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Most laser applications are based on the focusing of a Gaussian laser beam (GLB). When the latter is subject to a phase aberration such as the optical Kerr effect (OKE) or spherical aberration (SA), it is recognised that the focusing performance of the GLB is degraded. In this paper, it is demonstrated that high-order radial Laguerre–Gauss LGp0 beams are more resilient than the GLB when subject to the OKE or SA. This opens up opportunities to replace with advantages the usual GLB with a high-order LGp0 beam for some applications.

A major challenge in cancer prognostics is finding early biomarkers that can accurately identify cancer. Circulating tumor cells are rare and circulating tumor DNA can not provide information about the originating cell. Extracellular vesicles (EVs) contain cell specific information, are abundant in fluids, and have unique properties between cancerous and non-cancerous. Fluorescence measurements have limitations from intrinsic fluorescent background signals, photobleaching, non-specific labelling, and EV structural modifications. Here, we demonstrate a label-free approach to classification of 3 different EVs, derived from non-malignant, non-invasive cancerous, and invasive cancerous cell lines. Using double nanohole optical tweezers, the scattering from single trapped EVs is measured, and using a 1D convolutional neural network, we are able to classify the time series optical signal into its respective EV class with greater than 90% accuracy.

In this article, we explore the effect of two different infrared (IR) laser wavelengths on the optical properties of trapped nano-diamonds containing high-density ensembles of nitrogen vacancy (NV) centers. We investigate 975 nm and 1064nm wavelengths for trapping lasers and find that NV photoluminescence quenching is more prominent for 1064nm illumination than for 975 nm illumination when simultaneously excited with a 532 nm laser. In order to understand the underlying mechanism, we develop a rate-equation-based model that takes into account various transition probabilities. The model suggests that the findings cannot be explained only by imposing modification of the NV charge-state ratio under varied illumination wavelengths, and, thus, we speculate that the effective ionization and recombination rates associated with NV charge states for the studied samples are highly wavelength-dependent in the probed regime. Importantly, the results demonstrate that 975 nm laser is desirable for optical trapping of NV-diamonds, especially for NV-based sensing applications.

Chloroquine has been used as a potent antimalarial, anticancer drug, and prophylactic. While chloroquine is known to interact with DNA, the details of DNA–ligand interactions have remained unclear. Here we characterize chloroquine–double-stranded DNA binding with four complementary approaches, including optical tweezers, atomic force microscopy, duplex DNA melting measurements, and isothermal titration calorimetry. We show that chloroquine intercalates into double stranded DNA (dsDNA) with a KD ~ 200 µM, and this binding is entropically driven. We propose that chloroquine-induced dsDNA intercalation, which happens in the same concentration range as its observed toxic effects on cells, is responsible for the drug’s cytotoxicity.

Optical tweezers (OT), or optical traps, are a device for manipulating microscopic objects through a focused laser beam. They are used in various fields of physical and biophysical chemistry to identify the interactions between individual molecules and measure single-molecule forces. In this work, we describe the development of a homemade optical tweezers device based on a cost-effective IR diode laser, the hardware, and, in particular, the software controlling it. It allows us to control the instrument, calibrate it, and record and process the measured data. It includes the user interface design, peripherals control, recording, A/D conversion of the detector signals, evaluation of the calibration constants, and visualization of the results. Particular stress is put on the signal filtration from noise, where several methods were tested. The calibration experiments indicate a good sensitivity of the instrument that is thus ready to be used for various single-molecule measurements.

For enhanced energy utilization with improved flexibility and capability for object manipulation, a focused acoustic vortex (FAV) is devised by installing a spherical acoustic lens on a circular array of planar sector transducers. Based on the acoustic refraction of a concave spherical acoustic lens, numerical simulations show that an FAV with considerable pressure gain and strengthened acoustic gradient force (AGF) can be produced by the effective concentration of acoustic waves. The performance of rotational object trapping is shown by the axial and radial distributions of the AGF for FAVs of different orders. Elastic objects of nanometer, micrometer, millimeter, and even larger-than-wavelength size can be captured with the trapping radius determined by the topological charge. With the established 16-channel experimental system, FAVs of different orders are verified by their clear pressure circles and phase spirals. The trapping radius and rotation speed of object capture are demonstrated using polyethylene particles of various sizes and FAVs of different orders. The favorable results provide an experimentally applicable method of FAV generation using the simplified circular transducer array to accomplish more accurate, stable, and flexible object manipulations with strengthened AGFs. Also, FAVs could offer an efficient means of high-intensity focused ultrasound therapy to improve the therapeutic effect of tumor treatments by accumulating drug particles, thereby enabling more potential applications in clinical practice. [ABSTRACT FROM AUTHOR]

Identification of defective DNA structures is a difficult task, since small differences in base-pair bonding are hidden in the local structural variability of a generally random base-pair sequence. Defects, such as base mismatches, missing bases, crosslinks, and so on, occur in DNA with high frequency and must be efficiently identified and repaired to avoid dire consequences such as genetic mutations. Here, we focus on the detection of base mismatches, which is local deviations from the ideal Watson–Crick pairing rule, which may typically originate from DNA replication process, foreign chemical attack, or ionizing radiation. Experimental detection of a mismatch defect demands the ability to measure slight deviations in the free energy and molecular structure. We introduce different mismatches in short DNA hairpins (10 or 20 base pairs plus a 4-base loop) sandwiched between dsDNA handles to be used in single-molecule force spectroscopy with optical tweezers. We perform both hopping and force-pulling experiments to measure the excess free energies and deduce the characteristic kinetic signatures of the mismatch from the force–distance curves. All-atom molecular dynamics simulations lend support to the detailed interpretation of the experimental data. Such measurements, at the lowest sensitivity limits of this experimental technique, demonstrate the capability of identifying the presence of mismatches in a random complementary dsDNA sequence and provide lower bounds for the ability to distinguish different structural defects. [ABSTRACT FROM AUTHOR]

