This PDF file contains the front matter associated with SPIE Proceedings Volume 12649, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

In our lab, we have developed the combination of optical tweezers and single-molecule fluorescence microscopy as a powerful tool to study biomolecules and biomolecular complexes. Combining these two technologies allows holding a sample molecule or complex, extending or deforming it, and measuring forces acting on it, while, at the same time, visualizing it with single-molecule sensitivity. We have applied this approach to different biological systems, including DNA, whole chromosomes, cytoskeletal components and membranes. Here, I will explain the concept of the technology, its potential and limitations. I will explain the technology by highlighting its application to our research on the mechanical properties of DNA and force-induced conformational transitions. I will also discuss our latest breakthroughs in applying this technology to intact mitotic human chromosomes, which provide novel insights in the mechanical properties of chromosomes and the way they are condensed in mitosis.

Biological nano-objects rapidly diffuse in the solution phase, impeding our efforts to monitor their physical and chemical properties for extended periods of time. To overcome this, we developed the Interferometric Scattering Anti-Brownian ELectrokinetic (ISABEL) Trap, which counteracts Brownian motion for an extended time by tracking a particle’s location via its scattering and rapidly applying positional feedback with electrokinetic forces. Recently, we improved the flexibility of these experiments by shifting the scattering detection beam to the near-infrared and opening the visible region for flexible and specific fluorescence measurements. These capabilities allow us to monitor the physical and chemical properties of the carboxysome, a ~100nm bacterial microcompartment responsible for CO₂ fixation by the enzyme Rubisco. With the ISABEL trap, we can rapidly interleave 405 and 488 nm fluorescence excitation beams to measure the redox properties inside individual carboxysomes using the redox reporting GFP mutant, roGFP2. The capabilities provided by the ISABEL trap allow us to design solution-phase single-particle experiments for a variety of biological nanoscale objects.

Optical tweezers have greatly impacted the development of mechanobiology by enabling high precision sub-piconewton measurements of mechanical forces developed by force generating proteins, called molecular motors, at the single-molecule level. Molecular motors, such as kinesins hydrolyze ATP to generate force (10 pN) and transport in a directional manner intracellular cargoes along cytoskeletal filamentous tracks called microtubules. The force developed by kinesins have been mainly studied using the “single-bead” assay, where an optically trapped bead is pulled by a bead-attached kinesin molecule as it steps along a surface immobilized microtubule. This assay, besides forces parallel to the long axis of the filament on which the kinesin processes, forces perpendicular to the filament due to the bead interacting with the underlying microtubule. These perpendicular forces, which cannot be directly measured, can accelerate the detachment of the molecular motor from its filamentous track. An alternative approach is the “three-bead” assay, in which the vertical force component is minimized, and the total opposing force is mainly parallel to the microtubule. Experiments with kinesin sho

The use of plasmonic nanopores for single molecule detection has attracted considerable attention due to their high sensitivity and selectivity. In this study, we present a phase analysis approach for characterizing the trapping of single molecules in an AC-driven plasmonic nanopore. By analyzing the phase response of the plasmonic nanopore at select frequencies, we can differentiate between a test ligand, the antibody targeting this ligand, and the complexes that these ligands form, as well as observe their dynamics while inside the optical trap of the plasmonic nanopore. This pilot work shows the feasibility of a new approach for rapid and accurate identification of single molecules in complex mixtures.

