Trapping Force Research Articles

Concurrently Probing the Mechanical and Electrical Characteristics of Living Cells via an Integrated Microdevice.

The mechanical and electrical properties of cells serve as critical indicators of their physiological and pathological state. Currently, distinct setups are required to measure the electrical and mechanical responses of cells. In addition, most existing methods such as optical trapping (OT) and atomic force microscopy (AFM) are labor-intensive, expensive, and low-throughput. Here, we developed a microdevice that integrates automated cell trapping, deformation, and electric impedance spectroscopy to overcome these limitations. Our device enables parallel aspiration of tens of trapped cells in a highly scalable manner by simply adjusting the applied pressures, allowing for rapid probing of the dynamic viscoelastic properties of cells. Furthermore, embedded microelectrodes enable concurrent investigations of the electrical impedance of the cells. Through testing on different cell types, our platform demonstrated superior capabilities in comprehensive cell characterization and phenotyping, highlighting its great potential as a versatile tool for single cell analysis, drug screening, and disease detection.

Optical trapping forces exerted by a pulsed Hermite–Gaussian beam on a dielectric nanosphere

An analytical expression for the optical forces exerted by a pulsed Hermite–Gaussian (HG) beam on a nano-dielectric sphere has been derived. This allows us to investigate how the forces are affected by different beam modes (p,l) and the duration of the light pulse (τ). Our findings demonstrate that these factors significantly influence the strength of the forces, the number of regions where the sphere can be trapped, and the size of these trapping zones. This knowledge paves the way for precise control of these tiny particles with light, potentially leading to improved techniques for trapping and sorting nanoparticles.

Comparative Evaluation of Interaction Force Characteristics for the Lipopolysaccharide of Yersinia pseudotuberculosis and Antibodies by Optical Trapping and Atomic Force Microscopy

Optical tweezers and atomic force microscopy were used for comparative evaluation of the interaction force between the lipopolysaccharide of Yersinia pseudotuberculosis and monoclonal antibodies. This paper discusses the peculiarities of two methods which allow determining significant differences in the values of the measured force required to rupture the interaction of probe sensitized by lipopolysaccharide (polystyrene microsphere for optical tweezers and silicon nitride cantilever for atomic force microscopy) with substrate (glass and mica, respectively) covered with monoclonal antibodies. In atomic force microscopy, the cantilever slides along the substrate for some time after the piezo stage is brought to a stop, causing changes in the spatial structure of sensitins and, therefore, redistribution of multiple bonds between the lipopolysaccharide agglomerate and antibodies. No significant displacement of the microsphere along the substrate occurs when an optical tweezers setup is used, and, unlike atomic force microscopy, the breaking of a complex bond between lipopolysaccharide and complementary antibodies is recorded in the form of a single and short-term (1–2 ms) leap of the photodetector signal employing optical tweezers. The recorded values of the force required to rupture the interaction measured by both methods are relative and vary depending on the chosen experimental conditions. It is shown that the non-specific component of the force needed to break the interaction measured by atomic force microscopy is significantly higher than that determined with optical tweezers.

Optical tweezing of microparticles and cells using silicon-photonics-based optical phased arrays

Integrated optical tweezers have the potential to enable highly-compact, low-cost, mass-manufactured, and broadly-accessible optical manipulation when compared to standard bulk-optical tweezers. However, integrated demonstrations to date have been fundamentally limited to micron-scale standoff distances and, often, passive trapping functionality, making them incompatible with many existing applications and significantly limiting their utility, especially for biological studies. In this work, we demonstrate optical trapping and tweezing using an integrated OPA for the first time, increasing the standoff distance of integrated optical tweezers by over two orders of magnitude compared to prior demonstrations. First, we demonstrate trapping of polystyrene microspheres 5 mm above the surface of the chip and calibrate the trap force. Next, we show tweezing of polystyrene microspheres in one dimension by non-mechanically steering the trap by varying the input laser wavelength. Finally, we use the OPA tweezers to demonstrate, to the best of our knowledge, the first cell experiments using single-beam integrated optical tweezers, showing controlled deformation of mouse lymphoblast cells. This work introduces a new modality for integrated optical tweezers, significantly expanding their utility and compatibility with existing applications, especially for biological experiments.

