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[Display omitted] • Raman spectroscopy reveals concentration dynamics during optical trapping. • Objective lens NA affects crystallization probability and induction time. • Higher NA generates stable liquid droplets, inhibiting crystallization. • This method offers precise control of crystallization dynamics. This study investigates concentration dynamics during optical trapping-induced crystallization (OTIC) of glycine using Raman spectroscopy. In-situ Raman spectroscopy demonstrated that tightly focused laser beams induced faster concentration increase and crystal nucleation at higher supersaturation compared to loosely focused beams. Also, by varying numerical aperture (NA) values of the objective lens used, it was revealed that higher NA led to achieving a shorter induction time and higher crystallization probability. Remarkably, optical trapping using objective lenses with higher NA generated stable liquid droplets, inhibiting crystallization until considerably higher supersaturation was realized. These findings elucidate the complex interplay between optical forces, supersaturation, and crystallization dynamics on the mechanism of OTIC and offer a new method for precise control of laser-induced crystallization. We believe that the insights gained by this study pave the way for innovative developments in crystal chemistry and promising advancements in photochemistry. [ABSTRACT FROM AUTHOR]

Plasmonic nanotweezers employing metallic nanostrctures provide a powerful tool for optical trapping of nanoscale objects; however, they are limited by strong heating effects resulting from the intrinsic loss in metallic materials. Alternatively, quasi-bound states in the continuum (q-BICs), supported in all-dielectric metasurfaces, offer a higher quality-factor (Q-factor) and electric field enhancement compared to plasmonic systems, making it a promising candidate for heatless nanotweezers with high performance. Here, we demonstrate an all-dielectric nanotweezer harnessing q-BIC for effective trapping of nanoparticles with low trapping power and negligible heating effects. The quasi-BIC system provides very high electromagnetic field intensity enhancement as well as high-quality-factor resonances. The q-BIC mode is induced by symmetry breaking of periodic double ring nanostructure, which leads to an increased optical force and potential energy in comparison to prior studies, enabling attractive promise in subwavelength particle trapping applications. Moreover, the q-BIC nanotweezer creates numerous optical hotspots characterized by significant field confinement and enhancement, generating multiple trapping sites and thus facilitating high-throughput trapping of nanoscale objects. Furthermore, the trapping wavelength (1047.59 nm) in our structure exactly corresponds with the current laser choice for working with biological samples. In addition, we show that trapped particles can improve the resonance mode of the cavity in a symmetry-broken system, which in turn enhances the trapping process. Our study paves the way for applying q-BIC systems to low-power particle trapping and sensing applications, especially for parallel analyses of biological cells and protein molecules. • All-dielectric nanotweezer harnessing q-BIC with low-power and heatless effects. • Trapping wavelength (1047.59 nm) suitable for working with biological samples. • Multiple trapping of nanoscale objects for parallel analyses applications. [ABSTRACT FROM AUTHOR]

Optical tweezers (OT) provide a noninvasive approach for delivering minute physical forces to targeted objects. Controlling such forces in living cells or in vitro preparations allows for the measurement and manipulation of numerous processes relevant to the form and function of cells. As such, OT have made important contributions to our understanding of the structures of proteins and nucleic acids, the interactions that occur between microscopic structures within cells, the choreography of complex processes such as mitosis, and the ways in which cells interact with each other. In this review, we highlight recent contributions made to the field of cell biology using OT and provide basic descriptions of the physics, the methods, and the equipment that made these studies possible. Optical tweezers (OT) can measure or apply minute forces inside cells noninvasively. Recent developments in OT technology have allowed insights into the structure, function, and behavior of cells. Particular progress has been made in understanding mitotic machinery, cellular viscoelasticity, and metastasis. Emerging methods in optical physics promise to extend the breadth and utility of OT in the years to come. [ABSTRACT FROM AUTHOR]

• We produce an optical fiber-based photonic hook for achieving selective particle manipulation in a lab-on-tip platform. • We experimentally demonstrate selectively manipulating and sorting biological cells. • The fiber tip with broken symmetry has emerged as a "lab-on-tip" compact ready-to-use flexible device for applications. Optical tweezers and trapping technologies have a crucial impact on scientific research by precisely manipulating mesoscale objects at wavelength scales. The development of simple fiber-based optical tweezers foreseeing sorting and manipulation of a single cell has been firstly encouraged by biomedical requirements. The ability to manipulate mesoscale objects with high flexibility and precision is essential for a wide class of different fields. The ability to precisely arrange cells into desired structures is important for numerous biomedical and physical applications. This study experimentally reports for the first time a simple and low-cost strategy to produce an optical fiber-based photonic hook for achieving new unprecedented functionalities to selective particle manipulation in a lab-on-tip platform. We show perspectives opened by combining the fields of structured light in the form of the photonic hook and optical manipulation method. This enables new applications for optical trapping setups based on structured fields in the form of the photonic hook produced by an optical fiber tip with broken symmetry, where it becomes possible to manipulate and sort cells selectively. [ABSTRACT FROM AUTHOR]

Optical tweezers have been widely used for optical trapping and manipulating particles at the microscopic scale with a tightly focused laser beam. Over the recent years, optical fiber tweezers have attracted extensive attention due to their simple fabrication process, compact structure, strong anti-interference ability, convenient utilization, compatibility with chip devices, and flexible operation. In this review, the principle of optical force-based trapping is described, and the different fabrication methods of optical fiber tweezers are comprehensively discussed, including heating and pulling, chemical etching, grinding and polishing, coaxial splicing, photopolymer manufacturing, focused ion beam milling, and other emerging super-surface processing techniques. Then, the applications of such tweezers in optical manipulation, optical drive, optical transportation, optical imaging, and optical measurement are summarized. Finally, the future development prospects of optical fiber tweezers are presented. [ABSTRACT FROM AUTHOR]

