.

Thursday, August 15, 2019

Rheological properties of cryptococcal polysaccharide change with fiber size, antibody binding and temperature

Glauber R de S Araújo, Nathan B Viana, Bruno Pontes‡ & Susana Frases‡

Aim:Cryptococcus neoformans is the major agent of cryptococcosis. The main virulence factor is the polysaccharide (PS) capsule. Changes in cryptococcal PS properties have been poorly elucidated. Materials & methods: We analyzed the mechanical properties of secreted PS and intact capsules, using dynamic light scattering and optical tweezers. Results: Storage and loss moduli showed that secreted PS behaves as a viscoelastic liquid, while capsular PS behaves as a viscoelastic solid. The secreted PS remains as a viscoelastic fluid at different temperatures with thermal hysteresis after 85°C. Antibody binding altered the viscoelastic behavior of both secreted and capsular PS. Conclusion: Deciphering the mechanical aspects of these structures could reveal features that may have consequences in novel therapies against cryptococcosis.

DOI

Grafted optical vortex with controllable orbital angular momentum distribution

Hao Zhang, Xinzhong Li, Haixiang Ma, Miaomiao Tang, Hehe Li, Jie Tang, and Yangjian Cai

In an optical vortex (OV) field, the orbital angular momentum (OAM) distribution strongly depends on the intensity, which results in difficulty in OAM independent modulation. To overcome this limitation, we propose a grafted optical vortex (GOV) via spiral phase reconstruction of two or more OVs with different topological charges (TCs). To remain the annular shape of the GOV’s intensity, the Dirac δ-function is employed to restrict the energy in a ring. Theoretical analysis and manipulation experiments of polystyrene microspheres show that the magnitude and direction of the GOV’s local OAM are controllable by modulating the grafted TCs while the intensity remains constant. The results of this work provide an ingenious method to control the local tangential force on the light ring, which will promote potential applications in optical trapping and rotating micro-particles.

DOI

Digital Assembly of Colloidal Particles for Nanoscale Manufacturing

Abhay Kotnala, Yuebing Zheng

From unravelling the most fundamental phenomena to enabling applications that impact our everyday lives, the nanoscale world holds great promise for science, technology, and medicine. However, the extent of its practical realization relies on manufacturing at the nanoscale. Among the various nanomanufacturing approaches being investigated, the bottom‐up approach involving assembly of colloidal nanoparticles as building blocks is promising. Compared to a top‐down lithographic approach, particle assembly exhibits advantages such as smaller feature size, finer control of chemical composition, less defects, lower material wastage, and higher scalability. The capability to assemble colloidal particles one by one or “digitally” has been heavily sought as it mimics the natural method of making matter and enables construction of nanomaterials with sophisticated architectures. An insight into the tools and techniques for digital assembly of particles, including their working mechanisms and demonstrated particle assemblies, is provided. Examples of nanomaterials and nanodevices are presented to demonstrate the strength of digital assembly in nanomanufacturing.

DOI

Periodic propagation properties and radiation forces of focusing off-axis hollow vortex Gaussian beams in a harmonic potential

Gengxin Chen, Jintao Xie, Dongsen Cai, Qiliang Sun, Dongmei Deng

Obtaining the analytical expression of focusing off-axis hollow vortex Gaussian (HVG) beams by solving the (2 + 1) dimensionless linear Schrödinger-like equation, we perform the propagation path, the intensity and phase distributions, the center of mass, the peak intensity and the beam width with different potential widths , different hollow orders , different topological charges , different off-axis coordinates (). In general, the off-axis HVG beams are swirled counterclockwise and periodically focus during the propagation. The topological charge separates the focusing center but the hollow order concentrates the focusing area. Moreover, the off-axis coordinate () significantly increases the focusing intensity and the potential width can also increase the focusing frequency during the propagation. Interestingly, the influences of the hollow order , the topological charge and off-axis coordinate () are the same on the peak intensity, which are different with the beam width. Furthermore, we also discuss the Poynting vector, angular momentum and radiation forces. In terms of the radiation forces, we can easily explore the position trapping particles stably regardless of the off-axis coordinate () selection.

DOI

Multiple trapping using a focused hybrid vector beam

Li Zhang, Xiaodong Qiu, Lingwei Zeng and Lixiang Chen

This paper proposes a simple and efficient method that uses a single focused hybrid vector beam to confine metallic Rayleigh particles at multiple positions. We study the force mechanisms of multiple trapping by analyzing gradient and scattering forces. It is observed that the wavelength and topological charges of the hybrid vector beam regulates the trapping positions and number of optical trap sites. The proposed method can be implemented easily in three-dimensional spaces, and it facilitates both trapping and organization of particles. Thus, it can provide an effective and controllable means for nanoparticle manipulation.

