Brownian motion reveals the mechanical environment of microscopic objects in thermal equilibrium. Mechanical fluctuations of microscopic objects, ubiquitous in living biological cells, are caused by a combination of thermal and biochemical forces; the latter are rich in spatiotemporal information of the forces and energies that drive such fluctuation. The question is how to distinguish the chemical driven from the thermal motion as they are often comparable in magnitude. This talk presents a proposed approach to decouple the motions produced by two independent stochastic forces by analyzing the motions of microscopic active particles individually confined by optical trapping. Applications of this approach to experiments are validated by comparison with Langevin-based numerical simulation. This approach applied to two distinctively driven active particles, one electrically and the other biologically, reveal surprising distinctive dynamics of these driven particles.

Imprecision in protein positioning and instrument dead time have hampered efforts to measure macromolecular association rates in optical trap assays. Here, we combine several technical improvements to the three-bead optical trap assay, including precise protein deposition, enhanced stage stability by feedback, and improved data filtering. These enhancements allow us to precisely and reliably detect interactions between cardiac heavy meromyosin (cHMM) and actin and quantify attachment and reattachment rates. These studies providing insights into strain-dependence of the power stroke and a proposed transition from super-relaxed (SRX) to disordered relaxed (DRX) states, which is thought to be disrupted in human hypertrophic cardiomyopathy.

Cancer cells tend to soften, which may enhance their ability to squeeze through dense tissue. This cell softening has been demonstrated with the optical stretcher technology. Based on these fundamental findings we have developed a histophatological prognostic marker for distant metastasis. In a retrospective clinical study with 1380 breast cancer patients we have validated this approach. The new marker should apply to 92% of all cancers and will avoid over- and undertreatment of patients..

Multicellular tissues are a defining feature of animal life, but how tissue-level organization arises from the interactions of the individual proteins present at intercellular adhesion complexes remains incompletely understood. In this talk, I will describe single-molecule optical trap experiments that reveal the molecular mechanisms by which proteins present at cellular adhesion complexes help to seed long-range order in the cytoskeleton, and by extension, in multicellular tissues. These and other findings support an emerging understanding of how cells regulate cellular adhesion in space and time to generate tissues that are both dynamic and physically robust.

Optical traps are widely used to study nucleic-acid-processing enzymes. To investigate these enzymes, we developed “force-activated” DNA substrates that contain a pair of nicks, allowing displacement of single-stranded DNA when pulled into DNA’s overstretching transition. We designed these substrates to include DNA hairpins and are using them to investigate the mechanism of E. coli RecQ helicase, an enzyme that unwinds double-stranded DNA. Force-activated DNA substrates also have the potential to provide an easy-to-use intrinsic force standard at ~15 pN, suitable for all three major force spectroscopy modalities (i.e., optical traps, magnetic tweezers, and AFM).

We will show results towards a new method to perform antibiotic or phage susceptibility test with single phages or bacteria trapped in an optical chip. The system used is a photonic chip containing photonic crystal hollow cavities topped by a microfluidic system allowing the transport of bacteria and phages. We will report the optical signature of the trapping of bacteria and phages in the transmitted light exciting the optical trap. This allows the distinction of different phages families as well as the level of stress or death of a single bacteria in the presence of antibiotics or phages.

Active matter bridges the fundamental physics of nonequilibrium thermodynamics with applications spanning from biophysics to robotics. Active particles can harness energy to generate complex motions and emerging behaviors. Most active-matter experiments are performed with microscopic particles and require advanced microfabrication and microscopy techniques. Here, we propose some macroscopic experiments with active matter employing commercially available toy robots, i.e., the Hexbugs. We show that Hexbugs perform active and chiral active motion, can set passive objects into motion and rotation. Finally, we show how to sort Hexbug by motility and chirality, and macroscopic demonstration of the Casimir-like activity-induced attraction between planar objects.

Understanding the collective motion of living systems can facilitate the protection of ecosystems as well as the development of swarm robotics. To overcome the system-specific and oversimplified issues of traditional investigation methods, we propose to use our fully steerable active particles powered by localized light fields to mimic and study the collective motion in a more controllable and realistic manner. By dynamically tailoring the laser patterns that drive the colloidal particles' self-propulsion with certain interaction rules, the active particles can spontaneously form collective structures, display density-dependent responses, and show high robustness to external perturbations.

