24 research outputs found
Manipulating and Characterizing Nanoscale Particles using Near-Field Optical Forces
In the three decades since the development of optical tweezers, optical trapping has become an invaluable technique for particle manipulation and is used widely in biology as well as material science. In more recent years, there has been a significant effort to integrate optical traps directly with microfluidics on-chip to produce stronger optical forces and manipulate even smaller particles. This is often achieved through the use of near-field forces produced by subwavelength optical confinement. By leveraging techniques and designs from photonics, near-field optics can generate very strong piconewton forces that act over nanometer length scales.
This dissertation aims to exploit these unique features of near-field optical forces-- their strength, tunability, and precise localization-- to build new nanostructures, develop new optical spectroscopy techniques, and probe the fundamental nature of particles and their interactions on the nanoscale. In the first half of this work, I focus on using optical gradient forces to drive the assembly of hybrid photonic-plasmonic resonators and using the amplified forces from these resonators to trap, manipulate, and bind other nanoparticles. These resonators are then used to optically drive the adsorption of individual proteins as a way of measuring the activation energy barrier of those adsorption reactions.
While colloidal nanoparticles are critical in a wide range of fields and industries, there is still no reliable theoretical framework to describe their behavior in realistic solution conditions. This issue is compounded by the difficulty of directly measuring nanoscale particles with conventional optical tools. In the latter half of this work, I have demonstrated that near-field optical forces, which operate at similar magnitudes and length scales as colloidal forces, can be used to study the properties of nanoparticles directly. By applying a known optical force to a particle with an optical waveguide, the size and properties of the particle can be extracted from its dynamic response to that applied force. This technique leverages the unique advantages of localized optical forces and allows for direct measurement of single nanoparticles at high throughput. Combined with the previous section on binding and assembly, this dissertation lays the groundwork for future work on near-field optical forces which has great potential for improving our understanding of physics at the nanoscale
Losses in plasmonics: from mitigating energy dissipation to embracing loss-enabled functionalities
Unlike conventional optics, plasmonics enables unrivalled concentration of
optical energy well beyond the diffraction limit of light. However, a
significant part of this energy is dissipated as heat. Plasmonic losses present
a major hurdle in the development of plasmonic devices and circuits that can
compete with other mature technologies. Until recently, they have largely kept
the use of plasmonics to a few niche areas where loss is not a key factor, such
as surface enhanced Raman scattering and biochemical sensing. Here, we discuss
the origin of plasmonic losses and various approaches to either minimize or
mitigate them based on understanding of fundamental processes underlying
surface plasmon modes excitation and decay. Along with the ongoing effort to
find and synthesize better plasmonic materials, optical designs that modify the
optical powerflow through plasmonic nanostructures can help in reducing both
radiative damping and dissipative losses of surface plasmons. Another strategy
relies on the development of hybrid photonic-plasmonic devices by coupling
plasmonic nanostructures to resonant optical elements. Hybrid integration not
only helps to reduce dissipative losses and radiative damping of surface
plasmons, but also makes possible passive radiative cooling of nano-devices.
Finally, we review emerging applications of thermoplasmonics that leverage
Ohmic losses to achieve new enhanced functionalities. The most successful
commercialized example of a loss-enabled novel application of plasmonics is
heat-assisted magnetic recording. Other promising technological directions
include thermal emission manipulation, cancer therapy, nanofabrication,
nano-manipulation, plasmon-enabled material spectroscopy and thermo-catalysis,
and solar water treatment.Comment: 43 pages, 18 figure
Investigating the use of a hybrid plasmonic–photonic nanoresonator for optical trapping using finite-difference time-domain method
We investigate the use of a hybrid nanoresonator comprising a photonic crystal (PhC) cavity coupled to a plasmonic bowtie nanoantenna (BNA) for the optical trapping of nanoparticles in water. Using finite difference time-domain simulations, we show that this structure can confine light to an extremely small volume of ~30,000 nm3 (~30 zl) in the BNA gap whilst maintaining a high quality factor (5400–7700). The optical intensity inside the BNA gap is enhanced by a factor larger than 40 compared to when the BNA is not present above the PhC cavity. Such a device has potential applications in optical manipulation, creating high precision optical traps with an intensity gradient over a distance much smaller than the diffraction limit, potentially allowing objects to be confined to much smaller volumes and making it ideal for optical trapping of Rayleigh particles (particles much smaller than the wavelength of light)
Plasmonic Optical Tweezers for Particle Manipulation: Principles, Methods, and Applications