Tunable Elliptical Cylinders for Rotational Mechanical Studies of Single DNA Molecules.

The angular optical trap (AOT) is a powerful technique for measuring the DNA topology and rotational mechanics of fundamental biological processes. Realizing the full potential of the AOT requires rapid torsional control of these processes. However, existing AOT quartz cylinders are limited in their ability to meet the high rotation rate requirement while minimizing laser-induced photodamage. In this work, we present a novel trapping particle design to meet this challenge by creating small metamaterial elliptical cylinders with tunable trapping force and torque properties. The optical torque of these cylinders arises from their shape anisotropy, with their optical properties tuned via multilayered SiO 2 and Si 3 N 4 deposition. We demonstrate that these cylinders can be rotated at about 3 times the rate of quartz cylinders without slippage while enhancing the torque measurement resolution during DNA torsional elasticity studies. This approach opens new opportunities for previously inaccessible rotational studies of DNA processing.

Nonlinear Langevin functionals for a driven probe.

When a probe particle immersed in a fluid with nonlinear interactions is subject to strong driving, the cumulants of the stochastic force acting on the probe are nonlinear functionals of the driving protocol. We present a Volterra series for these nonlinear functionals by applying nonlinear response theory in a path integral formalism, where the emerging kernels are shown to be expressed in terms of connected equilibrium correlation functions. The first cumulant is the mean force, the second cumulant characterizes the non-equilibrium force fluctuations (noise), and higher order cumulants quantify non-Gaussian fluctuations. We discuss the interpretation of this formalism in relation to Langevin dynamics. We highlight two example scenarios of this formalism. (i) For a particle driven with the prescribed trajectory, the formalism yields the non-equilibrium statistics of the interaction force with the fluid. (ii) For a particle confined in a moving trapping potential, the formalism yields the non-equilibrium statistics of the trapping force. In simulations of a model of nonlinearly interacting Brownian particles, we find that nonlinear phenomena, such as shear-thinning and oscillating noise covariance, appear in third- or second-order response, respectively.

(Invited) Ion Migration Influencing Perovskite Solar Cell Performance and Stability

The thermodynamic and redox properties of halide perovskites provide a strong driving force for hole trapping and oxidation of iodide species. When in contact with a non-polar solvent, the migration of iodine species is further extended to expulsion of iodine from the perovskite film. Thus, the mobility of halides and their susceptibility to hole-induced oxidation play a crucial role in determining the long-term stability of metal halide perovskite solar cells. When Ruddlesden-Popper 2D mixed-halide perovskite films with spacer cations such as butylammonium are introduced into three-dimensional (3D) perovskite films, they can stabilize them against moisture-induced degradation at room temperature. While such passivation of 3D perovskites using 2D perovskites has been reported widely, the instability of the 2D/3D interface during long term solar cell operation can be problematic, especially at higher temperatures. The cation migration under light and heat can significantly alter the 2D/3D interface, thus affecting the solar cell performance. We have now probed the cation migration between 2D and 3D perovskites by physically pairing X PbI (X=butylammonium BA, oleylammonium OA, or phenethylammonium PEA) 2D film and (CH3)PbI3 3D film at different temperatures by recording changes in the absorption and emission spectra. Thus, suppression of halide ion migration as well as cation migration remains a key factor in achieving long term stability and improving efficiency of perovskite solar cells and light emitting devices.

Impedance matching in optically induced dielectrophoresis: Effect of medium conductivity on trapping force.

An impedance analysis for optically induced dielectrophoresis is presented. A circuit model is developed for this purpose. The model parameters are fully defined in terms of the geometrical and material properties of the system. It is shown that trapping force can only be generated when the material properties follow certain impedance matching conditions. The impedance match factor is introduced to succinctly quantify the phenomenon. It is used to calculate bounds on the allowed electrical conductivity of the suspension medium. Results from the proposed model are found to be in good agreement with full-wave numerical simulations. By computing the acceptable set of material parameters with little computational cost, the presented analysis can streamline ODEP system design for various applications.

Microscale Diffractive Lenses Integrated into Microfluidic Devices for Size-Selective Optical Trapping of Particles.

