Optical Trapping and Optical Micromanipulation XXI

In this work, we have exploited the Optical Tweezers (OT) technique to investigate at the single-molecule level the interaction between the human Thymidylate Synthase (hTS) and its consensus mRNA, a biological process essential for cell survival. Nowadays TS is an enzyme widely employed in chemotherapy for the treatment of solid cancers and new therapeutic molecules have been recently developed to overcome the existing drug resistance phenomena. Despite the efficiency of these new TS-targeting drugs in promoting tumor cell death, little is known about their effects on the TS-mRNA binding mechanisms. Force spectroscopy measurements with OT have been carried out on individual mRNA molecules, and the free energy landscape of the mRNA as well as the main properties of its folding and unfolding pathways will be presented. Also, preliminary results obtained by manipulating the mRNA in the presence of TS will be discussed, highlighting the energetic changes induced in the biological system by the occurrence of the TS-mRNA binding event.

The mechanosensitive nature of the TCR-pMHC interaction in T cells has been studied via optical tweezer experiments. From these studies, populations of force responsive T cells (digital cells) that recover activation potential in sparse pMHC environments have been discovered. Through a series of optical tweezer experiments, the distinctions between the digital population and their counterpart T cells will be examined. These include triggering ability at varying pMHC copy numbers and the stiffness changes in the T cell membrane as measured through microrheology.

Optical tweezers have become ubiquitous tools in science with use in disciplines ranging from biology to physics, chemistry, and material sciences with thousands of users around the world and a continuously growing number of applications. Here we show how a specially designed instrument, called miniTweezers2.0, can be made both highly versatile and user friendly. We demonstrate the system on three different experiments, which thanks to the close integration of the various parts of the tweezers into a single software are performed largely autonomously. The first experiment involves DNA stretching, a fundamental single molecule force spectroscopy experiment. The second experiment involved the stretching of red blood cells, which can be used to gauge the membrane stiffness of the cells. Lastly, we investigate the interaction between core-shell particles in various environments. Showing how the soft polymer layer extends, or contracts depending on pH and salinity. Our work show potential of automated and versatile optical tweezers systems in advancing our understanding of nano and micro-scale systems.

Accurate chromosome segregation during cell division relies on coordinated actions of microtubule-based motor proteins in the mitotic spindle. Kinesin-14 motors play vital roles in spindle assembly and maintenance by crosslinking antiparallel MTs at the spindle midzone and anchoring spindle MTs’ minus ends at the poles. We investigate the force generation and motility of the kinesin-14 motors HSET and KlpA, revealing that both motors function as non-processive motors under load, producing single ~25 nm power strokes per MT encounter. Each homodimeric motor generates forces of ~0.5 pN, but when assembled in teams, they cooperate to generate forces of 1 pN or more. Importantly, cooperative activity among multiple motors leads to increased MT-sliding velocities. Our findings quantitatively elucidate the structure-function relationship of kinesin-14 motors and underscore the significance of cooperative behavior in their cellular functions.

To gain a better understanding of material properties of chromatin and successfully link them to chromatin organization and functions such as transcription, we develop novel methods to actively manipulate a genomic locus inside the nucleus of a living human cell. By targeting iron-containing nanoparticles to a specific genomic locus and applying a controlled magnetic field, we were able to physically move chromatin through nuclear space for the first time. Exertion of near-picoNewton forces led to displacements over microns within minutes. We observe partially reversible stretching of chromatin highlighting its’ viscoelastic nature. We could accurately recapitulate the observed behavior with a Rouse model that included only a weak obstructive effect of the surrounding chromatin and nucleoplasmic material. This challenges the view that interphase chromatin is a gel-like material.

Hypertrophic cardiomyopathy (HCM) is a symptomatic affliction due to mutations in cardiac contractile proteins. We compared a highly penetrant mutation in cardiac myosin, M493I, with wild type (WT) using an advanced optical trap assay capable of quantifying kinetic rates including actomyosin re-attachment. Kinetic changes in both the actomyosin attachment and detachment rates suggest that the equilibrium between a conformation termed the Interacting Head Motif (IHM) and freely available myosin heads is disturbed in M493I. This type of disruption has been hypothesized to lead to the toxic hypertrophy observed in patients.

Extracellular vesicles and particles (EVPs), once considered as a means for cells to expel wastes, are now recognized as vital mediators of cell-to-cell communication. They transport essential molecules like mRNA, miRNA, proteins, and lipids, facilitating both local and long-distance signaling. However, their diverse origins and sizes pose a challenge for understanding their roles in health and disease. Traditional optical tweezers face limitations due to the small size of EVPs and the diffraction limit of light. In this discussion, I will introduce innovative optical nanotweezers utilizing plasmonic and dielectric nanoantennas to rapidly trap and analyze single EVPs, overcoming previous obstacles. These novel non-invasive light-based tools with multifunctional capabilities are expected to open new horizons by enabling to address fundamental questions in EVP biology and drive translational applications in novel therapeutics, as well as environmental monitoring.

For over a decade, our group has been trapping and analyzing single proteins using a double nanohole in a metal film. Our recent investigations have sought to improve the nanofabrication, including bottom-up mass-fabrication and a new fiber-based platform for microwell format investigation. We have also been developing approaches to modify the environment around a single trapped protein, for example, by integrating microfluidics and allowing for varying the background temperature. This allows for measuring properties like the optical size, hydrodynamic size, charge and thermophoretic properties a trapped protein. These new capabilities will be presented in this work.

We present a method for trapping nanoscale biological particles without causing photothermal heating, using all-dielectric optical nanotweezers. This technique focuses the accessible electromagnetic energy to as small as 30 nm, enabling the trapping and imaging of nanosized biological specimens including extracellular vesicles and lipoproteins with minimal temperature increase. This advancement offers new opportunities in single molecule analysis and opens the door to understanding the diversity of extracellular particles.

Recent developments in design and fabrication techniques enables sub-wavelength field confinement in dielectric nanocavities and thereby provides a new regime of extreme field enhancement. We study the optical forces acting upon a nanosphere hosted in such a nanocavity and find that the strong light-matter interaction causes the presence of the dielectric sphere to alter the response of the electromagnetic resonator in what is known as self-induced back-action (SIBA). We analyze the effect using perturbation theory of the cavity quasi-normal mode and show that SIBA greatly modifies the gradient force, and thereby enables potential reshaping by detuning of the driving laser.

This talk will consider the future of metal halide perovskite (MHP) photovoltaic (PV) technologies as photovoltaic deployment reaches the terawatt scale. The requirements for significantly increasing PV deployment beyond current rates and what the implications are for technologies attempting to meet this challenge will be addressed. In particular how issues of CO2 impacts and sustainability inform near and longer-term research development and deployment goals for MHP enabled PV will be discussed. To facilitate this, an overview of current state of the art results for MHP based single junction, and multi-junctions in all-perovskite or hybrid configurations with other PV technologies will be presented. This will also include examination of performance of MHP-PVs along both efficiency and reliability axes for not only cells but also modules placed in context of the success of technologies that are currently widely deployed.