Biohybrid microbots integrate biological actuators and sensors into synthetic chassis with the aim of providing the building blocks of next-generation micro-robotics. One of the main challenges is the development of self-assembled systems with consistent behavior and such that they can be controlled independently to perform complex tasks. We shown that, using light-driven bacteria as propellers, 3D printed microbots can be steered by unbalancing light intensity over different microbot parts. We designed an optimal feedback loop in which a central computer projects onto each microbot a tailor-made light pattern, calculated from its position and orientation. In this way, multiple microbots can be independently guided through a series of spatially distributed checkpoints. By harnessing a natural light-driven proton pump, these bio-hybrid microbots can extract mechanical energy from light with much greater efficiency than in the case of force generation through radiation pressure. With a total optical power of only a few milliwatts, one could control hundreds of these microbots and use them to collect and deliver cells within microfluidic chips. Pellicciotta et al. Adv. Func. Mater. (2023) https://doi.org/10.1002/adfm.202214801

The Anti-Brownian ELectrokinetic (ABEL) Trap is a versatile platform for single-molecule fluorescence spectroscopy that can be modified to utilize a wide range of advanced single-molecule technique. To date, these efforts have focused largely on modifying either the trapping approach or the detection capabilities, most notably for multi-parameter detection including TCSPC, anisotropy, spectra, and transport parameters, as well as detection of interferometric scattering or high-precision FRET. Here we demonstrate the broad utility of advanced approaches to excitation for the ABEL trap: Using a programmable supercontinuum pulsed laser source, we first demonstrate temporal patterning of excitation brightness and wavelength to study photophysically induced responses in a trapped light-harvesting protein-pigment complex from cyanobacteria. In a second instance, we incorporate a pulse-picking system to achieve pulsed-interleaved excitation (PIE) to enable high-precision and acceptor-corrected FRET measurements of fluorescently labeled biomolecules.

Here, we propose an experiment, based on levitation optomechanics, to measure gravitational forces from nanoscale objects. In the experiment, two optically trapped particles in ultrahigh vacuum conditions represent the source and test masses. Importantly, the source mass is a rotating Janus nanoparticle such that the test mass (sensor) experiences a periodic gravitational potential. Using realistic experimental parameters, a signal-to-noise ratio ≥ 1 is obtained for a Janus particle with radius ≥ 100 nm and a mass ≥ 10 fg. The proposed experiment enables first steps towards table-top tests of quantum gravity.

An active experimental front in the modern study of Gravity is testing the (Newtonian) law of gravitation at the 1 μm – 100 μm length scale. Electromagnetic forces are several orders of magnitude stronger than gravity, and pose a formidable challenge in any experiment aiming to measure the latter. This work describes results from a platform based on optically trapped neutral microspheres that probes deviations from Newtonian gravity. In addition to improvements to a previous iteration of the experimental apparatus, we present a novel technique that allows further suppression of electromagnetic backgrounds. This technique, which relies an optomechanical force sensor, provides a complementary technique to previous searches that have largely relied on variations of mechanical springs.

We present experimental results on optical trapping of sub-wavelength-thickness high-aspect-ratio dielectric plates with over 10 micron radius. The prisms are trapped in vacuum using an optical standing wave, with the normal vector to their face oriented along the beam propagation direction, yielding much higher trapping frequencies than those typically achieved with microspheres of similar mass. This plate-like geometry simultaneously enables trapping with low photon-recoil-heating, high mass, and high trap frequency, potentially leading to advances in high frequency gravitational wave searches in the Levitated Sensor Detector, currently under construction.

Recent development in levitated optomechanics has presented new detection platforms for a diverse range of dark matter candidates. We discuss our recent application of using a nanogram-scale silica microparticle optically trapped in high vacuum to search for impulse signals induced by passing composite dark matter. The search is enabled by the achieved ~ 100 MeV/c momentum sensitivity of the system and the ability to stably trap and cool down micron-size particles. We also discuss our recent progress in constructing an array of levitated sensors and searching in the new parameter space with levitated nanoparticles.