A fully analytical model is established for the thermal fluctuations of the beatnote phase of an optically pumped dual-frequency vertical-external-cavity surface-emitting laser (VECSEL). This model starts with the resolution of the heat equation inside the semiconductor chip structure and follows with the evaluation of the induced thermo-optic phase shift. Both the fluctuations of the heat induced by the optical pumping and the thermodynamic fluctuations at room temperature are considered. On the one hand, the thermal response of the structure is investigated and a significant thermal lens effect caused by the pump is deduced. On the other hand, the power spectral density of the frequency noise is calculated in the presence of diffusion spatial anisotropy. The present model is in very good agreement with the phase noise measured for a dual-frequency VECSEL at 852 nm for application to metrology and the validity of the usual low-pass filter model is discussed. [ABSTRACT FROM AUTHOR]

Red blood cells of vertebrates have undergone evolutionary changes over time, leading to the diversification of morphological and mechanical properties of red blood cells (RBCs). Among the vertebrates, camelids have the most different RBC characteristics. As a result of adaptation to the desert environment, camelid RBCs can expand twice as much of their total volume in the case of rapid hydration yet are almost undeformable under mechanical stress. In this work, the mechanical and chemical differences in the RBC properties of the human and camelid species were examined using optical tweezers and Raman spectroscopy. We measured the deformability of camel and human RBCs at the single-cell level using optical tweezers. We found that the deformability index (DI) of the camel and the human RBCs were 0.024 ± 0.019 and 0.215 ± 0.061, respectively. To investigate the chemical properties of these cells, we measured the Raman spectra of the whole blood samples. The result of our study indicated that some of the Raman peaks observed on the camel’s blood spectrum were absent in the human blood’s spectrum, which further points to the difference in chemical contents of these two species’ RBCs.

Dynein is a minus-end-directed motor that generates oscillatory motion in eukaryotic flagella. Cyclic beating, which is the most significant feature of a flagellum, occurs by sliding spatiotemporal regulation by dynein along microtubules. To elucidate oscillation generated by dynein in flagellar beating, we examined its mechanochemical properties under three different axonemal dissection stages. By starting from the intact 9 + 2 structure, we reduced the number of interacting doublets and determined three parameters, namely, the duty ratio, dwell time and step size, of the generated oscillatory forces at each stage. Intact dynein molecules in the axoneme, doublet bundle and single doublet were used to measure the force with optical tweezers. The mean forces per dynein determined under three axonemal conditions were smaller than the previously reported stall forces of axonemal dynein; this phenomenon suggests that the duty ratio is lower than previously thought. This possibility was further confirmed by an in vitro motility assay with purified dynein. The dwell time and step size estimated from the measured force were similar. The similarity in these parameters suggests that the essential properties of dynein oscillation are inherent to the molecule and independent of the axonemal architecture, composing the functional basis of flagellar beating. [ABSTRACT FROM AUTHOR]

Optical tweezers have become essential tools to manipulate atoms or molecules at a single particle level. However, using standard diffraction-limited optical systems, the transverse size of the trap is lower bounded by the optical wavelength, limiting the application range of optical tweezers. Here we report trapping of single ultracold atom in an optical trap that can be continuously tuned from a standard Airy focus to a subwavelength hotspot smaller than the usual Abbe's diffraction limit. The hotspot was generated using the effect of superoscillations, by the precise interference of multiple free-space coherent waves. We argue that superoscillatory trapping and continuous potential tuning offer not only a way to generate compact and tenable ensembles of trapped atoms for quantum simulators but will also be useful in single molecule quantum chemistry and the study of cooperative atom-photon interactions within subwavelength arrays of quantum emitters. Optical trapping of single atoms is relevant for applications to quantum chemistry and quantum computing. This works demonstrates the use of superoscillatory field leading to rapid local spatial variations of the intensity and phase of light to trap a single cold Caesium atom into a reconfigurable sub-wavelength optical trap. [ABSTRACT FROM AUTHOR]

Colloids often behave in a manner similar to their counterparts in molecular space and are used as model systems to understand molecular behavior. Here, we study like-charged colloidal attractions between a permanent dipole on an interfacial particle and its induced dipole on a water-immersed particle caused by diffuse layer polarization. We find that the scaling behavior of the measured dipole-induced dipole (D‒I) interaction via optical laser tweezers is in good agreement with that predicted from the molecular Debye interaction. The dipole character propagates to form aggregate chains. Using coarse-grained molecular dynamic simulations, we identify the separate roles of the D‒I attraction and the van der Waals attraction on aggregate formation. The D‒I attraction should be universal in a broad range of soft matter, such as colloids, polymers, clays, and biological materials, motivating researchers to further conduct in-depth research on these materials. The Debye interaction is defined as the attraction between a polar molecule and a nonpolar molecule, which governs many self-assembling processes in materials. Here, Lee et al. design a like-charged colloidal model at the water-oil interface to characterize the Debye interaction for the first time. [ABSTRACT FROM AUTHOR]