DOI

Properties of a Tightly Focused Circularly Polarized Anomalous Vortex Beam and Its Optical Forces on Trapped Nanoparticles

Yihua Bai, Miao Dong, Mingyan Zhang, Yuanjie Yang

The characteristics of a circularly polarized anomalous vortex beam (CPAVB), focused by an objective lens with a high numerical aperture (NA), are studied analytically and theoretically. It shows that the topological charge can affect the beam profile significantly and a flat-topped (FT) beam can be obtained by modulating the NA and topological charge. It is interesting to find that spin-to-orbital angular momentum conversion can occur in the longitudinal component after tight focusing. Furthermore, optical forces of the tightly focused CPAVB on nanoparticles are analyzed in detail. It can be expected to trap two kinds of nanoparticles using such beam near the focus.

DOI

Investigation on the laser trapping mechanism of light-absorbing particles in air

Bo He, Xuemei Cheng, Yongjie Zhan, Qian Zhang, Haowei Chen, Zhaoyu Ren, Chen Niu, Jingjing Yao, Tengfei Jiao and Jintao Bai

We report on the micron-sized light-absorbing particle trapping in two configurations (horizontal and vertical), in order to elucidate the laser trapping mechanism based on the photophoretic force. Two types of carbon particles (irregular graphite particles and carbon microspheres) were tested in both Gaussian and hollow beam traps. By comparing the trapping efficiency and stability under various circumstances, we confirmed that there are two types of photophoretic forces: $F_{\Delta \alpha}$ and $F_{\Delta T}$ forces on the laser irradiating particle. Furthermore, the forces and moments exerting the particles in various traps were analyzed, which explained the experimental phenomena very well. It was found that the $F_{\Delta \alpha}$ force due to the thermal accommodation difference among the irregular particles helps the irregular particles to be balanced more easily and of higher trapping efficiency and stability. This work provides important references for people to choose a suitable trapping scheme according to the particles, which would be of significance in the applications of single-particle analysis.

DOI

Self-Assembly and Biogenesis of the Cellular Membrane are Dictated by Membrane Stretch and Composition

Akshata R. Naik, Eric R. Kuhn, Kenneth T. Lewis, Keith M. Kokotovich, Krishna R. Maddipati, Xuequn Chen, J. H. K. Hörber, Douglas J. Taatjes, Jeffrey J. Potoff, Bhanu P. Jena

The cell plasma membrane is a highly dynamic organelle governing a wide range of cellular activities including ion transport, secretion, cell division, growth, and development. The fundamental process involved in the addition of new membranes to pre-existing plasma membranes, however, is unclear. Here, we report, using biophysical, morphological, biochemical, and molecular dynamic simulations, the selective incorporation of proteins and lipids from the cytosol into the cell plasma membrane dictated by membrane stretch and composition. Stretching of the cell membrane as a consequence of volume increase following incubation in a hypotonic solution and results in the incorporation of cytosolic proteins and lipids into the existing plasma membrane. Molecular dynamic simulations further confirm that increased membrane stretch results in the rapid insertion of lipids into the existing plasma membrane. Similarly, depletion of cholesterol from the cell plasma membrane selectively alters the incorporation of lipids into the membrane.

DOI

Monday, August 12, 2019

Plasmonic optical tweezers based on nanostructures: fundamentals, advances and prospects

Domna G. Kotsifaki, Síle Nic Chormaic

The ability of metallic nanostructures to confine light at the sub-wavelength scale enables new perspectives and opportunities in the field of nanotechnology. Making use of this unique advantage, nano-optical trapping techniques have been developed to tackle new challenges in a wide range of areas from biology to quantum optics. In this work, starting from basic theories, we present a review of research progress in near-field optical manipulation techniques based on metallic nanostructures, with an emphasis on some of the most promising advances in molecular technology, such as the precise control of single biomolecules. We also provide an overview of possible future research directions of nanomanipulation techniques.

Nanopore-based sensing interface for single molecule electrochemistry

Rui Gao, Yao Lin, Yi-Lun Ying, Yi-Tao Long

Nanopore techniques are experiencing a gallop since it walked out the notebook and show its charm on the science arena. The nanoscale pore offers a single-molecule resolution with a label-free and high-selective manner for the research of molecular structures, molecular dynamics, single-molecule reactions and for a variety of applications in biophysics and bionanotechnology. In this review, we introduce the construction of three types of nanopore platforms along with the latest progress in DNA sensing, structure and dynamics analysis of peptides/proteins, and the detection of redox reactions with new sensing mechanisms. Then, we depict nanopore data processing methods which provide an insight of data mining under the background of big data. We could fully expect the great impact of nanopore techniques on not only for DNA sequencing and sensing applications, but also in protein sequencing and clinical diagnostics.

DOI