• Optothermal bubble generation at low CW power. • 3D steady-state-trapping induced by a potential well triggered by optothermal effects. • Bubble self-oscillation in pure ethanol driven by low-power NIR optothermal effects. In this study, we focus on the trapping and self-oscillation of microbubbles in ethanol using a low-power continuous-wave laser. The microbubble formation is achieved by heating of ethanol by light absorption (λ = 658 nm) at silver nanoparticles deposited on the distal end of a multi-mode optical fiber. Subsequently, a second low-power continuous-wave laser (λ = 1,550 nm) coupled to a single-mode optical fiber is used to trap the microbubble. To trap the microbubble, the red laser is turned off after its generation, and immediately the trapping laser is activated. The bulk light absorption at λ = 1,550 nm in ethanol modulates the surface tension of the bubble wall, creating a 3D potential well that effectively traps the bubble. Once the bubble is trapped, random variations in the bubble's radius led to instabilities in the trap, triggering the microbubble oscillation. The trapped bubble tends to oscillate along the light propagation between two points of quasi-steady-state equilibrium. These bubble oscillations result from the opposing competing forces: a changing-direction Marangoni force and drag forces and the upward buoyancy force. To explain the self-oscillation, we present a simple model that qualitatively describes the main features observed in the experimental data. [ABSTRACT FROM AUTHOR]

We introduce a new technique for manipulating silica gel particles suspended in a water-based solution using a stable mode-locked fiber laser (MDFL). We coated a side-polished fiber (SPF) with Au-NP which acts as a saturable absorber (SA). A stable MDFL was achieved at an operating wavelength of 1557.8 nm and a repetition rate of 60.8 MHz. The optical trapping of sub-micrometer-sized silica gel particles revealed remarkable characteristics of the optical force. This force was driven by the presence of surface plasmon polaritons (SPP) in the Au-NP SPF, which played a crucial role in facilitating the manipulation of silica gel particles. Specifically, the SPP generated a gradient optical force, propelling the particles toward the propagation region. Throughout the optical trapping process, we observed wavelength shifts towards higher values in the spectrum, ranging from 1557.8 to 1563.1 nm. To quantify the optical force, we conducted computational and experimental analyses, yielding a force range of 0.16 to 2.10 fN. The percentage errors associated with these measurements ranged from 3.37% to 7.48%. Importantly, simulation results closely align with the experimental findings, establishing a robust foundation for future applications. [Display omitted] • A method for trapping silica gel particles in water with experimental and simulation. • The use of a stable MDFL with Au-NP SPF as a saturable absorber (SA). • Au-NP SPF MDFL trapping microparticles measured via wavelength shifts. [ABSTRACT FROM AUTHOR]

Long-distance waveguiding and submicron focusing of light in a bio-medium are crucial for biomedical sensing and imaging. Disordered bio-mediums usually exhibit high scattering and absorption, which limits effective waveguiding and focusing. Here, we demonstrate an optofluidic cell chain, assembled via an optical trapping force from an optical fiber probe, to achieve long-distance waveguiding and submicron light focusing in a disordered bio-medium. By applying a trapping light at 980 nm to generate an optical force, stable binding of E. faecalis cells was achieved in a fluid to assemble cell chains of different lengths. The length could reach up to 360 µm and the incident light (at 675, 532 and 473 nm) could be focused into a beam with a waist radius of 400 nm. As a potential practical application, backscattered signals from human red blood cells were detected using the cell chains, which is expected to benefit biomedical sensing and single cell analysis. With the assistance of optofluidic techniques, we assembled an E. faecalis cell chain with a length up to 360 µm to achieve long-distance waveguiding and submicron focusing at a propagation loss of 0.03 dB/µm in the bio-medium. Visible lights were launched into the cell chain and the incident lights can converge into a beam with a waist radius of 400 nm. The cell chain was further used to detect the backscattering signals from human red blood cells (RBCs), and the results indicate that the cell chain can be applied as a fully biocompatible extension of the probe for the real-time detection of RBCs in healthy and pathological states. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Optical trapping (synonymous with optical tweezers) has become a core biophysical technique widely used for interrogating fundamental biological processes on size scales ranging from the single-molecule to the cellular level. Recent advances in nanotechnology have led to the development of 'nanophotonic tweezers,' an exciting new class of 'on-chip' optical traps. Here, we describe how nanophotonic tweezers are making optical trap technology more broadly accessible and bringing unique biosensing and manipulation capabilities to biological applications of optical trapping. [ABSTRACT FROM AUTHOR]

We consider a waveguide with a symmetrically integrated silicon cylinder. This design supports a symmetry protected bound state in the continuum (BIC) with Q -factor controlled by slight displacement of the cylinder. When excited by a TE 10 electromagnetic wave, the BIC leads to giant optical forces near the cylinder. These forces have a strong impact on nanoparticles being dragged by liquid flow over the waveguide as they approach the cylinder. At the same time, the nanoparticles perturb the resonant frequency of the BIC with a value proportional to their volume and proximity to the cylinder. Therefore, the interplay between the resonant width of the BIC and the nanoparticle frequency perturbation determines the positions of the nanoparticles trapped around the cylinder. This paradigm demonstrates resonant self-trapping and sorting of nanoparticles by size through BIC excitation. We highlight the extreme sensitivity of these effects to the frequency of the injected TE wave. Additionally, we show that these results remain valid when considering the finite conductivity of metal waveguides. • Waveguide with integrated Si cylinder supports BIC with controlled Q-factor. • Excitation of the BIC leads to giant optical forces near the cylinder. • Nanoparticles are being trapped around the cylinder by the optical force. [ABSTRACT FROM AUTHOR]

• Optical trapping forces of a Bessel-Gaussian correlated Schell-model beam acting on Rayleigh dielectric spheres is investigated. • The focused Bessel-Gaussian correlated Schell-model beam can be used to trap the particles with both high and low index of refraction. • The effects of optical parameters on the radiation forces are analyzed. • We investigate the influence of radius on the trapping stability and find the stable range. Optical trapping forces exerted by a focused Bessel-Gaussian correlated Schell-model (BGCSM) beam on Rayleigh dielectric spheres with different refractive indices are analyzed. The dependence of radiation forces on the transverse coherence width δ 0 , the coherence parameter β , refractive index of the particle, and particle radius are investigated. It is shown that the focused BGCSM beam can be used to trap particles with both high and low index of refraction near the focus, and as the transverse coherence width δ 0 or the relative refractive indices of the particle with respect to the host medium increases, or the coherence parameter β decreases, the trapping stability increase. Furthermore, the limits of the radius for two types of particles stably captured are determined. [ABSTRACT FROM AUTHOR]

