Thursday, October 18, 2018

Living Nanospear for Near-Field Optical Probing

Yuchao Li, Hongbao Xin, Yao Zhang, Hongxiang Lei, Tianhang Zhang, Huapeng Ye, Juan Jose Saenz, Cheng-Wei Qiu, and Baojun Li

Optical nanoprobes, designed to emit or collect light in the close proximity of a sample, have been extensively used to sense and image at nanometer resolution. However, the available nanoprobes, constructed from artificial materials, are incompatible and invasive when interfacing with biological systems. In this work, we report a fully biocompatible nanoprobe for subwavelength probing of localized fluorescence from leukemia single-cells in human blood. The bioprobe is built on a tapered fiber tip apex by optical trapping of a yeast cell (1.4 μm radius) and a chain of Lactobacillus acidophilus cells (2 μm length and 200 nm radius), which act as a high-aspect-ratio nanospear. Light propagating along the bionanospear can be focused into a spot with a full width at half-maximum (fwhm) of 190 nm on the surface of single cells. Fluorescence signals are detected in real time at subwavelength spatial resolution. These noninvasive and biocompatible optical probes will find applications in imaging and manipulation of biospecimens.


Temperature elevation and fluid convection under optical trapping condition as revealed by fluorescence correlation spectroscopy

Kenji Setoura; Keisuke Fujita; Syoji Ito; Hiroshi Miyasaka

Temperature of matter increases under intense photoirradiation owing to photothermal conversion. The photothermal effect is sometimes a significant issue in optical manipulation usually requiring intense optical fields. Quantitative evaluation of local temperature under photoirradiation can, therefore, provide indispensable information for optical manipulation. In a previous work, we have applied fluorescence correlation spectroscopy (FCS) to monitor the temperature under the optical trapping condition in water, ethanol, and ethylene glycol. We pointed out that analyses of diffusion time of fluorescent dyes could provide information about temperature on the basis of temperature-dependent viscosities of the solvents. In the present work, the FCS thermometry was applied to seven solvents including primary aliphatic alcohols, to examine universal applicability of the method. To verify the experimental results, numerical simulations were performed on the basis of two-dimensional heat conduction at a stationary state. The numerical results on the temperature field satisfactorily reproduced the experimental data, proving that the FCS thermometry is applicable to ordinary solvents. In addition, we also performed numerical simulations on velocity fields in the solvent, to evaluate contribution of natural convection under typical optical trapping condition at light intensity of ∼MW cm − 2. It was revealed that the contribution of the natural convection is not negligible for mass transfer in the solvents.


Nonparaxial propagation of abruptly autofocusing circular Pearcey Gaussian beams

Xingyu Chen, Dongmei Deng, Jingli Zhuang, Xiangbo Yang, Hongzhan Liu, and Guanghui Wang

We introduce a new class of abruptly autofocusing circular Pearcey Gaussian beams (AAFCPGBs) which tend to be abruptly autofocusing circular Pearcey beams with a small distribution factor, or Gaussian beams with a larger distribution factor. The nonparaxial propagation of the AAFCPGBs is investigated by numerical calculation. The radiation force of the AAFCPGBs exerted on a Rayleigh particle is analyzed in detail.


Electromagnetic binding and radiation force reversal on a pair of electrically conducting cylinders of arbitrary geometrical cross-section with smooth and corrugated surfaces

F. G. Mitri

The electromagnetic (EM) radiation force-per-length exerted on a pair of electrically-conducting cylindrical particles of circular and non-circular cross-sections is examined using a formal semi-analytical method based on boundary matching in cylindrical coordinates. Initially, the scattering coefficients of the particle pair are determined by imposing suitable boundary conditions leading linear systems of equations computed via matrix inversion and numerical integration procedures. Standard cylindrical (Bessel and Hankel) wave functions are used and closed-form expressions for the dimensionless longitudinal and transverse radiation force functions are evaluated assuming either magnetic (TE) or electric (TM) plane wave incidences. Particle pairs with smooth and corrugated surfaces are considered and numerical computations are performed with emphasis on the distance separating their centers of mass, the angle of incidence of the incident illuminating field and the surface roughness. Adequate convergence plots confirm the validity of the method to evaluate the radiation force functions, and the model is adaptable to any frequency range (i.e. Rayleigh, Mie or geometrical optics regimes). The results can find potential applications in optical tweezers and other related applications in fluid dynamics. In addition, the acoustical analogue is discussed.


Sizing and identification of nanoparticles by a tapered fiber

Huiling Pan, Weina Zhang and Hongxiang Lei

There is a strong desire for sizing and identification of nanoparticles in fields of advanced nanotechnology and environmental protection. Although existing approaches can size the nanoparticles, or identify nanoparticles with different refractive indexes, a fast and simple method that combines the two functions still remains challenges. Here, we propose a versatile optical method to size and identify nanoparticles using an optical tapered fiber. By detecting reflection signals in real time, 400–600 nm SiO2 nanoparticles can be sized and 500 nm SiO2, PMMA, PS nanoparticles can be identified. This method requires only an optical tapered fiber, avoiding the use of elaborate nanostructures and making the device highly autonomous, flexible and compact. The demonstrated method provides a potentially powerful tool for biosensing, such as identification of nano-contaminant particles and biological pathogens.


