Enhanced forward scattering of a cell in line optical tweezers with an astigmatic beam.

The line optical tweezers (LOT) has been proven to be an alternative technique to manipulating the biological cells because of the bigger potential compared with traditional optical tweezers with a highly focused spot. We deduce the 4 × 4 optical matrix of the astigmatic LOT to investigate the optical characteristics related to the systematic parameters. The comparison of the initial and scattered electric fields by the cell under the astigmatic and stigmatic LOT is implemented to illustrate that the forward scattered light from the astigmatic LOT is much stronger than that from the stigmatic LOT, so as to the cell deformations. It is demonstrated that the astigmatic LOT could provide a more efficient way to deform the cell not only in the focal plane, but also along the optical axis to screen large biomaterials in biomechanics.

Light sheet fluorescence microscopy with active optical manipulation.

We present a light sheet fluorescence microscopy (LSFM) with active optical manipulation by using linear optical tweezers (LOTs). In this method, two coaxially transmitting laser beams of different wavelengths are shaped using cylindrical lenses to form a linear optical trapping perpendicular to the optical axis and an excitation light sheet (LS) parallel to the optical axis, respectively. Multiple large-sized polystyrene fluorescent microspheres are stably captured by LOTs, and their rotation angles around specific rotation axes are precisely controlled. During a sample rotation, the stationary excitation LS scans the sample to obtain fluorescence sectioning images of the sample at different angles.

Analysis of reaction between vitamin B6 and bovine serum albumin based on a terahertz metamaterial sensor.

A four-peak terahertz metamaterial sensor was used to detect the reaction between different concentrations of vitamin B6 (VB6) and bovine serum albumin (BSA), which achieves a concentration range (0.015-0.125 mg/µl) of VB6 and a maximum binding concentration (0.05 mg/µl) of VB6 and 0.0875 mg/µl BSA. To understand the combination of VB6 and BSA, the reactants between VB (VB1, VB3, and VB5) with the same concentration (0.05 mg/µl) and a BSA solution with a concentration of 0.0875 mg/µl were carried on the surface of the sensor. Experimental results show that the reactants cause the four resonance peaks of the sensor to produce the coincident redshift, which is the same as the order of their binding coefficients determined by the fluorescence method. The experimental process indicates that it is feasible to use terahertz metamaterials to detect the reaction process of organic matter.

A 2D Magneto-Acousto-Electrical Tomography Method to Detect Conductivity Variation Using Multifocus Image Method.

As magneto-acoustic-electrical tomography (MAET) combines the merits of high contrast and high imaging resolution, and is extremely useful for electrical conductivity measurement, so it is expected to be a promising medical imaging modalities for diagnosis of early-stage cancer. Based on the Verasonics system and the MC600 displacement platform, we designed and implemented a MAET system with a chirp pulse stimulation (MAET-CPS) method and a focal probe was utilized for stepscan focus excitation to enhance the imaging resolution. The relevant experiments were conducted to explore the influence of excitation positions of the single-focus point, and the effect of the excitation position on the amplitudes of the conductivity variation was clearly demonstrated. In order to take advantage of the merits of multifocus imaging, we firstly proposed a single focus MAET system with a chirp pulse stimulation (sfMAET-CPS) method and a multifocus MAET system with a chirp pulse stimulation (mfMAET-CPS) method for high-resolution conductivity imaging, and a homogenous gelatin phantom with a cuboid-shaped hole was used to investigate the accuracy of mfMAET-CPS. Comparative experiments were carried out on the same uniform phantom by the sfMAET-CPS and the mfMAET-CPS, respectively. The results showed that: (1) the electrical conductivity distributions of the homogenous phantom with a cuboid-shaped hole were detected by the sfMAET-CPS but were easily affected by the focal point, which demonstrated that the sfMAET-CPS had a low imaging resolution. (2) Compared with the sfMAET-CPS, the imaging effect of the mfMAET-CPS was much better than that of the sfMAET-CPS. (3) A linear interpolation algorithm was used to process the 2D conductivity distribution; it increased the smoothness of the conductivity distribution and improved the imaging effect. The stepscan focus excitation and the linearly frequency-modulated theory provide an alternative scheme for the clinical application of MAET.

Effect of the object 3D shape on the viscoelastic testing in optical tweezers.

Viscoelastic testing of biological cells has been performed with the optical tweezers and stretcher. Historically, the cells were modeled by the spring-dashpot network or the power-law models, which can however characterize only the homogeneous, isotropic viscoelastic material, but not the 3D cell itself. Our mechanical and finite element analyses show that the cell elongations are different significantly for different cell 3D shapes in the creep testing. In the dynamic testing the loss tangent, which is measurable directly in the experiment, is not sensitive to the cell shape. However, the stress-strain hysteresis loop still depends on the cell 3D shape.

Mechanical analysis of the optical tweezers in time-sharing regime.

Time-sharing optical tweezers is a versatile technique to realize multiple traps for manipulating biological cells and macromolecules. It has been based on an intuitive hypothesis that the trapped viscoelastic object does not "sense" blinking of the optical beam. We present a quantitative analysis using mechanical modeling and numerical simulation, showing that the local stress and strain are jumping all the time and at all locations with the jumping amplitude independent of the recovery time of the viscoelastic material and the jumping frequency. Effects of the stress and strain jumping on the object deformation and the internal energy dissipation are analyzed.

Dynamic speckle illumination wide-field fluorescence microscopy with actively optical manipulation of rotational angles.