Highlights • The beams with phase gradient can guide microparticles along the predesigned trajectory automatically. • The beam can transport microparticles automatically to avoid obstacle. • The beam would be potentially applied optical trapping, optical sorting, and so on. Abstract The beams with phase gradients along the line trajectory, i.e., with the momentum flux transverse to the optical axis were generated with the beam shaping method and applied for optical manipulations in this paper. The phase distributions of the reconstructed beam in the focal plane of the objective and the moving velocity of the trapped microparticles were experimentally investigated. The experimental results showed that the moving velocity of the trapped microparticles is linearly dependent on the phase gradient possessed by the reconstructed beam. Furthermore, a generated curve beam was used to transport microparticles quickly and automatically along the curved route to avoid an obstacle. The generation method of the beams with phase gradients is simple. The beams would have potential applications in the fields such as optical trapping and optical sorting. [ABSTRACT FROM AUTHOR]

Abstract Previous JQSRT special issues devoted to the "Laser-light and Interactions with Particles (LIP)" conferences were accompanied by prefaces written for issues published in a single volume, followed by peer-reviewer papers based on the topics discussed during the conferences, see Gouesbet and Brunel (2013) [1] in [2] , Gouesbet and Onofri (2015) [3] in [4] , and Gouesbet and Onofri (2017) [5] in [6]. Papers associated to the last LIP-conference, however, have been published as a virtual topical issue, the word "virtual" meaning that the papers have been published once they have been accepted, rather than collected in a single issue of JQSRT. In other words, the authors of accepted manuscripts have seen their papers officially published without having to wait for the rest of the manuscripts to get accepted. The present text is therefore rather an afterword than a preface. [ABSTRACT FROM AUTHOR]

We demonstrate a non-contact trapping of a yeast cell by an optical fiber probe with a micron-size concave cavity both theoretically and experimentally. We fabricate the optical fiber tip with a micron-size concave cavity by the improved tube etching method. The size of the concave cavity can be controlled by the etching parameters, such as the etching time, the etching solution, and so on. The output fields from the fiber tips with concave cavities of two geometrical sizes (microns and tens of microns) are computed and analyzed. Then the optical forces on a yeast cell by these concave fiber tips (CFTs) are calculated and discussed. The theoretical results predicate that a micron-size CFT can be used for non-contact trapping of a yeast cell. We observe the non-contact trapping of a yeast cell by a micron-size CFT in the experiments and measure the trapping forces. The optical trapping and manipulation based on these micron-size CFTs may provide versatile applications in bio-science and medical research. • A non-contact trapping of a yeast cell has been observed by a micron-size CFT. • A micron-size CFT can be fabricated by the improved tube etching method. • The impacts of the cavity size on the optical trapping have been investigated. [ABSTRACT FROM AUTHOR]

We show that the optical trapping and manipulation of spherical-shaped semiconductor (germanium) particles can be strongly modulated and controlled using optical tweezers based on a highly focused Bessel beam. Depending on the setup parameters, the germanium beads can be stably trapped outside the optical axis, present a characteristic oscillatory dynamics near the focal plane or even be repelled from the focus. This intricate behavior was studied by varying relevant parameters such as the laser power, the radius of the Bessel beam and the focal height of the trap. The results show that Bessel beam optical tweezers using germanium beads are very versatile tools for applying pico- to femto-Newton constant or oscillatory forces on systems, opening perspectives for new applications in soft matter science and correlated fields, as well as in the construction of microdevices. • Optical trapping of semiconductors can be modulated for Bessel beam tweezers. • Germanium beads are handles to apply pico- to femto-Newton forces. • Perspectives are the development of single molecule machines and microdevices. [ABSTRACT FROM AUTHOR]

The thermally coupled energy states that contribute to the upconversion luminescence of rare earth element-doped nanoparticles have been the subject of intense research due to their potential nanoscale temperature probing. However, the inherent low quantum efficiency of these particles often limits their practical applications, and currently, surface passivation and incorporation of plasmonic particles are being explored to improve the inherent quantum efficiency of the particle. However, the role of these surface passivating layers and the attached plasmonic particles in the temperature sensitivity of upconverting nanoparticles while probing the intercellular temperature has not been investigated thus far, particularly at the single nanoparticle level. The analysis of the study on the thermal sensitivity of oleate-free UCNP, UCNP@SiO 2 , and UCNP@SiO 2 @Au particles is carried out at a single particle level in a physiologically relevant temperature range (299 K–319 K) by optically trapping the particle. The thermal relative sensitivity of the as-prepared upconversion nanoparticle (UCNP) is found to be greater than that of UCNP@SiO 2 and UCNP@SiO 2 @Au particles in an aqueous medium. An optically trapped single luminescence particle inside the cell is used to monitor the temperature inside the cell by measuring the luminescence from the thermally coupled states. The absolute sensitivity of optically trapped particles inside the biological cell increases with temperature, with a greater impact on the bare UCNP, which exhibits higher values for thermal sensitivity than UCNP@SiO 2 and UCNP@SiO 2 @Au. The thermal sensitivity of the trapped particle inside the biological cell at 317 K indicates the thermal sensitivity of UCNP > UCNP@SiO 2 @Au > UCNP@SiO 2 particles. Compared to bulk sample-based temperature probing, the present study demonstrates temperature measurement at the single particle level by optically trapping the particle and further explores the role of the passivating silica shell and the incorporation of plasmonic particles on thermal sensitivity. Furthermore, thermal sensitivity measurements inside a biological cell at the single particle level are investigated and illustrated that thermal sensitivity at a single particle is sensitive to the measuring environment. [Display omitted] • Design and development of optical tweezers setup coupled with luminescence measurement. • Optical trapping of single upconversion nanoparticle. • Power and time dependent emission studies of single upconversion particle. • Optical trapping of single upconversion particle inside the biological cell. • Use of single upconversion particle for intercellular temperature probing. [ABSTRACT FROM AUTHOR]

This study proposes a plasmonic tweezer using an array of plasmonic bowties which operates as a narrow band filter in an optical telecommunication window when the core–shell nanoparticle is fixed within the fluidic medium and the incident wave is considered as a polychromatic light. Conversely, in the case of manipulating the nanoparticle, the structure acts as an on/off optical router in a fixed wavelength ( λ = 1 . 55 micron). Optical forces acting on the nanoparticle have been calculated using the Maxwell stress tensor which enabled us to obtain the nanoparticle manipulation and consequently, the transmission/reflection spectra of the proposed structure over time during the movement of the nanoparticle. A plane wave source with the intensity of 130 mw ∕ m 2 was used to excite this plasmonic structure and the results were investigated using a numerical finite difference time domain (FDTD) method. [ABSTRACT FROM AUTHOR]

