We have constructed an integrated optical fiber tweezers (OFTs) platform based on double-core fibers (DCF) and Coreless fiber (CF), which is designed for trapping multiple particles. In this configuration, the DCF-guided LP<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> mode generates two mirror-symmetric Bessel-like beams within the CF. These beams form multiple independent optical potential well arrays at the end face of the CF. Using this OTFs, we successfully achieved stable trapping of three yeast cells. Furthermore, through precise optical power control, we demonstrated the trapping and dynamic rearrangement of three yeast cells.

Voltage sensor with tunable sensitivity and measurement range based on optical tweezers trapping magnetic microparticles

Analysis of optical tweezers single-molecule force spectroscopy based on a signal-enhanced denoising model

Active colloids that convert light into motion provide insight into nonequilibrium chemical systems and routes toward microscale engines. Here we quantify the propulsion dynamics and force generation of light-activated Au-TiO2 Janus particles and their optically trappable polystyrene (PS) core-shell Au-PS@TiO2 analogues. By varying particle size, metal thickness, fuel concentration, and illumination wavelength, we show how photochemical energy conversion at the Au-TiO2 interface governs propulsion, yielding average velocities 33.2 ± 2.99 μm s-1 with instantaneous velocities up to ∼100 μm s-1. Optical tweezers measurements on single Au-PS@TiO2 Janus particles reveal transient propulsion forces with a median of 4.5-6.2 pN lasting on average 21-41 ms and reaching up to 20 pN under optical confinement. Simulations incorporating these transient forces reproduce the observed trajectories, confirming their role in driving active motion. Functionalization with long DNA polymers further enhances directional motion by reducing rotational diffusion. These results establish a single-particle framework for quantifying active forces in photocatalytic Janus particles and offer design principles for light-powered micromotors.

The green alga Chlamydomonas reinhardtii (CR) has been explored as the live component of biohybrid microrobots due to its intrinsic motility. However, cell performance depends on physiological state, which evolves with culture age. Using optical tweezers, we quantify the rotational dynamics of individual CR cells across lag, exponential, stationary, and death phases. We reveal a clear performance trajectory: rotation speed and corresponding hydrodynamic torque peak during the mid-exponential phase and decrease as cultures mature. Additionally, counterclockwise rotation consistently generates higher hydrodynamic torque than clockwise rotation. These findings provide quantitative benchmarks linking CR's motility characteristics to growth phase, offering guidelines for designing living micromachines and establishing rotational dynamics as a sensitive proxy for cellular metabolic health.

ABSTRACT Artificial molecular machines often rely on chemical stimuli to switch between functional states, yet the real‐time dynamics of these transitions remain largely obscured by ensemble averaging. We describe the real‐time single‐molecule tracking of a Diels–Alder reaction that irreversibly alters the co‐conformational space of a two‐station [2]rotaxane. By tethering individual shuttles in optical tweezers, we observe the transformation of a fumaramide binding site into a non‐binding adduct in an aqueous environment. This covalent modification triggers a brisk shift in the macrocycle's positional preference, effectively erasing the thermodynamically favored state and leaving the secondary succinic amide‐ester station as the sole anchoring site. Our analysis allows us to reconstruct the energy landscape before and after the chemical event, revealing that the transformation reshapes the thermodynamic potential without measurably perturbing the intrinsic kinetics. This study highlights the potential of force spectroscopy for the in‐situ characterization of chemically driven changes in the function of individual molecular devices.

Artificial molecular machines often rely on chemical stimuli to switch between functional states, yet the real-time dynamics of these transitions remain largely obscured by ensemble averaging. We describe the real-time single-molecule tracking of a Diels-Alder reaction that irreversibly alters the co-conformational space of a two-station [2]rotaxane. By tethering individual shuttles in optical tweezers, we observe the transformation of a fumaramide binding site into a non-binding adduct in an aqueous environment. This covalent modification triggers a brisk shift in the macrocycle's positional preference, effectively erasing the thermodynamically favored state and leaving the secondary succinic amide-ester station as the sole anchoring site. Our analysis allows us to reconstruct the energy landscape before and after the chemical event, revealing that the transformation reshapes the thermodynamic potential without measurably perturbing the intrinsic kinetics. This study highlights the potential of force spectroscopy for the in-situ characterization of chemically driven changes in the function of individual molecular devices.