In this work we measure the time it takes for predatory Bdellovibrio bacteriovorus to attach to prey bacteria. B. bacteriovorus preys on Gram-negative bacteria such as E. coli. Some Gram-negative bacteria, including strains of E. coli, are resistant to antibiotics, so it is important to look for new ways to prevent its reproduction and spread, such as with predatory bacteria. The predation cycle includes an attack phase, during which B. bacteriovorus identifies and then attaches to its prey, followed by a growth phase, when it burrows into the periplasmic membrane of the prey cell, consumes its nutrients, and forms several bacteria that emerge, leaving the husk of the host cell behind. The attachment to the host is made with long fibers called type IV pili. The goal of this research is to measure the likelihood of B. bacteriovorus forming an attachment to its prey after different lengths of time. We optically trap a single B. bacteriovorus and position it against an E. coli bacterium fixed to a microscope slide. After a length of time from 15 seconds to three minutes, we release the B. bacteriovorus and observe whether the bacterium remains attached to the E. coli or moves away. Our results show an increase after 15 seconds in the percent of trials that result in attachments, with a percentage approaching 50% after two minutes. This investigation improves understanding of the time needed for secure attachment and informs how these bacteria use their type IV pili.

Cavity optomechanics has led to advances in quantum sensing, optical manipulation of mechanical systems, and macroscopic quantum physics. However, previous studies have typically focused on cavity optomechanical coupling to translational degrees of freedom, such as the drum mode of a membrane, which modifies the amplitude and phase of the light field. Here, we discuss recent advances in “imaging-based” cavity optomechanics – where information about the mechanical resonator’s motion is imprinted onto the spatial mode of the optical field. Torsion modes are naturally measured with this coupling and are interesting for applications such as precision torque sensing, tests of gravity, and measurements of angular displacement at and beyond the standard quantum limit. In our experiment, the high-Q torsion mode of a Si₃N₄ nanoribbon modulates the spatial mode of an optical cavity with degenerate transverse modes. We demonstrate an enhancement of angular sensitivity read out with a split photodetector, and differentiate the “spatial” optomechanical coupling found in our system from traditional dispersive coupling. We discuss the potential for imaging-based quantum optomechanics experiments, including pondermotive squeezing and quantum back-action evasion in an angular displacement measurement.

We inversely design plasmonic nanotweezers by topology optimization. Strikingly, the resulting structure resembles a double nanohole, but with additional surrounding features, surpassing the electric field enhancements of our previous algorithmically designed systems by ~45%.

We capture individual rubidium-85 atoms in steerable optical tweezers with high efficiency to study atomic interactions with a known number of atoms. These tweezers allow us to capture and move individual atoms, and to prepare them in a specific quantum states. We show the usefulness of this platform to study atomic interactions like individual molecule formation and spin changing collisions.

A single electromagnetic plane-wave propagating in free space possesses neither spin nor orbital angular momentum. Both types of angular momentum arise from interference between pairs of plane-waves having the same temporal frequency 𝜔 but differing 𝑘-vectors 𝒌1 and 𝒌2. While it is fairly straightforward to evaluate a wavepacket’s spin and orbital angular momenta in the (𝒌, 𝜔) continuum by means of Fourier transformation, obtaining the same results by discretizing the (𝒌, 𝜔) space, then attempting to approach the continuum limit via an infinite enlargement of the spatial volume under consideration, is fraught with danger.

Lateral optical forces (LOFs) exerted on metamaterials typically arise from the broken mirror symmetry in the system. It has been reported that a repeated pair of particles or circular motifs with different sizes or refractive indices can generate LOFs. Studies show that an optimised LOF could be large enough to manipulate the structure moving at a macroscopic scale. We demonstrate that this force can also be generated by a repeated single triangle motif. By adjusting the size and shape of the triangle, we can control the magnitude and direction of the LOF. The optimised structure parameters can be found by optimisation routines such as Bayesian optimisation combined with optical force calculation methods such as rigorous coupled-wave analysis.