Control over both amplitude and phase of optical beams plays an important role in optics, especially in the field of optical trapping. Trapping particles needs optical beams with specified intensity distribution and desired phase distribution, so joint control over light beams with high precision is indispensable. In this paper, a novel joint amplitude and phase control method specially designed for high precision using a digital micromirror device (DMD) is proposed. An off-axis 4f-configuration and a pattern formation algorithm are required for the implementation of the proposed method. Getting DMD pattern by considering the correlations among all pixels guarantees the high precision but increases the computation complexity, which makes it difficult to realize. Thus we present a pattern formation algorithm based on mixed integer programming and its improved version with higher computing efficiency. Experimental tests have been conducted to verify the superior performance of the proposed method over the conventional methods, such as Lee holography and Superpixel method. Measured results and quantitative analyses show that the proposed method enables simultaneous and independent control over amplitude and phase of light beams with a higher precision and performs better when steepest phase gradients exist in the target field. What is more, vortex beam and line beam can be generated accurately by the proposed method. [ABSTRACT FROM AUTHOR]

Optical tweezers, tools based on strongly focused light, enable optical trapping, manipulation, and characterisation of a wide range of microscopic and nanoscopic materials. In the limiting cases of spherical particles either much smaller or much larger than the trapping wavelength, the force in optical tweezers separates into a conservative gradient force, which is proportional to the light intensity gradient and responsible for trapping, and a non-conservative scattering force, which is proportional to the light intensity and is generally detrimental for trapping, but fundamental for optical manipulation and laser cooling. For non-spherical particles or at intermediate (meso)scales, the situation is more complex and this traditional identification of gradient and scattering force is more elusive. Moreover, shape and composition can have dramatic consequences for optically trapped particle dynamics. Here, after an introduction to the theory and practice of optical forces with a focus on the role of shape and composition, we give an overview of some recent applications to biology, nanotechnology, spectroscopy, stochastic thermodynamics, critical Casimir forces, and active matter. [ABSTRACT FROM AUTHOR]

The study of physical and chemical properties of a microscopic object, such as a single particle, is made possible using optical trapping (OT) technology combined with other measuring techniques. Here we show a universal optical trap combined with Raman spectroscopy (RS) and microscopy imaging for single-particle studies. The universal optical trap is constructed using two counter-propagating hollow beams and is able to stably levitate single particles of a wide range of properties, such as transparent or absorbing materials, organic (polymers, bioaerosols, etc.) or inorganic constituents (carbon, silica, glass, etc.), and spherical or irregularly shaped morphologies. Both physical and chemical properties and their temporal evolution of the trapped particle can be characterized simultaneously using the integrated OT-RS and imaging system. We created three sample cases to demonstrate the analytical merits of the system: (I) a single particle with no change, (II) partially degraded over the measuring period, and (III) one part from the fragmentized single particle. The particles' chemical compositions, crystalline states, etc. are inferred from their Raman spectra, while their physical properties (sizes, shapes, morphologies, etc.) are revealed by images. This integrated OT-RS system provides a new approach to concurrently characterize and monitor physical and chemical properties of single micrometer-sized objects optically trapped in air. [ABSTRACT FROM AUTHOR]

We calculate the trapping forces exerted by a highly focused Bessel-Gaussian beam on a double-layered sphere by means of vector diffraction integral, T-matrix method and Maxwell stress tensor integral. The Bessel-Gaussian beam is azimuthally polarized. Numerical results predicate that the double-layered sphere with air core can be stably trapped in three-dimensions. The trapping forces and efficiencies are dependent on the refraction index and size of the inner core. The trapping efficiency can be optimized by choosing the refraction indices of the inner core and outer layer. Our computational method can be easily modified for other laser beams and particles with arbitrary geometries and multilayers. [ABSTRACT FROM AUTHOR]

A focused partially coherent circular edge dislocations beam used to trap Rayleigh dielectric sphere with different refractive indices is studied. The dependence of radiation forces on the number of circular edge dislocations p , the spatial correlation length σ 0 , relative refractive index n r , and particle radius a are analyzed and illustrated by numerical examples. It is shown that the focused partially coherent circular edge dislocations beam can be used to trap high index of refraction particles at focus F and bright ring R 2 , and simultaneously to capture low index of refraction particles at dark ring R 1 . It is much easier to capture the high index of refraction particles at focus F and the low index of refraction particles at dark ring as for the larger number of circular edge dislocations p and the spatial correlation length σ 0 , therefore it is necessary to optimally choose on p and σ 0 for obtaining an optimal optical guiding. The ranges of the radius for two types of particles stably captured also have been determined. The obtained results are useful for analyzing the trapping efficiency of circular edge dislocations beams applied in micromanipulation technology. [ABSTRACT FROM AUTHOR]

We observe the entire temporal evolution process of fluorescence and Raman spectra of single solid particles optically trapped in air. The spectra initially contain strong fluorescence with weak Raman peaks, then the fluorescence was bleached within seconds, and finally only the clean Raman peaks remain. We construct an optical trap using two counter-propagating hollow beams, which is able to stably trap both absorbing and non-absorbing particles in air, for observing such temporal processes. This technique offers a new method to study dynamic changes in the fluorescence and Raman spectra from a single optically trapped particle in air. [ABSTRACT FROM AUTHOR]

Cellular endocytosis is an essential phenomenon which induces cellular reactions, such as waste removal, nutrient absorption, and drug delivery, in the process of cell growth, division, and proliferation. To observe capacitance responses upon endocytosis on a single-cell scale, this study combined an optical tweezer that can optically place a single cell on a desired location with a capacitance sensor and a cell incubation chamber. Single HeLa cancer cell was captured and moved to a desired location through optical trapping, and the single-cell capacitance change generated during the epidermal growth factor (EGF) molecule endocytosis was measured in real time. It was found that single HeLa cells showed a larger increase in capacitance values compared to that of the single NIH3T3 cells when exposed to varying EGF concentrations. In addition, the capacitance change was in proportion to the cell's EGF receptor (EGFR) level when cells of different levels of EGFR expression were tested. An equation derived from these results was able to estimate the EGFR expression level of a blind-tested cell. The biosensor developed in this research can not only quickly move a single cell to a desired location in a non-invasive manner but also distinguish specific responses between cancer and normal cells by continuous measurement of real-time interactions of a single cell in culture to the external ligands. [ABSTRACT FROM AUTHOR]