Integrin-mediated adhesion is essential for metazoan life. Integrin binding to ligand requires an activation step prior to binding ligand that depends on direct binding of talin and kindlin to the β-integrin cytoplasmic tail and the transmission of force from the actomyosin via talin to the integrin-ligand bonds. However, the affinity of talin for integrin tails is low. It is therefore still unclear how such low-affinity bonds are reinforced to transmit forces up to 10 to 40 pN. In this study, we use single-molecule force spectroscopy by optical tweezers to investigate the mechanical stability of the talin⋅integrin bond in the presence and absence of kindlin. While talin and integrin alone form a weak and highly dynamic slip bond, the addition of kindlin-2 induces a force-independent, ideal talin⋅integrin bond, which relies on the steric proximity of and the intervening amino acid sequences between the talin- and kindlin-binding sites in the β-integrin tail. Our findings show how kindlin cooperates with talin to enable transmission of high forces required to stabilize cell adhesion. [ABSTRACT FROM AUTHOR]

Single‐emitter luminescence is attractive for various applications, including single‐molecular biology, super‐resolution optical imaging, and single‐photon sources. Optical trapping as a particle positioning method is promising for enhancing luminescence by a precise matching of the nanoemitter to the sub‐wavelength mode volume of the photonic structure. Simultaneously satisfying the requirement of both luminescence and trapping enhancement, however, is challenging. Here, stable optical trapping and the in situ excitation of highly bright photoluminescence of a single up‐conversion nanoparticle (UCNP) are demonstrated. A quad‐nanohole structure with two bright‐field modes for enhanced excitation and emission of the UCNP, as well as a dark‐field mode for enhanced optical trapping is designed. It is experimentally demonstrated that the photoluminescence of the UCNP optically trapped in the quad‐nanohole is enhanced by a factor of 87 (as compared to a UCNP trapped in the single nanohole), and this enhancement factor surpasses that from a bowtie nanohole—one of the "gold standards" for local field enhancement. This work provides a route to assemble super‐bright single‐emitter luminescence by optical trapping. [ABSTRACT FROM AUTHOR]

Nonlinear stiffening is a ubiquitous property of major types of biopolymers that make up the extracellular matrices (ECM) including collagen, fibrin, and basement membrane. Within the ECM, many types of cells such as fibroblasts and cancer cells have a spindle-like shape that acts like two equal and opposite force monopoles, which anisotropically stretch their surroundings and locally stiffen the matrix. Here, we first use optical tweezers to study the nonlinear force-displacement response to localized monopole forces. We then propose an effective-probe scaling argument that a local point force application can induce a stiffened region in the matrix, which can be characterized by a nonlinear length scale R* that increases with the increasing force magnitude; the local nonlinear force-displacement response is a result of the nonlinear growth of this effective probe that linearly deforms an increasing portion of the surrounding matrix. Furthermore, we show that this emerging nonlinear length scale R* can be observed around living cells and can be perturbed by varying matrix concentration or inhibiting cell contractility. [ABSTRACT FROM AUTHOR]

Bridging optical tweezers and microfluidics can form a multifunctional platform, which can overcome the difficulties of precise manipulation in hydrodynamic flow in a noninvasive method. However, when integrated into a microfluidic chip, the fiber optic tweezer loses its flexibility. Here, we propose a compact single fiber optical tweezer–micropipette system. It can sort particles by differences in shape and refractive index in a completely noninvasive way while retaining the flexibility, high selectivity, and precision of a fiber optical tweezer. Compact microfluidic channels are formed by combining two different-diameter micropipettes. The internal diameter of the circular microfluidic channel is less than 30 μm. Furthermore, we calculated the trapping and pushing regions of Yeast and Chlorella and achieved the separation of Yeast from Chlorella in the experiments. We did 90 sets of tests on the sorting accuracy of single fiber optical tweezer (SFOT). SFOT was able to distinguish between two types of particles in each test. With the advantages of high selectivity, high accuracy, low optical power consumption, and compact structure, such methods can be used in the fields of optical separation, cell transportation, cell sorting, and single-cell analysis. [ABSTRACT FROM AUTHOR]

Acoustic tweezers can control target movement through the momentum interaction between an acoustic wave and an object. This technology has advantages over optical tweezers for in-vivo cell manipulation due to its high tissue penetrability and strong acoustic radiation force. However, normal cells are difficult to acoustically manipulate because of their small size and the similarity between their acoustic impedance and that of the medium. In this study, we use the heterologous expression of gene clusters to generate genetically engineered bacteria that can produce numerous sub-micron gas vesicles in the bacterial cytoplasm. We show that the presence of the gas vesicles significantly enhances the acoustic sensitivity of the engineering bacteria, which can be manipulated by ultrasound. We find that by employing phased-array-based acoustic tweezers, the engineering bacteria can be trapped into clusters and manipulated in vitro and in vivo via electronically steered acoustic beams, enabling the counter flow or on-demand flow of these bacteria in the vasculature of live mice. Furthermore, we demonstrate that the aggregation efficiency of engineering bacteria in a tumour is improved by utilizing this technology. This study provides a platform for the in-vivo manipulation of live cells, which will promote the progress of cell-based biomedical applications. In vivo manipulation of cells has applications in cell-based therapy, tissue engineering and targeted drug delivery. Here the authors demonstrate in vivo programmable acoustic manipulation of genetically engineered bacteria using holographic acoustic tweezers. [ABSTRACT FROM AUTHOR]