The optically driven mechanics of a 2.17 μm-diameter water droplet subjected to a linearly-polarized, zeroth-order, tightly-focused, continuous-wave, 532 nm wavelength, Hermite-Gaussian laser beam are simulated in the Kirchoff-Fresnel diffraction region. Coupled electrodynamic and weighted orthogonal multi-relaxation kinetic lattice-Boltzmann methods evaluate Maxwell and Navier-Stokes equations, and a central-difference analysis at each location in space and instant in time evaluates the momentum continuity postulated by seven electrodynamic formalisms. Morphology of the 2.17 μm diameter water droplet is unique for each electrodynamic formalism, electric field polarization, focal displacement, and beam divergence of the incident Hermite-Gaussian beam. Unique droplet morphology predicted by each electrodynamic formalism in a focused Hermite-Gaussian beam also results in distinct electromagnetic mode confinement and scattering patterns measurable from the far field. Therefore, an electrodynamic theory may be experimentally deduced from the irradiance, polarization, and phase of the far-field angular light scattering patterns when compared against numerical analysis and standard near-to- far field transformation. Probing water droplets in the Kirchoff-Fresnel diffraction region may experimentally disprove long-standing electrodynamic theories, or suggest an appropriate electrodynamic theory for predicting the nonlinear deformation of light-scattering droplets.

The viscoelastic properties of cells are an essential physical parameter in many biological processes. A crucial example is the softening of cancer cells during the metastatic cascade. The drivers behind the change in cell mechanics are still not fully understood and the mechanical properties of the substrate, the ECM, and crosstalk with other cells often influence measurements of cell mechanics. We used the optical stretcher (OS), a dual laser beam trap, to measure the active and passive viscoelastic properties of cancer cells in suspension. We compare cancerous cells with and without co-culturing them with adipose tissue cells. With this assay, we can investigate the impact of the cellular crosstalk between the cancerous and adipose tissue cells on the physical properties of cells, thereby disentangling it from any substrate effects. Our goal is to understand how cancer cells are able to migrate through soft fatty tissue and what mechanical properties are essential during this process.

We consider a system of colloidal particles, with two or more different refractive indices, which stick together to form mixed clusters. The behaviour of such clusters in optical traps will vary depending on the numbers of particles involved and the distribution of their refractive indices. Our own recent studies of heterodimers of such beads suggest there is a rich vein of novel behaviour to explore, including unusual dynamics and optical binding [O'Donnell et al. Proc. SPIE 12436, 124360J (2023)]. In the present computational study we will explore the dynamics of mixed refractive index clusters in different types of optical trap, as a function of number and composition of beads as well as their arrangement. In particular, we will highlighting the difference between symmetrical and asymmetrical arrangements of beads in conventional Gaussian beams as well as in OAM beams. The optics model used is based on the discrete dipole approximation and includes low Reynolds number hydrodynamics with bead separations maintained using SHAKE-HI constraints. Further studies will investigate optical binding between arrays of such clusters in different types of structured fields.

We present an optical trapping platform that replicates the ease and precision of macroscopic level manipulation, such as holding, observing, squeezing, rotating, and probing biological specimens in microfluidic environments. Most modern biophotonics techniques tend to structure light or the local environment at scales comparable with that of the biological specimens under examination. However, the versatility of photonic functions that can be realized is often limited by the finite numerical aperture of the microscope objective used to access the samples. Lab-on-chip solutions, coupled with optical tweezing, offer appealing alternatives to this configuration. Here, we present a new biophotonic platform that integrates metasurface technology into the microfluidic environment. These artificial two-dimensional materials are extremely versatile, and their photonic response can be tailored to specific experimental requirements. Here we show that we can use photonic metasurfaces to create environment-dependent holographic imaging devices and create optical trapping potentials with efficiency comparable to that of high NA objectives. Additionally, we show that miniaturized metasurfaces suspended in the microfluidic chamber are extremely stable when trapped optically and can be used effectively to explore and interact with their surroundings. This innovative platform will have transformative benefits for microscopy and biophotonic applications at the interface of molecular and cell biology.