ConspectusPolydiacetylene (PDA) is widely used in chromic sensing because it converts a broad range of stimuli into large, easy-to-read color and fluorescence changes. These responses have been extensively studied across diverse material formats, including nanovesicles, thin films, and fibrous assemblies, where chromism is typically interpreted in terms of stimulus-induced distortion of the conjugated backbone and headgroup packing. In this Account, we focus on microscale PDA particles produced by emulsion-based or microfluidic approaches. These particles are characterized by a polymerized outer layer that encloses an internal domain rich in unpolymerized diacetylene (DA) monomers, arising from the finite penetration depth of UV-induced polymerization. This structural feature introduces an additional chemical dimension to PDA chromism. Under solvent or thermal stimuli, these monomers can dissolve, migrate, and polymerize, creating a monomer-driven reconfiguration pathway involving dynamic structural rearrangement that complements conventional backbone-distortion chromism and enables chromic behavior with new forms of structural and optical response.This Account takes a single-particle view of PDA chromism and shows how that hidden monomer reservoir can be turned into a design feature. Using optical tweezers, we place individual PDA microparticles at controlled fluid-fluid interfaces and follow, in real time, how solvent infiltration generates chromic fronts and internal voids within one particle rather than across an ensemble. These experiments connect capillarity, particle topology, and chromic response, and they reveal how residual monomer participates in the restructuring. Mechanical inputs can likewise be read at the level of a single particle: a fluorogenic PDA sphere trapped in a stenosis-mimicking microchannel integrates shear and impact events into a mechanofluorescent signal, distinguishing viscous loading from discrete collisions of nanoparticles, red blood cells, or yeast.Building on these mechanistic insights, we design PDA particle architectures that deliberately use monomer mobility, confinement, and interfacial control. Core-shell PDA@PDMS particles contain a PDA core that houses a reservoir of unpolymerized PCDA, surrounded by a permeable PDMS shell. Upon solvent exposure, PCDA dissolves and diffuses into the PDMS layer, and subsequent UV-induced polymerization converts the migrated monomer into new blue phase PDA domains in both the core and shell. This solvent-driven monomer redistribution and polymerization constitute a reconfiguration process that yields semireversible, dual-region chromic signatures, enabling discrimination of even closely related organic solvents. Thermally driven reorganization at tuned interfacial tension produces Janus PDA microparticles whose two lobes, shaped by distinct monomer histories, respond differently to heat and solvent, enabling directional and ratiometric sensing. A gas-shearing microfluidic platform encapsulates PDA in alginate, producing monodisperse, biocompatible beads with strong polarity-selective solvatochromism.Together, these systems illustrate how a dynamic monomer reservoir, coupled with confinement and interface engineering, links molecular-scale reconfiguration to device-level performance. The single-particle PDA platform developed here offers practical molecular insight into chromic behavior in particulate systems and provides a foundation for designing semireversible, directional, and tunable sensors. These concepts may also be adaptable to other chromic conjugated polymers.

Halloysite nanotubes (HNTs), naturally occurring aluminosilicates with a tubular structure, are promising nanocarriers for drug delivery due to their biocompatibility and unique morphology. However, their interaction with lipid membranes remains not fully explored. In this work, we aim at elucidating on the adhesion of HNTs on unilamellar vesicles made of phospholipids used as model of biological membranes. The adhesion was modulated by varying the lipid composition, ionic strength, and the size ratio between HNTs and vesicles. The adhesion mechanism was also studied by trapping a single HNT with optical tweezers and let it interact with a single vesicle. These findings show a preferential adhesion of the HNT tip on the lipid bilayer, which represents an important step toward directional membrane targeting in biomedical applications.

Exposure to various environmental factors and endogenous agents can lead to double-strand DNA breaks. Bacteria are capable of restoring their genome integrity through a process known as the SOS response, which requires the RecA recombinase. Another protein critical for DNA repair is SMC-like RecN, which facilitates the location of the homologous DNA template by RecA. At present, the function and underlying mechanisms of RecN remain poorly understood. In this work, we use optical tweezers to demonstrate predominant binding of RecN to ssDNA and also show weak binding to dsDNA, resulting in a condition resembling DNA loop formation.

