelectric nanotweezers exploiting multiple coupling among light, heat, and electric fields enables the low-power optical trapping of nanoparticles on a plasmonic substrate. However, the management of light-to-heat conversion for the versatile and precise manipulation of nanoparticles is still elusive. Herein, we explore the opto-thermoelectric trapping at plasmonic antennas that serve as optothermal nanoradiators to achieve the low-power (?0.08 mW/?m2) and deterministic manipulation of nanoparticles. Specifically, precise optical manipulation of nanoparticles is achieved via optical control of the subwavelength thermal hot spots. We employ a femtosecond laser beam to further improve the heat localization and the precise trapping of single ?30 nm semiconductor quantum dots at the antennas where the plasmon-exciton coupling can be tuned. With its low-power, precise, and versatile particle control, the opto-thermoelectric manipulation can have applications in photonics, life sciences, and colloidal sciences.
Project description:We demonstrate for the first time plasmonic nanotweezers based on Au bowtie nanoantenna arrays (BNAs) that utilize a femtosecond-pulsed input source to enhance trapping of both Rayleigh and Mie particles. Using ultra-low input power densities, we demonstrate that the high-peak powers associated with a femtosecond source augment the trap stiffness to 2x that of nanotweezers employing a continuous-wave source, and 5x that of conventional tweezers using a femtosecond source. We show that for trapped fluorescent microparticles the two-photon response is enhanced by 2x in comparison to the response without nanoantennas. We also demonstrate tweezing of 80-nm diameter Ag nanoparticles, and observe an enhancement of the second-harmonic signal of ~3.5x for the combined nanoparticle-BNA system compared to the bare BNAs. Finally, under select illumination conditions, fusing of Ag nanoparticles to the BNAs is observed which holds potential for in situ fabrication of three-dimensional, bimetallic nanoantennas.
Project description:The ability to precisely manipulate nano-objects on a large scale can enable the fabrication of materials and devices with tunable optical, electromagnetic, and mechanical properties. However, the dynamic, parallel manipulation of nanoscale colloids and materials remains a significant challenge. Here, we demonstrate acoustoelectronic nanotweezers, which combine the precision and robustness afforded by electronic tweezers with versatility and large-field dynamic control granted by acoustic tweezing techniques, to enable the massively parallel manipulation of sub-100 nm objects with excellent versatility and controllability. Using this approach, we demonstrated the complex patterning of various nanoparticles (e.g., DNAs, exosomes, ~3 nm graphene flakes, ~6 nm quantum dots, ~3.5 nm proteins, and ~1.4 nm dextran), fabricated macroscopic materials with nano-textures, and performed high-resolution, single nanoparticle manipulation. Various nanomanipulation functions, including transportation, concentration, orientation, pattern-overlaying, and sorting, have also been achieved using a simple device configuration. Altogether, acoustoelectronic nanotweezers overcome existing limitations in nano-manipulation and hold great potential for a variety of applications in the fields of electronics, optics, condensed matter physics, metamaterials, and biomedicine.
Project description:The capabilities of manipulating and analyzing biological cells, bacteria, viruses, DNAs, and proteins at high resolution are significant in understanding biology and enabling early disease diagnosis. We discuss progress in developments and applications of plasmonic nanotweezers and nanosensors where the plasmon-enhanced light-matter interactions at the nanoscale improve the optical manipulation and analysis of biological objects. Selected examples are presented to illustrate their design and working principles. In the context of plasmofluidics, which merges plasmonics and fluidics, the integration of plasmonic nanotweezers and nanosensors with microfluidic systems for point-of-care (POC) applications is envisioned. We provide our perspectives on the challenges and opportunities in further developing and applying the plasmofluidic POC devices.
Project description:Optomechanics arises from the photon momentum and its exchange with low-dimensional objects. It is well known that optical radiation exerts pressure on objects, pushing them along the light path. However, optical pulling of an object against the light path is still a counter-intuitive phenomenon. Herein, we present a general concept of optical pulling-opto-thermoelectric pulling (OTEP)-where the optical heating of a light-absorbing particle using a simple plane wave can pull the particle itself against the light path. This irradiation orientation-directed pulling force imparts self-restoring behaviour to the particles, and three-dimensional (3D) trapping of single particles is achieved at an extremely low optical intensity of 10-2?mW??m-2. Moreover, the OTEP force can overcome the short trapping range of conventional optical tweezers and optically drive the particle flow up to a macroscopic distance. The concept of self-induced opto-thermomechanical coupling is paving the way towards freeform optofluidic technology and lab-on-a-chip devices.