Our investigation focuses on studying the forces induced on a chiral dipolar particle when exposed to optimally chiral light (OCL). The concept of OCL encompasses all structured light fields that achieve maximum helicity density at a given energy density. Examples of OCL include circularly polarized light (CPL) and the optimally chiral configurations of the azimuthally-radially polarized beam (ARPB), which is a phase-shifted superposition of an azimuthally and a radially polarized beams. The optimal chirality condition requires that light’s magnetic and electric fields along the same direction be phase-shifted by a quarter of a period and that the ratio of their magnitudes equals the characteristic impedance in free space [Hanifeh, Albooyeh, Capolino, ACS Phot 2020, 7, 10, 2682–2691]. By meeting these conditions, the resulting field also exhibits electric-magnetic symmetry in its energy and spin densities. Consequently, OCL simplifies the computation of forces induced on a chiral dipolar particle, while simultaneously boosting its ability to discern chirality. Notably, the gradient force depends exclusively on the gradient of the energy density (as opposed to a combination of gradients), whereas the remaining forces can be expressed using the Poynting vector and the field’s orbital momentum. Given these properties, optimally chiral fields represent a promising avenue for the precise manipulation of chiral nanoparticles. Additionally, the choice of the beam is dependent on the geometry of the optical trap, as different optimally chiral fields have different spatial features. While a beam with CPL induces more pronounced transverse forces that discriminate chirality perpendicular to the propagation direction, the optimally chiral ARPB produces strong longitudinal forces that discriminate chirality along the propagation direction, eliminating the problem of false chirality detection due to electric anisotropy of the nanoparticle.

Janus particles (JPs) are composite particles of two or more parts with distinct chemical and physical characteristics. As the current methods of manipulation rely on chemical reactions or thermal gradients, they are restricted by the carrier fluid’s content and characteristics. In addition, the high absorbance of the mettalo-dielectric JPs causes strong repulsion from the optical traps. This poses practical challenges in manipulating them effectively. To tackle such limitations, we propose manipulating JPs by the optical forces in the evanescent field of a nanofiber. The field locks the JP to the nanofiber, restricting motion in the radial direction while allowing propulsion along the propagation direction of the laser beam. This work theoretically examines a JP (here, silica microspheres concentric half-dome caps of titanium and gold) in the evanescent field of a nanofiber. The various effects of the force and torques are discussed.

In this study, the controlled formation, trapping, and self-oscillation of vapor microbubbles in ethanol was investigated using low-power continuous wave (CW) lasers. The formation of these microbubbles is achieved by evaporation of ethanol due to heating by light absorption (CW laser emitting at λ = 658 nm) in silver nanoparticles deposited at the distal end of a multimode optical fiber. A second low-power NIR laser (λ = 1,550 nm) coupled to a single-mode optical fiber is then used to trap the microbubbles. It has been shown that the bulk absorption of light at 1,550 nm in ethanol modulates the surface tension of the bubble wall, creating a three-dimensional potential well that efficiently traps the bubbles. Furthermore, it was observed that once the bubble is trapped, random variations in its radius create instabilities in the trap, resulting in microbubble oscillations. The trapped bubble tends to oscillate between two quasi-stationary equilibrium points along the propagation of light. These oscillations are the result of competition between several forces, such as the Marangoni, the upward of buoyancy, and the drag forces. The results presented in this work contribute significantly to the understanding of these phenomena and may have important applications in fields such as microfluidics and bubble manipulation.

It has been observed that a nanoparticle can exhibit underdamped motion while moving toward the focal point of an optical trap. It is unclear whether this motion is caused by laser or fluid forces. Dielectrophoretic forces can trap nanoparticles as an alternate approach to optical trapping. The electrical trap uses no laser, so we can determine which force causes the underdamped motion. A microchannel with a quad-electrode arrangement on its ceiling and floor was designed to explore this question. Supplying an oscillating voltage to these electrodes generates an oscillating electric field resulting in the dielectrophoretic force that traps the particle. However, matching common characteristics, such as trap stiffness, is difficult between the two methods. This paper compares the two approaches for a 2 μm diameter particle. Instead of matching the trapping characteristics, the next step in this work is to use the dielectrophoretic device to explore the effect of the particle’s momentum on its motion, which can explain the underdamped motion. Combining optical and dielectrophoretic trapping will offer new insights into the dynamic behavior of small particles in a fluid medium.