Viruses are complex supramolecular assemblies that propagate their genetic material from cell to cell, thereby relying on host cell mechanisms. Employing a combination of passive and active strategies, they efficiently package, transport and release nucleic acids. While structural and biochemical techniques offer insights into certain, static aspects of the viral life cycle, recent advancements in biophysical approaches now allow for direct measurement of their inherent dynamic activities in the research field commonly referred to as physical virology. One of these methods is optical tweezers, enabling the precise measurement of force and position at the single-molecule level over time. Over the past decades, the ability to optically trap beads and to manipulate biomolecules has revolutionised medical and biophysical research. In this paper, we provide a comprehensive analysis of optical tweezers, exploring its integration with imaging modalities and review its diverse applications in the study of viruses and viral components. In particular we focus on studies that use optical tweezers to study virus-cell interactions, genome packaging using molecular motors and co-assembly of viral assembly proteins with their nucleic acid.

ABSTRACT Purpose The migration and fusion of osteoclast precursors (OCPs) are critical steps in osteoclastogenesis and require substantial energy. Although oxidative phosphorylation (OXPHOS) is generally considered the major pathway supplying energy for these processes, it remains unclear how inhibiting OXPHOS affects the migration of OCPs. Materials and Methods To investigate the metabolic regulation of osteoclast migration, we used a recognized OXPHOS inhibitor rotenone to suppress the key energy-producing pathway in OCPs. We combined this intervention with bioinformatics approaches and machine learning algorithms to screen and identify genes associated with osteoclast dysfunction in patients with osteoporosis. The migratory capacity of OCPs was precisely quantified using optical tweezers. Results We found that rotenone inhibited osteoclastogenesis and markedly impaired the migratory capacity of OCPs. Although the level of OXPHOS in OCPs decreased, intracellular ATP content paradoxically increased, suggesting that the impairment of migratory capacity is unlikely to be driven by an overall energy shortage. Through machine learning algorithms, we identified genes associated with abnormal osteoclast function in patients with osteoporosis and discovered their critical regulatory roles in processes such as cell migration, adhesion, and OXPHOS. Rotenone significantly suppressed the expression of these genes in OCPs, suggesting a direct mechanism for the impaired migration. Conclusions In summary, our study reveals a novel mechanism for rotenone-induced inhibition of osteoclastogenesis, which is achieved by impairing the migration of OCPs in a manner uncoupled from overall energy status.

The protein corona redefines interfacial identity and dictates subsequent biological responses of nanoparticles. Nevertheless, the thermodynamic principles governing its formation and spatiotemporal evolution at the single-particle level remain poorly resolved. To address this, we developed an integrated surface plasmonic imaging and optical tweezing platform for real-time, label-free tracking of protein corona assembly on individual Au nanoparticles (AuNPs). By precise modulation of local temperature and pH, we demonstrated that corona formation can be energetically driven by minimization of interfacial free energy and coupled with protein molecule rearrangements. Kinetic analyses revealed distinct adsorption mechanisms: bovine serum albumin (BSA) followed Lagergren pseudo-first-order kinetics, whereas tetrameric hemoglobin (Hb) exhibited pseudo-second-order behavior, reflecting differences in molecular packing and structural stability. Furthermore, single-molecule fluctuation dissection of IgG/anti-IgG interactions revealed that the protein corona significantly quenched thermal fluctuations and restricted configurational transitions.

We synthesized two types of conjugated polymeric nanoparticles(CPNs), made with MEH-PPV (poly­[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene])and PFD (poly­(9,9-di-n-dodecyl fluorenyl-2,7-diyl)), that significantlyinteract with double-stranded DNA. The binding between these nanostructuresand the biopolymer was characterized via single-molecule force spectroscopyassays performed by optical tweezers and by direct visualization viaatomic force microscopy imaging. The results show that both typesof CPNs bind cooperatively outside the double helix, inducing bending,and with a considerably high equilibrium association constant, onthe order of 106 M–1. We thus demonstratethat conjugated polymeric nanostructures can strongly and cooperativelyinteract with double-stranded DNA using single-molecule force spectroscopy.These interactions may represent promising long-term perspectivesfor applications in DNA nanotechnology and functional nanomaterials,such as the design of DNA-based nanodevices and the development ofnew drug carriers based on functionalized nanoparticles for cancerchemotherapies, to cite a few.