Phase singularities are loci of darkness surrounded by monochromatic light in a scalar field, with applications in optical trapping, super-resolution imaging, and structured light-matter interactions. Although 1D singular structures, like optical vortices, are common due to their robust topological properties, uncommon 0D (point) and 2D (sheet) singularities can be generated by wavefront-shaping devices like metasurfaces. With the design flexibility of metasurfaces, we deterministically position ten identical point singularities using a single illumination source. The phasefront is inverse-designed using phase-gradient maximization with an automatically-differentiable propagator and produces tight longitudinal intensity confinement. The array is experimentally realized with a TiO2 metasurface. One possible application is blue-detuned neutral atom trap arrays, for which this field would enforce 3D confinement and a potential depth around 0.22 mK per watt of incident laser power. We show that metasurface-enabled point singularity engineering may significantly simplify and miniaturize the optical architecture for super-resolution microscopes and dark traps. Optical singularities are typically 1D structures like vortices. This study used metasurfaces to position ten identical point singularities with tight confinement. This could miniaturize optical systems for super-resolution microscopy and dark traps. [ABSTRACT FROM AUTHOR]

The ozone (O3) oxidation kinetics of cysteine in aqueous micro‐droplets at different acidities is investigated in this study via aerosol optical tweezers coupled with Raman spectroscopy. This study exploits the O3 oxidation of cysteine near the interface of micro‐droplets as a model system to elucidate the oxidation damage of amino acids in biosurfaces. For each optically trapped micro‐droplet, Raman spectroscopy is used to determine its droplet radius, concentrations of solutes, and droplet pH, as well as their time evolutions during the kinetics measurements. The bimolecular rate coefficients of the cysteine + O3 reaction measured in micro‐droplets are around 4 × 105 M−1 s−1 and 2 × 104 M−1 s−1 for pH ≈ 5 and 0.5, respectively. These results agree with the previous bulk measurements, indicating that the observed aerosol kinetics can be solely rationalized via diffusion‐limited kinetics. The results also indicate that a high‐ionic strength could enhance the cysteine + O3 reaction, particularly for the zwitterion form of cysteine. The results imply that when surfactant proteins in lung fluids are exposed to ambient O3, the cysteine residues in proteins will be attacked by O3 at first due to the high reactivity of the thiol moiety in cysteine. [ABSTRACT FROM AUTHOR]

Vinculin is an integral component of integrin adhesions, where it functions as a molecular clutch coupling intracellular contraction to the extracellular matrix. Quantitating its contribution to the reinforcement of newly forming adhesions, however, requires ultrasensitive cell force assays covering short time and low force ranges. Here, we have combined atomic force microscopy‐based single‐cell force spectroscopy (SCFS) and optical tweezers force spectroscopy to investigate the role of vinculin in reinforcement of individual nascent adhesions during the first 5 min of cell contact with fibronectin or vitronectin. At minimal adhesion times (5‐10 s), mouse embryonic fibroblast (MEF) wildtype (wt) and vinculin knock‐out (vin(−/−)) cells develop comparable adhesion forces on the scale of several individual integrin‐ligand bonds, confirming that vinculin is dispensable for adhesion initiation. In contrast, after 60 to 120 s, adhesion strength and traction reinforce quickly in wt cells, while remaining low in vin(−/−) cells. Re‐expression of full‐length vinculin or a constitutively active vinculin mutant (vinT12) in MEF vin(−/−) cells restored adhesion and traction with the same efficiency, while vinculin with a mutated talin‐binding head region (vinA50I) or missing the actin‐binding tail‐domain (vin880) was ineffective. Integrating total internal reflection fluorescence imaging into the SCFS setup furthermore enabled us to correlate vinculin‐green fluorescent protein (GFP) recruitment to nascent adhesion sites with the built‐up of vinculin‐dependent adhesion forces directly. Vinculin recruitment and cell adhesion reinforcement followed synchronous biphasic patterns, suggesting vinculin recruitment, but not activation, as the rate‐limiting step for adhesion reinforcement. Combining sensitive SCFS with fluorescence microscopy thus provides insight into the temporal sequence of vinculin‐dependent mechanical reinforcement in nascent integrin adhesions. [ABSTRACT FROM AUTHOR]

The integration of liquid exchange and microfluidic chips plays a critical role in the biomedical and biophysical fields as it enables the control of the extracellular environment and allows for the simultaneous stimulation and detection of single cells. In this study, we present a novel approach for measuring the transient response of single cells using a system integrated with a microfluidic chip and a probe with a dual pump. The system was composed of a probe with a dual pump system, a microfluidic chip, optical tweezers, an external manipulator, an external piezo actuator, etc. Particularly, we incorporated the probe with the dual pump to allow for high-speed liquid change, and the localized flow control enabled a low disturbance contact force detection of single cells on the chip. Using this system, we measured the transient response of the cell swelling against the osmotic shock with a very fine time resolution. To demonstrate the concept, we first designed the double-barreled pipette, which was assembled with two piezo pumps to achieve a probe with the dual pump system, allowing for simultaneous liquid injection and suction. The microfluidic chip with on-chip probes was fabricated, and the integrated force sensor was calibrated. Second, we characterized the performance of the probe with the dual pump system, and the effect of the analysis position and area of the liquid exchange time was investigated. In addition, we optimized the applied injection voltage to achieve a complete concentration change, and the average liquid exchange time was achieved at approximately 3.33 ms. Finally, we demonstrated that the force sensor was only subjected to minor disturbances during the liquid exchange. This system was utilized to measure the deformation and the reactive force of Synechocystis sp. strain PCC 6803 in osmotic shock, with an average response time of approximately 16.33 ms. This system reveals the transient response of compressed single cells under millisecond osmotic shock which has the potential to characterize the accurate physiological function of ion channels. [ABSTRACT FROM AUTHOR]