Optically levitated nano and microparticles are excellent force sensors and are used in many tests of fundamental physics, from probing the quantum mechanical properties of massive objects to modifications of gravity a small distances. Another possibility is to test the neutrality of matter, i.e. equivalence in magnitude of the charge of protons and electrons, or the existence of mini charges. Experiments with neutral levitated microparticles have so far excluded the abundance of mini-charged particles in matter to less than 10^(-5) e^- [Moore et al.]. Limitation to such measurements have been the backgrounds induced by permanent dipole moments and the noise floor. We report on a new experiment combining permanent dipole cancellation [Priel et al.] with an improved detection scheme [Mauer et al.] resulting in state of the art sensitivity on the abundance of minicharge particles and the neutrality of matter .

Optically levitated micro and nanoparticles in vacuum offer new approaches for precision measurement and fundamental physics. We will discuss the use of rotational degree of freedom and describe experiments and theory for rotating vaterite crystals. This will include rotation-translation coupling, achieving high Q values and studying limit cycles. The work will describe the extension to two particles with optical binding and the observation of sympathetic cooling.

Think globally; act locally. First, the big picture: there are clearly significant growth opportunities in areas of interest to the SPIE community, but at the same time there are concerns about how to grow the high-end workforce required to deliver on these opportunities. Here, we present U.S.-based data on the pipeline of talent, noting significant areas of concern, but also ways in which these present solvable problems. In the second part of the talk, we provide examples of the ways in which our professional societies and foundations are ready to support local actions.

A levitated non-spherical nanoparticle in a vacuum is ideal for studying quantum rotations and is an extremely sensitive torque and force detector. Here, we report optical levitation of a GHz rotating silica nanodumbbell in a vacuum at about 430 nm away from a sapphire surface. The rotating nanodumbbell near the surface demonstrate a torque sensitivity of (5.0 ± 1.1) × 10^(-26) NmHz^(−1/2) at room temperature. Moreover, we levitate a nanodumbbell near a gold nanograting and use it to probe the near-field intensity distribution beyond the optical diffraction limit. The system is promising to detect the Casimir torque.

We simulate the dynamics of particle motion during launching and loading into optical traps to enable strategies for controlled loading of optical traps in vacuum. Particle dynamics during trap loading are simulated in air and compared to measured trajectories to validate particle behavior at measured launch velocities. The simulated dynamics are analyzed in both ballistic (vacuum) and diffusive (air) regimes to determine the forces required so that particles can be trapped stably. These results provide a foundation for developing control algorithms to reliably launch and load particles into optical traps in vacuum, and examples of controllers will be presented.

Phonon lasers are extensively researched as mechanical counterparts to optical lasers for various applications. An optical tweezer phonon laser was developed, but it only affected one degree of movement. To address this, we introduced a multimode levitated nanoparticle to transfer coherence between different oscillation directions. Coupling was achieved by rotating the asymmetric optical potential via trap laser polarization rotation. The change in power spectral density showed the feature of lasing transfer before and after coupling, and the mean phonon number of the system was saturated. Coherence was confirmed by measuring second-order auto-correlation function of the oscillation modes. Coupled laser systems have potential in precision measurement and quantum information processing.

Levitated mesoscopic particles, with their intrinsic low coupling to the environment, are ideally suited as hybrid quantum platforms of mesoscopic size and mass. In vacuum, the only coupling to the environment is the levitation field itself, resulting in a mechanical oscillator with a very high-quality factor. Optically levitated systems in vacuum have recently entered the quantum realm with demonstration of cooling to the motional quantum ground state using passive and active feedback methods. The levitated particles in most of these experiments are optically inert such as SiO2 nanospheres. Here we are interested in studying and developing techniques suitable for the stable levitation of optically active nanoparticles such as rare-earth ion activated nanocrystals. In particular we will show experimental results on the laser refrigeration of levitated nanocrystals down to 150K and our efforts towards using measurement-based oscillator control for the absolute cooling of the levitated particle.