The recent advent of robust, refractory (having a high melting point and chemical stability at temperatures above 2000°C) photonic materials such as plasmonic ceramics, specifically, transition metal nitrides (TMNs), MXenes and transparent conducting oxides (TCOs) is currently driving the development of durable, compact, chip-compatible devices for sustainable energy, harsh-environment sensing, defense and intelligence, information technology, aerospace, chemical and oil & gas industries. These materials offer high-temperature and chemical stability, great tailorability of their optical properties, strong plasmonic behavior, optical nonlinearities, and high photothermal conversion efficiencies. This lecture will discuss advanced machine-learning-assisted photonic designs, materials optimization, and fabrication approaches for the development of efficient thermophotovoltaic (TPV) systems, lightsail spacecrafts, and high-T sensors utilizing TMN metasurfaces. We also explore the potential of TMNs (titanium nitride, zirconium nitride) and TCOs for switchable photonics, high-harmonic-based XUV generation, refractory metasurfaces for energy conversion, high-power applications, photodynamic therapy and photochemistry/photocatalysis. The development of environmentally-friendly, large-scale fabrication techniques will be discussed, and the emphasis will be put on novel machine-learning-driven design frameworks that leverage the emerging quantum solvers for meta-device optimization and bridge the areas of materials engineering, photonic design, and quantum technologies.

Artificial intelligence (AI) techniques have boosted the capability of optical imaging, sensing, and communication. Concurrently, photonics facilitate the tangible realization of deep neural networks, offering potential benefits in terms of latency, throughput, and energy efficiency. In this talk, I will discuss our efforts in AI photonics with two examples. The first involves employing a convolutional neural network for achieving single-shot full-field measurement of optical signals. The second example pertains to implementing a deep neural network with a multiple-scattering system featuring structural nonlinearity, thereby enabling nonlinear computations using linear optics.

Optical trapping in nanostructures has usually been achieved utilizing the strong field gradients of plasmonics resonances. However, given the inherent optical losses in metals to heat dissipation, their use can prove detrimental to biological trapping settings and can affect other trapping properties. Dielectric nanostructures do not suffer these intrinsic losses but it remains challenging to design dielectric structures with strong field gradients. In this work, we use inverse design by topology optimization to design a dielectric metamaterial that confines light to trap nanoparticles in air. The obtained trapping potential is deep enough – with a trapping depth below 10 kBT – to overcome thermal fluctuations.

Plasmonic apertures concentrate optical fields, enhancing the gradient force for precise trapping of nanoscale entities. Traditionally, design relied on intuition and simulations. We instead present a novel approach using topology optimization and adjoint sensitivity analysis. Our computational algorithm inversely designs plasmonic nanoapertures. Surprisingly, the algorithm produces an aperture reminiscent of the double nanohole, a structure that has been adopted by many groups. Our algorithm produces outer structures that surround the aperture and enhance the electric field intensity, increasing trapping potential by ~4.97 times. Compared to representative studies, our design achieves ~1.95 and ~27.9 times greater trapping potential than algorithm-designed and forward-designed nanotweezers, respectively. This work establishes topology optimization as an effective method for high-performance plasmonic nanotweezer design.

Our optical positioning and linking (OPAL) platform is based on optical tweezers and can assemble sub-micron heterogeneous materials in three dimensions (3D). OPAL is fully automated and can position hundreds of particles according to a set of desired predetermined coordinates. After positioning, particles are permanently liked together via biotin-avidin chemistry. We present how the fabrication speed, positional accuracy, and error rate depend on process parameters. The rapid prototyping of metamaterials and nanostructured optical chemical sensors will be discussed, as well as novel computational design approaches for these devices based on the discrete dipole approximation.

Optical skyrmions, that is particle-like optical fields with topologically protected polarization textures (such as Néel-, Bloch-, and anti-skyrmions), have been recently demonstrated. Optical skyrmions have been utilized in advanced applications such as free-space communications under turbulent conditions, and super-resolution microscopy with sub-wavelength spatial resolution. Optical skyrmions are also potentially expected to offer new fundamental physics via exotic light matter interactions, however, they are still in their infancy as a research topic, and there are few reports of the interaction between optical skyrmions and materials. We herein report on the first demonstration of direct imprint of the topologically protected polarization textures of optical Néel-, Bloch-, and anti-skyrmions onto a material, as a surface relief in azo-polymers. This demonstration strongly evidences the capacity of the optical skyrmions for new approaches to materials manipulation.

We use an optical positioning and linking (OPAL) platform based on optical tweezers to fabricate a grating coupler on a microtoroid-shaped optical resonator for highly efficient coupling of light into the resonator, which acts as a chemical sensor. Light is coupled into and out of the microtoroid through a grating fabricated from 0.5 µm polystyrene particles on the rim of the microtoroid, which acts as a fiber-free coupler. Unlike a tapered fiber coupler, this particle grating is highly robust and not susceptible to mechanical and vibrational noise, paving the way for field-portable sensing devices.

Optical manipulation and imaging play critical roles in biomedical applications, however, applying these technologies to hard-to-reach regions remains challenges. We introduce a series of innovative AI-driven methods designed to facilitate both high-fidelity light field control and image reconstruction through a lensless multicore fiber with an ultra-thin diameter below 0.4 mm. Our approach enables precise, controlled rotation of human cancer cells around all three axes, enabling 3D tomographic reconstructions of these cells with isotropic resolution. Moreover, we developed deep neural networks tailored for quantitative phase imaging through the lensless fiber endomicroscope by efficiently decoding phase information from speckles captured on the fiber's distal end. The integration of these advanced optical and computational techniques culminates in a powerful optical fiber probe, capable of sophisticated optical manipulation and phase imaging, offering new perspectives for optical manipulation and endoscopic imaging.

Micro (less than five millimeters in length) and nano (less than one micron) plastics exist in marine and terrestrial habitats and are detrimental to both the environment and animal health. A comprehensive study is necessary to understand their origin and distribution and to find environmental and human protection strategies. Recently, optical and Raman tweezers have proved to be an efficient tool to trap, manipulate and characterize micro and nano plastics. In this work, trapping configurations of micro and nano plastic particles have been investigated computationally. By combining the rigorous calculation based on the Transition matrix method with approaches based on machine learning, we investigate a broad range of dimensions and optical properties enhancing the efficiency of computations and unlocking new avenues for advancement in microplastics research.

Optical tweezers manipulate microscopic objects with light by exchanging momentum and angular momentum between particle and light, generating optical forces and torques. Understanding and predicting them is essential for designing and interpreting experiments. Here, we focus on geometrical optics and optical forces and torques in this regime, and we employ neural networks to calculate them. Using an optically trapped spherical particle as a benchmark, we show that neural networks are faster and more accurate than the calculation with geometrical optics. We demonstrate the effectiveness of our approach in studying the dynamics of systems that are computationally “hard” for traditional computation.