We present a dynamic speckle illumination wide-field fluorescence microscopy (DSIWFM) combined with a line optical tweezers (LOTs) for rotational fluorescence sectioning imaging. In this method, large polystyrene fluorescent microspheres are stably trapped with LOTs, and precisely manipulated to rotate around a specific rotation axis. During the rotation process, multiple raw fluorescence images of trapped microspheres are obtained with dynamic speckle illumination. The root-mean-square (RMS) algorithm is used to extract the drastically changing fluorescent signals in the focal plane to obtain the fluorescence sectioning images of the samples at various angles. The influence of speckle granularity on the image quality of fluorescence sectioning images is experimentally analyzed. The rotational fluorescence sectioning images obtained by DSIWFM with LOTs could provide an alternative technique for applications of biomedical imaging.

Three-dimensional light-scattering and deformation of individual biconcave human blood cells in optical tweezers.

For studying the elastic properties of a biconcave red blood cell using the dual-trap optical tweezers without attaching microbeads to the cell, we implemented a three-dimensional finite element simulation of the light scattering and cell's deformation using the coupled electromagnetic and continuum mechanics modules. We built the vector field of the trapping beams, the cell structure layout, the hyperelastic and viscoelastic cell materials, and we reinforced the constraints on the cell constant volume in the simulation. This computation model can be useful for studying the scattering and the other mechanical properties of the biological cells.

Maple Leaf Inspired Conductive Fiber with Hierarchical Wrinkles for Highly Stretchable and Integratable Electronics.

Stretchable and durable conductors are significant to the development of wearable devices, robots, human-machine interfaces, and other artificial intelligence products. However, the desirable strain-insensitive conductivity and low hysteresis are restricted by the failure of stretchable structures and mismatch of mechanical properties (rigid conductive layer and elastic core substrate) under large deformation. Here, based on the principles of fractal geometry, a stretchable conductive fiber with hierarchical wrinkles inspired by the unique shape of the maple leaf was fabricated by combining surface modification, interfacial polymerization, and improved prestrain finishing methods to break through this dilemma. The shape and size of wrinkles predicted by buckling analysis via the finite element method fit well with that of actual wrinkles (30-80 µm of macro wrinkles and 4-6 µm of micro wrinkles) on the fabricated fiber. Such hierarchically wrinkled conductive fiber (HWCF) exhibited not only excellent strain-insensitive conductivity denoted by the relative resistance change ΔR/R0 = 0.66 with R0 the original resistance and ΔR the change of resistance after the concrete strain reaching up to 600%, but also low hysteresis (0.04) calculated by the difference in area between stretching and releasing curve of the ΔR/R0 strain under 300% strain and long-term durability (>1000 stretching-releasing cycles). Furthermore, the elastic conductive fiber with such a bionic structure design can be applied as highly stretchable electrical circuits for illumination and monitors for the human motion under large strains through tiny and rapid resistance changes as well. Such a smart biomimetic material holds great prospects in the field of stretchable electronics.

Fiber-integrated optical tweezers for ballistic transport and trapping yeast cells.

Due to their unique operational flexibility and ability to facilitate functional integration, the fascinating application of optical fibers has recently attracted significant attention in the field of optical tweezers and optical manipulation. The traditional optical fiber tweezers (OFTs) can easily trap microparticles in the front or side of the trapping tool, instead of behind. Herein, we propose and demonstrate a novel capillary optical fiber tweezer (COFT) to break the limitation of the optical trapping direction and extend the spatial range of optical trapping. The device consists of a cascade structure of single-mode fiber and capillary optical fiber (COF), which was used to excite higher-order modes in the COF. A COF taper tip was introduced to converge the multimode field, which created a focused output beam, realizing the ballistic transport of multi-yeast cells at the surface of the COF taper tip and their trapping by multiple optical potential wells of the focused output beam. The experimental results showed that the maximum transport length and speed of the cells were greater than 150 µm and 10 µm s-1, respectively, and at least three cells could be trapped simultaneously. The simulation results showed that the trap stiffness of COFT in several potential wells was in the range of 10-40 pN µm-1 W-1, which indicates that COFT has a good trap performance. Therefore, COFT greatly expands the region of the optical potential well, thus guiding and trapping microparticles distributed on the entire surface of the COF taper tip. This device can also greatly improve the optical trapping ability of single or multiple microparticles, providing a new tool for researchers committed to research on micro-nano objects and cells, which is expected to be widely used in the fields of targeted drug delivery, cell dynamic analysis, microfluidic chip driving, etc.

[A method of obtaining vibrational dephasing time of molecular multi-vibrational modes simultaneously].

In the present paper, the authors used the time-resolved coherent anti-Stokes Raman scattering (CARS) spectroscopy based on supercontinuum developed by ourselves to acquire simultaneously the molecular vibration spectrum and vibrational dephasing time of the molecular various vibrational modes. Using benzonitrile as the sample, the authors measured its vibrational relaxation processes at its five typical vibrational modes and obtained their vibrational dephasing time respectively. In the experiment, the authors also found the phenomenon that oscillations appear in the vibrational dephasing of plane bending vibration mode of benzene ring in benzonitrile, which was caused by superposition of the two adjacent normal vibrational modes excited simultaneously. After mixing benzonitrile with anhydrous ethanol, the authors also measured their vibrational dephasing time. This method is capable of monitoring the changes of the molecular characteristics and its micro-environment, therefore it will find widespread applications in biology, chemistry and materials science.