Optical tweezers have become an important tool for various applications over the past couple of decades. However, as their range of applications increases, the calibration and sensitivity of detection schemes need to keep pace. Additionally, practical optical tweezer setups become very complex if there is more than one laser-beam trap. When an optical tweezer setup uses a high-repetition-rate femtosecond laser beam to immobilize the trapping object, the technique is known as a Femtosecond optical tweezer (FOT). The instantaneous trapping potential is due to the high peak power of each laser pulse. In contrast, the sustained stable trapping regime results from the high repetition rate of successive pulses. FOTs provide critical advantages in sensitivity through in situ two-photon detection capabilities due to the sensitive detection of background-free two-photon fluorescence. For a tightly focused beam as used in an optical tweezer, cumulative heating can occur despite the minimal absorption cross-section of the trapping medium or the trapped particle, which reaches its maximum value near the focus. A temperature gradient from the laser focal spot is thus generated outwards from the laser focus in the medium, creating a refractive index gradient across the focusing region. The refractive index attains its minimum value at the focus, gradually increasing as a function of increasing distance from it. Since the trapping force and potential depend on the refractive index of the medium, the thermal effect impacts the force and potential of the trapped particle significantly. FOTs offer an interesting balance of thermal aspects with inherent nonlinearities. In addition to providing sensitive measurements with super-resolution capabilities, FOTs also allow for sensitive monitoring of the colloidal aggregation processes, which is presented in some detail here.

Optical tweezers (OT) has proven to be an indispensable tool for elucidating phenomena in colloidal physics and for biomedical applications. Additionally, OT has been used to apply sub-piconewton forces on microscopic particles, for example in cells, as well as to measure displacements with nanometer resolution to extrapolate mechanical properties. Recently, an OT platform based on light sheet microscopy with a continuous wave laser has been developed to trap microscopic dielectric particles. However, the reduced gradient force resulting from the light sheet intensity distribution produces a trap stiffness an order of magnitude lower than its traditional circularly symmetric Gaussian counterpart. As a result, a high laser power, on the order of 50 mW is required, which risks phototoxicity for biological applications. In this work, we first compare the trap stiffnesses of continuous wave and femtosecond pulsed laser sources on dielectric particles in sub-1 mW scale. Next, we demonstrate the OT of dielectric spheres using a flat-top light sheet generated by a femtosecond pulsed laser source utilizing average powers as low as 1 mW. We propose leveraging flat-top light sheet OT to characterize the local and average mechanical properties of biological specimens.

Temperature measurement in plasmonic traps is important because biological molecules and quantum emitters are sensitive to temperature. While other works have used ion pore currents, fluorescence emission variation, and fluorescent diffusion tracking to measure the temperature dependence of shaped nanoapertures in metal films, here we make use of a stable erbium (Er) containing NaYF₄ nanocrystals that gives local temperature dependence. The local temperature variation is determined by a ratiometric analysis of the emission at different wavelengths.

The use of non-invasive, optical tweezers active microrheology provides invaluable information on the mechanobiological principles that govern most cellular processes. The principle of using a single laser beam to trap —either endogenous droplets or microinjected probe beads— and measure both the displacement and the force during an imposed oscillation has been proven insufficient for obtaining the response function, ˆχ(ω), and the G modulus, ˆG(ω). As a solution, an additional laser with very low power can be used to measure probe displacements independently, to the detriment of the simplicity of the optical trapping set-up, robustness and cost. Here, we present a method to carry out position and force measurements with a single trapping beam through the time-sharing mode of an optical micromanipulation unit modulated with acousto-optic deflectors.