Brain cells are complex and delicate materials with unique physical properties that can be influenced by physical stress. Recent studies have shown that physical stress affects the biological response of molecules inside living cells. We have been developing a single-objective light-sheet microscope and optical manipulation tools to investigate the dynamic properties of living brain cells. This integration allows us to observe 3D biological processes with high precision while enabling the manipulation and characterization of individual cells and microcompartments. In this presentation, I will explain the operating principles of multimodal optical force microscopy, share preliminary results, and discuss future applications.

We analyse the collective behaviours of Escherichia coli (E. coli) active matter. The individual movements of these E. coli can be accurately tracked and examined using a recently developed machine learning software called DeepTrack (Midvedt et al., 2021). This provides greater insight into the chaotic dynamics of E. coli swarms as well as the potential to critically assess current theoretical models. DeepTrack analysis can also be applied in more complex environments including interactions with microstructures made with photolithography. Analysing the movements of E. coli active matter with DeepTrack has promising implications in engineering and biomedical applications.

We examine motility-induced phase separation (MIPS) in two-dimensional run and tumble disk systems using both machine learning and noise fluctuation analysis. Our measures suggest that within the MIPS state there are several distinct regimes as a function of density and run time, so that systems with MIPS transitions exhibit an active fluid, an active crystal, and a critical regime. The different regimes can be detected by combining an order parameter extracted from principal component analysis with a cluster stability measurement. The principal component-derived order parameter is maximized in the critical regime, remains low in the active fluid, and has an intermediate value in the active crystal regime. The different regimes can also be characterized via changes in the noise power of the fluctuations in the average speed. Similar methods can be applied to active matter in the presence of substrates produced via optical means or for situations in which the particles are being manipulated optically.

The perhaps most widely used tool for measuring forces and manipulating particles at the micro and nano-scale are optical tweezers which have given them widespread adoption in physics, chemistry and biology. Despite advancements in computer interaction driven by large-scale generative AI models, experimental sciences—and optical tweezers in particular—remain predominantly manual and knowledge-intensive, owing to the specificity of methods and instruments. Here, we demonstrate how integrating the components of optical tweezers—laser, motor, microfluidics, and camera—into a single software simplifies otherwise challenging experiments by enabling automation through the integration of real-time analysis with deep learning. We highlight this through a DNA pulling experiment, showcasing automated single molecule force spectroscopy and intelligent bond detection, and an investigation into core-shell particle behavior under varying pH and salinity, where deep learning compensates for experimental drift. We conclude that automating experimental procedures increases reliability and throughput, while also opening up the possibility for new types of experiments.

For a fluorescence microscopy system, a set-up often costs upwards of one hundred thousand dollars, if not multiple hundreds of thousands. This makes research inaccessible to any institutions except those with the highest level of funding. Our research addresses the challenges of high-magnification fluorescence microscopy by using low-cost off-the-shelf components to create a fluorescence imaging system. We use a cost-effective widefield system for neuroimaging using an OLED array via an Arduino microcontroller and a custom-made image processing algorithm. The OLEDs enable fluorescence microscopy with their emissions having significant overlap with several well known fluorescent probes. We use this system for fourier ptychography and leverage image processing algorithms to achieve high-resolution images by combining low-resolution images within the fourier plane. A phase retrieval algorithm and a regression model are utilized to find optimal coefficients for our transform matrices. This project is promising to democratize neuroimaging, especially in resource-constrained settings with affordable costs and portability.

Light-powered microrobotic swarms, excelling in manipulation efficiency and motion pattern customization, are pivotal for micro-fabrication and biomedical applications. Herein, we introduce an integrated platform capable of autonomously transporting light-powered microrobotic swarms over long distances within complex environments. The embedded real-time feedback control algorithm ensures swarm integrity and facilitates the adept navigation around unpredictable obstacles. The successful operation of both trapping- and nudging-based microrobots prove the versatile applicability of our platform.

Information processing is vital for living systems and involves complex networks of active processes. These systems have influenced various forms of modern machine learning, including reservoir computing. Reservoir computing utilizes networks of nodes with fading memory to perform computations and make complex predictions. Reservoirs can be implemented on computer hardware or unconventional physical substrates like mechanical oscillators, spins, or bacteria, known as physical reservoir computing. We demonstrate physical reservoir computing with a synthetic active microparticle system that self-organizes from an active and passive component into inherently noisy nonlinear dynamical units. The self-organization and dynamical response of the unit is the result of a delayed propulsion of the microswimmer to a passive target. A reservoir of such units with a self-coupling via the delayed response can perform predictive tasks despite the strong noise resulting from the Brownian motion of the microswimmers. To achieve efficient noise suppression, we introduce an architecture that uses historical reservoir states for output. We discuss the node and collective reservoir dynamics.

Our research explores how electromagnetic forces are induced in three-dimensional photonic crystals when white light is directed at a cluster of SiO2 spheres known as artificial opals infused with Fe3O4 nanoparticles. Our study focuses on the electromagnetic propagation along the [111] crystal axis, which is a high symmetry direction of the crystal. We have previously utilized coherent light to activate different photonic modes, including confined and extended modes. We have gathered experimental evidence of the force induced when the photonic structure can make forced oscillations. Our measurements include peak displacements and velocities, which help pave the way for developing a new kind of energy harvester.

For a small particle in a Gaussian laser beam, the trapping force arises as a competition between gradient forces pulling the particle to the beam focus and scattering forces pushing the particle along the optical axis. Prior studies have shown that the balance of these competing forces causes particles which are approximately the same size as the beam waist of the trapping light to be optimally trapped. However, there is a clear scaling between trap stiffness and wavelength in 3D Optical tweezers that has not yet been fully studied. In this work, we compare optical trapping of silica nano-particles using both violet (405 nm) and infrared (1064 nm) light. We obtain a substantial improvement in the stiffness per unit of power for a subwavelength particle. We show trapping of 300nm diameter silica spheres with a trap stiffness of 11 pN/um/mW using 405nm light, which is a factor of 20 enhancement compared to what is achieved with a trapping wavelength of 1064nm.

This work presents the generation of pulses through the self-oscillation of a vapor microbubble. To achieve this a microbubble was injected into alcohol, becoming trapped at the tip of an optical fiber emitting light at a wavelength of 1550 nm. The self-oscillation of the microbubble occurs due to the imbalance between buoyancy and Marangoni forces, resulting in the modulation of reflected light within the optical fiber and, consequently, in the generation of pulses. The reflected signal is coupled to a three-port circulator, which is then connected to an oscilloscope for data visualization. The pulse frequency (7 Hz) and the Full Width at Half Maximum (3-5 ms) were measured as temperature functions and oscillation time. Additionally, was observed that the amplitude of the pulses is directly related to the separation distance between the vapor bubble and the optical fiber. The ability to modulate the frequency over time of these pulses is evident in a wide range of applications such as telecommunications, medical applications, and interferometry.