Optical tweezers (OTs) have made significant progress in recent years, realizing the non-contact optical manipulation of target objects through the interaction between light and matter. In addition to trapping particles with the intensity gradient of the beam, a series of complex optical elements are required to properly modulate the beams to expand the operation of optical manipulation. The development of metasurfaces alleviates this problem. Due to the merits of miniaturization, planarization, multi-function, and integration of metasurfaces, these kinds of novel devices have been applied in OT systems. Metasurface devices have been used to replace traditional objective lenses, achieving device integration and even obtaining multi-function of OTs with unique optical properties in applications. OTs with metasurfaces have developed rapidly, and a great deal of work has been carried out on OTs with metasurfaces, as well as discussions on their practical applications. In this review, we regard the latest progress in the field of OTs with metasurfaces. We classify OTs with metasurface and summarize the new impetus brought by metasurfaces for the development of OTs. [ABSTRACT FROM AUTHOR]

Optical centrifuges are laser-based molecular traps that can rotationally accelerate molecules to energies rivalling or exceeding molecular bond energies. Here we report time and frequency-resolved ultrafast coherent Raman measurements of optically centrifuged CO2 at 380 Torr spun to energies beyond its bond dissociation energy of 5.5 eV (Jmax = 364, Erot = 6.14 eV, Erot/kB = 71, 200 K). The entire rotational ladder from J = 24 to J = 364 was resolved simultaneously which enabled a more accurate measurement of the centrifugal distortion constants for CO2. Remarkably, coherence transfer was directly observed, and time-resolved, during the field-free relaxation of the trap as rotational energy flowed into bending-mode vibrational excitation. Vibrationally excited CO2 (ν2 > 3) was observed in the time-resolved spectra to populate after 3 mean collision times as a result of rotational-to-vibrational (R-V) energy transfer. Trajectory simulations show an optimal range of J for R-V energy transfer. Dephasing rates for molecules rotating up to 5.5 times during one collision were quantified. Very slow decays of the vibrational hot band rotational coherences suggest that they are sustained by coherence transfer and line mixing. In this work the authors use coherent anti-Stokes Raman scattering to study collisional vibrational excitation in highly rotationally excited CO2 molecules prepared in an optical centrifuge. [ABSTRACT FROM AUTHOR]

Cold atoms are important for precision atomic applications including timekeeping and sensing. The 3D magneto-optical trap (3D-MOT), used to produce cold atoms, will benefit from photonic integration to improve reliability and reduce size, weight, and cost. These traps require the delivery of multiple, large area, collimated laser beams to an atomic vacuum cell. Yet, to date, beam delivery using an integrated waveguide approach has remained elusive. Here we report the demonstration of a 87Rb 3D-MOT using a fiber-coupled photonic integrated circuit to deliver all beams to cool and trap > 1 ×106 atoms to near 200 μK. The silicon nitride photonic circuit transforms fiber-coupled 780 nm cooling and repump light via waveguides to three mm-width non-diverging free-space cooling and repump beams directly to the rubidium cell. This planar, CMOS foundry-compatible integrated beam delivery is compatible with other components, such as lasers and modulators, promising system-on-chip solutions for cold atom applications. Ultracold atoms are generated in the lab using optical trapping and cooling. Here the authors implement a fiber-coupled photonic integrated circuit for a beam delivery to a three-dimensional magneto-optical trap where greater than 1 million rubidium atoms are cooled near 200 μK. [ABSTRACT FROM AUTHOR]

While optical tweezers (OT) are mostly used for confining smaller size particles, the counter-propagating (CP) dual-beam traps have been a versatile method for confining both small and larger size particles including biological specimen. However, CP traps are complex sensitive systems, requiring tedious alignment to achieve perfect symmetry with rather low trapping stiffness values compared to OT. Moreover, due to their relatively weak forces, CP traps are limited in the size of particles they can confine which is about 100 μm. In this paper, a new class of counter-propagating optical tweezers with a broken symmetry is discussed and experimentally demonstrated to trap and manipulate larger than 100 μm particles inside liquid media. Our technique exploits a single Gaussian beam folding back on itself in an asymmetrical fashion forming a CP trap capable of confining small and significantly larger particles (up to 250 μm in diameter) based on optical forces only. Such optical trapping of large-size specimen to the best of our knowledge has not been demonstrated before. The broken symmetry of the trap combined with the retro-reflection of the beam has not only significantly simplified the alignment of the system, but also made it robust to slight misalignments and enhances the trapping stiffness as shown later. Moreover, our proposed trapping method is quite versatile as it allows for trapping and translating of a wide variety of particle sizes and shapes, ranging from one micron up to a few hundred of microns including microorganisms, using very low laser powers and numerical aperture optics. This in turn, permits the integration of a wide range of spectroscopy techniques for imaging and studying the optically trapped specimen. As an example, we will demonstrate how this novel technique enables simultaneous 3D trapping and light-sheet microscopy of C. elegans worms with up to 450 µm length. [ABSTRACT FROM AUTHOR]