In traditional cavity optomechanical models, a coupling between the cavity field and mechanical degrees of freedom is a result of dependence of the frequency or the life-time of a cavity mode on mechanical variables. However, optical cavities with degenerate modes may exhibit a different type of optomechanical coupling, which originates from the spatial reconfiguration of the cavity field caused by mechanical motion. Such coupling can, for instance, arise in the case of whispering-gallery-modes in spherical resonators interacting with a polarizable dipole. Here we introduce a model with this previously unexplored type of optomechanical coupling, and as a first step toward understanding the properties of this model we study its classical dynamics in the absence of dissipation and an external pump. We show that the dynamical properties of such a model are characterized by a bifurcation manifested by a loss of stability of a simple equilibrium and a transition to a more complex nonlinear dynamics.

The bound states in the continuum (BIC) were first discovered by von Neumann and Wigner in quantum mechanics. It was subsequently identified in photonics. BIC represents an embedded eigenmode that can perfectly confine light. The optical resonators that support this mode can have very large field enhancements and infinite Q factor in theory. Considering these advantages as well as the negligible heat generation, the dielectric metasurface using BIC mode is a more promising platform for sensor applications. Nevertheless, their performance is quite constrained by factors such as inevitable fabrication imperfections, the array size of chips, and up-down symmetry breaking. To mitigate these challenges, we construct merging BICs with the accessible electric field distribution in a Lieb lattice. Meanwhile, we integrated this system with a lateral photonic crystal mirror to enhance its performance in compact conditions. The design we propose remains robust, sustaining a very high Q factor (up to 10⁵) even when the up-down symmetry is broken, which provides a potential platform for optical trapping and biomedical sensing applications.

Raman fingerprinting of leukemic cells has potential applications in diagnosis and in vitro chemosensitivity assessment. A biochemical map of the contents of leukemic cells can not only help distinguish cancer patients from healthy ones but also shed light on different subtypes of leukemia such as ALL, AML, etc. Certain important requirements need to be fulfilled to effectively measure the Raman map of a single leukemic cell. Firstly, since the leukemia cells are suspension cells, it is preferred to keep them in a free solution rather than attached to a fixed surface during signal acquisition. Secondly, the cells need to be immobilized for several seconds, for the acquisition of the weak Raman signal even when using stimulated Raman Spectroscopy (SRS) which provides relatively stronger Raman signal. Thus, a device capable of sequentially flowing, holding, and releasing individual leukemia cells in a robust, efficient and high-throughput manner is required. We present an optofluidic fiber tweezers device comprised of a novel combination of 3D hydrodynamic flow focusing and optical fiber in a microfluidic chip. By exploiting the interplay between the optical and hydrodynamic forces acting on the cell, we demonstrate rapid, efficient, sequential delivery and trapping of single leukemic cells in a flow cytometer format followed by SRS imaging of the trapped cell. The specific Raman vibration bands corresponding to the lipids, nucleic acids, and proteins in the trapped cells were analyzed to distinguish cancerous cells from healthy cells. Our device is also capable of isolating cells with unique Raman signatures for further processing using techniques like gene sequencing etc.

Microscopic laser light interaction with matter has many consequences. That result depends on many factors: the medium, the matter involved, the light intensity, the wavelength, and the many ways of light, among others. In this contribution, we are going to discuss several results observed when light interacts with matter under different conditions. The observation did use a standard optical fiber and near-infrared radiation. We are going to discuss the basic linear and angular momentum transference, optical trapping; light energy conversions, such as absorption, heating, photochemical reactions, and micro-thermocavitation.

In this work we report an improved platform for testing and comparing particles for use in optical trap displays. We constructed seven prototypes, and deployed them to five different locations where they were successfully used to perform comparative optical particle trap tests. This improved rig makes it possible to expand optical trap display research by a decentralized group of citizen scientists.