The notable increase in fungal infections in humans, predominantly associated with various Candida species, notably including C. albicans, C. tropicalis, C. parapsilosis and C. auris, is accompanied by an increase on the fungal drug resistance. In response to the escalating challenges presented by antifungal resistance, novel approaches such as antimicrobial photodynamic therapy (aPDT) have been actively explored. Here, we present a novel method that combines optical tweezers (OT) and aPDT to monitor the health of individual fungal cells of C. tropicalis. While aPDT traditionally evaluates the overall health of cell colonies, our approach focuses on microscopic changes at the single-cell level. By capturing a lipid body and analyzing its Brownian motion, we can measure trap stiffness, revealing significant alterations in intracellular viscosity after aPDT treatment. This correlation, further confirmed by imaging, provides a powerful tool for understanding individual cell responses to aPDT.

Janus particles possess dual properties that makes them very versatile for soft and active matter applications. Modeling their interaction with light, including optical force and torque, presents challenges. We present here a model of spherical, metal-coated Janus particles in the geometric optics approximation. Via an extension of the Optical Tweezers Geometrical Optics (OTGO) toolbox, we calculate optical forces, torques, and absorption. Through numerical simulation, we demonstrate control over Janus particle dynamics in traveling-wave optical landscapes by adjusting speed and periodicity.

Intracavity optical tweezers have been proven successful for trapping microscopic particles at very low average power intensity – much lower than the one in standard optical tweezers. This feature makes them particularly promising for the study of biological samples. The modelling of such systems, though, requires time-consuming numerical simulations that affect its usability and predictive power. With the help of machine learning, we can overcome the numerical bottleneck – the calculation of optical forces, torques, and losses – and reproduce, in simulation, the results in the literature and generalize to the case of counterpropagating-beams intracavity optical trapping.

The ability to trap and analyze small extracellular vesicles (sEVs) and nanoparticles using low laser power is crucial to understanding their heterogeneity. In this work, we demonstrate low power trapping of trapped sEVs using plasmonic resonators in a ternary media, leveraging the temperature induced diffusophoresis of solute molecules to stably localize particles at the plasmonic hotspot. The plasmonic cavity, coupled with the diffusophoretic force, synergistically localizes single sEVs and provides significantly enhanced light-matter interaction for spectroscopic analysis at low laser powers.

Optical trapping allows the trapping and manipulation of dielectric microparticles. However, full control over all six degrees of freedom of the trapped object is challenging. Here, we use ferromagnetic iron-doped upconversion microparticles for simultaneous optical trapping and magnetic micromanipulation that allows full control over all translational and rotational degrees of freedom. These microparticles have a low absorption that allows optical trapping and a high coercivity and saturation magnetization that allow magnetic manipulation. The particles will enable micromanipulation experiments, for example, in single-molecule biophysics.

Coherent fiber bundle (CFB) based endoscopes extend optical imaging and optical micromanipulation techniques into the clinical environment, and show great potential for biomedical and clinical applications. However, fiber cores in CFB distort the wavefront, which brings difficulty for optical micromanipulation through CFB. Here, we proposed an unsupervised learning method for light field generation through a coherent fiber bundle. A diffraction model tailored to CFB is incorporated into the output of the neural network, so there is no need to calculate hologram for supervised training. The proposed method can generate high fidelity light field in video rate. It is expected to support in vivo scan-free multi-photon imaging through the CFB based endoscopes.

We discuss a new machine learning approach for simulation and design of optical traps, tailored for subwavelength particles. Given the time-consuming nature of full-wave simulation of nanostructures, we propose a predictive residual neural network for accurate modeling of near-field optical forces and trapping potentials in two configurations of meta-structures. The residual network architecture resolves the vanishing gradient problem in deep neural networks, allowing us to accurately predict the performance of optical traps. We will also discuss inverse design approaches based on our predictive model.

Quantifying viscoelastic material properties within active systems, such as cells, poses a challenging task. Due to the non-equilibrium nature of such systems, many tools from statistical physics, like the MSD, fail to predict material properties from passive observation of a tracer particle. Instead, active methods such as optical tweezers are used where typically external forces are applied to measure the material response. Here, we introduce a new statistical method based on three-point correlations. By quantifying the mean displacement of a probe particle after having transitioned a specific distance in the immediate time history, this new quantity allows the detection of the breaking of detailed balance in confined systems. Firstly, we test this novel approach on a well-controlled experimental model system, using optical tweezers to induce non-equilibrium motion to a tracer particle. Next, we turn to the most complex, but also highly relevant system, living cells. Strikingly, applying this novel approach not only allows us to measure the level of activity but also gives access to the viscoelastic material properties of a range of different cell types.

In 2019, Schmidt et al. demonstrated light-induced assembly of active colloidal molecules. They used two types of colloidal particles in a water-lutidine mixture: one transparent and one slightly absorbing light. In their experiment, this determined a non-reciprocal interaction between light-absorbing and transparent particles and promoted active molecule formation controlled by light. Beyond experimental details, we here explore the effects of this non-reciprocal interaction solely, showing its role in active molecule formation and self-propulsion. Simulation allows for the study of complex light profiles, enabling precise control over assembly and propulsion properties, relevant for targeted microscopic delivery.

A rigid body can have 6 degrees of freedom, namely the three translational degrees of freedom and further, the three rotational degrees of freedom. Of these, the translational degrees have been well explored in optical tweezers community. However, only the in-plane rotational degree of freedom which we call the yaw motion in the nomenclature of the airlines, has been explored. The pitch and roll degrees are only beginning to be explored recently. In this talk, I will exhibit 4 ways of generating pitch rotation using the optical tweezers. I will also show you one way of detection of pitch rotation at high resolution using birefringent particles. Further, I will also discuss some applications of this pitch rotation in soft matter systems and biology, particularly usage to detect cell membrane fluctuations and rheology in the cell interior.

Ballistic measurements using rotational optical tweezers determine the viscosity of fluids much faster than with conventional methods. They have the unique advantage of being calibration-free and using low laser powers that limit negative heating effects. This makes the technique ideal for performing ultrafast dynamic viscosity measurements in biological systems and will provide useful insight into the behaviour of dynamic environments.

We investigate the behavior of optical vortex propagation and Orbital angular momentum conservation in scattering media by observing phase characteristics and mode content of scattered vortex beam. Interaction of light with OAM carrying a singularity on its propagation axis and scattering particles provides a significant potential for employing the method in practical applications, such as studies of blood cells, and biological tissues. Therefore, micro-sized Polystyrene particles suspended in a mixture of Glycerin and water serve as a scattering medium capable of simulating the characteristics of red blood cells. The particles utilized in this investigation exhibit variability in concentration and optical path length, provides a thorough comprehension of how light dependence correlates with optical properties and thickness of the scattering media.