Geometric-phase dielectric meta-lenses made of silicon with high numerical aperture and short focal lengths are fabricated and characterised. For circularly polarised light, the same meta-lens can act as a converging or diverging lens, depending on the handedness of the circular polarisation. This effect enables application for optical tweezers that trap or release µm-size polymer beads floating in a microfluidic channel on demand. An electrically addressable polarisation converter based on liquid crystals may be used to switch between the two states of polarisation, at which the light transmitted through the meta-lens is focused (trapping) or defocussed (releasing), respectively. [ABSTRACT FROM AUTHOR]

A new electrically controlled photonic liquid crystal device in the form of a twist-q-plate for the generation of a given number of polarization and phase optical singularities on the wavefront of a light beam in a wide spectral range is proposed. The ability of the element to function in two modes was demonstrated experimentally: generation of a given number of singularities or generation of a Gaussian beam and application of this element in a scheme of optical tweezers. A theoretical model was developed to determine the range of controlling voltages for achromatic functioning of the proposed element. [ABSTRACT FROM AUTHOR]

To enable the accurate reproduction of organs in vitro, and improve drug screening efficiency and regenerative medicine research, it is necessary to assemble cells with single‐cell resolution to form cell clusters. However, a method to assemble such forms has not been developed. In this study, a platform for on‐site cell assembly at the single‐cell level using optically driven microtools in a microfluidic device is developed. The microtool was fabricated by SU‐8 photolithography, and antibodies were immobilised on its surface. The cells were captured by the microtool through the bindings between the antibodies on the microtool and the antigens on the cell membrane. Transmembrane proteins, CD51/61 and CD44 that facilitate cell adhesion, commonly found on the surface of cancer cells were targeted. The microtool containing antibodies for CD51/61 and CD44 proteins was manipulated using optical tweezers to capture HeLa cells placed on a microfluidic device. A comparison of the adhesion rates of different surface treatments showed the superiority of the antibody‐immobilised microtool. The assembly of multiple cells into a cluster by repeating the cell capture process is further demonstrated. The geometry and surface function of the microtool can be modified according to the cell assembly requirements. The platform can be used in regenerative medicine and drug screening to produce cell clusters that closely resemble tissues and organs in vivo. [ABSTRACT FROM AUTHOR]

Optical tweezers that rely on laser irradiation to capture and manipulate nanoparticles have provided powerful tools for biological and biochemistry studies. However, the existence of optical diffraction-limit and the thermal damage caused by high laser power hinder the wider application of optical tweezers in the biological field. For the past decade, the emergence of optothermal tweezers has solved the above problems to a certain extent, while the auxiliary agents used in optothermal tweezers still limit their biocompatibility. Here, we report a kind of nanotweezers based on the sign transformation of the thermophoresis coefficient of colloidal particles in low-temperature environment. Using a self-made microfluidic refrigerator to reduce the ambient temperature to around 0 °C in the microfluidic cell, we can control a single nanoparticle at lower laser power without adding additional agent solute in the solution. This novel optical tweezering scheme has provided a new path for the manipulation of inorganic nanoparticles as well as biological particles. [ABSTRACT FROM AUTHOR]

It is very important for holographic optical tweezers (OTs) to develop high-quality phase holograms through calculation by using some computer algorithms, and one of the most commonly used algorithms is the Gerchberg–Saxton (GS) algorithm. An improved GS algorithm is proposed in the paper to further enhance the capacities of holographic OTs, which can improve the calculation efficiencies compared with the traditional GS algorithm. The basic principle of the improved GS algorithm is first introduced, and then theoretical and experimental results are presented. A holographic OT is built by using a spatial light modulator (SLM), and the desired phase that is calculated by the improved GS algorithm is loaded onto the SLM to obtain expected optical traps. For the same sum of squares due to error SSE and fitting coefficient η, the iterative number from using the improved GS algorithm is smaller than that from using traditional GS algorithm, and the iteration speed is faster about 27%. Multi-particle trapping is first achieved, and dynamic multiple-particle rotation is further demonstrated, in which multiple changing hologram images are obtained continuously through the improved GS algorithm. The manipulation speed is faster than that from using the traditional GS algorithm. The iterative speed can be further improved if the computer capacities are further optimized. [ABSTRACT FROM AUTHOR]

To form a diffraction-free beam with a complex structure, we propose to use a set of primitives calculated iteratively for the ring spatial spectrum. We also optimized the complex transmission function of the diffractive optical elements (DOEs), which form some primitive diffraction-free distributions (for example, a square or/and a triangle). The superposition of such DOEs supplemented with deflecting phases (a multi-order optical element) provides to generate a diffraction-free beam with a more complex transverse intensity distribution corresponding to the composition of these primitives. The proposed approach has two advantages. The first is the rapid (for the first few iterations) achievements of an acceptable error in the calculation of an optical element that forms a primitive distribution compared to a complex one. The second advantage is the convenience of reconfiguration. Since a complex distribution is assembled from primitive parts, it can be reconfigured quickly or dynamically by using a spatial light modulator (SLM) by moving and rotating these components. Numerical results were confirmed experimentally. [ABSTRACT FROM AUTHOR]