Integration of optical components into microfluidic devices can enhance particle manipulations, separations, and analyses. We present a method to fabricate microscale diffractive lenses composed of aperiodically spaced concentric rings milled into a thin metal film to precisely position optical tweezers within microfluidic channels. Integrated thin-film microlenses perform the laser focusing required to generate sufficient optical forces to trap particles without significant off-device beam manipulation. Moreover, the ability to trap particles with unfocused laser light allows multiple optical traps to be powered simultaneously by a single input laser. We have optically trapped polystyrene particles with diameters of 0.5, 1, 2, and 4 μm over microlenses fabricated in chromium and gold films. Optical forces generated by these microlenses captured particles traveling at fluid velocities up to 64 μm/s. Quantitative trapping experiments with particles in microfluidic flow demonstrate size-based differential trapping of neutrally buoyant particles where larger particles required a stronger trapping force. The optical forces on these particles are identical to traditional optical traps, but the addition of a continuous viscous drag force from the microfluidic flow introduces tunable size selectivity across a range of laser powers and fluid velocities.

Optical torque calculations and measurements for DNA torsional studies

The angular optical trap (AOT) is a powerful instrument for measuring the torsional and rotational properties of a biological molecule. Thus far, AOT studies of DNA torsional mechanics have been carried out using a high numerical aperture oil-immersion objective, which permits strong trapping but inevitably introduces spherical aberrations due to the glass-aqueous interface. However, the impact of these aberrations on torque measurements is not fully understood experimentally, partly due to a lack of theoretical guidance. Here, we present a numerical platform based on the finite element method to calculate forces and torques on a trapped quartz cylinder. We have also developed a new experimental method to accurately determine the shift in the trapping position due to the spherical aberrations by using a DNA molecule as a distance ruler. We found that the calculated and measured focal shift ratios are in good agreement. We further determined how the angular trap stiffness depends on the trap height and the cylinder displacement from the trap center and found full agreement between predictions and measurements. As a further verification of the methodology, we showed that DNA torsional properties, which are intrinsic to DNA, could be determined robustly under different trap heights and cylinder displacements. Thus, this work has laid both a theoretical and experimental framework that can be readily extended to investigate the trapping forces and torques exerted on particles with arbitrary shapes and optical properties.

Impact of Gaussian Beam Spot Size on Trapping Forces: Continuous versus Pulsed Beams

Impact of Gaussian Beam Spot Size on Trapping Forces: Continuous versus Pulsed Beams

Controllable multi-autofocusing of chirped multi-Pearcey beams and their trapping performance on Rayleigh particles

The exploration of structured light created through autofocusing beams has attracted widespread attention in optical manipulation. Here, we investigate the propagation dynamics of chirped multi-Pearcey beams (CMPBs) in theory and experiment, especially exploring the impact of chirped factors on the autofocusing characteristics of CMPBs. It is found that the autofocusing characteristics of the beams can be significantly modulated by introducing first-order and second-order chirped factors. Specifically, the first-order chirped factor greatly improves the autofocusing coefficient of CMPBs, while the second-order chirped factor introduces multiple autofocusing propagations. By analyzing the transverse power flow of CMPBs both without and with chirped factors, we explain why the chirped factors can remarkably strengthen the autofocusing performance of CMPBs. Finally, our theoretical analysis on trapping force on Rayleigh particles indicates that the introduction of chirped factors optimizes the intensity gradient and trapping capability of CMPBs, potentially enabling multiple longitudinal trapping positions. These findings offer a comprehensive insight into the propagation dynamics of CMPBs, opening avenues for flexible optical manipulation of multiple particles.

Optical tweezers for probing the interactions of ZnO and Ag nanoparticles with E. coli.