Optics researchers have seen huge developments in the understanding, control, and measurement of optical angular momentum in the 21st century. These insights have generally been enabled by advances in semi-conductor technology in both experiments and computation. I will cover three areas of optical angular momentum transfer that was enabled by these developments: spin—orbit coupling, beam shaping, and materials design. Recent technological advancements have enabled investigations of optical angular momentum and activity across a wide range of size scales. We have a good understanding of the optical elements through careful modelling of both the light that reaches objects and the scattering they cause. Structuring light enhances control of optical angular momentum transfer to matter, for example, to allow transfer of transverse angular momentum to wavelength sized particles. This approach can be generalised to optimise reflection, anisotropy, and absorption to enable control and measurement of matter. This in turn provides the impetus to create new devices for the same. I will cover previously published and new research of informed design of light fields and particles.

A rigid body can have six degrees of freedom, of which three are with rotational origin. In the nomenclature of the airlines, the in-plane degree of rotational freedom can be called yaw while the first out-of-plane degree of freedom can be called pitch with the second one being called roll. Among these, only the yaw sense has been studied extensively in the optical tweezers literature, while the pitch rotation is starting to be explored. In this paper, we show a way to detect the pitch rotation in a hexagonal-shaped particle using photonic force microscopy using the forward scattered light under crossed polarizers and making it incident on a split photodiode. In this way, the pitch angle can be detected at high resolution and bandwidth. We apply this technique to detect continuous pitch rotation and also exhibit a power spectral density for an anisotropic particle optically trapped in a linearly polarized light and exhibiting Brownian motion.

Self-propelled particles are becoming crucial components for various applications such as targeted drug delivery systems, active rheometry and powering microactuators for lab-on-chip devices among others. However, due to its size and the nature of the suspending medium, Brownian motion overcomes self-propulsion at some temporal ranges. Thus, one of the major challenges in autonomous operation is to overcome random fluctuations. In this work, we show a strategy to manipulate half metal-coated Janus particles using optical vortex beam. We observed that the Janus particles were confined and moves persistently along the ring trap. Angular speed measurements show a linear increase at increasing laser powers. Furthermore, we found that the orientation vector of the Janus particle aligns with the direction of the tangential driving. Our findings leads to new way of controlling self-propelled particles without the use of complex techniques such as feedback-loops.

In the past three decades, the orbital angular momentum (OAM) of vortex beams has found numerous applications, including optical manipulation, quantum cryptography, free-space information transfer and communications. In this talk, firstly, I will give a brief review of our recent works on the generation and manipulation of structured beams. Secondly, I will introduce a novel optical manipulation, namely, mind controlled optical manipulation. We know that the ability to control objects with the mind has fascinated humankind since ancient times. Recently, we proposed and experimentally demonstrated a mind-controlled optical manipulation (MCOM), which is merged by two important non-contact technologies, brain-computer interfaces (BCI) and optical tweezers. Thus far, to our knowledge, all the BCI are exploited in the macroscopical field, and our work provides unprecedented access to the microscopic world. Lastly, I will discuss a kind of ultrafast optical spanners with ultrashort pulsed beams, based on the spin-to-angular momentum conversion.

Microengines have shown promise for a variety of applications in nanotechnology, from microfluidics to nanomedicine and targeted drug delivery. However, their precise control over their dynamics is still challenging. We introduce a micro engine that exploits both optical and thermal effects to achieve a high degree of controllability. We find that a gold-silica Janus particle illuminated by a high focused laser beam can be confined at the stationary point where the optical and thermal forces balance. By using circularly polarized light the symmetry between these forces can be broken by transferring angular momentum to the particle, resulting in a tangential force that induces an orbital motion of the particle. We can simultaneously control the velocity and direction of rotation of the particle, changing the ellipticity of the incoming light beam while tuning the radius of the orbit with laser power. We validate our results using a geometrical optics model that incorporates optical force, the absorption of optical power, and the resulting heating of the particle.

Optical diffraction tomography (ODT) is a valuable imaging technique in biomedicine, particularly for live cell and tissue studies, offering insights into cellular structures via refractive index assessment. However, traditional methods face limitations in scanning ranges, affecting resolution and imaging completeness. To address this, a compact multi-core fiber-optic system enables precise cell rotation within microfluidic chips, enhancing tomography resolution. Introducing an AI-driven reconstruction workflow promises automation and efficiency. Validation through phantom and cancer cell reconstructions showcases performance. Yet, ODT is hindered by weak scattering sample requirements, limiting its applicability to shallow single cells. A novel algorithm addresses this for thicker samples like C. Elegans, albeit with spatial resolution constraints. Combining this algorithm with the cell rotation system could revolutionize applications in flow cytometry and acoustic rotation tomography.

Optical levitation in ultra-high vacuum (UHV) and cryogenic environments provides a platform potentially capable of providing quantum coherences of tens to hundreds of milliseconds for objects such as silica nano-spheres which are much more massive than atoms and molecules. Demonstration of matter-wave interference with optically levitated nanospheres has the potential to extend the current limit on matter-wave interference by three to four orders of magnitude, pushing the experimental limits on matter-wave duality. This would provide pathways towards the realization of gravity-induced entanglement experiments, tests of decoherence and wave function collapse models. To preserve a coherence time of approximately 200ms, experimental challenges such as near motional ground state cooling pressures below 10−13mbar, internal temperatures below 100K, and relative position stability on the order of tens of nanometers must be overcome. This apparatus additionally allows for precision measurements of short-range forces to test Newtonian gravity at sub-micron scales, the Casimir Polder force, matter neutrality, and other fundamental forces.

We describe the characterization of single nanoparticles based on the measurement of their rotational and oscillatory motion when optically levitated within vacuum. Using colloidally grown yttrium lithium fluoride nanocrystals of different sizes, trapped in a single-beam optical tweezer, we demonstrate the utility of this method which is in good agreement with simulations of the dynamics. Size differences as small as a few nanometers could be resolved using this technique offering a new optical spectroscopic tool for non-contact characterization of single nanoparticles in the absence of a substrate

Due to its isolation from the environment, a single nanoparticle, optically levitated in an ultrahigh vacuum, provides a promising experimental platform for weak force sensing and for testing fundamental physics at the boundary between the classical and quantum regimes. Extending levitational optomechanics to arrays of multiple, interacting particles is an exciting new development, still in its infancy, which promises to open new research directions in quantum gravity, quantum friction measurements, dark matter detection or probing quantum correlations and entanglement. To fully exploit the potential of these optomechanical arrays we explored optical interaction between nanoparticles levitated in vacuum, and demonstrated its tunability and developed new protocols to control of this complex system.

Coupling two silica nanoparticles via optical interaction can be used to observe non-Hermitian dynamics. We use Digital Micromirror Device (DMD) to create two pairs of counter-propagating laser beams. This allows us to dymanically change the relative phase, distance and separation of the trapping beams. Breaking the symmetry of the coupling between the nanoparticles via non-zero relative phase of the two beams leads to non-reciprocal interaction between the nanoparticles. This leads to Hopf bifurcation and the formation of collective limit cycle oscillations.

We describe the creation of an optical centrifuge for nanorotors formed by anisotropic nanoparticles levitated within an optical tweezer for the study of non-classical rotational motion. We also report on the experimental realization of the centrifuge enabled by a fast in-line polarization controller. This approach to the creation of well-defined rotational velocities is also compared to rapid switching between linear and elliptically polarized fields using the same polarization controller.