We investigated the interaction between the monocationic aromatic drug propranolol (PPL) and double-stranded DNA (dsDNA) to elucidate how small molecules can drive higher-order DNA frameworks and nanoparticles (NPs) formation. Single-molecule force spectroscopy with optical tweezers revealed that, at concentrations below 4 mM, PPL interacts with dsDNA through an intercalation-like mode, altering contour length, persistence length, and stretch modulus. At higher concentrations, PPL induced dsDNA compaction, corroborated by atomic force microscopy imaging of condensed structures. Multimolecular assays supported these findings: electrophoretic mobility shift assays revealed progressive mobility loss with increasing PPL concentrations, consistent with aggregate formation, while UV-vis spectroscopy confirmed intercalation-like behavior and strong binding affinity (Kb=1.67 × 10⁶ M⁻¹). At millimolar PPL/DNA ratios (10-14), NPs formulations were obtained with hydrodynamic diameters of 120-244nm, low polydispersity (0.19-0.30), negative zeta potential (-25 to -35 mV), and particle concentrations up to 5.26 × 10¹¹ NPs/mL. These NPs exhibited very high drug loading (59-72%) and stability under both biological and storage conditions. Collectively, our results demonstrate that PPL engages dsDNA through intercalation-like behavior, compaction, aggregation, and stabilization processes, uncovering a previously unreported mechanism for a monocationic aromatic drug and allowing the efficient formation of NPs. This work expands the current understanding of small molecule-DNA interactions and may be extended to other hydrophilic aromatic drugs, positioning DNA as a versatile building block and ultimately for the development of nucleic acid-based nanomedicines.

DNA ends generated by double-strand breaks are vulnerable intermediates that must be rapidly recognized, protected, and resolved to preserve genome integrity. We present optical tweezers (OT)-Curtains, a single-molecule method inspired by DNA curtains that uses a custom branched DNA substrate containing multiple accessible ends for simultaneous observation on dual-trap OT coupled to confocal fluorescence microscopy. Eliminating DNA surface anchoring, facilitating rapid protein and buffer exchange, and offering the possibility for force-free experiments, OT-Curtains overcomes common limitations of flow-stretch-based methods. OT-Curtains allows real-time visualization and quantification of end recognition, protection, resection, and cleavage at several DNA ends in parallel. We demonstrate compatibility with well-studied DNA-binding systems by monitoring Ku-mediated DNA break recognition, AddAB-mediated DNA break resection, ParB-mediated DNA condensation, and KpnI-mediated DNA cleavage. We show that kinetic and mechanistic parameters can be extracted from the data under defined forces and solution conditions. OT-Curtains offers an accessible and multiplexed route to interrogate DNA-end transactions central to double-stranded DNA break repair pathways and telomere biology, as well as a general framework for benchmarking proteins acting at DNA ends.

We present a quantitative investigation of one- and two-body light-mediated processes that occur to few erbium atoms in an optical tweezer, when exposed to near-resonant light. In order to study the intertwined effects of recoil heating, cooling, and light-assisted collisions, we develop a first-principles Monte Carlo algorithm that solves the coupled dynamics of both the internal and external degrees of freedom of the atoms. After validating our theoretical model against experimental data, we use the predictive power of our code to guide our experiment and, in particular, we explore the performance of different transitions of erbium for light-assisted collisions in terms of their efficiency and fidelity for single-atom preparation.