The antibacterial effect of nanoparticles is mainly studied on the ensembles of the bacteria. In contrast, the optical tweezer technique allows the investigation of similar effects on individual bacterium. E. coli is a self-propelled micro-swimmer and ATP-driven active microorganism. In this work, an optical tweezer is employed to examine the mechanical properties of E. coli incubated with ZnO and Ag nanoparticles (NP) in the growth medium. ZnO and Ag NP with a concentration of 10µg/ml were dispersed in growth medium during active log-growth phase of E. coli. This E. coli-NP incubation is further continued for 12h. The E. coli after incubation for 2h, 6h and 12h were separately studied by the optical tweezer for their mechanical property. The IR laser (λ = 975 nm; power = 100mW) was used for trapping the individual cells and estimated trapping force, trapping stiffness and corner frequency. The optical trapping force on E. coli incubated in nanoparticle suspension shows linear decreases with incubation time. This work brings the importance of optical trapping force measurement in probing the antibacterial stress due to nanoparticles on the individual bacterium.

Programmable photoacoustic patterning of microparticles in air.

Optical and acoustic tweezers, despite operating on different physical principles, offer non-contact manipulation of microscopic and mesoscopic objects, making them essential in fields like cell biology, medicine, and nanotechnology. The advantages and limitations of optical and acoustic manipulation complement each other, particularly in terms of trapping size, force intensity, and flexibility. We use photoacoustic effects to generate localized Lamb wave fields capable of mapping arbitrary laser pattern shapes. By using localized Lamb waves to vibrate the surface of the multilayer membrane, we can pattern tens of thousands of microscopic particles into the desired pattern simultaneously. Moreover, by quickly and successively adjusting the laser shape, microparticles flow dynamically along the corresponding elastic wave fields, creating a frame-by-frame animation. Our approach merges the programmable adaptability of optical tweezers with the potent manipulation capabilities of acoustic waves, paving the way for wave-based manipulation techniques, such as microparticle assembly, biological synthesis, and microsystems.

Trade-off between local chemical order and lattice distortion in affecting dislocation motion in NbTiZr multi-principal element alloys

Local chemical order (LCO) is energetically favorable in multi-principal element alloys (MPEAs) due to the chemical affinity difference among constituent species. Here we show that the increase of LCO is often accompanied by a decrease of lattice distortion in body-centered-cubic (BCC) MPEAs. This leads to a trade-off between LCO and lattice distortion in their effects on retarding the glide of edge and screw dislocations. With a random solid solution without LCO as a reference, the emergence of LCO at the expense of lattice distortion could weaken the local trapping force for dislocation glide and promote dislocation mobility. However, when the LCO becomes sufficiently large and robust, it acts to hinder dislocation glide. We found that the mobility of edge dislocation is more affected by local lattice distortion, while the kink-pair based screw dislocation motion is more governed by LCO. We further quantitatively evaluate the contribution of LCO and lattice distortion to the overall critical shear stress for dislocation glide using analytical models. For the present equiatomic NbTiZr MPEAs, the critical shear stress is dominated by lattice distortion when the LCO is still limited to chemical short-range order (CSRO). However, LCO could even surpass lattice distortion to become a major contributor to the critical shear stress once it grows to a sufficiently large size. Our work indicates that increasing the degree and extent of LCO may provide an effective means to regulate dislocation motion, shedding light on how to use LCOs to improve the strength of BCC MPEAs.

Trapping of low and high refractive index nano-spherical particles by using a highly focused Laguerre-Gaussian beam.

We have investigated the trapping force on low and high refractive index nano-particles using a highly focused Laguerre-Gaussian beam. An analytical expression for the gradient force has been derived in closed form. It was clearly found that the increase of the beam mode p causes a substantial increase in the number of trapping zones, which frequently increases the number of particles to be captured simultaneously. Also, the decrease of p values would increase the trap area, which consequently leads to simultaneous trapping of multiple particles in the same area. The change of p, l, Δ n, and z 1 values has a direct influence on the gradient forces. The smaller values of scattering and thermal forces relative to the gradient force values represent essential conditions for the stability of the trapping performance.