In optical levitation, a focused, vertically aligned laser beam is used to trap micrometer sized where the photon pressure from the light is balancing gravity. I will in this work review the field by presenting a number of different experiments. I will show how the Foerster Resonance Energy Transfer (FRET) mechanism can be used to track the dynamics of two coalescing glycerol droplets. Second, I will show the directional Mie spectrum of evaporating water droplets arrange in consecutive Fano Combs. This observation is explained by a quantum analogy where the droplet can be seen as an "optical atom" with angular momentum, tunneling, and excited states. Third, I will show how we have used optical levitation to create a single droplet version of Millikan's experiment where the effects of a single electron removal can be observed by the naked eye and measured with a ruler. Finally, I will present our ongoing efforts to trap nanometer sized particles in vacuum and a method to levitate metallic particles.

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. In our lab, we are interested in studying and developing techniques suitable for the stable levitation of optically active nanoparticles, in particular, rare-earth ion activated nanocrystals. These 'smart' nanoparticles enable new modalities, such as monitoring and controlling the internal temperature of the levitated object. We will present experimental results on the internal and motional cooling of these fluorescent nanoparticles and discuss their potential for macroscopic quantum physics.

Optical levitation of dielectric objects in vacuum provides a unique optomechanical platform due to versatile optical control of potentials and good isolation from the environment. Recently, tunable and nonreciprocal optical interactions have been measured between two nanoparticles, levitated in two distinct optical tweezers, with single-site readout of particle motion. I will present our experimental platform for tweezer arrays of nanoparticles, and show our recent results on non-Hermitian collective dynamics of two nonreciprocally interacting nanoparticles. We also observe a mechanical lasing transition once a threshold coupling rate is achieved, supported by our nonlinear theory model. Nonreciprocal interactions are expected to result in an even richer phase diagram of nonequilibrium dynamics for larger arrays of nanoparticles. This work paves the way towards upscaling this platform to such multiparticle arrays, in view of studying their nonequilibrium and collective mechanical behaviour in the quantum regime.

Precise rotation of biological cells plays a pivotal role in in-situ bio-imaging and bioengineering. Here, we propose an integrated platform that enables the rotation of various ellipsoidal cells along their major and minor axes via tailoring the laser patterns and corresponding optothermal fields. Label-free in-situ three-dimensional(3D) imaging of living cells is achieved by 3D reconstruction.

In the field of in vitro fertilisation (IVF), there is a need to understand how cell properties of the cumulus oocyte complex may be used to predict successful pregnancy and live birth rates post-IVF. Here we used optical tweezers for the first time to measure the viscosity of the cumulus cell matrix surrounding the oocyte (egg). This study aimed to determine whether the viscosity of the cumulus cell matrix – prior to fertilisation – is reflective of subsequent embryo developmental potential and indicative of pregnancy success. Measurements were performed using a 1µm diameter silica probe particle trapped by a focused 1064nm laser. We benchmarked the accuracy of the system by measuring the viscosity of glycerol with varying mass fractions. Viscosity measurements of the cumulus cell matrix were performed in isolation from both the cumulus cells and the oocyte. This showed that the viscosity of cumulus matrix was significantly higher when sampled from oocytes with a higher developmental potential (in vivo matured) compared to those of lower quality (in vitro matured).

Living cells are among the most complex systems studied from both biological and physical perspectives. While cell biology has made tremendous advances in understanding the molecular composition of cells, our understanding of the physical characteristics within cells is not as advanced. We use optical tweezer-based active and passive microrheology to characterize the intracellular viscoelasticity and active forces, revealing significant variability in physical properties among different cell types. Furthermore, to facilitate passive microrheology in active systems, we introduce a novel stochastic observable based on a three-point correlations function. We will discuss these innovative approaches and the underlying analysis, which paves the way for a deeper physical understanding of living materials through "feeling" the cells using optical forces.

Biosensing with optically trapped, intracellular nanodiamonds carrying NV-centers, is a promising route for in-cell thermometry and mechano-biology measurements. It requires controlled intracellular uptake of nanodiamonds as well as protocols to ensure stable optical trapping while keeping NV sensing modalities unaffected by the trapping laser. The presentation will discuss both aspects.

How local nonlinear stresses propagate through soft matter systems remains an important open question. Here, I present a powerful approach–Optical Tweezers integrating Differential Dynamic Microscopy (OpTiDDM)–that simultaneously imposes local strains, measures resistive forces, and analyzes the motion of the surrounding polymers. By coupling optical tweezers with fluorescence microscopy, we are able to precisely map the time-dependent deformation fields arising from local nonlinear straining in biopolymer networks and complex fluids. Specifically, we measure the stresses imposed in the fluids by local optically-driven strains, and simultaneously image labeled biopolymers surrounding the strain site. Using DDM, we characterize the macromolecular dynamics and deformation as a function of strain rate and distance from the applied strain. With its robust suite of capabilities, as well as its modular and adaptable design, we anticipate broad interdisciplinary use of OpTiDDM to elucidate non-trivial phenomena that dictate and are impacted by the propagation of local stresses through a system–critically important to commercial materials applications and cell mechanics alike.

Particle uptake is of huge interest in pharmacology and medicine, but a user-controlled uptake of particles into GUVs has been technically demanding. Here, we indent the membrane of differently composed GUVs with optically trapped particles until particle uptake. By continuous 1MHz back-focal-plane interferometric tracking and autocorrelating the particle’s positions within 30µs delays for different indentations, the fluctuations’ amplitude, the damping, the mean forces, and the energy profiles were obtained. The study demonstrates that soft matter can interact completely differently on different temporal and spatial frequency modes, which are excited by the environmental thermal noise.

Integrated optofluidic nanopore sensor technologies have enabled label-free quantification of molecular biomarkers by digital detection of target biomolecules with the electrical translocation signal created during passage through a nanoscale opening. The approach utilizes planar waveguide-based optical trapping combined with a customized microfluidic channel geometry for million-fold target concentration enhancement underneath a nanopore. The optofluidic device design is optimized for better optical trapping performance utilizing both gradient and scattering optical forces. Combined with a target-specific bioassay, this simple, direct, and highly sensitive detection method enables amplification-free and calibration-free biomarker quantification. Using this platform, we show viral load day progression of Zika and SARS-CoV-2 infections from different biofluids in primate models across the clinically relevant concentrations range (five orders) down to 10 aM –comparable to and sometimes improving upon qRT-PCR results. We also report the use of this integrated sensor for extracellular vesicle cargo monitoring from cerebral organoids grown in conditioned media.

Accurate optical trapping and micromanipulation requires sensitive measurements of the position, orientation, and dynamics of the small particles or objects that are under consideration. The signals acquired for the feedback control of these particles and objects are inevitably contaminated by quantum fluctuations and noise that accompany the process of photodetection. In this presentation, we discuss the origins of signal fluctuation and the noise associated with such sensitive measurements.