Project description:Optical microscopes and optical tweezers, which were invented to image and manipulate microscale objects, have revolutionized cellular and molecular biology. However, the optical resolution is hampered by the diffraction limit; thus, optical microscopes and optical tweezers cannot be directly used to image and manipulate nano-objects. The emerging plasmonic/photonic nanoscopes and nanotweezers can achieve nanometer resolution, but the high-index material structures will easily cause mechanical and photothermal damage to biospecimens. Here, we demonstrate subdiffraction-limit imaging and manipulation of nano-objects by a noninvasive device that was constructed by trapping a cell on a fiber tip. The trapped cell, acting as a biomagnifier, could magnify nanostructures with a resolution of 100?nm (?/5.5) under white-light microscopy. The focus of the biomagnifier formed a nano-optical trap that allowed precise manipulation of an individual nanoparticle with a radius of 50?nm. This biomagnifier provides a high-precision tool for optical imaging, sensing, and assembly of bionanomaterials.
Project description:Opto-thermoelectric tweezers present a new paradigm for optical trapping and manipulation of particles using low-power and simple optics. New real-life applications of opto-thermoelectric tweezers in areas such as biophysics, microfluidics, and nanomanufacturing will require them to have large-scale and high-throughput manipulation capabilities in complex environments. Here, we present opto-thermoelectric speckle tweezers, which use speckle field consisting of many randomly distributed thermal hotspots that arise from an optical speckle pattern to trap multiple particles over large areas. By further integrating the speckle tweezers with a microfluidic system, we experimentally demonstrate their application for size-based nanoparticle filtration. With their low-power operation, simplicity, and versatility, opto-thermoelectric speckle tweezers will broaden the applications of optical manipulation techniques.
Project description:Light-based manipulation of colloidal particles holds great promise in fabrication of functional devices. Construction of complex colloidal superstructures using traditional optical tweezers is limited by high operation power and strong heating effect. Herein, we demonstrate low-power opto-thermophoretic manipulation and construction of colloidal superstructures in photocurable hydrogels. By introducing cationic surfactants into a hydrogel solution under a light-directed temperature field, we create both thermoelectric fields and depletion attraction forces to control the suspended colloidal particles. The particles of various sizes and compositions are thus trapped and organized into various superstructures. Furthermore, the colloidal superstructures are immobilized and patterned onto solid-state substrates through UV-induced photopolymerization of the hydrogel. Our opto-thermophoretic technique will open up avenues for bottom-up assembly of colloidal materials and devices.
Project description:We describe the molecular dynamics (MD)-aided engineering design of mutant peptides based on the alpha-helical coiled-coil GCN4 leucine zipper peptide (GCN4-p1) in order to obtain environmentally-responsive nanotweezers. The actuation mechanism of the nanotweezers depends on the modification of electrostatic charges on the residues along the length of the coiled coil. Modulating the solution pH between neutral and acidic values results in the reversible movement of helices toward and away from each other and creates a complete closed-open-closed transition cycle between the helices. Our results indicate that the mutants show a reversible opening of up to 15 A (1.5 nm; approximately 150% of the initial separation) upon pH actuation. Investigation on the physicochemical phenomena that influence conformational properties, structural stability, and reversibility of the coiled-coil peptide-based nanotweezers revealed that a rationale- and design-based approach is needed to engineer stable peptide or macromolecules into stimuli-responsive devices. The efficacy of the mutant that demonstrated the most significant reversible actuation for environmentally responsive modulation of DNA-binding activity was also demonstrated. Our results have significant implications in bioseparations and in the engineering of novel transcription factors.
Project description:A new kind of nanodevice that acts like tweezers through remote actuation by an external magnetic field is designed. Such device is meant to mechanically grab micrometric objects. The nanotweezers are built by using a top-down approach and are made of two parallelepipedic microelements, at least one of them being magnetic, bound by a flexible nanohinge. The presence of an external magnetic field induces a torque on the magnetic elements that competes with the elastic torque provided by the nanohinge. A model is established in order to evaluate the values of the balanced torques as a function of the tweezers opening angles. The results of the calculations are confronted to the expected values and validate the overall working principle of the magnetic nanotweezers.