We succeeded in demonstration of the nanoscale rotation for a nanodiamond trapped by the nano-vortex field of a plasmonic nanoantenna irradiated with circularly polarized light. We also applied the optical torque to chiral crystallization from achiral compounds with the giant crystal enantiomeric excess. Here, we present a novel method to map the local displacements of a manipulated nanoparticle and molecules. This method enables extracting the motion driven by the scattering force and filtering out the effect of the gradient force. The results provide a new perspective for understanding light–matter linear and angular momentum transfer mechanisms at the nanoscale.

We introduce an innovative fiber-optic trapping system that utilizes multicore fibers to enable precise control of cell rotation about all three axes. This is achieved through the development of a physics-informed neural network that generates tailored light fields in the trapping region via the multicore fiber, allowing real-time control of the optical force. Our system facilitates precise and controlled cell rotation in all three axes, making it possible to capture projections of the cell at various angles. By leveraging this capability, our system enables accurate three-dimensional optical diffraction tomography with isotropic resolution. Overall, our fiber-optic trapping system offers a promising solution for high-precision cellular imaging and analysis, with significant potential applications in various fields, including biomedicine and nanotechnology.

Soft matter – from polymers over molecular assemblies up to cells – exhibit unique mechanical properties, as being easily deformable under external forces. When subject to optical forces, they may on the one hand be analyzed in their features as viscoelasticity or scattering. On the other hand, complex light may transfer momentum or orbital angular momentum to soft matter, allowing to arrange, structure, and assemble functional particles. In this keynote, we showcase examples of optical trapping of droplets, viscoelastic complex matter, active swimmers, and cells, and demonstrate the versatile features of interaction of light with soft matter from analysis to control.

ECM stiffness is a potential instructive cue during capillary morphogenesis. Bulk measurements have often been used to investigate matrix stiffness as a cellular cue. However, local peri-cellular stiffness can be heterogeneous and vary greatly from measured bulk properties spatially and temporally. Here, we utilize bulk rheology and optical tweezers active microrheology (AMR) to investigate the dynamic mechanical crosstalk between cells and the surrounding matrix during capillary morphogenesis across length scales with various supporting stromal cells. We will present our current findings focusing on the discrepancies between bulk and microrheological distributions of measured stiffness across different stromal cell types.

Phase singularities are loci of darkness surrounded by light in a scalar field. We engineer an array of closely-spaced identical point singularities structured along the optic axis. The array is experimentally realized with a TiO2 metasurface under 760 nm narrowband illumination. We study possible application in blue-detuned neutral atom trap arrays, for which this field would enforce 3D confinement and a potential depth around 0.22 mK per watt of trapping power. The field is tolerant to around 10 nm changes in wavelength with a 0.11 degree angular bandwidth. Metasurface-enabled point singularity engineering may simplify and miniaturize the architecture required for super-resolution microscopes and dark traps.

We explore the ability of existing mechanical systems to detect the force associated with chameleon dark energy. We show that the current generation of two mechanical systems experiments involving levitated microspheres and torsion balances have the sensitivity to rule out a significant portion of unprobed chameleon parameter space. We also indicate regions of theoretically well-motivated chameleon parameter space to guide future experimental work.

Optical trapping is a powerful tool for studying fundamental physics on the nanoscale as described by electric field-based light-matter interactions. However, the range of capabilities would be greatly enhanced by understanding its magnetic counterpart. Our studies provide experimental evidence of optical magnetic trapping. In particular, our work identifies new forces in optical trapping of Si nanoparticles stemming from the Photonic Hall Effect. We also discovered optical-driven Brownian engines at the single-particle level whose counterintuitive behavior originates from optical magnetic light-matter interactions. As a result, optical magnetic trapping now offers new opportunities for particle manipulation in optical beams.

Combining nanotechnology with optical trapping offers many possibilities for developing directed nanoscale probes that can target and report on specific types of physical, biological, and chemical interactions. Nanodiamonds containing many nitrogen-vacancy centre defects are among the most promising candidates, as they possess both desirable trapping properties and exquisite sensing capabilities. In this presentation I’ll discuss our progress in understanding the most effective ways of combining optical tweezers with spin-sensitive optical detection schemes in order to unlock the full potential of nanodiamond-based sensing.