When light, or electromagnetic radiation, impacts a surface, it generates a force known as radiation pressure. In this study, we explore the radiation pressure generated by a finite, structured light beams and how it differs from that of a plane wave at an identical frequency. A notable characteristic of structured beams, especially as they pass through their focal point, is the accumulation of an extra phase shift, unlike a plane wave traveling the same distance. This phenomenon, known as the Gouy phase, underpins the difference in radiation pressure that we observe. One case we focus on is for Laguerre-Gaussian modes, and we detail specific experimental approaches to quantify the variance in radiation pressure, which amounts to approximately 20fN/W for each unit of orbital angular momentum.

In this work we theoretically and experimentally study the the induction of electromagnetic forces in three-dimensional photonic crystals when light impinges normally onto an assembly of SiO2 spheres known as artificial opals infiltrated with Fe3O4 nanoparticles.

Often beams, such as optical bottle beams (OBBs), possess rotational asymmetry, or other defects in the beam's intensity distribution. These beams are often due to nodal surfaces formed by the discontinuous phases which are typically necessary for the beam's unique intensity distribution. But must this always be the case? We use a combination of computational modeling with novel phase retrieval techniques and polarization-dependent vector wavefront shaping to explore the creation of computer-generated holographic beams. We discuss how to apply this method to creating obscured beams, such as uniformly enclosed optical bottle beams. and the properties these types of beams possess.

Optical trapping relies on the momentum transfer from light to trapped particles to exert force and torque. Leveraging holographic principles, we extract phase and amplitude information from a single far-field interference pattern of the trapping beam. This approach provides comprehensive insights into all individual components of optical force and torque. Through optimized computational analysis, we enable real-time measurements, paving the way for enhanced experimentation in optical trapping studies.

Constant magnetic fields are known to interact with electrically charged particles inducing Lorentz forces that point in a direction perpendicular to the field. However, if the particle is electrically discharged, it is impossible to induce a force using a constant magnetic field. An exotic option is to mimic a magnetic charge on a neutral particle. This false magnetic monopole will interact with the magnetic field just as an electric charge would do with an electric field through the Coulomb interaction. Attempts to generate this magnetic charge have mainly relied on quasiparticles generated using condensed matter spin ice networks. In this work we present another option based on neutral magneto-optical particles illuminated by a spinning monochromatic light field. We will analyze the behavior of these particles under different isotropic optical configurations, and we will calculate the value of the induced magnetic charge.

Since Ashkin's early work on optical tweezers, theoretical models and computational methods have been developed to characterize the optical trapping behavior of spherical and some non-spherical symmetric particles. However, actual particles frequently have asymmetric or non-spherical shapes. In this study, we present experimental data and statistical assessments of the optical trapping stability of various microplastic materials, colors, sizes, and shapes, as well as responses for different optical trapping wavelengths. This research is based on an analysis of over 600 unsymmetric lab-made microplastic particles.

Freely propagating optical skyrmions may be generated from combinations of vector beams with orthogonal polarisation states to form both Néel (hedgehog) and Bloch (spiral) types. Constructions are possible using both paraxial and focussed Laguerre Gaussian beams. Here we simulate beams with different skyrmion numbers and calculate the optical forces and torques exerted on different types of particle. Dynamic behaviour will be simulated and potential applications discussed.

When an intense laser interacts with a gas of atoms, high-order harmonics are generated. In the time domain, this radiation forms a train of extremely short light pulses, of the order of 100 attoseconds. Attosecond pulses allow the study of the dynamics of electrons in atoms and molecules, using pump-probe techniques. This presentation will highlight some of the key steps of the field of attosecond science.

Nanometer-scale liquid droplets are of considerable interest across a wide range of interdisciplinary fields, including materials science, pharmaceutical processing, and nano-medical technologies, due to their potential applications in these areas. The conventional methods for generating and transporting these minuscule droplets have predominantly relied on mechanical pressurization and electric field-assisted techniques. However, these methods, while effective, often face limitations in terms of precision and control at the nanoscale. In response to these challenges, this invited paper introduces an innovative approach to liquid manipulation that utilizes the precise control capabilities of light momentum and energy. This method represents a significant departure from traditional techniques, offering a novel paradigm for the manipulation of liquid at the nanometer scale. The focus of this presentation will be on the recent experimental work conducted in the speaker's laboratory, which has successfully demonstrated the formation and ejection of liquid droplets from a specialized hollow optical fiber using continuous wave (CW) light at milliwatt (mW) power levels.

In this paper, we present an innovative optofluidic system that leverages cascaded bowtie photonic crystal (BPhC) to achieve subwavelength-scale control of temperature and fluid motion. The strong electromagnetic field enhancement of the bowtie structure can generate a hotspot at the resonance of BPhC, due to the absorption of bulk water in the infrared wavelength range (around 1600 nm). With the assistance of a cationic surfactant, cetyltrimethylammonium chloride (CTAC), a thermoelectric field is established to attract particles towards the hot region. Our experiments show that suspended particles as small as 800 nanometers can be rapidly transported to bowtie region and become trapped at the bowtie cavity on the resonance of BPhC. The trapped particles can be released simply by tuning the wavelength from on to off resonant conditions. Our work paves the way for non-plasmonic nanophotonics to manipulate microfluidic dynamics and precisely control trapping by tuning the wavelength

Optothermal and optofluidic manipulation have been proven successful tools to precisely steer the motion of particles, cells and biomolecules using a combination of optical, thermal and hydrodynamic forces. Here, we show that a proper 3D engineering of thermal landscapes induces short- and long-range microfluidic flows to guide, trap and sort microparticles. By alternating between different patterns of illumination over time, various types of microfluidic actuators are created such pumps, traps, and valves, all within a single chip environment.

Here, we present a versatile state-of-the-art toolbox for performing integrated optical tweezers-confocal scanning microscopy measurements, including: 1) the preparation of protein:DNA complex samples; 2) design of a microfluidic flow cell incorporated with optical tweezers; 3) automation of optical tweezers-confocal scanning measurements, and 4) the development and implementation of a streamlined data analysis package for force and fluorescence spectroscopy data processing. This toolbox will facilitate single-molecule optical tweezers-fluorescence spectroscopy studies on a large variety of biological systems, and improve the reproducibility and quality of such measurements.

This study introduces an innovative methodology that merges quantitative imaging techniques with laser-induced shockwaves (LIS) to examine astrocyte morphological changes in response to shear stress. Leveraging quantitative phase microscopy (QPM) enables comprehensive label-free 3D imaging and real-time monitoring of cellular dynamics. Quantitative analysis post-LIS exposure reveals significant changes in astrocyte circularity, volume, surface area, and other cell features. These statistics provide insight into mechanical stimulus-induced morphological transformations of the astrocytes. This study’s research enhances understanding of astrocyte reactivity to shear stress, opening the doors for targeted therapeutic interventions of TBI and related neurological disorders.