Inspired by the idea of combining conventional optical tweezers with plasmonic nanostructures, a technique named plasmonic optical tweezers (POT) has been widely explored from fundamental principles to applications. With the ability to break the diffraction barrier and enhance the localized electromagnetic field, POT techniques are especially effective for high spatial-resolution manipulation of nanoscale or even subnanoscale objects, from small bioparticles to atoms. In addition, POT can be easily integrated with other techniques such as lab-on-chip devices, which results in a very promising alternative technique for high-throughput single-bioparticle sensing or imaging. Despite its label-free, high-precision, and high-spatial-resolution nature, it also suffers from some limitations. One of the main obstacles is that the plasmonic nanostructures are located over the surfaces of a substrate, which makes the manipulation of bioparticles turn from a three-dimensional problem to a nearly two-dimensional problem. Meanwhile, the operation zone is limited to a predefined area. Therefore, the target objects must be delivered to the operation zone near the plasmonic structures. This review summarizes the state-of-the-art target delivery methods for the POT-based particle manipulating technique, along with its applications in single-bioparticle analysis/imaging, high-throughput bioparticle purifying, and single-atom manipulation. Future developmental perspectives of POT techniques are also discussed
Additive nanomanufacturing: a review
Additive manufacturing has provided a pathway for inexpensive and flexible manufacturing of specialized components and one-off parts. At the nanoscale, such techniques are less ubiquitous. Manufacturing at the nanoscale is dominated by lithography tools that are too expensive for small- and medium-sized enterprises (SMEs) to invest in. Additive nanomanufacturing (ANM) empowers smaller facilities to design, create, and manufacture on their own while providing a wider material selection and flexible design. This is especially important as nanomanufacturing thus far is largely constrained to 2-dimensional patterning techniques and being able to manufacture in 3-dimensions could open up new concepts. In this review, we outline the state-of-the-art within ANM technologies such as electrohydrodynamic jet printing, dip-pen lithography, direct laser writing, and several single particle placement methods such as optical tweezers and electrokinetic nanomanipulation. The ANM technologies are compared in terms of deposition speed, resolution, and material selection and finally the future prospects of ANM are discussed. This review is up-to-date until April 2014
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Optothermal manipulation of colloidal particles and biological objects
Optical based manipulation techniques play an important role in bottom-up assembly of micro- and nano-structures, discovery of new materials, and biomedical diagnostics. Traditional optical tweezers have limitations for the requirement of rigorous optics and high optical power. Optothermal manipulation, which exploits light-heat conversion and particle migration under a light-directed temperature field, is an emerging strategy for achieving diverse manipulation functionalities in a low-power fashion. In this work, we have developed a series of optothermal manipulation techniques, including bubble-pen lithography, opto-thermophoretic tweezers, opto-thermoelectric tweezers, and opto-thermoeletric printing. In bubble-pen lithography, microbubbles generated at solid-liquid interfaces through laser heating of a plasmonic substrate are used to pattern diverse colloidal particles on the substrate. Through directing the laser beam to move the bubble, we create arbitrary single-particle patterns and particle assemblies with different resolutions and architectures. The key to optothermal tweezers is the ability to achieve negative Soret effect, or deliver colloidal particles from cold to hot regions in a temperature field. Two types of optothermal tweezers with different driving forces are explored for versatile manipulation of colloidal particles and biological objects. Opto-thermophoretic tweezers rely on an abnormal permittivity gradient built by layered solvent molecules at the particle-solvent interface, while opto-thermoelectric tweezers exploit a thermophoresis-induced thermoelectric field for low-power trapping of nanoparticles. Furthermore, we have demonstrated opto-thermoelectric printing of colloidal particles on substrates in salt solutions and hydrogel solutions. With the low-power operation, simple optics, and diverse functionalities, optothermal manipulation techniques will find a myriad of applications in colloidal science, materials science, nanotechnology, and life sciences, as well as in developing functional colloidal devices and biomedical devices.Materials Science and Engineerin
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Optothermal approaches to architected functional nanomaterials and nanostructures
The manipulation and engineering of nanomaterials are the core techniques in modern nanotechnology and have been extensively investigated over the past decades. Many optical techniques were developed to manipulate, assemble, and pattern nanomaterials, which have inspired numerous progress in various fields, such as microrobotics, bottom-up nanofabrication, nanomedicine, and microelectronics. With the entropically favorable photon-to-phonon conversion and tailorable opto-thermo-matter coupling, various thermal forces in the light-controlled temperature field can be harnessed to achieve the precise control of nanomaterials at a high spatial and temporal resolution.