Phase state and morphology of aerosol particles play a critical role in determining their effect on climate. While aerosol acidity has been identified as a key factor affecting the multiphase chemistry and phase transitions, the impact of acidity on phase transition of multicomponent aerosol particles has not been extensively studied in situ. In this work, we employ an aerosol optical tweezer (AOT) to probe the impact of acidity on the phase transition behavior of levitated aerosol particles. Our results reveal that higher acidity decreases the separation relative humidity (SRH) of aerosol droplets mixed with ammonium sulfate (AS) and secondary organic aerosol (SOA) proxy, such as 3-methylglutaric acid (3-MGA), 1,2,6-hexanetriol (HEXT) and 2,5-hexanediol (HEXD) across aerosol pH in atmospheric condition. Phase separation of organic acids was more sensitive to acidity compared to organic alcohols. We found the mixing relative humidity (MRH) was consistently higher than the SRH in several systems. Phase-separating systems, including 3-MGA/AS, HEXT/AS, and HEXD/AS, exhibited oxygen-to-carbon ratios (O:C) of 0.67, 0.50, and 0.33, respectively. In contrast, liquid-liquid phase separation (LLPS) did not occur in the high O:C system of glycerol/AS, which had an O:C of 1.00. Additionally, the morphology of 38 out of the 40 aerosol particles that underwent LLPS was observed to be a core-shell. Our findings provide a comprehensive understanding of the pH-dependent LLPS in individual suspended aerosol droplets and pave the way for future research on phase separation of atmospheric aerosol particles. [ABSTRACT FROM AUTHOR]

Replication protein A (RPA) is a eukaryotic single-stranded (ss) DNA-binding (SSB) protein that is essential for all aspects of genome maintenance. RPA binds ssDNA with high affinity but can also diffuse along ssDNA. By itself, RPA is capable of transiently disrupting short regions of duplex DNA by diffusing from a ssDNA that flanks the duplex DNA. Using single-molecule total internal reflection fluorescence and optical trapping combined with fluorescence approaches, we show that S. cerevisiae Pif1 can use its ATP-dependent 5' to 3' translocase activity to chemomechanically push a single human RPA (hRPA) heterotrimer directionally along ssDNA at rates comparable to those of Pif1 translocation alone. We further show that using its translocation activity, Pif1 can push hRPA from a ssDNA loading site into a duplex DNA causing stable disruption of at least 9 bp of duplex DNA. These results highlight the dynamic nature of hRPA enabling it to be readily reorganized even when bound tightly to ssDNA and demonstrate a mechanism by which directional DNA unwinding can be achieved through the combined action of a ssDNA translocase that pushes an SSB protein. These results highlight the two basic requirements for any processive DNA helicase: transient DNA base pair melting (supplied by hRPA) and ATP-dependent directional ssDNA translocation (supplied by Pif1) and that these functions can be unlinked by using two separate proteins. [ABSTRACT FROM AUTHOR]

Plasmonic nanoparticles (NP) possess great potential in photothermal therapy and diagnostics. However, novel NP require a detailed examination for potential toxicity and peculiarities of interaction with cells. Red blood cells (RBC) are important for NP distribution and the development of hybrid RBC-NP delivery systems. This research explored RBC alterations induced by noble (Au and Ag) and nitride-based (TiN and ZrN) laser-synthesized plasmonic NP. Optical tweezers and conventional microscopy modalities indicated the effects arising at non-hemolytic levels, such as RBC poikilocytosis, and alterations in RBC microrheological parameters, elasticity and intercellular interactions. Aggregation and deformability significantly decreased for echinocytes independently of NP type, while for intact RBC, all NP except Ag NP increased the interaction forces but had no effect on RBC deformability. RBC poikilocytosis promoted by NP at concentration 50 μ g mL − 1 was more pronounced for Au and Ag NP, compared to TiN and ZrN NP. Nitride-based NP demonstrated better biocompatibility towards RBC and higher photothermal efficiency than their noble metal counterparts. [ABSTRACT FROM AUTHOR]

Optical vortices, which have been extensively studied over the last decades, offer an additional degree of freedom useful in many applications, such as optical tweezers and quantum control. Stimulated Brillouin scattering (SBS), providing a narrow linewidth and a strong nonlinear response, has been used to realize quasi-continuous wave lasers. Here, stable oscillation of optical vortices and acoustic modes in a Brillouin laser based on chiral photonic crystal fiber (PCF) is reported, which robustly supports helical Bloch modes (HBMs) that carry circularly polarized optical vortex and display circular birefringence. A narrow-linewidth Brillouin fiber laser that stably emits 1stand 2nd-order vortex-carrying HBMs is implemented. Angular momentum conservation selection rules dictate that pump and backward Brillouin signals have opposite topological charge and spin. Additionally, it is shown that when the chiral PCF is placed within a laser ring cavity, the linewidth-narrowing associated with lasing permits the peak of the Brillouin gain that corresponds to acoustic mode to be measured with resolution of 10 kHz and accuracy of 520 kHz. The results pave the way to a new generation of vortex-carrying SBS systems with applications in optical tweezers, quantum information processing, and vortex-carrying nonreciprocal systems. [ABSTRACT FROM AUTHOR]

Counter-propagating optical tweezers are experimental platforms for the frontier exploration of science and precision measurement. The polarization of the trapping beams significantly affects the trapping status. Using the T-matrix method, we numerically analyzed the optical force distribution and the resonant frequency of counter-propagating optical tweezers in different polarizations. We also verified the theoretical result by comparing it with the experimentally observed resonant frequency. Our analysis shows that polarization has little influence on the radial axis motion, while the axial axis force distribution and the resonant frequency are sensitive to polarization change. Our work can be used in designing harmonic oscillators which can change their stiffness conveniently, and monitoring polarization in counter-propagating optical tweezers. [ABSTRACT FROM AUTHOR]