Mechanical forces play a pivotal role in cellular adhesions, where a vast array of proteins interacts with the cell cytoskeleton, affecting focal adhesions and adherens junctions, and regulating cell behavior and fate. To directly observe such events, we developed an experimental assay that combines several advanced single molecule techniques. Here, ultrafast force-clamp spectroscopy is employed to directly probe the force-dependence of molecular interactions between a single actin filament and a binding protein with sub-ms time resolution. Stabilization of the microscope through local gradient localization enables the resolution of protein conformational changes and binding position with sub-nm accuracy. An experimental arrangement, termed oriented dumbbell, allows us to determine the actin filament orientation and, thus, asymmetries in the force response of the interacting proteins. We applied our methodology to the interaction between α-catenin and F-actin, revealing that α-catenin switches between a slip and an asymmetric cooperative catch-bond with F-actin. This mechanism may underlie fluid-to-solid phase transitions that occur at the membrane-cytoskeleton interface.

Laser-based techniques offer powerful tools for studying the complex cellular mechanisms underlying neurodegeneration and neuroprotection. Laser scissors enable the precise induction of axonal injury, allowing investigation into axonal degenerative processes and evaluation of potential neuroprotective treatments. Laser scissors can also be utilized to kill a single cell and monitor the response in nearby astrocytes. For example, using this method, we found that a single-cell death can be disruptive to spontaneous calcium activity in surrounding cells. Additionally, focused lasers can be utilized to induce cavitation bubbles that produce shockwaves and subject cells to conditions like those experienced during a blast-induced traumatic brain injury. This allows us to have a window into the immediate cellular responses to traumatic brain injury and investigate potential mechanisms that may be targeted to mitigate damage. Laser-induced shockwaves have allowed us to study calcium signaling in response to nearby injury and determine that the

T cell clones can exhibit varying potencies towards their cognate peptide major histocompatibility complex molecule (pMHC), which may not be seen in traditional bulk assays. Performing single molecule and single cell experiments, including profiling through Single Cell Activation Requirements allow for further discrimination and selection of the highest quality clones. Using these techniques will help reveal how T cells function and advance screening methods for selecting the best T cells to use therapeutically.

We use a combination of optical trapping, microfluidics, and fluorescence microscopy to track individual, motile E. coli cells during infection by fluorescently labeled bacteriophages. Dual-trap optical tweezers immobilize swimming cells in a flow chamber, into which phages can be perfused. We measure the absorption of phages onto the cell surface with fluorescence imaging, while simultaneously monitoring the cell’s flagellar rotation with the optical traps. Utilizing the flagellar rotation frequency as a proxy for proton motive force, we examine phage-induced changes to E. coli’s membrane potential. These measurements reveal perturbations to host membrane integrity by phage attachment, followed by its recovery. This technique allows us to illuminate for the kinetics of viral infection of cells at the level of individual phages and bacteria.

We investigate the thermalization of two colloidal suspensions in diffusive contact driven by random forces created with holographic optical tweezers. The effective temperature exhibits non-monotonic behavior with the switching frequency and adheres to the static fluctuation-dissipation relation only at high frequencies. By independently driving each side of the sample, we create two systems in contact, observing particle flow. Arrest of particle flow occurs when the chemical potential to effective temperature ratio is equal on both sides, as expected in thermal equilibrium.

Active matter is a term encompassing particle-based assemblies with some form of self-propulsion, including certain biological systems as well as synthetic systems such as artificial colloidal swimmers, all of which can exhibit a remarkable variety of new kinds of nonequilibrium phenomena. A wealth of non-active condensed matter systems can be described in terms of a collection of particles coupled to periodic substrates, leading to the emergence of commensurate-incommensurate effects, Mott phases, tribology effects, and pattern formation. It is natural to ask how such phases are modified when the system is active. Here we provide an overview and future directions for studying individual and collectively interacting active matter particles coupled to periodic substrates, where new types of commensuration effects, directional locking, and active phases can occur. Further directions for exploration include directional locking effects, the realization of active solitons or active defects in incommensurate phases, active Mott phases, active artificial spin ice, active doping transitions, active floating phases, active surface physics, active matter time crystals, and active tribology.

In counter propagating plane waves, spherical beads occupy the interference fringes and optically bind with separations of around a wavelength. The binding strength depends on particle size and refractive index with the particle arrangement also dependent on the polarisation. Some combinations of refractive index and size do not optically bind: instead, the particles experience a force in the propagation direction that leads to a transition to longitudinal binding. These instabilities are assessed computationally with different particle numbers and polarisation states.

Active matter is based on the concepts of nonequilibrium thermodynamics applied to the most diverse disciplines. Active Brownian particles, unlike their passive counterparts, self-propel and give rise to complex behaviors distinctive of active matter. As the field is relatively recent, active matter still lacks curricular inclusion. Here, we propose macroscopic experiments using Hexbugs, a commercial toy robot, demonstrating effects peculiar of active systems, such as the setting into motion of passive objects via active particles, the sorting of active particles based on their mobility and chirality. Additionally, we provide a demonstration of Casimir-like attraction between planar objects mediated by active particles.

Optical nanotweezers are actively investigated as a powerful means to reversibly trap and study the properties of nanoscale biological objects and nanoparticles. To ensure that the objects can be reversibly trapped and released on demand, while also preventing undesired adsorption onto surfaces, surface passivation is of paramount importance. Although the surface chemistries examined in this study hold broad applicability across diverse nanotweezing platforms, our investigation primarily focuses on the newly reported Geometry-induced Electrohydrodynamic Tweezers (GET) as the nanotweezing platform. Geometry-induced electrohydrodynamic tweezer (GET) is a scalable and high-throughput technique for trapping and manipulating nanoscale objects. Here, we are investigating the antifouling properties of a GET nanotweezer passivated with Poly(ethylene glycol) methyl ether thiol (PEG), (1-Mercaptoundec-11-yl)tetra(ethylene glycol) (OEG), 11-Mercaptoundecanoic acid (MUA) and 1-Mercapto-11-hydroxy-3,6,9-trioxaundecane (DMOL). The confirmation of the passivated surfaces' wettability and the SAM vibrational properties is achieved through contact angle analysis and FTIR spectroscopy respectively.

Leveraging temperature fields in optical manipulation technology offers efficient energy usage and expanded capabilities for particle manipulation, surpassing conventional methods' limitations. Recent advancements in optical tweezers and biomedical research have propelled the development of an innovative nano-tweezing system driven by temperature fields. The highly adaptable optothermal nanotweezer (HAONT) traps, sorts, and assembles diverse nanoparticles. HAONT capitalizes on thermophoresis and thermo-osmotic flow, enabling manipulation and identification of bio-nanoparticles sized 10 nm to 1000 nm. Integrated with CRISPR biosensing systems, HAONT enhances single-nucleotide polymorphism (SNP) detection and introduces a novel CRISPR methodology for nucleotide cleavage observation. Refinement of this technology promises enhanced biomolecule capture, in-situ single-molecule analysis, and significant contributions to biomedical research advancement.