We are interested in the optomechanical manipulation of nanodiamonds with a high concentration of SiV centers. Optical tweezers usually rely on the interaction of light and the ‘bulk’ polarizability of the nanoparticle itself. Here we exploit the polarizability of electronic resonances of optical centers embedded in the solid-state matrix to enhance the optical forces. This effect becomes particularly relevant for ensembles of active centers. The emitters being closely packed in a sub-wavelength volume, can act cooperatively, enhancing further the optical forces. We will show the optical force spectroscopy of nanodiamonds with different levels of brightness in a specifically designed optofluidic microchip. Our results open the possibility to extend the use of optical tweezers beyond current capabilities and apply the powerful toolbox of atomic physics for the quantum manipulation of ‘massive’ mesoscopic objects.

Defects in 2D colloidal crystals are of fundamental interests in condensed matter physics as they serve as model systems for systems with topological order and topological phase transitions. Optical tweezers played an essential role in the studies of colloidal defects in the past 20 years. In this talk I will discuss the dynamics of interstitials and vacancies in 2D colloidal crystals. I will discuss the possible new directions in this area.

A liquid mixture close to its critical demixing point is a perfect example of critical bath where the thermal fluctuations are enhanced and can be tuned by slight changes in the temperature. Although studied in equilibrium by micromanipulation techniques, with results going from Casimir-like forces or the effect of the increasing correlation length in bacterial motility, very little has been done out of equilibrium. Here, we will present our results on the relaxation dynamics of optically trapped particles coupled to critical baths. Our experiments have the novelty of using local laser induced heating for producing temperature quenches. We report on the microrheology of the critical fluid at different critical distances as well as in the relaxation of critical Casimir forces after temperature or distance quenches.

We show assembly of functional and reconfigurable three-dimensional photonic crystals aided by opto-thermal effects due to localized optical heating of a thin gold film on a glass substrate. The optical stop bands of the photonic crystals are probed using Fourier plane imaging and angle resolved spectroscopy of locally excited dye molecules present in the solution. Additionally, dark field scattering spectroscopy indicates the structural colors of the assembled structures and changes with the lattice constants. The results have direct implications for low power manipulation and assembly of functional photonic structures.

Our optical positioning and linking (OPAL) platform combines optical tweezers and a biochemical linking mechanism to assemble complex 3D microstructures that can incorporate particles of different sizes and materials and augment existing devices. Updates to system components have increased the maximum speed with which particles can be moved while implementation of a 3D calibration procedure has decreased positional errors. Collecting and processing the backscattered signal using a quadrant photodiode enables classification of the trap particle population and is key for a fully automated assembly process. These updates will permit rapid prototyping and fabrication of even larger, more functional structures.

Typical optical manipulation methods operate in fluidic media. We report a novel optical manipulation technique that enables optical manipulation in a pseudo-solid media, and can immobilize particles in 3D at any prescribed locations for reconfigurable colloidal assembly and tunable light-matter interactions.

High-index dielectric metasurfaces that deflect light or alter its polariztion state experience photon recoil forces and torques due to conservation of linear and angular momentum. We utilized this effect to construct miniature "metavehicles" able to navigate across a surface in water under plane-wave illumination while being steered through the incident polarization [1]. The control scheme does not involve gradient forces, in contrast to the vast majority of previous optical manipulation studies, yet the forces generated are strong enough to let the metavehicles work as transporters of microscopic cargo, such as biological cells. Depending on how the metasurface is constructed, metavehicles can be optimized for different behaviours and functionalities, thereby opening the door to novel fundamental studies and applications in fields like microrobotics, micromachines, and active matter. [1] Andrén et al, Nature Nanotechnology 16, 970-974 (2021).