In this paper, partially coherent radially polarized (RP) Laguerre-Gaussian (LG) rotationally symmetrical power-exponent phase vortex (RSPEPV) beams with the LG-correlated Schell-model (LGSM) were introduced. The statistical properties of the tightly focused beams, including intensity distribution, degrees of polarization and coherence, and Stokes vector, were studied based on vectorial Richards-Wolf diffraction integral theory. Moreover, when the distance between focal plane and the observation plane z = 0, the relationships between the tight-focusing properties of RP-LG-RSPEPV beams with LGSM and the order of LGSM p', topological charges l, power exponent n, spatial correlation δ, and radial index p were investigated. The results show that by changing the order of LGSM, topological charge, power exponent, spatial correlation length, and radial index, the focal spot distribution of various shapes can be obtained. This work provides ideas for the application of partially coherent beams in particle capture and optical tweezers. [ABSTRACT FROM AUTHOR]

The endosomal sorting complexes required for transport (ESCRTs) I, -II and -III, and their associated factors are a collection of ∼20 proteins in yeast and ∼30 in mammals, responsible for severing membrane necks in processes that range from multivesicular body formation, HIV release and cytokinesis, to plasma and lysosomal membrane repair. ESCRTs are best known for 'reverse-topology' membrane scission, where they act on the inner surface of membrane necks, often when membranes are budded away from the cytosol. These events are driven by membrane-associated assemblies of dozens to hundreds of ESCRT molecules. ESCRT-III proteins form filaments with a variety of geometries and ESCRT-I has now been shown to also form helical structures. The complex nature of the system and the unusual topology of its action has made progress challenging, and led to controversies with regard to its underlying mechanism. This Review will focus on recent advances obtained by structural in vitro reconstitution and in silico mechanistic studies, and places them in their biological context. The field is converging towards a consensus on the broad outlines of a mechanism that is driven by a progressive ATP-dependent treadmilling exchange of ESCRT subunits, as well as compositional change and geometric transitions in ESCRT filaments.

The endosomal sorting complexes required for transport (ESCRTs) I, -II and -III, and their associated factors are a collection of ∼20 proteins in yeast and ∼30 in mammals, responsible for severing membrane necks in processes that range from multivesicular body formation, HIV release and cytokinesis, to plasma and lysosomal membrane repair. ESCRTs are best known for 'reverse-topology' membrane scission, where they act on the inner surface of membrane necks, often when membranes are budded away from the cytosol. These events are driven by membrane-associated assemblies of dozens to hundreds of ESCRT molecules. ESCRT-III proteins form filaments with a variety of geometries and ESCRT-I has now been shown to also form helical structures. The complex nature of the system and the unusual topology of its action has made progress challenging, and led to controversies with regard to its underlying mechanism. This Review will focus on recent advances obtained by structural in vitro reconstitution and in silico mechanistic studies, and places them in their biological context. The field is converging towards a consensus on the broad outlines of a mechanism that is driven by a progressive ATP-dependent treadmilling exchange of ESCRT subunits, as well as compositional change and geometric transitions in ESCRT filaments.

Since their inception, optical tweezers have proven to be a useful tool for improving human understanding of the microscopic world with wide-ranging applications across science. In recent years, they have found many particularly appealing applications in the field of biomedical engineering which harnesses the knowledge and skills in engineering to tackle problems in biology and medicine. Notably, metallic nanostructures like gold nanoparticles have proven to be an excellent tool for OT-based micromanipulation due to their large polarizability and relatively low cytotoxicity. In this article, we review the progress made in the application of optically trapped gold nanomaterials to problems in bioengineering. After an introduction to the basic methods of optical trapping, we give an overview of potential applications to bioengineering specifically: nano/biomaterials, microfluidics, drug delivery, biosensing, biophotonics and imaging, and mechanobiology/single-molecule biophysics. We highlight the recent research progress, discuss challenges, and provide possible future directions in this field.

Over the last few decades, in vitro single-molecule manipulation techniques have enabled the use of force and displacement as controlled variables in biochemistry. Measuring the effect of mechanical force on the real-time kinetics of a biological process gives us access to the rates, equilibrium constants and free-energy landscapes of the mechanical steps of the reaction; this information is not accessible by ensemble assays. Optical tweezers are the current method of choice in single-molecule manipulation due to their versatility, high force and spatial and temporal resolutions. The aim of this review is to describe the contributions of our lab in the single-molecule manipulation field. We present here several optical tweezers assays refined in our laboratory to probe the dynamics and mechano-chemical properties of biological molecular motors and synthetic molecular devices at the single-molecule level.

The levitated optomechanics, because of its ultra-high mechanical Q > 1010, is considered to be one of the best testbeds for macroscopic quantum superpostions. In this perspective, we give a brief review on the development of the levitated optomechanics, focusing on the macroscopic quantum phenomena, and the applications in quantum precision measurement. The levitated nanodiamond with built-in nitrogen-vacancy centers is discussed as an example. Finally, we discuss the future dirctions of the levtated optomechanics, such as the space-based experiments, the arrays of levitated optomechanics and applications in quantum simulation.