• Generation and 2D manipulation of monolayer colloidal crystals by optothermal effects. • Stability of colloidal crystals by electrostatic stabilization by modulating the pH. • Spatial extension induced by a potential well associated with convective currents. Colloidal crystal plays a major role in novel optical devices such as waveguides, photonic crystals, and colloidal crystal lasers, among others. It has been known that colloidal crystals may self-assemble due to optical, electric, or chemical potentials, and light-induced thermal effects, such as thermophoresis and convective currents. In this work, the formation and manipulation of a self-limiting assembly of monolayer colloidal crystals using a 20 nm absorbing thin film of titanium and a CW-laser emitting at 1070 nm is reported. The colloidal particles, dragged by thermally induced convective currents, self-assembling over the titanium thin film around the laser focal spot. The self-assembled monolayer colloidal crystal tends to form a circular shape. Using numerical simulation, we obtained a potential well associated with the convective currents that spatially govern the radial extension of the monolayer colloidal crystal. We also show, that by changing the pH of the solution i.e., by tuning the electrostatic interaction, the monolayer colloidal crystal can be formed or destroyed. In addition, it was possible to create a larger monolayer colloidal structure covering an area of 600 μm2 using an array of six laser spots. [ABSTRACT FROM AUTHOR]

Room-temperature optical manipulation of small molecules is a challenging issue in the field of material science. To increase optical force for a single molecule trapping, it has been recognized that resonant excitation of molecules should be controlled under the light illumination. Strongly interacting molecules with solid surfaces at electrified interfaces show the exotic behavior of electronic excitation by localized surface plasmon. In this review, we emphases that surface-enhanced Raman scattering can be used to evaluate the resonant excitation of target molecules at interfaces. Under such excitation, the diffusion of small molecules can be controlled by the optical force generated by the intensity gradient of a highly localized electric field. • The plasmon enhanced electric field has the potential for single molecule manipulation at room temperature due to its ability for enhancing optical force. • Surface-enhanced Raman scattering observation observations are promising to evaluate molecular trapping behavior because of its high sensitivity. • Electrochemical control could be a key for the realization of small size molecular trapping because it can tune the molecular behavior and resonant process. • Strong interactions between molecules play an important role for the molecular trapping to enhance the optical force. [ABSTRACT FROM AUTHOR]

We report on a two-laser holographic optical tweezers setup and present its two major advantages over single-laser one. First, the trap stiffness of a weak trapping beam can be measured with a considerable accuracy. Second, a novel method of examining local viscosity of fluid is proposed. Both measurements are performed based on forcing the oscillations of a microscopic polystyrene bead placed between two optical traps. The two beams are generated by separate laser sources and therefore their trapping power can vary. Moreover, a stronger trap ‘blinks’, modulated by an electronic shutter. The blinking frequency can be precisely adjusted to the experimental conditions, which results in high accuracy of the measurements. [ABSTRACT FROM AUTHOR]

In optical trapping applications, the optical force should be investigated within a wide range of parameter space in terms of beam configuration to reach the desirable performance. A simple but reliable way of conducting the related investigation is to evaluate optical forces corresponding to all possible beam configurations. Although the optical force exerted on arbitrarily shaped particles can be well predicted by boundary element method (BEM), such investigation is time costing because it involves many repetitions of expensive computation, where the forces are calculated from the equivalent surface currents. An algorithm is proposed to alleviate the difficulty by exploiting our previously developed skeletonization framework. The proposed algorithm succeeds in reducing the number of repetitions. Since the number of skeleton beams is always much less than that of beams in question, the computation can be very efficient. The proposed algorithm is accurate because the skeletonization is accuracy controllable. [ABSTRACT FROM AUTHOR]

Direct analysis of biomolecules in complex biological samples remains a major challenge for fluorescence-based approaches due to the interference of background signals. Herein, we report an analytical methodology by exploiting a single low-cost near-infrared sub-nanosecond pulse laser to synchronously actualize optical trapping and two-photon excitation fluorescence for senstive detection of carcinoembryonic antigen (CEA) in buffer solution and human whole serum with no separation steps. The assay is performed by simultaneously trapping and exciting the same immune-conjugated microsphere fabricated with a sandwich immunization strategy. Since the signal is strictly limited in the region of a three-dimensional focal volume where the microsphere is trapped, no obvious background signal is found to contribute the detected signals and thus high signal-to-background data are obtained. As a proof-of-concept study, the constructed platform exhibits good specificity for CEA and the detection limit reaches as low as 8 pg/mL (45 fM) with a wide linear range from 0.01 to 60 ng/mL in the both cases. To investigate the potential application of this platform in clinical diagnosis, 15 cases of serum samples were analyzed with satisfactory results, which further confirm the applicability of this method. [ABSTRACT FROM AUTHOR]

Laser-induced breakdown spectroscopy (LIBS) was employed for investigating the influence of particle size on the dissociation efficiency and the absolute production of photons per mass unit of airborne solid graphite spheres under single-particle regime. Particles of average diameter of 400 nm were probed and compared with 2 μm particles. Samples were first catapulted into aerosol form and then secluded in an optical trap set by a 532 nm laser. Trap stability was quantified before subjecting particles to LIBS analysis. Fine alignment of the different lines comprising the optical catapulting-optical trapping-laser-induced breakdown spectroscopy instrument and tuning of excitation parameters conditioning the LIBS signal such as fluence and acquisition delay are described in detail with the ultimate goal of acquiring clear spectroscopic data on masses as low as 75 fg. The atomization efficiency and the photon yield increase as the particle size becomes smaller. Time-resolved plasma imaging studies were conducted to elucidate the mechanisms leading to particle disintegration and excitation. [ABSTRACT FROM AUTHOR]

Particle inhalation is an effective and rapid delivery method for a variety of pharmaceuticals, particularly bronchodilation drugs used for treating asthma and COPD. Conditions of relative humidity and temperature inside the lungs are generally very different from the outside ambient air, with the lung typically being warmer and more humid. Changes in humidity, from inhaler to lung, can cause hygroscopic phase transitions and particle growth. Increasing particle size and mass can negatively affect particle deposition within the lung leading to inefficient treatment, while deliquescence prior to impaction is liable to accelerate drug uptake. To better understand the hygroscopic properties of four pharmaceutical aerosol particles; pharmaceutical particles from four commercially available pressurised metered dose inhalers (pMDIs) were stably captured in an optical trap, and their composition was examined online via Raman spectroscopy. Micron-sized particles of salbutamol sulfate, salmeterol xinafoate, fluticasone propionate and ciclesonide were levitated and examined over a range of relative humidity values inside a chamber designed to mimic conditions within the respiratory tract. The effect of temperature upon hygroscopicity was also investigated for salbutamol sulfate particles. Salbutamol sulfate was found to have significant hygroscopicity, salmeterol xinafoate showed some hygroscopic interactions, whilst fluticasone propionate and ciclesonide revealed no observable hygroscopicity. Thermodynamic and structural modelling is used to explain the observed experimental results. [ABSTRACT FROM AUTHOR]