Metamaterials were assembled using the force of a light gradient in a one-dimensional Standing Wave Optical Trap (SWOT) that was time-shared across the 2-D lattice to create a three-dimensional (3D) array of traps, which was then populated with monodispersed dielectric or metallic nanoparticles (NPs). The NP structure was anchored to a hydrogel scaffold, and then the process was repeated to create macroscopic metamaterials. The error in particle position within a voxel (σ=55 nm) was limited by dark time Brownian motion, whereas the error between voxels, (σ=88 nm) was limited by the microscope stage repeatability. Also, compared to a Gaussian beam SWOT, a non-diffractive, pseudo-Bessel beam SWOT produced a longer array due to greater focus-depth and self-healing distance.

We have successfully multiplied the chiral crystallization of sodium chlorate; polymorphic transition and the induced crystal chirality are controllable by the condition of plasmonic trapping. After a few seconds of laser irradiation on trimer, a metastable crystal of sodium chlorate is firstly generated, then through the polymorphic transition to stable crystal (chiral). The polymorphic transition is only observed when the use of 230 nm trimer, absence while the 170 nm trimer is used. Furthermore, the induced crystal chirality can be controlled by the irradiation left and right-handed circular polarization of 230 nm trimer, realizes giant crystal enantiomeric excess over 50%.

The inertial behaviour of a microscopic particle is obscured by its Brownian motion within a fluid. Collisions with fluid molecules give the particle velocity which dissipates on exceedingly short time scales due to the opposing drag forces from the fluid. Studying the motion at these very short time scales provides useful information about dynamic systems. In this work, we detail our approach to measure the angular velocity at these short time scales using Rotational Optical Tweezers enabling novel measurements of rotational dynamics and studying systems that are out of equilibrium.

We have developed a software platform to provide real-time readout of neuronal activity and downstream analysis which enables informed real-time modulation of neuronal activity through photostimulation during image acquisition. The downstream analysis within the real-time loop is rapid enough (at 30Hz for 250 neurons) to operate at widely used image acquisition rates.

This conference presentation was prepared for the Optical Trapping and Optical Micromanipulation XX conference at SPIE Optics + Photonics 2023.

We present the dynamics of microparticle launching and loading into optical traps in air. To address repeatable launching and loading of particles into the trap remained as a stubborn obstacle to realization of robust trapping systems, we investigated launching and trapping mechanism, analyzing particle trajectories during the three phases of particle loading: vibration and launching from a substrate, entrainment into the trap with dissipation, and steady state trapping. We identify characteristics that can be exploited to enable more repeatable launching, including in situ measurement of adhesion or natural frequency and the existence of stable subharmonic modes of particle vibration.

We present an approach where this information is retrieved by a holographic measurement of phase and amplitude, employing a high-NA condenser lens to collect all forward scattered light. It uses iterative phase retrieval to infer optical phase directly from a single intensity image of all light reaching the camera.

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.

The number of microplastics in aquatic environments is increasing rapidly in recent years and making ocean microplastics one of the major environmental problems. In our research, we focus on the isolation of nature-found microplastics by collecting sand from Los Angeles beaches. Since the optical studies of nature-found microplastics are nontrivial, we generate a standard database by creating and studying different types of irregular-shaped lab-made microplastics using optical tweezer setup. The created database is used to characterize the optical properties of nature-found microplastics. We are planning to apply these results to investigate microplastic interactions with ocean microplankton at a cellular level.

Mechanobiology has become an important and ever-growing field of science that combines biology, engineering, chemistry and physics. It provides invaluable tool to studies of how the application of physical forces influences development, cell differentiation, physiology and disease. Many techniques have been developed throughout the time that enable these studies to contribute to our knowledge of complex biological systems. Optical or light technologies on the nano and micro-scale have enabled unprecedented advances in our understanding of mechanobiology. We will review the new developments in this rich field and point at further developments in this area that could lead to use of these nanotools to a further biomedical research community.

The breaking of bilateral symmetry in most vertebrates is critically dependent upon the motile cilia of the embryonic left-right organizer (LRO), which generate a directional fluid flow; however, it remains unclear how this flow is sensed. Here, we demonstrated that immotile LRO cilia are mechanosensors for shear force using a methodological pipeline that combines optical tweezers, light sheet microscopy, and deep learning to permit in vivo analyses in zebrafish. Mechanical manipulation of immotile LRO cilia activated intraciliary calcium transients that required the cation channel Polycystin-2. Furthermore, mechanical force applied to LRO cilia was sufficient to rescue and reverse cardiac situs in zebrafish that lack motile cilia. Thus, LRO cilia are mechanosensitive cellular levers that convert biomechanical forces into calcium signals to instruct left-right asymmetry.