Reversible Selbstassemblierung von Nukleinsäuren in einer diffusiophoretischen Falle

AbstractDie Bildung und Dissoziation von Duplexen oder komplexeren Strukturen aus Nukleinsäuresträngen ist ein fundamentaler Prozess mit vielfältigen Anwendungen in Biochemie und Nanotechnologie. Hier führen wir ein einfaches experimentelles System – eine diffusiophoretische Falle – für die Nichtgleichgewichts‐Selbstassemblierung von Nukleinsäurestrukturen ein, das einen Elektrolytgradienten als Antrieb nutzt. DNA‐Stränge können durch Diffusiophorese im elektrischen Feld eines Elektrolytgradienten bis zu hundertfach konzentriert werden. Geeignete Elektrolyte für diese diffusiophoretische Falle können mit Hilfe einer einfachen Gleichung bestimmt werden. Experimente mit carboxylierten Siliziumdioxidpartikeln zeigen, dass die diffusiophoretische Kraft langreichweitig und über hunderte von Mikrometern wirksam ist. Als Anwendung untersuchen wir die reversible Selbstassemblierung verzweigter DNA‐Nanostrukturen in der Falle zu einem makroskopischen Gel. Die Strukturen assemblieren in Anwesenheit eines Elektrolytgradienten und lösen sich bei dessen Entfernung wieder auf, was eine prototypische adaptive Reaktion auf einen makroskopischen Nichtgleichgewichtszustand darstellt.DiffusiophoreseDNA‐NanosterneSelbstorganisationDNA‐StrukturenNichtgleichgewichtsprozesse

Reversible Self-Assembly of Nucleic Acids in a Diffusiophoretic Trap.

The formation and dissociation of duplexes or higher order structures from nucleic acid strands is a fundamental process with widespread applications in biochemistry and nanotechnology. Here, we introduce a simple experimental system-a diffusiophoretic trap-for the non-equilibrium self-assembly of nucleic acid structures that uses an electrolyte gradient as the driving force. DNA strands can be concentrated up to hundredfold by a diffusiophoretic trapping force that is caused by the electric field generated by the electrolyte gradient. We present a simple equation for the field to guide selection of appropriate trapping electrolytes. Experiments with carboxylated silica particles demonstrate that the diffusiophoretic force is long-ranged, extending over hundreds of micrometers. As an application, we explore the reversible self-assembly of branched DNA nanostructures in the trap into a macroscopic gel. The structures assemble in the presence of an electrolyte gradient, and disassemble upon its removal, representing a prototypical adaptive response to a macroscopic non-equilibrium state.

Artificial neural network assisted the design of subwavelength-grating waveguides for nanoparticles optical trapping.

In this work, we propose artificial neural networks (ANNs) to predict the optical forces on particles with a radius of 50 nm and inverse-design the subwavelength-grating (SWG) waveguides structure for trapping. The SWG waveguides are applied to particle trapping due to their superior bulk sensitivity and surface sensitivity, as well as longer working distance than conventional nanophotonic waveguides. To reduce the time consumption of the design, we train ANNs to predict the trapping forces and to inverse-design the geometric structure of SWG waveguides, and the low mean square errors (MSE) of the networks achieve 2.8 × 10-4. Based on the well-trained forward prediction and inverse-design network, an SWG waveguide with significant trapping performance is designed. The trapping forces in the y-direction achieve-40.39 pN when the center of the particle is placed 100 nm away from the side wall of the silicon segment, and the negative sign of the optical forces indicates the direction of the forces. The maximum trapping potential achieved to 838.16 kBT in the y-direction. The trapping performance in the x and z directions is also quite superior, and the neural network model has been further applied to design SWGs with a high trapping performance. The present work is of significance for further research on the application of artificial neural networks in other optical devices designed for particle trapping.

Non-Hermitian non-equipartition theory for trapped particles

The equipartition theorem is an elegant cornerstone theory of thermal and statistical physics. However, it fails to address some contemporary problems, such as those associated with optical and acoustic trapping, due to the non-Hermitian nature of the external wave-induced force. We use stochastic calculus to solve the Langevin equation and thereby analytically generalize the equipartition theorem to a theory that we denote the non-Hermitian non-equipartition theory. We use the non-Hermitian non-equipartition theory to calculate the relevant statistics, which reveal that the averaged kinetic and potential energies are no longer equal to kBT/2 and are not equipartitioned. As examples, we apply non-Hermitian non-equipartition theory to derive the connection between the non-Hermitian trapping force and particle statistics, whereby measurement of the latter can determine the former. Furthermore, we apply a non-Hermitian force to convert a saddle potential into a stable potential, leading to a different type of stable state.