Cooperative and mobile manipulation of multiple microscopic objects based on micro-hands and laser-stage control☆

Quang MinhTa, Chien Chern Cheah

While various techniques have been developed for manipulation of biological cells or micro-objects using optical tweezers, the performance and feasibility of these techniques are mostly dependent on the physical properties of the target objects to be manipulated. In these existing techniques, direct trapping and manipulation of the manipulated objects using laser traps are performed, and therefore, existing techniques for optical manipulation are not capable of coordinating and manipulating various types of objects in the micro-world, including untrappable micro-objects, relatively large micro-objects, and laser sensitive biological cells. In this paper, a cooperative control technique is proposed for coordinative and mobile manipulation of multiple microscopic objects using micro-hands with multiple laser-driven fingertips and robot-assisted stage control. Several virtual micro-hands are formed by coordinating multiple optically trapped micro-particles that serve as the laser-driven fingertips, and then utilized for individual and coordinative manipulation of the target micro-objects. Simultaneously, global transportation of all the grasped target objects is performed by controlling the robot-assisted stage. While it is difficult to design multi-fingered hands in micro-scale due to scaling effect, this paper presents the first result on cooperative and mobile manipulation of multiple micro-objects using multiple micro-hands with laser-driven fingertips and robot-assisted stage control. In this paper, a primary study on repositioning strategy of the laser-driven fingertips is also introduced to allow the fingertips in a grasping formation to be repositioned. Rigorous mathematical formulations and solutions are derived to achieve the control objective, and experimental results are presented to demonstrate the effectiveness of the proposed control technique.


Wednesday, October 17, 2018

Switching and Torque Generation in Swarming E. coli

Katie M. Ford, Jyot D. Antani, Aravindh Nagarajan, Madeline M. Johnson and Pushkar P. Lele

Escherichia coli swarm on semi-solid surfaces with the aid of flagella. It has been hypothesized that swarmer cells overcome the increased viscous drag near surfaces by developing higher flagellar thrust and by promoting surface wetness with the aid of a flagellar switch. The switch enables reversals between clockwise (CW) and counterclockwise (CCW) directions of rotation of the flagellar motor. Here, we measured the behavior of flagellar motors in swarmer cells. Results indicated that although the torque was similar to that in planktonic cells, the tendency to rotate CCW was higher in swarmer cells. This suggested that swarmers likely have a smaller pool of phosphorylated CheY. Results further indicated that the upregulation of the flagellin gene was not critical for flagellar thrust or swarming. Consistent with earlier reports, moisture added to the swarm surface restored swarming in a CCW-only mutant, but not in a FliG mutant that rotated motors CW-only (FliGCW). Fluorescence assays revealed that FliGCW cells grown on agar surfaces carried fewer flagella than planktonic FliGCW cells. The surface-dependent reduction in flagella correlated with a reduction in the number of putative flagellar preassemblies. These results hint toward a possibility that the conformational dynamics of switch proteins play a role in the proper assembly of flagellar complexes and flagellar export, thereby aiding bacterial swarming.


Optical Method for Formation of Nanostructure in Nanosuspension

Valerii Ivanovich Ivanov, Vladimir Kancherovich Khe, Vladimir Ivanovich Krylov, Denis Alexeyevich Syrnikov

It is proposed to use light pressure forces to form nanostructures in a transparent nanosuspension. We have discussed the theoretical model of formation of crystal from nanoparticles on a bottom of cuvette by using the laser effect in liquid. It was received the steady-state solution of one-dimensional task of the light induced mass transfer as depending on intensity of laser beam.


Orientation-Control of Two Plasmonically Coupled Nanoparticles in an Optical Trap

Hamideh Kermani and Alexander Rohrbach
Optical monitoring of nanoparticle (NP) dynamics is typically beyond the spatial and temporal resolution limit of light microscopy. However, the orientation and assembly of NPs can be controlled by various light scattering methods. Here we demonstrate how two 80 nm silver NPs form a dimer inside an optical trap and orient along the electric field of the trapping laser, therefore allowing to rotate them stably in the horizontal plane. We built a dual-path spectrometer for two orthogonal polarization directions to determine the azimuthal dimer angle for different plasmonic coupling strengths by the difference in the measured spectral intensity maxima. The azimuthal angle of the dimer could be retrieved with an accuracy of a few degrees independent of the spectral frequency or the distance between the NPs. Our results coincide well with a developed theoretical model predicting polarization-dependent scattering spectra for dimers with different orientations and NP distances. Our study points out another strategy for a highly controlled assembly of single NPs using optical tweezers and multimodal scattered light.


Optical funnel for living cells trap

Zhihai Liu, Lu Wang, Yu Zhang, Chao Liu, Jiaze Wu, Yaxun Zhang, Xinghua Yang, Jianzhong Zhang, Jun Yang, Libo Yuan

We proposed and experimentally demonstrated an optical funnel for living cells trap based on an annular-core optical fiber. The proposed optical funnel employed the annular dark field to trap the living cell to avoid the laser damages. To perform the dark field trap, we placed the living cells in the glycerol solution. The refractive index of glycerol liquid was higher than yeast cells, which helped to perform the dark field trap; the viscosity of glycerol was significant, which helped to perform the viscosity-assisted 3-D trapping. The experimental results showed that the donut shape intensity field introduced by a single fiber probe performed 3D trapping easily and efficiently. Such funnel-shaped hollow conical beam could find ample potentials in optical manipulation on biological living cells, avoiding optical damages. All-fiber and seamlessly integrated structure of the proposed scheme could find ample potentials in manipulating biological cells.