The DEAD-box family of RNA helicases is the largest of all known RNA helicase families, where they restructure RNA by binding and unwinding the RNA double helix via an ATP-energy-dependent mechanism. Lacking translocation capability, i.e., the ability to ‘walk’ down the RNA strand, these helicases are known to unwind only a limited amount, < 10-20 RNA bases, locally nearby the site of binding. However, some DEAD-box RNA helicases have recently been shown to unwind efficiently upon oligomerization, i.e., multiple proteins joining forces to work together. The DEAD-box RNA helicase Ded1p has been observed to efficiently unwind RNA possessing a single-stranded RNA (ssRNA) tail as a trimer (i.e., an assembly of three identical Ded1p proteins). The mechanism of Ded1p trimer assembly and unwinding of RNA remains unknown. Using optical tweezers, it is possible to grab and stretch single nucleic acid strand and observe the activity of individual protein molecular machines like Ded1p in real-time. Here, we combined single-molecule fluorescence spectroscopy with high-resolution optical tweezers to directly observe the detailed step-by-step binding and dissociation of Ded1p proteins and subsequent unwinding and rezipping of RNA. The overall trimer activity previously observed in ensemble experiments was recapitulated. A complete general model of unwinding is developed whereby unwinding is initiated by binding of a single Ded1p to the duplex adjacent ssRNA tail. Subsequently, in sequence two additional Ded1p bind and unwind a 5-7 bp portion of the duplex each resulting in the full 16 bp duplex unwinding. The reaction is highly dynamic and stochastic, with unwinding combining with frequent rezipping reversals. Rezipping reversals are suppressed when ATP hydrolysis is suppressed via use of an ATP analog. While unwinding and rezipping are easily captured by high-resolution tweezers, Ded1p binding and dissociation on ssRNA tail was measured via the protein-induced-fluorescence-enhancement (PIFE) signal from the fluorophore-labeled tail. The combined methods allowed us to fully observe the coordinated binding and unwinding of the RNA substrate by individual protomers of the Ded1p trimer.

Trapping a diamond particle at high vacuum is a challenge due to impurities that absorb photons and cause heating. The heating is evitable due to the necessity of laser usage for initialization and readout of the Nitrogen-Vacancy (NV) centers. Here, we demonstrate a method to launch, select, and trap a diamond at high vacuum using a surface Paul trap without too much heating. By carefully adjusting the probe laser power, the internal temperature is even lower than 350 K in high vacuum. In addition, we electrically drive the nanodiamond to rotate at a high angular velocity (up to 20 MHz). Microwave is applied for driving the electronic states of the NV center through a homemade bias-tee. We manage to trap a diamond and measure an Optically Detected Magnetic Resonance (ODMR) at a pressure of 10^-6 Torr which is limited by the setup. Our work is helpful for studying the spin-mechanical coupling and may provide an opportunity for the realization of quantum superposition at macroscopic scales.

We investigate the optical properties of opto-thermally assembled reconfigurable three-dimensional photonic crystals through localized optical heating of a thin gold film on a glass substrate. The assembly process is aided by the resulting thermal gradient induced hydrodynamic, thermophoretic as well as depletion effects. The band structure and the corresponding stop bands of the photonic crystals are probed using Fourier plane imaging and angle resolved spectroscopy of locally excited dye molecules present in the fluidic solution. The results hold direct implications for low power manipulation and assembly of functional photonic structures.

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.

Janus particles are microscopic objects characterized by one feature with dual properties. Typical examples are metal-coated Janus particles, widely used in soft and active matter applications because of their versatility and their fabrication simplicity. Janus particles are often utilized in the presence of optical potentials. Here, we provide an implementation for calculating forces and torques on partially coated Janus particles of spherical and ellipsoidal shape in the geometrical optics approximation. We first validate our model against the known experimental results and show that interesting effects arise in the presence of travelling-wave optical potential.