This Dissertation focuses on optothermal approaches for optical manipulation and structuring of functional nanomaterials and nanostructures on solid substrates for the development of on-chip devices. First, thermophoresis of colloidal species is exploited to optically trap various nanoparticles and biological objects. The assembly and printing of colloidal matter on the substrate from the suspension are demonstrated with the assistance of optothermally controlled depletion forces. Next, by optothermally modulating the nanomaterial-substrate interactions, versatile manipulation and assembly of nanomaterials on solid substrates can be achieved. Precise manipulation of nanomaterials, orbital rotation of nanomotors, and reconfigurable assembly of functional nanostructures on the solid substrate are demonstrated. Last, opto-thermoplasmonic nanolithography is developed for on-demand patterning of a variety of two-dimensional materials through plasmon-enhanced thermal oxidation and sublimation. It is anticipated that the studies presented here provide an ideal platform for studying colloidal science, materials science, and nanophotonics, and the optothermally architected nanomaterials and nanostructures are expected to stimulate more advances in a broad range of fields.Materials Science and Engineerin
Roadmap for Optical Tweezers 2023
Optical tweezers are tools made of light that enable contactless pushing, trapping, and manipulation of objects ranging from atoms to space light sails. Since the pioneering work by Arthur Ashkin in the 1970s, optical tweezers have evolved into sophisticated instruments and have been employed in a broad range of applications in life sciences, physics, and engineering. These include accurate force and torque measurement at the femtonewton level, microrheology of complex fluids, single micro- and nanoparticle spectroscopy, single-cell analysis, and statistical-physics experiments. This roadmap provides insights into current investigations involving optical forces and optical tweezers from their theoretical foundations to designs and setups. It also offers perspectives for applications to a wide range of research fields, from biophysics to space exploration
The Boston University Photonics Center annual report 2015-2016
This repository item contains an annual report that summarizes activities of the Boston University Photonics Center in the 2015-2016 academic year. The report provides quantitative and descriptive information regarding photonics programs in education, interdisciplinary research, business innovation, and technology development. The Boston University Photonics Center (BUPC) is an interdisciplinary hub for education, research, scholarship, innovation, and technology development associated with practical uses of light.This has been a good year for the Photonics Center. In the following pages, you will see that this year the Center’s faculty received prodigious honors and awards, generated more than 100 notable scholarly publications in the leading journals in our field, and attracted $18.9M in new research grants/contracts. Faculty and staff also expanded their efforts in education and training, and cooperated in supporting National Science Foundation sponsored Sites for Research Experiences for Undergraduates and for Research Experiences for Teachers. As a community, we emphasized the theme of “Frontiers in Plasmonics as Enabling Science in Photonics and Beyond” at our annual symposium, hosted by Bjoern Reinhard. We continued to support the National Photonics Initiative, and contributed as a cooperating site in the American Institute for Manufacturing Integrated Photonics (AIM Photonics) which began this year as a new photonics-themed node in the National Network of Manufacturing Institutes. Highlights of our research achievements for the year include an ambitious new DoD-sponsored grant for Development of Less Toxic Treatment Strategies for Metastatic and Drug Resistant Breast Cancer Using Noninvasive Optical Monitoring led by Professor Darren Roblyer, continued support of our NIH-sponsored, Center for Innovation in Point of Care Technologies for the Future of Cancer Care led by Professor Cathy Klapperich, and an exciting confluence of new grant awards in the area of Neurophotonics led by Professors Christopher Gabel, Timothy Gardner, Xue Han, Jerome Mertz, Siddharth Ramachandran, Jason Ritt, and John White. Neurophotonics is fast becoming a leading area of strength of the Photonics Center. The Industry/University Collaborative Research Center, which has become the centerpiece of our translational biophotonics program, continues to focus onadvancing the health care and medical device industries, and has entered its sixth year of operation with a strong record of achievement and with the support of an enthusiastic industrial membership base
Optical trapping and manipulation of nanostructures
Optical trapping and manipulation of micrometre-sized particles was first reported in 1970. Since then, it has been successfully implemented in two size ranges: the subnanometre scale, where light-matter mechanical coupling enables cooling of atoms, ions and molecules, and the micrometre scale, where the momentum transfer resulting from light scattering allows manipulation of microscopic objects such as cells. But it has been difficult to apply these techniques to the intermediate-nanoscale-range that includes structures such as quantum dots, nanowires, nanotubes, graphene and two-dimensional crystals, all of crucial importance for nanomaterials-based applications. Recently, however, several new approaches have been developed and demonstrated for trapping plasmonic nanoparticles, semiconductor nanowires and carbon nanostructures. Here we review the state-of-the-art in optical trapping at the nanoscale, with an emphasis on some of the most promising advances, such as controlled manipulation and assembly of individual and multiple nanostructures, force measurement with femtonewton resolution, and biosensors