• The focal spot with accurate position can be straightforwardly realized. • Apply two non-iterative methods to achieve multifocal spots with accurate position. • The complex amplitude coding method produced multifocal spots with higher uniformity and stability than the fan-shaped subzone phase method. • Three-dimensional particle manipulation dynamic optical trapping experiment. Holographic optical trapping enables three-dimensional (3D) particle manipulation based on a traditional iterative algorithm. However, this type of particle manipulation is typically unstable. It is challenging to realize continuous dynamic 3D optical trapping because a unique solution of uniformity cannot be obtained over several time-consuming iterations. In this study, 3D multifocal spots with high uniformity were generated via non-iterative algorithms (using a complex amplitude coding method and fan-shaped subzone phase method) to realize stable dynamic optical trapping for 3D particle manipulation. The corresponding experimental results pave the way for potential applications of colloid transport and the micro-assembly of objects in the micro-operation field. [ABSTRACT FROM AUTHOR]

• Measuring the viscosity of liquids by oscillation in optical tweezers. • Oscillation of the optical trap to local liquid measurements. • Measurement the viscosity of medium in biological samples. • Power spectral density to measure the liquids viscosity in optical tweezers. • Compare measurement of fluid viscosity by oscillation and viscometer in optical trap. We present a modified method of measuring liquid viscosity in an optical tweezer system. The oscillating viscosity measurement was developed theoretically and then experimentally verified. The presented method enables quick measurement, does not require much space and the use of a camera enables other measurements, e.g. in the field of molecular biology, to be carried out in the same sample. Measurement of liquid viscosity using the presented method is possible for viscosities up to 2,5 mPa*s. [ABSTRACT FROM AUTHOR]

[Display omitted] • Optically-trapped, chemically-purposed, micron-sized, single-particle reactor (SPR) in air. • Heterogeneous reaction of solid-state Hg(II) halides on the surface SPR. • A new platform for the study of surface and heterogeneous chemistry of aerosol particles in air. We created a micron-sized, single-particle reactor (SPR) freely levitated in air using optical trapping of a single particulate-bound mercury particle formed by mixing HgCl 2 , HgBr 2 , or HgBrCl (HgX 2 , X = Cl, Br) with single-walled carbon nanotubes. Position- and time-resolved, single-particle Raman spectra show clear evidence of reactions of solid-state HgX 2 in the presence of excessive O 3 under the illumination of 532-nm light. We propose a reaction mechanism: Hg(II)X 2 (solid) + O → Hg(I)X + XO, XO + O → O 2 + X on the surface of the SPR. This exploratory study demonstrates that the SPR is a new tool for the study the surface and heterogeneous chemistry of mercury at atmospherically relevant surfaces, e.g., aerosols. [ABSTRACT FROM AUTHOR]

Light possesses momentum, and hence, force is exerted on materials if they absorb and/or scatter light. Laser techniques that use optical forces are currently attracting considerable attention. Optical manipulation for trapping, transporting small particles, and measuring the interparticle force is a representative technique. In addition, photoinduced force microscopy is a promising scanning type of microscopy using optical force. Optical force techniques have recently been used in various fields of research, such as molecular bioscience, organic photochemistry, materials engineering, and molecular fluid dynamics. In these techniques, several types of optical forces such as scattering, absorption, and gradient forces play their respective roles. In this article, we summarize the basics of optical forces and present their elementary expressions for using simplified models of light and matter systems. This will help the readers of this Special Issue to understand how different types of forces are distinguished in the basic expressions used for analyzing the optical force phenomena that appear depending on the light geometry and matter systems. After observing simplified cases of scattering and absorption forces, we introduce general formulae for the optical force and then discuss how different components appear in particular cases of laser geometry and materials. • Optical force of simple scattering and absorption cases. • Optical force based on the photon picture. • General Expressions for the Optical Force. • Components of the optical force under a focused laser beam. [ABSTRACT FROM AUTHOR]

We present a novel and direct technique to map the incident laser intensity across the active area of a spatial light modulator (SLM) by using diffraction based setup in a holographic optical tweezers (HOTs) system to generate structured light. The incident laser beam profile on the SLM is used as input to the optical trap generating algorithms such as weighted Gerchberg Saxton algorithm, generalized adaptive additive algorithm etc. The input laser beam profile is generally assumed to be located at the center of SLM in these algorithms. However, it is not straight-forward to ensure that the center of the Gaussian laser beam coincides with the center of SLM. The importance of mapping the laser intensity across the SLM is demonstrated by a study of the effect of mismatch between the input laser beam center and the actual beam center on the trap properties such as uniformity of intensity, and sharpness of the focal spots. We also propose a method of centering the laser beam profile on the SLM which enables the use of known beam profile. This method allows the use of HOTs with any spatial transverse distribution of a laser beam, such as elliptical profile of diode lasers, Laguerre Gaussian beams or with any distorted beam shape deviating from Gaussian profile. [ABSTRACT FROM AUTHOR]

We present a strategy of dual-component gene detection for avian influenza A virus H7N9 by combining optical trapping and bead-based fluorescence bioassays. A low-cost 473 nm continuous DPSS laser, polystyrene (PS) beads with two different sizes (3 µm and 5 µm in diameter) and streptavidin-modified 605 nm quantum dots (SA-QDs) were exploited in this platform. The beads were employed to enrich the targets using the classic sandwich mode and tagged with the SA-QDs, then the QDs-tagged beads floating in the suspension were directly trapped and excited by the optical tweezers to give strong and stable fluorescence signal, which was applied to quantify the targets. The distinctive size information from the image of the trapped beads enabled the sorting of the different targets. The results show that tiny laser power 40 μW is applicable for both trapping and fluorescence excitation of the beads. Moreover, the limits of detection for hemagglutinin7 (H7) gene and neuraminidase 9 (N9) gene are 1.0–2.0 pM with good selectivity for the complex sample, which is two orders of magnitude lower than that of the conventional method. More importantly, this strategy was successfully used to identify the subtype of the avian influenza A virus by simultaneous detection of H7 and N9 gene sequences. The high sensitivity, good selectivity, typing ability and the low cost of the laser make this strategy a promising method for life sciences and clinical applications. [ABSTRACT FROM AUTHOR]