Single-cell green algae (C. Reinhardtii) is a key model organism to study ciliogenesis. Cilia have important roles in sensory signaling pathways and in clearing the airways of mucus and dirt in multiple systems of the human body. As cilia are found on most eukaryotic cells, defects in ciliogenesis result in many symptoms and disorders. We are testing the hypothesis that when a flagellum is removed, the long flagellum shrinks because it is competing with the shorter regrowing flagellum. We used a 780-nm 200-fs laser to perform laser ablation to amputate one of two flagella on wildtype and mutant algae. Fla3 and Fla10 mutants were altered to inhibit the KAP kinesin motor that drives the intraflagellar transport (IFT) pathway. Impaired IFT pathways would demonstrate a lag in response to flagellar length equalization and a reduced disassembly rate. Quantified images following the long flagellum for 20 min post-ablation demonstrate a delayed disassembly rate in the Fla3 mutant compared to wildtype; Fla10 was inconclusive. Therefore, it was concluded that the proper function of KAP motor protein serves a significant role in length control of cilia. In the future, we will compare the assembly rates of flagellar regrowth for the wildtype and mutants.

Neuronal responses to injury are of interest to the development of methods to mitigate damage and stimulate repair. We utilized a single pulse from a 1030nm laser to create a laser induced shockwave (LIS) to subject neuronal cells to injury and compare the effects of injury on neurons from an Alzheimer’s Disease (AD) mouse model and wild type (WT) mice. We found differences in the calcium response to LIS in AD versus WT neurons. Additionally, we found that LIS induced cell death led to a calcium elevation which differed from that in cells that stayed alive. Therefore, the calcium response can be utilized to separate dead cells from live cells.

Axonal degeneration is a key component of neurodegenerative diseases such as Huntington’s disease, Alzheimer’s disease, and amyotrophic lateral sclerosis (ALS). (NAm), an NAD+ precursor, has long since been implicated in axonal protection and reduction of degeneration. On the other hand, hydrogen peroxide (H₂O₂) has been implicated in oxidative stress and axonal degeneration. The effects of laser-induced axonal damage in wild-type (WT) and Huntington’s disease(HD) mouse dorsal root ganglion neurons (DRGs) treated with NAm or H₂O₂ were investigated and the cell body width, axon width, axonal strength, and axon shrinkage post laser-induced injury were measured. We found that HD mouse DRGs have increased strength against laser damage compared to wild-type DRGs. We additionally found that treatment with NAm reduces the neuronal strength against laser damage in both WT and HD DRGs. Interestingly, when comparing HD DRGs treated with H₂O₂ and WT DRGs treated with H₂O₂, we found that treatment with H₂O₂ reduced the time required for the RoboLase laser system to cut through HD DRGs. We additionally found that both NAm and H₂O₂ treatments resulted in morphological changes in both WT and HD DRG cell bodies, respectively. We did not find any difference in shrinkage across the models. Ultimately, our results suggest that H₂O₂ at the same concentration may have less damaging effects on WT neurons than previously expected. Our results additionally indicate that higher concentrations of NAm, previously deemed to be safe, may have a neurotoxic effect rather than an axonal protective effect on HD and WT DRGs.

The Anti-Brownian ELectrokinetic (ABEL) trap uses electrophoresis or electroosmosis to trap fluorescent single molecules in free solution. Several photophysical parameters, such as brightness, lifetime, anisotropy, emission spectrum, can be simultaneously measured with very high precision. Here we demonstrate the added capabilities of the ABEL trap upon modifying the excitation technique. First, we utilize dynamic excitation brightness to observe photophysically induced responses in a trapped light-harvesting protein-pigment complex from cyanobacteria. Second, we trap fluorescently labeled biomolecules using two colors via pulsed interleaved excitation (PIE) to enable acceptor-corrected FRET measurements. These advances in excitation patterning for the ABEL trap allow for novel sensing abilities that combine the benefits of cutting-edge single-molecule imaging and spectroscopy with the long isotropic view of single molecules provided by the ABEL trap.

Publisher's Note: This oral presentation, originally published on 5 October 2023, was replaced with a corrected/revised version of the presentation slides on 19 April 2024. No change was made to the published manuscript accompanying this video presentation.