Abstract Optical tweezers are widely used in biophysics to trap and manipulate microscopic particles and enable precise measurements of forces, diffusion, and mechanical properties at the single-particle level. In this project, we modeled the stochastic dynamics of asymmetric particles in optical tweezers using an overdamped Langevin equation that included a full translational-rotational (TR) diffusion tensor. We performed numerical simulations for particles of increasing geometric complexity and reconstructed diffusion tensors from simulated average trajectory data. We compared the reconstructed tensors to the true inputs and computed the resulting estimation error. The simulations showed that increasing particle asymmetry strengthened TR coupling and systematically increased diffusion tensor reconstruction error. These results suggest limitations of diffusion-based inference methods for complex particle geometries and motivate further study of how particle geometry influences stochastic dynamics in confined optical systems. Lay Summary At microscopic scales, particles in a fluid constantly undergo seemingly random movement, called Brownian motion, as they collide with surrounding molecules. Because shape influences drag, and drag determines diffusion, motion should carry geometric information. We therefore asked: Can motion alone be used to determine a particle’s geometry? To investigate this, we built a computational model of a particle confined in an optical tweezer, which is a tightly focused laser beam used to trap microscopic objects. Optical tweezers were recognized with the 2018 Nobel Prize in Physics and are widely used in biophysics and medical research to manipulate cells, bacteria, and molecules. They are also widely used in research laboratories such as JILA. By assuming the restoring force increases linearly with distance from the trap center, we were able to isolate how shape influences motion. For a sphere, which is symmetrical in every direction, movement along one axis does not affect movement along another. For more complex shapes, rotation and translation become linked: turning slightly can produce sideways motion. We implemented a model that accounts for both the restoring force and Brownian motion and can be applied to particles of any shape. Using this framework, we simulated shapes based on real bacteria – a sphere, a rod, a comma-shaped form, and a spiral – and tracked motion inside the trap. From trajectories alone, we inferred the component of the particle’s motion determined by its shape and compared it to the values we had built into the model. Our results showed that a particle’s movement contains information about its shape. For simple particles, recovery was accurate. As shapes became more irregular, estimates became less reliable. We also observed a tradeoff introduced by the optical trap: while it confines motion and enables experimental measurement, it also limits the natural motion that reveals geometric differences.

Breast cancer cells experience distinct mechanical forces within the 3D tumor microenvironment, and these forces strongly influence cell behavior, invasion potential, and treatment response. While conventional two-dimensional culture systems offer experimental simplicity, they fail to reproduce the complex mechanical interactions present in vivo, which play an important role in the development of therapeutic resistance. In this work, we investigate the mechanical properties of breast cancer cells grown under both 2D and 3D conditions using dual-beam optical tweezers. Our measurements show that cells cultured in 3D exhibit lower deformability compared with cells cultured in 2D, consistent with the increased physical confinement imposed by a physiologically relevant extracellular matrix. These biomechanical differences correlate with cellular plasticity and drug resistance mechanisms previously observed in 3D cultures. The findings emphasize the critical role of mechanical forces in the tumor microenvironment and highlight the limitations of 2D models for studying cancer cell mechanics. Incorporating biomechanical context using 3D culture systems may therefore provide a more accurate understanding of tumor progression and therapeutic responses.

Microorganisms represent the Earth's most abundant biomass and a vast reservoir of genetic diversity. However, traditional agar plate methods fail to recover the vast majority of these species, leaving a "microbial dark matter" that holds immense potential for the discovery of novel antibiotics and bioactive compounds. While conventional techniques such as selective media and enrichment culture remain foundational, they are inherently limited by community biases and the inability to support low-abundance, oligotrophic species. To address these bottlenecks, a diverse array of innovative isolation strategies has emerged. This review systematically categorizes and evaluates these methodologies, ranging from in situ cultivation to high-resolution single-cell manipulation. We first examine membrane diffusion-based cultivation (e.g., iChip), which mimics natural microenvironments to resuscitate recalcitrant microbes. Subsequently, we explore high-throughput single-cell technologies, including microfluidics for physicochemical separation, optical tweezers for precise manipulation, and fluorescence-activated cell sorting (FACS). Special attention is given to Raman-activated cell sorting (RACS) as a label-free functional screening tool and reverse genomics for targeted capture. By synthesizing the strengths and limitations of these approaches, we propose integrated workflows designed to accelerate the mining of untapped microbial resources.