The ultra-short optical pulses can be used for the confinement of neutral particles by an additional optical longitudinal force, connected with the Poynting vector and the influence of the magnetic field on their polarizability. The Poynting vector is connected also to the intensity of the electromagnetic field. On other hand, the intensity of a laser pulse can be manipulated by an optical lens, and thus, indirectly, the optical force can be increased or decreased or its direction to be changed. This in turn enables a unique possibility for the compression of neutral atoms, molecules, and particles into the focus of the lens. Here, we reported on an experimental study of neutral particle confinement in the focus of femtosecond laser pulses and further confirmed by a theoretical investigation. The findings demonstrate an innovative approach to the compression and confinement of neutral particles within the focal plane of a lens and their further manipulation. Feasible applications could be in the field of cold nuclear fusion and cooling of light-neutral atoms and molecules. [ABSTRACT FROM AUTHOR]

• Used a combined single/dual fiber optical trapping system. • Each fiber first captures a single microsphere near its tip by focus-induced gradient force. • Two fibers (with trapped particles) were then aligned and adjusted to allow additional particles to be trapped and manipulated in the middle by the dual-fiber scattering trapping scheme. Fiber-based optical tweezers have attracted increasing attention as a more flexible tool over conventional lens-based optical tweezers for particle manipulation. Stable trapping can be realized by single fiber gradient force, or dual fiber counter-propagating scattering forces. Both trapping modes and systems are often separately built and researched. In this paper, we demonstrate a combined single/dual fiber optical trapping (SD-FOT) system which allows dual trapping modes (i.e., single fiber gradient mode and dual fiber scattering mode) to be realized simultaneously in a single setup. Two tapered single fibers were used, with each fiber first captures a single microsphere near its tip by focus-induced gradient force; The two fibers (with trapped particles) were then aligned and adjusted to allow additional particles to be trapped and manipulated in the middle by the dual-fiber scattering trapping scheme. At least three particles will be trapped and manipulated by the combined trapping system, and each of particle can be used for in-situ experimental activity and analysis. Meanwhile, theoretical modeling of the optical force was established to quantify both trapping processes, and the process of the particle movement in the experiment is in accordance with the simulated force field. The developed system offers new possibilities in comparative research of single and dual fiber trapped objects and will find important applications in microsphere-based super-resolution imaging and others. [ABSTRACT FROM AUTHOR]

Based on the generalized Lorenz–Mie theory (GLMT), a theoretical approach is introduced to study the radiation force exerted on a uniaxial anisotropic sphere illuminated by dual zero-order Bessel beams (ZOBBs). The beams propagate with arbitrary direction, and are expanded in terms of the spherical vector wave functions (SVWFs) in the particle coordinate system using the coordinate rotation theorem. The total expansion coefficients of the incident fields are derived by superposition of the vector fields. Applying the Maxwell's stress tensor, the analytical expressions of the radiation forces on a homogeneous absorbing uniaxial anisotropic sphere are derived. Comparing the radiation forces of dual ZOBBs with those results of dual ZOBBs simplified into single ZOBBs and dual plane waves, the accuracy and correctness of the theory are verified. In order to study the equilibrium state, the effects of beam parameters, particle size parameters, and anisotropy parameters on the radiation forces are discussed in detail. Comparing with the isotropic particle, the equilibrium status is sensitive to the anisotropic parameters. Moreover, the properties of optical force on a uniaxial anisotropic sphere in single ZOBB trap and zero-order Bessel standing wave trap are compared. The theory and results of this paper are hopeful to provide an effective theoretical basis for the study of optical micromanipulation of biological and anisotropic complex particles by multi-beams. • Based on GLMT, the radiation force exerted on a uniaxial anisotropic sphere by dual arbitrary incident ZOBBs is studied. • The expansion coefficients of the ZOBB with arbitrary propagation direction in terms of the SVWFs are derived. • Comparing with the isotropic particle, the equilibrium status is sensitive to the anisotropy in ZOBB standing wave trap. • The CP ZOBBs or GB trap is easier capture or confine the anisotropic particle comparing with a single ZOBB or GB trap. [ABSTRACT FROM AUTHOR]

Noninvasive and nondestructive techniques for monitoring and manipulating cells or biomolecules are essential for understanding biological processes. Optical methodologies have been used for the noninvasive and nondestructive monitoring of intracellular molecules and manipulation of cellular activities to elucidate the localization and interactions of these biomolecules. Since the pioneering work of Ashkin, optical trapping has been used to study cellular elasticity and mechanical characteristics of intracellular molecules. In recent years, there has been a substantial amount of research on the optical manipulation of nanometer-sized objects, including the manipulation of the assembly of nanomaterials and the enhancement of optical forces with optical resonance effects. In the study of biomolecular manipulation by optical forces, the functions and roles of biomolecules have been clarified by analyzing the changes in cellular functions induced by manipulation. In this review, we focus on recent studies on optical trapping for the manipulation of living cells or biomolecules and introduce techniques for the manipulation of cellular functions using optical forces. [Display omitted] • Optical manipulation of cellular functions to clarify biological processes. • Measurement methods for manipulating biomolecules under optical trapping. • Direct manipulation of biomolecules and single cells by optical forces. • Extreme biomolecule manipulation by optical trapping and surrounding environmental change in cell manipulation by optical forces. [ABSTRACT FROM AUTHOR]

Optical energy flow inside a dielectric microsphere exposed to an optical wave is usually codirected with its wave vector. At the same time, if the optical field in a microparticle is in resonance with a high-quality spatial eigenmode, referred to as the whispering-gallery mode (WGM), at least two regions of reverse energy flow emerge in the illuminated and shadow particle hemispheres. These areas are of considerable practical interest due to their enhanced optical trapping potential provided they should be previously cleared from particle material. In this paper, we consider a perforated microsphere with an air-filled pinhole fabricated along the particle diameter and theoretically analyze the conditions for WGMs excitation. A pinhole isolates the energy backflow regions of WGM and multiple enhances the optical pull-in force that transforms a perforated microsphere into an efficient optical tweezer for trapping various nanoobjects. • A miniature dielectric sphere structured with nano-hole and exposed to optical radiation produces an energy backflow at hole ends. • The backflow magnitude is manifold increased at resonant whispering-gallery modes excitation. • The concept of an efficient optical trap based on a perforated dielectric microsphere is proposed and numerically simulated. [ABSTRACT FROM AUTHOR]

Silver nanoparticles (AgNPs) with radius of ∼20 nm were optically trapped and immobilized on thiophenol (TP)-covered Ag films under a gap mode resonance with extremely weak power density of ∼1 μW/μm 2 at 532 nm. Intensity of Raman scattering from TP markedly increased with the accumulation of AgNPs. Trapping efficiency of AgNPs for p-polarization was 2–4 times higher than that for s-polarization. The observed optical trapping and immobilization were theoretically rationalized using a dipole–dipole coupling under a gap mode and van der Waals interaction between AgNPs and Ag films, which facilitate to fabricate versatile substrates for surface enhanced Raman scattering. [ABSTRACT FROM AUTHOR]

The radiation force on a Rayleigh dielectric particle produced by highly focused modified hollow Gaussian (MHG) beams is investigated numerically and theoretically. The results show that the highly focused MHG beams can be used to trap and manipulate the particles with low or high index of refractive larger than that of ambient at the focus point and in the neighbourhood of the focal plane simultaneously in the different region. Also, the conditions for trapping stability are analyzed in this paper. [ABSTRACT FROM AUTHOR]

This paper presents computational analysis on higher order optical vortex lattices. Tunability of higher order topological charge can be done by tuning the predetermined phase of phase engineered beams. Simultaneously we report the symmetrical annular intensity profile around the higher order topological charge. It is also presented that generated topological rings around the higher order topological charge used in trapping of low index particle varies with topological charge at the center of vortex lattice. Laguerre–Gaussian modes are also defined using the interference method. [ABSTRACT FROM AUTHOR]

Optical vortex beams carry optical orbital angular momentum (OAM) and can induce an orbital motion of trapped particles in optical trapping. We show that the state of polarization (SOP) of vortex beams will affect the details of this optically induced orbital motion to some extent. Numerical results demonstrate that focusing the vortex beams with circular, radial or azimuthal polarizations can induce a uniform orbital motion on a trapped Rayleigh particle, while in the focal field of the vortex beam with linear polarization the particle experiences a non-uniform orbital motion. Among the formers, the vortex beam with circular polarization induces a maximum optical torque on the particle. Furthermore, by varying the topological charge of the vortex beams, the vortex beam with circular polarization gives rise to an optimum torque superior to those given by the other three vortex beams. These facts suggest that the circularly polarized vortex beam is more suitable for rotating particles. [ABSTRACT FROM AUTHOR]

For a long time, transverse optical forces with continuous-wave laser beams have been used for non-contact manipulation of micro-scale objects. By replacing the continuous-wave lasers with pulse-mode lasers many novel physical effects related with the influence of Poynting vector on the longitudinal part of the optical force can be observed. The following question arises: What is the impact of this longitudinal addition to the optical force, connected with the flow of energy, on the ensemble of thousand particles in continuous media? The aim of this work is to find analytical expressions of the radiation force and potential densities arising from a laser pulse propagating in a dielectric media. This allows us to find an effective averaged longitudinal real force at the level of the laser pulse's spot. The obtained force is proportional to the initial pulse energy and inversely proportional to its time duration. In the femtosecond region the force becomes strong enough to confine neutral particles into the pulse envelope and translate them with the group velocity in gases. Additionally, if the trapped particles into the pulse's spot are with high density, the probability of collision with the free atoms and molecules in air become significant. The collision energies are in the range of 12–24 GeV and high enough to ionize the neutral atoms. Thus, a new type of collision ionization can be observed, when powerful femtosecond pulses propagate in gaseous media. [ABSTRACT FROM AUTHOR]

Precise manipulation and sorting of nanomaterials cannot rely on techniques used for micro- and macro-scale objects because of their nanoscale size, which is smaller than the diffraction limit, and their fast Brownian diffusion. To overcome the limitations of standard optical tweezers, new techniques have recently emerged that make use of optical forces acting on nanomaterials in the vicinity of photonic and plasmonic nanostructures. This review focuses on the techniques that have been recently developed to either optically transport, sort, trap, rotate, assemble, or deposit nanomaterials using photonic or plasmonic devices. The first part is dedicated to the optical transport and sorting of nanomaterials using photonic waveguides. The second part provides an overview of the recent work on optical trapping and manipulation of nanomaterials using photonic and plasmonic nanoresonators. The third part provides a short summary of recent work on optical trapping and manipulation using metalenses and metasurfaces. This review aims to highlight some specific functionalities enabled by photonic and plasmonic devices that make it possible to tailor the optical forces acting on nanomaterials. • Optical transport using solid-core and hollow-core photonic waveguides. • Optical sorting and characterization of nanomaterials using photonic waveguides. • Optical trapping using photonic and plasmonic nanotweezers. • Optical rotation, assembly, and deposition of trapped nanomaterials. • New opportunities of optical manipulation using metalenses and other metamaterials. [ABSTRACT FROM AUTHOR]

• 2D elastic-scattering patterns of single particles. • Orientation control of optically trapped particles. • Comparison with diffraction calculations. We demonstrate a method for recording 2D forward-scattering patterns from optically trapped single airborne particles at multiple angular orientations. We collected images of trapped particles simultaneously with their scattering patterns to observe changes in the patterns with orientation. We present measurements of particles with wide-ranging morphologies from nearly spherical to highly irregular and with various compositions. The highly irregularly shaped particles have scattering patterns with spots of high intensity whose locations change with particle orientation. Additionally, measurements of a manufactured polystyrene spheroid of a known size are compared with calculated diffraction patterns. Such controlled-orientation measurements have the potential to help develop algorithms to characterize airborne aerosol particles using morphological information inferred from remote-sensing or other elastic light scattering measurements. [ABSTRACT FROM AUTHOR]

We numerically investigate the trapping effect of the focused generalized Multi-Gaussian Schell model (GMGSM) beam of the first kind which produces dark hollow beam profile at the focal plane. By calculating the radiation forces on the Rayleigh dielectric sphere in the focused GMGSM beam, we show that such beam can trap low-refractive-index particles at the focus, and simultaneously capture high-index particles at different positions of the focal plane. The trapping range and stability depend on the values of the beam index N and the coherence width. Under the same conditions, the low limits of the radius of low-index and high-index particles for stable trapping are indicated to be different. [ABSTRACT FROM AUTHOR]